Solute Carrier Transporters as Targets for Drug Delivery and Pharmacological Intervention for Chemotherapy

Solute Carrier Transporters as Targets for Drug Delivery and Pharmacological Intervention for Chemotherapy TAKEO NAKANISHI, IKUMI TAMAI Department of Membrane Transport and Biopharmaceutics, Faculty of Pharmacy, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan Received 19 January 2011; revised 29 March 2011; accepted 31 March 2011 Published online 31 May 2011 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/jps.22576 ABSTRACT: Many solute carrier transporters that interact with anticancer agents and contribute to their pharmacokinetics have been shown to be differentially upregulated in cancer cells as a result of adaptive response to altered nutritional requirements. This review focuses on pathophysiological function of membrane transporters responsible for the influx of physiological substances including oligopeptides, amino acids, and organic cations and anions, and summarizes the recent knowledge regarding mechanisms in their gene expressions. Broad substrate specificity of enhanced oligopeptide H+ /peptide cotransporter 1 activity in cancer cells is useful for tumor tissue-specific delivery of chemotherapeutic agents and positron emission tomography diagnostic probes. Amino acid transporters such as LAT1 and ASCT2 are upregulated in human cancer cells and are thought to stimulate tumor growth by regulating mammalian target of rapamycin through nutrient pathway. Especially, LAT1 could be a molecular target to deprive cancer cells of amino acids in combination with aminopeptidase inhibitors. As organic anion transporting polypeptides carry estrone-3-sulfate that is intracellularly hydrolyzed to estrone, their overexpression may provide a pharmacological merit to treat hormone-responsive breast tumors. Therefore, it is important to understand the pathophysiological significance and gene expression in cancer to develop new rationales for drug delivery and pharmacological interventions for chemotherapy. © 2011 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 100:3731–3750, 2011 Keywords: slute transporters; ABC transporters; cancer; chemotherapy; nutriome; drug transport; signal transduction; gene expression; amino acids; targeted drug delivery.

INTRODUCTION Abbreviations used: SLC, solute carrier; ABC, ATP-binding cassette; MDR, multidrug resistance; MRP1, multidrug resistanceassociated protein 1; BCRP, breast cancer resistance protein; NIS, Na+ / I− symporter; FDG, 2-[fluorine-18]-fluoro-2-deoxy-D-glucose; PEPT, the H+ /peptide cotransporter; AARE, amino acid response element; EGF, epidermal growth factor; PI3K, phosphatidylinositol 3-kinase; SGK, serum and glucocorticoid-inducible kinase; mTOR, mammalian target of rapamycin; PDT, photodynamic therapy; ALA, aminolevulinic acid; IGF, insulin growth factor 1; PKB, protein kinase B, also known as AKT; PKC, protein kinase C; GH, growth hormone; MAPK, mitogen-activated protein kinase; SNAP, S-nitroso-N-acetyl-D,L-penicillamine; NO, nitric oxide; NOS, NO synthase; PMA, phorbol 12-myristate 13-acetate; PDGF, plateletderived growth factor; BCH, 2-aminobicyclo-2(2,2,1)-heptane-2carboxylic acid; ROS, oxygen species; GSH, reduced glutathione; 3-MCA, 3-methylcholanthrene; DDP, diamminedichloroplatinum; CML, chronic myelogenous leukemia; OCT, organic cation transporter; OATP, organic anion transporting polypeptide; DHEAS, dehydroepiandrosterone sulfate; E3S, estrone-3-sulfate; E17$G, estradiol-17$-glucuronide. Correspondence to: Ikumi Tamai (Telephone: +81-76-234-4479; Fax: +81-76-264-6284; E-mail: [email protected]) Journal of Pharmaceutical Sciences, Vol. 100, 3731–3750 (2011) © 2011 Wiley-Liss, Inc. and the American Pharmacists Association

Plasma membrane transporter proteins are encoded by numerous gene families and play key roles in cell survival by regulating the influx and efflux of myriad substances across the plasma membranes. On the basis of function, transporter proteins are divided into two superfamilies, that is, the solute carrier (SLC) and the ATP-binding cassette (ABC) transporters. Most of the SLC family members function as influx transporters for nutrients and substances essential for cell survival, such as sugars, digested peptides, amino acids, nucleosides, and inorganic ions, whereas ABC members serve as efflux transporters for unwanted metabolites and toxins, including many anticancer drugs in clinical use.1 Over the past two decades, considerable evidence has accumulated to show that increased expression of several ABC transporter genes is associated with acquired multidrug resistance (MDR) of many human cancer cells. In particular, upregulation of p-glycoprotein (a product

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of MDR1/ABCB1 gene),2 multidrug resistanceassociated proteins including MRP1/ABCC1,3 and breast cancer resistance protein (BCRP/ABCG2)4 has been established as a molecular basis of transporterbased MDR in various human cancer cells. On the contrary, there is growing interest in the use of SLC transporters to deliver anticancer agents to cancer cells. It is likely feasible to selectively deliver drugs to tumor tissue(s) if we utilize influx transporters that are differentially upregulated in cancer cells.1,5 Classically, iodine-131 therapy has been recommended to treat patients with thyroid cancers because of the ability of the thyroid to accumulate iodide (I− ). Differential expression of Na+ / I− symporter (NIS/SLC7A5) has been shown to be the basis of this internal radiation therapy since its cDNA was identified.6 Another SLC transporter application is for tumor-specific delivery of a positron emission tomography (PET) imaging agent, 2-[fluorine18]-fluoro-2-deoxy-D-glucose (FDG), making use of the enhanced glucose transport activity that is a consequence of the increased requirement for sugar in cancer cells (the so-called Warburg hypothesis). We have shown that differential upregulation of oligopeptide transporters may alter the sensitivity of cancer cells to peptide-mimetic antiproliferative agents in an experimental animal model.7 Indeed, cancer cells are likely to have a considerably different genotype to that of normal cells in the host individual, and could respond differently to the same nutriome environment. Namely, cancer cells amplify the expression of SLC transporters for specific nutritional requirements, giving them a growth advantage over normal cells when nutrients are limited. Understanding the changes in expression and function of SLC transporters in cancer cells is therefore vital to develop a strategy for transporter-targeted chemotherapy. However, current knowledge is insufficient to allow efficient utilization of such transporters for chemotherapy. Further work is needed to obtain a complete understanding. This review focuses on oligopeptide, amino acid, and organic cation and anion transporters whose expression is altered in cancer cells; glucose transporters related to the Warburg hypothesis in tumor tissues are not covered because they are already well reviewed.8,9 Furthermore, we describe recent progress in studies of the molecular mechanisms underlying tumor-associated changes of gene expression and function, focusing on the potential for drug delivery and pharmacological intervention.

OLIGOPEPTIDE TRANSPORTERS The H+ /peptide cotransporter (PEPT) 1 (SLC15A1)10,11 and PEPT2 (SLC15A2)12 mediate JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 100, NO. 9, SEPTEMBER 2011

transport of dipeptides and tripeptides across plasma membranes into cells with the aid of an inwardly directed H+ gradient. PEPT1 generally has lower affinity and higher capacity than PEPT2 for substrate oligopeptides, and is functionally expressed in epithelial cells of the small intestine,13 bile duct, and kidney. PEPT1 predominantly contributes to intestinal absorption and renal reabsorption of various types of peptidomimetic drugs,14 including $-lactam antibiotics,13,15 angiotensin-converting enzyme inhibitors, including nonpeptide antiviral drugs such as valacyclovir16 and peptide derivatives (Table 1).17 As we originally noticed that oligopeptide transport activity was upregulated in human fibrosarcoma HT1080 cells in comparison with that in normal fibroblast IMR90 cells,51 functional expression of PEPT1 has been found in a variety of human cancer cell lines,7,22,52 and primary colorectal tumor tissues.18 This led us to experimentally examine whether or not PEPT1-targeted therapy is possible in mice bearing xenografts of human cervical cancer Hela cells with enforced expression of PEPT1.7 Since the potent aminopeptidase inhibitor bestatin is a known substrate of PEPT1, 4-week consecutive oral administration of bestatin suppressed the growth of xenografts expressing PEPT1.53 Therefore, both the limited tissue distribution (mainly small bowel and kidneys) and broad substrate specificity of PEPT1 may be advantageous for tumor-specific drug delivery, if PEPT1 is differentially upregulated in cancer cells. Recently, Mitsuoka et al. detected significant mRNA expression of PEPT1 and PEPT2 in 16 and 54 of 58 human cancer cell lines, respectively.22 It is noteworthy that most of the cell lines tested (93.1%) expressed PEPT2, although its pathological significance remains to be clarified. A question raised by these studies was whether or not the preferential expression of PEPT1/ 2 in cancer cells is sufficient to allow peptide-mimetic agents to be selectively accumulated in tumor tissue. [11 C]Gly–Sar, which is a nonmetabolizable dipeptide, was demonstrated by means of a positron planar imaging system to be an efficient probe to visualize cancer cells in a mouse model bearing human cancer xenografts that express endogenous PEPT1.22 A distinctive feature was found that [11 C]Gly–Sar was minimally present in inflammatory tissues, which do not express PEPT1 and PEPT2, compared with [18 F]FDG. The selectivity index of [11 C]Gly–Sar was more than 25.1, whereas [18 F]FDG was highly accumulated in inflammatory tissues, with an index value of 0.72. This observation indicates that [11 C]Gly–Sar is a promising tumor-imaging agent, and may be superior to [18 F]FDG because it enables to tell us difference between tumors and inflammatory tissue. Therefore, it is worthwhile to establish criteria for PEPT1/2 expression levels sufficient for PEPT-targeted diagnosis DOI 10.1002/jps

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Table 1.

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SLC Transporters Upregulated in Cancer and Anticancer Drugs/Agents Identified as Substrates

Transport System Oligopeptide

Protein Name

Gene Symbol

Predominant Substrate(s)

Transport Type/ Coupling Ionc C/H+

PEPT1 PEPT2

SLC15A1 SLC15A2

Oligopeptide

System ASC System B0,+

ATA1 SN1 SN2 ASCT2 (ATB0 ) ATB0,+

SLC38A1 SLC38A3 SLC38A5 SLC1A5 SLC6A14

A,G,S,M,P,Q,N,H,Ta A,G, H,Q,N A,G,S,Q,N,H K,R,A,S,C,T,N,Q,H M,I,L,V,F,Y,W

C/Na+ C/Na+ & E/H+ C/Na+ & E/H+ C/Na+ C/Na+ & Cl−

System L

LAT1

SLC7A5

H,M,L,I,V,F,Y,W,Q

E/AA(e.g., Q)a

System xc−

xCT

SLC7A11

E, Cystine

Organic cation

OCT1

SLC22A1

Organic cations

F

OCT2

SLC22A2

Organic cations

F

OCTN1

SLC22A4

OCTN2

SLC22A5

CT2

SLC22A16

Carnitine, Ergothioneine, Organic cations Carnitine, Organic cations Carnitine, Betaine

OATP1B1

SLCO1B1

Organic anions

F

OATP1B3

SLCO1B3

Organic anions

F

OATP1A2

SLCO1A2

Organic anions

F

Amino Acid System A System N

Organic anion

E/AA

C/Na+ F C/Na+ F F

Major Anticancer Drug(s)/Agent(s)b Bestatin (T)7 *-ALA (T)18,19 Amino acid ester of floxuridine (T)20 Dipeptide monoester of floxuridine (T)21 [11 C]Gly–Sar(T)22 Bip(OMe)–Sar (G, I)23 MeAIB (T)24 Not reported Not reported Not reported Acv–Glu (T)25 NOS inhibitors (T)26 "-methyltryptophan (T)27 Melphalan (T, I)28 , (G)29 KYT-0353 (G, I)30 BCH (T/G, I) [18 F]FET 31 6-[18 F]FDOPA 31 [11 C]ACBC 31 anti-[18 F]FACBC 31 L-alanosine (T)32 Sulfasalazine (T, I)33 Monosodium glutamate (T, I)34 Oxaliplatin (T)35 Cisplatin (T)35,36 Carboplatin (T)35 Imatinib (T)37 Bamet-R2 (T)38 Bamet-UD2 (T)38 Oxaliplatin (T)35 Cisplatin (T)36 , (G)39 Ormaplatin (G)39 Tetraplatin (G)39 Transplatin (G)39 Bamet-R2 (T)38 Bamet-UD2 (T)38 Not Reported

Imatinib(T)40 Doxorubicin (T)41 Bleomycin-A5 (T)42 Flavopiridol (T)43 Methotrexate (T)44 SN-38 (Irinotecan) (T)45 Atrasentan (T)46 Bamet-R2 (T)38 Bamet-UD2 (T)38 Docetaxel (T)47 Paclitaxel (T)48 Methotrexate (T)49 SN-38 (T) 50 Imatinib (T)40 Imatinib (T)40 Bamet-R2 (T)38 Bamet-UD2 (T)38

a Amino

acid substrates are shown in one-letter code. substrate drugs were determined by transport assay (T) or by cell growth assay (G). (I) indicates inhibitor but not substrate. cotransporter; E, exchanger; F, facilitated transporter.

b Major c C,

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and therapy, as well as to seek to optimize substrates for efficient delivery to cancer cells. Indeed, amino acid ester20 and dipeptide monoester21 prodrugs of the antineoplastic agent floxuridine, which is effective for the treatment of tumors including colorectal cancers, were more highly accumulated than the parent floxuridine in PEPT1-expressing cancer cells. Therefore, chemical derivatization of biologically and pharmacologically active compounds to form a peptide bond may be effective to improve membrane permeation via PEPT1,17,20,21,54 supporting the potential effectiveness of the above strategy. It remains unknown exactly how the gene expression of PEPT1 is controlled in cancer cells. Increased expression of PEPT1 in the intestines of starved rats was detected by means of immunohistochemistry55 and reverse transcription-polymerase chain reaction (RT-PCR).56 Shiraga et al.57 first reported that the amino acid response element (AARE), identified in the putative promoter region of rat PepT1, is involved in transcriptional upregulation of PEPT1 by amino acids (e.g., Phe, which shows the highest stimulation) or dipeptides (e.g., Gly–Phe). As manyAARE-inducible genes were reported to be induced in response to amino acid limitation, transcription of SLC15A1 gene may be regulated by intracellular amino acid availability in cancer cells as well. Currently, however, there is no direct evidence that amino acid depletion results in upregulation of PEPT1 in cancerous cells. There are a few reports of transcriptional upregulation of PEPT1 by pharmacological agents, including cyclophosphamide58 and 5-fluorouracil.59,60 The mechanism is unknown; however, PEPT1 is thought to play a role in resistance to severe stress and cellular damage caused by these toxic agents. Insulin and epidermal growth factor (EGF) stimulated dipeptide uptake by intestinal Caco-2 cells by increasing the membrane population of PEPT1, with the mRNA level or H+ -motive driving force being unchanged.61,62 As the binding of insulin and EGF to their receptors leads to activation of the phosphatidylinositol 3-kinase (PI3K) and AKT (serine/threonine protein kinase B; PKB) survival pathways in many mammalian cells, the effect of pharmacological inhibition of these kinases on the enhancement of dipeptide uptake has been tested.63 Dipeptide-induced decrease of intracellular pH in cells isolated from mouse jejunum was significantly blunted in the presence of PI3K inhibitor (e.g., wortmannin or LY294002). This was further demonstrated in PDK1 knockout mice (PDK1 is the upstream kinase from AKT).63 PDK1 also stimulates serum and glucocorticoid-inducible kinase (SGK) isoforms, but basal intestinal oligopeptide transport was shown not to require SGK stimulation in SGK1−/− mice.64 Accordingly, intracellular localization could be regulated by the PI3K/PDK1/AKT pathway in response JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 100, NO. 9, SEPTEMBER 2011

to extracellular stimuli such as growth hormones (GHs). Intriguingly, human pancreatic and gastrointestinal cancer cell lines were highly resistant to nutrient depletion, and PI3K/AKT signaling was found to be activated, particularly under conditions of amino acid deprivation.65 As PEPT1 expression in pancreatic and colorectal cancer cells is relatively high18,52 and PI3K/AKT signaling enhances the PEPT1 activity by translocating PEPT1 into plasma membranes, increased PEPT1 activity may be a rationale for tolerance mechanisms to cell survival under the conditions lacking nutrients, although further study is needed to establish an association between PEPT1 expression and the tolerance. Furthermore, one study has indicated a predominant role of the PEPT1 orthologue pep-2 in the assimilation of dietary protein in Caenorhabditis elegans to deliver large quantities of amino acids for growth and development, concomitantly stimulating target of rapamycin (TOR) signaling pathways that regulate metabolism and aging.66 If this link also occurs in humans, the enhanced expression of PEPT1 may be a pharmacologically attractive target to eradicate cancer cells. The putative regulation mechanism is summarized in Figure 1 and Table 2. In regard to posttranslational protein–protein interaction of PEPT1, it is noteworthy that plasma membrane stabilization of PEPT1 function at apical membranes by the small GTP-binding protein Rab8 resulted in augmented activity of PEPT1 in the small intestine.67,68 Although such stabilization of PEPT1 function has not yet been established in nonpolarized cells, it will be important to clarify whether or not this could occur in cancer cells in relation to their cell survival in the case of limited nutrient supply.

Figure 1. Regulation of gene expression of PEPT1. Figure illustrates the molecular mechanism of gene expression of PEPT1. Solid line, reported regulation; dotted line, putative regulation; NHE, Na+ /H+ exchanger; NKE, Na+ /K+ exchanger; GF, growth factor; GFR, growth factor receptor; AARE, amino acid response element; 5-FU, 5-fluorouracil. DOI 10.1002/jps

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Table 2.

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Possible Mechanisms Involved in Regulation of Gene Expression of Transporters for Oligopeptide and Amino Acids

Transport System

Name

Modulators of gene expression of transporters Gly–Phe57

Type of modulation

Oligopeptide

PEPT1/SLC15A1

Phe, Cyclophosphamide58 5-Fluorouracil59,60 Insulin, EGF61,62 PI3K inhibitors63 GTP-binding protein Rab867,68

Transcriptional upregulation through AARE Transcriptional upregulation Transcriptional upregulation Functional upregulation (translocated to PM) Inhibition of insulin/EGF-stimulated upregulation Protein stabilization at PM

Amino Acid System A

ATA1/SLC38A1

System N

SN1/SLC38A3

Amino acid depletion (acute)69 Amino acid depletion (chronic)69 IGF170 SGK/AKT activation71

System ASC

SN2/SLC38A5 ASCT2/SLC1A5

Inhibin " subunit knockout mice72 EGF73,74

Functional upregulation by translocating to PM Transcriptional upregulation through AARE Functional upregulation (detail is not known) Functional upregulation by inhibiting downregulation of SN1 by the ubiquitin ligase Nedd4-2 Unknown Transcriptional upregulation78 Functional upregulation (translocated to PM by Rho-mediated trafficking)77 Inhibition of EGF-stimulated upregulation Transcriptional upregulation Partial transcriptional upregulation Transcriptional upregulation via FXR/RXR to the ASCT2 promoter Transcriptional upregulation Functional upregulation Transcriptional upregulation Transcriptional upregulation Transcriptional upregulation Transcriptional upregulation Protein downregulation

MEK1 inhibitor74 PMA75 SNAP76 Gln77 System B0,+

ATB0,+ /SLC6A14

System L

LAT1/SLC7A5

System xc−

xCT/SLC7A11

GH78 PMA79 PDGF80 PMA81 Oxygen82 Diethyl maleate (GSH depletion)83 Irinotecan84

PM, plasma membranes.

These observations raise the question of whether tumor growth is dependent on the transport activity of PEPTs. Because elimination of adaptive enhancement of PEPT1 might be a novel strategy for chemotherapy, a newly synthesized dipeptide, 4-(4-methoxyphenyl)-L-phenylalanyl sarcosine [Bip(OMe)–Sar], was tested for this purpose in human pancreatic cancer AsPC-1 cells with a high level of PEPT1 expression.23 PEPT1 inhibition by Bip(OMe)–Sar resulted in almost complete suppression of cell growth of AsPC1, implying a major contribution of PEPT1 to tumor progression, although its intracellular mechanism of action still needs to be clarified. Other possible clinical applications of PEPT1 in chemotherapy lie in fluorescence imaging and photodynamic therapy (PDT). *-Aminolevulinic acid (ALA) has attracted interest in connection with PDT of tumors, including gastrointestinal adenocarcinoma and dysplastic mucosa85,86 because it is metabolized to the photosensitizer protoporphyrin IX. As ALA is transported by PEPT1, PEPT1 expressed on epithelial cells of the bile duct19 and colorectal carcinoma18 has been proposed as a useful target for delivery of *-ALA.

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AMINO ACID TRANSPORTERS Transport of amino acids across the plasma membrane is tightly controlled by and dependent upon amino acid transport systems that differ in structure, mechanism, and substrate specificity (reviewed in Ref. 87). There is compelling evidence, accumulated over the past two decades, that amino acid availability regulates cellular physiology by modulating gene expression as well as signal transduction pathways in cancer cells. Tumor cells compete with the host for circulating Gln, which is the major respiratory fuel for their survival and is essential as an N-containing substrate for biosynthesis of nucleotides and proteins and production of crucial metabolic intermediates.88 Cancer cells also have a greater need for certain amino acids. In particular, a bacterial asparaginase has been used to treat acute lymphoblastic leukemia because asparagine (Asn) plays a critical role in the survival of malignant lymphoblastic cells.89 Besides, numerous tumor cell lines are methionine dependent, whereas normal human cells are not, suggesting a potential antitumor activity of Met restriction.90 Furthermore, amino acid-dependent signaling has been

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described in many cells.91 The mammalian target of rapamycin (mTOR) is a serine/threonine kinase that regulates fundamental biological processes and plays essential roles, in particular, in cell growth control and tumorigenesis.92,93 As mTOR is regulated by nutritional factors, such as amino acids, independent of GHs, the association of amino acid transporters, especially those transporting Leu, with the mTOR signaling pathway has drawn greater attention in recent years. Thus, the role of amino acid transporters in cancer cell survival and the mechanisms regulating their gene expression (as summarized in Table 2) are discussed in this section.

of the process, ATA2 protein could be recruited to the plasma membranes from an intracellular pool without de novo mRNA synthesis in an adaptive response to nutrition shortage.100 Insulin growth factor 1 (IGF1) may be involved in this posttranscriptional upregulation of ATA2 function in differentiated syncytiotrophoblast in a PI3K-dependent manner, although details of the signaling pathway remain unclear.70 Thus, cancer cells may promptly respond to a temporary nutrient shortage by concentrating ATA2 at the plasma membranes until further ATA2 is newly biosynthesized.

System A

System N mediates Na+ -coupled influx transport of neutral amino acids, including Gln, Asn, and His in exchange with H+ .101,102 To date, two human isoforms (SN1/SNAT3/SLC38A3 and102,103 SN2/SNAT5/ SLC38A5104 ) are known, which differ in tissue distribution pattern. As shown previously, mRNA expression of SN1, but not SN2, increased in native glioblastoma, implying that SN1 plays a role in primary malignant gliomas.105 Furthermore, the same group showed later that incubation of cells in acidic medium decreased SN1 mRNA expression selectively in glioma cells; however, neither total nor the system N-mediated Gln uptake was affected.106 This may be explained by decrease in transcription rate and mRNA stability in which acid-responsive element present in this mRNA involved,106 although the precise molecular mechanism for SN1 expression in glioma cells is unclear. SN1 mRNA may be sensitive to altered milieu associated or coincident with metabolic stress in tumors. In another study, SN1 transport activity has been suggested to be upregulated by SGK1 because downregulation of SN1 by the ubiquitin ligase Nedd4-2 was inhibited by coexpression of S422D SGK1, SGK3, and T308D,S473D AKT in an experimental model.71 It is not known whether such posttranslational regulation occurs in actual human cancer cells, although PKB activity is often enhanced by stimuli such as growth factors in tumor tissues. Bode and Fuchs107 discussed in their review the possibility of SN2 upregulation in cancerous tissues in eye, kidney, head, and neck, based on the human expressed sequence tag database at the Cancer Genome Anatomy Project. So far this has not been demonstrated in biological specimens. To date, there is one report showing upregulation of Sn2 gene in ovarian and adrenal tumors of inhibin "-subunit knockout mice.72 As inhibin is a tumor suppressor that works by antagonizing signaling via activin, which accelerates tumor progression, this implies a pathological role(s) of SN2 in tumor development. In contrast, we recently showed that human SN2 expression may be decreased in several human ovarian cancer cell lines, compared with their normal counterparts.108 These

System A occurs in nearly all cell types, and catalyzes the symport of most small neutral amino acids, including Ala, Ser, and Gln, with Na+ ion. There are three isoforms of system A (ATA1/SNAT1/ SLC38A1, ATA2/SNAT2/SLC38A2, and ATA3/ SNAT4/SLC38A4), which primarily differ in their tissue distribution. ATA1 is highly expressed in placenta and heart, and to a lesser extent in brain, lung, and skeletal muscle.94 In the postnatal animals, ATA1 protein is found in the neocortex, hippocampus, and neuroepithelium, so it has been suggested that ATA1 plays a role in glutamate and glutamine cycles between astrocytes and glia to sustain availability of Gln as a precursor of major neurotransmitters, glutamate, and (-aminobutyric acid.95 Expression of ATA2 is ubiquitous,24 whereas expression of ATA3, which accepts cationic as well as neutral amino acids, is restricted to the liver and skeletal muscle.96 Although there is limited information on the expression of system A members in cancer cells, their dysregulation has recently been reported in human primary hepatocellular cancer97 and hilar cholangiocarcinoma cells.98 mRNA levels of ATA1 and ATA2 significantly increased in human hepatoma cancer cell lines, as well as patient-derived hepatocellular cancer cells.97 Increased expression of ATA1 is significantly correlated with the progression of cholangiocarcinoma, suggesting the prognostic importance of ATA1 in cancer development and progression. Furthermore, as silencing of ATA1 mRNA expression reduced the viability of HepG2 cells, ATA1 is likely a requisite for tumor survival. Thus, ATA1 expression may serve as not only a clinical prognostic factor but also a promising target for therapy of hepatocellular malignancy. However, the molecular cause of the upregulation is so far unknown. Little is known about ATA1 transcriptional regulation, although there are a few reports describing upregulation of ATA2 under amino acid starvation.69,99,100 Chronic exposure of cells to amino acid depletion leads to increased RNA polymerase II recruitment to AARE in the promoter.69,100 In contrast, at the acute phase JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 100, NO. 9, SEPTEMBER 2011

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conflicting observations need to be reconciled if a better understanding of the role of SN2 in these cancer cells is to be reached. System ASC The amino acid transporter ASCT2 (SLC1A5), also termed ATB0 , is an isotype of system ASC for neutral amino acids. ASCT2 acts as not only a Na+ -dependent influx transporter for neutral amino acids, including Gln, but also an amino acid exchanger.109,110 ASCT2 expression is elevated in variety of human cancer cells,107 including hepatocellular carcinoma, colorectal cancer,111 glioma, and its metastases,112,113 suggesting an important role in tumor progression. Previously, EGF and GH were shown to enhance intestinal Gln and Ala transport in patients who had undergone massive enterectomy.114 As the contribution of ASCT2 to intestinal Gln transport was predominant in human enterocytes,73 it has been investigated whether transcriptional upregulation of ASCT2 is induced by signaling pathways activated by EGF. Exposure of human colorectal adenocarcinoma Caco-2 cells to EGF stimulated Gln transport activity and ASCT2 mRNA expression.74 This EGFinduced Gln transport activity was individually inhibited by PD98059, a specific mitogen-activated protein kinase kinase (MAPKK) MEK1 inhibitor and the protein kinase inhibitor chelerythrine chloride.74 In addition, a protein kinase C (PKC) stimulator, phorbol 12-myristate 13-acetate (PMA), also stimulated Gln transport activity, with de novo synthesis of ASCT2 mRNA.75 As PMA activates MAPKKK Raf through activation of PKC, these observations suggest that EGF activates ASCT2 transcription at the intestinal epithelial cells through a signaling mechanism that involves activation of PKC and the MAPKK MEK1/ 2 cascade. EGF is an endogenous ligand for EGF receptor (EGFR/HER1) and is involved in human cancer development. Thus, it is conceivable that ASCT2 is upregulated in human cancer cells, including gastrointestinal and colorectal tumor tissues, where EGF signaling is upregulated (reviewed in Refs. 115 and 116). Another report showed that the upregulation of this transporter occurs when Caco-2 cells are treated with S-nitroso-N-acetyl-D,L-penicillamine (SNAP).76 Kinetic analyses indicated that SNAP increases the maximal velocity (Vmax ) of Na+ -dependent alanine uptake in Caco-2 cells without affecting the Michaelis— Menten constant (Km ). The stimulatory effect was partially eliminated by actinomycin D and cycloheximide. Caco-2 cells expressed the Na+ -dependent neutral amino acid transporter ASCT2, but not other transporters, such as ATB0,+ and B0 AT1. Therefore, the SNAP-induced functional upregulation of ASCT2 may be associated with an increase in the amount of transporter protein via de novo synthesis. SNAP activates diverse signaling pathways to regulate gene DOI 10.1002/jps

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expression mediated by PI3K, PKC, nuclear factor-6 beta (NF-6B), and p53; however, the molecular mechanism remains unclear. EGF-induced intestinal Gln uptake may also be explained by posttranslational regulation of ASCT2 involving a cellular GTPase, Rho, which is associated with multiple cellular functions, including cell polarity, vesicular trafficking, and the cell cycle. Recent research has shown that brief exposure of human enterocytes to EGF resulted in an increase in ASCT2-mediated Gln transport. As this increase was inhibited by EGF receptor inhibitor AG1478, MEK1 inhibitor PD98059, and siRNA to Rho, it is considered that ASCT2 is recruited at plasma membranes by Rho-mediated trafficking, which is activated through the MAPK signaling pathway.73 In contrast, PMA was reported to decrease ASCT2 protein expression, despite the occurrence of Glnstimulated cell growth of human hepatoma HepG2 cells,117 suggesting that transcriptional upregulation of ASCT2 occur in a tissue-specific manner. In the same report, Bungard and McGivan117 noted that Gln availability upregulates ASCT2, showing Gln-dependent ASCT2 promoter activity. Later, they demonstrated that the stimulatory effect of Gln on ASCT2 mRNA expression involves binding of FXR/ RXR to the ASCT2 promoter because the activity of the FXR promoter was also increased in response to Gln in the same cells.77 Furthermore, Fuchs et al.118 reported that antisense RNA targeting ASCT2 elicited apoptosis in human hematoma SK-Hep cells. This suggested that the adaptation of growth in response to Gln availability may be essential for survival of hepatoma cells, which consume Gln at a rate 5–10 times greater than normal hepatocytes. Furthermore, ASCT2 is also responsible for influx transport of Leu and to lesser extent Ile,119 and thought to have an essential role in cell growth and viability via the translational machinery mediated through mTOR.118,120 Therefore, the differential expression of ASCT2 in human hepatoma may represent an interesting pharmacological target. System B0,+ (ATB0,+ ) ATB0,+ (SLC6A14) was originally cloned from human mammary gland121 and characterized as an amino acid transporter energized by transmembrane gradients of Na+ and Cl− and membrane potential.121 ATB0,+ transports small and large neutral amino acids including Gln and Leu, as well as cationic amino acids (e.g., Arg).122 We have characterized lowaffinity ATB0,+ -mediated transport of carnitine.122 Hatanaka et al.123 have also shown that this transporter accepts stereoisomers (e.g. D-Ser) and an antiviral agent, acyclovir-conjugated glutamic acid (ester (Acv–Glu).25 Thus, the broad substrate specificity of ATB0,+ appears to be advantageous as a JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 100, NO. 9, SEPTEMBER 2011

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drug delivery system for amino acid-based prodrugs. ATB0,+ is distributed in lung, salivary gland, mammary gland, stomach, and pituitary gland. Recently, ATB0,+ expression was shown to be upregulated in human colorectal124 and cervical125 tumor tissues. This upregulation is accompanied with a parallel increase in expression of inducible nitric oxide synthase (iNOS), which generates nitric oxide (NO) from Arg. Although Arg can be synthesized in normal cells, some tumors required Arg for their cell growth. In humans, NO is one of the few gaseous signaling molecules, and, in certain human cancer cells, NO may contribute to the carcinogenic process by modulating proapoptotic caspases (e.g., caspase 9126 ). It may also contribute to tumor progression and aggressiveness through stimulation of angiogenesis and regulation of angiogenic factor expression.127 NO is biosynthesized from Arg and oxygen by NOS, and ATB0,+ is the only transporter that is able to concentrate Arg intracellularly, utilizing the inward gradient of Na+ and Cl− , and membrane potential, although cationic amino acid transporter system y+ maintains basal Arg availability in most cells by facilitated diffusion. The upregulation of ATB0,+ in colon and cervical cancer cells may be an adaptive response to the increase in Arg metabolism required for their survival. Indeed, NO has been suggested to contribute to tumor progression from colorectal adenoma to colorectal carcinoma.128 Although the association of ATB0,+ gene expression with cellular NO availability is not yet known, ATB0,+ gene expression may be mediated by NO signaling. These observations suggest that differential upregulation of ATB0,+ transporter associated with NOS, in particular iNOS, expression might be a promising target to deliver antiangiogenic NOS inhibitors to tumors, including colorectal or gynecological cancers. ATB0,+ is able to transport a series of NOS inhibitors,26 most of which are structurally similar to Arg. A recent publication described remarkable suppression of colony-forming ability of ATB0,+ -positive tumor cells treated with "-methyltryptophan, which is an immunostimulant and substrate of ATB0,+ .27 Further studies seem warranted to clarify the pharmacological efficacy of these ATB0,+ substrates as a basis for the development of cancer chemotherapeutic agents. Another clue to understand the mechanism of the transcriptional upregulation of the ATB0,+ gene may be found by investigating its relation with GH and EGF. Short-term EGF and GH treatment (60 min) synergistically increased Gln transport activity mediated by system B0,+ in human intestinal C2BBe 1 cells,129 although no evidence of transcriptional upregulation of ATB0,+ is available. Another study in porcine mammary glands showed transcriptional upregulation of ATB0,+ during lactation, with the greatJOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 100, NO. 9, SEPTEMBER 2011

est mRNA abundance at the late stage (day 18).78 As GH is generally considered to be the predominant galactopoietic hormone in ruminants, these observations suggest that ATB0,+ gene transcription is influenced by local and systemic GH levels. The precise mechanism needs to be further investigated in human cancer cells. Increased phosphorylation of ATB0,+ on serine in rat astrocytes treated with PMA resulted in augmented Leu transport activity following an increase of the transporter at the cell surface.79 This suggests the involvement of posttranslational regulation PKC because PMA is a well-known activator of PKC. PKC belongs to a family of serine/threonine kinases that is involved in regulation of diverse biological processes, including cell proliferation and differentiation. Numerous studies have shown that aberrant PKC is associated with neoplastic transformation, carcinogenesis, and cancer cell invasion. System L System L is regarded as the main route for entry of large neutral amino acids with bulky side chains such as Leu, Ile, and Phe. Members of System L (SLC7A5–11) are characterized as glycoproteinassociated amino acid transporters (gpaAT), which heterodimerize with the associated glycoprotein (heavy chains) 4F2hc (SLC3A2) or rBAT (SLC3A1) to function, except for two relatively new members (termed LAT3/SLC43A1130 and LAT4/SLC43A2131 ). The diversity in the structure and function of system L amino acid transporters has been reviewed in Ref. 132 Several studies have described elevated expression of LAT1 (SLC7A5) in human cells derived from colorectal tissues,133,134 glioma,135 esophageal carcinoma,136 and ovary.108 Elevated expression has been reported to be a prognostic marker in patients with astrocytoma,135 prostate tumor,137 resectable pulmonary adenocarcinoma138 and nonsmall cell lung cancer.139 Thus, this strong association between LAT1 expression and cancer cells may be interpreted when we understand the role of LAT1 in cell growth. LAT heterodimerizes with 4F2hc, and the complex imports large neutral amino acids (e.g., Leu) in exchange for intracellular small neutral amino acids (e.g., Gln) in a Na+ -independent manner.140,141 Actually, the occurrence of amino acid (Leu in most cases)-dependent nutritional regulation of the mTOR-signaling pathway has been described for many types of cancer cells. As mTOR is a serine/threonine protein kinase that regulates cell proliferation and survival by modulating protein synthesis, which is often upregulated in malignant tumors,92 association of mTOR and LAT1 gene expression has been studied in cancer cells. LAT1 mRNA expression was stimulated by DOI 10.1002/jps

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platelet-derived growth factor (PDGF) in smooth muscle cells, and the enhanced LAT1 expression was dependent upon mTOR activity.80 The resultant increase in Leu influx would stimulate mTOR. Actually, this compelling notion is supported by recent studies showing that LAT1-mediated Leu influx contributes to stimulating mTOR activity in human head and neck squamous cell carcinoma142 and ovarian cancer cells.108 Thus, this reciprocal relation of the two may represent a critical mechanism by which mitogenic signaling provides cells with the necessary levels of amino acid availability. These observations are consistent with the previously hypothesized role of mTOR in intracellular stabilization and plasma membrane sorting of amino acid transporters, which are critical to adjust the growth rate of the cells to the nutritional conditions.143 Intracellular Gln, which is obligatory for the LAT1-mediated exchange with extracellular Leu, is concentrated via Na+ -dependent amino acid transporters including systems A, B, N, and ASC. This could be the molecular basis for the Gln susceptibility observed in a wide spectrum of human cancer cells. Namely, Gln influx may eventually regulate translation and autophagy through mTOR activity to coordinate cell growth and proliferation.144 To date, there is no clear evidence concerning how Leu transmits the signal through the nutrient pathway to activate mTOR, in particular mTOR complex 1, and this central issue should be addressed in future. Another possible explanation underlying upregulation of LAT in cancer may involve PKC because LAT1 mRNA was significantly enhanced in T cells activated by PMA and ionomycin,81 both of which synergistically enhance PKC.145 Although it remains unclear how LAT1 is regulated by PKC, there is a report that signaling mediated by EGFR to mTOR is critically dependent on PKC in human glioblastoma tumors.146 Therefore, LAT1 upregulation may result from stimulation of mTOR by PKC in the presence of PMA and ionomycin. It is unlikely that LAT1 transcription is activated by hypoxia because it has been shown that hypoxia causes an initial destabilization of LAT1 mRNA.147 The putative regulatory mechanism is illustrated in Figure 2. Considering that LAT1 is essential for cell growth, it may be a potential target for chemotherapy. A nonmetabolizable analogue of Leu, 2-aminobicyclo-2(2, 2, 1)-heptane-2-carboxylic acid (BCH), is often used to test LAT1 function in relation to cell survival. Treating cells with BCH markedly inhibited cell growth of human cancer cell lines derived from breast,148 ovarian,108 colorectal tumors, and osteosarcoma.149 Recently, a potent inhibitor of LAT1, KYT-0353, was reported to show antiproliferative activity with a 50% inhibitory concentration (IC50 ) value of 4.1 :M, comparable to those of cisplatin and 5-fluorouracil, in human colorectal cancer HT-29 cells.30 However, DOI 10.1002/jps

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Figure 2. Regulation of gene expression of LAT1. Figure illustrates the molecular mechanism of gene expression of PEPT1. Solid line, reported regulation; dotted line, putative regulation; GlnT, Na+ -dependent Gln transporter; GF, growth factor; GFR, growth factor receptor; mTOR, mammalian target of rapamycin.

the IC50 value for cell growth was about 70-fold higher than the IC50 value (0.06 :M) for inhibition of [14 C]Leu uptake. A similar observation was made in BCH.149 Although a role of LAT1 in Leu uptake is evident, this great difference in susceptibility between cell growth and Leu uptake implied that other biological factors, rather than Leu influx, are involved in the potent effect of these LAT1 inhibitors on cell growth. Indeed, our recent study indicated that LAT1mediated amino acid transport alone may have a limited impact on cell proliferation, based on a LAT1knockdown study in human ovarian cancer cells108 because amino acids can be supplied from other intracellular sources, such as via autophagy and the ubiquitin–proteasome pathway, where degraded peptides are eventually taken apart into amino acids by several classes of intracellular aminopeptidase. Besides, as combination use of BCH and an antiproliferative aminopeptidase inhibitor bestatin synergistically kills human ovarian cancer and leukemia cells, LAT1 should be considered as a promising target for combination therapy with aminopeptidase inhibitors in clinical trials such as tosedostat150 or clinically used proteasome inhibitors, including bortezomib. LAT1 may also be a useful target molecule to deliver amino acid-derived cytostatic agents and PET probes for cancer diagnosis. LAT1-mediated [14 C]Phe uptake was strongly inhibited in a competitive manner by various aromatic amino acid derivatives, including L-dopa, "-methyldopa, triiodothyronine, thyroxine, and an alkylating agent, melphalan (Table 1).28 Previous studies have shown a significant JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 100, NO. 9, SEPTEMBER 2011

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association of LAT1 expression with cellular sensitivity to melphalan in human esophageal adenocarcinomas and Barrett’s adenocarcinoma cell lines.29 Hosoya et al.151 studied transport of synthetic amino acid-mustards by LAT1, and found that phenylglycine-mustard was a better substrate for LAT1 than melphalan and others, providing important information for development of an efficient alkylating agent to be delivered via LAT1 expressed in cancer. Currently, the glucose analogue [18 F]FDG is the only PET agent in clinical use. However, numerous infections and noninfectious inflammatory conditions result in increased local [18 F]FDG accumulation, leading to false positives. In addition, the high physiological uptake activity by normal tissues, such as brain and urinary tract, make the diagnostic evaluation of tumors difficult in these locations. On the contrary, radiolabeled amino acids, including [11 C]Leu, [11 C]Met, and [11 C]Tyr, have been evaluated as PET probes for tumor imaging. Nonmetabolizable derivatives of these amino acids have been studied with the aim of developing amino acid-based imaging agents without such limitations as [18 F]FDG does. These three amino acids are good substrates for system L, and many of their derivatives have been reported to be substrates for LAT1. Recent progress in nonnaturally occurring amino acid-based tumor imaging in relation to amino acid transporters is reviewed in Ref. 31. Current evidence suggests that analogues of Phe and Trp (e.g., [18 F]FET and 6-[18 F]FDOPA) and alicyclic amino acids (e.g., [11 C]ACBC and anti-[18 F]FACBC), both of which are particularly promising for brain tumors, are transportable by system L.31 Hence, upregulation of LAT1 in malignant tumor tissues should contribute to intratumoral accumulation of these PET probes, although precise characterization of their transport mechanism remains to be done. System xc− The amino acid transporter xCT (SLC7A11) is classified into system xc− for anionic amino acids, and it heterodimerizes with 4F2hc to function as an amino acid exchanger that preferentially mediates influx of extracellular cystine in exchange for intracellular Glu. Subsequent reduction of cystine to cysteine (Cys) is essential to maintain intracellular reduced glutathione (GSH) levels because Cys is a rate-limiting substrate for GSH synthesis. xCT was originally isolated as a molecular entity of system xc− from a human cDNA library, and is thought to be essential for cellular defense against reactive oxygen species (ROS) in macrophages, brain, and liver because GSH is the most powerful and prevalent biological antioxidant.82 Cystine transport activity and mRNA expression of xCT are significantly enhanced by oxygen82 and by diethyl maleate-mediated GSH JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 100, NO. 9, SEPTEMBER 2011

depletion,83 suggesting that xCT is regulated by intracellular GSH levels in human. Initiation of cancer is closely associated with chronic inflammation induced by bacterial and viral infection. As a part of the self-defense mechanisms, macrophages kill invading organisms by producing ROS. Recently, Nabeyama et al.152 found that macrophages from xCTmu/mu mice showed cell death in association with excessive release of high mobility group box chromosomal protein 1 upon stimulation with lipopolysaccharide, suggesting that xCT deficiency causes unremitting inflammation because of the impaired survival of activated macrophages at the inflammatory site. It is known that injection of 3-methylcholanthrene (3-MCA) generates fibrosarcoma in association with inflammation. When 3-MCA was administered to xCTmu/mu mice, development of 3-MCA-induced fibrosarcoma was accelerated by production of inflammatory cytokines due to loss of xCt function.152 This observation suggested that xCT plays an essential role in the protective system against oxidative stress. As cystine/Cys starvation results in depletion of intracellular GSH level, inhibition of xCT-mediated cystine–Glu exchange may be a potential therapeutic approach for cancer treatment.153 Consistent with this notion, previous research showed that xCT transporter inhibitors, including sulfasalazine33 or monosodium glutamate, almost completely suppressed cell growth of human lymphoma,33 lung,154 and pancreatic cancer34 cell lines, in which xCT transporter gene was relatively highly expressed. Irinotecan also downregulated xCT expression, resulting in tumor growth retardation due to increased ROS, which is correlated with increased DNA damage as evidenced by histone 2 (H2) AX.84 These observations suggest that inhibition of cystine–Glu exchange mediated by xCT renders cancer cells more vulnerable to chemotherapeutics, so that combination therapy with xCT inhibitor and anticancer agents might synergistically eradicate cancer cells. This transporter may play a critical role in conferring drug resistance to the chemotherapeutic agent cisplatin. In cisplatin-resistant human ovarian cancer A2780 cells (A2780/diamminedichloroplatinum; DDP), cellular GSH levels are significantly increased due to enhanced expression of xCT in A2780/DDP cells, compared with the parental cells, suggesting that xCT is a critical factor for cisplatin resistance in cancer cells.155 In pancreatic cancer, an association of xCT expression with cellular resistance to gemcitabine was also reported.84 On the contrary, xCT may serve as a sensitizer to the anticancer agent Lalanosine, an amino acid analog that is a xCT substrate. Microarray transporter gene profiling assay in the NCI-60 human cancer cell line panel showed that both xCT and 4F2hc were expressed at relatively high DOI 10.1002/jps

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levels in lung, colon, and CNS cancer cells.32 Examination of the correlation of xCT expression to the antiproliferative potencies of 1400 drugs resulted in the identification of L-alanosine.32 Further study is necessary to investigate the potential of xCT as a therapeutic target for delivery of anticancer agents.

ORGANIC CATION TRANPORTERS Organic Cation Transporters Polyspecific organic cation transporters (OCTs) consist of three isoforms (OCT1/SLC22A1, OCT2/ SLC22A2, and OCT3/SLC22A3) and mediate bidirectional transport of various organic cations, including monoamine neurotransmitters, choline, and xenobiotics, as well as drugs. OCT1 and OCT2 are found in the basolateral membrane of hepatocytes, enterocytes, and renal proximal tubular cells, whereas OCT3 is distributed more ubiquitously and is considered to be the major component of the extraneuronal monoamine transport system (also known as uptake-2) responsible for the peripheral elimination of monoamine neurotransmitters.156 OCT1 and OCT2 have been implicated in cellular uptake of platinum-based drugs, including oxaliplatin35 and cisplatin (Table 1).36 In addition, higher expression of OCT2 has shown to increase cellular sensitivity to ormaplatin, tetraplatin, and transplatin.39 Thus, the activity of these transporters may determine the cytotoxicity of various platinum compounds, particularly oxaliplatin. As an oxaliplatin regimen with infusional fluorouracil (e.g., FOLFOX) is one of the most recommended treatments for colon cancer patients,157 functional upregulation of OCT1 and OCT2 may be a critical factor in platinum-based chemotherapy. Indeed, OCT1 mRNA level was found to increase in human colon cancer cell lines and patient-derived colorectal tumor samples more frequently than was OCT2 mRNA level, suggesting that tumor OCT1 expression serves as a prognostic factor.35 As distinct upregulation of OCT2 is seen in ovarian cancer cell lines,39 OCT2 expression may determine the cytotoxicity of platinum-based drugs in ovarian tumors. In the studies aimed at OCT-targeted delivery into hepatocellular carcinomas, antiproliferative bile acid–cisplatin derivatives, cis-diammine-chloro-cholylglycinate-platinum (II) (Bamet-R2) and cis-diammine-bisursodeoxycholateplatinum (II) (Bamet-UD2), were reported to be transported by both OCT1 and OCT2, suggesting that they are determinants of intracellular accumulation of these agents in hepatocellular carcinoma cells.38 Furthermore, OCT1 mediates transport of imatinib mesylate.37 Imatinib is a small-molecular inhibitor of the fusion protein BCR-ABL, the causal molecule of DOI 10.1002/jps

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chronic myelogenous leukemia (CML). There is considerable evidence to show an association of OCT1 expression with the therapeutic outcome of imatinib. White et al.37 found a significant correlation between sensitivity (IC50 ) to and intracellular concentration of imatinib in peripheral blood leukocytes collected from CML patients prior to imatinib therapy. OCT1mediated imatinib transport activity, defined as the difference of uptakes in the presence and absence of the potent OCT1 inhibitor prazosin, was shown to be useful to individualize dosage regimens for patients with CML in order to maximize molecular response and optimize long-term outcome.158 Furthermore, OCT1 mRNA expression prior to treatment in mature, but not primitive, CML cells was the most potent predictor of complete cytogenetic response in 70 consecutive imatinib-naive CML patients at 6 months (p = 0.002) among transporters expressed in CML, including efflux pumps for imatinib.159,160 Thus, expression of OCT1 is now established as a good prognostic factor for therapeutic outcome of imatinib in BCR-ABL positive CML patients. To date, little information is available about the association of OCT3 with anticancer agents. Recently, OCT3 has been suggested to be an appropriate candidate for individualized kidney tumor therapy because the sensitivity of several human renal carcinoma cell lines to major chemotherapeutics including irinotecan and vincristine depends on the expression of OCT3.161 In future, OCT3 expression in cancer cells, as well as OCT1 and OCT2 expression, should be evaluated in order to tailor cytostatic therapy. Organic Cation/Carnitine Transporter OCTN1 (SLC22A4) and OCTN2 (SLC22A5) intracellularly concentrate zwitterions (e.g., L-carnitine) in a Na+ -dependent manner and also mediate bidirectional-facilitated transport of various organic cationic substances, including quinidine and tetraethyl ammonium. L-Carnitine plays an essential role in $-oxidation of fatty acids by facilitating entry of long-chain fatty acids into mitochondria in many tissues. Although cancer cells seem to have reduced levels of fatty acid oxidation,162 high levels of OCTN1 as well as OCTN2 mRNA expression have been reported in some human tumor-derived cell lines, such as lung carcinoma A549, colorectal carcinoma SW480, CML K562, and carcinoma of cervix HeLa S3 cells.163,164 However, the relevance of the high expression to tumor growth is unknown. In human choriocarcinoma BeWo cells, transcriptional upregulation of OCTN2 was observed under low-oxygen conditions,165 implying that OCTN2 is regulated by hypoxia inducible factor 1, which is stabilized by intratumoral hypoxia. The role of OCTN2 in cancer cells needs to be further clarified because, interestingly, a recent article showed JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 100, NO. 9, SEPTEMBER 2011

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that OCTN2-mediated imatinib transport was even greater than the OCT1-mediated transport in cultured HEK293 cells, implying that OCTN2 is a potential pharmacological target for imatinib therapy.40 So far, no evidence has yet been provided that OCTN2 could affect the pharmacological action of imatinib in BCR-ABL-positive CML cells or gastrointestinal stromal tumor. Other OCTs CT2 (FLIPT2/OCT6/SLC22A16) was originally shown to mediate bidirectional transport of carnitine and betaine across plasma membranes in human testis166 and leukemia cells.167 CT2 mediates the high-affinity transport of L-carnitine but does not accept mainstream OCT/OCTN cationic or anionic substrates.166 Quantitative real-time RT-PCR analyses showed that this gene is highly expressed in human leukemiaderived cells, including promyelocytic HL60 and lymphoblastic Molt4 cells, and leukemic blasts obtained from patients at the time of initial diagnosis.167 As a recent study demonstrated that CT2 is a transporter of anticancer agents, doxorubicin,41 and polyamine analogue bleomycin-A5,42 CT2 gene expression in human cancer cells may prove valuable for improving existing treatments and designing novel cancer therapeutic regimens. Further study to reveal the precise molecular mechanism underlying the upregulation of CT2 in leukocytes seems worthwhile.

ORGANIC ANION TRANSPORTING POLYPEPTIDES Organic anion transporting polypeptides (OATPs) are currently classified into the SLCO superfamily.168 We first identified human cDNAs encoding OATPs that affect drug pharmacokinetics, and reported their expression in human cancer cell lines.169 Members of this family generally mediate Na+ -independent transport of amphipathic organic anion compounds, including bile salts, steroid conjugates, thyroid hormones, and oligopeptides, as well as numerous drugs and xenobiotics, and recent progress in research regarding OATP family members was reviewed in Refs. 170 and 171. The physiological roles of these transporters are not yet fully understood, but evidence accumulated to date is both compelling and persuasive as to the importance of these transporters in the pharmacokinetics of xenobiotics and drugs, including anticancer agents (Table 1). Certain members of this family have been suggested to be important for cell proliferation and survival of human malignant tissues. This section focuses on OATP1B1 and OATP1B3 because they are well characterized as drug transporters. JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 100, NO. 9, SEPTEMBER 2011

OATP1B1 OATP1B1 was originally isolated in human liver169,172 and named LST1, based on its exclusive expression in the liver.172 It was characterized as an influx transporter for endogenous substances, including conjugated steroids [e.g., dehydroepiandrosterone sulfate (DHEAS),173 estradiol-17$-glucuronide (E17$G), and estrone-3-sulfate (E3S)],174 eicosanoids (e.g., prostaglandin E2), and thyroid hormones, as well as xenobiotics and many drugs used for chemotherapy. We first noticed that OATP1B1 is responsible for the hepatic disposition of SN-38, the major active metabolite of irinotecan (also known as CPT-11) because genetic polymorphisms of OATP1B1 contributed to the known interpatient variability in disposition of irinotecan.45,175 In addition to SN38, OATP1B1 is now recognized as a molecular determinant of clinically important chemotherapeutics, including flavopiridol,43 methotrexate,44 and atrasentan.46 OATP1B1 has been reported to be involved in hepatocellular uptake of cytostatic bile acid cisplatin derivatives, Bamet-R2, and Bamet-UD2.38 On the basis of its liver-specific expression among normal tissues and broad substrate specificity, differential upregulation of OATP1B1 in cancer cells may be a potential therapeutic target for drug delivery to tumor tissues. Although alteration of OATP1B1 expression in cancer is not clearly understood, an SLCO and SLC22 transporter gene profiling assay in NCI60 cancer cell lines suggested a relatively high expression of OATP1B1 in human cancer cell lines from lung (e.g., A549 and EKVX cells) and colon (e.g., HCT-15 and KM12 cells).176

OATP1B3 OATP1B3 (LST2/OATP8/SLCO1B3) has been shown to be differentially upregulated in human cancer cells since it was first isolated from human liver.49 OATP1B3 has been characterized as an influx transporter for bile acids and hormone conjugates including E17bG, E3S,174 and DHEAS.177 Recently, OATP1B3 was also reported to transport active steroid hormone such as testosterone,178 so that enhanced expression of OATP1B3 has been suggested as a prognostic factor in prostate cancer. In addition to prostate cancer, increased expression of OATP1B3 was also reported in gastric, colorectal, pancreatic, and breast cancer but not hepatocellular carcinomas, whereas it is almost exclusively expressed in liver among human normal tissues.49,179,180 As OATP1B3 transports major anticancer agents, including methotrexate,49 paclitaxel,48 SN-38,50 decetaxel,47 and imatinib,40 it is thought to be a clinically important determinant for chemosensitivity. However, overexpression of OATP1B3 may DOI 10.1002/jps

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cause resistance to these anticancer agents by modulating the function of p53, a cancer suppressor gene, to exert its antiapoptotic effect. Recently, human colon cancer HCT116 cells with enforced expression of OATP1B3 showed a lowered frequency of SN38-induced apoptosis due to alterations of tumorsuppressive p53-dependent pathways, resulting in a survival advantage during chemotherapy.180 Although the precise mechanism underlying this event is unknown, OATP1B3 may take up substance(s) essential for transcriptional activity of p53. Further investigation of OATP1B3 and apoptotic processes may provide clues to understand the pathological significance of OATP1B3 overexpression for tumor progression. Other OATPs Expressed in Breast Cancer and Gliomas Several other OATP molecules have putative roles in cell survival of hormone-responsive human breast cancer cells. We have previously shown that both OATP3A1 and OATP4A1 were highly expressed in estrogen receptor " positive MCF-7 and T-47D cells.181,182 Also, mRNA expression levels of OATP2A1, OATP5A1, and OATP4C1 were greater in MCF-7 cells than those in nontumorous MCF-10A cells.183 Recently, OATP1A2 was shown to be upregulated in neoplastic breast tissues obtained from patients with breast cancer.184 We have recently shown that OATP1B3 is differentially upregulated in a subpopulation of MCF-7 cells.185 However, the other study has shown that OATP1B3 immunoreactivity inversely correlated with tumor growth in human breast cancer.179 OATP1B3 expression should be further investigated. Previously, steroid sulfatase (STS) activity was found to be present in tumor cells at a considerably higher level than aromatase but its activity was detectable in only about 60% of tumors. As STS catalyzes the hydrolysis of steroid sulfates to unconjugated and biologically active form (e.g., estrone), it would allow E3S to be eventually utilized as active estrogen by breast cancer cells under estrogen-depleted conditions such as in postmenopausal women. Thus, efficient E3S uptake may contribute to breast tumor progression. We tested this hypothesis by feeding hormone-responsive breast cancer cells with E3S (Fig. 3). A significant increase in MCF-7181 and T-47D182 cell growth was observed. Recently, Meyer zu Schwabedissen et al.184 demonstrated that increased OATP1A2 expression mediated by PXR promotes the pathogenesis of breast tumor tissues by feeding them E3S, further supporting the above idea. More interestingly, STS expression levels positively correlated with increasing grade of breast tumors in 120 clinical specimens from patients, although OATP2B1 mRNA expression was not positively correlated with clinical outcome.186 These observations suggest that many OATPs are involved DOI 10.1002/jps

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Figure 3. Putative role of OATPs in hormone-dependent breast cancer cells. Figure illustrates the putative role of OATPs, especially in postmenopausal women, in cell proliferation and progression of hormone-dependent breast cancer cells via uptake of estrone 3-sufate (E3S), which is reverted to active form, for example, estrone, by steroid sulfatase (STS). ERE, estrogen-response element.

in tumor growth by regulating hormone dependency; however, the significance and role of each transporter largely remain unknown. It is has to be understood how much these OATPs contribute to tumor growth, however, developing a potent OATPs inhibitor with high affinity may overcome resistance to aromatase inhibitors such as anastrozole and letroxole, and the estrogen receptor antagonist tamoxifen. Furthermore, remarkable expression of OATP1A2 and OATP2B1 was reported in patient-derived human gliomas.187 Considering the wide spectrum of substrate specificity of these transporters, this observation may provide a clue to deliver chemotherapeutics to the restricted accessibility of human gliomas to chemotherapeutic agents.

CONCLUSION It is essential to specifically deliver anticancer drugs to tumor cells in order to increase clinical efficiency and reduce the side effects of anticancer agents. The effectiveness of cancer chemotherapy is often dependent on the relative transport capacities of normal and cancer cells. Cancer cells are capable of altering their genotype in an adaptive response to maximally utilize the nutriome of the host. It is therefore of clinical and pharmacological importance to investigate alterations of SLC transporters in cancer cells. As transporters are gatekeepers that regulate the entry of anticancer drugs into cells, transporters that are differentially expressed in cancer and tumor cells can be targets for chemotherapy. Broad substrate specificity and limited tissue distribution of oligopeptide transporters, in particular PEPT1, enhanced in cancer cells may be useful for tumor tissue-specific JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 100, NO. 9, SEPTEMBER 2011

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delivery of chemotherapeutic agents or PET probe. In addition, LAT1 that accepts amino acid derivatives with bulky side chains is also a promising amino acid transporter to deliver PET probe(s) for the purpose of diagnosis of cancer. Therefore, drug design or prodrug derivatization of anticancer agents based on the substrate specificities and tissue distributions of transporters could create efficient anticancer agents and improve currently available chemotherapies with minimal effect on normal tissues. Amino acid transporters such as LAT1 and ASCT2 are thought to stimulate cell growth of tumors by regulating mTOR signaling through nutrient pathway, resulting in enhanced cell proliferation. OATPs that transport conjugated steroid hormones may contribute to tumor growth through feeding cancer cells conjugated steroid hormones as a source of estrogen. These observations clearly suggest that inhibitors specific to the function and/or putative gene expression mechanisms of such transporters that play a role in tumor cell survival may possess pharmacological merits as anticancer agents. Finally, this review of SLC transporters as drug transporters and their importance in cancer biology and chemotherapy highlights the potentially pivotal role of these transporters for drug delivery and pharmacological intervention. The large variety of human transporter proteins underscores the need for further studies of pathophysiological function and expression pattern of drug transporters for optimization and individualized use of anticancer medicines.

REFERENCES 1. Nakanishi T. 2007. Drug transporters as targets for cancer chemotherapy. Cancer Genomics Proteomics 4(3):241–254. 2. Gottesman MM, Ling V. 2006. The molecular basis of multidrug resistance in cancer: The early years of P-glycoprotein research. FEBS Lett 580(4):998–1009. 3. Deeley RG, Westlake C, Cole SPC. 2006. Transmembrane transport of endo- and xenobiotics by mammalian ATPbinding cassette multidrug resistance proteins. Physiol Rev 86(3):849–899. 4. Ross DD, Nakanishi T. 2010. Impact of breast cancer resistance protein on cancer treatment outcomes1st ed., Clifton, NJ: Humana Press, pp 251–290. 5. Tsuji A. 1999. Tissue selective drug delivery utilizing carrier-mediated transport systems. J Control Release 62(1–2):239–244. 6. Dadachova E, Carrasco N. 2004. The Na+ /I− symporter (NIS): Imaging and therapeutic applications. Semin Nucl Med 34(1):23–31. 7. Nakanishi T, Tamai I, Takaki A, Tsuji A. 2000. Cancer celltargeted drug delivery utilizing oligopeptide transport activity. Int J Cancer 88(2):274–280. 8. Ganapathy V, Thangaraju M, Prasad PD. 2009. Nutrient transporters in cancer: Relevance to Warburg hypothesis and beyond. Pharmacol Ther 121(1):29–40. 9. Amann T, Hellerbrand C. 2009. GLUT1 as a therapeutic target in hepatocellular carcinoma. Expert Opin Ther Targets 13(12):1411–1427. JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 100, NO. 9, SEPTEMBER 2011

10. Fei Y-J, Kanai Y, Nussberger S, Ganapathy V, Leibach FH, Romero MF, Singh SK, Boron WF, Hediger MA. 1994. Expression cloning of a mammalian proton-coupled oligopeptide transporter. Nature 368(6471):563–566. 11. Miyamoto K, Shiraga T, Morita K, Yamamoto H, Haga H, Taketani Y, Tamai I, Sai Y, Tsuji A, Takeda E. 1996. Sequence, tissue distribution and developmental changes in rat intestinal oligopeptide transporter. Biochim Biophys Acta 1305(1–2):34–38. 12. Liu W, Liang R, Ramamoorthy S, Fei Y-J, Ganapathy ME, Hediger MA, Ganapathy V, Leibach FH. 1995. Molecular cloning of PEPT2, a new member of the H+ /peptide cotransporter family, from human kidney. Biochim Biophys Acta 1235(2):461–466. 13. Sai Y, Tamai I, Sumikawa H, Hayashi K, Nakanishi T, Amano O, Numata M, Iseki S, Tsuji A. 1996. Immunolocalization and pharmacological relevance of oligopeptide transporter PepT1 in intestinal absorption of [beta]-lactam antibiotics. FEBS Lett 392(1):25–29. 14. Tsuji A. 2002. Transporter-mediated drug interactions. Drug Metab Pharmacokinet 17(4):253–274. 15. Tamai I, Nakanishi T, Hayashi K, Terao T, Sai Y, Shiraga T, Miyamoto K, Takeda E, Higashida H, Tsuji A. 1997. The predominant contribution of oligopeptide transporter PepT1 to intestinal absorption of beta-lactam antibiotics in the rat small intestine. J Pharm Pharmacol 49(8):796–801. 16. Balimane PV, Tamai I, Guo A, Nakanishi T, Kitada H, Leibach FH, Tsuji A, Sinko PJ. 1998. Direct evidence for peptide transporter (PepT1)-mediated uptake of a nonpeptide prodrug, valacyclovir. Biochem Biophys Res Commun 250(2):246–251. 17. Kikuchi A, Tomoyasu T, Tanaka M, Kanamitsu K, Sasabe H, Maeda T, Odomi M, Tamai I. 2009. Peptide derivation of poorly absorbable drug allows intestinal absorption via peptide transporter. J Pharm Sci 98(5):1775–1787. 18. Anderson CMH, Jevons M, Thangaraju M, Edwards N, Conlon NJ, Woods S, Ganapathy V, Thwaites DT. 2010. Transport of the photodynamic therapy agent 5-aminolevulinic acid by distinct H+ -coupled nutrient carriers coexpressed in the small intestine. J Pharmacol Exp Ther 322(1):220–228. 19. Neumann J, Brandsch M. 2003. *-Aminolevulinic acid transport in cancer cells of the human extrahepatic biliary duct. J Pharmacol Exp Ther 305(1):219–224. 20. Landowski CP, Vig BS, Song X, Amidon GL. 2005. Targeted delivery to PEPT1-overexpressing cells: Acidic, basic, and secondary floxuridine amino acid ester prodrugs. Mol Cancer Ther 4(4):659–667. 21. Tsume Y, Hilfinger JM, Amidon GL. 2008. Enhanced cancer cell growth inhibition by dipeptide prodrugs of floxuridine: Increased transporter affinity and metabolic stability. Mol Pharm 5(5):717–727. 22. Mitsuoka K, Miyoshi S, Kato Y, Murakami Y, Utsumi R, Kubo Y, Noda A, Nakamura Y, Nishimura S, Tsuji A. 2008. Cancer detection using a PET tracer, 11C-glycylsarcosine, targeted to H+ /peptide transporter. J Nucl Med 49(4):615–622. 23. Mitsuoka K, Kato Y, Miyoshi S, Murakami Y, Hiraiwa M, Kubo Y, Nishimura S, Tsuji A. 2010. Inhibition of oligopeptide transporter suppress growth of human pancreatic cancer cells. Eur J Pharm Sci 40(3):202–208. 24. Sugawara M, Nakanishi T, Fei Y-J, Huang W, Ganapathy ME, Leibach FH, Ganapathy V. 2000. Cloning of an amino acid transporter with functional characteristics and tissue expression pattern identical to that of system A. J Biol Chem 275(22):16473–16477. 25. Hatanaka T, Haramura M, Fei Y-J, Miyauchi S, Bridges CC, Ganapathy PS, Smith SB, Ganapathy V, Ganapathy ME. 2004. Transport of amino acid-based prodrugs by the Na+ - and Cl− -coupled amino acid transporter ATB0,+ and DOI 10.1002/jps

DRUG TRANSPORTERS FOR CHEMOTHERAPY

26.

27.

28.

29.

30.

31.

32.

33.

34.

35.

36.

37.

38.

39.

40.

expression of the transporter in tissues amenable for drug delivery. J Pharmacol Exp Ther 308(3):1138–1147. Hatanaka T, Nakanishi T, Huang W, Leibach FH, Prasad PD, Ganapathy V, Ganapathy ME. 2001. Na+ - and C− -coupled active transport of nitric oxide synthase inhibitors via amino acid transport system B0,+ . J Clin Invest 107(8):1035– 1043. Karunakaran S, Umapathy NS, Thangaraju M, Hatanaka T, Itagaki S, Munn DH, Prasad PD, Ganapathy V. 2008. Interaction of tryptophan derivatives with SLC6A14 (ATB0,+ ) reveals the potential of the transporter as a drug target for cancer chemotherapy. Biochem J 414(3):343–355. Uchino H, Kanai Y, Kim DK, Wempe MF, Chairoungdua A, Morimoto E, Anders MW, Endou H. 2002. Transport of amino acid-related compounds mediated by L-type amino acid transporter 1 (LAT1): Insights into the mechanisms of substrate recognition. Mol Pharmacol 61(4):729–737. Lin J, Raoof D, Thomas D, Greenson J, Giordano T, Robinson G, Bourner M, Bauer C, Orringer M, Beer D. 2004. L-type amino acid transporter-1 overexpression and melphalan sensitivity in Barrett’s adenocarcinoma. Neoplasia 6(1):74–84. Oda K, Hosoda N, Endo H, Saito K, Tsujihara K, Yamamura M, Sakata T, Anzai N, Wempe MF, Kanai Y, Endou H. 2010. l-Type amino acid transporter 1 inhibitors inhibit tumor cell growth. Cancer Sci 101(1):173–179. McConathy J, Goodman M. 2008. Non-natural amino acids for tumor imaging using positron emission tomography and single photon emission computed tomography. Cancer Metastasis Rev 27(4):555–573. Huang Y, Dai Z, Barbacioru C, Sad´ee W. 2005. Cystineglutamate transporter SLC7A11 in cancer chemosensitivity and chemoresistance. Cancer Res 65(16):7446–7454. Gout P, Buckley A, Simms C, Bruchovsky N. 2001. Sulfasalazine, a potent suppressor of lymphoma growth by inhibition of the x(c)- cystine transporter: A new action for an old drug. Leukemia 15(10):1633–1640. Lo M, Ling V, Wang YZ, Gout PW. 2008. The xc- cystine/ glutamate antiporter: a mediator of pancreatic cancer growth with a role in drug resistance. Br J Cancer 99(3):464–472. Zhang S, Lovejoy KS, Shima JE, Lagpacan LL, Shu Y, Lapuk A, Chen Y, Komori T, Gray JW, Chen X, Lippard SJ, Giacomini KM. 2006. Organic cation transporters are determinants of oxaliplatin cytotoxicity. Cancer Res 66(17):8847–8857. Yonezawa A, Masuda S, Yokoo S, Katsura T, Inui K. 2006. Cisplatin and oxaliplatin, but not carboplatin and nedaplatin, are substrates for human organic cation transporters (SLC22A1–3 and multidrug and toxin extrusion family). J Pharmacol Exp Ther 319(2):879–886. White DL, Saunders VA, Dang P, Engler J, Zannettino ACW, Cambareri AC, Quinn SR, Manley PW, Hughes TP. 2006. OCT-1-mediated influx is a key determinant of the intracellular uptake of imatinib but not nilotinib (AMN107): Reduced OCT-1 activity is the cause of low in vitro sensitivity to imatinib. Blood 108(2):697–704. Briz O, Serrano MA, Rebollo N, Hagenbuch B, Meier PJ, Koepsell H, Marin JJG. 2002. Carriers involved in targeting the cytostatic bile acid-cisplatin derivatives cis-diammine-chloro-cholylglycinate-platinum(II) and cis-diammine-bisursodeoxycholate-platinum(II) toward liver cells. Mol Pharmacol 61(4):853–860. Burger H, Zoumaro-Djayoon A, Boersma AWM, Helleman J, Berns E, Mathijssen RHJ, Loos WJ, Wiemer EAC. 2010. Differential transport of platinum compounds by the human organic cation transporter hOCT2 (hSLC22A2). Br J Pharmacol 159(4):898–908. Hu S, Franke RM, Filipski KK, Hu C, Orwick SJ, de Bruijn EA, Burger H, Baker SD, Sparreboom A. 2008. Interaction of

DOI 10.1002/jps

41.

42.

43.

44.

45.

46.

47.

48.

49.

50.

51.

52.

53.

54.

3745

imatinib with human organic ion carriers. Clin Cancer Res 14(10):3141–3148. Okabe M, Unno M, Harigae H, Kaku M, Okitsu Y, Sasaki T, Mizoi T, Shiiba K, Takanaga H, Terasaki T, Matsuno S, Sasaki I, Ito S, Abe T. 2005. Characterization of the organic cation transporter SLC22A16: A doxorubicin importer. Biochem Biophys Res Commun 333(3):754–762. Aouida M, Poulin R, Ramotar D. 2010. The human carnitine transporter SLC22A16 mediates high affinity uptake of the anticancer polyamine analogue bleomycin-A5. J Biol Chem 285(9):6275–6284. Ni W, Ji J, Dai Z, Papp A, Johnson AJ, Ahn S, Farley KL, Lin TS, Dalton JT, Li X, Jarjoura D, Byrd JC, Sadee W, Grever MR, Phelps MA. 2010. Flavopiridol pharmacogenetics: Clinical and functional evidence for the role of SLCO1B1/ OATP1B1 in flavopiridol disposition. PLoS One 5(11):e13792. van de Steeg E, van Der Kruijssen CMM, Wagenaar E, Burggraaff JEC, Mesman E, Kenworthy KE, Schinkel AH. 2009. Methotrexate pharmacokinetics in transgenic mice with liver-specific expression of human organic aniontransporting polypeptide 1B1 (SLCO1B1). Drug Metab Dispos 37(2):277–281. Nozawa T, Minami H, Sugiura S, Tsuji A, Tamai I. 2005. Role of organic anion transporter OATP1B1 (OATP-C) in hepatic uptake of irinotecan and its active metabolite, 7ethyl-10-hydroxycamptothecin: In vitro evidence and effect of single nucleotide polymorphisms. Drug Metab Dispos 33(3):434–439. Katz DA, Carr R, Grimm DR, Xiong H, Holley-Shanks R, Mueller T, Leake B, Wang Q, Han L, Wang PG, Edeki T, Sahelijo L, Doan T, Allen A, Spear BB, Kim RB. 2006. Organic anion transporting polypeptide 1B1 activity classified by SLCO1B1 genotype influences atrasentan pharmacokinetics. Clin Pharmacol Ther 79(3):186–196. Baker SD, Verweij J, Cusatis GA, van Schaik RH, Marsh S, Orwick SJ, Franke RM, Hu S, Schuetz EG, Lamba V, Messersmith WA, Wolff AC, Carducci MA, Sparreboom A. 2008. Pharmacogenetic pathway analysis of docetaxel elimination. Clin Pharmacol Ther 85(2):155–163. Smith NF, Acharya MR, Desai N, Figg W, Sparreboom A. 2005. Identification of OATP1B3 as a high-affinity hepatocellular transporter of paclitaxel. Cancer Biol Ther 4(8):815–818. Abe T, Unno M, Onogawa T, Tokui T, Noriko Kondo T, Nakagomi R, Adachi H, Fujiwara K, Okabe M, Suzuki T, Nunoki K, Sato E, Kakyo M, Nishio T, Sugita J, Asano N, Tanemoto M, Seki M, Date F, Ono K, Kondo Y, Shiiba K, Suzuki M, Ohtani H, Shimosegawa T, Iinuma K, Nagura H, Ito S, Matsuno S. 2001. LST-2, a human liver-specific organic anion transporter, determines methotrexate sensitivity in gastrointestinal cancers. Gastroenterology 120(7):1689–1699. Yamaguchi H, Kobayashi M, Okada M, Takeuchi T, Unno M, Abe T, Goto J, Hishinuma T, Mano N. 2008. Rapid screening of antineoplastic candidates for the human organic anion transporter OATP1B3 substrates using fluorescent probes. Cancer Lett 260(1-2 ):163-169. Nakanishi T, Tamai I, Sai Y, Sasaki T, Tsuji A. 1997. Carriermediated transport of oligopeptides in the human fibrosarcoma cell line HT1080. Cancer Res 57(18):4118–4122. Gonzalez DE, Covitz K-MY, Sad´ee W, Mrsny RJ. 1998. An oligopeptide transporter is expressed at high levels in the pancreatic carcinoma cell lines AsPc-1 and Capan-2. Cancer Res 58(3):519–525. Nakanishi T, Tamai I, Takaki A, Tsuji A. 2000. Cancer celltargeted drug delivery utilizing oligopeptide transport activity. Int J Cancer 88(2):274–280. Tamai I, Nakanishi T, Nakahara H, Sai Y, Ganapathy V, Leibach FH, Tsuji A. 1998. Improvement of L-dopa

JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 100, NO. 9, SEPTEMBER 2011

3746

55.

56.

57.

58.

59.

60.

61.

62.

63.

64.

65.

66.

67.

68.

69.

NAKANISHI AND TAMAI

absorption by dipeptidyl derivation, utilizing peptide transporter PepT1. J Pharm Sci 87(12):1542–1546. Ogihara H, Suzuki T, Nagamachi Y, Inui K, Takata K. 1999. Peptide transporter in the rat small intestine: Ultrastructural localization and the effect of starvation and administration of amino acids. Histochem J 31(3):169– 174. Naruhashi K, Sai Y, Tamai I, Suzuki N, Tsuji A. 2002. PepT1 mRNA expression is induced by starvation and its level correlates with absorptive transport of cefadroxil longitudinally in the rat intestine. Pharm Res 19(10):1417–1423. Shiraga T, Miyamoto K-I, Tanaka H, Yamamoto H, Taketani Y, Morita K, Tamai I, Tsuji A, Takeda E. 1999. Cellular and molecular mechanisms of dietary regulation on rat intestinal H+/peptide transporter PepT1. Gastroenterology 116(2):354–362. Satoh JIN, Tsujikawa T, Fujiyama Y, Bamba T. 2003. Nutritional benefits of enteral alanyl-glutamine supplementation on rat small intestinal damage induced by cyclophosphamide. J Gastroenterol Hepatol 18(6):719–725. Inoue M, Terada T, Okuda M, Inui K. 2005. Regulation of human peptide transporter 1 (PEPT1) in gastric cancer cells by anticancer drugs. Cancer Lett 230(1):72–80. Tanaka H, Miyamoto K, Morita K, Haga H, Segawa H, Shiraga T, Fujioka A, Kouda T, Taketani Y, Hisano S, Fukui Y, Kitagawa K, Takeda E. 1998. Regulation of the PepT1 peptide transporter in the rat small intestine in response to 5-fluorouracil-induced injury. Gastroenterology 114(4):714–723. Thamotharan M, Bawani SZ, Zhou X, Adibi SA. 1999. Hormonal regulation of oligopeptide transporter Pept-1 in a human intestinal cell line. Am J Physiol Cell Physiol 276(4):C821–C826. Nielsen CU, Amstrup J, Nielsen R, Steffansen B, Frokjaer S, Brodin B. 2003. Epidermal growth factor and insulin shortterm increase hPepT1-mediated glycylsarcosine uptake in Caco-2 cells. Acta Physiol Scand 178(2):139–148. Rexhepaj R, Rotte A, Pasham V, Gu S, Kempe D, Lang F. 2010. PI3 kinase and PDK1 in the regulation of the electrogenic intestinal dipeptide transport. Cell Physiol Biochem 25(6):715–722. Rexhepaj R, Rotte A, Kempe D, Sopjani M, F¨oller M, Gehring ¨ E-M, Bhandaru M, Gruner I, Mack A, Rubio-Aliaga I, Naßl A-M, Daniel H, Kuhl D, Lang F. 2009. Stimulation of electrogenic intestinal dipeptide transport by the glucocorticoid ¨ dexamethasone. Pflugers Arch 459(1):191–202. Izuishi K, Kato K, Ogura T, Kinoshita T, Esumi H. 2000. Remarkable tolerance of tumor cells to nutrient deprivation: Possible new biochemical target for cancer therapy. Cancer Res 60(21):6201–6207. Meissner B, Boll M, Daniel H, Baumeister R. 2004. Deletion of the intestinal peptide transporter affects insulin and TOR signaling in Caenorhabditis elegans. J Biol Chem 279(35):36739–36745. Sato T, Mushiake S, Kato Y, Sato K, Sato M, Takeda N, Ozono K, Miki K, Kubo Y, Tsuji A, Harada R, Harada A. 2007. The Rab8 GTPase regulates apical protein localization in intestinal cells. Nature 448(7151):366–369. Kato Y, Sugiura T, Nakadera Y, Sugiura M, Kubo Y, Sato T, Harada A, Tsuji A. 2009. Investigation of the role of oligopeptide transporter PEPT1 and sodium/glucose cotransporter SGLT1 in intestinal absorption of their substrates using small GTP-binding protein Rab8-null mice. Drug Metab Dispos 37(3):602–607. Palii SS, Chen H, Kilberg MS. 2004. Transcriptional control of the human sodium-coupled neutral amino acid transporter system A gene by amino acid availability is mediated by an intronic element. J Biol Chem 279(5):3463–3471.

JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 100, NO. 9, SEPTEMBER 2011

70. Fang J, Mao D, Smith CH, Fant ME. 2006. IGF regulation of neutral amino acid transport in the BeWo choriocarcinoma cell line (b30 clone): Evidence for MAP kinase-dependent and MAP kinase-independent mechanisms. Growth Horm IGF Res 16(5–6):318–325. 71. Boehmer C, Okur F, Setiawan I, Br¨oer S, Lang F. 2003. Properties and regulation of glutamine transporter SN1 by protein kinases SGK and PKB. Biochem Biophys Res Commun 306(1):156–162. 72. Burns KH, Owens GE, Ogbonna SC, Nilson JH, Matzuk MM. 2003. Expression profiling analyses of gonadotropin responses and tumor development in the absence of inhibins. Endocrinology 144(10):4492–4507. 73. Avissar N, Sax H, Toia L. 2008. In human entrocytes, GLN transport and ASCT2 surface expression induced by shortterm EGF are MAPK, PI3K, and Rho-dependent. Dig Dis Sci 53(8):2113–2125. 74. Wolfgang CL, Lin C, Meng Q, Karinch AM, Vary TC, Pan M. 2003. Epidermal growth factor activation of intestinal glutamine transport is mediated by mitogenactivated protein kinases. J Gastrointest Surg 7(1):149– 156. 75. Pan M, Wolfgang CA, Karinch AM, Lin C, Meng Q, Vary TC, Souba WW. 2002. Protein kinase C activation of intestinal glutamine transport is mediated by mitogen-activated protein kinases. J Surg Res 106(1):137–144. 76. Uchiyama T, Matsuda Y, Wada M, Takahashi S, Fujita T. 2005. Functional regulation of Na+-dependent neutral amino acid transporter ASCT2 by S-nitrosothiols and nitric oxide in Caco-2 cells. FEBS Lett 579(11):2499–2506. 77. Bungard CI, McGivan JD. 2005. Identification of the promoter elements involved in the stimulation of ASCT2 expression by glutamine availability in HepG2 cells and the probable involvement of FXR/RXR dimers. Arch Biochem Biophys 443(1–2):53–59. 78. Laspiur JP, Burton JL, Weber PSD, Moore J, Kirkwood RN, Trottier NL. 2009. Dietary protein intake and stage of lactation differentially modulate amino acid transporter mRNA abundance in porcine mammary tissue. J Nutr 139(9):1677–1684. 79. Samluk Ł, Czeredys M, Nałecz ˛ KA. 2010. Regulation of amino acid/carnitine transporter B0,+ (ATB0,+ ) in astrocytes by protein kinase C: Independent effects on raft and nonraft transporter subpopulations. J Neurochem 115(6):1386– 1397. 80. Liu XM,Reyna SV, Ensenat D, Peyton KJ, Wang H, Schafer AI, Durante W. 2004. Platelet-derived growth factor stimulates LAT1 gene expression in vascular smooth muscle: Role in cell growth. FASEB J 18(6):768–770. 81. Nii T, Segawa H, Taketani Y, Tani Y, Ohkido M, Kishida S, Ito M, Endou H, Kanai Y, Takeda E, Miyamoto K. 2001. Molecular events involved in upregulating human Na+-independent neutral amino acid transporter LAT1 during T-cell activation. Biochem J 358(3):693–704. 82. Sato H, Tamba M, Kuriyama-Matsumura K, Okuno S, Bannai S. 2000. Molecular cloning and expression of human xCT, the light chain of amino acid transport system xc-. Antioxid Redox Signal 2(4):665–671. 83. Kim JY, Kanai Y, Chairoungdua A, Cha SH, Matsuo H, Kim DK, Inatomi J, Sawa H, Ida Y, Endou H. 2001. Human cystine/glutamate transporter: cDNA cloning and upregulation by oxidative stress in glioma cells. Biochim Biophys Acta 1512(2):335–344. 84. Chintala S, T´oth K, Yin M-B, Bhattacharya A, Smith S, Ola M, Cao S, Durrani F, Zinia T, Dean R, Slocum H, Rustum Y. 2010. Downregulation of cystine transporter xc − by irinotecan in human head and neck cancer FaDu xenografts. Chemotherapy 56(3):223–233. DOI 10.1002/jps

DRUG TRANSPORTERS FOR CHEMOTHERAPY

85. Peng Q, Warloe T, Berg K, Moan J, Kongshaug M, Giercksky K, Nesland J. 1997. 5-Aminolevulinic acid-based photodynamic therapy. Cancer 79(12):2282–2308. 86. Zopf T, Riemann JF. 1997. The change in laser usage in gastroenterology—The status in 1997. Z Gastroenterol 35(11):987–997. 87. Christensen H. 1989. Distinguishing amino acid transport systems of a given cell or tissue. Methods Enzymol 173:576–616. 88. Souba W. 1993. Glutamine and cancer. Ann Surg 218(6):715–728. 89. Holcenberg J. 2004. Optimal asparaginase therapy. J Pediatr Hematol Oncol 26(5):273–274. 90. Cellarier E, Durando X, Vasson MP, Farges MC, Demiden A, Maurizis JC, Madelmont JC, Chollet P. 2003. Methionine dependency and cancer treatment. Cancer Treat Rev 29(6):489–499. 91. van Sluijters D, Dubbelhuis P, Blommaart E, Meijer A. 2000. Amino-acid-dependent signal transduction. Biochem J 351(3):545–550. 92. Yang Q, Guan K-L. 2007. Expanding mTOR signaling. Cell Res 17(8):666–681. 93. Bjornsti M-A, Houghton PJ. 2004. The tor pathway: A target for cancer therapy. Nat Rev Cancer 4(5):335– 348. 94. Wang H, Huang W, Sugawara M, Devoe LD, Leibach FH, Prasad PD, Ganapathy V. 2000. Cloning and functional expression of ATA1, a subtype of amino acid transporter A, from human placenta. Biochem Biophys Res Commun 273(3):1175–1179. 95. Weiss MD, Derazi S, Rossignol C, Varoqui H, Erickson JD, Kilberg MS, Anderson KJ. 2003. Ontogeny of the neutral amino acid transporter SAT1/ATA1 in rat brain. Dev Brain Res 143(2):151–159. 96. Sugawara M, Nakanishi T, Fei Y-J, Martindale RG, Ganapathy ME, Leibach FH, Ganapathy V. 2000. Structure and function of ATA3, a new subtype of amino acid transport system A, primarily expressed in the liver and skeletal muscle. Biochim Biophys Acta 1509(1–2):7–13. 97. Kondoh N, Imazeki N, Arai M, Hada A, Hatsuse K, Masuto H, Matsubara O, Ohkura S, Yamamoto M. 2007. Activation of a system A amino acid transporter, ATA1/SLC38A1, in human hepatocellular carcinoma and preneoplastic liver tissues. Int J Oncol 31(1):81–87. 98. Yu W-l, Cong W-M, Zhang Y, Chen Y, Wang F, Yu G. 2011. Overexpression of ATA1/SLC38A1 predicts future recurrence and death in Chinese patients with hilar cholangiocarcinoma. J Surg Res In Press, Corrected Proof. 99. Tanaka K, Yamamoto A, Fujita T. 2005. Functional expression and adaptive regulation of Na+ -dependent neutral amino acid transporter SNAT2/ATA2 in normal human astrocytes under amino acid starved condition. Neurosci Lett 378(2):70–75. 100. Ling R, Bridges CC, Sugawara M, Fujita T, Leibach FH, Prasad PD, Ganapathy V. 2001. Involvement of transporter recruitment as well as gene expression in the substrateinduced adaptive regulation of amino acid transport system A. Biochim Biophys Acta 1512(1):15–21. 101. Nakanishi T, Kekuda R, Fei Y-J, Hatanaka T, Sugawara M, Martindale RG, Leibach FH, Prasad PD, Ganapathy V. 2001. Cloning and functional characterization of a new subtype of the amino acid transport system N. Am J Physiol Cell Physiol 281(6):C1757–C1768. 102. Chaudhry FA, Reimer RJ, Krizaj D, Barber D, StormMathisen J, Copenhagen DR, Edwards RH. 1999. Molecular analysis of system N suggests novel physiological roles in nitrogen metabolism and synaptic transmission. Cell 99(7):769–780. DOI 10.1002/jps

3747

103. Fei YJ, Sugawara M, Nakanishi T, Huang W, Wang H, Prasad PD, Leibach FH, Ganapathy V. 2000. Primary structure genomic organization, and functional and electrogenic characteristics of human system N 1, a Na+ - and H+ -coupled glutamine transporter. J Biol Chem 275(31):23707–23717. 104. Nakanishi T, Sugawara M, Huang W, Martindale RG, Leibach FH, Ganapathy ME, Prasad PD, Ganapathy V. 2001. Structure, function, and tissue expression pattern of human SN2, a subtype of the amino acid transport System N. Biochem Biophys Res Commun 281(5):1343–1348. 105. Sidoryk M, Matyja E, Dybel A, Zielinska M, Bogucki J, Jask´olski DJ, Liberski PP, Kowalczyk P, Albrecht J. 2004. Increased expression of a glutamine transporter SNAT3 is a marker of malignant gliomas. Neuroreort 15(4):575–578. 106. Sidoryk M, Obara M, Albrecht J. 2006. Selective decrease of SN1(SNAT3) mRNA expression in human and rat glioma cells adapted to grow in acidic medium. Neurochem Int 48(6–7):547–552. 107. Fuchs BC, Bode BP. 2005. Amino acid transporters ASCT2 and LAT1 in cancer: Partners in crime? Semin Cancer Biol 15(4):254–266. 108. Fan X, Ross DD, Arakawa H, Ganapathy V, Tamai I, Nakanishi T. 2010. Impact of system L amino acid transporter 1 (LAT1) on proliferation of human ovarian cancer cells: A possible target for combination therapy with antiproliferative aminopeptidase inhibitors. Biochem Pharmacol 80(6):811–818. 109. Br¨oer S, Brookes N. 2001. Transfer of glutamine between astrocytes and neurons. J Neurochem 77(3):705–719. 110. Torres-Zamorano V, Leibach FH, Ganapathy V. 1998. Sodium-dependent homo- and hetero-exchange of neutral amino acids mediated by the amino acid transporter ATB0 . Biochem Biophys Res Commun 245(3):824–829. 111. Witte D, Ali N, Carlson N, Younes M. 2002. Overexpression of the neutral amino acid transporter ASCT2 in human colorectal adenocarcinoma. Anticancer Res 22(5):2555–2557. 112. Dolinska M, Dybel A, Zablocka B, Albrecht J. 2003. Glutamine transport in C6 glioma cells shows ASCT2 system characteristics. Neurochem Int 43(4–5):501–507. 113. Sidoryk M, Matyja E, Dybel A, Zielinska M, Bogucki J, Jaskolski DJ, Liverski PP, Kowalczyk P, Albrecht J. 2004. Increased expression of a glutamine transporter SNAT3 is a marker of malignant gliomas. Neuroreport 15(4):575– 578. 114. Iannoli P, Miller J, Ryan C, Gu L, Ziegler T, Sax H. 1997. Epidermal growth factor and human growth hormone accelerate adaptation after massive enterectomy in an additive, nutrient-dependent, and site-specific fashion. Surgery 122(4):728–729. 115. Salomon DS, Brandt R, Ciardiello F, Normanno N. 1995. Epidermal growth factor-related peptides and their receptors in human malignancies. Crit Rev Oncol/Hematol 19(3):183–232. 116. Biscardi JS, Ishizawar RC, Silva CM, Parson SJ. 2000. Tyrosine kinase signaling in breast cancer epidermal growth factor receptor and c-Src interactions in breast cancer. Breast Cancer Res 2:203–210. 117. Bungard CI, McGivan JD. 2004. Glutamine availability upregulates expression of the amino acid transporter protein ASCT2 in HepG2 cells and stimulates the ASCT2 promoter. Biochem J 382(1):27–32. 118. Fuchs BC, Perez JC, Suetterlin JE, Chaudhry SB, Bode BP. 2004. Inducible antisense RNA targeting amino acid transporter ATB0/ASCT2 elicits apoptosis in human hepatoma cells. Am J Physiol Gastrointest Liver Physiol 286(3):G467–G478. 119. Kekuda R, Prasad PD, Fei Y-J, Torres-Zamorano V, Sinha S, Yang-Feng TL, Leibach FH, Ganapathy V. 1996. Cloning of the sodium-dependent, broad-scope, neutral amino acid JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 100, NO. 9, SEPTEMBER 2011

3748

120.

121.

122.

123.

124.

125.

126.

127. 128.

129.

130.

131.

132.

133.

134.

NAKANISHI AND TAMAI

transporter Bo from a human placental choriocarcinoma cell line. J Biol Chem 271(31):18657–18661. Fuchs BC, Finger RE, Onan MC, Bode BP. 2007. ASCT2 silencing regulates mammalian target-of-rapamycin growth and survival signaling in human hepatoma cells. Am J Physiol Cell Physiol 293(1):C55–C63. Sloan JL, Mager S. 1999. Cloning and functional expression of a human Na+ and Cl− -dependent neutral and cationic amino acid transporter B0+ . J Biol Chem 274(34):23740–23745. Nakanishi T, Hatanaka T, Huang W, Prasad PD, Leibach FH, Ganapathy ME, Ganapathy V. 2001. Na+ - and Cl− -coupled active transport of carnitine by the amino acid transporter ATB0,+ from mouse colon expressed in HRPE cells and Xenopus oocytes. J Physiol 532(2):297–304. Hatanaka T, Huang W, Nakanishi T, Bridges CC, Smith SB, Prasad PD, Ganapathy ME, Ganapathy V. 2002. Transport of D-serine via the amino acid transporter ATB0,+ expressed in the colon. Biochem Biophys Res Commun 291(2):291–295. Gupta N, Miyauchi S, Martindale RG, Herdman AV, Podolsky R, Miyake K, Mager S, Prasad PD, Ganapathy ME, Ganapathy V. 2005. Upregulation of the amino acid transporter ATB0,+ (SLC6A14) in colorectal cancer and metastasis in humans. Biochim Biophys Acta 1741(1–2):215–223. Gupta N, Prasad PD, Ghamande S, Moore-Martin P, Herdman AV, Martindale RG, Podolsky R, Mager S, Ganapathy ME, Ganapathy V. 2006. Upregulation of the amino acid transporter ATB0,+ (SLC6A14) in carcinoma of the cervix. Gynecol Oncol 100(1):8–13. T¨or¨ok NJ, Higuchi H, Bronk S, Gores GJ. 2002. Nitric oxide inhibits apoptosis downstream of cytochrome c release by nitrosylating caspase 9. Cancer Res 62(6):1648–1653. Morbidelli L, Donnini S, Ziche M. 2004. Role of nitric oxide in tumor angiogenesis. Cancer Treat Res 117:155–167. Lagares-Garcia J, Moore R, Collier B, Heggere M, Diaz F, Qian F. 2001. Nitric oxide synthase as a marker in colorectal carcinoma. Am Surg 67(7):709–713. Ray EC, Avissar NE, Salloum R, Sax HC. 2005. Growth hormone and epidermal growth factor upregulate specific sodium-dependent glutamine uptake systems in human intestinal C2BBe 1 cells. J Nutr 135(1):14–18. Babu E, Kanai Y, Chairoungdua A, Kim DK, Iribe Y, Tangtrongsup S, Jutabha P, Li Y, Ahmed N, Sakamoto S, Anzai N, Nagamori S, Endou H. 2003. Identification of a novel system L amino acid transporter structurally distinct from heterodimeric amino acid transporters. J Biol Chem 278(44):43838–43845. Bodoy S, Marrt´ın L, Zorzano A, Palac´ın M, Est´evez R, Bertran J. 2005. Identification of LAT4, a novel amino acid transporter with system L activity. J Biol Chem 280(12):12002–12011. Verrey F, Closs E, Wagner C, Palacin M, Endou H, Kanai Y. 2004. CATs and HATs: The SLC7 family of amino acid ¨ transporters. Pflugers Arch 447(5):532–542. Yanagida O, Kanai Y, Chairoungdua A, Kim DK, Segawa H, Nii T, Cha SH, Matsuo H, Fukushima J-I, Fukasawa Y, Tani Y, Taketani Y, Uchino H, Kim JY, Inatomi J, Okayasu I, Miyamoto K-I, Takeda E, Goya T, Endou H. 2001. Human L-type amino acid transporter 1 (LAT1): Characterization of function and expression in tumor cell lines. Biochim Biophys Acta 1514(2):291–302. Wolf D, Wang S, Panzica M, Bassily N, Thompson N. 1996. Expression of a highly conserved oncofetal gene, TA1/ E16, in human colon carcinoma and other primary cancers: Homology to Schistosoma mansoni amino acid permease and Caenorhabditis elegans gene products. Cancer Res 56(21):5012–5022.

JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 100, NO. 9, SEPTEMBER 2011

135. Nawashiro H, Otani N, Shinomiya N, Fukui S, Ooigawa H, Shima K, Matsuo H, Kanai Y, Endou H. 2006. L-type amino acid transporter 1 as a potential molecular target in human astrocytic tumors. Int J Cancer 119(3):484–492. 136. Kobayashi H, Ishii Y, Takayama T. 2005. Expression of Ltype amino acid transporter 1 (LAT1) in esophageal carcinoma. J Surg Oncol 90(4):233–238. 137. Sakata T, Ferdous G, Tsuruta T, Satoh T, Baba S, Muto T, Ueno A, Kanai Y, Endou H, Okayasu I. 2009. L-type aminoacid transporter 1 as a novel biomarker for high-grade malignancy in prostate cancer. Pathol Int 59(1):7–18. 138. Kaira K, Oriuchi N, Imai H, Shimizu K, Yanagitani N, Sunaga N, Hisada T, Ishizuka T, Kanai Y, Nakajima T, Mori M. 2009. Prognostic significance of l-type amino acid transporter 1 (LAT1) and 4F2 heavy chain (CD98) expression in stage I pulmonary adenocarcinoma. Lung Cancer 66(1):120–126. 139. Kaira K, Oriuchi N, Imai H, Shimizu K, Yanagitani N, Sunaga N, Hisada T, Tanaka S, Ishizuka T, Kanai Y, Endou H, Nakajima T, Mori M. 2008. Prognostic significance of L-type amino acid transporter 1 expression in resectable stage I-III nonsmall cell lung cancer. Br J Cancer 98(4):742–748. 140. Kanai Y, Segawa H, Miyamoto K-I, Uchino H, Takeda E, Endou H. 1998. Expression cloning and characterization of a transporter for large neutral amino acids activated by the heavy chain of 4F2 antigen (CD98). J Biol Chem 273(37):23629–23632. 141. Prasad PD, Wang H, Huang W, Kekuda R, Rajan DP, Leibach FH, Ganapathy V. 1999. Human LAT1, a subunit of system L amino acid transporter: Molecular cloning and transport function. Biochem Biophys Res Commun 255(2):283– 288. 142. Yamauchi K, Sakurai H, Kimura T, Wiriyasermkul P, Nagamori S, Kanai Y, Kohno N. 2009. System L amino acid transporter inhibitor enhances anti-tumor activity of cisplatin in a head and neck squamous cell carcinoma cell line. Cancer Lett 276(1):95–101. 143. Schmelzle T, Hall MN. 2000. TOR, a central controller of cell growth. Cell 103(2):253–262. 144. Cohen A, Hall MN. 2009. An amino acid shuffle activates mTORC1. Cell 136(3):399–400. 145. Chatila T, Silverman L, Miller R, Geha R. 1989. Mechanisms of T cell activation by the calcium ionophore ionomycin. J Immunol 143(4):1283–1289. 146. Fan Q-W, Cheng C, Knight ZA, Haas-Kogan D, Stokoe D, James CD, McCormick F, Shokat KM, Weiss WA. 2009. EGFR signals to mTOR through PKC and independently of Akt in glioma. Sci Signal 2(55):ra4. 147. Boado RJ, Li JY, Tsukamoto H, Pardridge WM. 2003. Hypoxia induces de-stabilization of the LAT1 large neutral amino acid transporter mRNA in brain capillary endothelial cells. J Neurochem 85(4):1037–1042. 148. Shennan DB, Thomson J. 2008. Inhibition of system L (LAT1/ CD98hc) reduces the growth of cultured human breast cancer cells. Oncol Rep 20(4):885–889. 149. Kim CS, Cho S-H, Chun HS, Lee S-Y, Endou H, Kanai Y, Kim DK. 2008. BCH, an inhibitor of system L amino acid transporters, induces apoptosis in cancer cells. Biol Pharm Bull 31(6):1096–1100. 150. Krige D, Needham LA, Bawden LJ, Flores N, Farmer H, Miles LEC, Stone E, Callaghan J, Chandler S, Clark VL, Kirwin-Jones P, Legris V, Owen J, Patel T, Wood S, Box G, Laber D, Odedra R, Wright A, Wood LM, Eccles SA, Bone EA, Ayscough A, Drummond AH. 2008. CHR-2797: An antiproliferative aminopeptidase inhibitor that leads to amino acid deprivation in human leukemic cells. Cancer Res 68(16):6669– 6679. DOI 10.1002/jps

DRUG TRANSPORTERS FOR CHEMOTHERAPY

151. Hosoya K, Kyoko H, Toyooka N, Kato A, Orihashi M, Tomi M, Tachikawa M. 2008. Evaluation of amino acid-mustard transport as L-type amino acid transporter 1 (LAT1)-mediated alkylating agents. Biol Pharm Bull 31(11):2126–2130. 152. Nabeyama A, Kurita A, Asano K, Miyake Y, Yasuda T, Miura I, Nishitai G, Arakawa S, Shimizu S, Wakana S, Yoshida H, Tanaka M. 2010. xCT deficiency accelerates chemically induced tumorigenesis. Proc Natl Acad Sci USA 107(14):6436–6441. 153. Lo M, Wang Y-Z, Gout PW. 2008. The xc − cystine/glutamate antiporter: A potential target for therapy of cancer and other diseases. J Cell Physiol 215(3):593–602. 154. Guan J, Lo M, Dockery P, Mahon S, Karp C, Buckley A, Lam S, Gout P, Wang Y-Z. 2009. The xc − cystine/glutamate antiporter as a potential therapeutic target for small-cell lung cancer: Use of sulfasalazine. Cancer Chemother Pharmacol 64(3):463–472. 155. Okuno S, Sato H, Kuriyama-Matsumura K, Tamba M, Wang H, Sohda S, Hamada H, Yoshikawa H, Kondo T, Bannai S. 2003. Role of cystine transport in intracellular glutathione level and cisplatin resistance in human ovarian cancer cell lines. Br J Cancer 88(6):951–956. 156. Jonker JW, Schinkel AH. 2004. Pharmacological and physiological functions of the polyspecific organic cation transporters: OCT1, 2, and 3 (SLC22A1–3). J Pharmacol Exp Ther 308(1):2–9. 157. Pandor A, Eggington S, Paisley S, Tappenden P, Sutcliffe P. 2006. The clinical and cost-effectiveness of oxaliplatin and capecitabine for the adjuvant treatment of colon cancer: Systematic review and economic evaluation. Health Technol Assess 10(41):1–185. 158. White DL, Dang P, Engler J, Frede A, Zrim S, Osborn M, Saunders VA, Manley PW, Hughes TP. 2010. Functional activity of the OCT-1 protein Is predictive of long-term outcome in patients with chronic-phase chronic myeloid leukemia treated with imatinib. J Clin Oncol 28(16):2761–2767. 159. Wang L, Giannoudis A, Lane S, Williamson P, Pirmohamed M, Clark RE. 2007. Expression of the uptake drug transporter hOCT1 is an important clinical determinant of the response to imatinib in chronic myeloid leukemia. Clin Pharmacol Ther 83(2):258–264. 160. Engler JR, Frede A, Saunders VA, Zannettino ACW, Hughes TP, White DL. 2010. Chronic myeloid leukemia CD34+ cells have reduced uptake of imatinib due to low OCT-1 activity. Leukemia 24(4):765–770. ¨ 161. Shnitsar V, Eckardt R, Gupta S, Grottker J, Muller GA, Koepsell H, Burckhardt G, Hagos Y. 2009. Expression of human organic cation transporter 3 in kidney carcinoma cell lines increases chemosensitivity to melphalan, irinotecan, and vincristine. Cancer Res 69(4):1494–1501. 162. Peluso G, Nicolai R, Reda E, Benatti P, Barbarisi A, Calvani M. 2000. Cancer and anticancer therapy-induced modifications on metabolism mediated by carnitine system. J Cell Physiol 182(3):339–350. 163. Tamai I, Yabuuchi H, Nezu J, Sai Y, Oku A, Shimane M, Tsuji A. 1997. Cloning and characterization of a novel human pHdependent organic cation transporter, OCTN1. FEBS Lett 419(1):107–111. 164. Tamai I, Ohashi R, Nezu J-i, Yabuuchi H, Oku A, Shimane M, Sai Y, Tsuji A. 1998. Molecular and functional identification of sodium ion-dependent, high affinity human carnitine transporter OCTN2. J Biol Chem 273(32):20378–20382. 165. Rytting E, Audus KL. 2007. Effects of low oxygen levels on the expression and function of transporter OCTN2 in BeWo cells. J Pharm Pharmacol 59(8):1095–1102. 166. Enomoto A, Wempe MF, Tsuchida H, Shin HJ, Cha SH, Anzai N, Goto A, Sakamoto A, Niwa T, Kanai Y, Anders MW, Endou H. 2002. Molecular identification of a novel DOI 10.1002/jps

167.

168.

169.

170.

171.

172.

173.

174.

175.

176.

177.

178.

179.

180.

181.

3749

carnitine transporter specific to human testis. J Biol Chem 277(39):36262–36271. Gong S, Lu X, Xu Y, Swiderski CF, Jordan CT, Moscow JA. 2002. Identification of OCT6 as a novel organic cation transporter preferentially expressed in hematopoietic cells and leukemias. Exp Hematol 30(10):1162–1169. Hagenbuch B, Meier P. 2004. Organic anion transporting polypeptides of the OATP/SLC21 family: Phylogenetic classification as OATP/SLCO superfamily, new nomencla¨ ture and molecular/functional properties. Pflugers Arch 447(5):653–665. Tamai I, Nezu J-i, Uchino H, Sai Y, Oku A, Shimane M, Tsuji A. 2000. Molecular identification and characterization of novel members of the human organic anion transporter (OATP) family. Biochem Biophys Res Commun 273(1):251–260. Hagenbuch B, Meier PJ. 2003. The superfamily of organic anion transporting polypeptides. Biochim Biophys Acta 1609(1):1–18. Hagenbuch B, Gui C. 2008. Xenobiotic transporters of the human organic anion transporting polypeptides (OATP) family. Xenobiotica 38(7–8):778–801. Abe T, Kakyo M, Tokui T, Nakagomi R, Nishio T, Nakai D, Nomura H, Unno M, Suzuki M, Naitoh T, Matsuno S, Yawo H. 1999. Identification of a novel gene family encoding human liver-specific organic anion transporter LST-1. J Biol Chem 274(24):17159–17163. Wang X, Wolkoff AW, Morris ME. 2005. Flavonoids as a novel class of human organic anion-transporting polypeptide OATP1B1 (OATP-C) modulators. Drug Metab Dispos 33(11):1666–1672. Hirano M, Maeda K, Shitara Y, Sugiyama Y. 2004. Contribution of OATP2 (OATP1B1) and OATP8 (OATP1B3) to the hepatic uptake of pitavastatin in humans. J Pharmacol Exp Ther 311(1):139–146. Takane H, Kawamoto K, Sasaki T, Moriki K, Moriki K, Kitano H, Higuchi S, Otsubo K, Ieiri I. 2009. Life-threatening toxicities in a patient with UGT1A1∗ 6/∗ 28 and SLCO1B1∗ 15/ ∗ 15 genotypes after irinotecan-based chemotherapy. Cancer Chemother Pharmacol 63(6):1165–1169. Okabe M, Szakacs G, Reimers MA, Suzuki T, Hall MD, Abe T, Weinstein JN, Gottesman MM. 2008. Profiling SLCO and SLC22 genes in the NCI-60 cancer cell lines to identify drug uptake transporters. Mol Cancer Ther 7(9):3081–3091. Letschert K, Keppler D, K¨onig J. 2004. Mutations in the SLCO1B3 gene affecting the substrate specificity of the hepatocellular uptake transporter OATP1B3 (OATP8). Pharmacogenetics 14(7):441–452. Hamada A, Sissung T, Price DK, Danesi R, Chau CH, Sharifi N, Venzon D, Maeda K, Nagao K, Sparreboom A, Mitsuya H, Dahut WL, Figg WD. 2008. Effect of SLCO1B3 haplotype on testosterone transport and clinical outcome in caucasian patients with androgen-independent prostatic cancer. Clin Cancer Res 14(11):3312–3318. Muto M, Onogawa T, Suzuki T, Ishida T, Rikiyama T, Katayose Y, Ohuchi N, Sasano H, Abe T, Unno M. 2007. Human liver-specific organic anion transporter-2 is a potent prognostic factor for human breast carcinoma. Cancer Sci 98(10):1570–1576. Lee W, Belkhiri A, Lockhart AC, Merchant N, Glaeser H, Harris EI, Washington MK, Brunt EM, Zaika A, Kim RB, ElRifai W. 2008. Overexpression of OATP1B3 confers apoptotic resistance in colon cancer. Cancer Res 68(24):10315–10323. Nozawa T, Suzuki M, Takahashi K, Yabuuchi H, Maeda T, Tsuji A, Tamai I. 2004. Involvement of estrone-3sulfate transporters in proliferation of hormone-dependent breast cancer cells. J Pharmacol Exp Ther 311(3):1032– 1037.

JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 100, NO. 9, SEPTEMBER 2011

3750

NAKANISHI AND TAMAI

182. Nozawa T, Suzuki M, Yabuuchi H, Irokawa M, Tsuji A, Tamai I. 2005. Suppression of cell proliferation by inhibition of estrone-3-sulfate transporter in estrogen-dependent breast cancer cells. Pharm Res 22(10):1634–1641. 183. Wlcek K, Svoboda M, Sellner F, Krupitza G, Jaeger W, Thalhammer T. 2008. Altered expression of organic anion transporter polypeptide (OATP) genes in human breast carcinoma. Cancer Biol Ther 7(9):1450–1455. 184. Meyer zu Schwabedissen HE, Tirona RG, Yip CS, Ho RH, Kim RB. 2008. Interplay between the nuclear receptor pregnane X receptor and the uptake transporter organic anion transporter polypeptide 1A2 selectively enhances estrogen effects in breast cancer. Cancer Res 68(22):9338– 9347.

JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 100, NO. 9, SEPTEMBER 2011

185. Maeda T, Irokawa M, Arakawa H, Kuraoka E, Nozawa T, Tateoka R, Itoh Y, Nakanishi T, Tamai I. 2010. Uptake transporter organic anion transporting polypeptide 1B3 contributes to the growth of estrogen-dependent breast cancer. J Steroid Biochem Mol Biol 122(4):180–185. 186. Al SW, Mokbel R, Salhab M, Jiang W, Reed M, Mokbel K. 2006. The role of STS and OATP-B mRNA expression in predicting the clinical outcome in human breast cancer. Anticancer Res 26(6C):4985–4990. 187. Bronger H, K¨onig J, Kopplow K, Steiner H-H, Ahmadi R, Herold-Mende C, Keppler D, Nies AT. 2005. ABCC drug efflux pumps and organic anion uptake transporters in human gliomas and the blood-tumor barrier. Cancer Res 65(24):11419–11428.

DOI 10.1002/jps