Potential role of ABC transporters as a detoxification system at the blood–CSF barrier

Advanced Drug Delivery Reviews 56 (2004) 1793 – 1809 www.elsevier.com/locate/addr

Potential role of ABC transporters as a detoxification system at the blood–CSF barrier Elizabeth C.M. de Lange* Division of Pharmacology, Leiden/Amsterdam Center for Drug Research, Gorlaeus Laboratoria, Leiden University, PO BOX 9502, 2300RA Leiden, The Netherlands Received 18 June 2003; accepted 4 July 2004 Available online 25 August 2004

Abstract Exchange of compounds between blood and brain occurs at two barriers, the blood–brain barrier (BBB) and the blood– cerebrospinal fluid barrier (BCSFB). The barrier function is mainly a result of the functionality of the cerebral endothelial cells and choroidal epithelial cells, respectively. These cell types have restricted permeability due to the presence of tight junctions between the cells. Furthermore, these cells express a broad range of transporters. So far, the BBB has been viewed as the most important barrier, especially as its surface is about 3 orders of magnitude larger than that of the BCSFB. Today, there is a shift in the appreciation of the contribution of the BCSFB. In a few recent studies, it has been shown that the BCSFB expresses two types of ATP-binding cassette (ABC) transporters, being the multidrug transporters P-glycoprotein (P-gp) and the multidrug resistance-related protein 1 (MRP1). The knowledge on the function of these transporters in the BCSFB is relatively scarce, but in general, it seems that MRP1 transport is directed towards the blood side, which makes this transporter helpful in elimination of harmful compounds from the CSF. Thereby MRP1 potentially contributes to detoxification of the brain, as a whole, as it is also expressed at the level of the BBB. P-gp, however, while also functional as an efflux pump at the BBB, has an opposite transport direction at the level of the BCSFB, towards the CSF. P-gp may therefore raise the concentration of neurotoxic P-gp substrates in the CSF. Whether this will have a significant contribution to the toxicity in the regions directly exposed to the CSF (periventricular organs) remains to be determined. Specifically, in the epithelial cells of the choroid plexus of the BCSFB, P-gp and MRP1 together serve a protective role by preventing the accumulation of their overlapping and often toxic substrates. A concerted action of P-gp and MRP1 at the choroid plexus might contribute to the maintenance of the role of the BCSFB in brain homeostasis. D 2004 Elsevier B.V. All rights reserved. Keywords: Blood–cerebrospinal fluid barrier (BCSFB); ABC transporters; P-glycoprotein (P-gp); Multidrug resistance-related protein 1 (MRP1); Blood–brain barrier (BBB); Transport

* Tel.: +31 71 527 6330; fax: +31 70 514 1260. E-mail address: [email protected]. 0169-409X/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.addr.2004.07.009

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Contents 1. 2. 3.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Barriers between blood and brain . . . . . . . . . . . . . . . . . . . . . . . . ABC transporters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. ABC transporters in physiological perspective. . . . . . . . . . . . . . . 3.2. ABC transporters and multidrug resistance . . . . . . . . . . . . . . . . 3.2.1. P-glycoprotein . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2. Multidrug resistance-associated proteins . . . . . . . . . . . . . 3.2.3. Breast cancer resistance protein . . . . . . . . . . . . . . . . . 3.3. Factors in functionality of ABC transporters . . . . . . . . . . . . . . . 3.3.1. Polymorphism/genetic variation . . . . . . . . . . . . . . . . . 3.3.2. Modulation or reversal of MDR transporter functionality . . . . . 3.3.3. Drug–drug or drug–food interactions. . . . . . . . . . . . . . . 3.4. Regulation of ABC transporters . . . . . . . . . . . . . . . . . . . . . 4. Potential role of ABC transporters at the blood–cerebrospinal fluid barrier . . . . . 4.1. Active transport systems at the choroid plexus . . . . . . . . . . . . . . 4.2. The ABC transporters at the choroid plexus. . . . . . . . . . . . . . . . 4.3. Opposite directions of transport by P-gp and MRP1 in choroidal epithelium . 5. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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1. Introduction

2. Barriers between blood and brain

The blood–brain barrier (BBB) and the blood– cerebrospinal fluid barrier (BCSFB) are responsible for the transport of endogenous and exogenous compounds into and out of the brain. Thus, these barriers are involved in brain homeostasis. So far, the BBB received the most attention in research. Lately, the significance of the BCSFB has gained more attention by publications indicating that the role of the BCSFB has more impact than earlier appreciated. This article briefly provides general information on the blood–brain barriers, on the role of ATPbinding cassette (ABC) transporters in multidrug resistance and physiology, and on factors that modify the functionality of ABC transporters. Then, the contribution of the BCSFB in exchange of compounds between blood and brain is discussed in relation to active transport by the multidrug transporters P-glycoprotein (P-gp) and the multidrug resistance-related protein 1 (MRP1). These transporters are the ABC transporters so far known to be expressed at the choroid plexus, in subabluminal and basolateral positions, respectively.

Access to the brain is restricted by the presence of two barriers [1]. The first is the blood–brain barrier (BBB) [2–6]. This barrier is based on the characteristics of endothelial cells in the brain microvessel walls. These cells are attached to the continuous basal membrane at the apical (brain) site. The BBB is a blood-to-tissue barrier, and the functions of the cerebral endothelial cells are regulated either by direct contact with surrounding astrocytes, neurons, perivascular microglial cells and microvascular pericytes, or result from soluble factors released from these cells or are present in the blood. Astrocytes and other cells can release chemical factors that modulate endothelial permeability over a time-scale of seconds to minutes, in addition to a role in long-term barrier induction and maintenance. Cell culture models, both primary cells and cell lines, have been used to investigate aspects of barrier induction and modulation [7,8]. The second barrier is the blood–cerebrospinal fluid barrier (BCSFB). This is a composite barrier made up of the choroid plexus, the arachnoid membrane, and the periventricular organs (including the area postrema, median eminence, neurohypophysis, and pinal

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gland). The choroid plexus has fenestrated and therefore highly permeable (endothelial) capillaries at the blood side [9], being separated by a stroma from the epithelial cells that face the CSF. These epithelial cells actually form the basis of the barrier function of the choroid plexus. The choroid plexus is present in the ventricles of the brain as leaflike floating structures. It is the main source for cerebrospinal fluid production [10–12]. The BCSFB resides between circulating blood and circulating CSF, and therefore, soluble factors in these fluids may regulate the function of this barrier. The choroid plexus epithelium is involved in numerous exchange processes that increase the CSF concentrations of nutrients and hormones and decrease the CSF concentrations of potentially deleterious compounds and metabolites. The choroid plexus also contributes to neurohumoral brain modulation and neuroimmune interactions. Furthermore, the implication of the choroid plexus is increasingly documented in pathological processes [13,14]. The cerebral endothelial cells as well as the epithelial cells of the choroid plexus are connected by tight junctions, restricting the paracellular transport route. Furthermore, both cell types express numerous transport systems for influx and/or efflux of nutrients, metabolic products, and ions. This is of importance for the maintenance of an adequate environment for the brain cells, as needed for their proper functioning [13–21]. Both barriers also play a role in xenobiotics transport into the brain [22]. Thus, the diffusion of hydrophilic and/or large xenobiotics through the paracellular space is restricted. Actually, for passive transport, the lipophilicity and the size of the compound are rather good predictors for transport into the brain [23–28]. However, research on active transport mechanisms has made clear that the functionality of the blood–brain barriers depends, to a large extent, on the transporters. Many compounds have been found to be substrates to the transporters expressed at the BBB and BCSFB, including numerous commonly used drugs [29–36]. Another important barrier function is provided by metabolism within the cells of the BBB and BCSFB. Several enzymes that are involved in hepatic drug metabolism have been found in the small microvessels of the brain and the choroid plexus. Enzymes like cytochrome P450 haemoproteins, several cyto-

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chrome P450-dependent monooxygenases, NADPH– cytochrome P450 reductase, epoxide hydrolase, and also conjugating enzymes such as UDP-glucuronosyltransferase and aa-class glutathione S-transferase have been detected in blood vessels of the brain or closely surrounding cell types obtained from both rat and human brain tissue. All these enzymes may serve as benzymatic barriersQ to drug influx into the brain [37–41].

3. ABC transporters ABC transporters are found in all organisms and share the homology within the ATP-binding cassette (ABC) region. They often contain transmembrane domains that play a role in the recognition of their substrates. Most ABC proteins are involved in the transport of a very broad spectrum of substances across cell membranes, ranging from small ions to large polypeptides. Such transport occurs against steep concentration gradients at the costs of the energy provided by ATP-hydrolysis [42]. In humans, so far, 48 ABC transporters are known to be present. ABC genes can be divided into a number of families based on organization of domains and amino acid homology (ABCA, ABCB, ABCC, ABCD, ABCE, ABCF, and ABCG) [43]. These genes are essential for many processes in the cell, as exemplified by the fact that mutations in these genes cause or contribute to several human genetic disorders including anemia, cholesterol and bile transport defects, cystic fibrosis, neurological disease, and retinal degeneration [43–45]. The importance of ABC transporters in human physiology, toxicology, pharmacology, and disease has been extensively reviewed by Borst et al. [46]. 3.1. ABC transporters in physiological perspective The transport of specific molecules across lipid membranes is an essential factor in the physiology of all living organisms, and a large number of specific transporters have evolved to carry out this function. Many ABC genes play a role in the maintenance of the lipid bilayer and in the transport of fatty acids and sterols within the body [47–50]. Actually, the ABCA1 transporter is a key regulator of high-density lip-

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oprotein metabolism. The expression of a large number of ABC transporters in monocytes/macrophages and their regulation by cholesterol flux indicate that these transporter molecules are potentially critical players in chronic inflammatory diseases such as atherosclerosis [51]. ABC transporters have been implicated in cellular transmembrane lipid transport, and hereditary diseases have been causatively linked to defective ABC transporters translocating lipids [47]. Another ABC transporter is the ABCB1- or MDR1-encoded P-glycoprotein (P-gp). This transporter seems to be involved in the transport of cytokines (IL-2, IL-4, and IFN-g) in normal peripheral T lymphocytes and in the migration of dendritic cells from the periphery to lymph nodes to initiate T lymphocyte-mediated immunity [52,53]. P-gp may even play a role in allograft rejection and in the inhibition of apoptosis [54–56]. Another possible role of P-gp lies in the pathogenesis of Alzheimer’s disease. This has been indicated by the demonstration of direct interaction of P-gp with amyloid-h40 and amyloid-h42 and the finding that, in human brain tissue, the accumulation of amyloid-h seemed to be influenced by the expression of P-gp in blood vessels [57,58].

molecules, while the members of the MRP family can extrude both hydrophobic uncharged molecules and water-soluble anionic compounds (Table 1). By examining the interactions of the multidrug transporters with pharmacological and toxic agents, a prediction for the cellular and tissue distribution of these agents can be achieved [60–62].

3.2. ABC transporters and multidrug resistance

3.2.1. P-glycoprotein The first identified and so far best characterized multidrug resistance transporter is P-gp [63]. P-gp acts as an efflux pump, leading to lower intracellular concentrations of a very broad spectrum of natural, toxic products like anthracyclines, taxanes, epipodophyllotoxins, and vinca-alkaloids [63–65]. As quite a number of tumors express P-gp, multidrug resistance may be very important with regard to the development of resistance to chemotherapy. P-gp is also expressed in a variety of normal tissues such as the epithelial cells of the liver, the kidney, the choroid plexus and the intestine, and the capillary endothelial cells of the brain [66–69]. Numerous investigations with drugs such as cyclosporine, digoxin, domperidone, etoposide, loperamide, ondansteron, Taxol, and vinblastine have demonstrated that P-gp has an important role in determining the concentration–time profiles of P-gp substrates in the different parts of the body [63,70].

Part of the ABC transporters is involved in multidrug resistance. The major role of the multidrug transporters seems to be the protection of cells and tissues against xenobiotics, as these transporters play a key role in drug absorption, distribution, metabolism, and toxicity. Multidrug resistance is defined as the ability of cells to develop resistance to a broad range of structurally and functionally unrelated drugs after being exposed to these drugs. For intrinsic and/or acquired multidrug resistance of cells, three major groups of ABC transporters are involved: (i) the multidrug resistance gene 1 (ABCB1 or MDR1)encoded P glycoprotein (P-gp); (ii) (part of the) the multidrug resistance-associated protein family (ABCC1 or MRP1, MRP2, and probably MRP3, MRP4, and MRP5); and (iii) the breast cancer resistance protein (BCRP, MRX or ABCG2) (Table 1) [43,59]. In general, the P-gp and BCRP preferentially extrude large hydrophobic, positively charged

3.2.2. Multidrug resistance-associated proteins Alternative to P-gp, MDR transporters such as the multidrug resistance-related protein 1 (MRP1 or ABCC1) have been identified in multidrug resistance cells not expressing P-gp [71]. The finding of MRP1 has been the answer to the question how cells were able to remove the water-soluble products of phase II metabolism by conjugation of toxic compounds to glutathione, sulfate, or glucuronate from the cell [72– 77]. Today, it is known that MRP1 actually is a prototype GS-X pump that transports a variety of drugs conjugated to glutathione, to sulfate or to glucuronate, but also anionic drugs and dyes, neutral–basic amphiphatic drugs, and even oxyanions (Table 1). More specifically, MRP1 substrates include lipid peroxidation products, herbicides, tobacco-specific nitrosamines, mycotoxins, heavy metals, natural products, and antifolate anti-cancer agents [76]. MRP1 also transports unmodified xenobiotics but

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Table 1 Multidrug resistance ABC transporters with their gene codes, transporter names, and part of their substrates and inhibitors/modulators (-GS stands for the glutathione conjugate) Gene

Transporter (most common name)

Function

Substrates

Inhibitors/modulators

ABCB1 (PGY1, MDR1)

P-glycoprotein

multidrug resistance

amiodarone, amitryptilin, amprenavir, biricodar (VX-710), chlorpromazin, cyclosporin A, diltiazem, dipyridamol, fluphenazin, GF120918, gramicidine D, LY335979, mefipriston, midazolam, nelfinavir, pimozin, pluronic L61, progesterone, promethazin, propafenone, propanolol, quinidine, reserpine, ritonavir, saquinavir, spironolactone, staurosporin, tamoxifen, trifluoperazin, triflupromazin, V-104, valinomycine, valspodar (PSC 833), verapamil

ABCC1 (MRP1)

multidrug resistance-related protein

drug resistance

ABCC2 (MRP2)

cMOAT

organic anion efflux

ABCC3 (MRP3)

MRP3

drug resistance

ABCC4 (MRP4)

MRP4

nucleoside transport

ABCC5 (MRP5)

MRP5

nucleoside transport

ABCG2 (BCRP, MXR)

breast cancer resistance protein

drug resistance

actinomycine D, aldosteron, amprenavir, bisantrene, calcein-M, citalopram, colchicine, corticosterone, cortisol, cyclosporin A, dexamethasone, digoxin, domperidone, doxorubicin, daunorubicin, enaminonen, erythromycine, etoposide, FK506, indinavir, loperamide, lovastatin, morphine, nelfinavir, ondansetron, paclitaxel (taxol), phenytoin, prednisolone, quinidine, rifampin, ritonavir, sanquinavir, sparfloxacin, teniposide, terfenadine, (99m)-Tc-tetrofosfine, valspodar (PSC833), verapamil, vinblastine, vincristine aflatoxin B1-epoxide-GS, chlorambucil-GS, colchicine, dehydroepiandrosteron (DHEAS), 2,4-dinitrophenyl-GS, etoposide, fluorescein, 17-h-glucoronyl estradiol, S-glutathionyl prostaglandin A2, glucuronosyl etoposide, glutathione disulfide, 4-hydroxynonenol-GS, leukotriene C4/D4/E4, melphalan-GS, methotrexate, NNAL-O-glucuronide, rhodamine cisplatin, doxorubicin, epirubicin, etoposide, indinavir, phenytoin, ritonavir, saquinavir acetaminophen glucuronide, etoposide, leukotriene C4, methotrexate, teniposide conjugated steroids and bile acids, dehydroepiandrosterone (DHEAS), nucleotide analogs, 9-(2-phosphophenyl methoxylethyl)-adenine (PMEA), prostaglandins, taurolithocholate 3-sulfate, thiopurine monophosphates, zidovudin and other antiretroviral agents nucleotide analogs, 9-(2-phosphonomethoxyethyl) adenine (PMEA), thiopurine monophosphates anthracyclines, bisantrene, mitoxantrone, irinotecan, SN-38, topotecan

benzbromarone, biricodar (VX-710), probenecid, sulfinylpyrazone

leukotriene C4, probenecid

probenecid

probenecid

probenecid

GF120918

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often requires glutathione to do so. The oxyanions arsenite and antimonite and the neutral–basic drugs are co-transported with glutathione. The most important substrate of MRP1 is the endogenous glucoronide conjugate leukotriene C4 (LTC4) [77]. Later, other MRP family members have been discovered. The total family now includes MRP1–8, (or ABCC1–6 and ABCC10+11) [22,69,78–82]. These transporters appear to have a broad tissue distribution. MRP1 is ubiquitously expressed in normal tissues, in the rat with the highest levels in lung and choroid plexus [77,83–85]. For the expression and physiological function of MRPs in brain cells, not much details have been elucidated yet. On the cellular level, the presence of rat mrp1 has been identified in the epithelial cells of the choroid plexus [86] and in endothelial cells of brain microvessels [87,88], while the expression of Mrp4, Mrp5, and Mrp6 and low levels of Mrp3 mRNAs has been reported in these cells [89]. The mRNAs encoding for MRP1 and MRP5 have been detected in human brain [90]. The presence of Mrp2 immunoreactivity was demonstrated for isolated capillaries from rat and bovine brain [91]. Human brain endothelial cells contained mRNAs of MRP1, MRP2, MRP3 and MRP5, and their quantities increased with epilepsy [92]. An extensive overview of the substrate specificity and transport mode of the MRP family has been provided by Renes et al. [93]. In general, the MRPs are (multispecific) organic anion transporters, which can transport negatively charged anionic drugs and neutral drugs conjugated to glutathione, glucuronate, or sulfate (Table 1). The related transporters MRP2 and MRP3 have overlapping substrate specificities with MRP1 but different tissue distributions, and there is evidence that they also have chemoprotective functions [77]. MRP4 and MRP5 broaden the spectrum of drug resistance to nucleotide analogue drugs [94]. Some MRPs are able to transport neutral drugs if co-transported with glutathione. The transport of conjugated substrates and transport of substrates needing co-transport of glutathione, together with the toxicological relevance of MRP1, has been reviewed by Leslie et al. [76]. 3.2.3. Breast cancer resistance protein The breast cancer resistance gene BCRP (ABCG2, also known as MXR1 or ABCP) is a relatively novel

ABC half transporter and may have a protective function by preventing toxins from entering cells. It might also play a role in regulating stem cell differentiation. BCRP is involved in multidrug resistance in cancer, especially with regard to acute myeloid leukemia [95]. When overexpressed in cell lines, BCRP has the ability to confer high levels of resistance to anthracyclines, mitoxantrone, bisantrene, and the camptothecins topotecan and SN 38. Other BCRP substrates are, for example, topotecan or irinotecan [96,97]. The mechanism by which substrates are recognized by BCRP and how the energy of ATP hydrolysis is transduced into transport is unclear [98]. BCRP is expressed abundantly in the placenta, breast, as well as in liver, intestine, and stem cells. Also, BCRP is located at the BBB, mainly at the luminal surface of microvessel endothelium. This localization closely resembles that of P-gp. ABCG2 has several substrates in common with P-gp and may pose an additional barrier to drug access to the brain [99,100]. 3.3. Factors in functionality of ABC transporters The functionality of membrane associated ABC transporters varies with polymorphism and variations in the level of expression, post-translational processes, and membrane composition. Also, the transport of one particular substrate will be influenced by the presence of other substrates. 3.3.1. Polymorphism/genetic variation A number of mutations in several ABC-genes have been shown to lead to genetic diseases, such as cystic fibrosis, Tangier disease, and adrenoleukodystrophy. Other mutations seem to play a critical role in immune responses, cholesterol homeostasis [101], potassium transport, and the regulation of insulin secretion [43]. Functional genetic polymorphisms in the MDR1 gene have been identified which influence the distribution and bioavailability of P-gp substrates [102]. For MRP1, MRP2, and BCRP, the substrate specificity has shown to be sensitive to amino acid substitutions in the protein [51,103–106]. An overview of pharmacologically relevant genetic, structural, and functional data, as well as on hereditary polymorphisms, their pheno-

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typical consequences, and pharmacological implications on multidrug resistance transporters, is provided by Kerb et al. [107]. 3.3.2. Modulation or reversal of MDR transporter functionality Intrinsic and acquired multidrug resistance in many human cancers may be due to expression of P-gp. There is substantial evidence that P-gp is expressed both as an acquired mechanism (leukemias, lymphomas, myeloma, and breast and ovarian carcinomas) and constitutively (in colorectal and renal cancers) and that the expression of P-gp is of prognostic significance in many types of cancer. Therefore, lots of efforts have been put into investigations on modulation or reversal of the multidrug resistance by P-gp inhibitors [108–111]. However, this is complicated by the presence of a diversity of multiple-drug-resistance mechanisms in human cancers, by the pharmacokinetic interactions that result from the inhibition of P-gp in normal tissues, and also by the lack of potent and specific inhibitors of P-gp [112]. Several MDR-reversing agents from the first generation include verapamil, quinidine, and cyclosporin A. For these agents, the doses required to reverse MDR were associated with unacceptable toxicities. Second- and third-generation MDR inhibitors include PSC 833, GF120918, VX-710, and LY335979 (Table 1). LY335979 seems to be highly specific for P-gp and does not modulate MRP1- or BCRP-mediated resistance [113]. Verapamil is a substrate for P-gp, but is not (significantly) transported by MRP1 in either intact cells or membrane vesicles. However, verapamil appears to stimulate MRP1-mediated glutathione uptake by inside-out membrane vesicles in a concentration-dependent manner, and this uptake was inhibited by MRP1specific monoclonal antibodies. This may be linked to its effect on the glutathione status of the cells rather than on its ability to inhibit the MRP1 transporter itself [114]. The only inhibitors on MRP1 so far widely used are relatively nonspecific inhibitors of organic anion transport; sulfinpyrazone, probenecid, and benzobromarone. Indomethacin, a non-steroidal anti-inflammatory drug, was able to reverse resistance of MRP1 cells. Indomethacin shows direct interactions with MRP1; however, in

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cells, it is rapidly converted into a glucuronide conjugate, and it is possible that in the body, it is the conjugate rather than the free drug that is transported by MRP1 [115–118]. In order to prevent the development of multidrug resistance The newest concept is to administer P-gp inhibitors or modulators together with the anticancer drugs before or in an early stage of anticipated development of multidrug resistance [119]. 3.3.3. Drug–drug or drug–food interactions Pharmacokinetic drug–drug interactions often occur at the level of P-gp [120,121]. For example, interactions with P-gp were found for the newer antidepressants citalopram, fluoxetine, fluvoxamine, paroxetine, reboxetine, sertraline, and venlafaxine and a number of their major metabolites. The fact that some of these compounds exert P-gp inhibitory effects at similar concentrations as the potent P-gp substrate and inhibitor quinidine suggests pharmacokinetic drug–drug interactions between the newer antidepressants and P-gp substrates [122]. Also, dietary components may influence transporter characteristics. For example, bioflavonoids may modulate the organic anion and glutathione transport, ATPase, and/or drug resistance-conferring properties of MRP1 [51]. The bioflavonoids (apigenin, naringenin, genistein, and quercetin) stimulated MRP1mediated glutathione transport in membrane vesicles, and inhibition by several flavonoids was enhanced by GSH. Although the bioflavonoids increased the apparent affinity of the transporter for glutathione, no evidence was provided for the involvement of a co-transport mechanism [123]. 3.4. Regulation of ABC transporters The expression of several ABC transporters is under tight transcriptional regulation especially by the group of orphan nuclear receptors. Nuclear receptors constitute a family of transcription factors that act as heterodimers. These heterodimers bind to the promotor elements and induce gene expression. In this heterodimer, the obligatory partner is the retinoid receptor. It has long been known that the expression of the drug transporter MDR1 can be induced by various drugs [124]. A potential mechanism for this induction was provided recently,

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through the identification of another member of the family of nuclear receptors, the transcription factor SXR, as a regulator of MDR1 expression [125]. SXR can bind many structurally different ligands such as rifampicin [126], phenobarbital, paclitaxel, clotrimazole, hyperforin, lithocholate, ritonavir, and compounds from Saint John’s wort [46]. The role of SXR in MDR1 expression now explains why MDR1 is induced by these compounds.

4. Potential role of ABC transporters at the blood–cerebrospinal fluid barrier There is a shift in the appreciation of the contribution of the BCSFB to drug transport between blood and brain. The BBB has been considered to be the most important barrier, because its surface is thought to be about 3 orders of magnitude larger than that of the BCSFB. However, the characteristics of the BBB and BCSFB are different, and therefore, relative contributions of the two barriers in the exchange of compounds between blood and brain cannot be judged solely on the ratio of the respective surfaces of these blood–brain barriers. The BCSFB is considered to have a significant role in the exchange of xenobiotics between blood and brain for the following reasons [40]. First, the organization of the tight junctions of the epithelial cells of the choroid plexus is parallel by sparsely interconnected strands, which makes these tight junctions slightly more permeable than those between the brain endothelial cells. Second, the choroidal epithelial cells contain a high level of a number of detoxifying metabolizing enzymes. While the a and A classes of gluthathione S-transferase and glutathione peroxidase have been found in relatively high levels for both barriers, specifically at the BCSFB very high activities (similar to those in the liver) for UDPglucuronosyltransferase and epoxide hydrolase have been found. Also, the BCSFB has a relatively high expression level of several cytochrome P450 isoenzymes. Third, the BCSFB can also rapidly and specifically handle the efflux of a quite a number of xenobiotics. Also, the coupled metabolism-efflux process, as shown for 1-naphthol metabolite, adds a new facet to the understanding of the protective functions of choroid plexus [14].

4.1. Active transport systems at the choroid plexus A number of major active transport systems are expressed at the choroid plexus. These include the ABC transporter family, the Solute Carrier families SLC21 and SLC22 [127], and the peptide transport protein PepT2. The ABC transporter family has already been discussed in the previous section. Members of the SL21 family are the organic aniontransporting polypeptides (Oatps/OATPs) which form a growing gene superfamily and mediate transport of a wide spectrum of amphipathic organic solutes [128]. Different Oatps/OATPs have partially overlapping and partially distinct substrate preferences for organic such as bile salts, taurocholate, bromosulphophtaleine, thyroid hormones, and leukotrienes and various conjugates of steroids, anionic oligopeptides, toxins, drugs, and other xenobiotics [129]. While some Oatps/OATPs are preferentially or even selectively expressed in one tissue such as the liver, other members of this transporter family are expressed in multiple organs including the BBB, choroid plexus, lung, heart, intestine, kidney, placenta, and the testis [130–132]. Then, as indicated in vitro by immunohistochemistry, also, oatp3 is localized located at the brush-border membrane of choroid plexus epithelial cells. Oatp3 is involved in the estrone-3-sulfate efflux transport at the in vitro BCSFB and may play an important role in regulating estrone-3-sulfate levels in the brain [133]. The SCL22 transporter family include the bkidneyQ-type organic anion transporter (OAT) family that indirectly couple Na(+)/dicarboxylate cotransport and dicarboxylate/organic anion exchange [131] As an example, a key role for Oat3 in systemic detoxification and in control of the organic anion distribution in the CSF has been shown by Oat3 (or SLc22a8) knockout mice [134]. This specific transporter has also been indicated for transport of homovanillic acid at the brain capillary endothelial cells [135]. Lastly, the peptide transporters are integral plasma membrane proteins that are expressed at the choroid plexus and contribute to absorption, distribution, and elimination of peptides and peptidomimetics. In particular, the peptide transporter PepT2 is of importance [136,137]. It mediates the uptake of a diverse group of neuropeptides in the choroid plexus, suggesting a role for PEPT2 in the regulation of

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neuropeptides, peptide fragments, and peptidomimetics in the CSF [138,139]. 4.2. The ABC transporters at the choroid plexus Literature on the expression and functionality of specifically ABC transporters at the choroid plexus so far is scarce. Actually, the presence of P-gp and MDR1 expression at the choroid plexus have been indicated by Nishino et al. [77], Rao et al. [86], Sugiyama et al. [33], Wijnholds et al. [140], and Yan et al. [141]. Noninvasive single-photon-emission computed tomography (SPECT) studies with 99mTc-sestamibi, a membrane-permeant radiopharmaceutical that is a substrate of both P-gp and MRP, were performed by Rao et al. [86]. It was concluded that P-gp localizes subapically at the choroid plexus epithelium, with transport into the direction of the CSF. Conversely, MRP localizes basolaterally, conferring transport to the blood side of the epithelial cells. Wijnholds et al. [140] used Mrp1/Mdr1a/Mdr1b triple-knockout (TKO) mice, together with Mdr1a/Mdr1b doubleknockout (DKO) mice to study the contribution of Mrp1 to the tissue distribution and pharmacokinetics of etoposide. MRP1 was present at the choroid plexus epithelium. The functionality of MRP1 at the choroid plexus was indicated following an intravenous administration of etoposide. This resulted in a 10-fold lower concentration of etoposide in the CSF of DKO mice relative to TKO mice, without concomitant differences in brain concentrations, indicating the potential impact of transport at the level of the BCSFB (Fig. 1). Nishino et al. [77] found a four- to fivefold higher level of MRP1 expression at the choroid plexus compared with that in the lung, one of the tissues exhibiting high expression of MRP1. The in vivo vectorial transport of 17h-estradiol-17h-d-glucuronide indicated a basolateral localization of MRP1 in the choroid plexus. Sugiyama et al. [33] investigated the transport of 17h-estradiol-17h-d-glucuronide across the choroid plexus. The efflux of this compound from CSF was examined after intracerebroventricular administration. This indicated the presence of MRP in the choroid plexus, at a basolateral position based upon the direction of the transport. Other indications for transport including MRP transporters was by the study of Yan et al. [141], in which the efflux transport of neotrofin was studied following intracerebroventricu-

Fig. 1. Increased accumulation of etoposide into the CSF of mice lacking Mrp1 (TKO mice) compared with mice containing Mrp1 (DKO mice) 1 h after intravenous administration of EtopophosR (etoposide-phosphate, 60 mg/kg) via a tail vein A 10-fold higher concentration of etoposide in CSF of TKO relative to the concentration in DKO mice was observed, while plasma and total brain concentrations were not significantly different. The figure is reproduced with permission from the Journal of Clinical Investigations [140]. For details, see this reference.

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lar coadministration of, among others, the P-gp inhibitor verapamil and a MRP1 inhibitor. 4.3. Opposite directions of transport by P-gp and MRP1 in choroidal epithelium In the choroidal epithelium, P-gp and MRP1 seem to have opposite transport directions. This indicates

different situations for compounds that are (a) substrates for both P-gp and MRP1, (b) substratesfor P-gp alone, (c) substrates for MRP1 alone without need for a conjugation, and (d) substrates for MRP1 following conjugation (Fig. 2a–d). The compounds that are substrates for both P-gp and MRP1 (a) actually are cleared from the choroidal epithelial cells and may therefore protect these cells, thereby con-

Fig. 2. P-gp and MRP1 have opposite transport directions. This indicates different situations for compounds that are (a) substrates for both P-gp and MRP1, (b) substrates for P-gp alone, (c) substrates for MRP1 alone without need for a conjugation, and (d) substrates for MRP1 following conjugation.

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Fig. 2 (continued).

tributing to the detoxification of the choroid plexus itself [142]. Such compounds may be etoposide and colchicin, but so far, no report has indicated an increased vulnerability of the choroidal epithelial to toxicity of these compounds. For compounds that are substrates for MRP1 alone without need for a conjugation (b), failure of MRP1 efflux will lead to a higher net CSF influx of potentially toxic compounds. In fact, the opposite will occur upon failure of P-gp-mediated transport at the

choroid plexus, namely, a decrease in CSF concentrations for those compounds that are in fact selective substrates to P-gp (c). Under normal conditions, P-gp at the choroid plexus would contribute to higher concentrations of its substrates in the CSF, while Pgp-mediated efflux at the BBB counteracts the distribution into the rest of the brain. Actually, there has been one study particularly dealing with the brain distribution of a P-gp substrate, doxorubicin, using normal mice. Following intravenous injection, doxor-

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ubicin was found not to pass generally into the brain but entered the choroid plexus and periventricular organs [143]. It is, however, difficult to distinguish between P-gp functionality and higher diffusion into the CSF by the leaky BBB in this region as the major cause for the higher CSF concentrations found. Carefully designed studies on inhibition of P-gp functionality at the choroid plexus/brain should provide more information on the importance of P-gp at the choroid plexus in CSF distribution of P-gp substrates. For compounds that need to be conjugated before being transported by MRP1 (d), there is a need for a concerted action of glutathione metabolism and MRP1-mediated efflux. This is comparable to the absorption barrier created by the combined action of intestinal CYP3A and P-glycoprotein [41]. A failure in either MRP1 efflux or glutathione metabolism may lead to higher choroidal epithelial intracellular levels of potentially neurotoxic compounds. Under normal conditions, glutathione metabolism and MRP1 efflux act as a potential detoxification of the choroid plexus cells, but also contribute, via lowering of CSF concentrations, to the detoxification of mostly the periventricular organs of the brain. Finally, BCSFB transport should be put into perspective. Other factors like CSF turnover, the physico-chemical properties of the compound, the depth of effective diffusion from and into brain parenchyma, and the contribution of the BBB transport have to be taken into account [144]. To this end, a strong technique would be the molecular imaging of gene expression and protein function in vivo with positron emission tomography and single-photonemission computed tomography [145] and the use of mathematical modelling of distribution of compounds over brain compartments [3,146,147].

5. Conclusion Our current knowledge on the characteristics of transport across the BCSFB related to the functionality of ABC transporters is scarce. So far, it is known that two ABC transporters are expressed at the level of the BCSFB, being P-gp and MRP1. MRP1 transport is directed towards the blood side, thereby helpful in preventing the entering of harmful compounds into the CSF and/or in eliminating such

compounds from the CSF, thus potentially contributing to detoxification of the brain. P-gp has an opposite transport direction and may therefore raise the concentration of neurotoxic compounds in the CSF. If such a rise in CSF concentration contributes significantly to damage of the brain, mainly in the regions exposed to the CSF, remains to be investigated. A combined action of P-gp and MRP1, however, may be the protection of epithelial cells of the choroid plexus from accumulation of their shared potentially toxic substrates. Thereby, these transporters may contribute to maintenance of a functional choroid plexus that serve an important role in brain homeostasis.

References [1] H. Suzuki, T. Terasaki, Y. Sugiyama, Role of efflux transport across the blood–brain barrier and blood–cerebrospinal fluid barrier on the disposition of xenobiotics in the central nervous system, Adv. Drug Deliv. Rev. 25 (1997) 257 – 285. [2] M.W. Bradbury, The structure and function of the blood– brain barrier, Fed. Proc. 43 (2) (1984) 186 – 190. [3] J.M. Collins, L.D. Dedrick, Distributed model for drug delivery to CSF and brain tissue, J. Am. Physiol. 14 (1983) R303 – R310. [4] E.M. Cornford, The blood–brain barrier, a dynamic regulatory interface, Mol. Physiol. 7 (1985) 219 – 260. [5] J.D. Fenstermacher, C.S. Patlak, R.G. Blasberg, Transport of material between brain extracellular fluid, brain cells and blood, Fed. Proc. 33 (1974) 2070 – 2074. [6] W.M. Pardridge, Recent advances in blood–brain barrier transport, Annu. Rev. Pharmacol. Toxicol. 28 (1988) 25 – 39. [7] N.J. Abbott, Astrocyte–endothelial interactions and blood– brain barrier permeability, J. Anat. 200 (6) (2002) 629 – 638. [8] N.J. Abott, P.A. Revest, Control of brain endothelial permeability, Cerebrovasc. Brain Metab. Rev. 3 (1991) 39 – 72. [9] R.D. Broadwel, M.V. Sofroniew, Serum proteins bypass the blood–brain fluid barriers for extracellular entry to the central nervous system, Exp. Neurol. 120 (2) (1993) 245 – 263. [10] H. Davson, K. Welch, The permeation of several materials into the fluids of the rabbit’s brain, J. Physiol. 218 (2) (1971) 337 – 351. [11] H.F. Cserr, Physiology of the choroid plexus, Physiol. Rev. 51 (1971) 273 – 311. [12] M.R. Del Bigio, The ependyma: a protective barrier between brain and cerebrospinal fluid, Glia 14 (1995) 1 – 13. [13] N. Strazielle, J.F. Ghersi-Egea, Choroid plexus in the central nervous system: biology and physiopathology, J. Neuropathol. Exp. Neurol. 59 (7) (2000) 561 – 574. [14] N. Strazielle, J.F. Ghersi-Egea, Demonstration of a coupled metabolism-efflux process at the choroid plexus as a

E.C.M. de Lange / Advanced Drug Delivery Reviews 56 (2004) 1793–1809

[15]

[16] [17]

[18] [19]

[20]

[21] [22]

[23]

[24]

[25]

[26]

[27]

[28]

[29]

[30]

mechanism of brain protection toward xenobiotics, J. Neurosci. 19 (15) (1999) 6275 – 6289. F. Conti, L.V. Zuccarello, P. Barbaresi, A. Minelli, N.C. Brecha, M. Melone, Neuronal, glial, and epithelial localization of gamma-aminobutyric acid transporter 2, a highaffinity gamma-aminobutyric acid plasma membrane transporter, in the cerebral cortex and neighboring structures, J. Comp. Neurol. 409 (3) (1999) 482 – 494. R.R. Cavalieri, Iodine metabolism and thyroid physiology: current concepts, Thyroid 7 (2) (1997) 177 – 181. Y.M. Kuo, B. Zhou, D. Cosco, J. Gitschier, The copper transporter CTR1 provides an essential function in mammalian embryonic development, Proc. Natl. Acad. Sci. U. S. A. 98 (12) (2001) 6836 – 6841. J.E. Preston, Ageing choroid plexus–cerebrospinal fluid system, Microsc. Res. Tech. 52 (1) (2001) 31 – 37. V.K. Ramanathan, S.J. Chung, K.M. Giacomini, C.M. Brett, Taurine transport in cultured choroid plexus, Pharm. Res. 14 (4) (1997) 406 – 409. M.B. Segal, The choroid plexuses and the barriers between the blood and the cerebrospinal fluid, Cell. Mol. Neurobiol. 20 (2) (2000) 183 – 196. G.G. Somjen, Ion regulation in the brain: implications for pathophysiology, Neuroscientist 8 (3) (2002) 254 – 267. G. Lee, S. Dallas, M. Hong, R. Bendayan, Drug transporters in the central nervous system: brain barriers and brain parenchyma considerations, Pharmacol. Rev. 53 (4) (2001) 569 – 596. J.A. Gratton, M.H. Abraham, M.W. Bradbury, H.S. Chadha, Molecular factors influencing drug transfer across the blood–brain barrier, J. Pharm. Pharmacol. 49 (12) (1997) 1211 – 1216. V.A. Levin, Relationship of octanol/water partition coefficient and molecular weight to rat brain capillary permeability, J. Med. Chem. 23 (1980) 682 – 684. W.H. Oldendorf, Lipid solubility and drug penetration of the blood–brain barrier, Proc. Exp. Biol. Med. 14 (1974) 813 – 816. U. Norinder, M. Haeberlein, Computational approaches to the prediction of blood–brain distribution, Adv. Drug Deliv. Rev. 54 (2002) 291 – 313. H.H. Usansky, P.J. Sinko, Computation of LogBB values for compounds transported through carrier-mediated mechanisms using in vitro permeability data from brain microvessel endothelial cell (BMEC) monolayers, Pharm. Res. 20 (3) (2003) 390 – 396. G. Camenisch, G. Folkers, H. van de Waterbeemd, Review of theoretical passive drug absorption models: historical background, recent developments and limitations, Pharm. Acta Helv. 71 (1996) 309 – 327. G. Lee, S. Dallas, M. Hong, R. Bendayan, Drug transporters in the central nervous system: brain barriers and brain parenchyma considerations, Pharmacol. Rev. 53 (4) (2001) 569 – 596. H. Kusuhara, Z. He, Y. Nagata, Y. Nozaki, T. Ito, H. Masuda, P.J. Meier, T. Abe, Y. Sugiyama, Expression and functional involvement of organic anion transporting polypeptide

[31]

[32]

[33]

[34]

[35]

[36]

[37]

[38]

[39]

[40]

[41]

[42]

[43]

[44]

[45]

1805

subtype 3 (Slc21a7) in rat choroid plexus, Pharm. Res. 20 (5) (2003) 720 – 727. H. Kusuhara, Y. Sugiyama, Efflux transport systems for drugs at the blood–brain barrier and blood–cerebrospinal fluid barrier (part 1), Drug Discov. Today 6 (3) (2001) 150 – 156. H. Kusuhara, Y. Sugiyama, Efflux transport systems for drugs at the blood–brain barrier and blood–cerebrospinal fluid barrier (part 2), Drug Discov. Today 6 (4) (2001) 206 – 212. Y. Sugiyama, H. Kusuhara, H. Suzuki, Kinetic and biochemical analysis of carrier-mediated efflux of drugs through the blood–brain and blood–cerebrospinal fluid barriers: importance in the drug delivery to the brain, J. Control. Release 62 (1–2) (1999) 179 – 186. A.H. Schinkel, E. Wagenaar, C.A.A.M. Mol, L. Van Deemter, P. Borst, P-glycoprotein in the blood–brain barrier of mice influences the brain penetration and pharmacological activity of many drugs, J. Clin. Invest. 97 (1996) 2517 – 2524. A.H. Schinkel, E. Wagenaar, L. Van Deemter, C.AAM. Mol, P. Borst, Absence of the mdr1a p-glycoprotein in mice affects tissue distribution and pharmacokinetics of dexamethasone, digoxin, and cyclosporin A, J. Clin. Invest. 96 (1995) 1698 – 1705. A.H. Schinkel, The roles of P-glycoprotein and MRP1 in the blood–brain and blood–cerebrospinal fluid barriers, Adv. Exp. Med. Biol. 500 (2001) 365 – 372. J.F. Ghersi-Egea, B. Leininger-Muller, G. Suleman, G. Siest, A. Minn, Localization of drug-metabolizing enzyme activities to blood–brain interfaces and circumventricular organs, J. Neurochem. 62 (1994) 1089 – 1096. J.F. Ghersi-Egea, A. Minn, G. Siest, A new aspect of the protective functions of the blood–brain barrier; activities of four drug metabolizing enzymes in isolated brain microvessels, Life Sci. 42 (1998) 2515 – 2523. J.F. Ghersi-Egea, N. Strazielle, Brain drug delivery, drug metabolism, and multidrug resistance at the choroid plexus, Microsc. Res. Tech. 52 (1) (2001) 83 – 88. J.F. Ghersi-Egea, N. Strazielle, Choroid plexus transporters for drugs and other xenobiotics, J. Drug Target. 10 (4) (2002) 353 – 357. L.Z. Benet, C.L. Cummins, The drug efflux–metabolism alliance: biochemical aspects, Adv. Drug Deliv. Rev. 50 (Suppl 1) (2001) S3 – 11. Z.E. Sauna, M.M. Smith, M. Muller, K.M. Kerr, S.V. Ambudkar, The mechanism of action of multidrug-resistance-linked P-glycoprotein, J. Bioenerg. Biomembranes 33 (6) (2001) 481 – 491. M. Dean, A. Rzhetsky, R. Allikmets, The human ATPbinding cassette (ABC) transporter superfamily, Genome Res. 11 (7) (2001) 1156 – 1166. M.M. Gottesman, S.V. Ambudkar, Overview: ABC transporters and human disease, J. Bioenerg. Biomembranes 33 (6) (2001) 453 – 458. C.F. Higgins, ABC transporters: physiology, structure and mechanism—an overview, Res. Microbiol. 152 (3–4) (2001) 205 – 210.

1806

E.C.M. de Lange / Advanced Drug Delivery Reviews 56 (2004) 1793–1809

[46] P. Borst, R. Oude Elferink, Mammalian ABC transporters in health and disease, Annu. Rev. Biochem. 71 (2002) 537 – 592. [47] P. Borst, N. Zelcer, A. van Helvoort, ABC transporters in lipid transport, Biochim. Biophys. Acta 1486 (1) (2000) 128 – 144. [48] M. Dean, Y. Hamon, G. Chimini, The human ATP-binding cassette (ABC) transporter superfamily, J. Lipid Res. 42 (7) (2001) 1007 – 1017. [49] G. Schmitz, W.E. Kaminski, ABC transporters and cholesterol metabolism, Front. Biosci. 6 (2001) D505 – 514. [50] G. Schmitz, W.E. Kaminski, E. Orso, ABC transporters in cellular lipid trafficking, Curr. Opin. Lipidol. 11 (5) (2000) 493 – 501. [51] E.M. Leslie, Q. Mao, C.J. Oleschuk, R.G. Deeley, S.P. Cole, Modulation of multidrug resistance protein 1 (MRP1/ABCC1) transport and atpase activities by interaction with dietary flavonoids, Mol. Pharmacol. 59 (5) (2001) 1171 – 1180. [52] J. Drach, H. Kaufmann, New developments and treatment in multiple myeloma: new insights on molecular biology, Ann. Oncol. 13 (S4) (2002) 43 – 47. [53] G.J. Randolph, S. Beaulieu, S. Lebecque, R.M. Steinman, W.A. Muller, Differentiation of monocytes into dendritic cells in a model of transendothelial trafficking, Science 282 (5388) (1998) 480 – 483. [54] M. Pallis, J. Turzanski, M. Grundy, C. Seedhouse, N. Russell, Resistance to spontaneous apoptosis in acute myeloid leukaemia blasts is associated with p-glycoprotein expression and function, but not with the presence of FLT3 internal tandem duplications, Br. J. Haematol. 120 (6) (2003) 1009 – 1016. [55] M. Frank, M. Denton, S. Alexander, S. Khoury, M. Sayegh, D. Briscoe, Specific MDR1 P-glycoprotein blockade inhibits human alloimmune T cell activation in vitro, J. Immunol. 166 (4) (2001) 2451 – 2459. [56] M. Pallis, J. Turzanski, Y. Higashi, N. Russell, P-glycoprotein in acute myeloid leukaemia: therapeutic implications of its association with both a multidrug-resistant and an apoptosis-resistant phenotype, Leuk. Lymphoma 43 (6) (2002) 1221 – 1228. [57] F.C. Lam, R. Liu, P. Lu, A.B. Shapiro, J.M. Renoir, F.J. Sharom, P.B. Reiner, Beta-Amyloid efflux mediated by pglycoprotein, J. Neurochem. 76 (4) (2001) 1121 – 1128. [58] S. Vogelgesang, I. Cascorbi, E. Schroeder, J. Pahnke, H.K. Kroemer, W. Siegmund, C. Kunert-Keil, L.C. Walker, R.W. Warzok, Deposition of Alzheimer’s beta-amyloid is inversely correlated with P-glycoprotein expression in the brains of elderly non-demented humans, Pharmacogenetics 12 (7) (2002) 535 – 541. [59] J. Wijnholds, Drug resistance caused by multidrug resistance-associated proteins, Novartis Found. Symp. 243 (2002) 69 – 79 (discussion 80-2, 180-5). [60] A. Bodo, E. Bakos, F. Szeri, A. Varadi, B. Sarkadi, The role of multidrug transporters in drug availability, metabolism and toxicity, Toxicol. Lett. 140–141 (2003) 133 – 143. [61] T. Litman, T.E. Druley, W.D. Stein, S.E. Bates, From MDR to MXR: new understanding of multidrug resistance systems,

[62]

[63]

[64]

[65]

[66]

[67]

[68]

[69]

[70] [71]

[72]

[73]

[74]

[75]

their properties and clinical significance, Cell. Mol. Life Sci. 58 (7) (2001) 931 – 959. E. Schneider, S. Hunke, FEMS ATP-binding-cassette (ABC) transport systems: functional and structural aspects of the ATP-hydrolyzing subunits/domains, Microbiol. Rev. 22 (1) (1998) 1 – 20. A.H. Schinkel, J.J.M. Smit, O. Van Tellingen, J.H. Beijnen, E. Wagenaar, L. Van Deemter, C.A.A.M. Mol, M.A. Van der Valk, E.C. Robanus-Maandag, H.PJ. Te Riele, A.J.M. Berns, P. Borst, Disruption of the mouse mdr1a Pglycoprotein gene leads to a deficiency in the blood–brain barrier and to increased sensitivity to drugs, Cell 77 (1994) 491 – 502. A. Seelig, E. Landwojtowicz, Structure–activity relationship of P-glycoprotein substrates and modifiers, Eur. J. Pharm. Sci. 12 (1) (2000) 31 – 40. S. Tolle-Sander, J. Rautio, S. Wring, J.W. Polli, J.E. Polli, Midazolam exhibits characteristics of a highly permeable Pglycoprotein substrate, Pharm. Res. 20 (5) (2003) 757 – 764. B. Cordon-Cardo, J.P. O’Brien, D. Casals, L. RittmanGrauer, J.L. Biedler, M.R. Melamed, J.R. Bertino, Multidrug-resistance gene (P-glycoprotein) is expressed by endothelial cells at blood–brain barrier sites, Proc. Natl. Acad. Sci. U. S. A. 86 (1989) 689 – 695. F. Thiebaut, T. Tsuruo, H. Hamada, M.M. Gottesman, I. Pastan, M.C. Willingham, Cellular localization of the multidrug-resistant gene product P-glycoprotein in normal human tissues, Proc. Natl. Acad. Sci. U. S. A. 84 (1987) 7735 – 7738. R. Bendayan, G. Lee, M. Bendayan, Functional expression and localization of P-glycoprotein at the blood brain barrier, Microsc. Res. Tech. 57 (5) (2002) 365 – 380. H. Sun, H. Dai, N. Shaik, W.F. Elmquist, Drug efflux transporters in the CNS, Adv. Drug Deliv. Rev. 55 (1) (2003) 83 – 105. J.A. Silverman, Multidrug-resistance transporters, Pharm. Biotechnol. 12 (1999) 353 – 386. S.P. Cole, K.E. Sparks, K. Fraser, D.W. Loe, C.E. Grant, G.M. Wilson, R.G. Deeley, Pharmacological characterization of multidrug resistant MRP-transfected human tumor cells, Cancer Res. 54 (22) (1994) 5902 – 5910. D.R. Hipfner, R.G. Deeley, S.P. Cole, Structural, mechanistic and clinical aspects of MRP1, Biochim. Biophys. Acta. 1461 (2) (1999) 359 – 376. G. Jedlitschky, I. Leier, U. Buchholz, K. Barnouin, G. Kurz, D. Keppler, Transport of glutathione, and sulfur conjugates by the MRP gene-encoded conjugate export pump, Cancer Res. 56 (1996) 988 – 994. J.A. Johnson, A. Barbary, S.E. Kornguth, J.F. Brugge, F.L. Siegel, Glutathione S-transferase isoenzymes in rat brain neurons and glia, J. Neurosci. 13 (1993) 2013 – 2023. Y.M. Qian, W. Qiu, M. Gao, C.J. Westlake, S.P. Cole, R.G. Deeley, Characterization of binding of leukotriene C4 by human multidrug resistance protein 1: evidence of differential interactions with NH2- and COOH-proximal halves of the protein, J. Biol. Chem. 276 (42) (2001) 38636 – 38644.

E.C.M. de Lange / Advanced Drug Delivery Reviews 56 (2004) 1793–1809 [76] E.M. Leslie, R.G. Deeley, S.P. Cole, Toxicological relevance of the multidrug resistance protein 1, MRP1 (ABCC1) and related transporters, Toxicology 167 (1) (2001) 3 – 23. [77] J. Wijnholds, R. Evers, M.R. van Leusden, C.A. Mol, G.J. Zaman, U. Mayer, J.H. Beijnen, M. van der Valk, P. Krimpenfort, P. Borst, Increased sensitivity to anticancer drugs and decreased inflammatory response in mice lacking the multidrug resistance-associated protein, Nat. Med. 3 (11) (1997) 1275 – 1279. [78] Y. Guo, E. Kotova, Z.S. Chen, K. Lee, E. Hopper-Borge, M.G. Belinsky, G.D. Kruh, MRP8, ATP-binding cassette C11 (ABCC11), is a cyclic nucleotide efflux pump and a resistance factor for fluoropyrimidines 2V,3V-dideoxycytidine and 9V-(2V-phosphonylmethoxyethyl)adenine, J. Biol. Chem. 278 (32) (2003) 29509 – 29514. [79] P. Borst, R. Evers, M. Kool, J. Wijnholds, A family of drug transporters: the multidrug resistance-associated proteins, J. Natl. Cancer Inst. 92 (16) (2000) 1295 – 1302. [80] M.G. Belinsky, Z.-S. Chen, I. Shchaveleva, H. Zeng, G.D. Kruh, Characterization of the drug resistance and transport properties of multidrug resistance protein 6 (MRP6 ABCC6), Cancer Res. 62 (2002) 6172 – 6177. [81] Z.-S. Chen, E. Hopper-Borge, M.G. Belinsky, I. Shchaveleva, E. Kotova, G.D. Kruh, Characterization of the transport properties of human multidrug resistance protein 7 (MRP7, ABCC10), Mol. Pharmacol. 63 (2003) 351 – 358. [82] E. Hopper, M.G. Belinsky, H. Zeng, A. Tosolini, J.R. Testa, G.D. Kruh, Analysis of the structure and expression pattern of MRP7 (ABCC10), a new member of the MRP subfamily, Cancer Lett. 162 (2001) 181 – 191. [83] W. Wang, N. Ballatori, Endogenous glutathione conjugates: occurrence and biological functions, Pharmacol. Rev. 50 (3) (1998) 335 – 356. [84] J. Nishino, H. Suzuki, D. Sugiyama, T. Kitazawa, K. Ito, M. Hanano, Y. Sugiyama, Transepithelial transport of organic anions across the choroid plexus: possible involvement of organic anion transporter and multidrug resistanceassociated protein, J. Pharmacol. Exp. Ther. 290 (1) (1999) 289 – 294. [85] M.J. Flens, G.J. Zaman, P. van der Valk, M.A. Izquierdo, A.B. Schroeijers, G.L. Scheffer, P. van der Groep, M. de Haas, C.J. Meijer, R.J. Scheper, Tissue distribution of the multidrug resistance protein, Am. J. Pathol. 148 (4) (1996) 1237 – 1247. [86] V.V. Rao, J.L. Dahlheimer, M.E. Bardgett, A.Z. Snyder, R.A. Finch, A.C. Sartorelli, D. Piwnica-Worms, Choroid plexus epithelial expression of MDR1 P glycoprotein and multidrug resistance-associated protein contribute to the blood–cerebrospinal-fluid drug-permeability barrier, Proc. Nat. Acad. Sci. U. S. A. 96 (1999) 3900 – 3905. [87] H. Huai-Yun, D.T. Secrest, K.S. Mark, D. Carney, C. Brandquist, W.F. Elmquist, D.W. Miller, Expression of multidrug resistance-associated protein (MRP) in brain microvessel endothelial cells, Biochem. Biophys. Res. Commun. 243 (3) (1998) 816 – 820. [88] A. Regina, A. Koman, M. Piciotti, B. El Hafny, M.S. Center, R. Bergmann, P.O. Couraud, F. Roux, Mrp1 multidrug

[89]

[90]

[91]

[92]

[93]

[94]

[95]

[96]

[97]

[98]

[99]

[100]

[101]

1807

resistance-associated protein and P-glycoprotein expression in rat brain microvessel endothelial cells, J. Neurochem. 71 (2) (1998) 705 – 715. Y. Zhang, H. Han, W.F. Elmquist, D.W. Miller, Expression of various multidrug resistance-associated protein (MRP) homologues in brain microvessel endothelial cells, Brain Res. 876 (1–2) (2000) 148 – 153. M. Kool, M. de Haas, G.L. Scheffer, R.J. Scheper, M.J. van Eijk, J.A. Juijn, F. Baas, P. Borst, Analysis of expression of cMOAT (MRP2), MRP3, MRP4, and MRP5, homologues of the multidrug resistance-associated protein gene (MRP1), in human cancer cell lines, Cancer Res. 57 (16) (1997) 3537 – 3547. D.S. Miller, S.N. Nobmann, H. Gutmann, M. Toeroek, J. Drewe, G. Fricker, Xenobiotic transport across isolated brain microvessels studied by confocal microscopy, Mol. Pharmacol. 58 (6) (2000) 1357 – 1367. S.M. Dombrowski, S.Y. Desai, M. Marroni, L. Cucullo, K. Goodrich, W. Bingaman, M.R. Mayberg, L. Bengez, D. Janigro, Overexpression of multiple drug resistance genes in endothelial cells from patients with refractory epilepsy, Epilepsia 42 (12) (2001) 1501 – 1506. J. Renes, E.G. de Vries, P.L. Jansen, M. Muller, The (patho)physiological functions of the MRP family, Drug Resist. Updat. 5 (2000) 289 – 302. P.R. Wielinga, I. van der Heijden, G. Reid, J.H. Beijnen, J. Wijnholds, P. Borst, Characterization of the MRP4and MRP5-mediated transport of cyclic nucleotides from intact cells, Biol. Chem. 278 (20) (2003 (May 16)) 17664 – 17671. D.M. van der Kolk, E.G. de Vries, M. Muller, E. Vellenga, The role of drug efflux pumps in acute myeloid leukemia, Leuk. Lymphoma 43 (4) (2002) 685 – 701. M. Maliepaard, M.A. van Gastelen, A. Tohgo, F.H. Hausheer, R.C. van Waardenburg, L.A. de Jong, D. Pluim, J.H. Beijnen, J.H. Schellens, Circumvention of breast cancer resistance protein (BCRP)-mediated resistance to camptothecins in vitro using non-substrate drugs or the BCRP inhibitor GF120918, Clin. Cancer Res. 7 (4) (2001) 935 – 941. M. Maliepaard, G.L. Scheffer, I.F. Faneyte, M.A. Gastelen van, A.C. Pijnenborg, A.H. Schinkel, M.J. van De Vijver, R.J. Scheper, J.H. Schellens, Subcellular localization and distribution of the breast cancer resistance protein transporter in normal human tissues, Cancer Res. 61 (8) (2001) 3458 – 3464. K.F. Ejendal, C.A. Hrycyna, Multidrug resistance and cancer: the role of the human ABC transporter ABCG2, Curr. Protein Pept. Sci. 3 (5) (2002) 503 – 511. H.C. Cooray, C.G. Blackmore, L. Maskell, M.A. Barrand, Localisation of breast cancer resistance protein in microvessel endothelium of human brain, NeuroReport 13 (16) (2002) 2059 – 2063. T. Eisenblatter, S. Huwel, H.J. Galla, Characterisation of the brain multidrug resistance protein (BMDP/ABCG2/BCRP) expressed at the blood–brain barrier, Brain Res. 971 (2) (2003) 221 – 231. M.A. Wollmer, J.R. Streffer, D. Lutjohann, M. Tsolaki, V. Iakovidou, T. Hegi, T. Pasch, H.H. Jung, K. Bergmann,

1808

[102]

[103]

[104]

[105]

[106]

[107]

[108]

[109]

[110]

[111] [112]

[113]

[114]

[115]

E.C.M. de Lange / Advanced Drug Delivery Reviews 56 (2004) 1793–1809 R.M. Nitsch, C. Hock, A. Papassotiropoulos, ABCA1 modulates CSF cholesterol levels and influences the age at onset of Alzheimer’s disease, Neurobiol. Aging 24 (3) (2003) 421 – 426. U. Brinkmann, M. Eichelbaum, Polymorphisms in the ABC drug transporter gene MDR1, Pharmacogenomics 1 (1) (2001) 59 – 64. Y. Honjo, K. Morisaki, L.M. Huff, R.W. Robey, J. Hung, M. Dean, S.E. Bates, Single-nucleotide polymorphism (SNP) analysis in the ABC half-transporter ABCG2 (MXR/BCRP/ ABCP1), Cancer Biol. Ther. 1 (6) (2002) 696 – 702 (November–December). S. Conrad, H.M. Kauffmann, K. Ito, E.M. Leslie, R.G. Deeley, D. Schrenk, S.P. Cole, A naturally occurring mutation in MRP1 results in a selective decrease in organic anion transport and in increased doxorubicin resistance, Pharmacogenetics 2 (4) (2002) 321 – 330. K. Ito, S.L. Olsen, W. Qiu, R.G. Deeley, S.P. Cole, Mutation of a single conserved tryptophan in multidrug resistance protein 1 (MRP1/ABCC1) results in loss of drug resistance and selective loss of organic anion transport, J. Biol. Chem. 276 (19) 15616 – 15624. D.W. Zhang, S.P. Cole, R.G. Deeley, Identification of an amino acid residue in multidrug resistance protein 1 critical for conferring resistance to anthracyclines, J. Biol. Chem. 276 (16) (2001) 13231 – 13239. R. Kerb, S. Hoffmeyer, U. Brinkmann, ABC drug transporters: hereditary polymorphisms and pharmacological impact in MDR1 MRP1 and MRP2, Pharmacogenomics 2 (1) (2001) 51 – 64. E.V. Batrakova, D.W. Miller, S. Li, V.Y. Alakhov, A.V. Kabanov, W.F. Elmquist, Pluronic P85 enhances the delivery of digoxin to the brain: in vitro and in vivo studies, J. Pharmacol. Exp. Ther. 296 (2) (2001) 551 – 557. G. Klopman, M.S. Leming, R. Avner, Quantitative structure– activity relationship of multidrug resistance reversal agents, Mol. Pharmacol. 52 (1997) 323 – 334. W.D. Stein, Reversers of the multidrug resistance transporter P-glycoprotein, Curr. Opin. Investig. Drugs 3 (5) (2002) 812 – 817. A. Seelig, A general pattern for sustrate recognition by Pglycoprotein, Eur. J. Biochem. 251 (1998) 252 – 261. B. Tan, D. Piwnica-Worms, L. Ratner, Multidrug resistance transporters and modulation, Curr. Opin. Oncol. 12 (5) (2000) 450 – 458. R.L. Shepard, J. Cao, J.J. Starling, A.H. Dantzig, Modulation of P-glycoprotein but not MRP1- or BCRP-mediated drug resistance by LY335979, Int. J. Cancer 103 (1) (2003) 121 – 125. D.W. Loe, R.G. Deeley, S.P. Cole, Verapamil stimulates glutathione transport by the 190-kDa multidrug resistance protein 1 (MRP1), J. Pharmacol. Exp. Ther. 293 (2) (2000) 530 – 538. M.P. Draper, R.L. Martell, S.B. Levy, Indomethacin-mediated reversal of multidrug resistance and drug efflux in human and murine cell lines overexpressing MRP, but not P-glycoprotein, Br. J. Cancer 75 (6) (1997) 810 – 815.

[116] X. Decleves, A. Regina, J.L. Laplanche, F. Roux, B. Boval, J.M. Launay, J.M. Scherrmann, Functional expression of Pglycoprotein and multidrug resistance-associated protein (Mrp1) in primary cultures of rat astrocytes, J. Neurosci. Res. 60 (5) (2000) 594 – 601. [117] H. Huai-Yun, D.T. Secrest, K.S. Mark, D. Carney, C. Brandquist, W.F. Elmquist, D.W. Mille, Expression of multidrug resistance-associated protein (MRP) in brain microvessel endothelial cells, Biochem. Biophys. Res. Commun. 243 (3) (1998) 816 – 820. [118] R. Wheeler, S.Y. Neo, J. Chew, S.B. Hladky, M.A. Barrand, Use of membrane vesicles to investigate drug interactions with transporter proteins, P-glycoprotein and multidrug resistance-associated protein, Int. J. Clin. Pharmacol. Ther. 38 (3) (2000) 122 – 129. [119] B.I. Sikic, G.A. Fisher, B.L. Lum, J. Halsey, L. BeketicOreskovic, G. Chen, Modulation and prevention of multidrug resistance by inhibitors of P-glycoprotein, Cancer Chemother. Pharmacol. 40 (1997) S13 – 19 (suppl.). [120] S.C. Armstrong, K.L. Cozza, N.B. Sandson, Six patterns of drug–drug interactions, Psychosomatics 44 (3) (2003) 255 – 258 (May–June). [121] J.H. Lin, Drug–drug interaction mediated by inhibition and induction of P-glycoprotein, Adv. Drug Deliv. Rev. 55 (1) (2003) 53 – 81. [122] J. Weiss, S.M. Dormann, M. Martin-Facklam, C.J. Kerpen, N. Ketabi-Kiyanvash, W.E. Haefeli, Inhibition of P-glycoprotein by newer antidepressants, J. Pharmacol. Exp. Ther. 305 (1) (2003) 197 – 204. [123] E.M. Leslie, Q. Mao, C.J. Oleschuk, R.G. Deeley, S.P. Cole, Modulation of multidrug resistance protein 1 (MRP1/ABCC1) transport and atpase activities by interaction with dietary flavonoids, Mol. Pharmacol. 59 (5) (2001) 1171 – 1180. [124] M.F. Fromm, The influence of MDR1 polymorphisms on Pglycoprotein expression and function in humans, Adv. Drug Deliv. Rev. 54 (10) (2002) 1295 – 1310. [125] T.W. Synold, I. Dussault, B.M. Forman, The orphan nuclear receptor SXR coordinately regulates drug metabolism and efflux., Nat. Med. 7 (5) (2001) 584 – 590. [126] A. Takeshita, M. Taguchi, N. Koibuchi, Y. Ozawa, Putative role of the orphan nuclear receptor SXR (steroid and xenobiotic receptor) in the mechanism of CYP3A4 inhibition by xenobiotics, J. Biol. Chem. 277 (36) (2002) 32453 – 32458. [127] http://www.gene.ucl.ac.uk/nomenclature/genefamily.shtml. [128] R.G. Tirona, R.B. Kim, Pharmacogenomics of organic aniontransporting polypeptides (OATP), Adv. Drug Deliv. Rev. 54 (10) (2002) 1343 – 1352. [129] Y. Nagata, H. Kusuhara, H. Endou, Y. Sugiyama, Expression and functional characterization of rat organic anion transporter 3 (rOat3) in the choroid plexus, Mol. Pharmacol. 61 (5) (2002) 982 – 988. [130] B. Hagenbuch, P.J. Meier, The superfamily of organic anion transporting polypeptides, Biochim. Biophys. Acta 1609 (1) (2003) 1 – 18. [131] B. Gao, B. Hagenbuch, G.A. Kullak-Ublick, D. Benke, A. Aguzzi, P.J. Meier, Organic anion-transporting polypeptides

E.C.M. de Lange / Advanced Drug Delivery Reviews 56 (2004) 1793–1809

[132]

[133]

[134]

[135]

[136]

[137]

[138]

[139]

mediate transport of opioid peptides across blood–brain barrier, J. Pharmacol. Exp. Ther. 294 (1) (2000) 73 – 79. G.A. Kullak-Ublick, T. Fisch, M. Oswald, B. Hagenbuch, P.J. Meier, U. Beuers, G. Paumgartner, Dehydroepiandrosterone sulfate (DHEAS): identification of a carrier protein in human liver and brain, FEBS Lett. 424 (3) (1998) 173 – 176. S. Ohtsuki, T. Takizawa, H. Takanaga, N. Terasaki, T. Kitazawa, M. Sasaki, T. Abe, K. Hosoya, T. Terasaki, In vitro study of the functional expression of organic anion transporting polypeptide 3 at rat choroid plexus epithelial cells and its involvement in the cerebrospinal fluid-to-blood transport of estrone-3-sulfate, Mol. Pharmacol. 63 (3) (2003) 532 – 541. D.H. Sweet, D.S. Miller, J.B. Pritchard, Y. Fujiwara, D.R. Beier, S.K. Nigam, Impaired organic anion transport in kidney and choroid plexus of organic anion transporter 3 (Oat3 (Slc22a8)) knockout mice, J. Biol. Chem. 277 (30) (2002) 26934 – 26943. S. Mori, H. Takanaga, S. Ohtsuki, T. Deguchi, Y.S. Kang, K. Hosoya, T. Terasaki, Rat organic anion transporter 3 (rOAT3) is responsible for brain-to-blood efflux of homovanillic acid at the abluminal membrane of brain capillary endothelial cells, J. Cereb. Blood Flow Metab. 23 (2003) 432 – 440. U.V. Berger, M.A. Hediger, Distribution of peptide transporter PEPT2 mRNA in the rat nervous system, Anat. Embryol (Berl). 199 (5) (1999) 439 – 449. H. Shen, D.E. Smith, R.F. Keep, J. Xiang, F.C. Brosius III, Targeted disruption of the PEPT2 gene markedly reduces dipeptide uptake in choroid plexus, J. Biol Chem. 278 (7) (2003 (February 14)) 4786 – 47891. I. Rubio-Aliaga, H. Daniel, Mammalian peptide transporters as targets for drug delivery, Trends Pharmacol. Sci. 23 (9) (2002) 434 – 440. N.S. Teuscher, R.F. Keep, D.E. Smith, PEPT2-mediated uptake of neuropeptides in rat choroid plexus, Pharm. Res. 18 (6) (2001) 807 – 813.

1809

[140] J. Wijnholds, E.C.M. de Lange, G.L. Scheffer, D.J. van den Berg, C.A.A.M. Mol, M. van der Valk, A.H. Schinkel, R.J. Scheper, D.D. Breimer, P. Borst, Multidrug resistance protein 1 protects the choroid plexus epithelium and contributes to the blood–cerebrospinal fluid barrier, Clin. Invest. 105 (2000) 279 – 285. [141] R. Yan, E.M. Taylor, Neotrofin is transported out of brain by a saturable mechanism: possible involvement of multidrug resistance and monocarboxylic acid transporters, Drug Metab. Dispos. 30 (5) (2002) 513 – 518. [142] D. Begley, personal communication, King’s College, London, UK, 2002. [143] L. Bigotte, Y. Olsson, Cytotoxic effects of adriamycin on the central nervous system of the mouse—cytofluorescence and electron-microscopic observations after various modes of administration, Acta Neurol. Scand. Suppl. 100 (1984) 55 – 67. [144] E.C. de Lange, M. Danhof, Considerations in the use of cerebrospinal fluid pharmacokinetics to predict brain target concentrations in the clinical setting: implications of the barriers between blood and brain, Clin. Pharmacokinet. 41 (10) (2002) 691 – 703. [145] V. Sharma, G.D. Luker, D. Piwnica-Worms, Molecular imaging of gene expression and protein function in vivo with PET and SPECT, J. Magn. Reson. Imaging 16 (4) (2002) 336 – 351. [146] T. Ooie, T. Terasaki, H. Suzuki, Y. Sugiyama, Kinetic evidence for active efflux transport across the blood–brain barrier of quinolone antibiotics, J. Pharmacol. Exp. Ther. 283 (1) (1997) 293 – 304. [147] K. Takasawa, T. Terasaki, H. Suzuki, T. Ooie, Y. Sugiyama, Distributed model analysis of 3V-azido-3V-deoxythymidine and 2V,3V-dideoxyinosine distribution in brain tissue and cerebrospinal fluid, J. Pharmacol. Exp. Ther. 282 (3) (1997) 1509 – 1517.