Epidemic spreading with time delay in complex networks

NANOMEDICINE

Journal of Controlled Release 149 (2011) 65–71

Contents lists available at ScienceDirect

Journal of Controlled Release j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j c o n r e l

Review

The forthcoming applications of gold nanoparticles in drug and gene delivery systems Dakrong Pissuwan a, Takuro Niidome a,b,⁎, Michael B. Cortie c a b c

Department of Applied Chemistry, Faculty of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan Center for Future Chemistry, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan Institute for Nanoscale Technology, University of Technology Sydney, Broadway, NSW 2007, Australia

a r t i c l e

i n f o

Article history: Received 2 October 2009 Accepted 2 December 2009 Available online 11 December 2009 Keywords: Gold nanoparticles Drug and gene delivery Drug and gene release Surface modification

a b s t r a c t The unique optical, chemical, and biological properties of gold nanoparticles have resulted in them becoming of clinical interest in several applications including drug and gene delivery. The attractive features of gold nanoparticles include their surface plasmon resonance, the controlled manner in which they interact with thiol groups, and their non-toxic nature. These attributes can be exploited to provide an effective and selective platform to obtain a targeted intracellular release of some substance. The use of gold nanoparticles can also increase the stability of the payload. Here we review recent advances in the use of gold nanoparticles in drug and gene delivery systems. The topics of surface modification, site-specificity and drugs and gene and gene delivery are discussed. © 2009 Elsevier B.V. All rights reserved.

Contents 1. 2.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gold nanoparticle conjugates in drug delivery systems . . . . . . . . . . . . . . . 2.1. Direct conjugation of gold nanoparticles with pharmaceutical compounds . . 2.2. Surface modification of gold nanoparticles for drug delivery . . . . . . . . . 2.3. Using light as an external stimulus to release a drug from gold nanoparticles . 3. The use of gold nanoparticles for gene delivery . . . . . . . . . . . . . . . . . . 4. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. Introduction In recent years, gold nanoparticles have been extensively studied in biological and photothermal therapeutic contexts. Selected reviews on the use of gold nanoparticles in these applications and on their basic physical, chemical and optical properties are presented in [1–7]. The combination of pharmaceutical products with gold nanoparticles has been a recurring theme in these studies. This interest has been stimulated by the capability of the gold nanoparticles to bind a wide range of organic molecules, their low level of toxicity, and their strong and tunable optical absorption. This has resulted in a broad array of studies in which gold nanoparticles have played a role as drug and ⁎ Corresponding author. Department of Applied Chemistry, Faculty of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan. Tel./fax: +81 92 802 2851. E-mail address: [email protected] (T. Niidome). 0168-3659/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jconrel.2009.12.006

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

65 66 66 66 67 68 70 70

vaccine carriers into target cells or specific tissues. Generally, this has been achieved by modifying the surface of the gold nanoparticles so that they can bind to the specific targeting drugs or other biomolecules. The delivery of drugs with nanoparticles can result in higher concentrations than possible with normal drug delivery schemes [8] which, for example, could increase the overall efficiency of a drug used to destroy pathogenic cells. Furthermore, the unique chemical, physical, and photo-physical properties of gold nanoparticles can be exploited in innovative ways to control the transport and controlled release of pharmaceutical compounds [9,10]. The release of a drug from gold nanoparticles could proceed via internal stimuli (operated within a biologically controlled manner; such as pH or glutathione) or via external stimuli (operated with the support of stimuli-generating processes; such as the application of light) [7,11]. Although the general reviews mentioned above do allude to the use of gold nanoparticles in biomedical applications, here we narrow the focus to consider only recent studies in which gold nanoparticles

NANOMEDICINE

66

D. Pissuwan et al. / Journal of Controlled Release 149 (2011) 65–71

have been used as new agents for drug or gene delivery. Of specific interest are the variations in surface modification and bioconjugation that have been developed and, of course, the biodistribution of the resulting nanoparticles. 2. Gold nanoparticle conjugates in drug delivery systems A strong motivation for the new field of ‘nanomedicine’ is that it has the potential to dramatically improve therapeutic outcomes in drug-related therapies. Gold nanoparticles are one of the materials that are frequently mentioned in respect of nanomedical research and the conjugation of gold nanoparticles to specific drugs is one of the possibilities often cited. The motivation for this is the enhanced targeting and delivery of drug to target cells that might be obtained. Generally, there are two types of targeting, designated as ‘active’ and ‘passive’. The term ‘passive targeting’ most commonly refers to the accumulation of nanoparticles or pharmaceutical substances at a specific site by physiochemical factors (e.g. size, molecular weight), extravasation, or pharmacological factors [12]. In the case of ‘active targeting’, the nanoparticle or drug molecule has been conjugated with a specific active molecule that binds to the desired target cells or tissues. For example, nanoparticles can be targeted to specific phagocytic cells [13] or to tumors [14]. In the case of nanoparticles, modification and functionalization of the surface of the nanoparticle plays a major role in this kind of targeting. Here, we will describe how either type of targeting can be used to deliver a conjugated drug or gene. 2.1. Direct conjugation of gold nanoparticles with pharmaceutical compounds It has been shown that conjugates of gold nanoparticles with antibiotics provide promising results in the treatment of intracellular infections [15,16]. The involvement of gold nanoparticles in antibiotic therapy can evidently increase the efficiency of drug delivery to target cells in some cases, although this is not inevitably true [17,18]. In general, the amount of antibiotics used in therapy is much higher than the actual dose required for pathogenic destruction. The excess amount of antibiotics can cause adverse effects [19]. Therefore, the conjugation of gold nanoparticles with antibiotics in combination with some type of targeting would be a possible way to improve antibiotic efficacy. Gold nanoparticles can be directly conjugated with antibiotics or other drug molecules via ionic or covalent bonding, or by physical absorption. For example, methotrexate has been conjugated to 13 nm colloidal gold [20] (Fig. 1a). Methotrexate is an analogue of folic acid that has the ability to destroy folate metabolism of cells and has been commonly used as a cytotoxic anticancer drug. The carboxylic groups on the methotrexate molecule can bind to the surface of gold nanoparticles after overnight incubation. At the same volume, it has been reported that the concentration of the methotrexate conjugated to gold nanoparticle is higher than that of the free methotrexate. The cytotoxic effect of free methotrexate is about seven times lower than that of methotrexate conjugated to gold nanoparticles in the case of Lewis lung carcinoma cells [20]. In another example, Saha et al. [15] directly conjugated different antibiotics to non-functionalized spherical gold nanoparticles of about 14 nm diameter. The gold nanoparticles were conjugated to ampicillin, streptomycin, and kanamycin by physical means. The conjugated forms of the antibiotics were claimed to provide a greater degree of inhibition of the growth of bacteria than the free forms of the antibiotics. Moreover, the stability of the antibiotics after conjugation with gold was also higher than the unconjugated forms. However, the bluish color of the conjugates suggested that there was some aggregation after conjugation, a situation that other workers consider very deleterious [21]. Therefore, it is likely that modification of the surface of the gold nanoparticles to prevent aggregation would

Fig. 1. Schematic representation of methotrexate conjugated to the surface of spherical gold nanoparticles (a), the surface modification of gold nanoparticles using MPA and PEG-amines (b), and photodynamic therapy drugs (Pc 4) conjugated to PEGylated spherical gold nanoparticles.

improve the efficacy of such drug delivery systems further. This possibility will be discussed in the next section. 2.2. Surface modification of gold nanoparticles for drug delivery The surface chemistry of a nanomaterial plays an important role in the conjugation process between biomolecules and nanoparticles. In the case of systems intended for drug delivery there are at least four reasons why surface modification could be useful. The first is to increase the circulation lifetime of the conjugate and to prevent or slow its removal by the reticulo-endothelial system (RES). Another reason is so that the desired targeting and therapeutic molecules can be properly attached. A third reason is to improve the stability of the gold nanoparticles and to prevent their aggregation. Finally, the original capping ligands on some gold nanoparticles (such as gold nanorods) may be cytotoxic and it may be necessary to remedy this problem by modifying the surface. Studies on methods to improve the biocompatibility, bio-stability, and water-solubility of gold-bioconjugates have been recently carried out by several groups. Several studies have highlighted the attractive properties of polymer-modified gold nanoparticles. For example, Laio and Hafner [22] replaced the stabilizing surfactant bilayer surrounding gold nanorods using thiol-terminated methoxypoly(ethylene glycol) instead. This proved suitable for conjugation with anti-rabbit IgG via long chain hetero-bifunctional cross-linker. The amphiphilic characteristics of poly(ethylene glycol) (PEG) in particular ensures that particles coated with it have a high degree of biocompatibility and an affinity for cell membranes. The use of PEG to modify the surface of gold nanoparticles strongly increases the efficiency of cellular uptake compared to unmodified gold nanoparticles [23,24]. The use of

polymers such as PEG also prevents the aggregation of the gold nanoparticles in environments of high ionic strength and supports a longer circulation of the particles in in vivo systems [25,26]. Niidome et al. [27] compared the biodistribution of gold nanorods with and without PEG modification in mice. After an injection of PEG-modified gold nanorods into mice, around 54% of the gold nanorods were found in blood at 0.5 h while 35% of the gold nanorods were found to have accumulated in the liver at 72 h. In contrast, in the case of the unmodified gold nanorods, 30% had already accumulated in the liver at 0.5 h. Another way to modify the surface of gold nanoparticles can be performed by using PEG as a spacer. This can provide a diversity of conjugations on gold nanoparticles. For example, gold nanoparticles coated with courmarin-PEG-thiol were produced and found to be quickly internalized into cells by non-specific endocytosis [26]. The modified particles passed through the cytosol and localized in the perinuclear region. The length of the PEG chain required to stabilize gold nanorods for circulation in blood has also been studied [28] with short PEG chains (molecular weight less than 2000) providing a lower capability to stabilize gold nanorods for circulation in blood. An interesting use of PEG-modified gold nanorods is as a contrast agent for in vivo monitoring of organs in the near-infrared [27,29]. An example of drug delivery using PEG-modified gold nanoparticles is provided by Paciotti et al. [30]. In this study, gold nanoparticles of 26 nm diameter were coated with a mixture of tumor necrosis vector and PEG-thiol and used to target tumor cells by extravasation. However, methods for actively targeting tumor cells with gold nanoparticles are also available. For example Bhattacharya et al. reported that gold nanoparticles functionalised with folic acid and PEG-amines by non-covalent interactions were readily targeted to the folate receptors of cancer cells. Conjugates of folic acid with gold nanoparticle could have an important role for folate receptor-targeted drug delivery or targeted therapy in the future [14]. The ‘layer-by-layer’ technique is another interesting way to modify the surface. Takahashi et al. [31] used this technique to modify phosphatidylcholine-gold nanorods (PC-NR) with bovine serum albumin (BSA) and polyethylenimine (PEI). The BSA-PC-NRs were wrapped inside PEI after a layer-by-layer modification which increased the stability of gold nanorods in electrolyte buffer solution. This modification increased the cellular binding and uptake of the nanoparticles and also prevented their aggregation under physiological conditions. Recent work by Gu et al. [32] has demonstrated a new form of surface functionalized gold nanoparticle that has the capability to target a payload to the cell nucleus. The surfaces of spherical gold nanoparticles of 3.7 nm diameter were modified with 3-mercaptopropionic acid (MPA) to form a self-assembled monolayer. NH2-PEGNH2 was then conjugated to the MPA layer via amidation between the amine end-groups on the PEG and the carboxylic group on the gold nanoparticles (Fig. 1b). This conjugation results in good stability in an electrolyte environment and a high efficiency of intracellular transport, both factors being useful for delivery targeted to the nucleus. Another recent example of a nano-sized drug delivery system consists of gold nanoparticles functionalized with paclitaxel [33]. The C-7 position of paclitaxel was attached with hexa-ethylene glycol (carboxyl-terminated linker) which could in turn be directly conjugated to 4-mercaptophenol-coated gold nanoparticles of 2 nm diameter. These well-defined hybrid drug/gold nanoparticles could have potential in drug delivery systems [33]. As we have shown, there are several strategies to modify the surface of gold nanoparticles. In general, these can be divided into methods based on covalent or non-covalent reactions. Non-covalent interactions can provide interesting assemblies of gold nanoparticles with biomolecules [34] but, of course, a covalent interaction is far stronger. The high stability of a covalent interaction may even be a problem in some instances as the question of the efficient release of the drug payload once it has reached the target zone needs to be considered [14]. To overcome this problem, gold nanoparticles can be

67

modified instead to have a positive or negative charge on their surfaces with functional ligands containing amine or acidic groups acting as a non-covalent binding [35]. Many types of polyelectrolytes such as poly(sodium-4-stryrenesulfonate; PSS), poly(diallydimethyl ammonium chloride; PDADMAC), and poly(allylamine hydrochloride; PAH) have been used for this purpose to coat the surfaces of gold nanoparticles [36,37]. Careful consideration of the surface modification strategy is needed to avoid any agglomeration after surface modification and yet still retain a capability to deliver the payload. 2.3. Using light as an external stimulus to release a drug from gold nanoparticles It is well known that gold nanoparticles of various shapes can undergo a strong plasmon resonance with light, see for example [1,38]. Therefore, these nanoparticles have been considered for use in photothermal therapeutic schemes directed at different types of target cells including cancers, bacteria and parasites [1,13,39,40]. In this context the use of gold nanoparticles may be complementary to photodynamic therapy (PDT), in which light is used to generate oxidizing oxygen species at a target site. Light-induced plasmonic heating may also be exploited to release a chemical payload which had been attached to the gold nanoparticle. This might also provide an interesting approach to delivery material directly into the cytoplasm or nucleus of target cells. Photo-activated drug release by plasmonically active particles appears to have been first described in 2000 [41,42] followed by a related US patent [43]. These works exploited a polymer-gel permeated with gold nanoshells to control drug release. Shortly thereafter, Caruso et al. used spherical gold nanoparticles in a comparable role to achieve the light-induced bursting of lysozymecontaining packages in order to destroy Micrococcus lysodeikticus [44]. Although the plasmon resonance of the original spherical gold nanoparticles is in the middle of the visible wavelength, the resonance peak can be shifted to the near-infrared (NIR, ∼800–1200 nm) by using more complex shapes, for example gold nanorods or gold nanoshells. The use of these more complex nanoparticles could be valuable for in vivo therapy due to the increased transparency of body tissues at NIR wavelengths [45,46]. Recent studies of photoreactions using gold nanorods with pulsed laser irradiation have demonstrated good control of the release of bound PEG (mPEG5000-SH) molecules [47]. For example, about 65% of the PEG chains on the surface of gold nanorods were released after irradiation by a pulsed laser with 25 mJ/ pulse. The PEG was liberated by three processes: cleavage of the Au–S bonds, fragmentation of the chains, and reduction in the surface area of the gold nanoparticle as it morphed from rod to sphere [47]. A related development using gold nanorods coated with poly(Nisopropylacryamide) (PNIPAM) hydrogels has been reported by the same group. In this case, application of the NIR laser caused rapid shrinkage of the hydrogels and released the drug [48,49]. These studies support the idea of using gold nanoparticles in an opticallycontrolled drug release system in the future. In an extension of these principles, gold nanoparticles can be used as a substrate onto which a light-sensitive molecule can be attached. For example, spiropyran is a light-sensitive and fully reversible conformation-changing molecule. When it is irradiated by UV light, its conformation is changed from a closed form to an open form. The process can be reversed by the application of visible light or heat. The open form can construct complexes with amino acids but these complexes are destroyed when the molecule returns to its closed form. This results in release of the amino acids [50]. Such a conjugate could become the basis of an effective light-mediated, controlled release system to treat selected conditions. Although the optical properties of the gold nanoparticle itself are not exploited in this case, a light source is still needed to achieve the therapeutic effects [51]. In another example of this principle, it has been reported that PEGylated spherical

NANOMEDICINE

D. Pissuwan et al. / Journal of Controlled Release 149 (2011) 65–71

NANOMEDICINE

68

D. Pissuwan et al. / Journal of Controlled Release 149 (2011) 65–71

gold nanoparticle conjugates could be bound to silicon phthalocyanine 4 (Pc 4), a hydrophobic drug which is being considered for photodynamic therapy. The attachment is through N–Au bonding of the amine group on the Pc 4 axial ligand to the PEGylated gold surface [52] (Fig. 1c). After the PEGylated gold nanoparticle-Pc 4 conjugate attains the tumor site, irradiation with light of about 670 nm was used to liberate the Pc 4 molecules from the surface of the nanoparticle and initiate phototherapy. Accumulation of the Pc 4 was found at the tumor site only 2 h after injection (Fig. 2). Normally it would about two days for the unconjugated Pc 4 molecule to reach the target site in appreciable proportions due to its hydrophobic nature [52]. 3. The use of gold nanoparticles for gene delivery As we have shown, drug delivery systems based on nanoparticles offer some opportunities to improve the solubility, optimal biodistribution, in vivo stability, and pharmacokinetics of drugs. They can also be used to carry nucleic acids [53]. Generally, the use of nucleic acids to treat and control diseases is termed ‘gene therapy’. This type of therapy can be carried out by using viral and non-viral vectors to transport foreign genes into somatic cells to remedy defective genes there or provide additional biological functions [54,55]. The use of viruses as a vehicle for gene therapy is now well known [56], however, viral vectors have disadvantages such as irregular cytotoxicity, the stimulation of an immune response, limitations in targeting specific cell types, low DNA carrying capacity, lack of ability to infect non-dividing cells, and difficulties in production and packaging [7,54,57–59]. In contrast, non-viral gene delivery systems provide some potential benefits and have low toxicity. Unfortunately, the current non-viral gene delivery systems still suffer from low transfection efficiency due to the difficulty of controlling the process at the nanoscale. All the known vectors must overcome several barriers between the site of administration and the cell nucleus [60,61]. These difficulties include surviving the extracellular environment while en route to the target cells, successfully crossing the cellular membrane, protection of the nucleic acid from nuclease degradation and, finally, release of the functional form of the nucleic acid in the nucleus [62]. To date, nanoparticles such as magnetic nanoparticles, carbon nanotubes and liposomes have been of great interest as non-viral carriers for gene delivery [63–66]. Gold nanoparticles are also attractive because of their unique properties, which we have

Fig. 2. The fluorescence images of a tumor-bearing mouse after intravenous tail injection with PEGylated gold-Pc 4 conjugate in normal saline. Images captured at times ranging from 1 min to 2 h after injection are shown in (a), (b), and (c). Intrinsic fluorescence signals were detected on images (a) and (b). The control sample, (d), was performed by injecting a mouse with drug Pc 4 only. In the last case, the circulation of drug in the mouse body was not detected at 2 h after injection. Reproduced with permission from Cheng et al. [52].

described previously. For example, in 2001 there was an investigation of gold nanoparticles that had been functionalized with cationic quaternary ammonium groups and then electrostatically bound to plasmid DNA. This composite particle could protect the DNA from enzymatic degradation and could regulate DNA transcription of T7 RNA polymerase [66,67]. Thereafter, the same group has also reported the release of DNA from the modified gold nanoparticle after treatment with glutathione (GSH) [68], Fig. 3. In another report, cationic gold nanoparticles prepared by NaBH4 reduction in the presence of 2-aminoethanethiol formed a complex structure with plasmid DNA containing a luciferase gene [69]. This complex particle could be used to deliver a gene into the target HeLa cells in about 3 h. Gold nanorods also have the potential to deliver siRNA to target cells or tissues. The electrostatic binding of siRNA and gold nanorods has been recently reported by the Prasad group [70]. They conjugated cetyltrimethylammonium bromide (CTAB) gold nanorods to siRNA (against DARPP-32 gene in dopaminergic neuronal (DAN) cells) and studied the uptake of conjugates inside the DAN cells. Using both dark-field imaging and confocal microscopy, they found that the siRNA was efficiently delivered into DAN cells after treatment with the gold nanorod–siRNA conjugates and cell viability was 98%. Moreover, there was still about 67% knockdown of DARPP32 gene expression after 120 h for the cells that were incubated with the gold nanorod–siRNA conjugates, compared to only about 30% knockdown for cells treated with a commercial transfection agent as a control. This study also confirms that gold nanoparticles can be used as innovative vehicle to deliver genes into neuron cells. According to the authors of that study, this might one day provide the basis for a nanotherapy to treat drug addiction in patients. Recently, work has shown that the combination of phototherapy with conventional gene therapy offers a high possibility to improve the efficiency of gene delivery into cells [71]. For example, Niidome et al. [72] have investigated the release of plasmid DNA from spherical gold nanoparticles after exposure to pulsed laser irradiation. Spherical gold nanoparticles were produced by the similar method in [69] but in this case polyethylene-glycol-orthopyridyl-disulfide (PEG-OPSS) was added before conjugation with plasmid DNA to increase the stability of the complex particle. The plasmid DNA was released from gold– DNA complex particles by laser irradiation at a power density value of 80 mJ/pulse without any fragmentation of DNA. As mentioned earlier, gold nanorods have demonstrated strong and tunable surface plasmon absorption in the NIR range Therefore, a controlled release system for genes using gold nanorods offers significant possibilities in gene therapy. Chen et al. [73] have explored

Fig. 3. Schematic representation of a gold nanoparticle functionalized with cationic quaternary ammonium–DNA complexes that were dissociated by GSH to release DNA after treatment with GSH.

69

Fig. 4. Confocal microscope images showing the expression of EGFP in HeLa cells after transfection with gold nanorod–EGFP DNA conjugates in combination with NIR irradiation. The left image is the bright-field image of cells (in white circles). The right-hand image shows EGFP expression of the same cells under the fluorescent mode of confocal microscopy. Reproduced with permission from Chen et al. [73].

the remote control of green fluorescence protein (EGFP) expression in HeLa cells using gold nanorods excited with NIR irradiation. EGFP genes were attached to the surface of gold nanorods by linking of thiolated EGFP DNA through Au–S bonds. When femtosecond NIR irradiation was applied to the gold nanorod–EGFP DNA conjugates, a change of shape from rod to sphere was observed. It was proposed that the transformation of shape induced a release of DNA from gold nanorod–EGFP DNA conjugates. A similar phenomenon was described by the Yamada group [74]. When NIR irradiation of nanorod–EGFP DNA conjugates had been performed in HeLa cells, the expression of EGFP in cells was detected at the irradiated spot after NIR exposure at 79 µJ/pulse for 1 min (Fig. 4). At this condition, around 80% of cells were still alive. These studies indicated that plasmid DNA can be released from the surface of gold nanorods by application of NIR irradiation. An elegant further demonstration of this is in the work of Wijaya et al. [75] who used gold nanorods to selectively release multiple DNA oligonucleotides. They separately conjugated two different DNA oligonucleotides to short and long gold nanorods. The aspect ratio of the short and long gold nanorods was 4.0 and 5.4, corresponding to longitudinal plasmon resonances with light at 800 and 1100 nm respectively. When the

Fig. 5. Schematic representation of selective release of two plasmid DNAs attached to two different sizes of gold nanorods. The short rods (blue) were only spheroidised and purged of their attached plasmid DNA when exposed to 800 nm laser light. A similar action was observed with the long rods (pink) after laser irradiation at 1100 nm. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 6. Schematic representation of remote controlled release of DNA oligonucleotides using gold nanorods. The sense DNA oligonucleotides (the grey lines) are attached to the surface of gold nanorods with a thiol bond. The antisense DNA oligonucleotides (the red lines) are hybridized with the sense DNA oligonucleotides. These antisense DNA oligonucleotides are released after laser irradiation due to photothermal heating of the substrate. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

mixture of the two different sizes of gold nanorods was irradiated with a laser at the wavelength of 800 nm, only the short gold nanorods were melted but not the long ones. Alternatively, when a laser at the wavelength of 1100 nm was used to irradiate the mixture, the long rods transformed to spherical shapes but not the short ones. Transmission electron microscopy (TEM) images showed that the shapes remaining after 1100 nm irradiation were short rods, spheres, and a ‘candy-wrap’ shape. They further studied the selective release of two DNAs, as FAM-DNA and TMR-DNA, in the mixture of short and long gold nanorods, respectively. After laser irradiation at the wavelength of 800 nm, about 70% of the FAM-DNA attached to the short rods was released while only about 10% of the TMR-DNA conjugated to long rods was released. This showed that the selective release from gold nanorods could be a new and powerful technique to improve gene delivery (Fig. 5). Interference of gene expression can also be performed using gold nanorods. Lee et al. have demonstrated the idea of a remote optical switch for localized and selective control of gene interference. Thiolmodified sense oligonucleotides were conjugated with gold nanorods. Thereafter, the antisense oligonucleotides were hybridized to the sense oligonucleotides. After laser irradiation, the double strands of the oligonucleotides were denatured and the antisense oligonucleotides were released from the complex structure. These antisense oligonucleotides can bind to the corresponding mRNA while the sense oligonucleotides were still attached to gold nanorods through thiolbonds. Once the mRNA/oligodeoxynucleotide heteroduplex is formed, its structure will be recognized and degraded by RNaseH enzymes inside the cell, thereby inhibiting the normal genetic function of the mRNA (Fig. 6) [76]. Alloyed combinations of gold (Au) and silver (Ag) in the form of nanorods are another option for a photothermal vector for selective gene delivery. Huang et al. [77] have selectively targeted mixed cancer cells using DNA aptamers (sgc8c) that had been conjugated to Au–Ag nanorods through covalent linkages of aptamers. This rod-shaped, bimetallic nanoparticle provides flexible optical properties with a higher extinction efficiency in the NIR range than for nanorods comprised of gold alone. When DNA–aptamers/Au–Ag conjugates were incubated with the mixture of human acute lymphoblastic leukemia (CEM) and acute promyelotic leukemia (NB-4) cells, the relative dead cell percentages of both cell lines were ∼ 26 and ∼ 9% respectively after laser irradiation at 808 nm for 9 min. CEM cells

NANOMEDICINE

D. Pissuwan et al. / Journal of Controlled Release 149 (2011) 65–71

NANOMEDICINE

70

D. Pissuwan et al. / Journal of Controlled Release 149 (2011) 65–71

showed a higher number of dead cells than NB-4 due to the high specificity of sgc8c DNA aptamers on CEM. Evidently, the DNA aptamer conjugated Au–Ag rods selectively targeted the CEM cells which led to cell death by laser-induced heating. Electroporation is another external stimulus that can be used to release genes from a gold nanoparticle. Kawano et al. [78] have investigated gene delivery in vivo using gold nanoparticles excited with electrical pulses. In this investigation, gold nanoparticles were modified with mPEG-SH5000 and conjugated with plasmid DNA. These were then injected into anesthetized mice. After a suitable delay to allow the conjugates to spread in the mouse, electrical pulses were then applied to the left lobe of its liver. The result was that gene expression was detected in the major mouse organs. In contrast, the injection of naked DNA resulted in a ten-fold lower level of detection. The degradation of DNA in blood, which occurs in times as short as 5 min, is evidently the reason for the inefficient transfection in the latter case. This study illustrates yet another interesting approach to improve gene delivery using gold nanoparticles. 4. Conclusions Gold nanoparticles have come to the fore as a promising new vehicle for drug and gene delivery. Control of the manner, place and timing of release of the payload is vital in drug and gene delivery systems. The poor stability of conventional drugs and genes in biological fluids, their enzymatic degradation, and difficulties in securing their penetration through some barrier or nucleus of cells are some of the unfavorable attributes of the existing technologies. The loading of gold nanoparticles with drugs or genes offers the prospect of greater control and increased therapeutic efficacy. In particular, the combination of gold nanoparticles and laser irradiation to control the release of drugs and genes has the potential to provide useful therapeutic benefits. Nevertheless, it is early days still in this field and in vivo clinical trials are amongst the many key issues that still need to be rigorously explored. References [1] D. Pissuwan, S.M. Valenzuela, M.B. Cortie, Therapeutic possibilities of plasmonically heated gold nanoparticles, Trends Biotechnol. 24 (2) (2006) 62–67. [2] X. Huang, P.K. Jain, I.H. El-Sayed, M.A. El-Sayed, Plasmonic photothermal therapy (PPTT) using gold nanoparticles, Laser Med. Sci. 23 (2008) 217–228. [3] M. Hu, J. Chen, Z.-Y. Li, L. Au, G.V. Hartland, X. Li, D.M. Marquez, Y. Xia, Gold nanostructures: engineering their plasmonic properties for biomedical applications, Chem. Soc. Rev. (2006) 1084–1094. [4] M.-C. Daniel, D. Astruc, Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology, Chem. Rev. 104 (1) (2003) 293–346. [5] D. Pissuwan, S.M. Valenzuela, M.B. Cortie, Prospects for gold nanorod particles in diagnostic and therapeutic applications, Biotechnol. Gen. Eng. Rev. 25 (2008) 93–112. [6] L. Tong, Q. Wei, A. Wei, J.-X. Cheng, Gold nanorods as contrast agents for biological imaging: optical properties, surface conjugation and photothermal effects, Photochem. Photobiol. 85 (2009) 21–32. [7] P. Ghosh, G. Han, M. De, C.K. Kim, V.M. Rotello, Gold nanoparticles in delivery applications, Adv. Drug Deliv. Rev. 60 (11) (2008) 1307–1315. [8] P.C. Chen, S.C. Mwakwari, A.K. Oyelere, Gold nanoparticles: from nanomedicine to nanosensing, Nanotech. Sci. Appl. 1 (2008) 45–66. [9] A.G. Skirtach, A.M. Javier, O. Kreft, K. Köhler, A.P. Alberola, H. Möhwald, W.J. Parak, G.B. Sukhorukov, Laser-induced release of encapsulated materials inside living Cells, Angew. Chem. 118 (28) (2006) 4728–4733. [10] S.R. Sershen, S.L. Westcott, N.J. Halas, J.L. West, Temperature-sensitive polymernanoshell composites for photothermally modulated drug delivery, J. Biomed. Mater. Res. 51 (2000) 293–298. [11] P. Gupta, K. Vermani, S. Garg, Hydrogels: from controlled release to pH-responsive drug delivery, Drug Discov. Today 7 (10) (2002) 569–579. [12] J.K. Vasir, M.K. Reddy, V.D. Labhasetwar, Nanosystems in drug targeting: opportunities and challenges, Current Nanosci. 1 (2005) 47–64. [13] D. Pissuwan, S.M. Valenzuela, M.C. Killingsworth, X. Xu, M.B. Cortie, Targeted destruction of murine macrophage cells with bioconjugated gold nanorods, J. Nanopart. Res. 9 (2007) 1109–1124. [14] R. Bhattacharya, C.R. Patra, A. Earl, S. Wang, A. Katarya, L. Lu, J.N. Kizhakkedathu, M.J. Yaszemski, P.R. Greipp, D. Mukhopadhyay, P. Mukherjee, Attaching folic acid on gold nanoparticles using noncovalent interaction via different polyethylene glycol backbones and targeting of cancer cells, Nanomedicine 3 (3) (2007) 224–238.

[15] B. Saha, J. Bhattacharya, A. Mukherjee, A.K. Ghosh, C.R. Santra, A.K. Dasgupta, P. Karmakar, In vitro structural and functional evaluation of gold nanoparticles conjugated antibiotics, Nanoscale Res. Lett. 2 (2007) 614–622. [16] H. Gu, P.L. Ho, L. Tong, L. Wang, B. Xu, Presenting vancomycin on nanoparticles to enhance antimicrobial activities, Nano Lett. 3 (2003) 1261–1263. [17] M.J. Rosemary, I. MacLaren, T. Pradeep, Investigations of the antibacterial properties of ciprofloxacin@SiO2, Langmuir 22 (2006) 10125–10129. [18] G.L. Burygin, B.N. Khlebtsov, A.N. Shantrokha, L.A. Dykman, V.A. Bogatyrev, N.G. Khlebtsov, On the enhanced antibacteria activity of antibiotics mixed with gold nanoparticles, Nanoscale Res. Lett. 4 (2009) 794–801. [19] R.J. Geller, R.L. Chevalier, D.A. Spyker, Acute amoxicillin nephrotoxicity following an overdose, Clin. Toxicol. 24 (2) (1986) 175–182. [20] Y.-H. Chen, C.-Y. Tsai, P.-Y. Huang, M.-Y. Chang, P.-C. Cheng, C.-H. Chou, D.-H. Chen, C.-R. Wang, A.-L. Shiau, C.-L. Wu, Methotrexate conjugated to gold nanoparticles inhibits tumor growth in a syngeneic lungtumor model, Mol. Pharm. 4 (5) (2007) 713–722. [21] G.L. Burygin, B.N. Khlebtsov, A.N. Shantrokha, L.A. Dykman, V.A. Bogatyrev, N.G. Khlebtsov, On the enhanced antibacterial activity of antibiotics mixed with gold nanoparticles, Nanoscale Res. Lett. 4 (2009) 794–801. [22] H. Liao, J.H. Hafner, Gold nanorod bioconjugates, Chem. Mater. 17 (2005) 4636–4641. [23] S.-W. Choi, W.-S. Kim, J.-H. Kim, Surface modification of functional nanoparticles for controlled drug delivery, J. Dispers. Sci. Technol. 24 (3) (2003) 475–487. [24] G.F. Paciotti, D.G.I. Kingston, L. Tamarkin, Colloidal gold nanoparticles: a novel nanoparticle platform for developing multifunctional tumor-targeted drug delivery vectors, Drug Dev. Res. 67 (1) (2006) 47–54. [25] S. Kommareddy, M. Amiji, Poly(ethyleneglycol)-modified thiolated gelatin nanoparticles for glutathione-responsive intracellular DNA delivery, Nanomedicine 3 (1) (2007) 32–42. [26] D. Shenoy, W. Fu, J. Li, C. Crasto, G. Jones, C. DiMarzio, S. Sridhar, M. Amiji, Surface functionalization of gold nanoparticles using hetero-bifunctional poly(ethylene glycol) spacer for intracellular tracking and delivery, Int. J. Nanomedicine 1 (1) (2006) 51–57. [27] T. Niidome, M. Yamagata, Y. Okamoto, Y. Akiyama, H. Takahashi, T. Kawano, Y. Katayama, Y. Niidome, PEG-modified gold nanorods with a stealth character for in vivo applications, J. Control. Release 114 (3) (2006) 343–347. [28] T. Niidome, Y. Akiyama, M. Yamagata, T. Kawano, T. Mori, Y. Niidome, Y. Katayama, Poly(ethylene glycol)-modified gold nanorods as a photothermal nanodevice for hyperthermia, J. Biomater. Sci. Polym. Ed. 20 (9) (2009) 1203–1215. [29] T. Niidome, Y. Akiyama, K. Shimoda, T. Kawano, T. Mori, Y. Katayama, Y. Niidome, In vivo monitoring of intravenously injected gold nanorods using near-infrared light, Small 4 (7) (2008) 1001–1007. [30] G.F. Paciotti, L. Myer, D. Weinreich, D. Goia, N. Pavel, R.E. McLaughlin, L. Tamarkin, Colloidal gold: a novel nanoparticle vector for tumor directed drug delivery, Drug Deliv. 11 (3) (2004) 169–183. [31] H. Takahashi, T. Niidome, T. Kawano, S. Yamada, Y. Niidome, Surface modification of gold nanorods using layer-by-layer technique for cellular uptake, J. Nanopart. Res. 10 (1) (2008) 221–228. [32] Y.-J. Gu, J. Cheng, C.-C. Lin, Y.W. Lam, S.H. Cheng, W.-T. Wong, Nuclear penetration of surface functionalized gold nanoparticles, Toxicol. Appl. Pharmacol. 237 (2) (2009) 196–204. [33] J.D. Gibson, B.P. Khanal, E.R. Zubarev, Paclitaxel-functionalized gold nanoparticles, J. Am. Chem. Soc. 129 (37) (2007) 11653–11661. [34] N.O. Fischer, C.M. McIntosh, J.M. Simard, V.M. Rotello, Inhibition of chymotrypsin through surface binding using nanoparticle-based receptors, Proc. Natl. Acad. Sci. U.S.A. 99 (8) (2002) 5013–5018. [35] S. Srivastava, A. Verma, B.L. Frankamp, V.M. Rotello, Controlled assembly of protein-nanoparticle composites through protein surface recognition, Adv. Mater. 17 (5) (2005) 617–621. [36] T.S. Hauck, A.A. Ghazani, W.C.W. Chan, Assessing the effect of surface chemistry on gold nanorod uptake, toxicity, and gene expression in mammalian cells, Small 4 (1) (2008) 153–159. [37] A. Gole, C.J. Murphy, Polyelectrolyte-coated gold nanorods: synthesis, characterization and immobilization, Chem. Mater. 17 (6) (2005) 1325–1330. [38] N. Harris, M.J. Ford, M.B. Cortie, Optimization of plasmonic heating by gold nanospheres and nanoshells, J. Phys. Chem. B 110 (22) (2006) 10701–10707. [39] R.S. Norman, J.W. Stone, A. Gole, C.J. Murphy, T.L. Sabo-Attwood, Targeted photothermal lysis of the pathogenic bacteria, Pseudomonas aeruginosa, with gold nanorods, Nano Lett. 8 (1) (2007) 302–306. [40] D. Pissuwan, S.M. Valenzuela, C.M. Miller, M.C. Killingsworth, M.B. Cortie, Destruction and control of Toxoplasma gondii tachyzoites using gold nanosphere/antibody conjugates, Small 5 (9) (2009) 1030–1034. [41] S.R. Sershen, S.L. Westcott, N.J. Halas, J.L. West, Temperature-sensitive polymernanoshell composites for photothermally modulated drug delivery, J. Biomed. Mater. Res. 51 (2000) 293–298. [42] J.L. West, N.J. Halas, Applications of nanotechnology to biotechnology, Curr. Opin. Biotechnol. 11 (2000) 215–217. [43] J.L. West, S.R. Sershen, N.J. Halas, S.J. Oldenburg, R.D. Averitt, Temperaturesensitive polymer/nanoshell composites for photothermally modulated drug delivery, US Patent 6428811(2002). [44] B. Radt, T.A. Smith, F. Caruso, Optically addressable nanostructured capsules, Adv. Mat. 16 (23–24) (2004) 2184–2189. [45] C. Loo, A. Lin, L. Hirsch, M.H. Lee, J. Barton, N. Halas, J. West, R. Drezek, Nanoshellenabled photonics-based imaging and therapy of cancer, Technol. Cancer Res. Treat. 3 (1) (2004) 33–40.

[46] D.P. O'Neal, L.R. Hirsch, N.J. Halas, J.D. Payne, J.L. West, Photo-thermal tumor ablation in mice using near infrared-absorbing nanoparticles, Cancer Lett. 209 (2) (2004) 171–176. [47] S. Yamashita, Y. Niidome, Y. Katayama, T. Niidome, Photochemical reaction of poly (ethylene glycol) on gold nanorods induced by near infrared pulsed-laser irradiation, Chem. Lett. 38 (3) (2009) 226–227. [48] A. Shiotani, T. Mori, T. Niidome, Y. Niidome, Y. Katayama, Stable incorporation of gold nanorods into N-isopropylacrylamidehydrogels and their rapid shrinkage induced by near-infrared laser irradiation, Langmuir 23 (7) (2007) 4012–4018. [49] K. Takahito, N. Yasuro, M. Takeshi, K. Yoshiki, N. Takuro, PNIPAM gel-coated gold nanorods for targeted delivery responding to a near-infrared laser, Bioconj. Chem. 20 (2009) 209–212. [50] B.I. Ipe, S. Mahima, K.G. Thomas, Light-induced modulation of self-assembly on spiropyran-capped gold nanoparticles: a potential system for the controlled release of amino acid derivatives, J. Am. Chem. Soc. 125 (2003) 7174–7175. [51] K.G. Thomas, P.V. Kamat, Chromophore-functionalized gold nanoparticles, Acc. Chem. Res. 36 (12) (2003) 888–898. [52] Y. Cheng, C.S. Anna, J.D. Meyers, I. Panagopoulos, B. Fei, C. Burda, Highly efficient drug delivery with gold nanoparticle vectors for in vivo photodynamic therapy of cancer, J. Am. Chem. Soc. 130 (32) (2008) 10643–10647. [53] D. Felnerova, J.-F. Viret, G.-k. Reinhard, C. Moser, Liposomes and virosomes as delivery systems for antigens, nucleic acids and drugs, Curr. Opin. Biotechnol. 15 (6) (2004) 518–529. [54] D. Luo, W.M. Saltzman, Synthetic DNA delivery systems, Nature Biotech. 18 (2000) 33–37. [55] K. Roy, H.-Q. Mao, S.-K. Huanhg, K.W. Leong, Oral gene delivery with chitosan-DNA nanoparticles generates immunologic protection in amurine model of peanut allergy, Nat. Med. 5 (4) (1999) 387–391. [56] P. Yeh, M. Perricaudet, Advances in adenoviral vectors: from genetic engineering to their biology, FASEB J. 11 (8) (1997) 615–623. [57] E. Check, Gene therapy: a tragic setback, Nature 420 (6912) (2002) 116–118. [58] R.G. Crystal, Transfer of genes to humans: early lessons and obstacles to success, Science 270 (5235) (1995) 404–410. [59] X. Zhang, W.T. Godbey, Viral vectors for gene delivery in tissue engineering, Adv. Drug Deliv. Rev. 58 (4) (2006) 515–534. [60] S.M. Humbert, R.H. Guy, Physical methods for gene transfer: improving the kinetics of gene delivery into cells, Adv. Drug Deliv. Rev. 57 (5) (2005) 733–753. [61] C.M. Wiethoff, C.R. Middaugh, Barriers to nonviral gene delivery, J. Pharm. Sci. 92 (2) (2003) 203–217. [62] M. Thomas, A.M. Klibanov, Non-viral gene therapy: polycation-mediated DNA delivery, Appl. Microbiol. Biotechnol. 62 (1) (2003) 27–34. [63] C. Boyer, P. Priyanto, T.P. Davis, D. Pissuwan, V. Bulmus, M. Kavallaris, W.Y. Teoh, R. Amal, M. Carroll, R. Woodward, T.S. Pierree, Anti-fouling magnetic nanoparticlesfor siRNA delivery, J. Mat.Chem. In press (2010). DOI: 10.1039/b914063h.

71

[64] L. Gao, L. Nie, T. Wang, Y. Qin, Z. Guo, D. Yang, X. Yan, Carbon nanotube delivery of the GFPgene into mammalian cells, Chem. BioChem. 7 (2) (2006) 239–242. [65] R. Suzuki, T. Takizawa, Y. Negishi, N. Utoguchi, K. Maruyama, Effective gene delivery with novel liposomal bubbles and ultrasonic destruction technology, Int. J. Pharm. 354 (1–2) (2008) 49–55. [66] C.M. McIntosh, E.A. Esposito, A.K. Boal, J.M. Simard, C.T. Martin, V.M. Rotello, Inhibition of DNA transcription using cationic mixed monolayer protected gold clusters, J. Am. Chem. Soc. 123 (31) (2001) 7626–7629. [67] G. Han, C.T. Martin, V.M. Rotello, Stability of gold nanoparticle-bound DNA toward biological, physical, and chemical agents, Chem. Biol. Drug Des. 67 (1) (2006) 78–82. [68] G. Han, N.S. Chari, A. Verma, R. Hong, C.T. Martin, V.M. Rotello, Controlled recovery of the transcription of nanoparticle-bound DNA by intracellular concentrations of glutathione, Bioconj. Chem. 16 (6) (2005) 1356–1359. [69] T. Niidome, K. Nakashima, H. Takahashi, Y. Niidome, Preparation of primary amine-modified gold nanoparticles and their transfection ability into cultivated cells, Chem. Commun. (2004) 1978–1979. [70] A.C. Bonoiu, S.D. Mahajan, H. Ding, I. Roy, K.T. Yong, R. Kumar, R. Hu, E.J. Bergey, S.A. Schwartz, P.N. Prasad, Nanotechnology approach for drug addiction therapy: gene silencing using delivery of gold nanorod–siRNA nanoplex in dopaminergic neurons, PNAS 106 (14) (2009) 5546–5550. [71] U. Mariko, H.-S. Mariko, U. Kingo, N. Yasuhide, Photo-Control of the polyplexes formation between DNA and photo-cation generatable water-soluble polymers, Curr. Drug Deliv. 2 (3) (2005) 207–214. [72] Y. Niidome, T. Niidome, S. Yamada, Y. Horiguchi, H. Takahashi, K. Nakashima, Pulsed-laser induced fragmentation and dissociation of DNA immobilized on gold nanoparticles, Mol. Cryst. Liq. Cryst. 445 (2006) 201/[491]–206/[496]. [73] C.C. Chen, Y.P. Lin, C.W. Wang, H.C. Tzeng, C.H. Wu, Y.C. Chen, C.P. Chen, L.C. Chen, Y.C. Wu, DNA-gold nanorod conjugates for remote control of localized gene expression by near infrared irradiation, J. Am. Chem. Soc. 128 (2006) 3709–3715. [74] H. Takahashi, Y. Niidome, S. Yamada, Controlled release of plasmid DNA from gold nanorods induced by pulsed near-infrared light, Chem. Commun. (Camb.) 17 (2005) 2247–2249. [75] A. Wijaya, S.B. Schaffer, I.G. Pallares, K. Hamad-Schifferli, Selective release of multiple DNA oligonucleotides from gold nanorods, ACS Nano 3 (1) (2008) 80–86. [76] S.E. Lee, G.L. Liu, F. Kim, L.P. Lee, Remote optical switch for localized and selective control of geen interference, Nano Lett. 9 (2) (2009) 562–570. [77] Y.F. Huang, K. Sefah, S. Bamrungsap, H.T. Chang, W. Tan, Selective photothermal therapy for mixed cancer cells using aptamer-conjugated nanorods, Langmuir 24 (20) (2008) 11860–11865. [78] T. Kawano, M. Yamagata, H. Takahashi, Y. Niidome, S. Yamada, Y. Katayama, T. Niidome, Stabilizing of plasmid DNA in vivo by PEG-modified cationic gold nanoparticles and the gene expression assisted with electrical pulses, J. Control. Release 111 (3) (2006) 382–389.

NANOMEDICINE

D. Pissuwan et al. / Journal of Controlled Release 149 (2011) 65–71