Factors affecting the clearance and biodistribution of polymeric nanoparticles

A multifunctional envelope type nano device (MEND) for gene delivery to tumours based on the EPR effect: a strategy for overcoming the PEG dilemma

Gene and nucleic acid therapy are expected to play a major role in the next generation of medicine. We recently developed a multifunctional envelope-type nano device (MEND) for use as a novel non-viral gene delivery system. Poly(ethylene glycol) (PEG)ylation is a useful method for achieving a longer circulation time for delivery of the MEND to a tumour via the enhanced permeability and retention (EPR) effect. However, PEGylation strongly inhibits cellular uptake and endosomal escape, which results in significant loss of activity for the delivery system. For successful gene delivery for cancer treatment, the crucial issue associated with the use of PEG, the 'PEG dilemma' must be addressed. In this review, we describe the development and applications of MEND, and discuss strategies for overcoming the PEG dilemma, based on the manipulation of intracellular trafficking of cellular uptake and endosomal release using functional devices such as specific ligands, cleavable PEG systems and endosomal fusogenic/disruptic peptides.

PLGA nanoparticles containing various anticancer agents and tumour delivery by EPR effect

As mortality due to cancer continues to rise, advances in nanotechnology have significantly become an effective approach for achieving efficient drug targeting to tumour tissues by circumventing all the shortcomings of conventional chemotherapy. During the past decade, the importance of polymeric drug-delivery systems in oncology has grown exponentially. In this context, poly(lactic-co-glycolic acid) (PLGA) is a widely used polymer for fabricating 'nanoparticles' because of biocompatibility, long-standing track record in biomedical applications and well-documented utility for sustained drug release, and hence has been the centre of focus for developing drug-loaded nanoparticles for cancer therapy. Such PLGA nanoparticles have also been used to develop proteins and peptides for nanomedicine, and nanovaccines, as well as a nanoparticle-based drug- and gene-delivery system for cancer therapy, and nanoantigens and growth factors. These drug-loaded nanoparticles extravasate through the tumour vasculature, delivering their payload into the cells by the enhanced permeability and retention (EPR) effect, thereby increasing their therapeutic effect. Ongoing research about drug-loaded nanoparticles and their delivery by the EPR effect to the tumour tissues has been elucidated in this review with clarity.

Oxaliplatin long-circulating liposomes improved therapeutic index of colorectal carcinoma

Background

Cytotoxic drugs are non-selective between normal and pathological tissue, and this poses a challenge regarding the strategy for treatment of tumors. To achieve sufficient antitumor activity for colorectal carcinoma, optimization of the therapeutic regimen is of great importance. We investigated the ability of oxaliplatin long-circulating liposomes (PEG-liposomal L-oHP) to provide an improved therapeutic index of colorectal carcinoma.

Results

We determined that PEG- liposomes conjugated with cells at 2 h, with a mean fluorescence intensity that was enhanced upon extended induction time. The PEG-liposomal L-oHP induced a significant apoptotic response as compared with free L-oHP, 23.21% ± 3.38% vs. 16.85% ± 0.98%, respectively. Fluorescence imaging with In-Vivo Imaging demonstrated that PEG- liposomes specifically targeted tumour tissue. After intravenous injections of PEG-liposomal L-oHP or free L-oHP, the tumour volume suppression ratio was 26.08% ± 12.43% and 18.19% ± 7.09%, respectively, the percentage increased life span (ILS%) was 45.36% and 76.19%, respectively, and Bcl-2, Bax mRNA and protein expression in tumour tissue was 0.27-fold vs. 0.88-fold and 1.32-fold vs. 1.61-fold compared with free L-oHP, respectively.

Conclusion

The PEG-liposomal L-oHP exhibited a tendency to target tumour tissue and demonstrated a significantly greater impact on apoptosis compared to free oxaliplatin.

A DNA microarray-based analysis of the host response to a nonviral gene carrier: a strategy for improving the immune response

The purpose of this study was to investigate the host response to systemically administered lipid nanoparticles (NPs) encapsulating plasmid DNA (pDNA) in the spleen using a DNA microarray. As a model for NPs, we used a multifunctional envelope-type nano device (MEND). Microarray analysis revealed that 1,581 of the differentially expressed genes could be identified by polyethylene glycol (PEG)-unmodified NP using a threefold change relative to the control. As the result of PEGylation, the NP treatment resulted in the reduction in the expression of most of the genes. However, the expression of type I interferon (IFN) was specifically increased by PEGylation. Based on the microarray and a pathway analysis, we hypothesize that PEGylation inhibited the endosomal escape of NP, and extended the interaction of toll-like receptor-9 (TLR9) with CpG-DNA accompanied by the production of type I IFN. This hypothesis was tested by introducing a pH-sensitive fusogenic peptide, GALA, which enhances the endosomal escape of PEGylated NP. As expected, type I IFN was reduced and interleukin-6 (IL-6) remained at the baseline. These findings indicate that a carrier design based on microarray analysis and the manipulation of intracellular trafficking constitutes a rational strategy for reducing the host immune response to NPs.

The new toxicology of sophisticated materials: nanotoxicology and beyond

It has long been recognized that the physical form of materials can mediate their toxicity--the health impacts of asbestiform materials, industrial aerosols, and ambient particulate matter are prime examples. Yet over the past 20 years, toxicology research has suggested complex and previously unrecognized associations between material physicochemistry at the nanoscale and biological interactions. With the rapid rise of the field of nanotechnology and the design and production of increasingly complex nanoscale materials, it has become ever more important to understand how the physical form and chemical composition of these materials interact synergistically to determine toxicity. As a result, a new field of research has emerged--nanotoxicology. Research within this field is highlighting the importance of material physicochemical properties in how dose is understood, how materials are characterized in a manner that enables quantitative data interpretation and comparison, and how materials move within, interact with, and are transformed by biological systems. Yet many of the substances that are the focus of current nanotoxicology studies are relatively simple materials that are at the vanguard of a new era of complex materials. Over the next 50 years, there will be a need to understand the toxicology of increasingly sophisticated materials that exhibit novel, dynamic and multifaceted functionality. If the toxicology community is to meet the challenge of ensuring the safe use of this new generation of substances, it will need to move beyond "nano" toxicology and toward a new toxicology of sophisticated materials. Here, we present a brief overview of the current state of the science on the toxicology of nanoscale materials and focus on three emerging toxicology-based challenges presented by sophisticated materials that will become increasingly important over the next 50 years: identifying relevant materials for study, physicochemical characterization, and biointeractions.

Antibody-targeted nanoparticles for cancer therapy

In recent years, nanoparticulate-mediated drug delivery research has examined a full spectrum of nanoparticles that can be used in diagnostic and therapeutic cancer applications. A key aspect of this technology is in the potential to specifically target the nanoparticles to diseased cells using a range of molecules, in particular antibodies. Antibody–nanoparticle conjugates have the potential to elicit effective targeting and release of therapeutic targets at the disease site, while minimizing off-target side effects caused by dosing of normal tissues. This article provides an overview of various antibody-conjugated nanoparticle strategies, focusing on the rationale of cell-surface receptors targeted and their potential clinical application.

Biodegradable tri-block copolymer poly(lactic acid)-poly(ethylene glycol)-poly(l-lysine)(PLA-PEG-PLL) as a non-viral vector to enhance gene transfection

Low cytotoxicity and high gene transfection efficiency are critical issues in designing current non-viral gene delivery vectors. The purpose of the present work was to synthesize the novel biodegradable poly (lactic acid)-poly(ethylene glycol)-poly(l-lysine) (PLA-PEG-PLL) copolymer, and explore its applicability and feasibility as a non-viral vector for gene transport. PLA-PEG-PLL was obtained by the ring-opening polymerization of Lys(Z)-NCA onto amine-terminated NH(2)-PEG-PLA, then acidolysis to remove benzyloxycarbonyl. The tri-block copolymer PLA-PEG-PLL combined the characters of cationic polymer PLL, PLA and PEG: the self-assembled nanoparticles (NPs) possessed a PEG loop structure to increase the stability, hydrophobic PLA segments as the core, and the primary ɛ-amine groups of lysine in PLL to electrostatically interact with negatively charged phosphate groups of DNA to deposit with the PLA core. The physicochemical properties (morphology, particle size and surface charge) and the biological properties (protection from nuclease degradation, plasma stability, in vitro cytotoxicity, and in vitro transfection ability in HeLa and HepG2 cells) of the gene-loaded PLA-PEG-PLL nanoparticles (PLA-PEG-PLL NPs) were evaluated, respectively. Agarose gel electrophoresis assay confirmed that the PLA-PEG-PLL NPs could condense DNA thoroughly and protect DNA from nuclease degradation. Initial experiments showed that PLA-PEG-PLL NPs/DNA complexes exhibited almost no toxicity and higher gene expression (up to 21.64% in HepG2 cells and 31.63% in HeLa cells) than PEI/DNA complexes (14.01% and 24.22%). These results revealed that the biodegradable tri-block copolymer PLA-PEG-PLL might be a very attractive candidate as a non-viral vector and might alleviate the drawbacks of the conventional cationic vectors/DNA complexes for gene delivery in vivo.

Doxorubicin-loaded (PEG)₃-PLA nanopolymersomes: effect of solvents and process parameters on formulation development and in vitro study

This study is focused on the preparation of doxorubicin-loaded nanopolymersomes (PolyDoxSome) and assessment of the effects of various solvents and process variables on the size and drug loading during preparation of formulation. PolyDoxSome was prepared by nanoprecipitation method using amphiphilic (PEG)₃-PLA copolymer, and the formation of polymersomes was assessed by dynamic light scattering and optical and transmission electron microscopy and evaluated for in vitro release profile and in vitro cytotoxicity. A systematic investigation indicated that solvent composition, order of addition, aqueous phase, copolymer concentration, and external energy input have significant influence on size and dispersity of PolyDoxSome. Under optimized conditions, PolyDoxSome had a size range of 130-180 nm with PDI < 0.2, a zeta potential ∼-8 mV, and a drug loading at ∼11% w/w with an encapsulation efficiency at ∼53% w/w. In vitro release profile of PolyDoxSome at 37 °C demonstrated that doxorubicin release was pH dependent and gave higher release at pH 5.5 in comparison to the release at pH 7.4 (similarity factor, f₂ < 50). PolyDoxSome exhibited enhanced cellular uptake of doxorubicin compared to free doxorubicin solution in MCF-7 cell line and showed a better cytotoxicity of doxorubicin at equivalent dose in nanopolymersomes. In conclusion, size and dispersity were strongly influenced by duration of magnetic stirring and overall composition of organic/aqueous media; however, size and dispersity were retained against different degrees of dilution. PolyDoxSome was able to control the release of doxorubicin in pH dependent manner and effectively deliver the drug in active form to MCF-7 breast cancer cells.

Optical nano-constructs composed of genome-depleted brome mosaic virus doped with a near infrared chromophore for potential biomedical applications

We have engineered an optical nanoconstruct composed of genome-depleted brome mosaic virus doped with indocyanine green (ICG), an FDA-approved near-infrared (NIR) chromophore. Constructs are highly monodispersed with standard deviation of ±3.8 nm from a mean diameter of 24.3 nm. They are physically stable and exhibit a high degree of optical stability at physiological temperature (37 °C). Using human bronchial epithelial cells, we demonstrate the effectiveness of the constructs for intracellular optical imaging in vitro, with greater than 90% cell viability after 3 h of incubation. These constructs may serve as a potentially nontoxic and multifunctional nanoplatform for site-specific deep-tissue optical imaging, and therapy of disease.

Multimodality Imaging of Integrin α(v)β(3) Expression

Over the last decade, integrin α_vβ₃ has been studied with every single molecular imaging modality. Since no single modality is perfect and sufficient to obtain all the necessary information for a particular question, combination of certain molecular imaging modalities can offer synergistic advantages over any modality alone. This review will focus on multimodality imaging of integrin α_vβ₃ expression, where the contrast agent used can be detected by two or more imaging modalities, such as combinations of PET and optical, SPECT and fluorescence, PET and MRI, SPECT and MRI, and lastly, MRI and fluorescence. Most of these agents are based on certain type(s) of nanoparticles. Contrast agents that can be detected by more than two imaging modalities are expected to emerge in the future and a PET/MRI/fluorescence agent will likely find the most future biomedical/clinical applications. Big strides have been made over the last decade for imaging integrin α_vβ₃ expression and several PET/SPECT probes have been tested in human studies. For dualmodality and multimodality imaging applications, a number of proof-of-principle studies have been reported which opened up many new avenues for future research. The next decade will likely witness further growth and continued prosperity of molecular imaging studies focusing on integrin α_vβ₃, which can eventually impact patient management.

Targeted biocompatible nanoparticles for the delivery of (-)-epigallocatechin 3-gallate to prostate cancer cells

Molecular targeted cancer therapy mediated by nanoparticles (NPs) is a promising strategy to overcome the lack of specificity of conventional chemotherapeutic agents. In this context, the prostate-specific membrane antigen (PSMA) has demonstrated a powerful potential for the management of prostate cancer (PCa). Cancer chemoprevention by phytochemicals is emerging as a suitable approach for the treatment of early carcinogenic processes. Since (-)-epigallocatechin 3-gallate (EGCG) has shown potent chemopreventive efficacy for PCa, we designed and developed novel targeted NPs in order to selectively deliver EGCG to cancer cells. Herein, to explore the recent concept of "nanochemoprevention", we present a study on EGCG-loaded NPs consisting of biocompatible polymers, functionalized with small molecules targeting PSMA, that exhibited a selective in vitro efficacy against PSMA-expressing PCa cells. This approach could be beneficial for high risk patients and would fulfill a significant therapeutic need, thus opening new perspectives for novel and effective treatment for PCa.

The effect of surface charge on in vivo biodistribution of PEG-oligocholic acid based micellar nanoparticles

To systematically elucidate the effect of surface charge on the cellular uptake and in vivo fate of PEG-oligocholic acid based micellar nanoparticles (NPs), the distal PEG termini of monomeric PEG-oligocholic acid dendrimers (telodendrimers) are each derivatized with different number (n = 0, 1, 3 and 6) of anionic aspartic acids (negative charge) or cationic lysines (positive charge). Under aqueous condition, these telodendrimers self-assemble to form a series of micellar NPs with various surface charges, but with similar particle sizes. NPs with high surface charge, either positive or negative, were taken up more efficiently by RAW 264.7 murine macrophages after opsonization in fresh mouse serum. Mechanistic studies of cellular uptake of NPs indicated that several distinct endocytic pathways (e.g., clathrin-mediated endocytosis, caveolae-mediated endocytosis, and macropinocytosis) were involved in the cellular uptake process. After their cellular uptake, the majority of NPs were found to localize in the lysosome. Positively charged NPs exhibited dose-dependent hemolytic activities and cytotoxicities against RAW 264.7 cells proportional to the positive surface charge densities; whereas negatively charged NPs did not show obvious hemolytic and cytotoxic properties. In vivo biodistribution studies demonstrated that undesirable liver uptake was very high for highly positively or negatively charged NPs, which is likely due to active phagocytosis by macrophages (Kupffer cells) in the liver. In contrast, liver uptake was very low but tumor uptake was very high when the surface charge of NPs was slightly negative. Based on these studies, we can conclude that slightly negative charge may be introduced to the NPs surface to reduce the undesirable clearance by the reticuloendothelial system (RES) such as liver, improve the blood compatibility, thus deliver the anti-cancer drugs more efficiently to the tumor sites.

Interactions of nanoparticles with plasma proteins: implication on clearance and toxicity of drug delivery systems

INTRODUCTION

Intravenously injected nanoparticles, like any other foreign pathogen that enters the body, encounter multiple lines of defense intended to neutralize and eliminate the invading substance. Adsorption of plasma proteins on the nanoparticle surface is the first barrier of defense, which could lead to physical changes in the formulation, such as aggregation and charge neutralization, biochemical activation of defense cascades, and trigger elimination by multiple types of phagocytic cell.

AREAS COVERED

In this review, recent knowledge on the mechanisms that govern the interactions of nanoparticles (micelles, liposomes, polymeric and inorganic nanoparticles) with plasma proteins is discussed. In particular, the role of the nanoparticle surface properties and protective polymer coating in these interactions is described. The mechanisms of protein adsorption on different nanoparticles are analyzed and the implications on the clearance, toxicity and efficacy of drug delivery are discussed. The review provides readers with the biological insight into the plasma/blood interactions of nanoparticles.

EXPERT OPINION

The immune recognition of nanoparticles can seriously affect the drug delivery efficacy and toxicity. There is at present not enough knowledge on the mechanisms that dictate the nanoparticle immune recognition and stability in the biological milieu. Understanding the mechanisms of recognition will become an important part of nanoparticle design.

Internalization and biodistribution of polymersomes into oral squamous cell carcinoma cells in vitro and in vivo

The prognosis for oral squamous cell carcinoma (OSCC) is not improving despite advances in surgical treatment. As with many cancers, there is a need to deliver therapeutic agents with greater efficiency into OSCC to improve treatment and patient outcome. The development of polymersomes offers a novel way to deliver therapy directly into tumor cells. Here we examined the internalization and biodistribution of two different fluorescently labeled polymersome formulations; polyethylene oxide (PEO)-poly 2-(diisopropylamino)ethyl methacrylate (PDPA) and poly 2-(methacryloyloxy)ethyl phosphorylcholine (PMPC)-PDPA, into SCC4 OSCC cells in vitro and in vivo. In vitro SCC4 monolayers internalized PMPC-PDPA and PEO-PDPA at similar rates. However, in vivo PMPC-PDPA polymersomes penetrated deeper and were more widely dispersed in SCC4 tumors than PEO-PDPA polymersomes. In the liver and spleen PMPC-PDPA mainly accumulated in tissue macrophages. However, in tumors PMPC-PDPA was found extensively in the nucleus and cytoplasm of tumor cells as well as in tumor-associated macrophages. Use of PMPC-PDPA polymersomes may enhance polymersome-mediated antitumor therapy.

Doxorubicin loaded iron oxide nanoparticles overcome multidrug resistance in cancer in vitro

Multidrug resistance (MDR) is characterized by the overexpression of ATP-binding cassette (ABC) transporters that actively pump a broad class of hydrophobic chemotherapeutic drugs out of cancer cells. MDR is a major mechanism of treatment resistance in a variety of human tumors, and clinically applicable strategies to circumvent MDR remain to be characterized. Here we describe the fabrication and characterization of a drug-loaded iron oxide nanoparticle designed to circumvent MDR. Doxorubicin (DOX), an anthracycline antibiotic commonly used in cancer chemotherapy and substrate for ABC-mediated drug efflux, was covalently bound to polyethylenimine via a pH sensitive hydrazone linkage and conjugated to an iron oxide nanoparticle coated with amine terminated polyethylene glycol. Drug loading, physiochemical properties and pH lability of the DOX-hydrazone linkage were evaluated in vitro. Nanoparticle uptake, retention, and dose-dependent effects on viability were compared in wild-type and DOX-resistant ABC transporter over-expressing rat glioma C6 cells. We found that DOX release from nanoparticles was greatest at acidic pH, indicative of cleavage of the hydrazone linkage. DOX-conjugated nanoparticles were readily taken up by wild-type and drug-resistant cells. In contrast to free drug, DOX-conjugated nanoparticles persisted in drug-resistant cells, indicating that they were not subject to drug efflux. Greater retention of DOX-conjugated nanoparticles was accompanied by reduction of viability relative to cells treated with free drug. Our results suggest that DOX-conjugated nanoparticles could improve the efficacy of chemotherapy by circumventing MDR.

Preparation of poly(MePEGCA-co-HDCA) nanoparticles with confined impinging jets reactor: experimental and modeling study

In this work, the biodegradable copolymer poly(methoxypolyethyleneglycolcyanoacrylate-co-hexadecylcyanoacrylate) is used to prepare nanoparticles via solvent displacement in a confined impinging jets reactor (CIJR). For comparison, nanoparticles constituted by the homopolymer counterpart are also investigated. The CIJR is a small passive mixer in which very fast turbulent mixing of the solvent (i.e., acetone and tetrahydrofuran) and of the antisolvent (i.e., water) solutions occurs under controlled conditions. The effect of the initial copolymer concentration, solvent type, antisolvent-to-solvent ratio, and mixing rate inside the mixer on the final nanoparticle size distribution, surface properties, and morphology is investigated from the experimental point of view. The effect of some of these parameters is studied by means of a computational fluid dynamics (CFD) model, capable of quantifying the mixing conditions inside the CIJR. Results show that the CIJR can be profitably used for producing nanoparticles with controlled characteristics, that there is a clear correlation between the mixing rate calculated by CFD and the mean nanoparticle size, and therefore that CFD can be used to design, optimize, and scale-up these processes.

Surface functionalization of PLGA nanoparticles by non-covalent insertion of a homo-bifunctional spacer for active targeting in cancer therapy

This work reports the surface functionalization of polymeric PLGA nanoparticles by non-covalent insertion of a homo-bifunctional chemical crosslinker, bis(sulfosuccinimidyl) suberate (BS3) for targeted cancer therapy. We dissolved BS3 in aqueous solution of PVA during formulation of nanoparticles by a modified solid/oil/water emulsion solvent evaporation method. The non-covalent insertion of BS3 was confirmed by Fourier transform infrared (FTIR) spectroscopy. Curcumin and annexin A2 were used as a model drug and a cell specific target, respectively. Nanoparticles were characterized for particle size, zeta potential and surface morphology. The qualitative assessment of antibody attachment was performed by transmission electron microscopy (TEM) as well as confocal microscopy. The optimized formulation showed antibody attachment of 86%. However, antibody attachment was abolished upon blocking the functional groups of BS3. The availability of functional antibodies was evaluated by the presence of a light chain fraction after gel electrophoresis. We further evaluated the in vitro release kinetics of curcumin from antibody coated and uncoated nanoparticles. The release of curcumin is enhanced upon antibody attachment and followed an anomalous release pattern. We also observed that the cellular uptake of nanoparticles was significantly higher in annexin A2 positive cells than in negative cells. Therefore, these results demonstrate the potential use of this method for functionalization as well as to deliver chemotherapeutic agents for treating cancer.

Targeted delivery of a cisplatin prodrug for safer and more effective prostate cancer therapy in vivo

Targeted delivery and controlled release of inactive platinum (Pt) prodrugs may offer a new approach to improve the efficacy and tolerability of the Pt family of drugs, which are used to treat 50% of all cancers today. Using prostate cancer (PCa) as a model disease, we previously described the engineering of aptamer (Apt)-targeted poly(D,L-lactic-co-glycolic acid)-b-poly(ethylene glycol) (PLGA-b-PEG) nanoparticles (NPs) encapsulating a Pt(IV) prodrug c,t,c[Pt(NH(3))(2)-(O(2)CCH(2)CH(2)CH(2)CH(2)CH(3))(2)Cl(2)] (1) (Pt-PLGA-b-PEG-Apt-NP), which target the extracellular domain of the prostate specific membrane antigen (PSMA), for enhanced in vitro cytotoxicity. Here we demonstrate enhanced in vivo pharmacokinetics (PK), biodistribution, tolerability, and efficacy of Pt-PLGA-b-PEG-Apt-NP (150 ± 15 nm encapsulating ∼5% wt/wt Pt(IV) prodrug) when compared to cisplatin administered in its conventional form in normal Sprague Dawley rats, Swiss Albino mice, and the PSMA-expressing LNCaP subcutaneous xenograft mouse model of PCa, respectively. The 10-d maximum tolerated dose following a single i.v. injection of Pt-PLGA-b-PEG-NP in rats and mice was determined at 40 mg/kg and 5 mg/kg, respectively. PK studies with Pt-PLGA-b-PEG-NP revealed prolonged Pt persistence in systemic blood circulation and decreased accumulation of Pt in the kidneys, a major target site of cisplatin toxicity. Pt-PLGA-b-PEG-Apt-NPs further displayed the significant dose-sparing characteristics of the drug, with equivalent antitumor efficacy in LNCaP xenografts at 1/3 the dose of cisplatin administered in its conventional form (0.3 mg/kg vs. 1 mg/kg). When considering the simultaneous improvement in tolerability and efficacy, the Pt-PLGA-b-PEG-Apt NP provides a remarkable improvement in the drug therapeutic index.

Using mechanobiological mimicry of red blood cells to extend circulation times of hydrogel microparticles

It has long been hypothesized that elastic modulus governs the biodistribution and circulation times of particles and cells in blood; however, this notion has never been rigorously tested. We synthesized hydrogel microparticles with tunable elasticity in the physiological range, which resemble red blood cells in size and shape, and tested their behavior in vivo. Decreasing the modulus of these particles altered their biodistribution properties, allowing them to bypass several organs, such as the lung, that entrapped their more rigid counterparts, resulting in increasingly longer circulation times well past those of conventional microparticles. An 8-fold decrease in hydrogel modulus correlated to a greater than 30-fold increase in the elimination phase half-life for these particles. These results demonstrate a critical design parameter for hydrogel microparticles.

PET Imaging and Biodistribution of Silicon Quantum Dots in Mice

Investigation of nanomaterial disposition and fate in the body is critical before such material can be translated into clinical application. Herein a new macrocyclic ligand-(64)Cu(2+) complex was synthesized and used to label dextran-coated silicon quantum dots (QD), with an average hydrodynamic diameter of 15.1 ± 7.6 nm. The chelate showed exceptional stability, demonstrated by no loss radiolabel under a ligand competition reaction with EDTA. The QDs' biodistribution in mice was quantitatively evaluated by in vivo positron emission tomography (PET) imaging and ex vivo gamma counting. Results showed that they were excreted via renal filtration shortly postinjection and also accumulated in the liver.

NANOSCALE SELF-ASSEMBLY FOR DELIVERY OF THERAPEUTICS AND IMAGING AGENTS

Self-assemblies are complex structures spontaneously organized from simpler subcomponents, primarily through noncovalent interactions. These structures are being exploited as delivery vehicles of therapeutic and imaging agents. They have two unique advantages in comparison to other vehicles: 1) they are able to assume complex structures that are difficult to attain by chemical synthesis, and 2) the dissociation of self-assembled structures can be triggered by external stimuli, which can serve as a mechanism of payload release. In this review, we discuss two naturally occurring (proteins and viral capsids) and five engineered self-assemblies (vesicles, micelles, proteins, hydrogels, and inclusion complexes) that are under development for delivery of drugs and imaging agents. For each class of self-assembled supramolecular structures, we examine its structural and physicochemical properties, and potential applications within the context of assembly, loading, and payload release.

RNA interference in the clinic: challenges and future directions

Inherent difficulties with blocking many desirable targets using conventional approaches have prompted many to consider using RNA interference (RNAi) as a therapeutic approach. Although exploitation of RNAi has immense potential as a cancer therapeutic, many physiological obstacles stand in the way of successful and efficient delivery. This Review explores current challenges to the development of synthetic RNAi-based therapies and considers new approaches to circumvent biological barriers, to avoid intolerable side effects and to achieve controlled and sustained release.

Stability and in vivo evaluation of pullulan acetate as a drug nanocarrier

To develop pullulan acetate nanoparticles (PANs) as a drug nanocarrier, pullulan acetate (PA) was synthesized and characterized. Its acetylation degree determined by the proton nuclear magnetic resonance ((1)H NMR) was 2.6. PANs were prepared by the solvent diffusion method and characterized by transmission electron microscope (TEM), size distribution, and zeta potential techniques. PANs had nearly spherical shape with a size range of 200-450 nm and low zeta potentials both in distilled water and in 10% FBS. The storage stability of PANs was observed in distilled water. PANs were stored for at least 2 months with no significant size and zeta potential changes. The safety of PANs was studied through single dose toxicity test in mice, and the result showed that PANs were well tolerated at the dose of 200 mg/kg in mice. Epirubicin-loaded PANs (PA/EPI) were also prepared and characterized in this study. Moreover, the in vivo pharmacokinetics of PA/EPI was investigated. Compared with the free EPI group, the PA/EPI group exhibited higher plasma drug concentration, longer half-life time (t(1/2)) and the larger area under the curve (AUC). All results suggested that PANs were stable, safe, and showed a promising potential on improving the bioavailability of the loaded drug of the encapsulated drug.

Oil phase evaporation-induced self-assembly of hydrophobic nanoparticles into spherical clusters with controlled surface chemistry in an oil-in-water dispersion and comparison of behaviors of individual and clustered iron oxide nanoparticles

We report a general method for preparing nanoparticle clusters (NPCs) in an oil-in-water emulsion system mediated by cetyl trimethylammonium bromide (CTAB), where previously only individual nanoparticles were obtained. NPCs of magnetic, metallic, and semiconductor nanoparticles have been prepared to demonstrate the generality of the method. The NPCs were spherical and composed of densely packed individual nanoparticles. The number density of nanoparticles in the oil phase was found to be critical for the formation, morphology, and yield of NPCs. The method developed here is scalable and can produce NPCs in nearly 100% yield at a concentration of 5 mg/mL in water, which is approximately 5 times higher than the highest value reported in the literature. The surface chemistry of NPCs can also be controlled by replacing CTAB with polymers containing different functional groups via a similar procedure. The reproducible production of NPCs with well-defined shapes has allowed us to compare the properties of individual and clustered iron oxide nanoparticles, including magnetization, magnetic moments, and contrast enhancement in magnetic resonance imaging (MRI). We found that, due to their collective properties, NPCs are more responsive to an external magnetic field and can potentially serve as better contrast enhancement agents than individually dispersed magnetic NPs in MRI.

Synthesis and antitumor activity of stearate-g-dextran micelles for intracellular doxorubicin delivery

Stearate-g-dextran (Dex-SA) was synthesized via an esterification reaction between the carboxyl group of stearic acid (SA) and hydroxyl group of dextran (Dex). Dex-SA could self-assemble to form nanoscaled micelles in aqueous medium. The critical micelle concentration (CMC) depended on the molecular weight of Dex and the graft ratio of SA, which ranged from 0.01 to 0.08 mg mL(-1). Using doxorubicin (DOX) as a model drug, the drug encapsulation efficiency (EE%) using Dex-SA with 10 kDa molecular weight of Dex and 6.33% graft ratio of SA could reach up to 84%. In vitro DOX release from DOX-loaded Dex-SA micelles (Dex-SA/DOX) could be prolonged to 48 h, and adjusted by a different molecular weight of Dex, the graft ratio of SA, or the drug-loading content. Tumor cellular uptake test indicated that Dex-SA micelles had excellent internalization ability, which could deliver DOX into tumor cells. In vitro cytotoxicity tests demonstrated the Dex-SA/DOX micelles could maintain the cytotoxicity of commercial doxorubicin injection against drug-sensitive tumor cells. Moreover, Dex-SA/DOX micelles presented reversal activity against DOX-resistant cells. In vivo antitumor activity results showed that Dex-SA/DOX micelles treatments effectively suppressed the tumor growth and reduced the toxicity against animal body compared with commercial doxorubicin injection.

Chitosan-poly(ε-caprolactone)-poly(ethylene glycol) graft copolymers: synthesis, self-assembly, and drug release behavior

Biodegradable tri-component graft copolymers, chitosan-poly(ε-caprolactone)-poly(ethylene glycol) (CPP), were synthesized via a mild route, using sodium dodecyl sulfate-chitosan complex (SCC) as a precursor. Both PCL and PEG could be conveniently conjugated to the hydroxyl sites of chitosan without the need of tedious chemical protection/deprotection processes, thereby leaving the amino groups of chitosan intact. The self-assembly and release behavior of the copolymer micelles were investigated. Paclitaxel and rutin were used as model drugs. Spherical micelles could be formed through self-assembly of CPP in aqueous media. The micelle diameter increased with PEGylation degree and ranged from 30 to 45 nm. The incorporation of drugs into the micelles significantly raised the micelle diameter and diversified the micelle morphologies. The micelles were further subjected to glutaraldehyde treatment to prolong the release of the incorporated drugs. It was found that the crosslinking process shrunk the drug-loaded micelles. In addition, the micelles were endowed with self-luminescent properties after crosslinked with glutaraldehyde. By increasing crosslinking density, the release duration of the model drugs could be prolonged.

Drug delivery to the CNS and polymeric nanoparticulate carriers

The delivery of drugs to the CNS is hampered by the existence of the blood–brain barrier (BBB). Nowadays, medicinal chemists follow defined rules for the development of drugs able to cross the BBB. At the same time, the parameters needed in order to gain valuable estimates of brain drug delivery are well defined. Despite the limits in molecular weight that allow drugs to cross the BBB, it was shown that nanotech products, in particular properly functionalized nanoparticles, spherical particles of approximately 200 nm in diameter, are able to cross the BBB after intravenous administration and act as drug carriers for CNS. Moreover, peptides as ligands for receptors present on the brain endothelium, or able to cross the BBB and to act as carriers for CNS drug delivery in the form of conjugates with drugs, have been discovered and started to be studied as targeting moieties for nanoparticulate systems. This article will discuss the results obtained so far in the field of nanoparticle drug carriers for CNS and highlight the parameters needed in order to fully characterize these hitherto largely unknown delivery systems. Even if promising results have been obtained, more studies are needed in order to fully evaluate the clinical potential of this drug-delivery system.

Biodistribution of antisense nanoparticles in mammary carcinoma rat model

Efficient and specific delivery of antisenses (ASs) and protection of the sequences from degradation are critical factors for effective therapy. Sustained release nanoparticles (NP) offer increased resistance to nuclease degradation, increased amounts of AS uptake, and the possibility of control in dosing and sustained duration of AS administration. The biodegradable and biocompatible poly(D,L-lactic-co-glycolic acid) copolymer (PLGA) was utilized to encapsulate AS directed against osteopontin (OPN), which is a promising therapeutic target in mammary carcinoma. Whole body biodistribution of OPN AS NP was evaluated in comparison to naked AS, in intact and mammary carcinoma metastasis model bearing rats. Naked and NP encapsulated AS exhibited different biodistribution profiles. AS NP, in contrast to naked AS, tended to accumulate mostly in the spleen, liver, and at the tumor inoculation site. Drug levels in intact organs were negligible. The elimination of naked AS was faster, due to rapid degradation of the unprotected sequence. It is concluded that AS NP protect the AS from degradation, provide efficient AS delivery to the tumor tissue, and minimize AS accumulation in intact organs due to the AS sustained release profile as well as the favorable NP physicochemical properties.

Water-dispersible multifunctional hybrid nanogels for combined curcumin and photothermal therapy

We design a class of water-dispersible hybrid nanogels for intracellular delivery of hydrophobic curcumin. The core-shell structured hybrid nanogels were synthesized by coating the Ag/Au bimetallic nanoparticles (NPs) with a hydrophobic polystyrene (PS) gel layer as inner shell, and a subsequent thin hydrophilic nonlinear poly(ethylene glycol) (PEG)-based gel layer as outer shell. The uniqueness of these hybrid nanogels lies in the integration of the functional building blocks for combined curcumin and photothermal therapy to significantly improve the therapeutic efficacy. The Ag/Au core NPs cannot only emit strong fluorescence for imaging and monitoring at the cellular level, but also exhibit strong absorption in the near-infrared (NIR) region for photothermal conversion. While the inner PS gel layer is introduced to provide strong hydrophobic interactions with curcumin for high drug loading yields, the external nontoxic and thermo-responsive PEG analog gel layer is designed to trigger the release of the pre-loaded curcumin either by variation of surrounding temperature or exogenous irradiation with NIR light. Such designed multifunctional hybrid nanogels are well suited for in vivo studies and clinical trials, thereby likely to bring this promising natural medicine of curcumin to the forefront of therapeutic agents for cancers and other diseases.

Engineering of self-assembled nanoparticle platform for precisely controlled combination drug therapy

The genomic revolution has identified therapeutic targets for a plethora of diseases, creating a need to develop robust technologies for combination drug therapy. In the present work, we describe a self-assembled polymeric nanoparticle (NP) platform to target and control precisely the codelivery of drugs with varying physicochemical properties to cancer cells. As proof of concept, we codelivered cisplatin and docetaxel (Dtxl) to prostate cancer cells with synergistic cytotoxicity. A polylactide (PLA) derivative with pendant hydroxyl groups was prepared and conjugated to a platinum(IV) [Pt(IV)] prodrug, c,t,c-[Pt(NH(3))(2)(O(2)CCH(2)CH(2)COOH)(OH)Cl(2)] [PLA-Pt(IV)]. A blend of PLA-Pt(IV) functionalized polymer and carboxyl-terminated poly(D,L-lactic-co-glycolic acid)-block-poly(ethylene glycol) copolymer in the presence or absence of Dtxl, was converted, in microfluidic channels, to NPs with a diameter of ∼100 nm. This process resulted in excellent encapsulation efficiency (EE) and high loading of both hydrophilic platinum prodrug and hydrophobic Dtxl with reproducible EEs and loadings. The surface of the NPs was derivatized with the A10 aptamer, which binds to the prostate-specific membrane antigen (PSMA) on prostate cancer cells. These NPs undergo controlled release of both drugs over a period of 48-72 h. Targeted NPs were internalized by the PSMA-expressing LNCaP cells via endocytosis, and formation of cisplatin 1,2-d(GpG) intrastrand cross-links on nuclear DNA was verified. In vitro toxicities demonstrated superiority of the targeted dual-drug combination NPs over NPs with single drug or nontargeted NPs. This work reveals the potential of a single, programmable nanoparticle to blend and deliver a combination of drugs for cancer treatment.

Receptor-targeted nanocarriers for therapeutic delivery to cancer

Efficient and site-specific delivery of therapeutic drugs is a critical challenge in clinical treatment of cancer. Nano-sized carriers such as liposomes, micelles, and polymeric nanoparticles have been investigated for improving bioavailability and pharmacokinetic properties of therapeutics via various mechanisms, for example, the enhanced permeability and retention (EPR) effect. Further improvement can potentially be achieved by conjugation of targeting ligands onto nanocarriers to achieve selective delivery to the tumour cell or the tumour vasculature. Indeed, receptor-targeted nanocarrier delivery has been shown to improve therapeutic responses both in vitro and in vivo. A variety of ligands have been investigated including folate, transferrin, antibodies, peptides and aptamers. Multiple functionalities can be incorporated into the design of nanoparticles, e.g., to enable imaging and triggered intracellular drug release. In this review, we mainly focus on recent advances on the development of targeted nanocarriers and will introduce novel concepts such as multi-targeting and multi-functional nanoparticles.

Dynamic and cellular interactions of nanoparticles in vascular-targeted drug delivery

Vascular-targeted drug delivery systems could provide more efficient and effective pharmaceutical interventions for treating a variety of diseases including cardiovascular, pulmonary, inflammatory, and malignant disorders. However, several factors must be taken into account when designing these systems. The diverse blood hemodynamics and rheology, and the natural clearance process that tend to decrease the circulation time of foreign particles all lessen the probability of successful carrier interaction with the vascular wall. An effective vascular-targeted drug delivery system must be able to navigate through the bloodstream while avoiding immune clearance, attach to the vascular wall, and release its therapeutic cargo at the intended location. This review will summarize and analyze current literature reporting on (1) nanocarrier fabrication methods and materials that allow for optimum therapeutic encapsulation, protection, and release; (2) localization and binding dynamics of nanocarriers as influenced by hemodynamics and blood rheology in medium-to-large vessels; (3) blood cells' responses to various types of nanocarrier compositions and its effects on particle circulation time; and (4) properties that affect nanocarrier internalization at the target site.

Enhanced passive pulmonary targeting and retention of PEGylated rigid microparticles in rats

The current study examines the passive pulmonary targeting efficacy and retention of 6μm polystyrene (PS) microparticles (MPs) covalently modified with different surface groups [amine (A-), carboxyl (C-) and sulfate (S-)] or single (PEG(1)-) and double (PEG(2)-) layers of α,ω-diamino poly(ethylene glycol) attached to C-MPs. The ζ-potential of A-MPs (-44.0mV), C-MPs (-54.3mV) and S-MPs (-49.6mV) in deionized water were similar; however PEGylation increased the ζ-potential for both PEG(1)-MPs (-18.3mV) and PEG(2)-MPs (11.5mV). The biodistribution and retention of intravenously administered MPs to male Sprague-Dawley rats was determined in homogenized tissue by fluorescence spectrophotometry. PEG(1)-MPs and PEG(2)-MPs demonstrated enhanced pulmonary retention in rats at 48h after injection when compared to unmodified A-MPs (59.6%, 35.9% and 17.0% of the administered dose, respectively). While unmodified MPs did not significantly differ in lung retention, PEGylation of MPs unexpectedly improved passive lung targeting and retention by modifying surface properties including charge and hydrophobicity but not size.