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

Incorporation of paramagnetic, fluorescent and PET/SPECT contrast agents into liposomes for multimodal imaging

A series of metal-chelating lipid conjugates has been designed and synthesized. Each member of the series bears a 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) macrocycle attached to the lipid head group, using short n-ethylene glycol (n-EG) spacers of varying length. Liposomes incorporating these lipids, chelated to Gd(3+), (64)Cu(2+), or (111)In(3+), and also incorporating fluorescent lipids, have been prepared, and their application in optical, magnetic resonance (MR) and single-photon emission tomography (SPECT) imaging of cellular uptake and distribution investigated in vitro and in vivo. We have shown that these multimodal liposomes can be used as functional MR contrast agents as well as radionuclide tracers for SPECT, and that they can be optimized for each application. When shielded liposomes were formulated incorporating 50% of a lipid with a short n-EG spacer, to give nanoparticles with a shallow but even coverage of n-EG, they showed good cellular internalization in a range of tumour cells, compared to the limited cellular uptake of conventional shielded liposomes formulated with 7% 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[carboxy(polyethyleneglycol)(2000)] (DSPE-PEG2000). Moreover, by matching the depth of n-EG coverage to the length of the n-EG spacers of the DOTA lipids, we have shown that similar distributions and blood half lives to DSPE-PEG2000-stabilized liposomes can be achieved. The ability to tune the imaging properties and distribution of these liposomes allows for the future development of a flexible tri-modal imaging agent.

Particle tracking analysis for the intracellular trafficking of nanoparticles modified with African swine fever virus protein p54-derived peptide

Previous studies showed that the cytoplasmic transport of nanoparticles to the nucleus is driven by a vesicular sorting system. Artificial approaches for targeting a microtubule-associating motor complex is also a challenge. We describe herein the development of a liposomal nanoparticle, the surface of which is modified with stearylated octa-arginine (STR-R8), and a dynein light chain (LC8)-associated peptide derived from an African swine fever virus protein p54 (p54(149-161)) with polyethyleneglycol (PEG) as a spacer (p54(149-161)-PEG/R8-liposomal nanoparticles (LNPs)). The p54(149-161)-PEG/R8-LNPs preferentially gain access to the nucleus, resulting in a one- to two-order of magnitude higher transfection activity in comparison with p54(149-161)-free nanoparticles (PEG/R8-LNPs). Further studies of particle tracking in HeLa cells stably expressing green fluorescent protein (GFP)-tagged tubulin (GFP/Tub-HeLa) indicate that p54(149-161) stimulated the transport of nanoparticles along fibrous tubulin structures. Moreover, a part of the p54(149-161)-PEG/R8-LNPs appeared to undergo quasi-straight transport without sharing the tracks corresponding to PKH67, the plasma membrane of which had been prestained with a marker just before transfection, while corresponding movement was never observed in the case of PEG/R8-LNPs. These findings suggest that a portion of the p54(149-161)-modified nanoparticles can use microtubule-dependent transport without the need for an assist by a vesicular sorting system.

A pH-sensitive cationic lipid facilitates the delivery of liposomal siRNA and gene silencing activity in vitro and in vivo

Modification of liposomal siRNA carriers with polyethylene glycol, i.e., PEGylation, is a generally accepted strategy for achieving in vivo stability and delivery to tumor tissue. However, PEGylation significantly inhibits both cellular uptake and the endosomal escape process of the carriers. In a previous study, we reported on the development of a multifunctional envelope-type nano device (MEND) for siRNA delivery and peptide-based functional devices for overcoming the limitations and succeeded in the efficient delivery of siRNA to tumors. In this study, we synthesized a pH-sensitive cationic lipid, YSK05, to overcome the limitations. The YSK05-MEND had a higher ability for endosomal escape than other MENDs containing conventional cationic lipids. The PEGylated YSK05-MEND induced efficient gene silencing and overcame the limitations followed by optimization of the lipid composition. Furthermore, the intratumoral administration of the YSK05-MEND resulted in a more efficient gene silencing compared with MENDs containing conventional cationic lipids. Collectively, these data confirm that YSK05 facilitates the endosomal escape of the MEND and thereby enhances the efficacy of siRNA delivery into cytosol and gene silencing.

Polyethyleneimine/DNA polyplexes with reduction-sensitive hyaluronic acid derivatives shielding for targeted gene delivery

The natural anionic polysaccharide hyaluronic acid (HA) was modified by introducing reduction-sensitive disulfide bond between the carboxyl groups and the backbone of HA (HA-SS-COOH). HA-SS-COOH and its corresponding unmodified stable analog HA were used to shield DNA/PEI polyplexes (DP) to form ternary complexes (DPS and DPH complexes). The shielding/deshielding effect was tested along with size, zeta potential, cell viability and transfection. Both DPS and DPH complexes showed increase in size, decrease in zeta potential and low cytotoxicity in physiological conditions due to the anionic shielding. In the reductive environment, only HA-SS-COOH coated ternary complexes (DPS) demonstrated the size increase and recovered high positive zeta potential. DPS complexes showed an up to 14-fold higher transfection than the stable coated one, indicating the efficiency of the reduction-responsive deshielding design. Moreover, the presence of extra free HA inhibited the transfection of DPS on HepG2 and B16F10 cells with HA receptor expression, while displaying no effect on non-targeted NIH3T3 cells. More rapid cellular association of DPS with HepG2 was observed, thus confirming the targeting reservation of disulfide bond modified HA. Intratumoral injection of DPS complexes resulted in much higher accumulation and luciferase expression in the tumor bearing C57BL/6 mice. Both in vitro and in vivo results demonstrated the successful combination of deshielding and target functions in HA derivatives for gene delivery.

The multilayer nanoparticles formed by layer by layer approach for cancer-targeting therapy

The multilayer nanoparticles (NPs) were prepared for cancer-targeting therapy using the layer by layer approach. When drug-loaded Pluronic NPs were mixed with vesicles (liposomes) in the aqueous medium, Pluronic NPs were incorporated into the vesicles to form the vesicle NPs. Then, the multilayer NPs were formed by freeze-drying the vesicle NPs in a Pluronic aqueous solution. The morphology and size distribution of the multilayer NPs were observed using a TEM and a particle size analyzer. In order to apply the multilayer NPs as a delivery system for docetaxel (DTX), which is a model anticancer drug, the release pattern of the DTX was observed and the tumor growth was monitored by injecting the multilayer NPs into the tail veins of tumor (squamous cell carcinoma)-bearing mice. The cytotoxicity of free DTX (commercial DTX formulation (Taxotere®)) and the multilayer NPs was evaluated using MTT assay. We also evaluated the tumor targeting ability of the multilayer NPs using magnetic resonance imaging. The multilayer NPs showed excellent tumor targetability and antitumor efficacy in tumor-bearing mice, caused by the enhanced permeation and retention (EPR) effect. These results suggest that the multilayer NPs could be a potential drug delivery system for cancer-targeting therapy.

A multifunctional envelope-type nanodevice for use in nanomedicine: concept and applications

In the 21st century, drug development has shifted toward larger molecules such as proteins and nucleic acids, which require the use of new chemical strategies. In this process, the drug delivery system plays a central role and intracellular targeting using nanotechnology has become a key technology for the development of successful new medicines. We have developed a new delivery system, a multifunctional envelope-type nanodevice (MEND) based on "Programmed Packaging." In this new concept of packaging, multifunctional nanodevices are integrated into a nanocarrier system according to a program designed to overcome all barriers during the course of biodistribution and intracellular trafficking. In this Account, we introduce our method for delivering nucleic acids or proteins to intracellular sites of action such as the cytosol, nucleus, and mitochondria and for targeting selective tissues in vivo via systemic administration of the nanodevices. First, we introduce an octaarginine-modified MEND (R8-MEND) as an efficient intracellular delivery system, designed especially for vaccinations and transgene expression. Many types of cells can internalize the R8-MEND, mainly by inducing macropinocytosis, and the MEND escapes from macropinosomes via membrane fusion, which leads to efficient antigen presentation via the major histocompatibility complex I pathway in antigen-presenting cells. In addition, the transfection activities of the R8-MEND in dividing cells, such as HeLa or A549 cells, are as high as those for adenovirus. However, because the R8-MEND cannot induce sufficient transgene activity in primary cultured dendritic cells, which are critical regulators of the immune response, we converted the R8-MEND into a tetralamellar MEND (T-MEND). The T-MEND uses a new packaging method and delivers condensed pDNA into the nucleus via fusion between the envelopes and the nuclear membrane. To achieve efficient transfection activity, we also optimized the decondensation of nucleic acids within the nucleus. To optimize mitochondrial drug delivery, we introduced the MITOPorter. Many types of materials can be packaged into this liposome-based nanocarrier and then delivered to mitochondria via membrane fusion mechanisms. Finally, we describe an integrated strategy for in vivo tumor delivery and optimization of intracellular trafficking. Successful tumor delivery typically requires coating the surfaces of nanoparticles with PEG, but PEG can also limit uptake by the reticuloendothelial system and reduce the efficiency of intracellular trafficking. Here we integrate the optimum biodistribution and intracellular trafficking of the MEND with an innovative strategy such as enzymatically cleavable PEG and a short membrane peptide, GALA. Some of these strategies will soon be tested in the clinic.

Efficient intracellular delivery of nucleic acid pharmaceuticals using cell-penetrating peptides

Over the last 20 years, researchers have designed or discovered peptides that can permeate membranes and deliver exogenous molecules inside a cell. These peptides, known as cell-penetrating peptides (CPPs), typically consist of 6-30 residues, including HIV TAT peptide, penetratin, oligoarginine, transportan, and TP10. Through chemical conjugation or noncovalent complex formation, these structures successfully deliver bioactive and membrane-impermeable molecules into cells. CPPs have also gained attention as an attractive vehicle for the delivery of nucleic acid pharmaceuticals (NAPs), including genes/plasmids, short oligonucleotides, and small interference RNAs and their analogues, due to their high internalization efficacy, low cytotoxicity, and flexible structural design. In this Account, we survey the potential of CPPs for the design and optimization of NAP delivery systems. First, we describe the impact of the N-terminal stearylation of CPPs. Endocytic pathways make a major contribution to the cellular uptake of NAPs. Stearylation at the N-terminus of CPPs with stearyl-octaarginine (R8), stearyl-(RxR)(4), and stearyl-TP10 prompts the formation of a self-assembled core-shell nanoparticle with NAPs, a compact structure that promotes cellular uptake. Researchers have designed modifications such as the addition of trifluoromethylquinoline moieties to lysine residues to destabilize endosomes, as exemplified by PepFect 6, and these changes further improve biological responsiveness. Alternatively, stearylation also allows implantation of CPPs onto the surface of liposomes. This feature facilitates "programmed packaging" to establish multifunctional envelope-type nanodevices (MEND). The R8-MEND showed high transfection efficiency comparable to that of adenovirus in non-dividing cells. Understanding the cellular uptake mechanisms of CPPs will further improve CPP-mediated NAP delivery. The cellular uptake of CPPs and their NAP complex involves various types of endocytosis. Macropinocytosis, a mechanism which is also activated in response to stimuli such as growth factors or viruses, is a primary pathway for arginine-rich CPPs because high cationic charge density promotes this endocytic pathway. The use of larger endosomes (known as macropinosomes) rather than clathrin- or caveolae-mediated endocytosis has been reported in macropinocytosis which would also facilitate the endocytosis of NAP nanoparticles into cells.

Fabrication of functionalized double-lamellar multifunctional envelope-type nanodevices using a microfluidic chip with a chaotic mixer array

Multifunctional envelope-type nanodevices (MENDs) are very promising non-viral gene delivery vectors because they are biocompatible and enable programmed packaging of various functional elements into an individual nanostructured liposome. Conventionally MENDs have been fabricated by complicated, labor-intensive, time-consuming bulk batch methods. To avoid these problems in MEND fabrication, we adopted a microfluidic chip with a chaotic mixer array on the floor of its reaction channel. The array was composed of 69 cycles of the staggered chaotic mixer with bas-relief structures. Although the reaction channel had very large Péclet numbers (>10(5)) favorable for laminar flows, its chaotic mixer array led to very small mixing lengths (<1.5 cm) and that allowed homogeneous mixing of MEND precursors in a short time. Using the microfluidic chip, we fabricated a double-lamellar MEND (D-MEND) composed of a condensed plasmid DNA core and a lipid bilayer membrane envelope as well as the D-MEND modified with trans-membrane peptide octaarginine. Our lab-on-a-chip approach was much simpler, faster, and more convenient for fabricating the MENDs, as compared with the conventional bulk batch approaches. Further, the physical properties of the on-chip-fabricated MENDs were comparable to or better than those of the bulk batch-fabricated MENDs. Our fabrication strategy using microfluidic chips with short mixing length reaction channels may provide practical ways for constructing more elegant liposome-based non-viral vectors that can effectively penetrate all membranes in cells and lead to high gene transfection efficiency.

Transferrin-conjugated micelles: enhanced accumulation and antitumor effect for transferrin-receptor-overexpressing cancer models

As the transport protein for iron, transferrin can trigger cellular endocytosis once binding to its receptor (TfR) on the cell membrane. Using this property, we conjugated transferrin onto the surface of biodegradable polymeric micelles constructed from amphiphilic block copolymers. The core of micelle was either labeled with a near-infrared dye (NIR) or conjugated with a chemotherapeutic drug paclitaxel (PTX) to study the biodistribution or antitumor effect in nude mice bearing subcutaneous TfR-overexpressing cancers. DLS and TEM showed that the sizes of Tf-conjugated and Tf-free micelles were in the range of 85-110 nm. Confocal laser scanning microscopy and flow cytometry experiments indicated that the uptake efficiency of the micelles by the TfR-overexpressing cells was enhanced by Tf conjugation. Semiquantitative analysis of the NIR signals collected from the tumor site showed that the maximum accumulation was achieved at 28 h in the M(NIR) group, while at 22 h in Tf-M(NIR) groups; and the area under the intensity curve in the Tf-M(NIR) groups was more than that in M(NIR) group. Finally, the tumor inhibition effects of targeting micelles were studied with the gastric carcinoma model which overexpressed TfR. The analysis of tumor volumes and the observation of H&E-stained tumor sections showed that Tf-M(PTX) had the best antitumor effect compared with the control groups (saline, PTX, and M(PTX)). The results of this study demonstrated the potential application of Tf-conjugated polymeric micelles in the treatment of TfR-overexpressing cancers.

Reversible masking using low-molecular-weight neutral lipids to achieve optimal-targeted delivery

Intravenous injection of therapeutics is required to effectively treat or cure metastatic cancer, certain cardiovascular diseases, and other acquired or inherited diseases. Using this route of delivery allows potential uptake in all disease targets that are accessed by the bloodstream. However, normal tissues and organs also have the potential for uptake of therapeutic agents. Therefore, investigators have used targeted delivery to attempt delivery solely to the target cells; however, use of ligands on the surface of delivery vehicles to target specific cell surface receptors is not sufficient to avoid nonspecific uptake. PEGylation has been used for decades to try to avoid nonspecific uptake but suffers from many problems known as “The PEGylation Dilemma.” We have solved this dilemma by replacing PEGylation with reversible masking using low-molecular-weight neutral lipids in order to achieve optimal-targeted delivery solely to target cells. Our paper will focus on this topic.

A novel double-coating carrier produced by solid-in-oil and solid-in-water nanodispersion technology for delivery of genes and proteins into cells

A novel intracellular delivery method both for genes and proteins is one of the most coveted systems in the drug delivery field. In the present study, we developed a double-coating carrier loaded with gene and protein produced by solid-in-oil and solid-in-water nanodispersion technology. The double-coating carriers did not require electrostatic interactions during the preparation so were able to encapsulate plasmid DNA, ovalbumin (pI 4.5), horseradish peroxidase (pI 7.2), and cytochrome-c (pI 10.5) in a consistent manner. The carriers had practical encapsulation efficiencies and release profiles for genes and proteins. Furthermore, effective gene expression and cellular uptakes of both anionic and cationic proteins were achieved by modification of carriers with functional molecules. These findings indicate that the double-coating carrier has high potential for cellular delivery of various drugs and is a novel, superior method for both gene and protein delivery into cells.

HSP32 (HO-1) inhibitor, copoly(styrene-maleic acid)-zinc protoporphyrin IX, a water-soluble micelle as anticancer agent: In vitro and in vivo anticancer effect

We reported previously the antitumor effect of heme oxygenase-1 (HO-1) inhibition by zinc protoporphyrin IX (ZnPP). ZnPP per se is poorly water soluble and thus cannot be used as anticancer chemotherapeutic. Subsequently, we developed water-soluble micelles of ZnPP using styrene-maleic acid copolymer (SMA), which encapsulated ZnPP (SMA-ZnPP). In this report, the in vitro and in vivo therapeutic effects of SMA-ZnPP are described. In vitro experiments using 11 cultured tumor cell lines and six normal cell lines revealed a remarkable cytotoxicity of SMA-ZnPP against various tumor cells; average IC(50) is about 11.1 μM, whereas the IC(50) to various normal cells is significantly higher, that is, more than 50 μM. In the pharmacokinetic study, we found that SMA-ZnPP predominantly accumulated in the liver tissue after i.v. injection, suggesting its applicability for liver cancer. As expected, a remarkable antitumor effect was achieved in the VX-2 tumor model in the liver of rabbit that is known as one the most difficult tumor models to cure. Antitumor effect was also observed in murine tumor xenograft, that is, B16 melanoma and Meth A fibrosarcoma. Meanwhile, no apparent side effects were found even at the dose of ∼7 times higher concentration of therapeutics dose. These findings suggest a potential of SMA-ZnPP as a tool for anticancer therapy toward clinical development, whereas further investigations are warranted.

In vivo gene delivery by nonviral vectors: overcoming hurdles?

The promise of cancer gene therapeutics is hampered by difficulties in the in vivo delivery to the targeted tumor cells, and systemic delivery remains to be the biggest challenge to be overcome. Here, we concentrate on systemic in vivo gene delivery for cancer therapy using nonviral vectors. In this review, we summarize the existing delivery barriers together with the requirements and strategies to overcome these problems. We will also introduce the current progress in the design of nonviral vectors, and briefly discuss their safety issues.

Optimization of Landscape Phage Fusion Protein-Modified Polymeric PEG-PE Micelles for Improved Breast Cancer Cell Targeting

Amphiphilic landscape phage fusion proteins with high affinity and selectivity towards breast cancer MCF-7 (Michigan Cancer Foundation-7) cells self-assemble with polymeric PEG-PE conjugates to form mixed micelles (phage-micelles) capable of cancer cell-targeted delivery of poorly-soluble drugs. While the PEG corona provides the stability and longevity to the micelles, its presence is a potential steric difficulties for the interaction of phage fusion protein with cell surface targets. We attempted to address this problem by controlling the length of the PEG block and the phage fusion protein quantity, selecting the optimal ones to produce a reasonable retention of the targeting affinity and selectivity of the MCF-7-specific phage fusion protein. Three PEG-PE conjugates with different PEG lengths were used to construct phage- and plain-micelles, followed by FACS analysis of the effect of the PEG length on their binding affinity and selectivity towards target MCF-7 cells using either a MCF-7 cell monoculture or a cell co-culture model composed of target cancer MCF-7 cells and non-target, non-cancer C166 cells expressing GFP (Green Fluorescent Protein). Both, the length of PEG and quantity of phage fusion protein had a profound impact on the targetability of the phage-micelles. Phage-micelles prepared with PEG_2k-PE achieved a desirable binding affinity and selectivity. Incorporation of a minimal concentration of phage protein, up to 0.5%, produced maximal targeting efficiency towards MCF-7 cells. Overall, phage-micelles with PEG_2k-PE and 0.5% of phage protein represent the optimal formulation for targeting towards breast cancer cells.

Low molecular-weight chitosan as a pH-sensitive stealth coating for tumor-specific drug delivery

When a nanoparticle is developed for systemic application, its surface is typically protected by poly(ethylene glycol) (PEG) to help prolonged circulation and evasion of immune clearance. On the other hand, PEG can interfere with interactions between nanocarriers and target cells and negatively influence the therapeutic outcomes. To overcome this challenge, we propose low molecular-weight chitosan (LMWC) as an alternative surface coating, which can protect the nanomedicine in neutral pH but allow cellular interactions in the weakly acidic pH of tumors. LMWCs with a molecular weight of 2-4 kDa, 4-6.5 kDa, and 11-22 kDa were produced by hydrogen peroxide digestion and covalently conjugated with poly(lactic-co-glycolic acid) (PLGA). Nanoparticles created with PLGA-LMWC conjugates showed pH-sensitive cell interactions, which enabled specific drug delivery to cells in a weakly acidic environment. The hydrophilic LMWC layer reduced opsonization and phagocytic uptake. These properties qualify LMWCs as a promising biomaterial for pH-sensitive stealth coating.

Grafting of cell-penetrating peptide to receptor-targeted liposomes improves their transfection efficiency and transport across blood-brain barrier model

We report bifunctional liposomal delivery system, combining transferrin (Tf)-mediated receptor targeting and poly-L-arginine (PR)-facilitated cell penetration, which overcomes the drawback of saturation of delivery. PR was conjugated to the distal end of distearoyl phosphoethanolamine-polyethylene glycol (PEG) 2000 and was incorporated with other phospholipids in chloroform/methanol (2:1) to form PR liposomes using thin-film hydration technique. Tf-PEG phospholipid micelles were incorporated into PR liposomes using postinsertion technique to form Tf-PR liposomes. The bifunctional liposomes demonstrated significantly (p < 0.05) higher cellular uptake by brain endothelial cells (bEnd.3) and about eightfold higher transfection in primary culture of glial cells as compared with the Tf liposomes. Cell viabilities of Tf-conjugated and bifunctional liposomes were not markedly different; however, transport across in vitro blood-brain barrier model improved considerably after dual modification. The study underlines the potential of bifunctional liposomes as high-efficiency and low-toxicity gene delivery system for the treatment of central nervous system disorders.

Targeted polymeric therapeutic nanoparticles: design, development and clinical translation

Polymeric materials have been used in a range of pharmaceutical and biotechnology products for more than 40 years. These materials have evolved from their earlier use as biodegradable products such as resorbable sutures, orthopaedic implants, macroscale and microscale drug delivery systems such as microparticles and wafers used as controlled drug release depots, to multifunctional nanoparticles (NPs) capable of targeting, and controlled release of therapeutic and diagnostic agents. These newer generations of targeted and controlled release polymeric NPs are now engineered to navigate the complex in vivo environment, and incorporate functionalities for achieving target specificity, control of drug concentration and exposure kinetics at the tissue, cell, and subcellular levels. Indeed this optimization of drug pharmacology as aided by careful design of multifunctional NPs can lead to improved drug safety and efficacy, and may be complimentary to drug enhancements that are traditionally achieved by medicinal chemistry. In this regard, polymeric NPs have the potential to result in a highly differentiated new class of therapeutics, distinct from the original active drugs used in their composition, and distinct from first generation NPs that largely facilitated drug formulation. A greater flexibility in the design of drug molecules themselves may also be facilitated following their incorporation into NPs, as drug properties (solubility, metabolism, plasma binding, biodistribution, target tissue accumulation) will no longer be constrained to the same extent by drug chemical composition, but also become in-part the function of the physicochemical properties of the NP. The combination of optimally designed drugs with optimally engineered polymeric NPs opens up the possibility of improved clinical outcomes that may not be achievable with the administration of drugs in their conventional form. In this critical review, we aim to provide insights into the design and development of targeted polymeric NPs and to highlight the challenges associated with the engineering of this novel class of therapeutics, including considerations of NP design optimization, development and biophysicochemical properties. Additionally, we highlight some recent examples from the literature, which demonstrate current trends and novel concepts in both the design and utility of targeted polymeric NPs (444 references).

Effective gene delivery using stimulus-responsive catiomer designed with redox-sensitive disulfide and acid-labile imine linkers

A dual stimulus-responsive mPEG-SS-PLL(15)-glutaraldehyde star (mPEG-SS-PLL(15)-star) catiomer is developed and biologically evaluated. The catiomer system combines redox-sensitive removal of an external PEG shell with acid-induced escape from the endosomal compartment. The design rationale for PEG shell removal is to augment intracellular uptake of mPEG-SS-PLL(15)-star/DNA complexes in the presence of tumor-relevant glutathione (GSH) concentration, while the acid-induced dissociation is to accelerate the release of genetic payload following successful internalization into targeted cells. Size alterations of complexes in the presence of 10 mM GSH suggest stimulus-induced shedding of external PEG layers under redox conditions that intracellularly present in the tumor microenvironment. Dynamic laser light scattering experiments under endosomal pH conditions show rapid destabilization of mPEG-SS-PLL(15)-star/DNA complexes that is followed by facilitating efficient release of encapsulated DNA, as demonstrated by agarose gel electrophoresis. Biological efficacy assessment using pEGFP-C1 plasmid DNA encoding green fluorescence protein and pGL-3 plasmid DNA encoding luciferase as reporter genes indicate comparable transfection efficiency of 293T cells of the catiomer with a conventional polyethyleneimine (bPEI-25k)-based gene delivery system. These experimental results show that mPEG-SS-PLL(15)-star represents a promising design for future nonviral gene delivery applications with high DNA binding ability, low cytotoxicity, and high transfection efficiency.

Mesoporous silica nanoparticles: synthesis, biocompatibility and drug delivery

In the past decade, mesoporous silica nanoparticles (MSNs) have attracted more and more attention for their potential biomedical applications. With their tailored mesoporous structure and high surface area, MSNs as drug delivery systems (DDSs) show significant advantages over traditional drug nanocarriers. In this review, we overview the recent progress in the synthesis of MSNs for drug delivery applications. First, we provide an overview of synthesis strategies for fabricating ordered MSNs and hollow/rattle-type MSNs. Then, the in vitro and in vivo biocompatibility and biotranslocation of MSNs are discussed in relation to their chemophysical properties including particle size, surface properties, shape, and structure. The review also highlights the significant achievements in drug delivery using mesoporous silica nanoparticles and their multifunctional counterparts as drug carriers. In particular, the biological barriers for nano-based targeted cancer therapy and MSN-based targeting strategies are discussed. We conclude with our personal perspectives on the directions in which future work in this field might be focused.

Engineered redox-responsive PEG detachment mechanism in PEGylated nano-graphene oxide for intracellular drug delivery

In biomedical applications, polyethylene glycol (PEG) functionalization has been a major approach to modify nanocarriers such as nano-graphene oxide for particular biological requirements. However, incorporation of a PEG shell poses a significant diffusion barrier that adversely affects the release of the loaded drugs. This study addresses this critical issue by employing a redox-responsive PEG detachment mechanism. A PEGylated nano-graphene oxide (NGO-SS-mPEG) with redox-responsive detachable PEG shell is developed that can rapidly release an encapsulated payload at tumor-relevant glutathione (GSH) levels. The PEG shell grafted onto NGO sheets gives the nanocomposite high physiological solubility and stability in circulation. It can selectively detach from NGO upon intracellular GSH stimulation. The surface-engineered structures are shown to accelerate the release of doxorubicin hydrochloride (DXR) from NGO-SS-mPEG 1.55 times faster than in the absence of GSH. Confocal microscopy shows clear evidence of NGO-SS-mPEG endocytosis in HeLa cells, mainly accumulated in cytoplasm. Furthermore, upon internalization of DXR-loaded NGO with a disulfide-linked PEG shell into HeLa cells, DXR is effectively released in the presence of an elevated GSH reducing environment, as observed in confocal microscopy and flow cytometric experiments. Importantly, inhibition of cell proliferation is directly correlated with increased intracellular GSH concentrations due to rapid DXR release.

Recent advances in stealth coating of nanoparticle drug delivery systems

Modifying surfaces of nanoparticles (NPs) with polyethylene glycol (PEG), the so-called PEGylation, is the most commonly used method for reducing premature clearance of NPs from the circulation. However, several reports point out that PEGylation may negatively influence the performance of NPs as a drug carrier. Alternative surface modification strategies, including substitute polymers, conditional removal of PEG, and biomimetic surface modification, may provide solutions for the limitations of PEG.

Physico-chemical parameters that govern nanoparticles fate also dictate rules for their molecular evolution

Nanoparticles are efficient to safely deliver therapeutic and imaging contrast agents to tumors for cancer diagnostic and therapy, if they can escape the reticuloendothelial system (RES) and accumulate in tumors either passively due to the enhanced permeability and retention (EPR) effect or actively via a specific ligand. The main hallmark of nanoparticles is their large surface areas, which, depending of their chemical compositions, surface coatings, electric charges, sizes and shapes, will generate complex, extremely dynamic and continuous interactions and exchanges between the nanoparticles and the different molecules present in the blood. Special attention will be paid to explain how the nanoparticles were improved step by step in order to adapt our increasing knowledge on their biophysics. In particular, we will discuss the influence of PEGylation, the difficulties to generate actively targeted particles and finally the actual trends in the manufacturing of "third-generation" smart particles.

Sheddable ternary nanoparticles for tumor acidity-targeted siRNA delivery

Drug delivery systems for cancer therapy usually need to be sterically stabilized by a poly(ethylene glycol) (PEG) layer during blood circulation to minimize nonspecific interactions with serum components. However, PEGylation significantly reduces cellular uptake of the delivery systems after they accumulate at the tumor site, which markedly impairs the in vivo antitumor efficiency. Here, we develop a ternary small interfering RNA (siRNA) delivery system with tumor acidity-activated sheddable PEG layer to overcome the challenge. The sheddable nanoparticle is fabricated by introducing a tumor acidity-responsive PEGylated anionic polymer to the surface of positively charged polycation/siRNA complexes via electrostatic interaction. We show clear evidence that introducing the PEGylated anionic polymer to the surface of a nanoparticle markedly reduces its nonspecific interactions with protein. We further demonstrate that the nanoparticle is capable of deshielding the PEG layer at the slightly acidic tumor extracellular microenvironment to facilitate the delivery of siRNA to the tumor cells after accumulation at the tumor site. Accordingly, this promotes the RNA-interfering efficiencies and enhances the inhibition of tumor growth. Such delivery system with the ability to deshield the PEG layer at the target tissues has remarkable potential in cancer therapy.

Polypseudorotaxanes of pegylated α-cyclodextrin/polyamidoamine dendrimer conjugate with cyclodextrins as a sustained release system for DNA

Nonviral gene delivery suffers from a number of limitations including short transgene expression times and low transfection efficiency. In this study, we examined whether polypseudorotaxanes (PPRXs) of polyethylene glycol (PEG, molecular weight: 2,000)-grafted α-cyclodextrin (α-CyD)/polyamidoamine dendrimer conjugate (PEG-α-CDE) with CyDs have the potential for the novel sustained release systems for plasmid DNA (pDNA). The PEG-α-CDE/pDNA complex formed PPRXs with α-CyD and γ-CyD solutions, but not with β-CyD solution. In the PEG-α-CDE/CyDs PPRX systems, 20.6mol of α-CyD and 11.8mol of γ-CyD were involved in the PPRXs formation with one PEG chain by α-CyD and γ-CyD, respectively, consistent with in the PEG-dendrimer/CyDs systems. PEG-α-CDE/pDNA/α-CyD PPRX and PEG-α-CDE/pDNA/γ-CyD PPRX formed hexagonal and tetragonal columnar channels in the crystalline phase, respectively. In addition, the CyDs PPRX provided the sustained release of pDNA from PEG-α-CDE complex with pDNA at least 72 h in vitro. The release of pDNA from CyDs PPRX retarded as the volume of dissolution medium decreased. Furthermore, the PEG-α-CDE/γ-CyD PPRX system showed sustained transfection efficiency after intramuscular injection to mice at least for 14days. These results suggest that the PEG-α-CDE/CyD PPRX systems are useful for novel sustained DNA release systems.

Multifunctional PEGylated 2C5-immunoliposomes containing pH-sensitive bonds and TAT peptide for enhanced tumor cell internalization and cytotoxicity

pH-sensitive PEGylated (with PEG-PE) long-circulating liposomes (HSPC:cholesterol and Doxil®), modified with cell-penetrating TAT peptide (TATp) moieties and cancer-specific mAb 2C5 were prepared. A degradable pH-sensitive hydrazone bond between a long shielding PEG chains and PE (PEG(2k)-Hz-PE) was introduced. TATp was conjugated with a short PEG(1k)-PE spacer and mAb 2C5 was attached to a long PEG chain (2C5-PEG(3.4k)-PE). The "shielding" effect of TATp by long PEG chains was investigated using three liposomal models. At normal pH, surface TATp moieties are "hidden" by the long PEG chains. Upon the exposure to lowered pH, this multifunctional carrier exposes TATp moieties after the degradation of the hydrazone bond and removal of the long PEG chains. Enhanced cellular uptake of the TATp-containing immunoliposomes was observed in vitro after pre-treatment at lowered pH (using flow cytometry and fluorescence microscopy techniques). The presence of mAb 2C5 on the liposome surface further enhanced the interaction between the carrier and tumor cells but not normal cells. Furthermore, multifunctional immuno-Doxil® preparation showed increased cellular cytotoxicity of B16-F10, HeLa and MCF-7 cells when pre-incubated at lower pH, indicating TATp exposure and activity. In conclusion, a multifunctional immunoliposomal nanocarrier containing a pH-sensitive PEG-PE component, TATp, and the cancer cell-specific mAb 2C5 promotes enhanced cytotoxicity and carrier internalization by cancer cells and demonstrates the potential for intracellular drug delivery after exposure to lowered pH environment, typical of solid tumors.

A simple protocol for preparation of a liposomal vesicle with encapsulated plasmid DNA that mediate high accumulation and reporter gene activity in tumor tissue

The systemic delivery of gene therapeutics by non-viral methods has proven difficult. Transfection systems that are performing well in vitro have been reported to have disadvantageous properties such as rapid clearance and short circulation time often resulting in poor transfection efficiency when applied in vivo. Large unilaminary vesicles (LUV) with encapsulated nucleic acids designated stabilized-plasmid-lipo-particle (SPLP) have showed promising results in terms of systemic stability and accumulation in tumor tissue due to the enhanced permeability and retention effect (EPR). We have developed a simple protocol for the research-scale preparation of SPLPs from commercially available reagents with high amounts of encapsulated plasmid DNA. The SPLPs show properties of promising accumulation in tumor tissue in comparison to other organs when intravenously injected into xenograft tumor-bearing nude mice. Although transcriptionally targeted suicide gene therapy was not achieved, the SPLPs were capable of mediating reporter gene transfection in subcutaneous flank tumors originating from human small cell lung cancer.

Physicochemical and biological evaluation of siRNA polyplexes based on PEGylated Poly(amido amine)s

PURPOSE

Use of RNA interference as novel therapeutic strategy is hampered by inefficient delivery of its mediator, siRNA, to target cells. Cationic polymers have been thoroughly investigated for this purpose but often display unfavorable characteristics for systemic administration, such as interactions with serum and/or toxicity.

METHODS

We report the synthesis of a new PEGylated polymer based on biodegradable poly(amido amine)s with disulfide linkages in the backbone. Various amounts of PEGylated polymers were mixed with their unPEGylated counterparts prior to polyplex formation to alter PEG content in the final complex.

RESULTS

PEGylation effectively decreased polyplex surface charge, salt- or serum-induced aggregation and interaction with erythrocytes. Increasing amount of PEG in formulation also reduced its stability against heparin displacement, cellular uptake and subsequent silencing efficiency. Yet, for polyplexes with high PEG content, significant gene silencing efficacy was found, which was combined with almost no toxicity.

CONCLUSIONS

PEGylated poly(amido amine)s are promising carriers for systemic siRNA delivery in vivo.