Coating of DNA/Poly(l-lysine) Complexes by Covalent Attachment of Poly[N-(2-hydroxypropyl)methacrylamide]

Synthesis and Structure Optimization of Star Copolymers as Tunable Macromolecular Carriers for Minimal Immunogen Vaccine Delivery

Minimal immunogen vaccines are being developed to focus antibody responses against otherwise challenging targets, including human immunodeficiency virus (HIV), but multimerization of the minimal peptide immunogen on a carrier platform is required for activity. Star copolymers comprising multiple hydrophilic polymer chains ("arms") radiating from a central dendrimer unit ("core") were recently reported to be an effective platform for arraying minimal immunogens for inducing antibody responses in mice and primates. However, the impact of different parameters of the star copolymer (e.g., minimal immunogen density and hydrodynamic size) on antibody responses and the optimal synthetic route for controlling those parameters remains to be fully explored. We synthesized a library of star copolymers composed of poly[N-(2-hydroxypropyl)methacrylamide] hydrophilic arms extending from poly(amidoamine) dendrimer cores with the aim of identifying the optimal composition for use as minimal immunogen vaccines. Our results show that the length of the polymer arms has a crucial impact on the star copolymer hydrodynamic size and is precisely tunable over a range of 20-50 nm diameter, while the dendrimer generation affects the maximum number of arms (and therefore minimal immunogens) that can be attached to the surface of the dendrimer. In addition, high-resolution images of selected star copolymer taken by a custom-modified environmental scanning electron microscope enabled the acquisition of high-resolution images, providing new insights into the star copolymer structure. Finally, in vivo studies assessing a star copolymer vaccine comprising an HIV minimal immunogen showed the criticality of polymer arm length in promoting antibody responses and highlighting the importance of composition tunability to yield the desired biological effect.

Phosphorus-Containing Polymers as Sensitive Biocompatible Probes for 31P Magnetic Resonance

The visualization of organs and tissues using ³¹P magnetic resonance (MR) imaging represents an immense challenge. This is largely due to the lack of sensitive biocompatible probes required to deliver a high-intensity MR signal that can be distinguished from the natural biological background. Synthetic water-soluble phosphorus-containing polymers appear to be suitable materials for this purpose due to their adjustable chain architecture, low toxicity, and favorable pharmacokinetics. In this work, we carried out a controlled synthesis, and compared the MR properties, of several probes consisting of highly hydrophilic phosphopolymers differing in composition, structure, and molecular weight. Based on our phantom experiments, all probes with a molecular weight of ~3-400 kg·mol^-1, including linear polymers based on poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), poly(ethyl ethylenephosphate) (PEEP), and poly[bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)]phosphazene (PMEEEP) as well as star-shaped copolymers composed of PMPC arms grafted onto poly(amidoamine) dendrimer (PAMAM-g-PMPC) or cyclotriphosphazene-derived cores (CTP-g-PMPC), were readily detected using a 4.7 T MR scanner. The highest signal-to-noise ratio was achieved by the linear polymers PMPC (210) and PMEEEP (62) followed by the star polymers CTP-g-PMPC (56) and PAMAM-g-PMPC (44). The ³¹P T₁ and T₂ relaxation times for these phosphopolymers were also favorable, ranging between 1078 and 2368 and 30 and 171 ms, respectively. We contend that select phosphopolymers are suitable for use as sensitive ³¹P MR probes for biomedical applications.

Overcoming resistance to rituximab in relapsed non-Hodgkin lymphomas by antibody-polymer drug conjugates actively targeted by anti-CD38 daratumumab

B-cell non-Hodgkin lymphomas (B-NHL) represent the most common type of hematologic malignancies in the Western hemisphere. The therapy of all B-NHL is based on the combination of different genotoxic cytostatics and anti-CD20 monoclonal antibody (mAb) rituximab. Unfortunately, many patients relapse after the mentioned front-line treatment approaches. The therapy of patients with relapsed/refractory (R/R) B-NHL represents an unmet medical need. We designed, developed and tested novel actively targeted hybrid mAb-polymer-drug conjugate (APDC) containing anti-CD20, anti-CD38 or anti-CD19 mAbs. Biocompatible copolymers based on N-(2-hydroxypropyl)methacrylamide (HPMA) with cytostatic agent doxorubicin attached via stimuli-sensitive hydrazone bond were employed for the mAb grafting. Anti-lymphoma efficacy of the APDC nanotherapeutics was evaluated in vivo on a panel of three patient-derived lymphoma xenografts derived from two patients with R/R B-NHL and one patient with so far untreated B-NHL. In both PDX models derived from patients with R/R B-NHL, the targeting with anti-CD38 antibody daratumumab demonstrated highly improved anti-lymphoma efficacy compared to the targeting with anti-CD20 rituximab, two experimental anti-CD19 antibodies and non-targeted controls. The results represent a proof-of-concept of a new algorithm of personalized anti-tumor therapy based on highly innovative APDC biomaterials.

Methods for Modification of Therapeutic Viruses

The optimal clinical exploitation of viruses as gene therapy or oncolytic vectors will require them to be administered intravenously. Strategies must therefore be deployed to enable viruses to survive the harsh neutralizing environment of the bloodstream and achieve deposition within and throughout target tissues or tumor deposits. This chapter describes the genetic and chemical engineering approaches that are being developed to overcome these challenges.

Micelle-Forming Block Copolymers Tailored for Inhibition of P-gp-Mediated Multidrug Resistance: Structure to Activity Relationship

Multidrug resistance (MDR) is often caused by the overexpression of efflux pumps, such as ABC transporters, in particular, P-glycoprotein (P-gp). Here, we investigate the di- and tri- block amphiphilic polymer systems based on polypropylene glycol (PPO) and copolymers of (N-(2-hydroxypropyl)methacrylamide) (PHPMA) as potential macromolecular inhibitors of P-gp, and concurrently, carriers of drugs, passively targeting solid tumors by the enhanced permeability and retention (EPR) effect. Interestingly, there were significant differences between the effects of di- and tri- block polymer-based micelles, with the former being significantly more thermodynamically stable and showing much higher P-gp inhibition ability. The presence of Boc-protected hydrazide groups or the Boc-deprotection method did not affect the physico-chemical or biological properties of the block copolymers. Moreover, diblock polymer micelles could be loaded with free PPO containing 5–40 wt % of free PPO, which showed increased P-gp inhibition in comparison to the unloaded micelles. Loaded polymer micelles containing more than 20 wt % free PPO showed a significant increase in toxicity; thus, loaded diblock polymer micelles containing 5–15 wt % free PPO are potential candidates for in vitro and in vivo application as potent MDR inhibitors and drug carriers.

Virus oncolíticos: un arma contra el cáncer

Introducción. Los virus oncolíticos son virus atenuados, mutados o que por naturaleza se dirigen y matan específicamente células tumorales, sin afectar a las células normales. La administración intratumoral del virus ofrece la oportunidad de tratar el tumor primario pero no focos metastásicos, los cuales pueden ser alcanzados mediante la administración intravenosa. Sin embargo, su eficiencia puede disminuir por la presencia de una respuesta inmunológica preexistente en los sujetos tratados.Objetivo. Exponer las técnicas utilizadas para envolver y transportar los virus con el fin de eludir el sistema inmunológico antes de que el virus llegue al tumor.Materiales y métodos. Se realizó una búsqueda narrativa de la literatura original y de revisión en las bases de datos PubMed, JSTOR y EBSCO sobre métodos o técnicas utilizadas para el tratamiento del cáncer mediante el uso de virus oncolíticos.Resultados. La formación de nanocomplejos entre los virus oncolíticos y biopolímeros —ya sea mediante la unión química o mediante la unión a través de interacciones electrostáticas o el uso de micropartículas, células transportadoras, liposomas, ultrasonido o terapias combinadas– es eficaz para evitar la respuesta inmunológica del huésped contra el virus.Conclusión. Para evitar la respuesta inmunológica del huésped contra los virus oncolíticos se han desarrollo diversos métodos que permiten la liberación controlada y especifica de los mismos. Sin embargo, debido a la diversidad de los virus, se debe tener en cuenta que la eficacia de los métodos de protección y transporte depende de las características bioquímicas tanto del biomaterial como del virus.

Synthesis of water-soluble star polymers based on cyclodextrins

Novel star polymers based on the water-soluble N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer and cyclodextrin were synthesized and the physico-chemical behavior of these precursors was studied. Semitelechelic HPMA copolymers were grafted onto the cyclodextrin core, thus forming star-like structure. Both prepared systems were designed as possible polymer carriers for the controlled release of cytostatic drugs, which after the drug release and degradation will be eliminated from the organism. Two synthesis approaches were used to obtain similar polymer carriers with different degradation rates. All the polymers were prepared by reversible addition-fragmentation chain-transfer polymerization, which guarantees low dispersity of the prepared systems.

Antibody-pHPMA functionalised fluorescent silica nanoparticles for colorectal carcinoma targeting

The systemic application of highly potent drugs such as cytostatics poses the risks of side effects, which could be reduced by using a carrier system able to specifically deliver the encapsulated drug to the target tissue. Essential components of a nanoparticle-based drug delivery system include the drug carrier itself, a targeting moiety, and a surface coating that minimizes recognition by the immune system. The present work reports on the preparation, in vitro characterization and in vivo testing of a new delivery system consisting of fluorescent silica nanoparticles functionalised with a non-immunogenic stealth polymer poly(N-(2-hydroxypropyl)methacrylamide) (pHPMA) and a monoclonal antibody IgG M75 that specifically binds to Carbonic Anhydrase IX (CA IX). CA IX is a promising therapeutic target, as it is a hallmark of several hypoxic tumours including colorectal carcinoma. Uniquely in this work, the monoclonal antibody was covalently coupled to the surface of fluorescently labelled silica nanoparticles via a multivalent amino-reactive co-polymer rather than a traditional bivalent linker. The pHPMA-M75 functionalised SiO2 nanoparticles exhibited excellent colloidal stability in physiological media. Their in vitro characterisation by flow cytometry proved a highly specific interaction with colorectal carcinoma cells HT-29. In vivo study on athymic NU/NU nude mice revealed that the SiO2-pHPMA-M75 nanoparticles are capable of circulating in the blood after intravenous administration and accumulate in the tumour at tenfold higher concentration than nanoparticles without specific targeting, with a considerably longer retention time. Additionally, it was found that by reducing the dose administered in vivo, the selectivity of the nanoparticle biodistribution could be further enhanced in favour of the tumour.

Tumor-targeted micelle-forming block copolymers for overcoming of multidrug resistance

New amphiphilic diblock polymer nanotherapeutics serving simultaneously as a drug delivery system and an inhibitor of multidrug resistance were designed, synthesized, and evaluated for their physico-chemical and biological characteristics. The amphiphilic character of the diblock polymer, containing a hydrophilic block based on the N-(2-hydroxypropyl)methacrylamide copolymer and a hydrophobic poly(propylene oxide) block (PPO), caused self-assembly into polymer micelles with an increased hydrodynamic radius (R_h of approximately 15nm) in aqueous solutions. Doxorubicin (Dox), as a cytostatic drug, was bound to the diblock polymer through a pH-sensitive hydrazone bond, enabling prolonged circulation in blood, the delivery of Dox into a solid tumor and the subsequent stimuli-sensitive controlled release within the tumor mass and tumor cells at a decreased pH. The applicability of micellar nanotherapeutics as drug carriers was confirmed by an in vivo evaluation using EL4 lymphoma-bearing C57BL/6 mice. We observed significantly higher accumulation of micellar conjugates in a solid tumor because of the EPR effect compared with similar polymer-drug conjugates that do not form micellar structures or with the parent free drug. In addition, highly increased anti-tumor efficacy of the micellar polymer nanotherapeutics, even at a sub-optimal dose, was observed. The presence of PPO in the structure of the diblock polymer ensured, during in vitro tests on human and mouse drug-sensitive and resistant cancer cell lines, the inhibition of P-glycoprotein, one of the most frequently expressed ATP-dependent efflux pump that causes multidrug resistance. In addition, we observed highly increased rate of the uptake of the diblock polymer nanotherapeutics within the cells. We suppose that combination of unique properties based on MDR inhibition, stimuli sensitiveness (pH sensitive activation of drug), improved pharmacokinetics and increased uptake into the cells made the described polymer micelle a good candidate for investigation as potential drug delivery system.

Nanotherapeutics shielded with a pH responsive polymeric layer

Efficient intravenous delivery is the greatest single hurdle, with most nanotherapeutics frequently found to be unstable in the harsh conditions of the bloodstream. In the case of nanotherapeutics for gene delivery, viral vectors are often avidly recognized by both the innate and the adaptive immune systems. So, most modern delivery systems have benefited from being coated with hydrophilic polymers. Self-assembling delivery systems can achieve both steric and lateral stabilization following surface coating, endowing them with much improved systemic circulation properties and better access to disseminated targets; similarly, gene delivery viral vectors can be 'stealthed' and their physical properties modulated by surface coating. Polymers that start degrading under acidic conditions are increasingly investigated as a pathway to trigger the release of drugs or genes once the carrier reaches a slightly acidic tumor environment or after the carrier has been taken up by cells, resulting in the localization of the polymer in acidic endosomes and lysosomes. Advances in the design of acid-degradable drug and gene delivery systems have been focused and discussed in this article with stress placed on HPMA-based copolymers. We designed a system that is able to "throw away" the polymer coat after successful transport of the vector into a target cell. Initial biological studies were performed and it was demonstrated that this principle is applicable for real adenoviral vectors. It was shown that the transfection ability of coated virus at pH 7.4 is 75 times lower then transfection at pH 5.4.

The impact of the HPMA polymer structure on the targeting performance of the conjugated hydrophobic ligand

The structure of hydrophilic polymer plays a vital role in the targeting efficiency of the conjugated hydrophobic ligand.

Engineering biodegradable and multifunctional peptide-based polymers for gene delivery

The complex nature of in vivo gene transfer establishes the need for multifunctional delivery vectors capable of meeting these challenges. An additional consideration for clinical translation of synthetic delivery formulations is reproducibility and scale-up of materials. In this review, we summarize our work over the last five years in developing a modular approach for synthesizing peptide-based polymers. In these materials, bioactive peptides that address various barriers to gene delivery are copolymerized with a hydrophilic backbone of N-(2-hydroxypropyl)methacrylamide (HPMA) using reversible-addition fragmentation chain-transfer (RAFT) polymerization. We demonstrate that this synthetic approach results in well-defined, narrowly-disperse polymers with controllable composition and molecular weight. To date, we have investigated the effectiveness of various bioactive peptides for DNA condensation, endosomal escape, cell targeting, and degradability on gene transfer, as well as the impact of multivalency and polymer architecture on peptide bioactivity.

Combination chemotherapy using core-shell nanoparticles through the self-assembly of HPMA-based copolymers and degradable polyester

The preparation of core-shell polymeric nanoparticles simultaneously loaded with docetaxel (DTXL) and doxorubicin (DOX) is reported herein. The self-assembly of the aliphatic biodegradable copolyester PBS/PBDL (poly(butylene succinate-co-butylene dilinoleate)) and HPMA-based copolymers (N-(2-hydroxypropyl)methacrylamide-based copolymers) hydrophobically modified by the incorporation of cholesterol led to the formation of narrow-size-distributed (PDI<0.10) sub-200-nm polymeric nanoparticles suitable for passive tumor-targeting drug delivery based on the size-dependent EPR (enhanced permeability and retention) effect. The PHPMA provided to the self-assembled nanoparticle stability against aggregation as evaluated in vitro. The highly hydrophobic drug docetaxel (DTXL) was physically entrapped within the PBS/PBDL copolyester core and the hydrophilic drug doxorubicin hydrochloride (DOX·HCl) was chemically conjugated to the reactive PHPMA copolymer shell via hydrazone bonding that allowed its pH-sensitive release. This strategy enabled the combination chemotherapy by the simultaneous DOX and DTXL drug delivery. The structure of the nanoparticles was characterized in detail using static (SLS), dynamic (DLS) and electrophoretic (ELS) light scattering besides transmission electron microscopy (TEM). The use of nanoparticles simultaneously loaded with DTXL and DOX provided a more efficient suppression of tumor-cell growth in mice bearing EL-4 T cell lymphoma when compared to the effect of nanoparticles loaded with either DTXL or DOX separately. Additionally, the obtained self-assembled nanoparticles enable further development of targeting strategies based on the use of multiple ligands attached to an HPMA copolymer on the particle surface for simultaneous passive and active targeting and different combination therapies.

Advances in polymeric and inorganic vectors for nonviral nucleic acid delivery

Nonviral systems for nucleic acid delivery offer a host of potential advantages compared with viruses, including reduced toxicity and immunogenicity, increased ease of production and less stringent vector size limitations, but remain far less efficient than their viral counterparts. In this article we review recent advances in the delivery of nucleic acids using polymeric and inorganic vectors. We discuss the wide range of materials being designed and evaluated for these purposes while considering the physical requirements and barriers to entry that these agents face and reviewing recent novel approaches towards improving delivery with respect to each of these barriers. Furthermore, we provide a brief overview of past and ongoing nonviral gene therapy clinical trials. We conclude with a discussion of multifunctional nucleic acid carriers and future directions.

Tropism ablation and stealthing of oncolytic adenovirus enhances systemic delivery to tumors and improves virotherapy of cancer

Intravenous delivery of therapeutic virus particles remains a major goal for virotherapy of metastatic cancer. Avoiding phagocytic capture and unwanted infection of nontarget cells is essential for extended plasma particle kinetics, and simply ablating one or the other does not give extended plasma circulation. Here we show that polymer coating of adenovirus type 5 (Ad5) can combine with predosing strategies or Kupffer cell ablation to achieve systemic kinetics with a half-life >60 min, allowing ready access to peripheral tumors. Accumulation of virus particles within tumor nodules is proportional to the area under the plasma concentration/time curve. Polymer coating wild-type Ad5 in this way is known to decrease hepatic toxicity, increasing the dose of virus particles that can be safely administered. Using polymer-coating technology to deliver a replicating Ad5 systemically, virus replication and transgene expression was almost totally confined to tumor tissues, giving a much improved therapeutic index compared with uncoated virus, and complete control of human HepG2 tumor xenografts.

Polymer coatings for delivery of nucleic acid therapeutics

Gene delivery remains the greatest challenge in applying nucleic acid therapeutic for a broad range of diseases. Combining stability during the delivery phase with activation and transgene expression following arrival at the target site requires sophisticated vectors that can discriminate between cell types and respond to target-associated conditions to trigger expression. Efficient intravenous delivery is the greatest single hurdle, with synthetic vectors frequently found to be unstable in the harsh conditions of the bloodstream, and viral vectors often recognized avidly by both the innate and the adaptive immune system. Both types of vectors benefit from coating with hydrophilic polymers. Self-assembling polyelectrolyte non-viral vectors can achieve both steric and lateral stabilization following surface coating, endowing them with much improved systemic circulation properties and better access to disseminated targets; similarly viral vectors can be 'stealthed' and their physical properties modulated by surface coating. Both types of vectors may also have their tropism changed following chemical linkage of novel ligands to the polymer coating. These families of vectors go some way towards realizing the goal of efficient systemic delivery of genes and should find a range of important uses in bringing this still-emerging field to fruition.

HPMA-oligolysine copolymers for gene delivery: optimization of peptide length and polymer molecular weight

Polycations are one of the most frequently used classes of materials for non-viral gene transfer in vivo. Several studies have demonstrated a sensitive relationship between polymer structure and delivery activity. In this work, we used reverse addition-fragmentation chain transfer (RAFT) polymerization to build a panel of N-(2-hydroxypropyl)methacrylamide (HPMA)-oligolysine copolymers with varying peptide length and polymer molecular weight. The panel was screened for optimal DNA-binding, colloidal stability in salt, high transfection efficiency, and low cytotoxicity. Increasing polyplex stability in PBS correlated with increasing polymer molecular weight and decreasing peptide length. Copolymers containing K(5) and K(10) oligocations transfected cultured cells with significantly higher efficiencies than copolymers of K(15). Four HPMA-oligolysine copolymers were identified that met the desired criteria. Polyplexes formed with these copolymers demonstrated both salt stability and transfection efficiencies on-par with poly(ethylenimine) PEI in cultured cells.

Molecular weight and polydispersity of calf-thymus DNA: static light-scattering and size-exclusion chromatography with dual detection

Plausible calf-thymus DNA molecular weight distribution can be obtained by size-exclusion chromatography with dual low-angle light scattering/refractometric detection at sufficiently low flow rate. The distribution extends over three decades of molecular weight and is characterized by weight average molecular weight M(w) = 8418000 and polydispersity index M(w)/M(n) = 5.2. After strongly scattering impurities had been removed from the sample using adsorption properties of the 3 mum mixed-cellulose-ester filter membranes, static light-scattering measurement in flow injection mode was feasible and gave M(w) = 8580000, corroborating the veracity of SEC results.

Effect of hydrophobic interactions on properties and stability of DNA-polyelectrolyte complexes

Polyplexes are polyelectrolyte complexes of DNA and polycations, designed for potential gene delivery. We investigated the properties of new polyplexes formed from cholesterol-modified polycations and DNA. Three complexes were tested; their cholesterol contents were 1.4, 6.3, and 8.7 mol %. UV spectroscopy and fluorescence assay using ethidium bromide proved the formation of polyplexes. The kinetics of turbidity of polyplexes solutions in physiological solution showed that the colloid stability of polyplexes increases with increasing content of cholesterol in polycations. Dynamic, static, and electrophoretic light scattering, small-angle X-ray scattering, and atomic force microscopy were used for characterization of polyplexes. The observed hydrodynamic radii of polyplexes were in the range of 30-60 nm; they were related to the polycation/DNA ratio and hydrophobicity of the used polycations (the cholesterol content). The properties of polyplex particles depend, in addition to polycation structure, on the rate of polycation addition to DNA solutions.

High-molecular-weight Polymers Containing Biodegradable Disulfide Bonds: Synthesis and In Vitro Verification of Intracellular Degradation

The synthesis, physico-chemical behavior, and in vitro intracellular degradation of new biodegradable graft, diblock or multiblock polymer carriers that were designed to deliver bioactive compounds by passive tumor targeting were investigated. The graft polymer carriers consisted of the N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer backbone grafted with a semitelechelic HPMA copolymer. The diblock polymer carriers were prepared by condensation of two semitelechelic HPMA copolymers. The multiblock polymer drug carrier was prepared by oxidative polycondensation of PEG-bis-cysteine. In all three carrier systems, the single polymers were linked via biodegradable disulfide bonds forming the graft, diblock or multiblock polymers. These polymers are potential polymer carriers for solid tumor-specific drug delivery with subsequent intracellular degradation to short polymer fragments that can be excreted by glomerular filtration. Prolonged blood circulation, accumulation in solid tumors, and drug release from these carriers have been reported. Here, degradation of the polymers in model buffer solutions mimicking intracellular environment as well as after incubation with EL4 T-cell lymphoma cancer cells were investigated. In both cases, degradation resulted in polymer fragments of molecular weight below the renal threshold.

Facile synthesis of multivalent folate-block copolymer conjugates via aqueous RAFT polymerization: targeted delivery of siRNA and subsequent gene suppression

Cell specific delivery of small interfering ribonucleic acid (siRNA) using well-defined multivalent folate-conjugated block copolymers is reported. Primary amine functional, biocompatible, hydrophilic-block-cationic copolymers were synthesized via aqueous reversible addition-fragmentation chain transfer (RAFT) polymerization. N-(2-hydroxypropyl)methacrylamide) (HPMA), a permanently hydrophilic monomer, was copolymerized with a primary amine containing monomer, N-(3-aminopropyl)methacrylamide (APMA). Poly(HPMA) confers biocompatibility, while APMA provides amine functionality, allowing conjugation of folate derivatives. HPMA-stat-APMA was chain extended with a cationic block, poly(N-[3-(dimethylamino)propyl]methacrylamide), to promote electrostatic complexation between the copolymer and the negatively charged phosphate backbone of siRNA. Notably, poly(HPMA) stabilizes the neutral complexes in aqueous solution, while APMA allows the conjugation of a targeting moiety, thus, dually circumventing problems associated with the delivery of genes via cationically charged complexes (universal transfection). Fluorescence microscopy and gene down-regulation studies indicate that these neutral complexes can be specifically delivered to cancer cells that overexpress folate receptors.

Coating of adeno-associated virus with reactive polymers can ablate virus tropism, enable retargeting and provide resistance to neutralising antisera

BACKGROUND

Copolymers based on poly-[N-(2-hydroxypropyl) methacrylamide] (HPMA) have been used previously to enable targeted delivery of adenovirus. Here we demonstrate polymer-coating techniques can also be used to modify and retarget adeno-associated virus (AAV) types 5 and 8.

METHODS

Three strategies for modifying transductional targeting of AAV were employed. The first involved direct reaction of AAV5 or AAV8 with amino-reactive HPMA copolymer. The second approach used carbodiimide (EDC) chemistry to increase the number of surface amino groups on the AAV5 capsid, thereby improving coating efficiency. In the third approach, the AAV5 genome was isolated from capsid proteins and delivered in a synthetic polyplex consisting of polyethylenimine (PEI) and HPMA.

RESULTS

Efficient covalent attachment of HPMA copolymer to AAV5 could only be achieved following modification of the virus with EDC. Coating inhibited sialic acid dependent infection and provided a platform for retargeting via new ligands, including basic fibroblast growth factor. Retargeted infection was shown to be partially resistant to neutralising antisera. Delivery of AAV5 genomes using PEI and HPMA was efficient and provided absolute control of tropism and protection from antisera. In contrast AAV8 could be reacted directly with HPMA copolymer and allowed specific retargeting via the epidermal growth factor receptor, but gave no protection against neutralising antisera.

CONCLUSIONS

Reactive HPMA polymers can be used to ablate the natural tropism of both AAV8 and EDC-modified AAV5 and enable receptor-specific infection by incorporation of targeting ligands. These data show transductional targeting strategies can be used to improve the versatility of AAV vectors.

Coating of vesicles with hydrophilic reactive polymers

Vesicles bearing either cationic (amino) groups or zwitterionic (amino acid) groups on the surface were coated with a reactive multivalent hydrophilic N-(2-hydroxypropyl)methacrylamide polymer (PHPMA) and its positively charged analogue (3 mol % quaternary ammonium groups), both having reactive thiazolidine-2-thione (TT) groups randomly distributed along the polymer chain. The vesicles were dispersed in water at a concentration of 1 mg/mL. The effect of surface charges of model vesicles on the surface coating efficiency was evaluated. The changes in the weight-average molecular weight, in the hydrodynamic size, and in the zeta-potential of model vesicles were tested using light scattering methods. The most effective coating of vesicles was observed for the zwitterionic vesicles coated with the positively charged hydrophilic PHPMA-TT copolymer at a concentration of reactive polymer cp = 2 mg/mL. The coating efficiency was more than 1 order of magnitude higher than that obtained for positively charged vesicles coated by the uncharged hydrophilic polymer at the same cp.

Conjugates of doxorubicin with graft HPMA copolymers for passive tumor targeting

Synthesis, physicochemical behavior, tumor accumulation and preliminary anticancer activity of a new biodegradable graft copolymer-doxorubicin (DOX) conjugates designed for passive tumor targeting were investigated. In the graft high-molecular-weight conjugates the multivalent N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer was grafted with a similar but semitelechelic HPMA copolymer; both types of polymer chains were bearing doxorubicin attached by hydrazone bonds enabling intracellular pH-controlled drug release. The polymer grafts were attached to the main chain through spacers, degradable enzymatically or reductively, facilitating, after the drug release, intracellular degradation of the graft polymer carrier to short fragments excretable from the organism by glomerular filtration. The graft polymer-DOX conjugate exhibited prolonged blood circulation and enhanced tumor accumulation in tumor-bearing mice indicating the important role of the EPR effect in the anticancer activity. The graft polymer-DOX conjugates showed a significantly higher antitumor activity in vivo than DOX.HCl or the linear polymer conjugate when tested in mice bearing 38C13 B-cell or EL4 T-cell lymphoma, with a significant number of long-term-surviving (LTS) mice with EL4 T-cell lymphoma treated with a single dose 15 mg DOX equiv./kg on day 10.

Cationic lipids and polymers mediated vectors for delivery of siRNA

RNA interference (RNAi) is one of the most importantly protective phenomena forming from the process combating against virus. Since its high efficiency for silencing the expression of proteins at the posttranscriptional level, RNAi shows great prospect in therapeutics for diseases. However, the delivery of siRNA into cells, tissues or organs remains to be a big obstacle for its applications. Many vectors for siRNA delivery have been developed including viral vectors and non-viral vectors, among them non-viral vectors have the advantages of low toxicity, ease of synthesis and low immune response over viral ones. Cationic liposomes and polymer particles, major varieties of non-viral vectors, used for gene delivery, have shown to be suitable for the delivery of siRNA. Based on the concise introduction of RNAi, this article reviews the non-viral delivery systems of siRNA, hoping to provide helpful information for the development of delivery systems of siRNA, and to summarize literatures about siRNA delivery published in recent years.