Poly(alkylene oxide) copolymers for nucleic acid delivery

Nucleic acid-based artificial nanocarriers for gene therapy

Nucleic acid nanotechnology is a powerful tool in the fields of biosensing and nanomedicine owing to their high editability and easy synthesis and modification. Artificial nucleic acid nanostructures have become an emerging research hotspot as gene carriers with low cytotoxicity and immunogenicity for therapeutic approaches. In this review, recent progress in the design and functional mechanisms of nucleic acid-based artificial nano-vectors especially for exogenous siRNA and antisense oligonucleotide delivery is summarized. Different types of DNA nanocarriers, including DNA junctions, tetrahedrons, origami, hydrogels and scaffolds, are introduced. The enhanced targeting strategies to improve the delivery efficacy are demonstrated. Furthermore, RNA based gene nanocarrier systems by self-assembly of short strands, rolling circle transcription, chemical crosslinking and using RNA motifs and DNA-RNA hybrids are demonstrated. Finally, the outlook and potential challenges are highlighted. The nucleic acid-based artificial nanocarriers offer a promising and precise tool for gene delivery and therapy.

Micelle-Based Nanocarriers for Targeted Delivery of Cargo to Pancreas

Innovations in the field of amphiphilic block copolymers have led to the development of a series of attractive polymer-based drug and gene delivery micellar formulations. The amphiphilic block copolymers' low critical micelle concentration (CMC) results in highly stable nanoscale micelles possessing favorable in vivo safety profiles and biocompatibility, making them an excellent carrier choice for the systemic administration of various poorly soluble drugs. These micelles can also be used as an actively targeted drug delivery system. The targeting is achieved by conjugating specific targeting ligand molecules to the micelle surface. The conjugation takes place at the hydrophilic termini of the copolymers, which forms the shell or surface of the nanomicelles. In our lab, we have developed a targeted Pluronic^® F127-based nanoformulation to achieve targeting of specific cell types in the pancreas. To achieve active targeting based on the desired end application, we have conjugated several monoclonal antibodies (~150 kDa IgG) reactive to specific cell types in the pancreas by coupling lysine amino groups of the antibody to the p-nitrophenyl carbonate groups generated on the hydrophilic PEO segments of the Pluronic^® F127. The resultant targeted nanomicelles demonstrated high binding specificity and targeting efficiency. These nanomicelles can be used to encapsulate and deliver hydrophobic imaging agents and/or water-insoluble therapeutic small molecules to specific pancreatic cell types, enabling the development of diverse tools for use in the diagnosis and/or treatment of pancreas pathologies.

Adsorption and Interaction of Bovine Serum Albumin and Pluronic P103 Triblock Copolymer on a Gold Electrode: Double-Layer Capacitance Measurements

The interactions of proteins and other molecules and their adsorption onto substrates is a fascinating topic that has been applied to surface technologies, biosensors, corrosion studies, biotechnologies, and other fields. The success of these applications requires a previous characterization using some analytical techniques that, ordinarily, are not electrochemical. This work proposes analyzing the variation of the double-layer capacitance obtained through impedance electrochemical spectroscopy as an alternative strategy to show evidence of the interactions between proteins and triblock copolymers. The proposal is supported through the study of the interaction and adsorption of bovine serum albumin (BSA) and a commercial triblock copolymer (P103) in phosphate buffer on a gold electrode. The double-layer capacitance and the apparent interface thickness vs polarization potential curves as well as the potential of zero charge for pure P103 (0.6 wt %, corresponding to 6 g L^-1), pure BSA (3 mg mL^-1), and P103-BSA solutions (0.6 wt % and 3 mg mL^-1, respectively) are sensitive enough to show not only the interaction and the adsorption of the species but also the polarization potential where these interactions are taking place. A qualitative and quantitative analysis concerning the double-layer capacitance behavior is given. The significance and impact of this work is also presented.

pH-Triggered copolymer micelles as drug nanocarriers for intracellular delivery

We prepared pH-sensitive polymeric micelles which were used as nano-carriers and exhibited a high loading capacity and pH-triggered release of DOX.

Recent progress in biomedical applications of Pluronic (PF127): Pharmaceutical perspectives

Most of the administered anti-cancer drugs are hydrophobic in nature and are known to have poor water solubility, short residence time, rapid clearance from the body and systemic side effects. Polymeric-based targeted particulate carrier system has shown to directly deliver the encapsulated anti-cancer drug to the desired site of action and prevent the interaction of encapsulated drug with the normal cells. Pluronic F127 (PF127) has been widely investigated for its broad-range of therodiagnostic applications in biomedical and pharmaceutical sciences, but rapid dissolution in the physiological fluids, short residence time, rapid clearance, and weak mechanical strength are the main shortcomings that are associated with PF127 and have recently been overcome by making various modifications in the structure of PF127 notably through preparation of PF127-based mixed polymeric micelles, PF127-conjugated nanoparticles and PF127-based hydrophobically modified thermogels. In this article, we have briefly discussed the recent studies that have been conducted on various anti-cancer drugs using PF127 as nano-carrier modified with other copolymers and/or conjugated with magnetic nanoparticles. The key findings of these studies demonstrated that the modified form of PF127 can significantly increase the stability of incorporated hydrophobic drugs with enhanced in vitro cytotoxicity and cellular uptake of anti-cancer drugs. Moreover, the modified form of PF127 has also shown its therapeutic potentials as therodiagnostics in various types of tumors and cancers. Hence, it can be concluded that the modified form of PF127 exhibits significant therodiagnostic effects with increased tumor-specific delivery of anti-cancer drugs having minimal toxic effects as compared to PF127 alone and/or other copolymers.

Endogenous lung surfactant inspired pH responsive nanovesicle aerosols: pulmonary compatible and site-specific drug delivery in lung metastases

Concerns related to pulmonary toxicity and non-specificity of nanoparticles have limited their clinical applications for aerosol delivery of chemotherapeutics in lung cancer. We hypothesized that pulmonary surfactant mimetic nanoparticles that offer pH responsive release specifically in tumor may be a possible solution to overcome these issues. We therefore developed lung surfactant mimetic and pH responsive lipid nanovesicles for aerosol delivery of paclitaxel in metastatic lung cancer. 100-200 nm sized nanovesicles showed improved fusogenicity and cytosolic drug release, specifically with cancer cells, thereby resulting in improved cytotoxicity of paclitaxel in B16F10 murine melanoma cells and cytocompatibility with normal lung fibroblasts (MRC 5). The nanovesicles showed airway patency similar to that of endogenous pulmonary surfactant and did not elicit inflammatory response in alveolar macrophages. Their aerosol administration while significantly improving the biodistribution of paclitaxel in comparison to Taxol (i.v.), also showed significantly higher metastastes inhibition (~75%) in comparison to that of i.v. Taxol and i.v. Abraxane. No signs of interstitial pulmonary fiborisis, chronic inflammation and any other pulmonary toxicity were observed with nanovesicle formulation. Overall, these nanovesicles may be a potential platform to efficiently deliver hydrophobic drugs as aerosol in metastatic lung cancer and other lung diseases, without causing pulmonary toxicity.

Delivery of antisense oligonucleotides using poly(alkylene oxide)-poly(propylacrylic acid) graft copolymers in conjunction with cationic liposomes

The clinical application of gene silencing is hindered by poor stability and low delivery efficiency of naked oligonucleotides. Here, we present the in vitro and in vivo behaviors of a rationally designed, ternary, self-assembled nanoparticle complex, consisting of an anionic copolymer, cationic DOTAP liposome, and antisense oligonucleotide (AON). The multifunctional copolymers are based on backbone poly(propylacrylic acid) (PPAA), a pH-sensitive hydrophobic polymer, with grafted poly(alkylene oxides) (PAOs) varying in extent of grafting and PAO chemistry. The nanoparticle complexes with PPAA-g-PAO copolymers enhance antisense gene silencing effects in A2780 human ovarian cancer cells. A greater amount of AON is delivered to ovarian tumor xenografts using the ternary copolymer-stabilized delivery system, compared to a binary DOTAP/AON complex, following intraperitoneal injection in mice. Further, intratumoral injection of the nanoparticle complexes containing 1 mol% grafted PAO reduced tumoral bcl-2 expression by up to 60%. The data for complexes across the set of PAO polymers support a strong role for the hydrophilic-lipophilic balance of the graft copolymer in achieving serum stability and cellular uptake. Based upon these results, we anticipate that this novel nanoparticle delivery system can be extended to the delivery of plasmid DNA, siRNA, or aptamers for preclinical and clinical development.

Pentablock copolymers of pluronic F127 and modified poly(2-dimethyl amino)ethyl methacrylate for internalization mechanism and gene transfection studies

Cationic polymers are one of the major nonviral gene delivery vectors investigated in the past decade. In this study, we synthesized several cationic copolymers using atom transfer radical polymerization (ATRP) for gene delivery vectors: pluronic F127-poly(dimethylaminoethyl methacrylate) (PF127-pDMAEMA), pluronic F127-poly (dimethylaminoethyl methacrylate-tert-butyl acrylate) (PF127-p(DMAEMA-tBA)), and pluronic F127-poly(dimethylaminoethyl methacrylate-acrylic acid) (PF127-p(DMAEMA-AA)). The copolymers showed high buffering capacity and efficiently complexed with plasmid deoxyribonucleic acid (pDNA) to form nanoparticles 80–180 nm in diameter and with positive zeta potentials. In the absence of 10% fetal bovine serum, PF127-p(DMAEMA-AA) showed the highest gene expression and the lowest cytotoxicity in 293T cells. After acrylic acid groups had been linked with a fluorescent dye, the confocal laser scanning microscopic image showed that PF127-p(DMAEMA-AA)/pDNA could efficiently enter the cells. Both clathrin-mediated and caveolae-mediated endocytosis mechanisms were involved. Our results showed that PF127-p(DMAEMA-AA) has great potential to be a gene delivery vector.

Delivery of siRNA silencing Runx2 using a multifunctional polymer-lipid nanoparticle inhibits osteogenesis in a cell culture model of heterotopic ossification

Heterotopic ossification (HO) associated with traumatic neurological or musculoskeletal injuries remains a major clinical challenge. One approach to understanding better and potentially treating this condition is to silence one or more genes believed to be responsible for osteogenesis by small interfering RNA (siRNA) post-injury. Improved methods of delivering siRNA to myoprogenitor cells as well as relevant cell culture models of HO are needed to advance this approach. We utilize a model of HO featuring C2C12 myoprogenitor cells stimulated to the osteogenic phenotype by addition of BMP-2. For siRNA delivery, we utilize a nanocomposite consisting of DOTAP-based cationic liposomes coated with a graft copolymer of poly(propylacrylic acid) grafted with polyetheramine (Jeffamine), as this system has been shown previously to deliver antisense oligonucleotides safely into cells and out of endosomes for gene silencing in vitro and in vivo. Delivery of siRNA targeting Runx2, a transcription factor downstream of BMP-2, to stimulated C2C12 cells produced greater than 60% down-regulation of the Runx2 gene. This level of gene silencing was sufficient to inhibit alkaline phosphatase activity over the course of several days and calcium phosphate deposition over the course of 2 weeks. These results show the utility of the BMP-2/C2C12 model for capturing the cellular cell-fate decision in HO. Further, they suggest DOTAP/PPAA-g-Jeffamine as a promising delivery system for siRNA-based therapy for HO.

Graft copolymer polyelectrolyte complexes for delivery of cationic antimicrobial peptides

Peptides have enormous potential as therapeutic agents for the treatment of infection, in immunomodulation and for other medical applications, but their hydrolytic degradation in biological fluids is a serious limitation to their in vivo performance. Here we demonstrate the potential utility of polyelectrolyte nanoparticle complexes of novel self-assembling anionic graft copolymers for protecting peptides from degradation in human plasma. The anionic graft copolymers are synthesized by covalently attaching pendent polyetheramine chains to poly(alkylacrylic acid) backbones by carbodiimide coupling. The peptide:copolymer nanocomplexes' particle size, zeta-potential, peptide binding, and controlled release of the peptide are shown to be dependent upon the pendent chain graft density, polymer backbone alkyl groups (propyl vs. methyl), and the nanocomplexes' electrostatic charge ratio. The nanocomplexes can provide substantial protection to the bound peptides from degradation in human plasma for at least 24 h and, in standard microbiological assays are shown to retain some or all of the peptide's antimicrobial activity against a clinically relevant strain of Staphylococcus aureus.