Synthetic,pH-sensitive polymers that promote the intracellular delivery of nonviral gene therapy vectors

The potential for gene therapy to treat a wide range of diseases lies in the ability to deliver therapeutic genes and DNA effectively to affected cells. Currently, viruses are the predominant systems used for gene therapy due to their ability to attain high delivery efficiencies, but the prevalent safety concerns with viruses may limit their appeal. Nonviral vector systems represent an attractive alternative to viruses for gene therapy. However, the low transfection efficiencies attained with nonviral systems must be significantly increased before effective clinical application is realized. These low efficiencies are due to the multiple barriers encountered with nonviral delivery. One barrier is the trafficking of nonviral systems through the endocytic pathway. Retention of these vectors in the endocytic pathway results in vector degradation within lysosomes. Mechanisms that result in vector release from endosomes prior to degradation would enhance delivery of intact vectors to the cytoplasm, and hence enhance their therapeutic efficacy.; Synthetic, pH-sensitive polymers in the poly(alkylacrylic acid) family of polymers were designed to alter the trafficking of nonviral vectors, bypassing lysosomes to reduce vector degradation and allowing for greater vector delivery to the cytoplasm by mediating pH-sensitive endosomal membrane disruption. One particular polymer, poly(propylacrylic acid) (PPAA), maintains high membrane-destabilizing activity at near-endosomal pHs, with only minimal activity at neutral pH. Incorporation of PPAA into both polyplex and lipoplex nonviral gene therapy vectors increased transfection efficiencies with these vectors. Poly(methylacrylic acid) (PMAA) and poly(ethylacrylic acid) (PEAA) showed lower membrane-disruptive activity within the endosomal pH range and exhibited minimal enhancement in transfection with lipoplex vectors. Investigations into the mechanism of intracellular activity with PPAA determined that PPAA may be enhancing transfection by mediating both an increase in endosomal disruption as well as promoting the cellular internalization of lipoplex vectors. The addition of PPAA to lipoplexes also provided for serum-stable transfection. This serum-stabilization was attributed to the retention of lipoplex structural integrity and cellular internalization in the presence of PPAA. This serum-stability also demonstrates the in vivo therapeutic potential for vectors containing PPAA.