pH-sensitive polymers that enhance intracellular drug delivery in vivo

Cytosolic delivery from endosomes is critical for those drugs that are susceptible to attack by lysosomal enzymes, such as DNA, RNA, oligonucleotides, proteins and peptides. Therefore, we have designed pH-sensitive, membrane-disruptive polymers to enhance the release of drugs from the acidic endosomal compartment to the cytoplasm. We have found that one polymer in particular, poly(propylacrylic acid) (PPAA), is very effective at membrane disruption at pHs below 6.5, based on hemolysis studies. PPAA also significantly enhances in vitro transfections of lipoplex formulations in cell culture, and does so in the presence of as much as 50% serum. In this study, we have extended our in vitro hemolysis and cell culture studies to an in vivo murine excisional wound healing model. A pilot study with a green fluorescent protein (GFP)-encoding plasmid indicated that injection of formulations containing PPAA into healing wounds resulted in increased GFP expression. Subsequently, by administering sense and antisense DNA for the angiogenesis inhibitor thrombospondin-2 (TSP2), we were able to alter the wound healing response in TSP2-null and wild type mice, respectively. Our findings showed that when PPAA was added to lipoplex formulations, expression of TSP2 was enhanced in TSP2-null mice compared to control formulations. These results show that PPAA can enhance in vivo transfections and that inhibition of TSP2 expression may lead to improved wound healing. These results suggest that PPAA can provide significant improvements in the in vivo efficacy of drugs such as DNA.