pH-responsive polymers for intracellular delivery of biomolecules

Safe and efficient intracellular delivery of therapeutics remains a significant challenge in the pharmaceutical field. Stimuli responsive polymers that transition to a membrane destabilizing state at pH values found within endosomal/lysosomal compartments (pH 5-6.5) can be employed to achieve cytoplasmic delivery. In particular, poly(propylacrylic acid) (polyPAA) has been shown to dramatically enhance intracellular delivery of a variety of biomolecules. polyPAA based delivery systems have great potential for further improving cancer therapeutics.;Robust synthetic techniques were employed to prepare well-defined pH-responsive polymeric carriers to achieve intracellular delivery. Branched polyPAA architectures were prepared using state of the art RAFT polymerization techniques in tandem with click chemistry. These materials exhibited more robust pH-responsive membrane disruptive activity than linear formulations within late endosomal pH ranges. polyPAA graft copolymers containing a single biotin functionality were prepared for subsequent bioconjugations to the model protein avidin. The pharmacokinetics and biodistribution of polyPAA graft copolymer-avidin conjugates compared to linear polyPAA-avidin conjugates were evaluated in vivo. While both polymers enhanced circulation time of avidin, polyPAA graft copolymer conjugation sustained avidin circulation in the blood longer and also resulted in 1.5 times higher levels (p<0.05) of tumor accumulation of avidin compared to the branched PEG positive control. With more potent hemolytic activity than linear formulations coupled with significant circulation time and tumor accumulation enhancement, these graft copolymers hold great promise as polymeric carriers for biotherapeutics aimed at intracellular targets.;In addition to branched architectures, well-defined polyPAA-based antigen delivery systems were developed that segregate the membrane interactive and antigen conjugation sites into spatially discrete polymeric segments. Successful polymeric conjugation to the model antigen ovalbumin was achieved via disulfide exchange. This antigen delivery system delayed development of ovalbumin expressing tumors in vivo by 16 days and particulate forms of these carriers resulted in 2 times higher levels (p<0.02) of CD8+ T cells containing receptors for MHC 1 presented SIINFEKL ovalbumin peptides. These promising results warrant further investigation by either increasing the level of polyPAA associated per antigen or incorporating antigen presenting cell targeting moieties and adjuvants to achieve even more potent in vivo responses with these well-defined antigen delivery systems.