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(392d) pH Responsive Polypeptides for siRNA Complexation

Engler, A. C., Massachusetts Institute of Technology
Hammond, P. T., Massachusetts Institute of Technology

One of the key challenges of the systemic delivery of siRNA is the ability to effectively complex the small charged oligonucleotides. Linear and branched cationic polymers are often selected for complexation because of their ability to bind and condense nucleic acids and stimulate endosomal escape. However, some of these polymers, such as poly(ethyleneimine), have limited success due to their high toxicity. A new polypeptide, poly(propargyl-L-glutamate) (PPLG) has been developed that can be easily functionalized with a wide range of amino groups by ?click chemistry?. PPLG is synthesized by well-studied N-carboxyanhydride (NCA) ring-opening polymerization of propargyl-L-glutamate NCA. Similar to natural polypeptides, these polymers possess the ability to assemble into well-defined, ordered structures, have low toxicity, and have well-controlled dimensions. Both PPLG and PEG-b-PPLG have been synthesized and various amino groups have been coupled to the PPLG to introduce charge and pH responsive behavior. Circular dichroism studies have been performed to observe alpha-helix to random coil transitions of the polymers as a function of pH. Turbidity studies have been performed to determine polymer solubility as a function of pH. Light scattering and AFM have been used to observe the self-assembly behavior of the PEG-b-PPLG at various pH levels. Initial studies have also been performed to confirm that these polymers are able to complex with siRNA.