Organocatalytic Synthesis And Evaluation Of Polycarbonate Pendant Polymer:Beta-Cyclodextrin-Based Nucleic Acid Delivery Vectors

A family of mPEG-b-polycarbonate (mPEG-PC) diblock pendant polymers were synthesized from trimethylene carbonate and other cyclic carbonate monomers bearing hydrophobic guest ligands via organocatalytic ring-opening polymerization using 1,4,5-triazabicyclo[4.4.0]dec-5-ene catalyst or 1,8-diazabicyclo[5.4.0]undec-7-ene/thiourea cocatalyst. Diblock copolymers composed of a methoxypoly(ethylene oxide) (mPEG) block and a polycarbonate block containing either homopolymer or mixed polycarbonates (PC) were prepared by homopolymerization or copolymerization of the cyclic carbonate monomers in the presence of mPEG2000 or mPEG5000 initiator to give materials having a tunable pendant group density along the polycarbonate backbone. Polycarbonate blocks targeting the 2.4-10 kDa range were prepared with good molecular weight control and modest polydispersities (averaging similar to 1.3). Complexation of plasmid DNA with beta-cyclodextrin-polyethylenimine2.5 kDa produced nanoparticle cores that were then coated with the mPEG-PC diblock copolymers to produce transfection complexes in the 100-250 nm size range. Stable transfection complexes prepared at N/P ratios >10 had slightly positive zeta potentials and showed comparable or modestly better transfection efficiencies in HeLa cells than the commercial transfection agent, Lipofectamine2000. Transfection efficiencies were not dependent on polycarbonate block molecular weights. The mPEG-PC constructs displayed similar efficacy for adamantyl and cholesteryl pendants that strongly bind to beta-cyclodextrin; however, slightly better performance was observed for the weakly bound pendant, benzyl. These findings suggest that pDNA release is largely mediated by hydrolysis of the ester-bound pendant ligand within the endolysosomal compartment of the cell, with desorption of the mPEG-PC layer also contributing to plasmid release and activation in the case of weak binding pendant groups. We infer from these results that mPEG-PC may be an effective degradable transfection agent for in vivo applications.