Synthesis and characterization of homopolymers bearing acid-cleavable cationic side-chains for ph-modulated release of DNA

A new type of homopolymers, PMAOE, bearing acid-cleavable cationic side-chains is synthesized and characterized. PMAOE is obtained via free radical polymerization, and they could efficiently bind and condense plasmid DNA at neutral pH. The strength of DNA binding is dependent on the length of PMAOE chains. NMR analysis reveals that hydrolysis of the ortho ester group of PMAOE follows an exocyclic mechanism and the rate of hydrolysis is much accelerated at mildly acidic pH, leading to accelerated disruption of polyplexes and release of DNA in mildly acidic environment. PMAOE is not toxic to cultured NIH 3T3 and COS-7 cells measured by MTT. This study demonstrates a unique mechanism of achieving pH-modulated binding and release of DNA from polymers with potential applications for gene delivery. A new mechanism of pH-modulated release of DNA from polymeric carrier (PMAOE) through a combination of cationic side-chain cleavage with increased polymer hydrophilicity and neutralization of residual cationic charges is demonstrated. These structurally simple side-chain degradable PMAOE homopolymers may have great potential as gene delivery vectors capable of releasing DNA in response to external or intracellular pH environment.