Protective interactive noncondensing (PINC) polymers for enhanced plasmid distribution and expression in rat skeletal muscle.

We have developed protective interactive noncondensing (PINC) polymers, such as poly(N-vinyl pyrrolidone) (PVP) and poly(vinyl alcohol) (PVA), to protect plasmids from extracellular nuclease degradation while allowing the flexible complex to diffuse throughout the muscle tissue. Molecular modeling, zeta potential modulation, and ethidium bromide intercalation studies were performed to assess the mechanism of interaction between PVP and plasmid. The effect of salt concentration, pH, and polymer-plasmid ratios were investigated. We have correlated these variables with beta-galactosidase (beta-gal) expression after intramuscular administration to rats. PVP can form hydrogen bonds with the base pairs within the major groove of DNA at pH 4.0. The PVP-plasmid interaction results in a complex that is more hydrophobic (less negatively charged) than the uncomplexed plasmid due to the vinyl backbone of PVP. Up to a ten-fold enhancement in gene expression in rat muscle over the use of 'naked' DNA has been demonstrated using these systems. A linear structure-activity relationship (SAR) was found between the percent vinyl pyrrolidone monomer content in poly (vinyl pyrrolidone-covinyl acetate) polymers and beta-gal expression in muscle. Modulation of the interaction between PINC polymers and plasmid directly impacts the levels of gene expression in vivo. The linear SAR is being used to design novel PINC polymers with enhanced binding affinity to plasmids.