Polymeric vectors for gene delivery are a promising alternative for clinical applications as they are generally safer than viral counterparts. Our objective was to further our mechanistic understanding of polymer structure-function relationships to allow rational design of new biomaterials. Utilizing poly(beta-amino ester)s (PBAE), we investigated polymer-DNA binding by systematically varying polymer molecular weight, adding single carbons to the backbone and sidechain of the monomers that compose the polymers, as well as varying the type of polymer endgroup. We then sought to correlate how PBAE binding affects polyplex diameter and zeta potential, transfection efficacy and its associated cytotoxicity in human breast and brain cancer in vitro. Amongst other trends, we observed in both cell lines the PBAE-DNA binding constant is biphasic with transfection efficacy and optimal values for transfection efficacy are in the range of 1-6×104 M−1. A binding constant in this range is necessary but not sufficient for effective transfection.

The mechanism of polyethylenimine–DNA and poly(L-lysine)–DNA complex formation at pH 5.2 and 7.4 was studied by a time-resolved spectroscopic method. The formation of a polyplex core was observed to be complete at approximately N/P = 2, at which point nearly all DNA phosphate groups were bound by polymer amine groups. The data were analyzed further both by an independent binding model and by a cooperative model for multivalent ligand binding to multisubunit substrate. At pH 5.2, the polyplex formation was cooperative at all N/P ratios, whereas for pH 7.4 at N/P < 0.6 the polyplex formation followed independent binding changing to cooperative binding at higher N/Ps.

A large number of different polymers have been developed and studied for application as DNA carriers for non-viral gene delivery, but the DNA binding properties are not understood. This study describes the efficiency of nanoparticle formation by time-resolved fluorescence measurements for poly(β-amino esters), cationic biodegradable polymers with DNA complexation and transfection capability. From the large library of poly(β-amino esters) ten polymers with different transfection efficacies were chosen for this study. The binding constants for nanoparticle formation were determined and compared to polyethylene imines with the same method. Although the DNA binding efficiency of the amine groups are similar for both types of polymers, the overall binding constants are an order of magnitude smaller for poly(β-amino esters) than for 25 kDa polyethylenimines, but yet poly(β-amino esters) show comparable DNA transfection efficacy with polyethyleneimines. Within this series of polymers the transfection efficacy showed increasing trend in association with relative efficiency of nanoparticle formation.