Substrate-mediated DNA delivery: role of the cationic polymer structure and extent of modification.

DNA complex immobilization to substrates that support cell adhesion can enhance gene transfer by maintaining DNA within the cellular environment while limiting complex aggregation. This report examines the tether design (e.g., extent of functionalization) and cationic polymer structure for their effect on complex binding to the substrate and cellular transfection. DNA is complexed with cationic polymers (polylysine, PL; polyethylenimine, PEI), which are functionalized with biotin for binding to a neutravidin (NA) substrate. Surfaces densities ranging from 0.4 to 2.6 microg DNA/cm(2) were obtained for PL, and from 0.7 to 1.0 microg DNA/cm(2) for PEI. The distribution of biotin groups for PL/DNA complexes had a dual effect on cellular transfection. Increasing the fraction of PL with biotin residues decreased luciferase activity; however, increasing the number of biotin residues per PL increased luciferase activity. For PEI, the number of biotin groups present on the complex did not affect transgene expression. Release studies demonstrated that 20-30% of the immobilized DNA was released over 8 days, with 8-20% released during the first 24 h. Enzymatic degradation of cationic polymers is not necessary for transfection. Additionally, the duration of transgene expression was extended for surface-mediated delivery relative to bolus delivery.