Investigation of DNA Spectral Conformational Changes and Polymer Buffering Capacity in Relation to Transfection Efficiency of DNA/Polymer Complexes

Abstract

Purpose. The relation between transfection efficiency of DNA/polymer complexes and DNA conformational alterations is investigated. The buffering capacity of several synthetic polymers is also studied to relate their performance in transfection efficiency. Methods. The cationic polymer/DNA interaction was evaluated by measuring the alteration of DNA secondary structures in solution before and after the addition of polymer with ATR-FTIR technique. The degree of protonation in aqueous cationic polymers is varied upon pH and different structures. A polymer capable of protonation acts like a proton sponge to react with H+ in titration with HCl. This characteristic was evaluated in relation to transfection efficiency because the capacity would help the release of endocytotic DNA from endosome/lysosome on its way to expression. Results. IR results show that the antisymmetric PO2- vibration of DNA (at 1224 cm-1) shifts toward lower frequencies in complexation with PEI or PLLys (these polymers are able to transfect DNA). By contrast, the antisymmetric PO2- vibration of DNA in presence of PDAMA or dextran (these polymers are poor in DNA transfection) shows a shifting to higher frequencies or no alteration was observed. Interestingly, the polymers with best performance in transfection efficiency are in this order: PEI>PDMAEMA>PLLys>PDAMA>dextran which is in the same order as their polymer buffering capacity. These facts indicate polymers possessing better buffering capacity could result in higher transfection efficiency. Also, we have demonstrated in this paper that the antisymmetric PO2- stretching vibration in IR spectra is sensitive while binding of cationic polymers to DNA. These findings are useful for the development of polymer-based gene delivery systems with better performance in vitro and in vivo