The mechanism of selective transfection mediated by pentablock copolymers; Part I: Investigation of cellular uptake

Poly(diethylaminoethylmethacrylate) (PDEAEM) and Pluronic F127 based pentablock copolymer vectors with the ability to transfect cancer cells selectively over normal cells in in vitro cultures were developed, as described in a previous report. Understanding the mechanism of this selectivity will enable better polymeric vectors to be designed, with inherent selectivity for specific cell types based on intracellular differences and not on the use of targeting ligands, which have shown variable success, depending on the system. It is assumed that the selectivity was due to different intracellular barriers to transfection in the different cell types. Part I focuses on investigating whether cellular entry is one of the barriers to transfection, through conjugation of epidermal growth factor (EGF) to the pentablock copolymer vector. Results indicate that EGF conjugation increased transfection efficiency the most when conjugated to the outer surface of polyplexes, with minimal disruption to DNA packaging and maximal accessibility to receptors. The overall resulting enhancement in transfection, however, was a moderate three- to five-fold increase compared with the condition with no EGF involved, implying that the addition of EGF fails to overcome the intracellular barrier to transfection, which probably involves some step other than cellular uptake in pentablock copolymer system. Therefore, the differences observed in the selectivity of transfection between cancer and normal cell lines is probably not controlled by differences in cellular entry, and the intracellular barriers to transfection in this system are likely to be endosomal escape or nuclear entry, as investigated in Part II, the companion paper to this work.