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Ex vivo transfer of therapeutic genes to cells is one of the potential strategies to prolong the life span of cell transplants. However, relatively safe non-viral carriers have not been extensively investigated due to their lower transfection efficiency. In this study, poly(l-lysine)-g-sulfonylurea varying SU content (PLL-SU) was synthesized to promote gene delivery efficacy to an insulin secreting cell line, RINm5F, which is known to express sulfonylurea receptor (SUR). The polymer formed complexes with a model reporter gene of pCMV-Luc (DNA) and the size of resulting particles was around 100 nm. The transfection efficiency of a polymer synthesized with 5 mol% of SU in the reaction feed (PLL-SU5%) to RINm5F cell was at least 5 times higher than that of PLL. The cytotoxicity of PLL-SU5%/DNA complex was equivalent to that of PLL/DNA complex. PLL-SU5% showed less transfection efficiency than PLL to NIH3T3 and HepG2 cells which are SUR negative. In RINm5F cells, the addition of free SU decreased the transfection efficiency of PLL-SU5%/DNA complex, suggesting that the complex shares the same receptors for SU. The PLL-SU5%/DNA complex seems to be internalized via SUR-mediated endocytosis pathway as suggested by vacuolar ATPases inhibition by Bafilomycin A1. It is noted that RINm5F cells treated with PLL-SU5%/DNA complex secreted more insulin than control, untreated cells, suggesting the insulinotropic effect of SU in PLL-SU5%. In conclusion, PLL-SU may be useful for transfer of therapeutic genes into insulin secreting cells.