We recently proposed a novel gene regulation system responding to specifically and abnormally activated intracellular
enzymes in diseased cells. In the present study, we focused on
protein kinase C (PKC)alpha, which is hyper-activated in most
tumor cells, as a trigger for transgene regulation. We prepared cationic copolymers comprising hydrophilic and neutral
polymers in main chains and cationic
peptide substrates with different contents in side chains. Our copolymer with high
peptide content (>3 mol%) condensed with pDNA more weakly than with poly(
L-lysine) (pLL) having a similar molecular weight, but gene suppression was nearly identical to that of pLL, probably due to the steric hindrance of the main chains in our copolymer. Steric hindrance of the main chains barely affected the phosphorylation reaction of the pendant
peptide. In cell and mouse experiments, higher gene expression was observed in complexes of pDNA with copolymers pended PKC alpha-specific substrate
peptide than that in complexes with negative copolymers pended
peptide substituted phosphorylation site of
serine residues with
alanine. These results indicate that our system can recognize intracellular PKC alpha as a trigger to regulate transgene expression, and may be useful for
tumor gene therapy.