Bioactivation of doxorubicin by human NADPH-cytochrome P450 reductase

grantor: University of TorontoDoxorubicin (DOX) is a useful antineoplastic drug with multiple mechanisms of cytotoxicity. One such mechanism involves the reductive bioactivation of the quinone ring to a semi-quinone radical, and subsequent redox-cycling. It is known that rat NADPH-cytochrome P450 reductase (CYPRED) catalyzes DOX reduction and sensitizes human cancer cells to DOX in vitro. The purpose of this investigation was to determine whether human CYPRED also catalyzes DOX reduction. DOX reduction occurred in a human CYPRED cDNA heterologous expression system and also in human liver microsomes. Using a bank of 17 human livers, the rate of microsomal DOX reduction was correlated with CYPRED activity and immunoreactive protein expression. DOX reduction was inhibited by diphenyliodonium chloride, an inhibitor of CYPRED. DOX reduction was not inhibited by carbon monoxide, suggesting that the cytochromes P450 did not catalyze DOX reduction. These results suggest that human CYPRED catalyzes DOX reduction. A mammalian expression vector containing human CYPRED cDNA was constructed for future transfection into breast cancer cells to assess whether sensitivity to DOX will be increased.M.Sc