Role of cytochromes P450 and peroxidases in metabolism of the anticancer drug ellipticine: additional evidence of their contribution to ellipticine activation in rat liver, lung and kidney.

OBJECTIVE: Ellipticine is a potent antineoplastic agent exhibiting multiple mechanisms of action. This anticancer agent should be considered a pro-drug, whose pharmacological efficiency and/or genotoxic side effects are dependent on its cytochrome P450 (CYP)- and/or peroxidase-mediated activation to species forming covalent DNA adducts. The target of this study was to investigate a role of CYP and peroxidase enzymes in ellipticine oxidative activation in rats, a suitable model mimicking the fate of ellipticine in humans, in details. The contribution of pulmonary and renal CYP- and peroxidase enzymes to ellipticine metabolic activation is investigated and compared with that found in the liver.

METHODS: Ellipticine oxidation and DNA adduct formation in vitro were investigated using microsomes isolated from liver, lung and kidney of rats, either control (untreated) or treated i.p. with a single dose of 40 mg of ellipticine per kg of body weight. HPLC with UV detection was employed for the separation and characterization of ellipticine metabolites. Inhibitors of CYPs and cyclooxygenase (prostaglandin H synthase, COX) were used to characterize the enzymes participating in ellipticine oxidative activation in rat liver, lung and kidney. Ellipticine-derived DNA adducts were detected by 32P-postlabeling.

RESULTS: Using α-naphthoflavone, furafylline and ketoconazole, inhibitors of CYP1A, 1A2 and 3A, respectively, we found that the CYP1A and 3A enzymes play a major role in ellipticine activation to species forming DNA adducts in liver microsomes. Because of lower expression of these enzymes in lungs and kidneys, even after their induction by ellipticine, they play a minor role in ellipticine activation in these extrahepatic tissues. Arachidonic acid, a cofactor of COX, increased ellipticine activation in the microsomes of extrahepatic tissues. In addition, indomethacin, an inhibitor of COX, efficiently inhibited formation of ellipticine-derived DNA adduct in these microsomes. Based on these results, we attribute the higher activation of ellipticine in lung and kidney microsomes to COX than to CYP enzymes.

CONCLUSION: The results demonstrate that whereas CYP enzymes of 1A and 3A subfamilies are the major enzymes activating ellipticine in rat livers, peroxidase COX plays a significant role in this process in lungs and kidneys.