DNA adduct formation by the anticancer drug ellipticine in rats determined by 32P postlabeling.

Ellipticine is a potent antineoplastic agent whose mode of action is considered to be based mainly on DNA intercalation and/or inhibition of topoisomerase II. Recently, we found that ellipticine also forms covalent DNA adducts in vitro and that the formation of the major adduct is dependent on the activation of ellipticine by cytochrome P450 (CYP). Here, we investigated the capacity of ellipticine to form DNA adducts in vivo. Male Wistar rats were treated with ellipticine, and DNA from various organs was analyzed by (32)P postlabeling. Ellipticine-specific DNA adduct patterns, similar to those found in vitro, were detected in most test organs. Only DNA of testes was free of the ellipticine-DNA adducts. The highest level of DNA adducts was found in liver (19.7 adducts per 10(7) nucleotides), followed by spleen, lung, kidney, heart and brain. One major and one minor ellipticine-DNA adducts were found in DNA of all these organs of rats exposed to ellipticine. Besides these, 2 or 3 additional adducts were detected in DNA of liver, kidney, lung and heart. The predominant adduct formed in rat tissues in vivo was identical to the deoxyguanosine adduct generated in DNA by ellipticine in vitro as shown by cochromatography in 2 independent systems. Correlation studies showed that the formation of this major DNA adduct in vivo is mediated by CYP3A1- and CYP1A-dependent reactions. The results presented here are the first report showing the formation of CYP-mediated covalent DNA adducts by ellipticine in vivo and confirm the formation of covalent DNA adducts as a new mode of ellipticine action.

Rat microsomes activating the anticancer drug ellipticine to species covalently binding to deoxyguanosine in DNA are a suitable model mimicking ellipticine bioactivation in humans.

Ellipticine is a potent antineoplastic agent, whose mode of action is considered to be based mainly on DNA intercalation and/or inhibition of topoisomerase II. Recently, we found that ellipticine also forms covalent DNA adducts and that the formation of the major adduct is dependent on the activation of ellipticine by cytochrome P450 (P450). We examined rat, rabbit, and human hepatic microsomal samples for their ability to activate ellipticine. The extent of activation was determined by binding of 3H-labeled ellipticine to DNA and by analyzing DNA adducts by 32P-postlabeling. We demonstrate that cytochrome P450 of human hepatic microsomes activating ellipticine to species binding to DNA is analogous to that of rats, but not of rabbits. Most of the ellipticine activation in rat and human hepatic microsomes is attributed to P450 enzymes of the same subfamily, P450 3A1/2 and P450 3A4, respectively, while the orthologous enzyme in rabbit hepatic microsomes, P450 3A6, is much less efficient. With purified enzymes, the major role of P450 3A1 and 3A4 in ellipticine-DNA adduct formation was confirmed. We identified deoxyguanosine as the target for P450-mediated ellipticine binding to DNA using polydeoxyribonucleotides and deoxyguanosine 3'-monophosphate. The results strongly suggest that rats are more suitable models than rabbits mimicking the metabolic activation of ellipticine in humans.