Ellipticine is a potent
antineoplastic agent, whose mode of action is considered to be based mainly on
DNA intercalation, inhibition of
topoisomerase II and
cytochrome P450-mediated formation of covalent
DNA adducts. This is the first report on the molecular mechanism of
ellipticine oxidation by
peroxidases (human
myeloperoxidase, human and ovine
cyclooxygenases, bovine
lactoperoxidase,
horseradish peroxidase) to species forming
ellipticine-
DNA adducts. Using NMR spectroscopy, the structures of 2
ellipticine metabolites were identified; the major product is the
ellipticine dimer, in which the 2
ellipticine skeletons are connected via N(6) of the
pyrrole ring of one
ellipticine molecule and C9 in the second one. The minor metabolite is
ellipticine N(2)-oxide. Using (32)P-postlabeling and [(3)H]-labeled
ellipticine, we showed that
ellipticine binds covalently to
DNA after its activation by
peroxidases. The
DNA adduct pattern induced by
ellipticine consisted of a cluster of up to 4 adducts. The 2 adducts are indistinguishable from the 2 major adducts generated between
deoxyguanosine in
DNA and either 13-hydroxy- or
12-hydroxyellipticine or in rats treated with
ellipticine, or if
ellipticine was activated with human hepatic and renal microsomes. The results presented here are the first characterization of the
peroxidase-mediated oxidative metabolites of
ellipticine and we have proposed species, 2 carbenium
ions, ellipticine-13-ylium and ellipticine-12-ylium, as reactive species generating 2 major
DNA adducts seen in vivo in rats treated with
ellipticine. The study forms the basis to further predict the susceptibility of human
cancers to
ellipticine.