Covalent binding of elliptinium acetate (NSC 264137) to nucleic acids of L1210 cells in culture

Elliptinium acetate (9-OH-NME; Celiptium) is an antineoplastic agent currently used in the treatment of metastatic breast Cancer and is known to intercalate into DNA. Previous studies have demonstrated that this molecule can be oxidized, yielding a reactive electrophilic form, which is able to bind covalently to a nucleophilic biological molecule. In this work, we evidenced a covalent binding of this drug to nucleic acids of L1210 cells in culture. A high performance liquid chromatography technique allowed us to distinguish between reversible and nonreversible interaction and to determine the binding ratio (rb) of covalently bound elliptinium versus Bases of nucleic acids extracted from cells. After an 8-h incubation of L1210 cells with 0.1 microM elliptinium (the dose corresponding to the 50% inhibitory dose), we obtained 2.4 X 10(-6) and 3.4 X 10(-6) as the rb for RNA and DNA, respectively. The kinetics of binding was also studied. The dose-response relationship obtained is linear in a concentration range of 0.025 to 0.5 microM 9-OH-NME. Furthermore, we demonstrated that the covalent binding of 9-OH-NME to DNA is not repaired during a period of 40 h (during this period, the cell population has undergone two doublings). The nonhydroxylated and non-antitumoral derivative of 9-OH-NME, N2-methylellipticinium, is 20 to 30 times less active in terms of covalent binding to nucleic acids, compared to the antitumor compound 9-OH-NME. The implication of the covalent binding of 9-OH-NME is discussed with respect to its mechanism of action.