MECHANISM OF FORMATION OF NOVEL COVALENT DRUG-CENTER-DOT-DNA INTERSTRAND CROSS-LINKS AND MONOADDUCTS BY ENEDIYNE ANTITUMOR ANTIBIOTICS

The potent enediyne antitumor antibiotic C1027 has been previously rep orted to induce novel DNA interstrand cross-links and drug monoadducts under anaerobic conditions [Xu et al. (1997) J. Aln. Chem. Sec. 119, 1133-1134]. In the present study, we explored the mechanism of formati on of these anaerobic DNA lesions. We found that, similar to the aerob ic reaction, the diradical species of the activated drug initiates ana erobic DNA damage by abstracting hydrogen atoms from the C4', C1', and C5' positions of the Al, A2, and A3 nucleotides, respectively, in the most preferred 5'GTTA1T/5'ATA2A3C binding sequence. It is proposed th at the newly generated deoxyribosyl radicals, which cannot undergo oxi dation, likely add back onto the nearby unsaturated ring system of the postactivated enediyne core, inducing the formation of interstrand cr oss-links, connecting either Al to A2 or Al to A3, or drug monoadducts mainly on A2 or A3. Comparative studies with other enediynes, such as neocarzinostatin and calicheamicin gamma(1)(I) under similar reaction conditions indicate that the anaerobic reaction process is a kinetica lly competitive one, depending on the proximity of the drug unsaturate d ring system or dioxygen to the sugar radicals and their quenching by other hydrogen sources such as solvent or thiols. It was found that C 1027 mainly generates interstrand cross-links, whereas most of the ana erobic lesions produced by neocarzinostatin are drug monoadducts. Cali cheamicin gamma(1)(I) was found to be less efficient in producing both lesions. The anaerobic DNA lesions induced by enediyne antitumor anti biotics may have important implications for their potent cytotoxicity in the central regions of large tumors, where relative anaerobic condi tions prevail.