NEW INSIGHT INTO THE MECHANISM OF BASE PROPENAL FORMATION DURING BLEOMYCIN-MEDIATED DNA-DEGRADATION

The mechanism of interaction of the antitumor antibiotic bleomycin (BLM) and cofactors with DNA to produce base propenal and 3'-phosphoglycolate and 5'-phosphate ends has been investigated. Analytical methods have been developed that allow the isolation of glycolic acid from the modified DNA without washout of isotopic labels. Results using (O2)-O-18, (HO)-H-2-O-18, and (HO2)-H-2-O-18 under a variety of conditions show that 1 mol of O-18 is found per mole of glycolate in the carboxylate group and is derived from the (O2)-O-18 not used in the formation of activated BLM. Thc second oxygen in the carboxylate of glycolate is derived from the 4-oxygen in the deoxyribose moiety from which it is generated. The oxygen in the aldehyde of the base propenal appears to be derived exclusively from H2O. Studies using poly[dA(2'-pro-R-H-3)dU] and poly[dA(2'-pro-S-H-3)dU] demonstrate, as originally proposed by Burger et al. [Burger, R. M.; Projan, S. J.; Horwitz, S. B.; Peisach, J. J. Biol. Chem. 1986, 261, 15855], that 2'-pro-R-hydrogen cleavage and DNA strand scission occur more rapidly than thc rate of base propenal formation. An alternative mechanism to thc one currently favored involving intermediate 6 (Scheme I) is proposed to accommodate all of the available data.