Bleomycin May Be Activated for DNA Cleavage by NADPH-Cytochrome P-450 Reductase

In the presence of NADPH and O₂, NADPH-cytochrome P-450 reductase was found to activate Fe(III)-bleomycin A₂ for DNA strand scission. Consistent with observations made previously when cccDNA was incubated in the presence of bleomycin and Fe(II) + 0₂ or Fe(III) + C₆H₅IO, degradation of DNA by NADPH-cytochrome P-450 reductase activated Fe(III)-bleomycin A₂ produced both single- and double-strand nicks with concomitant formation of malondialdehyde (precursors). Cu(II)-bleomycin A₂ also produced nicks in SV40 DNA following activation with NADPH-cytochrome P-450 reductase, but these were not accompanied by the formation of malondialdehyde (precursors). These findings confirm the activity of copper bleomycin in DNA strand scission and indicate that it degrades DNA in a fashion that differs mechanistically from that of iron bleomycin. The present findings also establish the most facile pathways for enzymatic activation of Fe(III)-bleomycin and Cu(II)-bleomycin, provide data concerning the nature of the activated metallobleomycins, and extend the analogy between the chemistry of cytochrome P-450 and bleomycin.