ROLE OF THE C-10 SUBSTITUENT IN MITOMYCIN C-1-DNA BONDING

The structural requirements for mitomycin C-l bonding have been invest igated by comparing the bonding specificity of mitomycin C (1) with se lectively modified porfiromycins (N-methylmitomycin C) at the C-10 pos ition under reductive conditions and then comparing N-methyl-7-methoxy aziridinomitosene (10) with 7-methoxy-10-noraziridinomitosene (11) und er nonreductive conditions. Enzymatic and chemical reductive activatio n of mitomycin C in the presence of the 129-bp fragment from pBR322 le d to exclusive guanine (G) modification with drug bonding that occurr ed preferentially at 5'CG sites, while C-10 chloro (8) and C-10 bromo (9) deoxycarbamoylporfiromycins modified DNA at guanines but with sig nificantly diminished 5'CG sequence selectivity. A similar set of bon ding profiles were observed with 10 and 11 upon incubation with DNA. M itosene 10 selectively modified 5'G sites in DNA, while 11 did not. T hese studies provided support for the hypothesis that a hydrogen bond between the C-10 oxygen in the activated mitomycin species and the gua nine N(2)-amino proton on the nonbonding DNA strand in the precovalent complex permits selective modification of 5'CG sites in in vitro tra nsformations. We have also found that the kinetics of UVRABC incision of N-methyl-7-methoxyaziridinomitosene (10)-DNA adducts at different s equences are identical. This finding leads us to conclude that drug mo dification-induced UVRABC incision at different sites represents the s equence selectivity of drug-DNA bonding.