Single-strand and double-strand deoxyribonucleic acid breaks produced by several bleomycin analogs

Abstract

Production of single-strand breaks (ssb) and double-strand breaks (dsb) of PM2 phage DNA by several structurally related bleomycin (BLM) analogues [all antineoplastic drugs] was studied by gel electrophoresis. BLM A2 and BLM B2 produced a comparable extent of dsb. In various experiments, BLM A2 and BLM B2 at 22-41 ng/ml degraded 50% of the form I DNA into 33-38% form II and 12-17% form III DNA. BLM B1 produced ssb and dsb at a ratio similar to that of BLM A2, but both at a rate less than 1/2 that of BLM A2. Phleomycin (PLM) D1 induced an equivalent amount of ssb but only 1/8 of dsb induced by BLM B2. The relatively lower extent of dsb production for PLM D1 was observed in borate buffer (pH 9.5) or in Tris-HCl buffer (pH 7.5) and in the presence or absence of exogenous Fe(II). Deamido-BLM A2 produced ssb to an extent approximately 1/2 that of BLM A2 and dsb to less than 1/8 that of BLM A2. BLM analogues apparently produced ssb and dsb to different extents and ratios. The ratio of dsb to ssb varied depending on the analogue, indicating a lack of a direct correlation between ssb and dsb. The extent of ssb and dsb was affected by modifications on the C- and N-terminal half-molecules of BLM. Modification of the N-terminal amide or the bithiazole greatly reduced dsb; changes in structure or charge in the C-terminal amine affected ssb and dsb to a similar extent.