Distamycin A, a minor groove binder, changes enediyne-induced DNA cleavage sites and enhances apoptosis

We examined the effects of a minor groove binder, distamycin A, on DNA cleavage and apoptosis induced by an enediyne antitumor antibiotic, C1027, using 32P-labeled DNA fragments obtained from human genes. C1027 alone induced DNA cleavage particularly at the 5'-TTTT-3'/3'-AAAA-5' sequence (cutting sites are underlined). The addition of distamycin A enhanced the double-strand DNA cleavage at the 5'-CCT-3'/3'-GGA-5' and 5'-CCA-3'/3'-GGT-5' sequences, with a two-nucleotide 3'-stagger of the cleaved residues. These results suggest that distamycin A forms a heterodimer with C1027 to bind to DNA at GC-rich regions, resulting in amplification of DNA cleavage at these regions. Distamycin A enhanced C1027-induced DNA ladder formation and cytotoxicity in HL-60 cells. Therefore, amplification of DNA cleavage at GC-rich regions may result in enhancement of apoptosis. The present study on amplifiers of antitumor agents showed a novel approach to the potentially effective antitumor therapy.