Amplification of bleomycin-induced DNA cleavage at cytosine residues 3′ to GGG sequences by pyrrole triamide

Abstract

1 We investigated the amplification of bleomycin-induced DNA cleavage by synthetic triamides containing N-methylpyrrole (Py) and/or N-methylimidazole (Im), PyPyPy, PyPyIm, PyImPy, and PyImIm, using 32P-labeled DNA fragments obtained from the human c-Ha- ras-1 and p53 genes. Peplomycin, a bleomycin analog, plus Fe(II) caused DNA cleavage at the 5′-G C -3′ and 5′-G T -3′ sequences (damaged bases are underlined). The addition of PyPyPy dramatically enhanced the cleavage, particularly at cytosine residues 3′ to consecutive guanines. Alteration in the site specificity was not observed with other triamides (PyPyIm, PyImPy, and PyImIm). DNase I footprinting revealed that PyPyPy bound to the sites adjacent to the sites where DNA cleavage was enhanced by PyPyPy, and that PyPyPy enhanced DNase I-induced cleavage in GC-rich regions. These findings suggest that binding of PyPyPy to the DNA minor groove changes the DNA conformation to allow peplomycin to cleave DNA more efficiently at GC-rich sequences, resulting in intensive site-specific DNA cleavage particularly at cytosines at the 3′-side of polyguanines. The present study on amplifiers of antitumor drugs would appear to offer a novel approach to the establishment of more effective chemotherapy.