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

We investigated the amplification of bleomycin-induced DNA cleavage by synt hetic triamides containing N-methylpyrrole (Py) and/or N-methylimidazole (I m), PyPyPy, PyPyIm, PyImPy, and PyImIm, using P-32-labeled DNA fragments ob tained from the human c-Ha-ras-l and p53 genes. Peplomycin, a bleomycin ana log, plus Fe(II) caused DNA cleavage at the 5'-GC-3' and 5'-GT-3' sequences (damaged bases are underlined). The addition of PyPyPy dramatically enhanc ed the cleavage, particularly at cytosine residues 3' to consecutive guanin es. Alteration in the site specificity was not observed with other triamide s (PyPyIm, PyImPy, and PyImIm). DNase I footprinting revealed that PyPyPy b ound 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 region s. These findings suggest that binding of PyPyPy to the DNA minor groove ch anges the DNA conformation to allow peplomycin to cleave DNA more efficient ly 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. (C) 2001 Elsevier Scienc e Inc. All rights reserved.