UCN-01 selectively enhances mitomycin C cytotoxicity in p53 defective cells which is mediated through S and/or G(2) checkpoint abrogation

We have previously reported that UCN-01 (7-hydroxystaurosporine), a protein kinase inhibitor that is under clinical trials as an anti-cancer agent in the USA and Japan, enhanced the anti-tumor activity of mitomycin C (MMC) in vitro and in vivo. Subsequent studies from other laboratories revealed tha t UCN-01 could selectively enhance cytotoxicity of DNA damaging agents in p 53 defective cells and that this was mediated by abrogation of S and /or G( 2) arrest by UCN-01. In this study, we report that UCN-01 selectively enhan ces the cytotoxicity of MMC in human p53 mutant cell lines. In contrast, UC N-01 showed little, if any, effect on MMC cytotoxicity in human p53 wild-ty pe cell lines. Terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-ni ck end-labeling (TUNEL) assay revealed that the combination of MMC with UCN -01 increased DNA breaks consistent: with apoptosis in p53 defective A431 e pidermoid carcinoma cells. In p53 wild-type MCF-7 breast carcinoma cells, t he cyclin-dependent kinase inhibitor protein p21/WAF1 was markedly induced after the treatment with MMC alone, although this response was significantl y delayed from the time of MMC treatment. Detailed cell-cycle studies revea led that UCN-01 abrogated S and C, phase accumulation induced by MMC in p53 defective cells and to a lesser extent in p53 wild-type cell lines. The ab rogation of arrest in p53 wild-type cells was observed prior to significant induction of the p53 response, Since MMC was less effective against p53 de fective cell lines than against p53 wild-type cell lines and UCN-01 selecti vely enhanced MMC cytotoxicity in p53 defective cell lines, UCN-01 may prov ide a new modality of MMC-based cancer chemotherapy, particularly in p53 de fective cancer patients. (C) 2000 Wiley-Liss, Inc.