Abstract
Tumor suppressor gene BRCA1 is frequently mutated in familial breast and ovarian cancer. BRCA1 plays pivotal roles in maintaining genomic stability by interacting with numerous proteins in cell cycle control and DNA repair. Irofulven (6-hydroxymethylacylfulvene, HMAF, MGI 114, NSC 683863) is one of a new class of anticancer agents that are analogs of mushroom-derived illudin toxins. Preclinical studies and clinical trials have demonstrated that irofulven is effective against several tumor cell types. The exact nature of irofulven-induced DNA damage is not completely understood. We demonstrated previously that irofulven activates ATM and its targets, NBS1, SMC1, CHK2, and p53. In this study, we hypothesize that irofulven induces DNA double-strand breaks and that BRCA1 may affect chemosensitivity by controlling cell cycle checkpoints, DNA repair, and genomic stability in response to irofulven treatment. We observed that irofulven induces the formation of chromosome breaks and radials and the activation and foci formation of γ-H2AX, BRCA1, and RAD51. We also provided evidence that irofulven induces the generation of DNA double-strand breaks. By using BRCA1-deficient or -proficient cells, we demonstrated that in response to irofulven, BRCA1 contributes to the control of S and G2/M cell cycle arrest and is critical for repairing DNA double-strand breaks and for RAD51-dependent homologous recombination. Furthermore, we found that BRCA1 deficiency results in increased chromosome damage and chemosensitivity after irofulven treatment.
Footnotes
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This work was supported in part by National Institutes of Health grant R03CA107979, a grant from MGI Pharma, Inc. and funding from the Fannie Rippel Foundation (to W.W.).
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Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
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doi:10.1124/mol.106.029504.
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ABBREVIATIONS: IR, ionizing radiation; HR, homologous recombination; DSB, double-strand break; sh, short hairpin; RDS, radioresistant DNA synthesis assay; PFGE, pulse-field gel electrophoresis; FISH, fluorescent in situ hybridization; PBS, phosphate-buffered saline; NER, nucleotide excision repair; TC-NER, transcription-coupled nucleotide excision repair; DAPI, 4,6-diamidino-2-phenylindole; M/R/N, MRE11-RAD50-NBS1 complex.
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↵1 Current affiliation: Center for Disease Control and Prevention, Atlanta, Georgia.
- Received August 1, 2006.
- Accepted January 17, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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