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 gamma-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 G(2)/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.