Received for publication August 1, 2006.
Revised January 13, 2007.
Accepted for publication January 17, 2007.

BRCA1 Contributes to Cell Cycle Arrest and Chemoresistance in Response to Anticancer Agent, Irofulven

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. Previously, we have demonstrated 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 as well as the activation and foci formation of -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, 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.

Key words: DNA damage and repair, RNA/siRNA, Mechanisms of cell killing/apoptosis, Resistance, Tumor suppressors