Abstract 2509: CDDO-Im induces DNA damage, G2/M arrest and apoptosis in BRCA1-mutated breast cancer cells

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC The breast cancer-associated gene 1 (BRCA1) is the most frequently mutated tumor suppressor gene in familial breast cancers. BRCA1 mutations also predispose to other types of cancers, pointing to a fundamental role of this pathway in tumor suppression. BRCA1 plays important roles in DNA damage and repair, homologous recombination, cell-cycle regulation, and apoptosis. The synthetic triterpenoid 1-[2-cyano-3,12-dioxooleana-1, 9(11)-dien-28-oyl]imidazole (CDDO-Im) is a promising anticancer agent with potent anti-proliferative and apoptotic activities against a wide variety of cancer types. However the mechanisms responsible for the selective apoptotic effects of CDDO-Im in cancer cells remain elusive. In the present work, treatment of BRCA1-mutated mammary tumor cells with CCDO-Im (0.3-1 μM) led to apoptosis as characterized by decreased thymidine incorporation, increased annexin V-binding, and cleavage of PARP and caspases-3. In addition, 0.3 μM CDDO-Im treatment depleted the G1 population of cells, which was accompanied by an accumulation of cells at G2 phase. CDDO-Im also activated the DNA damage response by inducing the phosphorylation of Chk1/2 and the up-regulation of p21, prior to the induction of apoptosis in BRCA1-mutated cancer cells. The inhibition of Chk1 by UCN-01, a Chk1 inhibitor abrogated G2/M arrest induced by CDDO-Im. To investigate how CDDO-Im activates the DNA damage response in BRCA1-mutated breast cancer cells, we performed a comet assay and Western Blot for γH2AX, a marker of DNA damage. CDDO-Im induced DNA damage and the phosphorylation of H2AX in BRCA1-mutated mammary tumor cells. Pretreatment with 0.3 μM CDDO-Im sensitized BRCA1-mutated cancer cells to carboplatin, a DNA-damaging agent, suggesting that CDDO-Im potentiates the effect of this drug. Moreover, CDDO-Im also induced reactive oxygen species (ROS) generation in these tumor cells, which is associated with the induction of DNA damage. The inhibition of ROS generation by uric acid prevented CDDO-Im-induced DNA damage. Furthermore, treatment with CDDO-Im was not cytotoxic to normal mouse 3T3 fibroblasts, highlighting a selective therapeutic potential of CDDO-Im for BRCA1-associated breast cancer. Taken together, our results demonstrate that CDDO-Im induces ROS and subsequent DNA damage, thereby facilitating the activation of the DNA damage checkpoint, G2/M arrest and finally apoptosis in Brca1-mutated cancer cells. These findings are being explored in vivo to determine whether CDDO-Im could be used therapeutically for BRCA1-associated breast cancer. This study was supported by Breast Cancer Research Foundation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2509.