Abstract 1478: The DNA double-strand break repair genes BARD1 and RAD51 as molecular targets for brain metastases from breast cancer

Abstract

Abstract The DNA double-strand break repair genes BARD1 and RAD51 were identified as part of a 13-gene signature predictive of early brain metastasis development (≤3 years vs. >3 years, HR=3.03, p=0.0008) in primary tumor sections from patients with HER2+ metastatic breast cancer. These data suggested that BARD1 and RAD51 overexpression would act early in breast cancer progression. In a gene expression analysis, these two genes were overexperessed (1.5 fold, p=0.0008 and 1.5 fold, p=0.001, respectively) in brain metastases compared to primary breast tumors from the same women. Their expression was also significantly higher (1.5 fold, p=0.01 and 1.4 fold, p=0.008, respectively) in brain metastases compared to systemic (bone/lung) metastases. These observations led us to hypothesize that BARD1 and RAD51 may be drivers of brain metastasis development in breast cancer patients. To evaluate the role of BARD1 and RAD51 on primary tumorigenesis, each gene was overexpressed in non-tumorigenic immortal human breast epithelial MCF10A cells. Three-dimensional MCF10A morphology was categorized as: single acinus, multi-acinar, invasive or solid acinus. Overexpression of BARD1 and RAD51 significantly increased the number of multi-acinar structures (2.1 fold, p=0.02 and 1.9 fold, p=0.05, respectively), as well as the number of invasive structures (3.1 fold, p=0.03 and 6.1 fold, p=0.005, respectively). To evaluate the functional significance of BARD1 and RAD51 on promoting brain metastasis development, the two genes were overexpressed in brain-metastatic triple-negative breast carcinoma MDA-MB-231 BR cells. This resulted in a 30% increase in multiplicity of clonogenic colonies (BARD1 p=0.001, RAD51 p=0.004), without affecting cell proliferation rates. Importantly, BARD1 and RAD51 overexpression conferred significant chemoresistance to DNA double-strand break inducing agents such as 25µM carboplatin (BARD1 p=0.005, RAD51 p=0.03) and 25nM doxorubicin (BARD1 p=0.03, RAD51 p=0.02), but not to agents that do not cause DNA double-strand breaks, such as 2.5nM paclitaxel. We are currently investigating whether overexpression of BARD1 and/or RAD51 can increase brain metastasis formation in vivo and whether this depends on the presence of chemotherapy-induced DNA double-strand breaks. High expression of BARD1 and RAD51 in primary breast tumors was predictive of early brain metastasis development in a 13-gene signature and is a clinical feature of brain metastases from breast cancer. Their overexpression is associated with an aggressive tumorigenic phenotype and chemoresistance to DNA double-strand break inducing agents, both of which could drive primary tumor spread and brain metastases development. BARD1 and RAD51 overexpression are brain metastases-specific molecular attributes, and represent potential novel targets for brain metastasis prevention and treatment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1478. doi:10.1158/1538-7445.AM2011-1478