A Genetic Screen To Identify Tumor Suppressive Ddr Genes In Breast Cancer

To maintain genomic integrity, cells utilize a DNA damage response (DDR) mechanism that 1) functions to repair damaged DNA efficiently and 2) commits cells to apoptosis if damage is irreparable. Failure of this mechanism results in genomic instability and cancer predisposition. Defects in DDR have been implicated in both sporadic and familial breast and ovarian cancer predisposition syndromes (e.g. BRCA1, BRCA2, and PALB2), although the specific pathway components that are disrupted have not been elucidated. In particular, an impaired DDR may contribute to the pathophysiology of triple-negative (ER-/PR-/HER2-) breast cancer (TNBC) due to the extent and complexity of the genomic instability that is observed. We identified the DNA damage sensing Mre11- Rad50-Nbs1 (MRN) complex as an essential mediator of the oncogene-induced DDR. Disrupting the MRN complex in mouse models promotes the development of genomically unstable, metastatic breast cancer. The clinical relevance of this pathway is highlighted by the observation that components of the Mre11 complex are perturbed in a significant fraction of human TNBCs, which correlates with clinical outcomes. However, lack of MRN suppression in a majority of TNBCs indicates that alternative DDR components may also be inactivated to promote breast cancer development. Our goal is to identify additional DDR genes that, when perturbed, promote the development of genomically unstable breast cancers. In order to accurately distinguish driver genes from bystander genes we have developed a platform to identify DDR genes that mediate oncogene-induced senescence in mammary epithelial cells using both shRNA and CRISPR pooled libraries. Analysis of newly identified tumor suppressor genes, compared to what is already known about Mre11 and p53 (positive controls), will enable us to determine causality of specific DDR mutations in breast cancer development and importantly, the genomic instability phenotype that is typical for TNBC. The insights gleaned from this study may ultimately provide the means to determine the optimal treatment regimen for each patient with TNBC, and to prevent over-treatment of patients where certain chemotherapies may not be effective. Citation Format: Katerina D. Fagan-Solis, Gaorav P. Gupta. A genetic screen to identify tumor suppressive DDR genes in breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2745.