Abstract P5-08-01: Investigating the role of BRCA1 in sensitivity to GRN163L, a telomerase template antagonist

Abstract

Abstract Background: BRCA1 is a tumor suppressor gene with a variety of functions related to safeguarding genomic integrity. The regulation of telomere length is also crucial in maintaining genomic stability, with critically short telomeres leading to telomere uncapping, end-to-end fusions, activation of the DNA damage response, and cell cycle arrest. The objective of this study was to determine whether GRN163L, a telomerase template antagonist currently in clinical trials, has enhanced activity in BRCA1 mutant breast or ovarian cancer cell lines compared to BRCA1 wild-type breast/ovarian cancer cell lines. Methods: We utilized a panel of breast and ovarian cancer cell lines harboring both N-terminal and C-terminal BRCA1 mutations. This cell line panel included two isogenic cell line pairs reconstituted with wild-type BRCA1 (BRCA1 mutant: HCC1937 and UWB1.289; BRCA1 wild-type reconstituted: HCC1937+BRCA1 and UWB1.289+BRCA1). We assessed the effects of GRN163L or a mismatch oligonucleotide (MM) on telomerase activity and telomere length using the TRAP (Telomere Repeat Amplification Protocol) and TeloTAGGG (Roche) assays, respectively. Clonogenic survival assays, proliferation assays, and immunofluorescence were used to assess cellular responses to GRN163L and their molecular mechanisms. Results: All cell lines tested exhibited a dose-dependent response to treatment with GRN163L, but not a mismatch control oligonucleotide. The majority of the cell lines tested showed gross morphological changes as early as 12 hours following inhibitor treatment. Progressive telomere shortening was evident after 3-week treatment with GRN163L, but not after treatment with MM. We observed differential sensitivity between BRCA1 mutant and wild-type isogenic cell line pairs to GRN163L in clonogenic survival assays. GRN163L pretreatment was synergistic with cisplatin in UWB1.289 and UWB1.289+BRCA1 cells. Simultaneous treatment with GRN163L and doxorubicin was synergistic in HCC1937 and HCC1937+BRCA1 cells. Long-term (12-week) treatment with GRN163L preferentially induced complete cell death in HCC1937 (BRCA1 mutant) breast cancer cells compared to HCC1937 cells reconstituted with wild-type BRCA1. One-week treatment with GRN163L was sufficient to induce γ-H2AX foci, with more γ-H2AX positive cells in the UWB1.289 BRCA1 mutant cell line. Conclusions: Telomerase inhibition may be a viable treatment in BRCA1 mutant breast or ovarian cancers. These data provide insights into further investigations on the role of BRCA1 in the DNA damage response to GRN163L or combination treatment. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P5-08-01.