Abstract 2220: Repurposing statins for prevention of triple-negative breast cancer

Introduction: Although triple negative breast cancer (TNBC) accounts for 15% of the 250,000 annual cases of breast cancer, its more aggressive nature, coupled with lack of targeted therapy, results in a disproportionate rate of mortality in women with this disease underscoring the critical need for prevention-based approaches. We hypothesized that identifying miRNA-mRNA functional pairs and their driver pathway(s) deregulated during preneoplastic progression would provide the most informative insights into the molecular drivers of TNBC carcinogenesis. Methods: We performed next generation RNA sequencing of TNBC like MCF10A based model system and focused on detailing the molecular changes preceding the development of in situ carcinoma (DCIS). We used ki67, MTT and colony formation assays to study the growth inhibitory effect of miRNA and pathway targeting. To identify direct gene targets of a miRNA, we cloned the 3’untranslated region containing miRNA-binding sites from its predicted gene targets in a luciferase reporter vector, and studied the effect of miRNA overexpression on the repression of luciferase reporter activity. Results: In-silico analyses of small RNA seq data showed loss of miRNA-140-3p as one of the top deregulated miRNA relevant to preneoplastic transition from MCF10A parental to MCF 10AT1 preneoplastic cell line. Staining of breast tissue samples also confirmed loss of miRNA-140-3p in tumors compared to normal breast epithelial cells, suggesting a tumor suppressive role. To investigate the functional role of miRNA-140 during TNBC development, we ectopically expressed miRNA-140 in MCF10.AT1 and MCF10.DCIS cells. Interestingly, these studies revealed miRNA-140 replacement to preferentially inhibit colonizing ability and cell proliferation of preneoplastic MCF10.AT1 cells in contrast to a much weaker cell inhibitory effects in DCIS cells. Next, we identified the functional gene target/s of miRNA-140-3p by integromics studies involving next-generation RNA-seq on the MCF10A model employing bioinformatics pipeline, SigTerms. These analyses identified HMGCR and HMGCS1 as top 2 gene targets of miRNA-140-3p that map in cholesterol biosynthesis pathway. Consistently, we found miRNA-140-3p to directly bind in 3’UTR of HMGCR, HMGCS1 and repress their expression as shown by luciferase assays. miRNA-140 binding of these gene targets is also functionally relevant as inhibition of HMGCR activity by an FDA approved statin inhibitor, fluvastatin, preferentially inhibited the cell proliferation and colonizing ability of preneoplastic MCF10AT1 cells. Further studies focused on testing the potential of fluvastatin to prevent progression of breast atypia cells in mouse xenografts are underway. Conclusions: Our results suggest miRNA-140 and its downstream functional cholesterol biosynthesis pathway targeting, especially by FDA approved Fluvastatin, may be a novel strategy for targeted prevention of TNBC. Citation Format: Anjana Bhardwaj, Harpreet Singh, Kimal Rajapakshe, Cristian Coarfa, Isabelle Bedrosian. Repurposing statins for prevention of triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2220. doi:10.1158/1538-7445.AM2017-2220