Abstract P3-06-11: Understanding resistance mechanisms of PIK3a inhibition in breast cancer

Abstract

Abstract Breast cancer is the most common non-cutaneous cancer in women worldwide. PIK3CA is the most frequently mutated oncogene in all invasive breast cancers, with about one third of cases harboring activating mutations. Small molecule therapeutics targeting PI3K pathway has been developed and investigated for a decade. Everolimus (an mTOR inhibitor) is now successfully used in conjunction with hormonal therapy in patients with metastatic hormone-receptor positive breast cancers. Inhibitors of PI3Kα have shown promise as a single agent as well as in combination with hormonal therapies. The high rate of primary and acquired resistance; however, limits clinical usage of this class of drugs. There is an urgent need to understand the resistance mechanisms of PI3K inhibition and develop strategies to overcome the resistance in breast cancer. We took a genome-scale functional screening approach to identify resistance mechanisms to PI3K inhibition in breast cancer. We performed a whole-genome lentiviral open-reading frame (ORF) overexpression screen in a breast cancer cell line (T47D) in the presence of a PI3Kα inhibitor. We screened a total of 15,590 ORFs and identified 75 genes whose overexpression confers resistance to PI3K inhibition. Once we validate the hits, we plan to determine the mechanisms by which the genes confer resistance. We also plan to perform RNA-sequencing in patient samples with PI3Ka resistance to evaluate the clinical relevance of these genes and pathways. Citation Format: Le X, Luo F, Treacy D, Wulf G, Garraway L. Understanding resistance mechanisms of PIK3a inhibition in breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-06-11.