Abstract P1-13-04: Potentiating Alpelisib in PI3K Pathway Overactive Triple Negative Breast Cancers

Abstract

Abstract Potentiating Alpelisib in PI3K Pathway Overactive Triple Negative Breast Cancers David C. Boyd1,2, Amy L. Olex3, Tess Leftwich1, Nicole Hairr1, Alex K. Duong1, Narmeen S. Rashid1,3, Mohammad A Alzubi1,2, Holly Byers1, Aaron D. Valentine1, Julia E. Altman1, Emily Zboril1, Jacqueline M. Grible1, Madelyn Esquivel1, Scott A. Turner1, Andrea Ferreira-Gonzalez1, Mikhail G. Dozmorov5, J. Chuck Harrell1,2,6 1Department of Pathology, Virginia Commonwealth University; 2Integrative Life Sciences Program, VCU; 3Wright Center for Clinical and Translational Research, VCU; 4Department of Biology, University of Richmond; 5Department of Biostatistics, VCU; 6Massey Cancer Center, VCU. There is an urgent need for new therapeutic options for basal-like Triple Negative Breast Cancers (TNBC). To mirror the NCI-ComboMATCH study, and identify new synergistic drug combinations, we analyzed a set of 20 breast cancer patient-derived xenografts and 14 cell lines to identify targetable targets in each model. The Oncomine Comprehensive Assay v3 was performed to assess 161 genes for hotspot mutations, focal copy number variants, amplification/deletions, and RNA-fusion genes. Next, each PDX and their isogenic drug-resistant sublines were analyzed with bulk RNA-sequencing (217 samples) and cell single-cell RNA-sequencing (~100,000 cells). Of all NCI-MATCH defined targetable mutations, 37% of the models contained pathogenic PIK3CA amplifications or mutations. PIK3CA is one of the most common oncogenic aberrations identified in patients and the PI3K pathway is overactive in the majority of TNBCs, therefore we sought to target it across all models and identify the most efficacious synergistic drug partner. Short-term cultures of each PDX model were screened with a library of >1,000 FDA-approved/experimental drugs to identify compounds that were cytotoxic. Synergistic drug screens were then performed with each drug in combination with the PI3K inhibitor byl-719 (alpelisib) a current standard-of-care drug used for PI3K mutant ER+ disease. Synergism was identified using coefficient of drug interaction (CDI) calculations and 10 drugs were identified as synergistic across several models. Using several criteria, including clinical status and pathway analysis, 3 drugs were selected for CompuSyn-based synergism testing and each was confirmed to be synergistic in vitro. Testing with in vivo models of each drug combination has thus far confirmed that each is synergistic per CDI metrics. Those combinations are currently being tested for efficacy in the metastatic setting with a set of basal-like PDXs. Citation Format: David Boyd, Chuck Harrell. Potentiating Alpelisib in PI3K Pathway Overactive Triple Negative Breast Cancers [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-13-04.