Abstract 5869: Characterization and therapeutic implications of SMARCA4 mutations in cancer

Abstract

Abstract Genomic studies performed in cancer patients have identified a high frequency of alterations in the core catalytic subunit of the mammalian switch/sucrose non-fermentable (mSWI/SNF) chromatin remodeling complex, SMARCA4. Cells with inactivating SMARCA4 mutations rely on its paralog, SMARCA2, making it an attractive therapeutic target. Here we report the results of genomic profiling of 131,668 cases from patients with solid tumors and identified 8,588 cases with one or more SMARCA4 alterations. We observed a high prevalence of homozygous SMARCA4 truncating and non-truncating mutations in certain tumor types, notably non-small cell lung cancer (NSCLC) and cancers of unknown primary. We found that homozygous SMARCA4 mutations in NSCLC were mutually exclusive with other mutations in mSWI/SNF and oncogenic drivers, including KRAS and EGFR. A retrospective study of NSCLC patients who were treated in the Flatiron Health network (>265 oncology practices in the U.S.) and underwent FoundationOne® or FoundationOne CDx® tumor sequencing as part of routine care revealed that real-world patients with homozygous truncating SMARCA4 mutations had significantly reduced overall survival. The large sample size of our cohort also elucidated novel hotspot missense mutations within the helicase domain of SMARCA4. Functional modeling of these mutations using biochemical and cell-based (ATAC-seq) assays demonstrated that all evaluated mutations have significantly reduced nucleosome remodeling activity upon in vitro reconstitution in SMARCA4-deficient cells. We also addressed whether SMARCA4 missense mutations could rescue the cell growth defects and loss in chromatin accessibility induced upon SMARCA2 loss. Interestingly, we observe that a few missense mutants were able to either partially or fully rescue growth, suggesting hypomorphic activity under the selective pressure of SMARCA2 loss. Overall, these studies highlight NSCLC patients with homozygous truncating SMARCA4 mutations as a novel population with an unmet need who may benefit from SMARCA2-targeted therapy and underscore that careful selection criteria must be employed to identify patients with inactivating, homozygous SMARCA4 missense mutations. Citation Format: Tharu M. Fernando, Robert Piskol, Russell Bainer, Ethan Sokol, Sally Trabucco, Qing Zhang, Huong Trinh, Sophia Maund, Marc Kschonsak, Subhra Chaudhuri, Tom Januario, Zora Modrusan, Robert L. Yauch. Characterization and therapeutic implications of SMARCA4 mutations in cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5869.