LAUSR

Loss-of-function (LOF) mutations in genes encoding subunits of SWI/SNF chromatin remodeling complexes are found in approximately 25% of human cancers. Colorectal cancers (CRC), the second leading cause of cancer related deaths, are particularly vulnerable to SWI/SNF driver mutations, harboring subunit alterations in up to 55% of patient tumors. ARID1A, a BAF subcomplex specific subunit, is the most frequently mutated subunit in human cancers (12%) and CRCs (10-12%). Additionally, ARID1A was recently identified as a leading genetic alteration in inflammatory bowel diseases such as Crohn’s and Ulcerative Colitis, conditions which are at higher risk of developing CRC. These data suggest an important role in ARID1A regulation of colonic tissue homeostasis and the potential for ARID1A mutation as an initiating or early driving event in CRC, which has not yet been modeled in human colon tissues. To examine the role of ARID1A in colon cancer development, we took a bottom-up strategy using CRISPR edited patient-derived colon organoids to model ARID1A LOF mutations in combination with classic CRC mutations APC and TP53. We evaluated the functional consequences of ARID1A mutation on cell growth using colony formation and proliferation assays. To systematically investigate the phenotypic contribution of ARID1A loss in these cell contexts, we employed transcriptomic and epigenomic profiling with RNAseq and ATACseq. We found that triple knock-out (TKO) of ARID1A, APC and TP53 confers a growth advantage in colon organoids, and induces dramatic morphological changes such as loss of symmetry and the breakdown of cystic architectures. At the gene expression level, ARID1A mutations led to shared and cell context specific transcriptional changes enriched for pathways such as G2M checkpoint, KRAS Signaling, and STAT5 signaling. Mechanistically, we show that ARID1A dependent chromatin accessibility changes at putative enhancers are linked to promoters of differentially expressed genes. These data suggest that ARID1A can regulate multiple cancer hallmark pathways depending on the cellular context and indicate a pleiotropic tumor suppressive function requiring further investigation in clinically relevant genetic backgrounds. Citation Format: Luke T. Deary, Nicholas Sugiarto, Cameron Pigeon, Sara W. Mayo, Matthew Z. Wilson, Xiaofeng Wang. Modeling the role of ARID1A in colon cancer using patient-derived organoids [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB044.