Abstract 2908: WEE1 as a therapeutic target in <i>TP53</i> and <i>ARID1A</i> concurrent mutant colorectal cancers

The development of next-generation sequencing (NGS) technology has provided us a comprehensive mutation profile of colorectal cancer (CRC). However, large number of genetic alterations, especially tumor suppressers, remain undruggable. ARID1A, as a member of tumor suppresser complex SWI/SNF, is frequently mutated (∼9%) in CRC and its mutations contribute to the tumorigenesis of CRC. Recent evidence indicates targeting DNA damage response pathways exhibits promising efficacy in ARID1A-mutant cancers. WEE1 is a key regulator of G2/M cell cycle checkpoint, and WEE1 inhibition results in the accumulation of DNA damages and ultimately leads to cell death. Our present study demonstrates that WEE1 inhibitor (WEE1i) exhibits the highest sensitivity [ln (IC50) median difference = -1.85, P &amp;lt; 0.0001] among a panel of 199 compounds in ARID1A-mutant CRC cells based on GDSC2 dataset screening. As ARID1A mutation is considered as loss of function (LoF), ARID1A knockout was performed to simulate LoF in multiple CRC cell lines. Notably, ARID1A knockout sensitizes TP53-mutant, but not TP53-wildtype CRC cell lines, to WEE1 inhibitor MK-1775 or ZN-c3. In vivo study also indicated preferable efficacy to MK-1775 in COLO205 ARID1A knockout xenografts, compared with their wildtype counterparts. Mechanistically, TP53-wildtype cells exhibited robust rebound of P53 and P21 pathway under WEE1i treatment which significantly limited the efficacy. Besides, ARID1A deficiency enhanced replication stress (EdU incorporating assay) and DNA damage (γH2AX) through accumulation of pathological R-loops, which were detected by S9.6 nuclear intensity. Immunofluorescence colocalizing analysis also indicated that after WEE1i treatment, γH2AX signal tended to culminate in S9.6 positive loci, suggesting an R-loop associated DNA damage. These studies paralleled a phase 1b/2 clinical trial with SC0191 (a novel WEE1 inhibitor) based combination therapy in a cohort of late-line metastatic CRC patients (NCT06363552). In this cohort, one patient who had previously undergone 6 treatment regimens and harbored concurrent mutations in TP53 and ARID1A, achieved stable disease for at least five months, accompanied by tumor regression in the liver lesion. In conclusion, our research showed that targeting WEE1 is effective in TP53 and ARID1A mutant colorectal cancers. This therapeutic strategy is being tested in a phase 2 study for mCRC patients. Citation Format: Chi Zhang, Ke Peng, Qing Liu, Yanjing Zhu, Luoyan Ai, Jingyuan Wang, Qihong Huang, Tianshu Liu. WEE1 as a therapeutic target in TP53 and ARID1A concurrent mutant colorectal cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2908.