Abstract B043: Activation Lethality through the WNT/beta-catenin pathway drives efficacy in colorectal cancer

Abstract Activation of the WNT/beta-catenin pathway is a foundational driver of colorectal cancer (CRC) and there are no approved therapies directly targeting WNT/beta-catenin in CRC. Damaging mutations in APC, a member of the beta-catenin destruction complex, are the most frequent drivers of beta-catenin activation with >70% of CRC patients harboring biallelic APC mutations. In Familial Adenomatous Polyposis (FAP), germline mutation in one allele of APC leads to a condition in which mutation of the second APC allele drives formation of colonic polyps which often progress to malignant CRC. During FAP progression, APC mutations arise in a defined pattern with one mutant APC allele retaining residual beta-catenin binding and regulation, suggesting complete loss of beta-catenin regulation is not tolerated during CRC development, and that tumors may be unable to tolerate excessive WNT hyperactivation. This unusual genetic pattern is consistent with Activation Lethality, in which cancers are vulnerable to further hyperactivation of oncogenic drivers. We therefore sought to assess whether APC retains beta-catenin regulation in sporadic colorectal cancer and whether WNT mutant cancers have a therapeutic vulnerability to further activation of beta-catenin. Here we show APC mutant CRC obligately maintain one allele of APC which retains some beta-catenin binding domains and thus function. Further, we show that genetic depletion of APC or casein kinase 1 alpha (CK1 alpha), two core members of the beta-catenin destruction complex, leads to an increase in active beta-catenin and prevents the growth of APC-mutant CRC. In addition, targeting of CK1 alpha with DTX-861, a novel, potent and highly specific CK1 alpha degrader, can drive WNT hyperactivation and efficacy in CRC. Degradation of CK1 alpha is associated with enhancement of beta-catenin signaling as evidenced by induction of target gene expression and enhanced beta-catenin reporter activity in cells. This increase in beta-catenin signaling results in reduced colony formation in APC mutant CRC cell lines, while sparing APC wild-type cells. These in vitro effects translate to robust in vivo efficacy with oral delivery of DTX-861 leading to a dose-dependent reduction in CK1 alpha, induction of beta-catenin target gene expression, and tumor growth inhibition in multiple APC mutant CDX and PDX models. The potent in vivo efficacy observed across several CRC models highlights the potential for WNT activation as a novel treatment strategy for CRC and the promise of activation lethality as a novel approach in unlocking new therapeutic targets and ultimately treatment options for patients. Citation Format: Victoria Frank, Benjamin Stevens, Bo Wang, Yuji M. Mishina, Brendan Veeneman, Joseph D . Manna, Rebecca Lock, Aimee Usera. Activation Lethality through the WNT/beta-catenin pathway drives efficacy in colorectal cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2025 Oct 22-26; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2025;24(10 Suppl):Abstract nr B043.