Abstract Colorectal cancer (CRC) is one of the three major cancers, causing over 90,000 deaths worldwide annually. For unresectable metastatic CRC, cytotoxic, targeted, and immuno-oncology drugs are used, but these therapies only extend survival by about 30 months or less. Approximately 80% of CRCs carry APC mutations that upregulate Wnt/β-catenin signaling, yet this pathway has long been considered difficult to target due to the lack of druggable molecules. Tankyrase poly(ADP-ribosyl)ates (PARylates) AXIN, a negative regulator of β-catenin, promoting its ubiquitin-dependent degradation and β-catenin accumulation. Accordingly, tankyrase inhibitors have been proposed as potential therapeutics for Wnt-driven cancer. To establish a targeted therapy for Wnt-driven CRC, we developed an orally available tankyrase inhibitor, RK-582, and investigated its predictive biomarkers. In APC-mutated CRC cells, RK-582 inhibited tankyrase-mediated AXIN PARylation, resulting in AXIN accumulation and β-catenin degradation. RK-582 exhibited excellent bioavailability and suppressed Wnt-driven CRC growth in mouse xenograft models. Under approval of the JFCR Institutional Review Board and with patients’ informed consent, APC-mutated CRC patient-derived cells were analyzed, revealing that APC mutations lacking all seven 20-amino acid repeat domains and β-catenin accumulation are predictive biomarkers for sensitivity to tankyrase inhibitors. In original tumor tissues of inhibitor-sensitive cells, β-catenin expression was significantly higher than in inhibitor-resistant cells. Analysis of primary tumor location indicated that left-sided tumors were more common in the inhibitor-sensitive group, with elevated β-catenin levels. Ectopic expression of a gain-of-function CTNNB1 allele conferred resistance in drug-sensitive CRC cells. PIK3CA gain-of-function mutations were associated with inhibitor resistance, whereas KRAS, BRAF, or TP53 mutations were not. GLP-compliant toxicity studies, safety pharmacology assessments, and drug metabolism/pharmacokinetic evaluations were completed to generate the preclinical dataset required for clinical trials. Additionally, a large-scale synthesis method for RK-582 was developed, and a GMP-grade active pharmaceutical ingredient was produced, subsequently used to prepare the capsule formulation for the clinical trial. In summary, RK-582 targets the Wnt/β-catenin pathway, a key cancer pathway previously considered undruggable. An investigator-initiated first-in-human clinical trial of this drug is currently ongoing, and these findings are expected to contribute to the development of an innovative therapy for unresectable advanced and recurrent CRC. Citation Format: Hiroyuki Seimiya, Mingjue Chen, Taichi Oishi, Yukiko Muramatsu, Manabu Takamatsu, Naomi Kawata, Ayane Nakamura, Saori Inaba, Satoshi Nagayama, Ryohei Katayama, Kensei Yamaguchi, Fumiyuki Shirai, Tetsuo Mashima. RK-582, a tankyrase inhibitor, attacks Wnt-driven colorectal cancer cells with short-type APC mutations and high β-catenin expression abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 3052.
Seimiya et al. (Fri,) studied this question.