RK-582, a tankyrase inhibitor, attacks Wnt-driven colorectal cancer cells with short-type APC mutations and high beta-catenin expression

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/beta-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 beta-catenin, promoting its ubiquitin-dependent degradation and beta-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 beta-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 beta-catenin accumulation are predictive biomarkers for sensitivity to tankyrase inhibitors. In original tumor tissues of inhibitor-sensitive cells, beta-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 beta-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/beta-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.