An optimized tankyrase inhibitor with enhanced anticancer efficacy and safety for APC-mutant colorectal cancer

Tankyrase (TNKS) plays an essential role in Wnt/β-catenin signaling. Despite its potential as a therapeutic target in colorectal cancer (CRC) harboring adenomatous polyposis coli ( APC ) mutations, the clinical use of TNKS inhibitors is limited by intestinal toxicity and insufficient efficacy. Therefore, this study aimed to design and synthesize novel tetrahydrophthalazine-based TNKS inhibitors and evaluate their therapeutic potential in APC -mutant CRC. We identified and optimized a novel TNKS1/2 inhibitor (TI-61987) based on a tetrahydrophthalazine scaffold and assessed its inhibitory activity against TNKS1 and TNKS2. Effects on β-catenin signaling were assessed via immunoblotting, and antitumor efficacy was evaluated in APC -mutant CRC cell lines and a COLO320DM xenograft mouse model. Combination treatments with 5-fluorouracil or a mitogen-activated protein kinase kinase inhibitor were also investigated. TI-61987 potently inhibited TNKS1 and TNKS2 by stabilizing AXIN2 and reducing active β-catenin levels. TI-61987 substantially suppressed tumor cell proliferation in vitro and tumor growth in vivo without inducing apparent intestinal toxicity. Combination therapies further enhanced efficacy and overcame resistance in resistant CRC cells. Overall, TI-61987 is a novel and potent TNKS1/2 inhibitor with notable antitumor activity. Thus, TI-61987 is a promising therapeutic candidate for APC -mutant CRC, both alone and in combination treatments.