K-756 is a direct and selective inhibitor of tankyrase (TNKS), which inhibits the ADP-ribosylation activity of TNKS1 and TNKS2 (IC50s: 31 and 36 nM, respectively).

K-756 inhibits the cell growth of APC-mutant colorectal cancer COLO 320DM and SW403 cells by inhibiting the Wnt/β-catenin pathway. K-756 is a novel and selective Wnt/β-catenin pathway inhibitor targeting tankyrase (TNKS). TNKS is one of the members of the PARP family. K-756 binds to the induced pocket of TNKS and inhibits its enzyme activity. K-756 inhibits TNKS1 and TNKS2 by 97% and 100%, respectively. The inhibitory activity of K-756 against PARP1, PARP2, PARP3, PARP6, PARP7, and PARP11 is less than 13%. K-756 strongly inhibits the reporter activity in DLD-1/TCF-Luc cells (IC50: 110 nM) but does not inhibit DLD-1/mtTCF-Luc cells, even at 1,000 nM. APC-mutant colorectal cancer cell line COLO 320DM and SW403 cells are treated with K-756 and after 144 hours, cell growth inhibition is measured by an XTT assay. The application of K-756 inhibits the cell growth of COLO 320DM with a GI50 of 780 nM. K-756 also inhibits SW403 with a GI50 of 270 nM[1].

Vehicle (0.5% MC400) or K-756 is given orally once daily for three consecutive days at doses of 100, 200, and 400 mg/kg. The inhibition of the Wnt/β-catenin pathway in tumors is assessed by measuring the levels of FGF20 and LGR5, as well as luciferase activity. Inhibition of the Wnt/β-catenin pathway is evident at a 400 mg/kg dose after just one day of administration. After three days of treatment, significant reductions in FGF20 expression and reporter activity are observed at doses of 100 mg/kg and higher, while LGR5 expression significantly decreases at doses of 200 mg/kg and higher. The greatest inhibitory effect is achieved with a three-day administration of K-756 at 400 mg/kg [1].