The Discovery of Orally Bioavailable Tyrosine Threonine Kinase (TTK) Inhibitors: 3‑(4-(heterocyclyl)phenyl)‑1<i>H</i>‑indazole-5-carboxamides as Anticancer Agents

The acetamido and carboxamido substituted 3-(1<i>H</i>-indazol-3-yl)­benzenesulfonamides are potent TTK inhibitors. However, they display modest ability to attenuate cancer cell growth; their physicochemical properties, and attendant pharmacokinetic parameters, are not drug-like. By eliminating the polar 3-sulfonamide group and grafting a heterocycle at the 4 position of the phenyl ring, potent inhibitors with oral exposure were obtained. An X-ray cocrystal structure and a refined binding model allowed for a structure guided approach. Systematic optimization resulted in novel TTK inhibitors, namely 3-(4-(heterocyclyl)­phenyl)-1<i>H</i>-indazole-5-carboxamides. Compounds incorporating the 3-hydroxy-8-azabicyclo[3.2.1]­octan-8-yl bicyclic system were potent (TTK IC₅₀ < 10 nM, HCT116 GI₅₀ < 0.1 μM), displayed low off-target activity (>500×), and microsomal stability (<i>T</i>_1/2 > 30 min). A subset was tested in rodent PK and mouse xenograft models of human cancer. Compound <b>75</b> (CFI-401870) recapitulated the phenotype of TTK RNAi, demonstrated in vivo tumor growth inhibition upon oral dosing, and was selected for preclinical evaluation