The Discovery of Polo-Like Kinase 4 Inhibitors: Design and Optimization of Spiro[cyclopropane-1,3′[3<i>H</i>]indol]-2′(1′<i>H</i>)‑ones as Orally Bioavailable Antitumor Agents

Polo-like kinase 4 (PLK4), a unique member of the polo-like kinase family of serine-threonine kinases, is a master regulator of centriole duplication that is important for maintaining genome integrity. Overexpression of PLK4 is found in several human cancers and is linked with a predisposition to tumorigenesis. Previous efforts to identify potent and efficacious PLK4 inhibitors resulted in the discovery of (<i>E</i>)-3-((1<i>H</i>-indazol-6-yl)­methylene)­indolin-2-ones, which are superseded by the bioisosteric 2-(1<i>H</i>-indazol-6-yl)­spiro­[cyclopropane-1,3′-indolin]-2′-ones reported herein. Optimization of this new cyclopropane-linked series was based on a computational model of a PLK4 X-ray structure and SAR attained from the analogous alkene-linked series. The racemic cyclopropane-linked compounds showed PLK4 affinity and antiproliferative activity comparable to their alkene-linked congeners with improved physicochemical, ADME, and pharmacokinetic properties. Positive xenograft results from the MDA-MB-468 human breast cancer xenograft model for compound <b>18</b> support the investigation of PLK4 inhibitors as anticancer therapeutics. A PLK4 X-ray co-structure with racemate <b>18</b> revealed preferential binding of the 1<i>R</i>,2<i>S</i> enantiomer to the PLK4 kinase domain

The Discovery of PLK4 Inhibitors: (<i>E</i>)‑3-((1<i>H</i>‑Indazol-6-yl)methylene)indolin-2-ones as Novel Antiproliferative Agents

The family of Polo-like kinases is important in the regulation of mitotic progression; this work keys on one member, namely Polo-like kinase 4 (PLK4). PLK4 has been identified as a candidate anticancer target which prompted a search for potent and selective inhibitors of PLK4. The body of the paper describes lead generation and optimization work which yielded nanomolar PLK4 inhibitors. Lead generation began with directed virtual screening, using a ligand-based focused library and a PLK4 homology model. Validated hits were used as starting points for the design and discovery of PLK4 inhibitors of novel structure, namely (<i>E</i>)-3-((1<i>H</i>-indazol-6-yl)­methylene)­indolin-2-ones. Computational models, based on a published X-ray structure (PLK4 kinase domain), were used to understand and optimize the in vitro activity of the series; potent antiproliferative activity was obtained. The kinase selectivity profile and cell cycle analysis of selected inhibitors are described. The results of a xenograft study with an optimized compound <b>50</b> (designated CFI-400437) support the potential of these novel PLK4 inhibitors for cancer therapy

The Discovery of Polo-Like Kinase 4 Inhibitors: Identification of (1<i>R</i>,2<i>S</i>)‑2-(3-((<i>E</i>)‑4-(((<i>cis</i>)‑2,6-Dimethylmorpholino)methyl)styryl)‑1<i>H</i>‑indazol-6-yl)-5′-methoxyspiro[cyclopropane-1,3′-indolin]-2′-one (CFI-400945) as a Potent, Orally Active Antitumor Agent

Previous publications from our laboratory have introduced novel inhibitors of Polo-like kinase 4 (PLK4), a mitotic kinase identified as a potential target for cancer therapy. The search for potent and selective PLK4 inhibitors yielded (<i>E</i>)-3-((1<i>H</i>-indazol-6-yl)­methylene)­indolin-2-ones, which were superseded by the bioisosteric 2-(1<i>H</i>-indazol-6-yl)­spiro­[cyclopropane-1,3′-indolin]-2′-ones, e.g., <b>3</b>. The later scaffold confers improved drug-like properties and incorporates two stereogenic centers. This work reports the discovery of a novel one-pot double S_N2 displacement reaction for the stereoselective installation of the desired asymmetric centers and confirms the stereochemistry of the most potent stereoisomer, e.g., <b>44</b>. Subsequent work keys on the optimization of the oral exposure of nanomolar PLK4 inhibitors with potent cancer cell growth inhibitory activity. A short list of compounds with superior potency and pharmacokinetic properties in rodents and dogs was studied in mouse models of tumor growth. We conclude with the identification of compound <b>48</b> (designated CFI-400945) as a novel clinical candidate for cancer therapy

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