Synthesis and Biological Evaluation of Optimized Inhibitors of the Mitotic Kinesin Kif18A

The mitotic spindle, a highly dynamic structure composed of microtubules, mediates the segregation of the previously duplicated genome into the two nascent daughter cells. Errors in this process contribute to pathology including tumor formation. Key for the shape and function of the mitotic spindle are kinesins, molecular motor proteins that convert chemical energy into mechanical work. Due to their fast mode of action, small molecules are valuable tools to dissect the dynamic functions of kinesins during mitosis. In this study, we report the identification of optimized small molecule inhibitors of the mitotic kinesin Kif18A. Using BTB-1, the first identified Kif18A inhibitor, as a lead compound, we synthesized a collection of derivatives. We demonstrate that some of the synthesized derivatives potently inhibited the ATPase activity of Kif18A with a half maximal inhibitory concentration (IC<sub>50</sub>) value in the low micromolar range. <i>In vitro</i> analysis of a panel of Kif18A-related kinesins revealed that the two most potent compounds show improved selectivity compared to BTB-1. Structure–activity relationship studies identified substituents mediating undesired inhibitory effects on microtubule polymerization. In summary, our study provides key insights into the mechanism of action of BTB-1 and its analogs, which will have a great impact on the further development of highly selective and bioactive Kif18A inhibitors. Since Kif18A is frequently overexpressed in solid tumors, such compounds are not only of great interest for basic research but also have the potential to open up new strategies for the treatment of human diseases.