KIF2C-IN-1 (Compound 7S9) is a selective and potent small molecule inhibitor of KIF2C. It stabilizes the interaction between KIF2C and microtubule proteins, preventing the depolymerization of polyglutamylated microtubules. KIF2C-IN-1 enhances the cytotoxicity of Paclitaxel in Paclitaxel-resistant triple-negative breast cancer (TNBC) cells and, when combined with Paclitaxel, significantly reduces tumor growth in mouse models.