Discovery of Potent and Selective CDK4/6 Inhibitors for the Treatment of Chemotherapy-Induced Myelosuppression

Chemotherapy-induced myelosuppression (CIM) significantly impairs hematopoiesis. Trilaciclib (TC), originally developed for oncology application, is the only FDA-approved CDK4/6 inhibitor for CIM, which effectively protects bone marrow cells by inhibiting their proliferation. In this study, a series of TC derivatives were designed and synthesized as CDK4/6 inhibitors (CDK4/6i) for alleviating CIM. Among these, 42 displayed potent CDK4/6 inhibitory activity (IC₅₀ = 11 nM), lower cytotoxicity (CC₅₀ > 100 μM) and showed high selectivity among 86 kinases. Additionally, 42 possessed strong bone marrow penetration, favorable pharmacokinetic properties, excellent safety profiles, and superior efficacy in mitigating myelosuppression caused by 5-fluorouracil (5-FU) in vivo. In conclusion, as the first oral small-molecule CDK4/6 inhibitor optimized specifically for myelosuppression treatment, 42 expands the therapeutic applications of CDK4/6i, optimizes the mode of administration, and offers significant translational value and clinical potential.