Structure-Guided Discovery of Novel N⁴-(Substituted Thiazol-2-yl)- N²-(4-Substituted phenyl)pyrimidine-2,4-Diamines as Potent CDK2 and CDK9 Dual Inhibitors with High Oral Bioavailability

CDK2 and CDK9 play pivotal roles in cell cycle progression and gene transcription, respectively, making them promising targets for cancer treatment. Herein, we discovered a series of N⁴-(substituted thiazol-2-yl)-N²-(4-substituted phenyl)pyrimidine-2,4-diamines as highly potent CDK2/9 dual inhibitors. Especially, compound 20a significantly inhibited CDK2 (IC₅₀ = 0.004 μM) and CDK9 (IC₅₀ = 0.009 μM), achieving a 1000- and 2800-fold improvement over lead compound 11, and demonstrating broad antitumor efficacy. Mechanistic studies indicated that 20a effectively and simultaneously suppressed CDK2 and CDK9 proteins in the HCT116 cell line, leading to G2/M cell cycle arrest and cell apoptosis by regulating cell cycle- and apoptosis-related protein expression. Most importantly, 20a exhibited 86.7% oral bioavailability in rats and effectively inhibited tumor growth in HCT116 xenograft and C6 glioma rat models without significant toxicity. Overall, these observations clearly confirmed the promising therapeutic strategy of CDK2/9 dual inhibitors and provided a novel potent candidate for cancer therapy.