JHD205 is a novel small-molecule CDK4/6 inhibitor derived from the chemical structure of Abemaciclib. It selectively targets the G1 phase of the cell cycle by degrading CDK4 and CDK6 proteins and dose-dependently inhibiting retinoblastoma protein (Rb) phosphorylation, leading to downstream disruption of p-Rb, Rb, and E2F1 signaling. The compound also triggers apoptosis and DNA damage, evidenced by upregulated Caspase3 and p-H2AX levels, while impairing DNA repair mechanisms. JHD205 is designed for preclinical research into cell cycle regulation and apoptosis pathways in breast cancer cell lines and xenograft models.