An orally active, selective inhibitor of Cdk4 (IC50 = 11 nM) and Cdk6 (IC50 = 16 nM) with antiproliferative activity against retinoblastoma-positive tumor cells, blocking retinoblastoma phosphorylation and inducing G1 arrest; used to demonstrate a role for insulin-activated cyclin D1-Cdk4 signaling in the control of glucose metabolism.