PD 0332991 is an orally active, selective inhibitor of the cyclin D kinases Cdk4 (IC50 = 11 nM) and Cdk6 (IC50= 16 nM) with no activity against a panel of 36 additional protein kinases. It has been reported to have antiproliferative activity against retinoblastoma-positive tumor cells, blocking retinoblastoma phosphorylation and inducing G1 arrest at nanomolar concentrations. PD 0332991 can inhibit the growth of certain ER-positive or HER2-amplified breast cancer cells (IC50s as low as 4 nM) and demonstrates synergy with tamoxifen and trastuzumab, respectively. Recently, PD 0332991 inhibition of Cdk4 activity has been used to demonstrate a role for insulin-activated cyclinD1-Cdk4 signaling in the control of glucose metabolism that is independent of cell cycle progression.
