Palbociclib (PD0332991) Isethionate

PD 0332991 exhibits absolute selectivity for CDK4/6 with little or no activity against other CDKs. PD 0332991 is effective at reducing Rb phosphorylation at Ser780 and Ser795 in MDA-MB-435 breast carcinoma cells with IC50 of 66 nM and 63 nM, respectively. PD 0332991 is a potent inhibitor of cell growth and suppresses DNA replication by preventing cells from entering S phase. PD 0332991 inhibits thymidine incorporation into the DNA of Rb-positive human breast (such as MDA-MB-435, MCF-7), colon (H1299), and lung carcinomas (Colo-205) as well as human leukemias (CRRF-CEM and K562), with IC50 values ranging from 0.04-0.17 μM. PD 0332991 significant increases the percentage of MDA-MB-453 in G1 period. [1] PD 0332991 inhibits phosphorylation of Rb in cycling CD138+ primary bone marrow myeloma cells, nontransformed primary B cells, MM1.S and CAG HMCLs cells line with IC50 of <0.1 μM, 0.05 μM, and 60-70 nM, respectively. PD 0332991 treatment also induces G1 arrest of CD138+ primary bone marrow myeloma and nontransformed primary B cells. PD 0332991 induces G1 arrest in MM1.S with IC50 of ~0.05 μM. [2] PD 0332991 preferentially inhibits proliferation of luminal estrogen receptor-positive (including HER2-positive) human breast cancer cell lines. PD 0332991 increases gene expression of pRb and cyclin D1 and decreases gene expression of CDKN2A (p16) in most sensitive lines. PD 0332991 enhances sensitivity to tamoxifen in cell lines with conditioned resistance to ER blockade. [3]