Palbociclib (PD 0332991) is a CDK inhibitor that inhibits CDK4 and CDK6 (IC50=11/16 nM) and is orally active. Palbociclib has anti-tumorigenic activity and has investigational potential for use in ER-positive and HER2-negative breast cancer.

CDK6:16 nM, CDK4:11 nM

METHODS: Malignant rhabdomyosarcoma cells G401, MP-MRT-AN (AN), KP-MRT-RY (RY), KP-MRT-NS (NS), and KP-MRT-YM (YM) were treated with Palbociclib (0-1 mM) for 24 h, and cell viability was assayed by WST.
RESULTS: Palbociclib effectively inhibited AN, RY, G401 and NS cell lines in a concentration-dependent manner, with IC50s of 0.01 μM, 0.01 μM, 0.06 μM and 0.6 μM, respectively; on the contrary, the YM cell line was resistant to Palbociclib, with an IC50 >10 μM.[1]
METHODS: Human breast cancer cells MDA-MB-453 were treated with Palbociclib (0.02-10 μmol/L) for 24 h, and the cell cycle was examined by Flow Cytometry.
RESULTS: Palbociclib caused G1 phase block. [2]

METHODS: To detect antitumor activity in vivo, Palbociclib (12.5-150 mg/kg, sodium lactate buffer (50 mmol/L, pH 4.0)) was administered orally to immunodeficient mice harboring the tumors Colo-205 or MDA-MB-435 once daily for fourteen days.
RESULTS: Palbociclib showed significant anti-tumor efficacy in multiple human tumor xenograft models. In Colo-205 tumors, PD 0332991 administered for 14 days produced rapid tumor regression. [2]
METHODS: To assay antitumor activity in vivo, Palbociclib (150 mg/kg, sodium lactate buffer (50 mM, pH = 4.0)) was administered once daily for two weeks by gavage to nu/nu BALB/c mice bearing esophageal squamous cell carcinoma (ESCC) tumors EC109 or KYSE150.
RESULTS: Palbociclib effectively inhibited ESCC tumor growth and lung metastasis. [3]

CDK assays are performed in 96-well filter plates. All CDK-cyclin kinase complexes are expressed in insect cells through baculovirus infection and purified. The substrate for the assays is a fragment (amino acids 792-928) of pRb fused to GST (GST·RB-Cterm). The total volume in each well is 0.1 mL containing a final concentration of 20 mM Tris-HCl, pH 7.4, 50 mM NaCl, 1 mM dithiothreitol, 10 mM MgCl2, 25 μM ATP (for CDK4-cyclin D1, CDK6-cyclin D2, and CDK6-cyclin D3) or 12 μM ATP (for CDK2-cyclin E, CDK2-cyclin A, and CDC2-cyclin B) containing 0.25 μCi of [γ-32P]ATP, 20 ng of enzyme, 1 μg of GST·RB-Cterm, and Palbociclib (0.001-0.1 μM). All components except the [γ-32P]ATP are added to the wells, and the plate is placed on a plate mixer for 2 min. The reaction is started by adding the [γ-32P]ATP and the plate is incubated at 25°C for 15 min. The reaction is terminated by addition of 0.1 mL of 20% trichloroacetic acid and the plate is kept at 4°C for at least 1 hour to allow the substrate to precipitate. The wells are then washed 5 times with 0.2 mL of 10% trichloroacetic acid and radioactive incorporation is determined with a β plate counter.

Palbociclib (PD) is prepared in DMSO and stored (?80°C), and then diluted with appropriate media before use[1]. MRT cell lines, G401, MP-MRT-AN (AN), KP-MRT-RY (RY), KP-MRT-NS (NS), and KP-MRT-YM (YM) cell lines are seeded in normal growth medium into 96-well cell plates. After 24 h, the culture medium is replaced with culture medium containing Palbociclib (0.05 or 1 μM) or DMSO. Cells are cultured and treated in triplicate. Cell proliferation is determined 8 days after the treatment by WST-8 assay using a Cell Counting Kit-8.