NCIt definition : The isethionate salt form of palbociclib, an orally available cyclin-dependent kinase
(CDK) inhibitor with potential antineoplastic activity. Palbociclib selectively inhibits
cyclin-dependent kinase 4 (CDK4) and 6 (CDK6), thereby inhibiting retinoblastoma (Rb)
protein phosphorylation early in the G1 phase leading to cell cycle arrest. This suppresses
DNA replication and decreases tumor cell proliferation. CDK4 and 6 are serine/threonine
kinases that are upregulated in many tumor cell types and play a key role in the regulation
of cell cycle progression.;