Definition

An orally bioavailable, brain-penetrant, selective inhibitor of cyclin-dependent kinase (CDK) types 4 (CDK4) and 6 (CDK6), with potential antineoplastic activity. Upon oral administration, CDK4/6 inhibitor PRT3645 selectively targets and inhibits the activity of CDK4 and CDK6, which inhibits the phosphorylation of retinoblastoma protein (Rb) early in the G1 phase, prevents CDK-mediated G1-S-phase transition and leads 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 both cell cycle progression from the G1-phase into the S-phase and tumor cell proliferation. PRT3645 is able to penetrate the brain and could exert its activity against CNS metastases in tumors with CDK4/6 upregulation.