CDK4/6-IN-15 hydrochloride is an orally active selective inhibitor of CDK4/6. It effectively restrains the growth of cancer cells by arresting the cell cycle at the G1 phase. Additionally, CDK4/6-IN-15 hydrochloride inhibits phosphorylation of the retinoblastoma tumor suppressor protein (Rb) at site S780 and suppresses E2 factor (E2F)-regulated gene expression.

CDK4/6-IN-15, also known as compound 91, exhibits potent inhibitory activity against FLT3 and MYLK4, achieving inhibition rates of over 90% at a concentration of 10 μM over 24 hours. At concentrations ranging from 0 to 5 μM for 72 hours, CDK4/6-IN-15 selectively hinders tumor cell proliferation with GI50 values of 0.107 μM in MV4-11 cells and 0.325 μM in MDA-MB-453 cells. Additionally, CDK4/6-IN-15, at concentrations between 0.1 and 1 μM for 24 hours, induces cell cycle arrest at the G1 phase specifically in Rb-positive MV4-11 and MDA-MB-453 cell lines. This compound also initiates apoptosis in MV4-11 and MDA-MB-453 cells at concentrations of 0.1-1 μM or 0.3-3 μM over 24 to 96 hours. Furthermore, CDK4/6-IN-15 effectively inhibits Rb phosphorylation within a concentration range of 0.1 to 3.3 μM for periods spanning 4 to 24 hours.

CDK4/6-IN-15 (compound 91), administered as a single dose of 2 mg/kg intravenously or 10 mg/kg orally, demonstrates similar oral absorption in healthy adult male BALB/c mice (20-25 g) and male albino Wistar rats (250-350 g) when given at 5 mg/kg intravenously or 200 mg/kg orally.