Cdk4 inhibitor is a cell-permeable, asymmetrical indolocarbazole that exhibits antiproliferative activity by blocking cyclin D1/Cdk4 with an IC50 value of 0.8 μM. It is selective for cyclin D1/Cdk4, demonstrating 7-fold and 28-fold weaker activity against cyclin E/Cdk2 and cyclin B/Cdk1, respectively, and little activity against calcium/calmodulin-dependent protein kinase II and protein kinase A. This compound has been shown to inhibit HCT-116 and NCI-H460 tumor cell growth (IC50s < 3.0 μM) by blocking retinoblastoma protein phosphorylation and inducing G1 cell cycle arrest.
