A selective cyclin D1/CDK4 and cyclin D3/CDK6 inhibitor (nm IC50) that inhibits retinoblastoma protein phosphorylation, which prevents CDK-mediated G1-S phase transition, arresting the cell cycle in the G1 phase, suppressing DNA synthesis, and inhibiting cancer cell growth; reduces proliferation of several human neuroblastoma-derived cell lines (mean IC50 = 306 nM).