ZDLD13, a β-carboline, is an orally active and selective CDK4/CycD3 inhibitor with an IC 50 value of 0.38 μM. ZDLD13 exhibits potent anti-HCT116 activity including inhibition of colony formation, inhibition of invasion and migration, inducing of apoptosis , and arresting of G1 phase in cell cycle. ZDLD13 shows significant tumor growth inhibition in HCT116 tumor xenograft model.