Cinobufagin (Cinobufagine), an active ingredient of Venenum Bufonis, inhibits tumor development. Cinobufagin increases ATM and Chk2 and decreases CDC25C, CDK1, and cyclin B. Cinobufagin inhibits PI3K, AKT and Bcl-2 while increases levels of cleaved caspase-9 and caspase-3. Thus, Cinobufagin induces cell cycle arrest at the G2/M phase and apoptosis.