Here we demonstrated that in the cinobufagin-treated cancer cells, the G2/M checkpoint was quickly activated to induce G2 arrest through DDR-mediated phosphorylation of CDC25C and upregulation of p53 and p21Cip1/Waf1, which was followed by induction of apoptosis likely through p53-upregulated expression of pro-apoptotic proteins. The gene discussed is CDKN1A; the disease is cancer.