CDK4 and neoplasm: SR140333‐induced apoptosis in vivo was confirmed by positive terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining of tumor tissues (Figure 5F,G), accompanied by an increase in proapoptotic proteins cleaved Caspase 3 and BAX and a decrease in cell cycle‐associated proteins CDK4 and CDK1 in SR140333‐treated mice bearing HCT116 xenografts (Figure 5H).