CDK4 and neoplasm: Consistent with the cell cycle arrest, We found that b-AP15 significantly decreased the expression of cyclin D1, CDK6, CDK4, CDK2 and phosphorylation/inactivation of Rb-marker proteins from G1 to S phase, and up-regulated the expression of p27, which is a known tumour suppressor via inhibiting the cyclin-CDK function (Figure 2B and 2C).