CDK4 and cancer: Piperine treatment reduces HRT-18 cell division by 40%. Piperine results in inhibition of G0/G1 cell cycle progression by down-regulating the synthesis of CDK4/6 and cyclin D. Enhanced ROS and other superoxide anion synthesis is also an outcome of piperine treatment. Thus, ROS synthesis and inhibition of cell cycle progression result in apoptosis of cancer HRT-18 cells