Tetrandrine inhibits deregulated cell cycle in pancreatic cancer cells: Differential regulation of p21Cip1/Waf1, p27Kip1 and cyclin D1.

Current therapies in Pancreatic Cancer (PaCa) are ineffective due to deregulated cell cycle driven by landscape mutations. In this study, we show for the first time that tetrandrine (TET) inhibits proliferation of the PaCa cells and inhibits PaCa tumor growth. TET inhibits cell cycle transition at G1/S boundary. TET increased levels of p21Cip1/Waf1 and p27Kip1, had no effect on the levels of CDK4/6 proteins and decreased the levels of cyclin D1 and pRb proteins. TET resulted in changes in mRNA levels of cyclin D1 and p21Cip1/Waf1 but had no effect on the mRNA of p27Kip1. We show, for the first time in any system, that TET treatment downregulated Skp2, E3 ligase specific for degradation of p27Kip1 during the cell cycle. Taken together our results show, that TET indirectly impairs the activities of CDK4/6 to halt deregulated cell cycle and inhibit PaCa tumor growth. These results suggest that TET may serve as a novel agent for treatment of PaCa, for which there is no effective cure to date.