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Abstract
Pancreatic cancer is the fourth leading cause of cancer related deaths in United States. It has a very low five-year survival rate (<5%) and the current gemcitabine based therapy is highly ineffective. Signature mutations and stroma rich tumor microenvironment confer chemoresistance by deregulating cell cycle, promoting anti-apoptotic mechanisms and impaired drug delivery. All these factors render the current treatment incompetent and prompt an urgent need for new improved therapy. In this study we evaluated for the first time the anti-cancer potential of natural compound tetrandrine on pancreatic cancer cell lines and in vivo mouse model. Our results showed that TET inhibits proliferation of pancreatic cancer cells and reduces tumor growth by inhibiting G1 to S transition. TET treatment led to decreased cyclin D1 expression and Rb dephosphorylation. It was accompanied by an increase in protein levels of p21Cip1/Waf1 and p27Kip1. Similar results were found in vivo. The mechanistic studies revealed that TET treatment leads to Akt dephosphorylation resulting in decreased cyclin D1 expression, induces p21Cip1/Waf1 promoter activity and stabilizes p27Kip1 protein by preventing its degradation. These results suggest that TET reactivates G1/S checkpoint in pancreatic cancer cells. We also observed that TET decreases viability of pancreatic cancer lines in an irreversible manner by inducing apoptosis. TET treatment led to caspase 3 and PARP cleavage, and nuclear morphology changes. The mechanistic studies showed that TET treatment caused an early and transient activation of UPR sensors. This was followed by increased expression of ATF4 and CHOP (the apoptotic inducers of the UPR pathway) at later time points. The knockdown studies further validated the role of CHOP in TET induced apoptosis. The tumors also showed increased expression of CHOP and apoptosis after TET treatment. These results indicate that TET modulates UPR in pancreatic cancer cells and results in stress induced apoptosis. We also tested TET and gemcitabine combination in vitro and in vivo. Results showed that TET and gemcitabine combination significantly reduced the viability of pancreatic cancer cells in vitro and decreased tumor volume in vivo. The combination causes increased apoptosis of pancreatic cancer cells than either agent alone. It can be concluded that TET and gemcitabine combination is more effective than single agent treatment. Overall it can be concluded TET is a potent anti-cancer agent and can serve as a potential candidate for pancreatic cancer chemotherapy.
