The effects of Triptolide on cellular metabolism in pancreatic cancer and fibroblast cells
Background: Pancreatic cancer is the third leading cause of adult cancer death in the United States and each year approximately 41,800 patients die from the disease. Late diagnosis, limited treatment options, and low response rates to current standard of care make pancreatic cancer extremely lethal with devastatingly low survival rates (>94% of patients die within 5 years of diagnosis). One of the primary reasons for the dismal prognosis is that the tumor microenvironment (TME) in pancreatic cancer is incredibly dense, fibrotic, and hypo-vascular making it impenetrable to chemotherapeutics. Triptolide (Minnelide), a compound with anti-tumor activity, is in Phase I clinical trials to treat various solid tumors and is showing promising activity in several cancer types including pancreatic cancer.
Objective: Targeting the mitochondrial and glycolytic cellular energy pathways is an effective way to inhibit tumor cell growth. Therefore, this project aimed at elucidating the effect of triptolide on the cellular energetics of pancreatic cancer (MIAPaca-2) and fibroblast (PS1) cells, which predominate the TME.
Methods: The Seahorse XFe96 Analyzer was employed to probe cellular energy pathways including glycolysis and oxidative phosphorylation in MIAPaca-2 and PS1. The XF Cell Mito Stress Test (MST) measures oxygen consumption rate (OCR) to evaluate mitochondrial function and the XF Cell Glycolysis Stress Test (GST) detects changes in extracellular acidification rate (ECAR) to evaluate glycolytic function. Dose response and kinetic time course experiments were performed on triptolide treated MIAPaca-2 and PS1 cells. This was done to determine the minimal dose that elicits a significantly different response in oxidative phosphorylation and glycolysis as well as its time course of action when compared to control. Cells pretreated with different concentrations of triptolide (0.03uM to 3uM) for varying times up to six hours were subjected to the GST or MST.
Results: Our data suggests that triptolide reduces mitochondrial respiration and glycolysis in a dose dependent manner in MIAPaCa-2 and PS1 cells within six hours of treatment. Under the tested conditions, 0.3uM triptolide significantly reduced OCR and ECAR in both cell lines. This response is evident in key parameters of mitochondrial function (ATP production, maximal respiration, and spare respiratory capacity) and glycolytic function (glycolytic capacity and glycolytic reserve).
Conclusions and Future Directions: Triptolide adversely affects glycolytic and mitochondrial function in pancreatic cancer cells and fibroblasts. Future research should include similar experiments using other pancreatic cancer cell lines and correlate the effects on mitochondrial and glycolytic function to anti-tumor activities to provide a better understanding of the drug’s mechanism of action. Probing cellular energy pathways in cancer cells treated with triptolide in combination with currently used treatment options and/or other new agents may lead to a better alternative to treat pancreatic cancer.