S. Modi1, B. Giri1, K. Majumder1, S. Banerjee1, V. Dudeja1, A. K. Saluja1 1University Of Minnesota,Surgery,Minneapolis, MN, USA
Introduction: Gemcitabine with nab-paclitaxel is the current benchmark in the treatment of metastatic pancreatic ductal adenocarcinoma (PDA); however, the survival benefit of this combination is around 6 weeks more than gemcitabine alone. Drug combinations that help in reducing the doses of these drugs while providing better treatment response are required. Minnelide (triptolide prodrug, currently in phase I trials) has been shown to be effective against pancreatic cancer in preclinical models. In this study, we evaluated the efficacy of Minnelide in combination with reduced doses of standard therapy in PDA.
Methods: In vitro, pancreatic cancer cells (S2-VP10, S2-013 and PANC-1) were treated with low doses of paclitaxel (0-25nM), low dose of triptolide (25nM), and a combination of both for 24-72h. Cell viability was measured by the WST-8 assay. Cancer cell death by apoptosis was evaluated by measuring cleaved caspase-3 levels using flow cytometry. Cell cycle analysis was done using propidium iodide staining.
In vivo, combination therapy was tested in various models of PDA. Xenograft, subcutaneous, and orthotopic models were established using S2-VP10 and S2-013 pancreatic cancer cells. The immunocompetent subcutaneous model was established using KPC derived cells in C57BL/6J wild type mice. Due to the development of fatal immune reaction in mice treated with nab-paclitaxel (due to human albumin), equivalent doses of paclitaxel (dissolved in DMSO) were used in immunocompetent mice while immunodeficient mice were treated with nab-paclitaxel. Tumors were harvested, and tissues were used for various experiments.
Results: In vitro, proliferation of pancreatic cancer cells was markedly inhibited by the combination of triptolide and paclitaxel. Low doses of triptolide and paclitaxel led to significantly increased levels of cleaved caspase-3 and cleaved PARP suggesting that apoptotic cell death was induced in these cells. The combination therapy also led to an increased number of these cells trapped in the G2/M phase of the cell cycle.
In vivo: In the s/c model, combination of low doses of Minnelide and paclitaxel inhibited tumor progression. The tumor volumes in various groups were: Minnelide: 75.4 ±25 %, paclitaxel: 50.0 ±3%, Minnelide + paclitaxel: 11.0 ±1%. In the metastasis orthotopic cancer model, median survival (in days) of animals in different treatments groups was vehicle (13.0), Minnelide (20.5), paclitaxel (21.5) and combination (all alive). The combination of Minnelide and low doses of gemcitabine + nab-paclitaxel was effective in decreasing the tumor burden in orthotopic models and increasing survival of tumor-bearing mice. Besides decreasing tumor burden, combination treatment significantly reduced cancer-related morbidity by decreasing ascites and metastasis.
Conclusion: Minnelide synergizes with standard of care chemotherapy, reduces the doses of these toxic drugs and achieves better efficacy in treatment of PDA.