PPAR-alpha: a novel target in pancreatic cancer
Hua, Alexander Mach
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Background: Current targeted therapies in pancreatic cancer have been ineffective. The tumor stroma, including intra- and peri-tumoral inflammation and fibrosis, is increasingly implicated in pancreatic cancer. Pancreatic cancer is characterized by a highly fibrotic tumor environment resulting in stromal resistance to chemotherapy. Peroxisome proliferator-activated receptor-alpha (PPARα), a ligand-activated nuclear receptor/transcription factor, is a negative regulator of inflammation. In PPARα deficient mice, stromal processes inhibit tumor growth, resulting in dormant tumors. The presence of PPARα in the tumor cells as well as in the host is necessary for unabated tumor growth. Objective: We hypothesized that blocking the PPARα pathway with a small molecule PPARα antagonist (NXT) may prevent pancreatic cancer progression by targeting tumor cells as well as non-neoplastic cells in the tumor microenvironment. Methods: Growth inhibitory activity of the PPARα antagonist was assessed in murine as well as human pancreatic tumor cell lines (Panc0H7 and BxPC3) and in a murine macrophage cell line (RAW 264.7). Cell viability was determined by trypan blue exclusion assay. AKT, P-AKT, PCNA, BAX, and p27 levels were analyzed by western blot analysis. Cell cycle changes were detected by flow cytometry. Cellular senescence was determined by senescence-associated β-gal (SA-β-gal) staining. Results: The PPARα antagonist inhibited cell growth in macrophages and in pancreatic tumor cells as confirmed by reduced protein level expression of PCNA and activated AKT. Treatment of the PPARα antagonist was non-cytotoxic to tumor cells. Inhibition of PPARα induced cell cycle arrest at G0/G1 in tumor cells and macrophages. The induction of cellular senescence was observed in pancreatic cancer cells. Interestingly, we observed a reduction in protein level expression of BAX, a marker for apoptosis, and p27, an inhibitor of the cell cycle. Conclusion: We now demonstrate that a PPARα antagonist exerts its anti-growth activity by inducing G0/G1 cell cycle arrest, thereby inducing cellular senescence without cell death. These findings provide a mechanism for the anti-tumorigenic activity of PPARα inhibition, and the rationale to use PPARα antagonists as a novel therapeutic approach to pancreatic cancer.
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