Peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) ligands do not potentiate growth of human cancer cell lines

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Abstract
Ligands for peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) increase skeletal muscle fatty acid catabolism, improve insulin sensitivity, increase serum high-density lipoprotein cholesterol, elicit anti-inflammatory activity and induce terminal differentiation. Contradictory findings are also reported suggesting that PPARβ/δ ligands potentiate tumorigenesis by increasing cell proliferation, by inhibiting apoptosis through phosphorylation of Akt and by increasing cyclooxygenase-2 (COX2) and vascular endothelial growth factor (VEGF) expression. The contradictory findings could be due to differences in the model system (cancer cell line versus in vivo), differences in cell culture conditions (with and without serum) or differences in ligands. The present study examined the effect of two different PPARβ/δ ligands (GW0742 and GW501516) in human cancer cell lines (HT29, HCT116, LS–174T, HepG2 and HuH7) cultured in the presence or absence of serum and compared in vitro analysis with in vivo analysis. Neither PPARβ/δ ligand increased cell growth or phosphorylation of Akt and no increase in the expression of VEGF or COX2 were detected in any cancer cell line in the presence or absence of serum. Similarly, liver, colon and colon polyps from mice administered these PPARβ/δ ligands in vivo did not exhibit changes in these markers. Results from these studies demonstrate that serum withdrawal and/or differences in ligands do not underlie the disparity in responses reported in the literature. The quantitative nature of the present findings are inconsistent with the hypothesis that cancer cell lines respond differentially as compared with normal cells, and provide further evidence that PPARβ/δ ligands do not potentiate tumorigenesis.

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