Discovery of PPAR Alpha Lipid Pathway Modulators That Do Not Bind Directly to the Receptor as Potential Anti-Cancer Compounds

Peroxisome proliferator-activated receptors (PPARs) are considered good drug targets for breast cancer because of their involvement in fatty acid metabolism that induces cell proliferation. In this study, we used the KAIMRC1 breast cancer cell line. We showed that the PPARE-Luciferase reporter gets highly activated without adding any exogenous ligand when PPAR alpha is co-transfected, and the antagonist GW6471 can inhibit the activity. Using this reporter system, we screened 240 compounds representing kinase inhibitors, epigenetic modulators, and stem cell differentiators and identified compounds that inhibit the PPARα-activated PPARE-Luciferase reporter in the KAIMRC1 cell. We selected 11 compounds (five epigenetic modulators, two stem cell differentiators, and four kinase inhibitors) that inhibited the reporter by at least 40% compared to the controls (DMSO-treated cells). We tested them in a dose-dependent manner and measured the KAIMRC1 cell viability after 48 h. All 11 compounds induced the cell killing at different IC50 values. We selected two compounds, PHA665752 and NSC3852, to dissect how they kill KAIMRC1 cells compared to the antagonist GW6741. First, molecular docking and a TR-FRET PPARα binding assay showed that compared to GW6471, these two compounds could not bind to PPARα. This means they inhibit the PPARα pathway independently rather than binding to the receptor. We further confirmed that PHA665752 and NSC3852 induce cell killing depending on the level of PPARα expression, and as such, their potency for killing the SW620 colon cancer cell line that expresses the lowest level of PPARα was less potent than for the KAIMRC1 and MDA-MB-231 cell lines. Further, using an apoptosis array and fatty acid gene expression panel, we found that both compounds regulate the PPARα pathway by controlling the genes involved in the fatty acid oxidation process. Our findings suggest that these two compounds have opposite effects involving fatty acid oxidation in the KAIMRC1 breast cancer cell line. Although we do not fully understand their mechanism of action, our data provide new insights into the potential role of these compounds in targeting breast cancer cells.