Design, synthesis and molecular characterization of selective inverse agonists and antagonists of the Peroxisome Proliferator-Activated Receptor (PPAR) beta/delta

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The Peroxisome Proliferator-Activated Receptor PPARbeta/delta regulates its genes through binding to specific DNA elements. While its role in fatty acid catabolism and energy metabolism is quite well understood, its role in cell differentiation, proliferation, and inflammatory processes is controversially discussed. Genome-wide analyses of human myofibroblasts indicate that repression is the major mode of PPARbeta/delta-mediated transcriptional regulation. The development of subtype-specific, high-affinity, bioavailable PPARbeta/delta inhibitors with a distinct activity profile (agonist, antagonist, or inverse agonist) is of utmost importance to elucidate the complex mechanism of the PPARbeta/delta-mediated transcription. In our preliminary studies we succeeded in designing the first selective PPARbeta/delta inverse agonists and antagonists, respectively. Noteworthy, there is no direct correlation of the affinity of a compound towards the PPARbeta/delta ligand-binding domain and its ability to recruit a corepressor peptide in vitro. We could furthermore demonstrate that invasion of a three-dimensional matrigel matrix by human breast adenocarcinoma cells is inhibited by inverse PPARbeta/delta agonists. Further experiments identified ANGPTL4 as the major transcriptional PPARbeta/delta target gene in these cells. To elucidate the complex PPARbeta/delta inverse agonist-mediated repression of target genes, it is crucial to identify all relevant proteins and protein complexes which are recruited if an inverse agonist binds to the PPARbeta/delta-LBD. In contrast to the well-described sequential recruitment of components of the PIC in vitro, there is strong evidence that in vivo the sequence of events might be altered and, moreover, additional co-factors might be required, which we will investigate in detail by ChIP assays and additional biochemical and/or genetic methods to identify all proteins being essential for the PPARbeta/delta-mediated repression of target genes. Furthermore, to understand how small changes in the chemical structure of a ligand can shift its activity profile from pure inverse agonistic towards pure antagonistic, the determination of the binding mode of these ligands is irremissible.