Development of PPAR Modulators and Investigations on their Mode of Action

The peroxisome proliferator-activated receptors (PPARα, PPARβ/δ and PPARγ) are nuclear receptors whose target genes have fundamental roles in human health and disease. The PPAR-regulated expression of these genes influences a range of physiological processes, including cell differentiation and proliferation, inflammation and lipid metabolism. Thus, the ligand-dependent modulation of PPAR activity is a potential point of pharmacological intervention in e.g. metabolic-, neurodegenerative- and dermatologic diseases. Recent reports on the involvement of PPARβ/δ in the pathophysiologies of breast cancer and psoriasis, highlight this PPAR subtype as a target of particular interest. The effects of agonistic ligands on PPAR target gene expression have been studied for nearly two decades and a structurally diverse collection of agonists has been reported. In contrast, fewer PPAR antagonists have been reported and the knowlegde about their various modes of action is less developed than that of agonists. In this thesis, the development of new members of a class of covalent PPARβ/δ antagonists is presented. Our studies demonstrate that the selectivity of the new antagonists for PPARβ/δ could be increased through subtle modifications of the structure of a previously reported antagonist, without affecting its mode of action. In extension of these studies, an investigation into the modes of action of the reported antagonistic ligands of PPARβ/δ was undertaken. In this study, an emphasis was put on the possible involvement of covalent bond formation between PPARβ/δ and the antagonistic ligands. Through a series of chemical and biological assays, it could be demonstrated that the reported antagonistic ligands differ markedly in their modes of action. Our results thus contribute to a more nuanced classification of the studied PPARβ/δ ligands. Finally, the recent dicovery of a novel post-translational modification of PPARγ, has impacted on the understanding of the beneficial effects of PPARγ agonists as drugs to treat metabolic diseases. The nature of the ligand-dependent inhibition of this undesired regulatory event, has shifted the focus of PPARγ ligand development away from full agonists, towards the development of partial- and non-agonists. The large body of structural data from x-ray crystallography on PPARγ in complex with ligands displaying a diverse set of binding modes, permitted a collective analysis of these data, aiming to identify structural trends in the influences of the ligands on PPARγ. Our study employed principal component analyses of the atomic coordinates and dihedral angles of PPARγ. The results of this investigation demonstrate a separation of the PPARγ structures, corresponding to a varying degree of stabilization of a region of the protein, known to be important for the undesired biological effects of full agonists. Thus, our analysis provides a mapping of the PPARγ structures with potential utility in the development of new partial- and non-agonistic PPARγ ligands.