Exploring allosteric modulation of the transcription factor PPARγ

• Applicant: Professor Dr. Daniel Merk
• Subject Area: Pharmacy ; Organic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 545080789

The ligand-activated transcription factor peroxisome proliferator-activated receptor gamma (PPARγ) controls gene expression in response to lipid and fatty acid metabolite binding. It is involved in the regulation of lipid and glucose metabolism, adipose tissue homeostasis, macrophage polarization, and inflammation. Pharmacological PPARγ activation by the thiazolidinedione drugs (glitazones) has clinical relevance in type 2 diabetes and non-alcoholic fatty liver treatment. In addition, glitazones have been clinically studied, for example, in multiple sclerosis, Alzheimer's disease, and cancer. However, adverse effects of traditional PPARγ agonists prevent broader therapeutic application and new approaches with so-called selective PPARγ modulators (sPPARγM) or ligands blocking Cdk5-mediated PPARγ phosphorylation have not been a breakthrough, yet. New modes of PPARγ modulation are hence needed. We have discovered PPARγ modulation by oxidized vitamin E metabolites like garcinoic acid which interestingly bound to two sites in the PPARγ ligand binding domain. The orthosteric binding resembled that of glitazones while the mechanisms and effects of the unprecedented allosteric interaction were elusive. Notably, garcinoic acid exhibited remarkably different effects on PPARγ co-regulator interactions and gene expression compared to pioglitazone suggesting different modulation by orthosteric and allosteric ligands. Based on these intriguing findings, we aimed to target the allosteric site selectively and developed a new type of PPARγ ligand binding to the allosteric but not the orthosteric site. Like observed for the double binding garcinoic acid, molecular effects of this novel PPARγ modulator were significantly different from pioglitazone. The new allosteric ligand could bind to PPARγ simultaneously with orthosteric agonists and exhibited a unique solvent exposed binding mode in the co-crystal structure. Preliminary pharmacological evaluation of this allosteric ligand suggested different effects from glitazones potentially opening new therapeutic avenues. In the proposed project, we aim to explore and exploit allosteric PPARγ modulation from different angles: we will (i) optimize the allosteric ligand to a selective high-affinity tool suitable for in vivo studies in a structure-based fashion using the knowledge from the co-crystal structure; (ii) evaluate whether other endogenous molecules exhibit allosteric PPARγ modulation like vitamin E metabolites; and (iii) exploit the unique solvent-exposed binding mode of the allosteric ligand to develop proximity inducing conjugates (i.e., PROTACs) which was previously hindered by the fully enclosed binding mode of orthosteric PPARγ ligands. Thereby, the project will generate novel innovative chemical tools to study the biology and therapeutic potential of (allosteric) PPARγ modulation and provide insights into a potential physiological relevance of the allosteric binding site.

• DFG Programme: Research Grants