Shifting the PPARγ conformational ensemble towards a transcriptionally repressive state improves covalent inhibitor efficacy
The nuclear receptor peroxisome proliferator-activated receptor gamma (PPAR{gamma}) regulates transcription in response to ligand binding at an orthosteric pocket within the ligand-binding domain (LBD). We previously showed that two covalent ligands, T0070907 and GW9662--extensively used as PPAR{gamma} inhibitors to assess off-target activity--weaken but do not completely block ligand binding via an allosteric mechanism associated with pharmacological inverse agonism (Shang et al., 2024). These covalent inhibitors shift the LBD towards a repressive conformation, where the activation function-2 (AF-2) helix 12 occupies the orthosteric pocket, competing with orthosteric ligand binding. Here, we provide additional support for this allosteric mechanism using two covalent inverse agonists, SR33065 and SR36708, which better stabilize the repressive LBD conformation and are more effective inhibitors of--but also do not completely inhibit--ligand cobinding. Furthermore, we show that ligand cobinding can occur with a previously reported PPAR{gamma} dual-site covalent inhibitor, SR16832, which appears to weaken ligand binding through a direct mechanism independent of the allosteric mechanism. These findings underscore the complex nature of the PPAR{gamma} LBD conformational ensemble and highlight the need to develop alternative methods for designing more effective covalent inhibitors.