The Dipeptide H‐Trp‐Glu‐OH Shows Highly Antagonistic Activity against PPARγ: Bioassay with Molecular Modeling Simulation

The peroxisome proliferator‐activated receptor γ (PPARγ) is an important therapeutic drug target for several conditions, including diabetes, inflammation, dyslipidemia, hypertension, and cancer. It is shown that an antagonist or partial agonist of PPARγ has attractive potential applications in the discovery of novel antidiabetic agents that may retain efficacious insulin‐sensitizing properties and minimize potential side effects. In this work, the dipeptide H‐Trp‐Glu‐OH (G3335) was discovered to be a novel PPARγ antagonist. Biacore 3000 results based on the surface plasmon resonance (SPR) technique showed that G3335 exhibits a highly specific binding affinity against PPARγ ( K D =8.34 μ M ) and is able to block rosiglitazone, a potent PPARγ agonist, in the stimulation of the interaction between the PPARγ ligand‐binding domain (LBD) and RXRα‐LBD. Yeast two‐hybrid assays demonstrated that G3335 exhibits strong antagonistic activity (IC 50 =8.67 μ M ) in perturbing rosiglitazone in the promotion of the PPARγ‐LBD–CBP interaction. Moreover, in transactivation assays, G3335 was further confirmed as an antagonist of PPARγ in that G3335 could competitively bind to PPARγ against 0.1 μ M rosiglitazone to repress reporter‐gene expression with an IC 50 value of 31.9 μ M . In addition, homology modeling and molecular‐docking analyses were performed to investigate the binding mode of PPARγ‐LBD with G3335 at the atomic level. The results suggested that residues Cys285, Arg288, Ser289, and His449 in PPARγ play vital roles in PPARγ‐LBD–G3335 binding. The significance of Cys285 for PPARγ‐LBD–G3335 interaction was further demonstrated by PPARγ point mutation (PPARγ‐LBD‐Cys285Ala). It is hoped our current work will provide a powerful approach for the discovery of PPARγ antagonists, and that G3335 might be developed as a possible lead compound in diabetes research.