Identification of New Lupane-Type Triterpenoids as Inverse Agonists of RAR-Related Orphan Receptor Gamma (RORγ)

Area of Science:

• Medicinal Chemistry
• Molecular Pharmacology
• Immunology

Background:

• Retinoic acid-related orphan receptor gamma (RORγ) is a key target for autoimmune disease therapies.
• Inverse agonists of RORγ offer a promising therapeutic strategy for conditions like psoriasis, rheumatoid arthritis, and multiple sclerosis.

Purpose of the Study:

• To identify novel RORγ inverse agonists using structure-based virtual screening.
• To characterize the activity and binding of identified compounds and their analogues.

Main Methods:

• Structure-based virtual screening to identify potential RORγ inverse agonists.
• In vitro assays including luciferase reporter assays (Gal4-RORγ and full-length RORγ) and thermal shift assays.
• Real-time quantitative PCR to assess target gene downregulation.
• Molecular docking and site-directed mutagenesis for binding mode analysis.

Main Results:

• A novel lupane-type pentacyclic triterpenoid, compound 15, was identified as a potent RORγ inverse agonist (IC50 values of 0.4 μM and 0.9 μM).
• Compound 15 demonstrated superior potency and efficacy compared to betulinic acid.
• Two analogues (15.2 and 15.3) also exhibited RORγ inverse agonist activity, and all three downregulated RORγ target genes.
• Binding assays confirmed stabilization of the RORγ ligand-binding domain, with distinct binding modes elucidated through docking and mutagenesis.

Conclusions:

• Pentacyclic triterpenoids represent a viable scaffold for developing novel RORγ inverse agonists.
• Compound 15 and its analogues show therapeutic potential for RORγ-mediated autoimmune diseases.
• Detailed structural and mechanistic insights were gained into RORγ inverse agonism.