Glycyrrhizin alleviates the toxicity of hydroxychloroquine in treating oral lichen planus by occupying heat shock protein 90 alpha

Background: Oral lichen planus (OLP) is a common chronic inflammatory disease with the potential of malignant transformation. Hydroxychloroquine (HCQ), derived from quinine originating from Cinchona spp. bark, is a commonly prescribed off-label for OLP. However, it lacks robust evidence-based medicine practice, as well as theoretical guidance for its pharmacodynamic targets and for mitigating adverse reactions. Purpose: To compare the efficacy of HCQ with first-line treatment prednisone for treating severe erosive OLP and to identify compatible phytomedicine that is reasonably available based on elucidating the molecular targets related to clinical benefits and adverse reactions. Methods: We performed a single-center, randomized, investigator-blinded, positive-controlled, non-inferiority trial. Patients who met the enrollment criteria were randomly allocated (1:1) to receive either HCQ or prednisone therapy for 4 weeks and follow-up for 3 months. The primary outcome measures included reductions in the erosion area and pain level. Potential targets of HCQ and associated toxic effects in treating OLP were identified through in silico analysis and validated through histological evaluation. Common hepatoprotective agents, including glycyrrhizin and total glucosides of peony, were analyzed for their potential targets. Then tri-molecular docking study was performed to screen available phytomedicine agent for alleviating adverse reaction of HCQ. Finally, in vitro experiments were performed to validate these targeted effects. Results: A total of 62 patients were enrolled from January 2021 to August 2023. After a 4-week treatment, there's no significant difference between patients receiving HCQ and PDN in the reduction of erosion area (median, 44 vs 58.5; HCQ - PDN difference: -11; 95 % CI, -39 to 13; p = 0.438) or pain level (median, 3 vs 3; HCQ - PDN difference: 0; 95 % CI, -1 to 1; p = 0.925). Heat shock protein 90 (HSP90) alpha and beta were identified as potential therapeutic targets of HCQ for treating OLP, while HSP90 alpha is also associated with the adverse reactions of HCQ. The expressions of HSP90 alpha and HSP90 beta in OLP tissue were significantly reduced compared to normal tissue. The phytomedicine glycyrrhizin was selected due to its specific interaction with the GLY-181 site of HSP90 alpha, same as HCQ's toxic targets. HCQ exerted pro-proliferative and anti-inflammatory effects in vitro. And both HCQ and glycyrrhizin treatment restore the expression of HSP90 beta, while HCQ treatment also restored the expression of HSP90 alpha. Conclusions: HCQ was not inferior to prednisone for treating severe erosive OLP, suggesting it as an alternative to first-line treatment. Integrating phytopreparation glycyrrhizin into conventional HCQ treatment in OLP can help detoxify by occupying the HSP90 alpha binding site.