Xerophenone H, a naturally-derived proteasome inhibitor, triggers apoptosis and paraptosis in lung cancer.

Abstract

Background: Polycyclic polyprenylated acylphloroglucinols (PPAPs) characterized by unique chemical architectures, exhibit diverse pharmacological activities. Xerophenone H (XeH) is a PPAP extracted from the plant Garcinia multiflora Champ. ex Benth. (Clusiaceae) with a novel and unique chemical structure. Although in vitro screening has revealed the anti-cancer activity of XeH, whose in vivo effectiveness and mechanistic basis required systematic investigation.

Methods: Cytotoxic effects were evaluated through MTT and colony formation assays. A subcutaneous xenograft model was established to assess in vivo anti-cancer efficacy. To elucidate the underlying mechanism of the anti-cancer effect of XeH, RNA-sequencing and western blotting were performed. A proteasome activity assay was conducted to quantify the effect of XeH. Molecular docking and cellular thermal shift assays were conducted to identify the potential molecular target for XeH.

Results: XeH demonstrated concentration-dependent cytotoxicity in A549 cells (IC₅₀ = 12.16 μM at 48 h). Intratumoral administration (10 mg/kg triweekly) achieved 38.6 % tumor growth inhibition. XeH simultaneously triggered apoptosis and paraptosis in A549 and H460 cells. Mechanistically, XeH promoted the formation of protein aggregates and induced significant endoplasmic reticulum stress in lung cancer cells by directly interacting with PSMB5 and inhibiting proteasome activity.

Conclusions: XeH, a novel PPAP, was identified as a novel proteasome inhibitor. It effectively downregulated proteasome activity, and induced both apoptosis and paraptosis in lung cancer cells.