Inhibition of CHOP accentuates the apoptotic effect of α-mangostin from the mangosteen fruit (Garcinia mangostana) in 22Rv1 prostate cancer cells

• α-Mangostin, the main xanthone from the mangosteen fruit promotes ER stress.
• Combination of CHOP siRNA and α-mangostin increases caspase3 activity in 22Rv1 cells.
• α-Mangostin promotes PERK expression in prostate cancer cells.
• α-Mangostin inhibits PERK expression in prostate epithelial cells.

The mangosteen (Garcinia mangostana) fruit has been a popular food in Southeast Asia for centuries and is increasing in popularity in Western countries. We identified α-Mangostin as a primary phytochemical modulating ER stress proteins in prostate cancer cells and propose that α-Mangostin is responsible for exerting a biological effect in prostate cancer cells. Two human prostate cancer cell lines, 22Rv1 and LNCaP, and prostate epithelial cells procured from two patients undergoing radical prostatectomy were treated with α-Mangostin and evaluated by RT-PCR, Western blot, fluorescent microscopy and siRNA transfection to evaluate ER stress. Next, we evaluated α-Mangostin for microsomal stability, pharmacokinetic parameters, and anti-cancer activity in nude mice. α-Mangostin significantly upregulated ER stress markers in prostate cancer cells. Interestingly, α-Mangostin did not promote ER stress in prostate epithelial cells (PrECs) from prostate cancer patients. CHOP knockdown enhanced α-Mangostin-induced apoptosis in prostate cancer cells. α-Mangostin significantly suppressed tumor growth in a xenograft tumor model without obvious toxicity. Our study suggests that α-Mangostin is not the only active constituent from the mangosteen fruit requiring further work to understand the complex chemical composition of the mangosteen.