Gambogic Acid Inhibits Malignant Melanoma Cell Proliferation Through Mitochondrial p66shc/ROS-p53/Bax-Mediated Apoptosis

Background/Aims: Malignant melanoma has high metastatic potential, is highly resistant to chemotherapy, and has a poor survival rate. Gambogic acid (GA), a polyprenylated xanthone extracted from a traditional Chinese medicinal herb, has been proven to exhibit antitumor activity. The present study aimed to investigate the signaling pathways that mediated GA-induced inhibition of human malignant skin melanoma proliferation. Methods: The study was conducted using A375 cells and the corresponding tumor transplanted in nude mice. Results: Incubation of A375 cells with 1-10 μg/ml GA decreased cell viability and increased apoptosis. GA concentration-dependently increased p66shc expression and intracellular ROS levels. GA also decreased the oxygen consumption rate and the mitochondrial membrane potential (MMP) in A375 cells. Experimental inhibition of p66shc by siRNA suppressed GA-induced increase of ROS, decrease of oxygen consumption rate, MMP and cell viability, whilst suppressing GA-induced increase of apoptosis. GA concentration-dependently upregulated p53 and Bax expression in A375 cells. GA also increased p53-TA-luciferase activity and p53-binding to Bax promoter, which was inhibited by Sip53. Experimental inhibition of p53 with Sip53 blocked GA-induced decrease of the oxygen consumption rate and cell viability, and blocked the increase of apoptosis. In tumor-bearing nude mice, GA notably inhibited tumor growth, and this action was suppressed by N-acetylcysteine (NAC), a potent antioxidant, and by PFT-α, a p53 inhibitor. In A375 tumors transplanted in nude mice, GA increased both p66shc and p53 expression. NAC and PFT-α treatment did not significantly affect p66shc expression in tumors grown in mice treated with GA. In contrast, both NAC and PFT-α treatment inhibited GA-induced p53 expression in mouse tumors. Conclusion: Results provided novel preclinical insights into the chemotherapeutic use of GA by highlighting the importance of p66shc/ROS-p53/Bax pathways in the antitumor effect of GA in malignant melanoma