title: Calcium channel blocker verapamil accelerates gambogic acid-induced cytotoxicity via enhancing proteasome inhibition and ROS generation.
abstract: Verapamil (Ver), an inhibitor of the multidrug resistance gene product, has been proved to be a promising combination partner with other anti-cancer agents including proteasome inhibitor bortezomib. Gambogic acid (GA) has been approved for Phase II clinical trials in cancer therapy in China. We have most recently reported that GA is a potent proteasome inhibitor, with anticancer efficiency comparable to bortezomib but much less toxicity. In the current study we investigated whether Ver can enhance the cytotoxicity of GA. We report that (i) the combination of Ver and GA results in synergistic cytotoxic effect and cell death induction in HepG2 and K562 cancer cell lines; (ii) a combinational treatment with Ver and GA induces caspase activation, endoplasmic reticulum (ER) stress and reactive oxygen species (ROS) production; (iii) caspase inhibitor z-VAD blocks GA+Ver-induced apoptosis but not proteasome inhibition; (iv) cysteine-containing compound N-acetylcysteine (NAC) prevents GA+Ver-induced poly(ADP-ribose) polymerase cleavage and proteasome inhibition. These results demonstrate that Ver accelerates GA-induced cytotoxicity via enhancing proteasome inhibition and ROS production. These findings indicate that the natural product GA is a valuable candidate that can be used in combination with Ver, thus representing a compelling anticancer strategy.
authors.affiliation: Protein Modification and Degradation Lab, Department of Pathophysiology, Guangzhou Medical University, Guangzhou, Guangdong 510182, People's Republic of China.
authors.forename: Ningning
authors.initials: N
authors.lastname: Liu
authors.affiliation: Protein Modification and Degradation Lab, Department of Pathophysiology, Guangzhou Medical University, Guangzhou, Guangdong 510182, People's Republic of China.
authors.forename: Hongbiao
authors.initials: H
authors.lastname: Huang
authors.affiliation: Protein Modification and Degradation Lab, Department of Pathophysiology, Guangzhou Medical University, Guangzhou, Guangdong 510182, People's Republic of China.
authors.forename: Shouting
authors.initials: S
authors.lastname: Liu
authors.affiliation: Protein Modification and Degradation Lab, Department of Pathophysiology, Guangzhou Medical University, Guangzhou, Guangdong 510182, People's Republic of China.
authors.forename: Xiaofen
authors.initials: X
authors.lastname: Li
authors.affiliation: Protein Modification and Degradation Lab, Department of Pathophysiology, Guangzhou Medical University, Guangzhou, Guangdong 510182, People's Republic of China.
authors.forename: Changshan
authors.initials: C
authors.lastname: Yang
authors.affiliation: Protein Modification and Degradation Lab, Department of Pathophysiology, Guangzhou Medical University, Guangzhou, Guangdong 510182, People's Republic of China; The Molecular Therapeutics Program, Barbara Ann Karmanos Cancer Institute, Departments of Oncology, Pharmacology and Pathology, School of Medicine, Wayne State University, Detroit, MI 48201-2013, USA.
authors.forename: Q Ping
authors.initials: QP
authors.lastname: Dou
authors.affiliation: Protein Modification and Degradation Lab, Department of Pathophysiology, Guangzhou Medical University, Guangzhou, Guangdong 510182, People's Republic of China. Electronic address: jliu@gzhmc.edu.cn.
authors.forename: Jinbao
authors.initials: J
authors.lastname: Liu
mesh_terms: D000111:Acetylcysteine / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020169:Caspases / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects; D004357:Drug Synergism; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects; D056945:Hep G2 Cells; D006801:Humans; D020014:K562 Cells; D061988:Proteasome Inhibitors / Q000008:administration & dosage / Q000494:pharmacology*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D014700:Verapamil / Q000008:administration & dosage / Q000494:pharmacology*; D044004:Xanthones / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D002121:Calcium Channel Blockers; D061988:Proteasome Inhibitors; D017382:Reactive Oxygen Species; D044004:Xanthones; C052659:gambogic acid; D014700:Verapamil; D020169:Caspases; D000111:Acetylcysteine
keywords: Apoptosis; CYP1A2; Cancer therapy; Gambogic acid; Proteasome; Ubiquitin-proteasome system; Verapamil