Liu Ningning, Huang Hongbiao, Liu Shouting, Li Xiaofen, Yang Changshan, Dou Q Ping, Liu Jinbao
Protein Modification and Degradation Lab, Department of Pathophysiology, Guangzhou Medical University, Guangzhou, Guangdong 510182, People's Republic of China.
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.
Toxicol In Vitro. 2014 Apr;28(3):419-25. doi: 10.1016/j.tiv.2013.12.008. Epub 2013 Dec 27.
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.
维拉帕米（Ver）是一种多药耐药基因产物抑制剂，已被证明是与包括蛋白酶体抑制剂硼替佐米在内的其他抗癌药物联用的理想搭档。藤黄酸（GA）在中国已获批用于癌症治疗的II期临床试验。我们最近报道，GA是一种有效的蛋白酶体抑制剂，其抗癌效果与硼替佐米相当，但毒性要小得多。在本研究中，我们调查了Ver是否能增强GA的细胞毒性。我们发现：（i）Ver与GA联合使用可在肝癌细胞系HepG2和白血病细胞系K562中产生协同细胞毒性作用并诱导细胞死亡；（ii）Ver与GA联合处理可诱导半胱天冬酶激活、内质网（ER）应激和活性氧（ROS）生成；（iii）半胱天冬酶抑制剂z-VAD可阻断GA+Ver诱导的细胞凋亡，但不能阻断蛋白酶体抑制；（iv）含半胱氨酸的化合物N-乙酰半胱氨酸（NAC）可防止GA+Ver诱导的聚（ADP-核糖）聚合酶裂解和蛋白酶体抑制。这些结果表明，Ver通过增强蛋白酶体抑制和ROS生成来加速GA诱导的细胞毒性。这些发现表明，天然产物GA是一种有价值的候选药物，可与Ver联合使用，因此代表了一种引人注目的抗癌策略。
