mTOR inhibitor RAD001 (everolimus) induces apoptotic, not autophagic cell death, in human nasopharyngeal carcinoma cells

Cai,Yuchen; Xia,Qing; Su,Quanguan; Luo,Rongzhen; Sun,Yueli; Shi,Yanxia; Jiang,Wenqi

doi:10.3892/ijmm.2013.1282

mTOR inhibitor RAD001 (everolimus) induces apoptotic, not autophagic cell death, in human nasopharyngeal carcinoma cells

Authors:
- Yuchen Cai
- Qing Xia
- Quanguan Su
- Rongzhen Luo
- Yueli Sun
- Yanxia Shi
- Wenqi Jiang
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Affiliations: State Key Laboratory of Oncology in South China, Guangzhou, Guangdong, P.R. China
Published online on: February 21, 2013 https://doi.org/10.3892/ijmm.2013.1282
Pages: 904-912

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Abstract

Mammalian target of rapamycin (mTOR) is a serine/threonine protein kinase and a key element in the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) signaling pathway. Moreover, it is a negative regulator of autophagy and acts as a central regulator in cell growth. For the treatment of cancer, mTOR is a novel and validated therapeutic target. Previous studies have shown that Akt is frequently activated in nasopharyngeal carcinoma (NPC) tissues; thus, the inhibition of mTOR may be a treatment strategy for this tumor type. To evaluate the effect of the mTOR inhibitor RAD001 on NPC cell lines, we performed 4-[3-(4-iodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate (WST-1) assays, lactate dehydrogenase (LDH) assays, western blotting and flow cytometry to evaluate the mechanisms of cell death. The growth of both CNE-1 and HONE-1 cells was inhibited in a time- and dose-dependent manner. CNE-1 was more sensitive, with a 50% growth inhibition (GI50) of 30.0±1.0 µM compared to HONE-1, cells which had a GI50 of 56.9±13.1 µM. RAD001 induced apoptosis and autophagy in both cell lines. RAD001 induced a significant increase in growth inhibition in the two cell lines when used in combination with the autophagy inhibitor, 3-methyladenine; however, the percentages of apoptotic cells decreased when RAD001 was combined with the caspase inhibitor, z-VAD-fmk. In conclusion, the main mechanism of the mTOR inhibitor RAD001 in these two NPC cells was apoptotic, not autophagic cell death. The combination of RAD001 with autophagy inhibitors may be a useful therapeutic strategy for nasopharyngeal carcinoma.

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