RICTOR/mTORC2 affects tumorigenesis and therapeutic efficacy of mTOR inhibitors in esophageal squamous cell carcinoma

Zhaoming Lu; Xiaojing Shi; Fanghua Gong; Shenglei Li; Yang Wang; Yandan Ren; Mengyin Zhang; Bin Yu; Yan Li; Wen Zhao; Jianying Zhang; Guiqin Hou

doi:10.1016/j.apsb.2020.01.010

RICTOR/mTORC2 affects tumorigenesis and therapeutic efficacy of mTOR inhibitors in esophageal squamous cell carcinoma

Acta Pharm Sin B. 2020 Jun;10(6):1004-1019. doi: 10.1016/j.apsb.2020.01.010. Epub 2020 Jan 26.

Authors

Zhaoming Lu^{1

2}, Xiaojing Shi¹, Fanghua Gong³, Shenglei Li⁴, Yang Wang¹, Yandan Ren¹, Mengyin Zhang¹, Bin Yu¹, Yan Li⁵, Wen Zhao¹, Jianying Zhang⁶, Guiqin Hou¹

Affiliations

¹ School of Pharmaceutical Sciences, Zhengzhou University, Zhengzhou 450001, China.
² Collaborative Innovation Center of Cancer Chemoprevention, Zhengzhou 450001, China.
³ School of Pharmacy, Wenzhou Medical University, Wenzhou 325035, China.
⁴ The First Affiliated Hospital, Zhengzhou University, Zhengzhou 450052, China.
⁵ Center of Advanced Analysis & Gene Sequencing, Zhengzhou University, Zhengzhou 450001, China.
⁶ Henan Academy of Medical and Pharmaceutical Sciences, Zhengzhou University, Zhengzhou 450052, China.

Abstract

Dysregulation of mTORC1/mTORC2 pathway is observed in many cancers and mTORC1 inhibitors have been used clinically in many tumor types; however, the mechanism of mTORC2 in tumorigenesis is still obscure. Here, we mainly explored the potential role of mTORC2 in esophageal squamous cell carcinoma (ESCC) and its effects on the sensitivity of cells to mTOR inhibitors. We demonstrated that RICTOR, the key factor of mTORC2, and p-AKT (Ser473) were excessively activated in ESCC and their overexpression is related to lymph node metastasis and the tumor-node-metastasis (TNM) phase of ESCC patients. Furthermore, we found that mTORC1/ mTORC2 inhibitor PP242 exhibited more efficacious anti-proliferative effect on ESCC cells than mTORC1 inhibitor RAD001 due to RAD001-triggered feedback activation of AKT signal. Another, we demonstrated that down-regulating expression of RICTOR in ECa109 and EC9706 cells inhibited proliferation and migration as well as induced cell cycle arrest and apoptosis. Noteworthy, knocking-down stably RICTOR significantly suppresses RAD001-induced feedback activation of AKT/PRAS40 signaling, and enhances inhibition efficacy of PP242 on the phosphorylation of AKT and PRAS40, thus potentiates the antitumor effect of RAD001 and PP242 both in vitro and in vivo. Our findings highlight that selective targeting mTORC2 could be a promising therapeutic strategy for future treatment of ESCC.

Keywords: 4EBP-1, E binding protein-1; AKT; AKT, protein kinase B (PKB); ESCC, esophageal squamous cell carcinoma; Esophageal squamous cell carcinoma; FDA, U.S. Food and Drug Administration; H&E staining, hematoxylin and eosin staining; IC50, half maximal inhibitory concentration; PI3K, phosphatidylinositol 3 kinase; RAD001; RICTOR; RICTOR, rapamycin-insensitive companion of mTOR; TNM, tumor-node-metastasis; TUNEL, terminal deoxynucleotidyl transferase dUTP nick end labeling; mTOR, mammalian target of rapamycin; mTORC1, mTOR complex 1; mTORC2, mTOR complex 2; p70S6K, p70 ribosomal S6 kinase-1; pp242; rapalogs, rapamycin and its analogs.