A dual mTORC1 and mTORC2 inhibitor shows antitumor activity in esophageal squamous cell carcinoma cells and sensitizes them to cisplatin

Abstract

The mammalian target of rapamycin (mTOR) signaling pathway is critical for the growth and proliferation of various malignant tumors, including esophageal squamous cell carcinoma (ESCC). Therefore, targeting of mTOR protein is a promising strategy for therapy in this disease. In the present study, we examined the antitumor effects of a specific mTOR kinase inhibitor, PP242, which blocks both mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2) pathways, in two ESCC cell lines: Eca-109 and TE-1. We showed that PP242, but not rapamycin, attenuated the activities of both mTORC1 and mTORC2 signaling in ESCC. PP242 inhibited 4E-binding protein-1 phosphorylation and abrogated mTORC1-dependent PI3K/Akt feedback activation. Significantly, PP242 effectively suppressed ESCC cell proliferation, induced apoptosis, and arrested the cell cycle. Furthermore, PP242 promoted cisplatin-induced apoptosis and enhanced the antitumor efficacy of cisplatin in ESCC cells, which was likely to be associated with inhibition of Akt activity. Our results show that simultaneous targeting of both mTORC1 and mTORC2 pathways leads to effective antitumor actions in ESCC, and strongly suggest that dual mTORC1/2 inhibitors should be developed as potential agents for the treatment of ESCC.