Abstract 657: Inhibition of mTORC1 by dihydroartemisinin

mTOR functions as two complexes, mTORC1 and mTORC2, and is a central controller for cell growth and metabolism. Both mTORC1 and mTORC2 are activated in numerous cancers, and have become the focus of anticancer drug development. Rapalogs and mTOR kinase inhibitors (TORKIs) have been developed. However, the anticancer efficacy of rapalogs is clinically weak or mild to most cancers, and the adverse effects of rapalogs and TORKIs are greatly concerned. So, it is imperative to discover and develop new generation of mTOR inhibitors. Dihydroartemisinin (DHA) is an anti-malarial agent showing good safety in both children and adults. Recently, we have shown that DHA, at pharmacological concentrations, inhibits proliferation and induces apoptosis in cells derived from various cancer types but not in normal or immortalized cell lines, implying that DHA is potentially a selective anticancer agent and may be repurposed for cancer therapy. Of interest, DHA potently suppresses mTORC1-mediated phosphorylation of S6K1 and 4E-BP1, but does not obviously affect mTORC2-mediated phosphorylation of Akt, which is often activated by classic mTOR inhibitors (rapalogs) via a feedback mechanism. The results suggest that DHA is a novel mTORC1 inhibitor. This study was set to determine how DHA inhibits mTORC1. Here we found that DHA did not bind to any mTORC1 components (mTOR, mLST8 or raptor) directly, as determined by in vivo [3H]-DHA radiolabeling. Besides, our molecular docking revealed that DHA did not have the ability to bind FKBP12 or mTOR kinase domain, in contrast to the positive controls rapamycin (binding FKBP12) and INK128 (binding mTOR kinase domain). These data suggest that DHA inhibits mTORC1 via indirect mechanism(s). Further research revealed that DHA altered neither the phosphorylation of IGF-1R/PI3K/PTEN and ERK, nor the expression of REDD1, but induced phosphorylation of AMPKα (T172). Interestingly, DHA-induced mTORC1 inhibition was profoundly attenuated by inhibition with Compound C (AMPK inhibitor) or ectopic expression of dominant negative AMPKα2 (AMPKα2-DN), indicating that activation of AMPK links to inhibition of mTORC1. Collectively, the results support that DHA inhibits mTORC1 by activating AMPK. (Supported by the Feist-Weiller Cancer Center, LSU Health Sciences Center, Shreveport, LA, USA.) Citation Format: Wang Liu, Jun Luo, Yoshinobu Odaka, Shile Huang. Inhibition of mTORC1 by dihydroartemisinin [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 657.