Abstract 2961: Ganoderma lucidum extracts inhibit mTORC1/2 by activating AMPK and inhibiting IGFR/PI3K/Rheb in tumor cells

Abstract

Ganoderma lucidum (G. lucidum) extracts, as dietary supplements, have been found to possess potent anticancer activity, which is attributed to the presence of polysaccharides and triterpenes. However, the molecular mechanism underlying the anticancer action of G. lucidum extracts remains to be elucidated. Here we show that ReishiMax GLp, containing both polysaccharides and triterpenes of G. lucidum (GLPT), inhibited cell proliferation and induced cell death in human lung cancer cells (A549 and A427), and concurrently suppressed the signaling pathways mediated by the mammalian target of rapamycin (mTOR), a central regulator of cell proliferation and survival. Interestingly, GLPT not only inhibited mTORC1-mediated phosphorylation of p70 S6 kinase 1 (S6K1) and eukaryotic initiation factor 4E binding protein 1 (4E-BP1), but also repressed mTORC2-mediated phosphorylation of Akt. Mechanistically, GLPT downregulated the phosphorylation and protein levels of insulin-like growth factor 1 receptor (IGFR) and phosphoinositide 3-kinase (PI3K), as well as the protein level of RAS homolog enriched in brain (Rheb). Besides, GLPT also activated AMP-activated protein kinase (AMPK) network. This is supported by the findings that GLPT increased the phosphorylation of AMPKα (T172), as well as its substrates tuberous sclerosis complex 2 (TSC2, S1387) and regulatory-associated protein of mTOR (raptor, S792). Ectopic expression of dominant negative AMPKα partially attenuated the inhibitory effect of GLPT on mTORC1, indicating that GLPT inhibits mTORC1 partly via activating AMPK. The results suggest that G. lucidum extracts execute the anticancer action at least partly by inhibiting the mTORC1/2 signaling through activation of AMPK and inhibition of IGFR/PI3K/Rheb in tumor cells. Supported by the Feist-Weiller Cancer Center, LSU Health Sciences Center, Shreveport, LA, USA. Citation Format: Shile Huang, Didem Sohretoglu, Chao Zhang, Jun Luo. Ganoderma lucidum extracts inhibit mTORC1/2 by activating AMPK and inhibiting IGFR/PI3K/Rheb in tumor cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2961.