Prevention of Akt phosphorylation is a key to targeting cancer stem-like cells by mTOR inhibition

CD133 expression in pancreatic cancer correlates with poor prognosis and increased metastasis. CD133 + pancreatic cancer cells exhibit cancer stem cell (CSC)-like properties. We established a CD133 + cell-rich subline from Capan-1 pancreatic cancer cells as a pancreatic CSC model and compared the effects of KU-0063794, a dual mTORC1/mTORC2 inhibitor, against those of mTORC1-specific rapamycin. We found that KU-0063794 prevents sphere formation, a self-renewal index, at high concentrations. Rapamycin inhibited sphere formation but to a lesser degree. In the present study, we aimed to determine the mechanistic roles of mTOR complex 2 (mTORC2) in maintaining CSC-like properties. By examining the PI3K/Akt/mTOR signaling pathway, we observed lower Akt phosphorylation in KU-0063794-treated cells. Phosphorylation of mTORC1 downstream effectors was inhibited by both inhibitors. Thus, mTORC2 activates Akt and modulate stem-like properties, whereas mTORC1 downstream signaling correlates directly with stem-like properties.