AMPK inhibits mTORC1 activation through stimulation of TSC2 function, leading to accumulation of Rheb-GDP and by direct phosphorylation of Raptor, which disrupts its association with mTOR, leading to dissociation of the mTORC1 complex. The precise consequence of suppression of Cabozantinib c-Met inhibitor negative feedback loops mediated by the mTORC1/S6K axis in response to metformin remains poorly defined and, in particular, it is not known whether rapamycin, Navitoclax active-site mTOR inhibitors and metformin lead to over-activation of similar upstream pathways in PDAC cells. Here, we demonstrate that treatment of PANC-1 or MiaPaCa-2 pancreatic cancer cells with either rapamycin or active-site mTOR inhibitors suppressed S6K and S6 phosphorylation induced by insulin, a combination of insulin and the GPCR agonist neurotensin or serum. Rapamycin caused a striking augmentation of Akt phosphorylation at Ser473 while the active-site mTOR inhibitors KU63794 and PP242 completely abrogated Akt phosphorylation at this site. A salient feature of the results presented here is that active-site inhibitors of mTOR, in contrast to rapamycin, cause a marked increase in ERK activation in PDAC cells. The results imply that first and second generation mTOR inhibitors promote over-activation of different prooncogenic pathways in PDAC cells, namely Akt and ERK. Metformin also abolished mTORC1 activation but without overstimulating Akt phosphorylation on Ser473. Furthermore, metformin prevented ERK activation in response to cross-talking agonists in PDAC cells. Our results demonstrate that the effects of metformin on Akt and ERK activation are strikingly different from those elicited by allosteric or active-site mTOR inhibitors, though all these agents potently inhibited the mTORC1/S6K axis. Aberrant stimulation of the mTOR pathway in many cancer cells, including PDAC, is eliciting intense interest for targeting this pathway. However, it is increasingly appreciated that the mTORC1/S6K axis also mediates negative feedback loops that attenuate signaling via insulin/IGF receptor and other tyrosine kinase receptors. Suppression of these feed-back loops unleashes over-activation of upstream pathways that potentially counterbalance the anti-proliferative effects of mTOR inhibitors. Consequently, the identification of negative feedback loops by either allosteric or active-site mTOR inhibitors has emerged as an area of major interest in cancer therapy. Because the operation of these complex feedback loops is cell-context specific, we examined the patterns of Akt and ERK feedback activation in response to mTORC1 inhibition by rapamycin, active-site mTOR inhibitors and metformin in human PDAC cells. PDAC is one of the most lethal human diseases, with overall 5-year survival rate of only 3�C 5% and a median survival period of 4�C6 months.