title: Different patterns of Akt and ERK feedback activation in response to rapamycin, active-site mTOR inhibitors and metformin in pancreatic cancer cells.
abstract: The mTOR pathway is aberrantly stimulated in many cancer cells, including pancreatic ductal adenocarcinoma (PDAC), and thus it is a potential target for therapy. However, 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 antiproliferative effects of mTOR inhibitors. 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 and the GPCR agonist neurotensin. Rapamycin caused a striking increase in Akt phosphorylation at Ser(473) while the active-site inhibitors of mTOR (KU63794 and PP242) completely abrogated Akt phosphorylation at this site. Conversely, active-site inhibitors of mTOR cause a marked increase in ERK activation whereas rapamycin did not have any stimulatory effect on ERK activation. The results imply that first and second generation of mTOR inhibitors promote over-activation of different pro-oncogenic pathways in PDAC cells, suggesting that suppression of feed-back loops should be a major consideration in the use of these inhibitors for PDAC therapy. In contrast, metformin abolished mTORC1 activation without over-stimulating Akt phosphorylation on Ser(473) and prevented mitogen-stimulated ERK activation in PDAC cells. Metformin induced a more pronounced inhibition of proliferation than either KU63794 or rapamycin while, the active-site mTOR inhibitor was more effective than rapamycin. Thus, the effects of metformin on Akt and ERK activation are strikingly different from allosteric or active-site mTOR inhibitors in PDAC cells, though all these agents potently inhibited the mTORC1/S6K axis.
authors: Division of Digestive Diseases, Department of Medicine; CURE: Digestive Diseases Research Center David Geffen School of Medicine and Molecular Biology Institute, University of California at Los Angeles, Los Angeles, California, United States of America.
authors: Heloisa P
authors: HP
authors: Soares
authors: Yang
authors: Y
authors: Ni
authors: Krisztina
authors: K
authors: Kisfalvi
authors: James
authors: J
authors: Sinnett-Smith
authors: Enrique
authors: E
authors: Rozengurt
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D021441:Carcinoma, Pancreatic Ductal / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D025461:Feedback, Physiological / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D008687:Metformin / Q000494:pharmacology*; D009025:Morpholines / Q000494:pharmacology; D009496:Neurotensin / Q000494:pharmacology; D010190:Pancreatic Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D011687:Purines / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism
chemical_list: D000903:Antibiotics, Antineoplastic; D007004:Hypoglycemic Agents; D007211:Indoles; D007328:Insulin; D009025:Morpholines; D011687:Purines; D011743:Pyrimidines; D009496:Neurotensin; C541932:Ku 0063794; D008687:Metformin; C546842:MTOR protein, human; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; C572919:PP242; D020123:Sirolimus