title: Dual PI3K/mTOR Inhibitors Induce Rapid Overactivation of the MEK/ERK Pathway in Human Pancreatic Cancer Cells through Suppression of mTORC2.
abstract: The PI3K/AKT/mTOR pathway, which is aberrantly stimulated in many cancer cells, has emerged as a target for therapy. However, mTORC1/S6K also mediates negative feedback loops that attenuate upstream signaling. Suppression of these feedback loops opposes the growth-suppressive effects of mTOR inhibitors and leads to drug resistance. Here, we demonstrate that treatment of PANC-1 or MiaPaCa-2 pancreatic ductal adenocarcinoma (PDAC) cells with the dual PI3K/mTOR kinase inhibitor (PI3K/TOR-KI) BEZ235 blocked mTORC1/S6K activation (scored by S6 phosphorylation at Ser(240/244)), mTORC1/4E-BP1 (assayed by 4E-BP1 phosphorylation at Thr(37/46)), and mTORC2-mediated AKT phosphorylation at Ser(473), in a concentration-dependent manner. Strikingly, BEZ235 markedly enhanced the MEK/ERK pathway in a dose-dependent manner. Maximal ERK overactivation coincided with complete inhibition of phosphorylation of AKT and 4E-BP1. ERK overactivation was induced by other PI3K/TOR-KIs, including PKI-587 and GDC-0980. The MEK inhibitors U126 or PD0325901 prevented ERK overactivation induced by PI3K/TOR-KIs. The combination of BEZ235 and PD0325901 caused a more pronounced inhibition of cell growth than that produced by each inhibitor individually. Mechanistic studies assessing PI3K activity in single PDAC cells indicate that PI3K/TOR-KIs act through a PI3K-independent pathway. Doses of PI3K/TOR-KIs that enhanced MEK/ERK activation coincided with those that inhibited mTORC2-mediated AKT phosphorylation on Ser(473), suggesting a role of mTORC2. Knockdown of RICTOR via transfection of siRNA markedly attenuated the enhancing effect of BEZ235 on ERK phosphorylation. We propose that dual PI3K/mTOR inhibitors suppress a novel negative feedback loop mediated by mTORC2, thereby leading to enhanced MEK/ERK pathway activity in pancreatic cancer cells.
authors: Division of Hematology-Oncology, David Geffen School of Medicine, Los Angeles, California.
authors: Heloisa P
authors: HP
authors: Soares
authors: Division of Digestive Diseases, Department of Medicine, David Geffen School of Medicine, Los Angeles, California.
authors: Ming
authors: M
authors: Ming
authors: Division of Digestive Diseases, Department of Medicine, David Geffen School of Medicine, Los Angeles, California.
authors: Michelle
authors: M
authors: Mellon
authors: Division of Digestive Diseases, Department of Medicine, David Geffen School of Medicine, Los Angeles, California. CURE: Digestive Diseases Research Center, University of California at Los Angeles, Los Angeles, California.
authors: Steven H
authors: SH
authors: Young
authors: Division of Digestive Diseases, Department of Medicine, David Geffen School of Medicine, Los Angeles, California.
authors: Liang
authors: L
authors: Han
authors: Division of Digestive Diseases, Department of Medicine, David Geffen School of Medicine, Los Angeles, California. CURE: Digestive Diseases Research Center, University of California at Los Angeles, Los Angeles, California.
authors: James
authors: J
authors: Sinnet-Smith
authors: Division of Digestive Diseases, Department of Medicine, David Geffen School of Medicine, Los Angeles, California. CURE: Digestive Diseases Research Center, University of California at Los Angeles, Los Angeles, California. Molecular Biology Institute, University of California at Los Angeles, Los Angeles, California. erozengurt@mednet.ucla.edu.
authors: Enrique
authors: E
authors: Rozengurt
mesh_terms: D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D002352:Carrier Proteins / Q000235:genetics; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004357:Drug Synergism; D066246:ErbB Receptors; D055785:Gene Knockdown Techniques; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D000076225:Mechanistic Target of Rapamycin Complex 2; D009025:Morpholines / Q000494:pharmacology; D046912:Multiprotein Complexes / Q000037:antagonists & inhibitors*; D010190:Pancreatic Neoplasms / Q000235:genetics / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011743:Pyrimidines / Q000494:pharmacology; D011804:Quinolines / Q000494:pharmacology; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; D017526:Receptor, IGF Type 1; D011972:Receptor, Insulin / Q000378:metabolism; D017451:Receptors, Somatomedin / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors*; D014227:Triazines / Q000494:pharmacology
chemical_list: C569670:1-(4-((2-(2-aminopyrimidin-5-yl)-7-methyl-4-morpholinothieno(3,2-d)pyrimidin-6-yl)methyl)piperazin-1-yl)-2-hydroxypropan-1-one; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002352:Carrier Proteins; C000597236:IGF1R protein, human; D007093:Imidazoles; D009025:Morpholines; D046912:Multiprotein Complexes; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors; D011743:Pyrimidines; D011804:Quinolines; C492571:RICTOR protein, human; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; D017451:Receptors, Somatomedin; D014227:Triazines; C549060:gedatolisib; D066246:ErbB Receptors; D017526:Receptor, IGF Type 1; D011972:Receptor, Insulin; D000076225:Mechanistic Target of Rapamycin Complex 2; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; C531198:dactolisib