title: Efficacy of combined inhibition of mTOR and ERK/MAPK pathways in treating a tuberous sclerosis complex cell model.
abstract: Tuberous sclerosis complex (TSC) is an autosomal dominant tumor syndrome which afflicts multiple organs and for which there is no cure, such that TSC patients may develop severe mental retardation and succumb to renal or respiratory failure. TSC derives from inactivating mutations of either the TSC1 or TSC2 tumor suppressor gene, and the resulting inactivation of the TSC1/TSC2 protein complex causes hyperactivation of the mammalian target of rapamycin (mTOR), leading to uncontrolled cell growth and proliferation. Recent clinical trials of targeted suppression of mTOR have yielded only modest success in TSC patients. It was proposed that abrogation of a newly identified mTOR-mediated negative feedback regulation on extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) signaling pathway and on the well-documented RTK-PI3K-AKT signaling cascade could limit the efficacy of mTOR inhibitors in the treatment of TSC patients. Therefore, we speculate that dual inhibition of mTOR and ERK/MAPK pathways may overcome the disadvantage of single agent therapies and boost the efficacy of mTOR targeted therapies for TSC patients. Investigation of this hypothesis in a TSC cell model revealed that mTOR suppression with an mTOR inhibitor, rapamycin (sirolimus), led to up-regulation of ERK/MAPK signaling in mouse Tsc2 knockout cells and that this augmented signaling was attenuated by concurrent administration of a MEK1/2 inhibitor, PD98059. When compared with monotherapy, combinatorial application of rapamycin and PD98059 had greater inhibitory effects on Tsc2 deficient cell proliferation, suggesting that combined suppression of mTOR and ERK/MAPK signaling pathways may have advantages over single mTOR inhibition in the treatment of TSC patients.
authors.affiliation: Department of Physiology, Institute of Basic Medical Sciences and School of Basic Medicine, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China.
authors.forename: Ruifang
authors.initials: R
authors.lastname: Mi
authors.forename: Jianhui
authors.initials: J
authors.lastname: Ma
authors.forename: Dechang
authors.initials: D
authors.lastname: Zhang
authors.forename: Limin
authors.initials: L
authors.lastname: Li
authors.forename: Hongbing
authors.initials: H
authors.lastname: Zhang
mesh_terms: D000818:Animals; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D004195:Disease Models, Animal; D015536:Down-Regulation / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D014402:Tuberous Sclerosis / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D005419:Flavonoids; C000624653:TSC2 protein, human; C000624654:Tsc2 protein, mouse; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D011494:Protein Kinases; C546842:MTOR protein, human; C546843:mTOR protein, mouse; D058570:TOR Serine-Threonine Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D020928:Mitogen-Activated Protein Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D020123:Sirolimus