title: Targeting cancer stem cells in glioblastoma multiforme using mTOR inhibitors and the differentiating agent all-trans retinoic acid.
abstract: Glioblastoma multiforme (GBM), the most aggressive primary brain tumor, portends a poor prognosis despite current treatment modalities. Recurrence of tumor growth is attributed to the presence of treatment-resistant cancer stem cells (CSCs). The targeting of these CSCs is therefore essential in the treatment of this disease. Mechanistic target of rapamycin (mTOR) forms two multiprotein complexes, mTORC1 and mTORC2, which regulate proliferation and migration, respectively. Aberrant function of mTOR has been shown to be present in GBM CSCs. All-trans retinoic acid (ATRA), a derivative of retinol, causes differentiation of CSCs as well as normal neural progenitor cells. The purpose of this investigation was to delineate the role of mTOR in CSC maintenance, and to establish the mechanism of targeting GBM CSCs using differentiating agents along with inhibitors of the mTOR pathways. The results demonstrated that ATRA caused differentiation of CSCs, as demonstrated by the loss of the stem cell marker Nestin. These observations were confirmed by western blotting, which demonstrated a time-dependent decrease in Nestin expression following ATRA treatment. This effect occurred despite combination with mTOR (rapamycin), PI3K (LY294002) and MEK1/2 (U0126) inhibitors. Expression of activated extracellular signal-regulated kinase 1/2 (pERK1/2) was enhanced following treatment with ATRA, independent of mTOR pathway inhibitors. Proliferation of CSCs, determined by neurosphere diameter, was decreased following treatment with ATRA alone and in combination with rapamycin. The motility of GBM cells was mitigated by treatment with ATRA, rapamycin and LY29002 alone. However, combination treatment augmented the inhibitory effect on migration suggesting synergism. These findings indicate that ATRA-induced differentiation is mediated via the ERK1/2 pathway, and underscores the significance of including differentiating agents along with inhibitors of mTOR pathways in the treatment of GBM.
authors.affiliation: Department of Neurosurgery, New York Medical College, Valhalla, NY 10595, USA.
authors.forename: Marissa D
authors.initials: MD
authors.lastname: Friedman
authors.forename: Dhruve S
authors.initials: DS
authors.lastname: Jeevan
authors.forename: Michael
authors.initials: M
authors.lastname: Tobias
authors.forename: Raj
authors.initials: R
authors.lastname: Murali
authors.forename: Meena
authors.initials: M
authors.lastname: Jhanwar-Uniyal
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D001932:Brain Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D002070:Butadienes / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D002867:Chromones / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000096:biosynthesis / Q000187:drug effects; D005909:Glioblastoma / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D006801:Humans; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors; D000076222:Mechanistic Target of Rapamycin Complex 1; D000076225:Mechanistic Target of Rapamycin Complex 2; D009025:Morpholines / Q000494:pharmacology; D046912:Multiprotein Complexes / Q000037:antagonists & inhibitors; D014411:Neoplastic Stem Cells / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D064231:Nestin / Q000096:biosynthesis / Q000378:metabolism; D009570:Nitriles / Q000494:pharmacology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors; D014212:Tretinoin / Q000494:pharmacology*
chemical_list: D000903:Antibiotics, Antineoplastic; D002070:Butadienes; D002867:Chromones; D004791:Enzyme Inhibitors; D009025:Morpholines; D046912:Multiprotein Complexes; D064231:Nestin; D009570:Nitriles; D000081082:Phosphoinositide-3 Kinase Inhibitors; C113580:U 0126; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D014212:Tretinoin; D000076222:Mechanistic Target of Rapamycin Complex 1; D000076225:Mechanistic Target of Rapamycin Complex 2; D058570:TOR Serine-Threonine Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D048369:MAP Kinase Kinase 1; D020123:Sirolimus