title: Targeted inhibition of mTORC1 and mTORC2 by active-site mTOR inhibitors has cytotoxic effects in T-cell acute lymphoblastic leukemia.
abstract: The mammalian Target Of Rapamycin (mTOR) serine/threonine kinase belongs to two multi-protein complexes, referred to as mTORC1 and mTORC2. mTOR-generated signals have critical roles in leukemic cell biology by controlling mRNA translation of genes that promote proliferation and survival. However, allosteric inhibition of mTORC1 by rapamycin has only modest effects in T-cell acute lymphoblastic leukemia (T-ALL). Recently, ATP-competitive inhibitors specific for the mTOR kinase active site have been developed. In this study, we have explored the therapeutic potential of active-site mTOR inhibitors against both T-ALL cell lines and primary samples from T-ALL patients displaying activation of mTORC1 and mTORC2. The inhibitors affected T-ALL cell viability by inducing cell-cycle arrest in G(0)/G(1) phase, apoptosis and autophagy. Western blot analysis demonstrated a Ser 473 Akt dephosphorylation (indicative of mTORC2 inhibition) and a dephosphorylation of mTORC1 downstream targets. Unlike rapamycin, we found a marked inhibition of mRNA translation in T-ALL cell lines treated with active-site mTOR inhibitors. The inhibitors strongly synergized with both vincristine and the Bcl-2 inhibitor, ABT-263. Remarkably, the drugs targeted a putative leukemia-initiating cell sub-population (CD34(+)/CD7(-)/CD4(-)) in patient samples. In conclusion, the inhibitors displayed remarkable anti-leukemic activity, which emphasizes their future development as clinical candidates for therapy in T-ALL.
authors.affiliation: Department of Human Anatomy, University of Bologna, Bologna, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Evangelisti
authors.forename: F
authors.initials: F
authors.lastname: Ricci
authors.forename: P
authors.initials: P
authors.lastname: Tazzari
authors.forename: G
authors.initials: G
authors.lastname: Tabellini
authors.forename: M
authors.initials: M
authors.lastname: Battistelli
authors.forename: E
authors.initials: E
authors.lastname: Falcieri
authors.forename: F
authors.initials: F
authors.lastname: Chiarini
authors.forename: R
authors.initials: R
authors.lastname: Bortul
authors.forename: F
authors.initials: F
authors.lastname: Melchionda
authors.forename: P
authors.initials: P
authors.lastname: Pagliaro
authors.forename: A
authors.initials: A
authors.lastname: Pession
authors.forename: J A
authors.initials: JA
authors.lastname: McCubrey
authors.forename: A M
authors.initials: AM
authors.lastname: Martelli
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D001343:Autophagy / Q000187:drug effects*; D015153:Blotting, Western; D020134:Catalytic Domain; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D005434:Flow Cytometry; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D046912:Multiprotein Complexes; D010766:Phosphorylation / Q000187:drug effects; D054218:Precursor T-Cell Lymphoblastic Leukemia-Lymphoma / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D011506:Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: C493245:CRTC2 protein, human; D007166:Immunosuppressive Agents; D046912:Multiprotein Complexes; D047428:Protein Kinase Inhibitors; D011506:Proteins; D012333:RNA, Messenger; D014157:Transcription Factors; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus