title: Pan-mammalian target of rapamycin (mTOR) inhibitor AZD8055 primes rhabdomyosarcoma cells for ABT-737-induced apoptosis by down-regulating Mcl-1 protein.
abstract: The PI3K/mammalian Target of Rapamycin (mTOR) pathway is often aberrantly activated in rhabdomyosarcoma (RMS) and represents a promising therapeutic target. Recent evaluation of AZD8055, an ATP-competitive mTOR inhibitor, by the Preclinical Pediatric Testing Program showed in vivo antitumor activity against childhood solid tumors, including RMS. Therefore, in the present study, we searched for AZD8055-based combination therapies. Here, we identify a new synergistic lethality of AZD8055 together with ABT-737, a BH3 mimetic that antagonizes Bcl-2, Bcl-xL, and Bcl-w but not Mcl-1. AZD8055 and ABT-737 cooperate to induce apoptosis in alveolar and embryonal RMS cells in a highly synergistic fashion (combination index < 0.2). Synergistic induction of apoptosis by AZD8055 and ABT-737 is confirmed on the molecular level, as AZD8055 and ABT-737 cooperate to trigger loss of mitochondrial membrane potential, activation of caspases, and caspase-dependent apoptosis that is blocked by the pan-caspase inhibitor Z-VAD-fmk. Similar to AZD8055, the PI3K/mTOR inhibitor NVP-BEZ235, the PI3K inhibitor NVP-BKM120 and Akt inhibitor synergize with ABT-737 to trigger apoptosis, whereas no cooperativity is found for the mTOR complex 1 inhibitor RAD001. Interestingly, molecular studies reveal a correlation between the ability of different PI3K/mTOR inhibitors to potentiate ABT-737-induced apoptosis and to suppress Mcl-1 protein levels. Importantly, knockdown of Mcl-1 increases ABT-737-induced apoptosis similar to AZD8055/ABT-737 cotreatment. This indicates that AZD8055-mediated suppression of Mcl-1 protein plays an important role in the synergistic drug interaction. By identifying a novel synergistic interaction of AZD8055 and ABT-737, our findings have important implications for the development of molecular targeted therapies for RMS.
authors.affiliation: From the Institute for Experimental Cancer Research in Pediatrics, Goethe University Frankfurt, Komturstrasse 3a, 60528 Frankfurt, Germany.
authors.forename: Ellen
authors.initials: E
authors.lastname: Preuss
authors.forename: Manuela
authors.initials: M
authors.lastname: Hugle
authors.forename: Romy
authors.initials: R
authors.lastname: Reimann
authors.forename: Marcel
authors.initials: M
authors.lastname: Schlecht
authors.forename: Simone
authors.initials: S
authors.lastname: Fulda
mesh_terms: D000970:Antineoplastic Agents / Q000008:administration & dosage; D017209:Apoptosis / Q000187:drug effects; D001713:Biphenyl Compounds / Q000008:administration & dosage*; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000187:drug effects; D004357:Drug Synergism; D055785:Gene Knockdown Techniques; D006801:Humans; D000076222:Mechanistic Target of Rapamycin Complex 1; D000076225:Mechanistic Target of Rapamycin Complex 2; D009025:Morpholines / Q000008:administration & dosage*; D046912:Multiprotein Complexes / Q000037:antagonists & inhibitors; D064549:Myeloid Cell Leukemia Sequence 1 Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D009596:Nitrophenols / Q000008:administration & dosage*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010879:Piperazines / Q000008:administration & dosage; D047428:Protein Kinase Inhibitors / Q000008:administration & dosage; D012208:Rhabdomyosarcoma / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D015398:Signal Transduction / Q000187:drug effects; D013449:Sulfonamides / Q000008:administration & dosage*; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors*
chemical_list: C501332:ABT-737; D000970:Antineoplastic Agents; D001713:Biphenyl Compounds; C579095:MCL1 protein, human; D009025:Morpholines; D046912:Multiprotein Complexes; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009596:Nitrophenols; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010879:Piperazines; D047428:Protein Kinase Inhibitors; D013449:Sulfonamides; C546624:(5-(2,4-bis((3S)-3-methylmorpholin-4-yl)pyrido(2,3-d)pyrimidin-7-yl)-2-methoxyphenyl)methanol; C546842:MTOR protein, human; D000076222:Mechanistic Target of Rapamycin Complex 1; D000076225:Mechanistic Target of Rapamycin Complex 2; D058570:TOR Serine-Threonine Kinases; D020169:Caspases
keywords: Apoptosis; Cancer; Cell Death; Rhabdomyosarcoma; mTOR