title: Effect of rapamycin, an mTOR inhibitor, on radiation sensitivity of lung cancer cells having different p53 gene status.
abstract: Activation to a large extent of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway and mutations in the p53 gene are involved in lung cancer therapeutic resistance. The mammalian target of rapamycin (mTOR) acts as a downstream effector for Akt. Activation of the Akt/mTOR signal is a contributing factor to decreased radiation sensitivity. The purpose of this study was to examine whether the effect of rapamycin on radiation sensitivity is affected by cellular p53 gene status. Cellular radiation sensitivity was evaluated by using two human non-small cell lung cancer (NSCLC) cell lines with the same genetic background except for their p53 gene status (H1299/wtp53 and H1299/mp53). The cells were treated with rapamycin and/or radiation. Cell viability, cell proliferation, apoptosis, cell cycle and Akt/mTOR signaling activity were explored. Rapamycin synergistically enhanced the cytotoxicity of radiation, promoting the induction of apoptosis. Moreover, the combined treatment augmented the cytostatic effects of radiation regardless of cellular p53 gene status. Rapamycin in combination with radiation increased G1 arrest and suppressed progression to S phase in both cell lines. Furthermore, the combined treatment conduced to a prominent p53-independent down-regulation of the mTOR signal and pro-survival molecule, cyclin D1. Rapamycin can enhance the effect of radiation through the repression of pro-survival signals and the reduction in the apoptotic threshold. Taken together, inhibition of the mTOR signal may be a promising strategy for radiosensitization with no relevance to p53 gene status from the aspects of cell lethality and cell growth depression.
authors.affiliation: Department of Thoracic and Cardiovascular Surgery, School of Medicine, Nara Medical University, Kashihara, Nara 634-8521, Japan. oyjsyk@naramed-u.ac.jp
authors.forename: Yoko
authors.initials: Y
authors.lastname: Nagata
authors.forename: Akihisa
authors.initials: A
authors.lastname: Takahashi
authors.forename: Ken
authors.initials: K
authors.lastname: Ohnishi
authors.forename: Ichiro
authors.initials: I
authors.lastname: Ota
authors.forename: Takeo
authors.initials: T
authors.lastname: Ohnishi
authors.forename: Takashi
authors.initials: T
authors.lastname: Tojo
authors.forename: Shigeki
authors.initials: S
authors.lastname: Taniguchi
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D002289:Carcinoma, Non-Small-Cell Lung / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects / Q000528:radiation effects; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D019938:Cyclin D1 / Q000378:metabolism; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D008175:Lung Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011836:Radiation Tolerance / Q000187:drug effects*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects / Q000528:radiation effects; D020123:Sirolimus / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*
chemical_list: C530104:CCND1 protein, human; D047428:Protein Kinase Inhibitors; D011838:Radiation-Sensitizing Agents; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D019938:Cyclin D1; C546842:MTOR protein, human; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus