title: Everolimus synergizes with gefitinib in non-small-cell lung cancer cell lines resistant to epidermal growth factor receptor tyrosine kinase inhibitors.
abstract: OBJECTIVE
  Epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) therapy is considered as one of the most important treatments for patients with advanced non-small-cell lung cancer (NSCLC). However, not all patients benefit from this therapy because of primary or acquired resistance, both of which are usually caused by the activation of alternative signaling pathways. Thus, a combination of different signaling pathway inhibitors is a promising strategy. We used the mammalian target of rapamycin (mTOR) inhibitor everolimus in combination with gefitinib in NSCLC cell lines to analyze the efficacy of this combination regimen and the underlying molecular mechanism.
  
  
  METHODS
  Acquired gefitinib-resistant cell lines, together with EGFR wild-type and mutant primary gefitinib-resistant NSCLC cell lines, were treated with everolimus alone, gefitinib alone, or the combination of the two drugs, and the effects were evaluated using cell proliferation assays. The effects of everolimus and gefitinib on the EGFR pathway in NSCLC cell lines were determined by Western blot analysis.
  
  
  RESULTS
  Combined treatment resulted in synergistic antitumor effects in gefitinib-resistant cells A549 and H1975. The combination index (CI) of cells increased with increasing dose of everolimus. Everolimus demonstrated no apparent inhibition of phosphorylated Akt (p-Akt) and phosphorylated p44/42 MAPK (p-MAPK) in H1650 cells. Additionally, in gefitinib-resistant cell lines, the combination of gefitinib and everolimus not only showed stronger inhibition of phosphorylated mTOR and phosphorylated p70S6K expression than either drug alone but also reduced the levels of p-Akt and p-MAPK in both cell lines.
  
  
  CONCLUSIONS
  Our data showed that the combination of everolimus and gefitinib exhibits dose-dependent synergism in primary and acquired gefitinib-resistant NSCLC cells. Thus, a preclinical rationale exists for the use of everolimus to enhance the efficacy of gefitinib in EGFR-TKI-resistant patients with NSCLC.
authors.affiliation: Guangdong Lung Cancer Institute, Guangdong General Hospital, Guangdong Academy of Medical Sciences, Guangzhou, China.
authors.forename: Song
authors.initials: S
authors.lastname: Dong
authors.forename: Xu-Chao
authors.initials: XC
authors.lastname: Zhang
authors.forename: Hua
authors.initials: H
authors.lastname: Cheng
authors.forename: Jian-Quan
authors.initials: JQ
authors.lastname: Zhu
authors.forename: Zhi-Hong
authors.initials: ZH
authors.lastname: Chen
authors.forename: Yi-Fang
authors.initials: YF
authors.lastname: Zhang
authors.forename: Zhi
authors.initials: Z
authors.lastname: Xie
authors.forename: Yi-Long
authors.initials: YL
authors.lastname: Wu
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000008:administration & dosage / Q000627:therapeutic use*; D015153:Blotting, Western; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy* / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm; D004357:Drug Synergism; D066246:ErbB Receptors / Q000037:antagonists & inhibitors; D000068338:Everolimus; D000077156:Gefitinib; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000473:pathology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology / Q000627:therapeutic use; D011799:Quinazolines / Q000008:administration & dosage / Q000494:pharmacology*; D015398:Signal Transduction; D020123:Sirolimus / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D047428:Protein Kinase Inhibitors; D011799:Quinazolines; D000068338:Everolimus; D066246:ErbB Receptors; D000077156:Gefitinib; D020123:Sirolimus