title: The combination of gefitinib and RAD001 inhibits growth of HER2 overexpressing breast cancer cells and tumors irrespective of trastuzumab sensitivity.
abstract: BACKGROUND
  HER2-positive breast cancers exhibit high rates of innate and acquired resistance to trastuzumab (TZ), a HER2-directed antibody used as a first line treatment for this disease. TZ resistance may in part be mediated by frequent co-expression of EGFR and by sustained activation of the mammalian target of rapamycin (mTOR) pathway. Here, we assessed feasibility of combining the EGFR inhibitor gefitinib and the mTOR inhibitor everolimus (RAD001) for treating HER2 overexpressing breast cancers with different sensitivity to TZ.
  
  
  METHODS
  The gefitinib and RAD001 combination was broadly evaluated in TZ sensitive (SKBR3 and MCF7-HER2) and TZ resistant (JIMT-1) breast cancer models. The effects on cell growth were measured in cell based assays using the fixed molar ratio design and the median effect principle. In vivo studies were performed in Rag2M mice bearing established tumors. Analysis of cell cycle, changes in targeted signaling pathways and tumor characteristics were conducted to assess gefitinib and RAD001 interactions.
  
  
  RESULTS
  The gefitinib and RAD001 combination inhibited cell growth in vitro in a synergistic fashion as defined by the Chou and Talalay median effect principle and increased tumor xenograft growth delay. The improvement in therapeutic efficacy by the combination was associated in vitro with cell line dependent increases in cytotoxicity and cytostasis while treatment in vivo promoted cytostasis. The most striking and consistent therapeutic effect of the combination was increased inhibition of the mTOR pathway (in vitro and in vivo) and EGFR signaling in vivo relative to the single drugs.
  
  
  CONCLUSIONS
  The gefitinib and RAD001 combination provides effective control over growth of HER2 overexpressing cells and tumors irrespective of the TZ sensitivity status.
authors.affiliation: Experimental Therapeutics, British Columbia Cancer Agency, 675 West 10th Ave, Vancouver, BC V5Z 1L3, Canada. vdragows@bccrc.ca
authors.forename: Wieslawa H
authors.initials: WH
authors.lastname: Dragowska
authors.forename: Sherry A
authors.initials: SA
authors.lastname: Weppler
authors.forename: Mohammed A
authors.initials: MA
authors.lastname: Qadir
authors.forename: Ling Yan
authors.initials: LY
authors.lastname: Wong
authors.forename: Yannick
authors.initials: Y
authors.lastname: Franssen
authors.forename: Jennifer H E
authors.initials: JH
authors.lastname: Baker
authors.forename: Anita I
authors.initials: AI
authors.lastname: Kapanen
authors.forename: Guido J J
authors.initials: GJ
authors.lastname: Kierkels
authors.forename: Dana
authors.initials: D
authors.lastname: Masin
authors.forename: Andrew I
authors.initials: AI
authors.lastname: Minchinton
authors.forename: Karen A
authors.initials: KA
authors.lastname: Gelmon
authors.forename: Marcel B
authors.initials: MB
authors.lastname: Bally
mesh_terms: D000818:Animals; D061067:Antibodies, Monoclonal, Humanized / Q000494:pharmacology*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000009:adverse effects / Q000494:pharmacology / Q000627:therapeutic use*; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D004357:Drug Synergism; D066246:ErbB Receptors / Q000037:antagonists & inhibitors; D000068338:Everolimus; D005260:Female; D000077156:Gefitinib; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D051379:Mice; D010766:Phosphorylation / Q000187:drug effects; D011799:Quinazolines / Q000008:administration & dosage / Q000627:therapeutic use*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics*; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000627:therapeutic use; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D000068878:Trastuzumab; D023041:Xenograft Model Antitumor Assays
chemical_list: D061067:Antibodies, Monoclonal, Humanized; D066246:ErbB Receptors; D000068338:Everolimus; D000077156:Gefitinib; D011799:Quinazolines; D018719:Erb-b2 Receptor Tyrosine Kinases; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; D000068878:Trastuzumab; C546842:MTOR protein, human