title: Inhibition of RET increases the efficacy of antiestrogen and is a novel treatment strategy for luminal breast cancer.
abstract: OBJECTIVE
  Recent findings suggest that combination treatment with antiestrogen and anti-RET may offer a novel treatment strategy in a subset of patients with breast cancer. We investigated the role of RET in potentiating the effects of antiestrogen response and examined whether RET expression predicted the ability for tyrosine kinase inhibitor (TKI) to affect extracellular signal-regulated kinase 1/2 (ERK1/2) activation in primary breast cancer.
  
  
  METHODS
  Growth response, ERK1/2 activation, Ki-67, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling were assessed in breast cancer cell lines in vitro and in xenografts with vandetanib and/or tamoxifen. Thirty tumors with matched normal breast tissue were evaluated for RET expression and response to TKI treatment.
  
  
  RESULTS
  Vandetanib potentiated the inhibitory effect of tamoxifen in hormone responsive (P = 0.01) and hormone insensitive (P < 0.001) estrogen receptor α (ERα)-positive breast cancer cells. Vandetanib significantly repressed tumorigenesis of MCF-7 xenografts (P < 0.001), which displayed decreased activation of ERK1/2 and AKT. Vandetanib and tamoxifen reduced the growth of established tumors with a greater effect of dual therapy compared with single agent (P = 0.003), with tamoxifen-reducing proliferative index and vandetanib-inducing apoptosis. In primary breast cancers, RET expression correlated with the ERα-positive subtype. Relative decrease in ERK1/2 phosphorylation with TKI treatment was 42% (P < 0.001) in RET-positive tumors versus 14% (P = ns) in RET-negative tumors.
  
  
  CONCLUSIONS
  Vandetanib potentiated the antigrowth effects of tamoxifen in breast cancer, which was mediated through RET activation. RET predicted response to TKI therapy with minimal effects on ERK1/2 activation in RET-negative tumors. The preclinical data support evaluation of antiestrogen in combination with TKI as a potential treatment strategy for RET-positive luminal breast cancer.
authors: Authors' Affiliations: Departments of Surgery, Pathology, Internal Medicine, and Biochemistry, University of Iowa, Iowa City, Iowa.
authors: Philip M
authors: PM
authors: Spanheimer
authors: Jung-Min
authors: JM
authors: Park
authors: Ryan W
authors: RW
authors: Askeland
authors: Mikhail V
authors: MV
authors: Kulak
authors: George W
authors: GW
authors: Woodfield
authors: James P
authors: JP
authors: De Andrade
authors: Anthony R
authors: AR
authors: Cyr
authors: Sonia L
authors: SL
authors: Sugg
authors: Alexandra
authors: A
authors: Thomas
authors: Ronald J
authors: RJ
authors: Weigel
mesh_terms: D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004357:Drug Synergism; D020847:Estrogen Receptor Modulators / Q000008:administration & dosage / Q000494:pharmacology*; D047628:Estrogen Receptor alpha / Q000378:metabolism; D005260:Female; D006801:Humans; D061986:MCF-7 Cells; D008819:Mice, Nude; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D010880:Piperidines / Q000008:administration & dosage / Q000494:pharmacology*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051096:Proto-Oncogene Proteins c-ret / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D011799:Quinazolines / Q000008:administration & dosage / Q000494:pharmacology*; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D013629:Tamoxifen / Q000008:administration & dosage; D023041:Xenograft Model Antitumor Assays
chemical_list: D020847:Estrogen Receptor Modulators; D047628:Estrogen Receptor alpha; D010880:Piperidines; D011799:Quinazolines; D013629:Tamoxifen; D051096:Proto-Oncogene Proteins c-ret; C099282:RET protein, human; D051057:Proto-Oncogene Proteins c-akt; C535150:MAPK1 protein, human; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; C452423:vandetanib