title: Treatment of human epidermal growth factor receptor 2-overexpressing breast cancer xenografts with multiagent HER-targeted therapy.
abstract: BACKGROUND
  Human epidermal growth factor receptor 2 (HER2) is a member of the HER signaling pathway. HER inhibitors partially block HER signaling and tumor growth in preclinical breast cancer models. We investigated whether blockade of all HER homo- and heterodimer pairs by combined treatment with several inhibitors could more effectively inhibit tumor growth in such models.
  
  
  METHODS
  Mice carrying xenograft tumors of HER2-overexpressing MCF7/HER2-18 (HER2-transfected) or BT474 (HER2-amplified) cells were treated with estrogen supplementation or estrogen withdrawal, alone or combined with tamoxifen. One to three HER inhibitors (pertuzumab, trastuzumab, or gefitinib) could also be added (n > or = 8 mice per group). Tumor volumes, HER signaling, and tumor cell proliferation and apoptosis were assessed. Results were analyzed with the t test or Wilcoxon rank sum test and survival analysis methods. All statistical tests were two-sided.
  
  
  RESULTS
  Median time to tumor progression was 21 days for mice receiving estrogen and 28 days for mice receiving estrogen and pertuzumab (difference = 7 days; P = .001; hazard ratio [HR] of progression in mice receiving estrogen and pertuzumab versus mice receiving estrogen = 0.27, 95% confidence interval [CI] = 0.09 to 0.77). Addition of gefitinib and trastuzumab to estrogen and pertuzumab increased this time to 49 days (difference = 21 days; P = .004; HR of progression = 0.28, 95% CI = 0.10 to 0.76). MCF7/HER2-18 tumors disappeared completely and did not progress (for > or = 189 days) after combination treatment with pertuzumab, trastuzumab, and gefitinib plus tamoxifen (19 of 20 mice) or plus estrogen withdrawal (14 of 15 mice). Both combination treatments induced apoptosis and blocked HER signaling and proliferation in tumor cells better than any single agent or dual combination. All BT474 tumors treated with pertuzumab, trastuzumab, and gefitinib disappeared rapidly, regardless of endocrine therapy, and no tumor progression was observed for 232 days.
  
  
  CONCLUSIONS
  Combined treatment with gefitinib, trastuzumab, and pertuzumab to block signals from all HER homo- and heterodimers inhibited growth of HER2-overexpressing xenografts statistically significantly better than single agents and dual combinations.
authors.affiliation: Breast Center, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
authors.forename: Grazia
authors.initials: G
authors.lastname: Arpino
authors.forename: Carolina
authors.initials: C
authors.lastname: Gutierrez
authors.forename: Heidi
authors.initials: H
authors.lastname: Weiss
authors.forename: Mothaffar
authors.initials: M
authors.lastname: Rimawi
authors.forename: Suleiman
authors.initials: S
authors.lastname: Massarweh
authors.forename: Lavina
authors.initials: L
authors.lastname: Bharwani
authors.forename: Sabino
authors.initials: S
authors.lastname: De Placido
authors.forename: C Kent
authors.initials: CK
authors.lastname: Osborne
authors.forename: Rachel
authors.initials: R
authors.lastname: Schiff
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000627:therapeutic use; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents / Q000627:therapeutic use; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D004815:Epidermal Growth Factor / Q000502:physiology; D066246:ErbB Receptors / Q000235:genetics*; D004967:Estrogens / Q000494:pharmacology; D005260:Female; D000077156:Gefitinib; D015972:Gene Expression Regulation, Neoplastic; D018734:Genes, erbB-2; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D011799:Quinazolines / Q000627:therapeutic use; D018719:Erb-b2 Receptor Tyrosine Kinases; D015398:Signal Transduction; D014183:Transplantation, Heterologous; D000068878:Trastuzumab
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D004967:Estrogens; D000077156:Gefitinib; D011799:Quinazolines; D018719:Erb-b2 Receptor Tyrosine Kinases; D000068878:Trastuzumab; C508053:ERBB2 protein, human; C485206:pertuzumab