title: Herceptin sensitizes ErbB2-overexpressing cells to apoptosis by reducing antiapoptotic Mcl-1 expression.
abstract: OBJECTIVE
  Monoclonal antibodies, such as herceptin and trastuzumab, against the epidermal growth factor receptor ErbB2 (also known as HER2/neu) are an effective therapy for breast cancer patients with overexpression of ErbB2. Herceptin, in combination with standard chemotherapy, such as taxol or etoposide, gives a synergistically apoptotic response in breast tumors.
  
  
  METHODS
  The mechanism underlying this synergy between chemotherapy and herceptin treatment is not well understood. Herein, we have determined that addition of herceptin, sensitized breast cancer cell lines MDA-MB-231 and MCF-7 to etoposide- or taxol-induced apoptosis.
  
  
  RESULTS
  This treatment resulted in reduced expression of ErbB2 and the antiapoptotic Bcl-2 family member Mcl-1 in MDA-MB-231 cells. Using antisense oligonucleotides against Mcl-1, MDA-MB-231 cells were rendered sensitive to etoposide-induced apoptosis similar to herceptin, but combined treatment of antisense against Mcl-1 and herceptin failed to give a significant increase in apoptosis. In 29 human breast tumors immunostained for ErbB2 and Mcl-1, we found that when ErbB2 was overexpressed, there was a corresponding increase in Mcl-1 expression.
  
  
  CONCLUSIONS
  Using murine fibroblasts that express human ErbB2, but no other ErbB family member (NE2), these cells showed resistance to both taxol- and etoposide-induced apoptosis compared with parental cells. In addition, NE2 cells preferentially express the antiapoptotic Bcl-2 family member Mcl-1 compared with parental cells, and treatment with herceptin reduces Mcl-1 expression. Taken together, these results suggest that herceptin sensitizes ErbB2-overexpressing cells to apoptosis by reducing antiapoptotic Mcl-1 protein levels.
authors.affiliation: Manitoba Institute of Cell Biology, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: Elizabeth S
authors.initials: ES
authors.lastname: Henson
authors.forename: Xiaojie
authors.initials: X
authors.lastname: Hu
authors.forename: Spencer B
authors.initials: SB
authors.lastname: Gibson
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D061067:Antibodies, Monoclonal, Humanized; D017209:Apoptosis / Q000187:drug effects*; D045744:Cell Line, Tumor; D005047:Etoposide / Q000037:antagonists & inhibitors / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D018734:Genes, erbB-2 / Q000187:drug effects* / Q000235:genetics; D006801:Humans; D051379:Mice; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D020320:Oligoribonucleotides, Antisense / Q000494:pharmacology; D017239:Paclitaxel / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D012680:Sensitivity and Specificity; D000068878:Trastuzumab; D014407:Tumor Cells, Cultured
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; C579094:Mcl1 protein, mouse; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins; D020320:Oligoribonucleotides, Antisense; D019253:Proto-Oncogene Proteins c-bcl-2; D005047:Etoposide; D000068878:Trastuzumab; D017239:Paclitaxel