title: Downregulation of histone H2A and H2B pathways is associated with anthracycline sensitivity in breast cancer.
abstract: BACKGROUND
  Drug resistance in breast cancer is the major obstacle to effective treatment with chemotherapy. While upregulation of multidrug resistance genes is an important component of drug resistance mechanisms in vitro, their clinical relevance remains to be determined. Therefore, identifying pathways that could be targeted in the clinic to eliminate anthracycline-resistant breast cancer remains a major challenge.
  
  
  METHODS
  We generated paired native and epirubicin-resistant MDA-MB-231, MCF7, SKBR3 and ZR-75-1 epirubicin-resistant breast cancer cell lines to identify pathways contributing to anthracycline resistance. Native cell lines were exposed to increasing concentrations of epirubicin until resistant cells were generated. To identify mechanisms driving epirubicin resistance, we used a complementary approach including gene expression analyses to identify molecular pathways involved in resistance, and small-molecule inhibitors to reverse resistance. In addition, we tested its clinical relevance in a BR9601 adjuvant clinical trial.
  
  
  RESULTS
  Characterisation of epirubicin-resistant cells revealed that they were cross-resistant to doxorubicin and SN-38 and had alterations in apoptosis and cell-cycle profiles. Gene expression analysis identified deregulation of histone H2A and H2B genes in all four cell lines. Histone deacetylase small-molecule inhibitors reversed resistance and were cytotoxic for epirubicin-resistant cell lines, confirming that histone pathways are associated with epirubicin resistance. Gene expression of a novel 18-gene histone pathway module analysis of the BR9601 adjuvant clinical trial revealed that patients with low expression of the 18-gene histone module benefited from anthracycline treatment more than those with high expression (hazard ratio 0.35, 95 % confidence interval 0.13-0.96, p = 0.042).
  
  
  CONCLUSIONS
  This study revealed a key pathway that contributes to anthracycline resistance and established model systems for investigating drug resistance in all four major breast cancer subtypes. As the histone modification can be targeted with small-molecule inhibitors, it represents a possible means of reversing clinical anthracycline resistance.
  
  
  BACKGROUND
  ClinicalTrials.gov identifier NCT00003012 . Registered on 1 November 1999.
authors: Ontario Institute for Cancer Research, MaRS Centre, 661 University Avenue, Toronto, ON, M5G 0A3, Canada. marsela.braunstein@oicr.on.ca.|Department of Immunology, University of Toronto, Toronto, ON, Canada. marsela.braunstein@oicr.on.ca.
authors: Marsela
authors: M
authors: Braunstein
authors: Ontario Institute for Cancer Research, MaRS Centre, 661 University Avenue, Toronto, ON, M5G 0A3, Canada. linda.liao@oicr.on.ca.
authors: Linda
authors: L
authors: Liao
authors: Ontario Institute for Cancer Research, MaRS Centre, 661 University Avenue, Toronto, ON, M5G 0A3, Canada. nicola.lyttle@oicr.on.ca.
authors: Nicola
authors: N
authors: Lyttle
authors: Ontario Institute for Cancer Research, MaRS Centre, 661 University Avenue, Toronto, ON, M5G 0A3, Canada. nazleen.lobo@oicr.on.ca.
authors: Nazleen
authors: N
authors: Lobo
authors: Edinburgh Cancer Research Centre, Western General Hospital, Edinburgh, UK.
authors: Karen J
authors: KJ
authors: Taylor
authors: Ontario Institute for Cancer Research, MaRS Centre, 661 University Avenue, Toronto, ON, M5G 0A3, Canada. paul.krzyzanowski@oicr.on.ca.
authors: Paul M
authors: PM
authors: Krzyzanowski
authors: Ontario Institute for Cancer Research, MaRS Centre, 661 University Avenue, Toronto, ON, M5G 0A3, Canada. irina.kalatskaya@oicr.on.ca.
authors: Irina
authors: I
authors: Kalatskaya
authors: Ontario Institute for Cancer Research, MaRS Centre, 661 University Avenue, Toronto, ON, M5G 0A3, Canada. cindy.yao@oicr.on.ca.
authors: Cindy Q
authors: CQ
authors: Yao
authors: Ontario Institute for Cancer Research, MaRS Centre, 661 University Avenue, Toronto, ON, M5G 0A3, Canada. lincoln.stein@gmail.com.|Department of Molecular Genetics, University of Toronto, Toronto, ON, Canada. lincoln.stein@gmail.com.
authors: Lincoln D
authors: LD
authors: Stein
authors: Ontario Institute for Cancer Research, MaRS Centre, 661 University Avenue, Toronto, ON, M5G 0A3, Canada. paul.boutros@oicr.on.ca.|Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada. paul.boutros@oicr.on.ca.|Department of Pharmacology & Toxicology, University of Toronto, Toronto, Canada. paul.boutros@oicr.on.ca.
authors: Paul C
authors: PC
authors: Boutros
authors: Leeds Institute of Cancer and Pathology and Cancer Research UK Centre, St James's University Hospital, Leeds, UK. c.j.twelves@leeds.ac.uk.
authors: Christopher J
authors: CJ
authors: Twelves
authors: Ontario Institute for Cancer Research, MaRS Centre, 661 University Avenue, Toronto, ON, M5G 0A3, Canada. richard.marcellus@oicr.on.ca.
authors: Richard
authors: R
authors: Marcellus
authors: Ontario Institute for Cancer Research, MaRS Centre, 661 University Avenue, Toronto, ON, M5G 0A3, Canada. john.bartlett@oicr.on.ca.|Edinburgh Cancer Research Centre, Western General Hospital, Edinburgh, UK. john.bartlett@oicr.on.ca.|Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada. john.bartlett@oicr.on.ca.
authors: John M S
authors: JM
authors: Bartlett
authors: Ontario Institute for Cancer Research, MaRS Centre, 661 University Avenue, Toronto, ON, M5G 0A3, Canada. melanie.spears@oicr.on.ca.
authors: Melanie
authors: M
authors: Spears
mesh_terms: D000328:Adult; D018943:Anthracyclines / Q000008:administration & dosage*; D017209:Apoptosis / Q000187:drug effects; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology; D002166:Camptothecin / Q000008:administration & dosage / Q000031:analogs & derivatives; D004317:Doxorubicin / Q000008:administration & dosage; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D015251:Epirubicin / Q000008:administration & dosage; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D056572:Histone Deacetylase Inhibitors / Q000008:administration & dosage; D006657:Histones / Q000096:biosynthesis* / Q000235:genetics; D006801:Humans; D000077146:Irinotecan; D061986:MCF-7 Cells; D008875:Middle Aged; D015398:Signal Transduction / Q000187:drug effects; D055815:Young Adult
chemical_list: D018943:Anthracyclines; C468783:H2AX protein, human; D056572:Histone Deacetylase Inhibitors; D006657:Histones; D015251:Epirubicin; D000077146:Irinotecan; D004317:Doxorubicin; D002166:Camptothecin