title: Hydroxychloroquine inhibits autophagy to potentiate antiestrogen responsiveness in ER+ breast cancer.
abstract: OBJECTIVE
  Estrogen receptor-α (ERα)-targeted therapies including tamoxifen (TAM) or Faslodex (ICI) are used to treat ER(+) breast cancers. Up to 50% of tumors will acquire resistance to these interventions. Autophagy has been implicated as a major driver of antiestrogen resistance. We have explored the ability of hydroxychloroquine (HCQ), which inhibits autophagy, to affect antiestrogen responsiveness.
  
  
  METHODS
  TAM-resistant MCF7-RR and ICI-resistant/TAM cross-resistant LCC9 ER(+) breast cancer cells were injected into mammary fat pads of female athymic mice and treated with TAM and/or ICI in combination with oral low-dose HCQ.
  
  
  RESULTS
  We show that HCQ can increase antiestrogen responsiveness in MCF7-RR and LCC9 cells and tumors, likely through the inhibition of autophagy. However, the combination of ICI+HCQ was less effective than HCQ alone in vivo, unlike the TAM+HCQ combination. Antiestrogen treatment stimulated angiogenesis in tumors but did not prevent HCQ effectiveness. The lower efficacy of ICI+HCQ was associated with ICI effects on cell-mediated immunity within the tumor microenvironment. The mouse chemokine KC (CXCL1) and IFNγ were differentially regulated by both TAM and ICI treatments, suggesting a possible effect on macrophage development/activity. Consistent with these observations, TAM+HCQ treatment increased tumor CD68(+) cells infiltration, whereas ICI and ICI+HCQ reduced peripheral tumor macrophage content. Moreover, macrophage elimination of breast cancer target cells in vitro was reduced following exposure to ICI.
  
  
  CONCLUSIONS
  HCQ restores antiestrogen sensitivity to resistant tumors. Moreover, the beneficial combination of TAM+HCQ suggests a positive outcome for ongoing neoadjuvant clinical trials using this combination for the treatment of ER(+) ductal carcinoma in situ lesions.
authors.affiliation: Authors' Affiliations: Department of Oncology and Lombardi Comprehensive Cancer Center, Georgetown University Medical Center, Washington, D.C.; and Department of Pathology, National Cancer Institute, NIH, Bethesda, Maryland.
authors.forename: Katherine L
authors.initials: KL
authors.lastname: Cook
authors.affiliation: Authors' Affiliations: Department of Oncology and Lombardi Comprehensive Cancer Center, Georgetown University Medical Center, Washington, D.C.; and Department of Pathology, National Cancer Institute, NIH, Bethesda, Maryland.
authors.forename: Anni
authors.initials: A
authors.lastname: Wärri
authors.affiliation: Authors' Affiliations: Department of Oncology and Lombardi Comprehensive Cancer Center, Georgetown University Medical Center, Washington, D.C.; and Department of Pathology, National Cancer Institute, NIH, Bethesda, Maryland.
authors.forename: David R
authors.initials: DR
authors.lastname: Soto-Pantoja
authors.affiliation: Authors' Affiliations: Department of Oncology and Lombardi Comprehensive Cancer Center, Georgetown University Medical Center, Washington, D.C.; and Department of Pathology, National Cancer Institute, NIH, Bethesda, Maryland.
authors.forename: Pamela Ag
authors.initials: PA
authors.lastname: Clarke
authors.affiliation: Authors' Affiliations: Department of Oncology and Lombardi Comprehensive Cancer Center, Georgetown University Medical Center, Washington, D.C.; and Department of Pathology, National Cancer Institute, NIH, Bethesda, Maryland.
authors.forename: M Idalia
authors.initials: MI
authors.lastname: Cruz
authors.affiliation: Authors' Affiliations: Department of Oncology and Lombardi Comprehensive Cancer Center, Georgetown University Medical Center, Washington, D.C.; and Department of Pathology, National Cancer Institute, NIH, Bethesda, Maryland.
authors.forename: Alan
authors.initials: A
authors.lastname: Zwart
authors.affiliation: Authors' Affiliations: Department of Oncology and Lombardi Comprehensive Cancer Center, Georgetown University Medical Center, Washington, D.C.; and Department of Pathology, National Cancer Institute, NIH, Bethesda, Maryland clarker@georgetown.edu.
authors.forename: Robert
authors.initials: R
authors.lastname: Clarke
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001343:Autophagy / Q000187:drug effects*; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D002454:Cell Differentiation / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D004958:Estradiol / Q000031:analogs & derivatives* / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000494:pharmacology; D020847:Estrogen Receptor Modulators / Q000494:pharmacology*; D005260:Female; D000077267:Fulvestrant; D006801:Humans; D006886:Hydroxychloroquine / Q000494:pharmacology*; D007124:Immunoenzyme Techniques; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008819:Mice, Nude; D011960:Receptors, Estrogen / Q000378:metabolism*; D013629:Tamoxifen / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D023041:Xenograft Model Antitumor Assays
chemical_list: D004965:Estrogen Antagonists; D020847:Estrogen Receptor Modulators; D011960:Receptors, Estrogen; D013629:Tamoxifen; D000077267:Fulvestrant; D006886:Hydroxychloroquine; D004958:Estradiol