Journal
CLINICAL CANCER RESEARCH
Volume 20, Issue 12, Pages 3222-3232Publisher
AMER ASSOC CANCER RESEARCH
DOI: 10.1158/1078-0432.CCR-13-3227
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Funding
- US Department of Health and Human Services [R01-CA131465, U54-CA149147]
- DOD Breast Cancer Research Program Postdoctoral Fellowship [BC112023]
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Purpose: Estrogen receptor-alpha (ER alpha)-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. Experimental Design: 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 IFN gamma 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. Conclusion: 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. (C) 2014 AACR.
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