Hydroxychloroquine inhibits autophagy to potentiate antiestrogen responsiveness in ER+ breast cancer (Clin Cancer Res) (original) (raw)

Purpose: Estrogen receptor-a (ERa)-targeted therapies including tamoxifen (TAM) or Faslodex (ICI) are used to treat ER þ 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 þ 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 ICIþHCQ was less effective than HCQ alone in vivo, unlike the TAMþHCQ combination. Antiestrogen treatment stimulated angiogenesis in tumors but did not prevent HCQ effectiveness. The lower efficacy of ICIþHCQ was associated with ICI effects on cell-mediated immunity within the tumor microenvironment. The mouse chemokine KC (CXCL1) and IFNg were differentially regulated by both TAM and ICI treatments, suggesting a possible effect on macrophage development/activity. Consistent with these observations, TAMþHCQ treatment increased tumor CD68 þ cells infiltration, whereas ICI and ICIþHCQ 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 TAMþHCQ suggests a positive outcome for ongoing neoadjuvant clinical trials using this combination for the treatment of ER þ ductal carcinoma in situ lesions. Clin Cancer Res; 1-11. Ó2014 AACR. 42 tumors fail to respond (de novo resistance) or acquire 43 resistance over time (2-4). 44 Autophagy is a process by which a double membrane 45 vesicle surrounds cellular contents, such as damaged orga-46 nelles and misfolded or protein aggregates, and recycles 47 the material through lysosomal degradation (5). Studies in 48 breast cancer cells show that the induction of autophagy by 49 various therapeutics is usually prosurvival (6-8). Further-50 more, TAM and ICI both induce autophagy in ER þ breast 51 cancer cells (6, 9-13). Antiestrogen-resistant cell lines 52 exhibit increased basal autophagy when compared with 53 their antiestrogen-sensitive parental cells (10). Inhibiting 54 autophagy through autophagy-related gene 5 (ATG5) 55 silencing potentiated antiestrogen-mediated cell death, 56 indicating that antiestrogen-stimulated autophagy is pro-57 survival and a critical mechanism of therapy resistance (10). 58 Analysis of publically available human datasets indicates 59 that autophagy-related genes, ATG5, ATG7, and p62 60 (SQSTM1), are elevated in early recurring breast cancer 61 when compared with breast cancer that never recurs. More-62 over, elevated p62 is significantly correlated with poor 63 survival in patients with breast cancer (Supplementary Fig. 64 S1), suggesting a role for autophagy in breast cancer reoc-65 currence (14-18).