Mifepristone-induced tumor regression in C4-HD tumors

Comparison of gene expression data between control and MFP-treated C4-HD tumors. The role of active antitumor immunity in hormone receptor positive (HR+) breast cancer has been historically underlooked. The aim of this study was to determine the contribution of the immune system to antiprogestin-induced tumor growth inhibition using a hormone-dependent breast cancer model. BALB/c-GFP+ bone marrow (BM) cells were transplanted into immunodeficient NSG mice to generate an immunocompetent NSG/BM-GFP+ (NSG-R) mouse model. Treatment with the antiprogestin Mifepristone (MFP) inhibited growth of 59-2-HI tumors with similar kinetics in both animal models. Interestingly, MFP treatment reshaped the tumor microenvironment, enhancing the production of proinflammatory cytokines and chemokines. Tumors in MFP-treated immunocompetent mice showed increased infiltration of F4/80+ macrophages, NK, and CD8 T cells, displaying a central memory phenotype. Mechanistically, MFP induced immunogenic cell death in vivo and in vitro, as depicted by the expression and subcellular localization of the alarmins calreticulin and HMGB-1 and the induction of an immunogenic cell death gene program. Moreover, MFP-treated tumor cells efficiently activated immature dendritic cells, evidenced by enhanced expression of MHC-II and CD86, and induced a memory T cell response, attenuating tumor onset and growth after re-challenge. Finally, MFP treatment increased the sensitivity of HR+ 59-2-HI tumor to PD-L1 blockade, suggesting that antiprogestins may improve immunotherapy response rates. These results contribute to a better understanding of the mechanisms underlying the antitumor effect of hormonal treatment and the rational design of therapeutic combinations based on endocrine and immunomodulatory agents in HR+ breast cancer. Gene expression profiling of control and MFP-treated C4-HD tumors (12-24-48hs). The gene expression profiles of two independent replicates per condition were compared by microarray analysis. For this analysis, we used C4-HD tumors growing in MPA treated BALB/c mice. When tumors reached 50 mm , MPA pellets were removed by surgery and replaced by a sc. MFP pellet (10 mg/kg/day). Two days later, tumors were excised and fixed in formalin. RNA was extracted from formalin-fixed paraffin-embedded (FFPE) tumors using the RNeasy FFPE kit (Qiagen; Germantown, MD). RNA integrity was assessed with an Agilent Bioanalyzer 2100 (Agilent Technologies, Palo Alto, CA, USA). RNA was then labeled and hybridized to Gene Chip Mouse Genome 430 2.0 (Affymetrix, Santa Clara, CA, USA) according to the manufacturer’s instructions