Abstract PD01-05: Analysis of patients with ER-positive breast tumors treated with neoadjuvant aromatase inhibition identifies chemokine receptors as potential modulators of endocrine resistance
Authors: Ribas R , Ghazoui Z , Dowsett M , Martin L-A 
Published: August 2014

Background: Most breast cancers (BC) at primary diagnosis are estrogen receptor positive (ER+). Estrogen (E) mediates its effects by binding to the ER. Therapies targeting the estrogenic stimulation of tumor growth reduce mortality from ER+ BC. However, resistance remains a clinical problem. To identify molecular mechanisms associated with early resistance to E-deprivation, we overlaid global gene transcription data from patients treated with neoadjuvant anastrazole with those from MCF7 cells adapted to long-term E-deprivation (LTED).

Methods: Global gene expression and Ki67 data were available from 81 postmenopausal women with ER+ early BC, at baseline and 2-weeks post anastrazole treatment. Genes, that changed expression in response to anastrozole, were identified using multiple testing corrected multi-group analyses. In vitro global gene expression was available from MCF7 cells adapted to LTED. Functional consequence of target genes on proliferation, ER-mediated transcription and downstream cell signaling was assessed using siRNA.

Results: Overlay of genes that predicted for a poor change in Ki67 in patients treated with anastrazole (p &lt; 0.01) with those from LTED cells (p &lt; 0.001) identified 32 genes of interest. Genes associated with inflammation and immunity such as chemokine receptors (CXCR) were highlighted as potential biomarkers of poor response. LTED cells showed a 17-fold higher level of CXCR7 and 1.5-fold higher level of CXCR4 versus wt-MCF7. High CXCR7 but not CXCR4 was associated with reduced relapse free survival in ER+ BC patients in 4 clinical public data sets. SiRNA knockdown of CXCR4 had no specific effect on the proliferation of wt-MCF7 or LTED cells. In contrast, siCXCR7 significantly inhibited the proliferation of the LTED cells versus wt-MCF7. Furthermore, LTED cells were inhibited in a dose-dependent manner by CXC733, a CXCR7 antagonist, whilst wt-MCF7 cells were not. We hypothesized CXCR7 via BCL2 may lead to pro-survival signals. However, siCXCR7 had a minimal effect on BCL2 expression in LTED cells and did not increase apoptosis. Of note, siCXCR7 significantly decreased expression of cyclinD1, CDK4 and phosphorylated-Rb in LTED cells but not wt MCF7 ± estradiol, indicating a likely role in cell cycle arrest. As LTED cells require ER for proliferation, we hypothesized CXCR7 was required for ER-transactivation. SiCXCR7 significantly inhibited ER-mediated transcription of an estrogen response element linked reporter construct in LTED but not wt MCF7. Previously CDK4 mediated phosphorylation of PELP1, a major coactivator of ER, was shown to be critical for its interaction with ER. Of note, siCXCR7 decreased association between ER and PELP1 in LTED cells and was associated with a decrease in expression of the endogenous E-regulated gene TFF1.

Conclusion: We have demonstrated for the first time that CXCR7 expression associates with poor relapse free survival in ER+ BC patients. Our in vitro model of endocrine resistance, provided evidence of novel cross talk between ER and CXCR7 leading to ligand-independent ER-mediated transactivation via PELP1. These data highlight the role of CXCR7 as a potential therapeutic target in endocrine resistant BC.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr PD01-05.