Endothelial CXCR7 regulates breast cancer metastasis

Atypical chemokine receptor CXCR7 (ACKR3) functions as a scavenger receptor for chemokine CXCL12, a molecule that promotes multiple steps in tumor growth and metastasis in breast cancer and multiple other malignancies. Although normal vascular endothelium expresses low levels of CXCR7, marked upregulation of CXCR7 occurs in tumor vasculature in breast cancer and other tumors. To investigate effects of endothelial CXCR7 in breast cancer, we conditionally deleted this receptor from vascular endothelium of adult mice, generating CXCR7ΔEND/ΔEND animals. CXCR7ΔEND/ΔEND mice appeared phenotypically normal, although these animals exhibited a modest 35±3% increase in plasma CXCL12 as compared with control. Using two different syngeneic, orthotopic tumor implant models of breast cancer, we discovered that CXCR7ΔEND/ΔEND mice had significantly greater local recurrence of cancer following resection, elevated numbers of circulating tumor cells and more spontaneous metastases. CXCR7ΔEND/ΔEND mice also showed greater experimental metastases following intracardiac injection of cancer cells. These results establish that endothelial CXCR7 limits breast cancer metastasis at multiple steps in the metastatic cascade, advancing understanding of CXCL12 pathways in tumor environments and informing ongoing drug development targeting CXCR7 in cancer.