Abstract 1496: The role of endothelial ACKR1 in breast cancer metastasis

Abstract Background: Tumor cells can co-opt mechanisms of leukocyte extravasation. Atypical Chemokine Receptor 1 (ACKR1) expression in endothelial cells has an established role in promoting leukocyte extravasation; however, the potential for endothelial ACKR1 to facilitate the metastatic process through the extravasation of tumor cells has not been studied. Methods: To understand ACKR1 function, we investigated endothelial ACKR1 expression at the distant metastatic site of the lung, a common site of breast cancer metastasis. We analyzed lung endothelial ACKR1 expression using immunofluorescent staining of lung vasculature during tumor progression in immunocompetent mice bearing orthotopically implanted E0771.LMB breast tumor cells. We assessed the timing of metastatic tumor cell arrival in the lung and evaluated the spatial relationship between disseminated tumor cells and ACKR1-positive vessels. To investigate secreted tumor factors that may mediate ACKR1 regulation in the lung, we performed intratracheal injections of TNF-alpha. We developed an endothelial cell specific ACKR1 conditional knockout mouse model (ACKR1 ECKO) to understand the impact of endothelial ACKR1 on primary tumor growth and subsequent lung metastasis in breast cancer. Results: Our results reveal a significant upregulation of ACKR1 in the lung endothelium of mice implanted with breast cancer cells in the mammary fat pad. Tumor-dependent ACKR1 expression was specifically localized to pulmonary venule endothelium, a common site of leukocyte and tumor cell extravasation. Lung endothelial ACKR1 expression became evident by day 13 after implantation, persisting through endpoint at day 28. Notably, ACKR1 upregulation occurred prior to tumor cell arrival in lungs of tumor bearing mice. We observed spatial clustering of disseminated tumor cells in proximity to ACKR1-positive vessels, implying a preferential site of tumor cell extravasation. In the absence of primary tumors, intratracheal delivery of TNF-alpha induced ACKR1 expression within lungs. When tumors were orthotopically implanted into our ACKR1 ECKO mouse model, we observed a marked decrease in lung metastases compared to control mice. Conclusion/Future Directions: We have determined that pulmonary ACKR1 expression is induced by breast tumors, and vessels expressing ACKR1 appear to act as entry points for lung metastasis. Loss of endothelial ACKR1 reduced metastasis, suggesting that endothelial ACKR1 regulates tumor cell extravasation at distant metastatic sites. We will upregulate lung endothelial ACKR1 expression and directly test its requirement for extravasation using an intravenous tumor cell injection metastasis model. Citation Format: Samuel Tanner Roach, Rishi Patel, Serena Thomas, Chinwe Ewenighi-Amankwah, Joseph Dufraine, L A. Naiche, Jan Kitajewski. The role of endothelial ACKR1 in breast cancer metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1496.