A Preclinical Model of Inflammatory Breast Cancer to Study the Involvement of CXCR4 and ACKR3 in the Metastatic Process

Inflammatory breast cancer (IBC) is an aggressive and invasive tumor, accounting for 2.5% of all breast cancer cases, and characterized by rapid progression, regional and distant metastases, younger age of onset, and lower overall survival. Presently, there are no effective therapies against IBC and a paucity of model systems. Our aim was to develop a clinically relevant IBC model that would allow investigations on the role of chemokine receptors in IBC metastasis. Primary cultures of tumor cells were isolated from pleural exudates of an IBC patient and grown as spheres or monolayers. We developed a human xenograft model where patient-derived IBC cells, stably transduced with lentiviral vectors expressing fluorescent and bioluminescent markers, were inoculated directly into the left ventricle of mice. Our in vivo data show that these IBC cells (FC-IBC02A) are able to seed and proliferate into various organs, including brain, lungs, lymph nodes, and bone, closely replicating the metastatic spread observed in IBC patients. Moreover, cells were able to generate tumors when grafted in the mammary fat pad of mice. RT-PCR and microscopy studies revealed expression of both CXCR4 and ACKR3 receptors in FC-IBC02A cells. Furthermore, CXCL12 (the endogenous chemokine ligand of these receptors) induced transendothelial migration of these cells and stimulated signaling pathways involved in cell survival and migration - an effect reduced by CXCR4 or ACKR3 antagonists. This new model can be used to develop chemokine-based pharmacological approaches against the IBC metastatic process. This work also provides the first evidence of ACKR3 expression in IBC cells.