The Anti-EMMPRIN Monoclonal Antibody hMR18-mAb Induces Tumor Dormancy and Inhibits the EMT Process in Human Carcinoma Cell Lines Co-Cultured with Macrophages

Background: The epithelial-to-mesenchymal transition (EMT) process is necessary for metastasis as it enables tumor cells’ migration and invasion. In the remote organ, tumor cells can develop into metastatic lesions or arrest their proliferation and become dormant, thus suspending metastatic development. EMMPRIN is a membrane glycoprotein, implicated in cell–cell interactions, proliferation, angiogenesis, and EMT. We asked whether neutralizing EMMPRIN with the new anti-EMMPRIN monoclonal antibody hMR18-mAb can inhibit EMT. Methods: We co-cultured tumor cell lines (breast carcinoma MCF-7, MDA-MB-231, or oral squamous cell carcinoma SCC-40) together with U937 monocytic-like cells, with or without hMR18-mAb or its negative control rabbit IgG. Results: We demonstrate that depending on the initial state of the cells along the epithelial–mesenchymal axis (E/M axis), co-culture enhanced the EMT process, whereas hMR18-mAb reversed this effect. The co-culture increased EMT-inducer cytokines in all cell lines (by 2.5-fold), while hMR18-mAb reduced them (by ~55–70% in the breast cancer cells and by 81% in the SCC-40 cells). The co-culture reduced E-cadherin (by 2-fold in MCF-7 and SCC-40 cells) and increased vimentin expression (by 2–3-fold in MDA-MB-231 and SCC-40), while hMR18-mAb reverted this effect. Co-culture enhanced proliferation, migration, and angiogenic potential of the tumor cells, while hMR18-mAb reduced these by ~20%, 30–44% and ~60–80%, respectively. Co-culture reduced the standard markers of dormancy (NR2F1, p21, p27) and stemness (SOX2, Nanog) (by 30–60% in MCF-7 and SCC-40), while hMR18-mAb elevated gene expression of these markers (by 1.5–3.5-fold) in all cell lines, pushing the cells towards dormancy. Conclusions: We conclude that EMMPRIN is a gatekeeper that prevents cells from entering dormancy, and that hMR18-mAb disrupts this effect. As it is the first antibody shown to induce dormancy in tumor cells and stop the development of metastases, this could become a new therapeutic strategy to prevent and treat metastasis.