Membrane‐type 1 matrix metalloproteinase as predictor of survival and candidate therapeutic target in Ewing sarcoma

Background Ewing sarcoma (ES) is the second most common primary bone malignancy, with an urgent need for new treatments. ES is associated with high rates of progression and relapse, driven by drug‐resistant cells capable of migration, self‐renewal and single‐cell tumorigenesis, termed cancer stem‐like cells (CSCs). Membrane‐type 1 matrix metalloproteinase (MT1‐MMP) is a membrane‐bound proteolytic enzyme, which, via direct and indirect mechanisms, digests four of the main types of collagen. This can be hijacked in malignancy for invasion and metastasis, with high expression predicting decreased survival in multiple cancers. In this study, we have examined the hypothesis that MT1‐MMP is expressed by ES cells and explored the relationship between expression and outcomes. Procedure MT1‐MMP expression in ES established cell lines, primary patient‐derived cultures and daughter ES‐CSCs was characterised by RNA sequencing, Western blotting, immunocytochemistry and flow cytometry. Immunohistochemistry was used to detect MT1‐MMP in tumour biopsies, and the relationship between expression, event‐free and overall survival examined. Results MT1‐MMP was detected at both RNA and protein levels in five of six established cell lines, all primary cultures (n = 25) and all daughter ES‐CSCs (n = 7). Immunohistochemistry of treatment‐naïve biopsy tissue demonstrated that high MT1‐MMP expression predicted decreased event‐free and overall survival (p = .017 and .036, respectively; n = 47); this was not significant in multivariate analysis. Conclusions MT1‐MMP is expressed by ES cells, including ES‐CSCs, making it a candidate therapeutic target. The level of MT1‐MMP expression at diagnosis may be considered as a prognostic biomarker if validated by retrospective analysis of a larger cohort of clinical trial samples.