Ganglioside SSEA-4 surface expression as a marker of clonogenic, invasive and metastatic properties in Ewing sarcoma
Final Report Abstract
Carbohydrate markers of immature cells during prenatal human development can be aberrantly expressed in cancers and serve as immune targets. Here we studied expression of the globo-series ganglioside stage-specific embryonic antigen-4 (SSEA-4) and its functional significance in Ewing sarcoma, a bone cancer occurring in children and young people. We found SSEA-4 expression at low (3 of 14), moderate (8 of 14) and high densities (4 of 14) on the cell surface of all analyzed EwS cell lines and in primary EwS tumor biopsies (68%, 21 of 31) independent of molecular and clinical disease parameters. Cell surface density of SSEA-4 was unaffected during the course of in vitro cell culture. Among paired subpopulations of tumor cells with high versus low SSEA-4 expression selected from 8 individual EwS cell lines, SSEA-4high expression was significantly and consistently associated with various functional characteristics of tumor aggressiveness, including higher cell proliferation, colony formation, chemoresistance and propensity to migrate. SSEA-4lowcells within bulk populations of SSEA-4 expressing EwS cell lines regained SSEA-4 expression in continued in vitro culture and during in vivo tumor growth in a murine xenograft model. SSEA-4high expression in EwS cells was not associated with expression levels of the EWSR1-FLI1 fusion transcript or its direct targets, nor with markers of epithelial/mesenchymal plasticity. SSEA-4 specific CAR T cells specifically interacted with SSEA-4 positive EwS cells in a strictly antigen-dependent manner and exerted effective tumor cell lysis in vitro. Thus, CAR targeting of SSEA-4 could be an attractive strategy to eliminate EwS cells, including tumor cell subsets with high propensity to drive disease progression, and deserves further evaluation for clinical translation.
