Remodeling the sarcoma microenvironment by simultaneous targeting of urokinase-type plasminogen activator receptors and epidermal growth factor receptors to promote antitumor activity.

We evaluated the antitumor effects of remodeling the MC17 mouse sarcoma microenvironment (SME) by targeting urokinase-type plasminogen activator receptor (uPAR)- and epidermal growth factor receptor (EGFR)-expressing cells. Specifically, we used eBAT (a bispecific ligand-targeted toxin directed to EGFR and uPAR), and its mouse counterpart, meBAT, to ablate uPAR- and/or EGFR-expressing cells. We chose the MC17 model because the cells are resistant to eBAT, allowing us to exclusively evaluate the role of uPAR- and EGFR-expressing cells in the SME. Our results show that uPAR expression, both by the tumor cells and by the SME, was dispensable for tumor formation. However, uPAR-deficient tumors grew considerably slower than uPAR-expressing tumors. To specifically address mechanisms responsible for antitumor effects of remodeling the SME, we used uPAR-knockout bone marrow chimeras. In uPAR-replete chimeras, systemic administration of eBAT or meBAT depleted tumor-associated macrophages, increased the proportion of phagocytic myeloid cells, and promoted T cell infiltration into the SME, which was associated with delayed tumor growth. All of these effects were reduced or abrogated in uPAR-deficient bone marrow chimeras. We conclude that targeting uPAR- and EGFR-expressing stromal cells led to remodeling of the inflammatory SME, diminished tumor-associated immunosuppression, and improved survival of mice with transplantable sarcomas. SIGNIFICANCE STATEMENT: This study demonstrated that targeting urokinase-type plasminogen activator receptor- and/or epidermal growth factor receptor-expressing cells in the sarcoma microenvironment reprograms tumor-associated inflammation, leading to delayed progression in an aggressive, therapy-resistant mouse model of fibrosarcoma. The results indicate that the therapeutic benefit of remodeling the inflammatory microenvironment is achieved by making the tumors more visible to the immune system, highlighting the potential to incorporate this novel strategy into the management of advanced, treatment-refractory sarcomas.