UPAR AS A NOVEL IMMUNOTHERAPEUTIC TARGET IN RECURRENT GLIOBLASTOMA

Glioblastoma (GBM) is the common malignant brain tumor in adults, accounting for approximately 15% of all CNS tumors, and 48.6% of malignant brain tumors, with a median survival of approximately 15 months, and minimal clinical progress having been made in the past two decades. GBM is characterized by extensive inter- and intra-tumoral heterogeneity as well as an extremely immunosuppressive tumor microenvironment. Following Standard-of-Care (SoC) surgical resection and chemoradiotherapy at primary diagnosis, few therapeutic avenues exist at recurrence, owing in part due to a lack of clinically relevant targets. Data from our multi-institutional target pipeline suggests that the extracellular urokinase plasminogen activator receptor (uPAR) is significantly upregulated at recurrence on putative GBM brain tumor initiating cells (BTICs), which are believed to drive de novo tumor formation, tumor recurrence, and therapeutic resistance. uPAR plays an important role in the plasminogen activation system, and in the context of cancer, has been implicated in numerous pro-tumorigenic processes such as invasion, proliferation, epithelial-to-mesenchymal transition, and therapy resistance. In vitro, knockout of uPAR expression in recurrent GBM cells significantly reduces proliferation and sphere formation capacity, two stem-like traits associated with BTICs. Additionally, uPAR knockout cells display increased sensitivity to standard-of-care chemoradiotherapy, implicating uPAR expression in therapy resistance, as seen in recurrent disease. From these initial studies, we believe uPAR to be a clinically relevant target in recurrent GBM, and further investigation into therapeutic strategies to target uPAR-positive GBMs should be investigated further.