A Hyper-Thrombotic State and Immunosuppression in GBM - Project Abstract: Cancer-related thrombosis is the second leading cause of death for cancer patients. Glioblastoma (GBM), the most common primary malignant brain tumor, is associated with a 30% risk of venous thromboembolism (VTE). High platelet counts and a hyper-thrombotic state have been associated with poor clinical outcome in many cancers, and while platelets are known to promote progression of other tumors, the mechanisms by which this hyper-thrombotic state drives GBM progression has not been explored. Moreover, sex-biases are well established in GBM with men being 1.6 times more likely to develop GBM and have a poorer prognosis than females. Despite this, no work has explored how sex-biases contribute to the hyper-thrombotic state in GBM. New preliminary data suggests that GBM patient platelets have an increase in PAR4 receptor mediated platelet activation. PAR receptor expression is found on platelets and T cells setting the stage for platelet – T cell interaction in the GBM TME. Our laboratory has previously shown that specific immune cell populations in the tumor microenvironment function in a sex dependent manner. Pharmacologically targeting the thrombin-PAR4 axis in murine models of GBM results in prolonged survival in females but not males and preliminary data suggest this sex-bias may be due to the platelet T-cell interaction. Aim 1 will test the hypothesis that GBM results in platelet hyperactivity leading to enhanced tumor growth. Aim 1a I will expand on my initial observations and interrogate the function of PAR1 and PAR4 receptor signal transduction using flow cytometry, confocal microscopy, and aggregometry in GBM patient and mouse bearing tumors platelets in the context of six differences. In Aim 1B, I will build on my initial observations and deplete platelets in multiple orthotopic pre- clinical models and assess overall survival and changes in the immune landscape. Aim 2 will test the hypothesis that that the thrombin-PAR4 signaling axis in GBM regulates T cell function to enhances the immunosuppressive tumor microenvironment in a sex-dependent manner. I will intracranially inject murine GBM cells into wild-type mice and treat with a PAR4 followed by subsequent immune profiling using flow cytometry and histology. Bone marrow chimera experiments will be performed to determine the relative contribution of biological sex of the immune cells versus the host on survival and to the tumor associated immune landscape. In parallel, we will assess platelet and T cell depletion studies to determine how the thrombin-PAR4 signaling axis regulates T cell function. The proposed research will provide me with a foundation in new areas including platelet biology, GBM immunology and cancer associated thrombosis. Expertise in neurobiology, platelet biology, clinical neuro- oncology, and cancer associated thrombosis from my mentors, postdoctoral advisory committee, and my lab members at the Cleveland Clinic will aid in successful completion of this proposal.
