STEM-17. THE GLIOMA STEM CELL PLATELET INTERACTION DRIVES GBM ONCOGENESIS IDENTIFYING A NOVEL THERAPEUTIC APPROACH

The effect of platelets on oncogenesis has been studied extensively in cancer metastasis, but not in glioblastoma (GBM), where metastasis is rare. Here we identify the unique crosstalk between glioma stem cells (GSCs) and platelets within GBM solid tumors that enhance disease progression. Targeting GSCs is considered a promising therapeutic approach; however, no clear method has been identified. High platelet counts have been associated with poor clinical outcome in many cancers including ovarian and endometrial cancer. While platelets are known to affect progression of other tumors, mechanisms by which platelets influence GBM oncogenesis are unknown. Immunofluorescence, qPCR, and western blot were used to evaluate the presence of GSCs and platelets and their colocalization in GBM patient tissue at University Hospitals-Seidman Cancer Center. Functional assays followed by RNA sequencing were conducted to determine the functional effect of healthy and GBM platelets on growth of patient derived, autologous GSCs. Our clinical studies suggest elevated platelet counts positively correlate with GSC proliferation and negatively correlate with overall survival in patients with GBM. Patients with high platelet counts ( >350k/µl) had a median survival time of 9 months compared to 16 months median survival for patients with normal platelet count (150-350/µl) (p<0.05). We demonstrate platelet and GSC co-localization in GBM solid tissue and platelet exposure to patient derived GSCs cell lines results in a ≥ 3-fold increase in GSC proliferation compared to GSCs not exposed to platelets (p<0.0005). Similarly we found that platelets increased the self-renewing capacity by enhancing the average sphere size (p < 0.005), and increasing the GSC “Stem-like” transcriptional pattern (P< 0.05). Conversely, pharmacologic inhibition of platelet activation reversed the effect of platelets on GSC proliferation (p ranging from 0.05-0.005). These studies suggests the platelet-GSC interactions appear to stimulate GBM oncogenesis, identifying a potential therapeutic target for the treatment of GBM.