DDDR-72. Macropinocytosis as a novel target for pediatric high grade glioma therapy

Abstract Childhood brain tumors are the leading cause of cancer-related death in children, with pediatric high-grade gliomas (pHGGs) having a poor prognosis and limited therapeutic options. Pediatric gliomas differ biologically, molecularly, and clinically from their adult counterparts, causing adult treatment strategies to fail in children. To address treatment resistance, we explore one mechanism of extracellular nutrient scavenging through macropinocytosis, a nonselective endocytosis process that internalizes extracellular material for degradation and utilization. Macropinocytosis, typically restricted in normal physiology, is upregulated in certain malignancies to support tumor growth and survival. Recent studies show adult gliomas can undergo macropinocytosis, making it a potential pathway to disrupt tumor growth. Using DQ-BSA, a pH-dependent fluroprobe, as well as TMR and Oregon Green with conjugated 70kDa fluoroprobe, we have demonstrated that pHGGs, including patient-derived glioma cell lines, can undergo macropinocytosis. Enhancing micropinocytosis using a commercially available macropinocytosis stimulator, (ie. silmitasertib) results in increased cell apoptosis (95% CI: [8%, -4%]; P = 0.0014; R2 = 0.94) at 5uM silmitasertib compared to DMSO controls. In addition, silmitasertib synergizes with temozolomide to decrease cell proliferation (ZIP synergy score = 15.23). These findings suggest that pHGGs undergo macropinocytosis in vitro and targeting this pathway may be an additional avenue for therapy. In addition, to further understand the genetic signatures underlying macropinocytosis, we are currently conducting a targeted CRISPR screen with an endocytosis, macropinocytosis, phagocytosis, and lysosomal processing library.