575 - Exploring Mechanisms of Resistance in Medulloblastoma

Poster Number: 575
Publication Number: 575.321

Sucheta Telang, University of Louisville, Medicine and Pediatrics, Louisville, KY, United States; Simone Chang, Department of Pediatrics, Louisville, KY, United States

Background: Medulloblastoma is the most common pediatric malignant brain tumor. Although current treatment protocols have improved survival, they cause devastating long-term sequelae and lack benefit in metastatic and recurrent disease where survival remains poor. Effective therapies are urgently needed to improve outcomes in this cancer.
The development of medulloblastoma is driven by dysregulated cerebellar proliferation wherein aberrant sonic hedgehog (Shh) pathway signaling is frequently implicated as a driver of aggressive growth. Poor outcomes in Shh-driven tumors have prompted the evaluation of Shh-targeting agents in their treatment but these have had limited success - likely due to resistance from upregulation of additional oncogenic pathways (e.g. Ras/MAPK and HIF-1α). These pathways stimulate glycolysis, in part by increasing the activity of the 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase enzymes (PFKFB1-4) to produce fructose-2,6-bisphosphate (F26BP) which activates a key rate-limiting glycolytic enzyme, 6-phosphofructo-1-kinase. We have found that the PFKFB4 enzyme is highly expressed in patient-derived Shh medulloblastomas. We further have demonstrated that silencing PFKFB4 in Shh-medulloblastoma cells suppressed glycolysis and proliferation in normoxia and, more markedly, in hypoxia, indicating a critical role for PFKFB4 in their growth, particularly under hypoxia. To simulate Shh antagonist resistance, we recently subjected Shh medulloblastoma cells to prolonged Shh inhibitor exposure and found PFKFB4 expression was increased in resistant cells relative to sensitive cells.

Objective: We hypothesize that PFKFB4 is critical for survival and growth of treatment-resistant medulloblastoma and that targeted PFKFB4 inhibition will significantly decrease their growth and metastasis.  

Design/Methods: See below.

Results: We compared Shh-medulloblastoma cells exposed to increasing concentrations of an Shh inhibitor for a prolonged period to inhibitor-sensitive cells. We found that inhibitor-resistant cells demonstrated increased proliferation, glycolysis, anchorage independence and PFKFB4 relative to sensitive cells and additionally showed greater sensitivity to a novel PFKFB4 inhibitor. We also observed increased expression of glycolytic enzymes in these cells and are now evaluating their metabolic alterations and expression/activity of upstream oncogenic mediators. Conclusion(s): Taken together, our data indicate that targeting PFKFB4 may be an effective therapeutic option in aggressive, treatment-resistant medulloblastoma and strongly support the examination of PFKFB4 inhibitors in these tumors.