Supplement: Targetable Mechanisms of Therapeutic Resistance in Pediatric Gliomas (FY24)

ABSTRACT Diffuse Intrinsic Pontine Glioma (DIPG) is a childhood brain cancer with a <1% survival rate. DIPG is an aggressive tumor that grows in the pons of the brain stem, which controls critical processes like heart rate, breathing, swallowing and vision. For the last 40 years, and today, the standard of care for DIPG is radiation therapy. This, at best, provides some symptom relief to patients as the tumor shrinks. However, it will inevitably regrow, and 90% of patients will die from DIPG within 2 years, and 99% will die within 5 years of diagnosis. Why the tumor invariably in every patient after radiation, despite each patient’s tumor having different genetic mutations, is an open question in the field. We believe it is related to the cell-of-origin in DIPG, or the neural stem cell. Normal neural stem cells are necessarily long-lived, and harbor survival, quiescence, and resistance mechanisms. We hypothesize that DIPG cells co- opt these survival mechanisms during the transformation process and, once the tumor is established, use them to survive radiation therapy. By defining these pathways, which should be common in all DIPG, we can establish novel drug targets that could sensitize DIPG to radiation. The goals of the project will be to 1) Define the genes and pathways that mediate radiation resistance. We will treat DIPG stem cell populations isolated from untreated, primary patient samples with radiation and track their evolution, 2) Assess the role various p53 mutations in radiation resistance—this is gene is commonly mutated in DIPG but it is not clear if it is a loss of function or altered function/potential drug target, and 3) Determine how radiation affects DIPG stem cell clones in their niche/tumor microenvironment, which can provide key survival signals to the stem cell. In total, this research extends the impact of our parent grant by addressing the major clinical issue in DIPG, radiation resistance, and approaching it using our laboratory’s unique expertise in cancer stem cells and zebrafish models. We also leveraged key collaborations to obtain patient derived cell lines from DIPG biopsy tissue, which are rare. Once drug targets are found and validated in this supplement, the PHOTACS developed in the parent grant can be easily adapted to target any protein of interest with low toxicity to the patient.