MDB-36. SONIDEGIB, GANT61, AND VELIPARIB TREATMENT BOTH ALONE AND IN COMBINATION INCREASES RADIATION SENSITIVITY IN PEDIATRIC SONIC HEDGEHOG MEDULLOBLASTOMA

Medulloblastoma is the most common malignant brain tumor in children, accounting for 20-25% of all pediatric brain tumors. The current standard of care includes both craniospinal and focal radiation therapy which lead to negative long term consequences in the pediatric population such as bone and tissue hypoplasia, decreased neurocognitive functioning, as well as an increased risk for secondary radiation induced cancers. Thus, there is a need for novel approaches to radiation therapy that can effectively target and kill tumor cells while minimizing radiation toxicity in healthy tissue. Here, we investigate a new approach to radiation therapy relying on two classes of therapeutic agents, Sonic Hedgehog (SHH) inhibitors and Poly (ADP-ribose) Polymerase (PARP) inhibitors. The dysregulation and constitutive activation of the SHH signaling pathway accounts for ~30% of all medulloblastomas. In addition to playing a role in tumorigenesis, the SHH pathway is known to play a role in the radiation sensitivity of various cancer types. PARP1 is known to play a key role in DNA damage repair, and it has previously been shown to affect the radiation sensitivity of pediatric brain cancers including high grade glioma, medulloblastoma, and ependymoma. We hypothesize that both inhibiting the SHH pathway at Smoothened (Smo) or Gli1 and inhibiting PARP1 will enhance medulloblastoma tumor cell killing following radiation therapy. We found that in vitro treatment with Sonidegib, GANT61, and Veliparib alone without radiation was sufficient to decrease tumor cell viability and self-renewal. When followed by radiation, pre-treatment with Sonidegib, GANT61, and Veliparib, both alone and in combination, resulted in further decreased tumor cell viability and self-renewal. These data suggest that inhibition of Smo, Gli1, or PARP1 alone or in combination is a promising therapeutic strategy for increasing the radiation sensitivity of pediatric SHH medulloblastoma.