DIPG-54. TREATMENT OF A PEDIATRIC PATIENT WITH AN H3.3 K27M MUTANT DIPG WITH ONC201, A SELECTIVE DRD2 ANTAGONIST

Abstract Although radiotherapy is the mainstay of treatment for children with diffuse intrinsic pontine gliomas (DIPG), fewer than 10% of patients survive past two years from diagnosis despite 30 years of clinical trials. ONC201 is an oral, selective DRD2 antagonist that induces p53-independent apoptosis and has been reported to produce a durable response in an adult with a H3 K27M mutant recurrent glioblastoma. In April 2017, a 33 month old female presented with headaches, right 6th nerve palsy and MRI findings consistent with a DIPG. A biopsy revealed an H3.3 K27M mutant glioblastoma. A patient-derived DIPG tumorsphere cell line was created from the biopsy sample and in vitro studies revealed a potent reduction in cell viability following 5 days of treatment with ONC201, with an IC50 of approximately 600nM. She received involved field irradiation (54Gy). Starting one month following irradiation, single agent, oral ONC201 125mg (11mg/kg) was given weekly on a compassionate use protocol. An MRI, 4 months later revealed stable disease. Clinically, her 6th nerve palsy and left hemiparesis have improved. She is otherwise asymptomatic. Pharmacokinetic studies are being analyzed. She has had no side effects detected. Based on our in vitro and clinical findings as well as other experience in vitro and in adults, ONC201 is currently being investigated with a phase 1 trial in pediatric patients with H3 K27M mutant gliomas.