A Study of the Safety, Dosing, and Delivery of NEO100 in Patients With Pediatric Brain Tumors

Inclusion Criteria: * Patient must have radiographically confirmed, newly diagnosed or recurrent pediatric-type high grade glioma: Diffuse Midline Glioma, H3 K27-altered; Diffuse hemispheric glioma, H3 G34-mutant, Diffuse pediatric-type HGG, grade III and IV H3-wildtype and IDH-wildtype with imaging and/or pathology consistent with a DMG, (including spinal cord tumors); or Recurrent malignant tumors involving the brainstem or posterior fossa (choroid plexus carcinoma, CNS embryonal tumors, and pineoblastoma). * Karnofsky ≥ 50 for patients \> 16 years of age or Lansky ≥ 50 for patients ≤ 16 years of age. Participants who are unable to walk because of paralysis, but who are up in a wheelchair, will be considered ambulatory for the purpose of assessing the performance score. * If clinically indicated, participants must be willing to provide adequate tissue for PK analysis, either from a surgical biopsy or needle biopsy. * Aged ≥5 to ≤18 years. * Patients recurrent or progressive disease must have recovered from all acute side effects of prior therapy. * From the projected start of scheduled study treatment, the following time periods must have elapsed: At least 7 days after last dose of a biologic agent or beyond time during which adverse events are known to occur for a biologic agent, 5 half-lives from any investigational agent, 4 weeks from cytotoxic therapy (except 23 days for temozolomide and 6 weeks from nitrosoureas), 6 weeks from antibodies, or 4 weeks (or 5 half-lives, …