ATRT Recurrent

This clinical trial is studying a drug called SGT-53 along with radiation and another drug called Nivolumab. It's for children with brain tumors that have come back, gotten worse, or didn't get better with earlier treatments. The main questions it aims to answer are: What is the right dose of SGT-53 that children can safely receive when it is used with radiation and Nivolumab? This dose will be used in the second phase of the trial. What side effects are there of SGT-53 when it is used with radiation and Nivolumab? How does SGT-53 move through the body when given with radiation and Nivolumab? How much of the SGT-53 drug is found in the tumor tissue? This will be tested in a small group of patients? Participants will: For the first treatment cycle: Get SGT-53 twice per week Get Nivolumab every 2 weeks Receive radiation therapy during week 2 For Cycles 2-6: Get SGT-53 once per week during even cycles and twice per week during odd cycles Get Nivolumab every 2 weeks For Cycles 7+ Get both SGT-53 and Nivolumab every 2 weeks In the phase 0 part of the study, 4 participants will have genetic testing performed on their tumor tissue after receiving SGT-53. These samples will be compared to another sample taken from the skin.

Patients with with recurrent or progressive medulloblastoma, ependymoma, atypical teratoid rhabdoid tumor (ATRT), and CNS tumors of various histologies have a very poor prognosis whether treated with conventional chemotherapy, high-dose chemotherapy with stem cell rescue, irradiation or combinations of these modalities. Antiangiogenesis therapy has emerged as a new treatment option in solid malignancies. The frequent delivery of low doses of chemotherapy, referred to as metronomic or antiangiogenic chemotherapy, targets endothelial cells while reducing the toxicity associated with standard dose chemotherapy. The aim of the study is to extend therapy options for children with recurrent or progressive medulloblastoma, ependymoma, ATRT, and CNS tumors of various histologies, for whom no known curative therapy exists, by prolonging survival while maintaining good quality of life. The study will be conducted in independent strata. Stratum I (recurrent medulloblastoma): recently completed (Peyrl, 2023). Stratum II (recurrent ependymoma), III (recurrent ATRT) and V (recurrent CNS tumors of various histologies, patients with exclusion criteria and adult patients): The primary objective is to determine the response rate defined as the percentage of patients with complete response (CR), partial response (PR), stable disease (SD) or lack of recurrence at 6 months after start of antiangiogenic treatment. Stratum IV (recurrent medulloblastoma): To determine whether temozolomide, irinotecan, bevacizumab, thalidomide, celecoxib, fenofibrate, etoposide ivt, cytarabine ivt can increase the response rate after 6 months of treatment, compared with etoposid, cyclophosphamide, bevacizumab, thalidomide, celecoxib, fenofibrate, etoposide ivt, cytarabine ivt. Additionally, PFS, OS, toxicity, QoL, performance status, predictive and prognostic markers will be examined. In stratum II and III, the study will follow an open label, single arm phase 2 design, and an open label randomized two-arm phase 2 design in Stratum IV, and the exploratory Stratum V.