This is an open label, intra-patient dose escalation, to evaluate ADI-PEG 20, in combination with Temozolomide (TMZ) and radiation therapy (RT) in children, adolescents and young adult patients with newly diagnosed high grade glioma (HGG).

PRIMARY OBJECTIVES:

I. To evaluate the safety and estimate the RP2D of ADI-PEG 20 in combination with RT and TMZ in with children, adolescents, and young adults with newly diagnosed high-grade glioma, and the RP2D of ADI-PEG 20 during maintenance therapy with TMZ (Phase 1)

II. To assess the anti-tumor activity of the combination of ADI-PEG 20 with RT and TMZ based on progression-free survival (PFS) at 12 months for HGG histone-WT participants, 12 months for H3K27 altered DMG, and 10 months for H3G34 mutant DHG in children, adolescents, and young adult participants (Phase 2)

EXPLORATORY OBJECTIVES:

I. To assess the anti-tumor activity of the combination of ADI-PEG 20 with RT and TMZ based on overall survival at 12 months for HGG histone-WT, Histone 3 lysine 27 (H3K27) altered DMG, and Histone 3 G34-mutant (H3G34) DHGs. II. To correlate argininosuccinate synthase 1 (ASS1) and arginase tumor expression and Cerebral spinal fluid (CSF)/systemic arginine levels with survival.

III. To correlate levels of cell free DNA and other liquid biomarkers in the context of imaging response criteria and clinical outcome.

IV. To assess the microbiome in the context of imaging response criteria and clinical outcome.

V. To describe the pharmacokinetics of ADI-PEG 20 in combination with radiotherapy and TMZ and in maintenance treatment in children, adolescent and young adults with HGG.

VI. To describe the pharmacodynamics of ADI-PEG 20 in combination with radiotherapy and TMZ and in maintenance treatment in children, adolescent and young adults with HGG.

VII. To assess immunogenicity of ADI-PEG 20 in combination with radiotherapy and TMZ and in maintenance treatment in children, adolescent and young adults with HGG.

VIII. To explore the use of serial single voxel magnetic resonance (MR) spectroscopy to evaluate on-target tumor metabolic changes with the use of ADI-PEG 20.

IX. To explore sex differences in arginine metabolism in participants with newly diagnosed high-grade glioma pre and post treatment with ADI-PEG 20.

X. To characterize immune micro-environment of tumor edge in comparison to tumor core. Inclusion of normal/reactive brain tissue will be used to compare baseline reactive transcriptional signature, including immune pathways activated in peritumoral regions of the brain.

OUTLINE: Participants will be enrolled into Phase 1 (dose escalation) where the pediatric RP2D of ADI-PEG 20 in combination with radiotherapy and daily TMZ (DLT period 1) as well as ADI-PEG 20 with TMZ during maintenance (DLT period 2) will be determined through a rolling-6 design and then followed by a planned Phase 2. Participants in Phase 2 will further be analyzed by cohort based on confirmed diagnosis of the following expressed biomarkers:

Cohort 1: Participants with newly diagnosed histone wild type (WT) HGG. (N=25).

Cohort 2: Participants with newly diagnosed H3K27 altered diffuse midline gliomas (DMG). (N=30).

Cohort 3: Participants with newly diagnosed H3G34 mutant diffuse hemispheric gliomas (DHG). (N=18).

Participants can receive treatment up to 104 weeks. After completing the 30-day toxicity evaluation period, participants will enter follow-up and additional follow-up data will be documented under the Pediatric Neuro-oncology Consortium (PNOC) COMP protocol. Participants will be followed under the PNOC COMP protocol until death or withdrawal from the study.

Inclusion Criteria:

1. Participants must have histologically and molecularly confirmed newly diagnosed World Health Organization (WHO) grade 3 or 4 glioma.

   1. Phase 1: any newly diagnosed HGG (including DMG of any location and primary spinal cord tumors).

   2. Phase 2:

      • Cohort 1: Newly diagnosed non-pontine, non-spinal cord HGG histone-wildtype.
      • Cohort 2: Newly diagnosed non-pontine, non-spinal cord H3K27 altered diffuse midline glioma (DMG).
      • Cohort 3: Newly diagnosed non-pontine, non-spinal cord H3G34 mutant diffuse hemispheric glioma (DHG).

2. Prior surgery: must have undergone maximal safe resection. For patients with DMG of the pons, biopsy is sufficient.

3. Prior Therapy: Participants must NOT have received ANY prior therapy (except surgery) before enrollment on study.

4. Tumor Tissue Requirement: Participants must have sufficient tumor tissue (5-10 unstained formalin-fixed paraffin-embedded (FFPE) slides or a tumor block) for study enrollment.

5. Age:

   Phase 1:

   o 3 to <18 years of age.

   Phase 2:

   • Cohort 1: 3 to 25 years of age.
   • Cohorts 2 & 3: 3 to 39 years of age.

6. Performance Score: Karnofsky >= 50 for participants > 16 years of age and Lansky >= 50 for participants <=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.

7. Corticosteroids: Participants who are receiving dexamethasone must be on a stable or decreasing dose for at least 1 week prior to registration.

8. Organ Function Requirements:

   1. Peripheral absolute neutrophil count (ANC) >= 1000/mm^3.
   2. Platelet count >= 100,000/mm^3 (transfusion independent, defined as not receiving platelet transfusions for at least 7 days prior to enrollment).
   3. Creatinine Clearance (CrCl) or estimated glomerular filtration rate (eGFR) with cutoff value of ≥ 60 mL/min for renal function in participants with age ≥ 18 years. For participants < 18 years old, estimate eGFR using the Schwartz equation. eGFR (mL/min/1.73 m^2) = (k × Height (cm)) / Serum Creatinine (mg/dL).
   4. Total bilirubin <= 1.5 x upper limit of normal (ULN) for age; in presence of Gilbert's syndrome, total bilirubin < 3 x ULN or direct bilirubin < 1.5 x ULN.
   5. alanine aminotransferase (ALT) <= 3 x ULN.
   6. aspartate aminotransferase (AST) <= 3 x ULN.
   7. Participants with seizure disorder may be enrolled if well controlled. Participants on non-enzyme inducing anticonvulsants may be excluded pending interaction(s) with study drug.

9. The effects of ADI-PEG 20 have been shown to be associated with embryofetal toxicity in rodents. For this reason and because chemotherapy used in this trial are known to be teratogenic, women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry, for the duration of study participation and 4 months after completion of treatment. Should a woman become pregnant or suspect she is pregnant while she or her partner is participating in this study, she should inform her treating physician immediately.

10. A legal parent/guardian or participant must be able to understand, and willing to sign, a written informed consent and assent document, as appropriate.

11. Participants must enroll on PNOC COMP if PNOC COMP is open to accrual at the enrolling institution.

Exclusion Criteria:

1. Participants who have received any systemic therapy or RT, including any investigational agents.
2. History of allergic reactions attributed to compounds of similar chemical or biologic composition to ADI-PEG 20 such as pegylated compounds.
3. Phase 2 cohorts: tumors with epicenter in pons or spinal cord
4. Participants with metastatic or leptomeningeal disease. Multi-focal disease should be discussed with the study chairs,
5. Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection that would interfere with the study.
6. Women of childbearing potential must not be pregnant or breast-feeding.
7. Human immunodeficiency virus (HIV)-positive participants will be ineligible if HIV therapy regimen has not been stable for at least 4 weeks or there is intent to change the regimen within 8 weeks following enrollment, or if they are severely immunocompromised.
8. Corrected QT Interval (QTc) cutoff >480 ms.

Important note: The eligibility criteria listed above are interpreted literally and cannot be waived.

De-identified datasets will be shared with study collaborators during the course of the study.