Inclusion Criteria:

• 18 years of age or older.
• Written informed consent has been provided and documented.
• Primary malignant or metastatic brain tumor that is either asymptomatic or symptomatic patients with the life expectancy estimation of 3 months or more
• A pretreatment MRI brain scan must identify at least 1 dominant tumor lesion and related PBE that is radiologically (or visibly) distinct from the main tumor mass; the combined tumor-edema lesion must be > 2 cm in longest diameter (for at least 1 slice) and visible in 3 consecutive, 4 mm sections on MRI.
• No dexamethasone or anti-angiogenic treatment for at least 14 days prior to the Baseline and throughout the study.
• A Karnofsky Performance Score > 60 at Screening (Visit 1) and at Baseline
• A negative serum pregnancy test at the Screening (Visit 1) is required for women of childbearing potential.

Exclusion Criteria:

• • Low-grade gliomas, recurrent gliomas, suspected lymphoma, or known human immunosuppressive virus (HIV) infection.

  • Patients requiring surgery, radiosurgery or radiation surgery therapy
  • Patients experiencing severe symptoms related to PBE
  • Patients where MRI is contraindicated for any reason.
  • Signs and/or symptoms of relatively severe cerebral herniation.
  • Concurrent enrollment in any other investigational drug or device study, or plan to enroll in such a study during the 3 to 4 weeks of study treatment.
  • Systemic corticosteroid use (with the exception of inhalers for asthma).
  • Use of dexamethasone (eg, as an anti-emetic) during screening or during the study
  • Use of anti-angiogenic/anti-vascular endothelial growth factor (VEGF) therapy or anticonvulsant therapy (if patient's liver function tests (LFTs) are > 3 times upper limit of normal) 14 days prior to randomization
  • Serious concomitant cardiovascular, pulmonary, renal, gastrointestinal, or endocrine metabolic disease, which in the opinion of the Investigator or the Medical Monitor, would put the patient as unusual risk during study participation.
  • Known renal insufficiency or screening glomerular filtration rate (GFR) < 60 mL/min/1.73 m2.
  • Central nervous system infection, human immunosuppressive virus (HIV) positive or ongoing infectious process.
  • For female patients: pregnancy, breastfeeding or refusal to practice birth control if of childbearing potential during the study.
  • Inability of the patient to follow the treatment regimen.
  • Known history of methionine allergy.