DISEASE CHARACTERISTICS:

• Histologically confirmed malignant glioma of 1 of the following types:

  • Anaplastic astrocytoma
  • Anaplastic oligodendroglioma
  • Glioblastoma multiforme

• Progressive or recurrent disease after prior radiotherapy with or without chemotherapy

  • Low-grade glioma that progressed after prior radiotherapy with or without chemotherapy and is found to be high-grade glioma after biopsy allowed
  • No more than 2 prior treatment regimens
• Measurable disease by CT scan or MRI
• Documented absence of methylthioadenosine phosphorylase (MTAP) on fixed tumor specimens

PATIENT CHARACTERISTICS:

Age

• 18 and over

Performance status

• Karnofsky 60-100%

Life expectancy

• Not specified

Hematopoietic

• Absolute neutrophil count ≥ 1,500/mm^3
• Platelet count ≥ 100,000/mm^3

Hepatic

• Bilirubin ≤ 1.5 mg/dL
• Transaminases ≤ 4 times upper limit of normal

Renal

• Creatinine ≤ 1.5 mg/dL

Other

• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective barrier contraception before, during, and for 4 weeks after study participation
• Mini mental state exam score of ≥ 15
• No psychological or sociological condition, addictive disorder, or family problem that would preclude study compliance
• No other malignancy within the past 5 years except curatively treated basal cell or squamous cell skin cancer or carcinoma in situ of the cervix or breast
• No concurrent serious infection or medical illness that would preclude study participation

PRIOR CONCURRENT THERAPY:

Biologic therapy

• No concurrent prophylactic growth factors (e.g., filgrastim [G-CSF] or sargramostim [GM-CSF])

Chemotherapy

• See Disease Characteristics
• At least 3 weeks since prior chemotherapy (6 weeks for nitrosoureas)

Endocrine therapy

• Must be maintained on a stable or lower corticosteroid regimen from the time of the baseline scan until the start of study treatment
• No concurrent steroids as antiemetics

Radiotherapy

• See Disease Characteristics
• At least 3 months since prior radiotherapy

Surgery

• Not specified

Other

• Recovered from prior therapy
• More than 10 days since prior anticonvulsant drugs that induce hepatic metabolic enzymes
• No other concurrent investigational agents