Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically confirmed anaplastic astrocytoma, anaplastic oligodendroglioma, or
glioblastoma multiforme

- Progressive or recurrent disease previously treated with radiotherapy with or without
chemotherapy

- Prior low-grade disease that progressed to high-grade after therapy allowed

- Measurable disease by MRI or CT scan

PATIENT CHARACTERISTICS:

Age:

- 18 and over

Performance status:

- Karnofsky 60-100%

Life expectancy:

- Not specified

Hematopoietic:

- Absolute neutrophil count at least 1,500/mm^3

- Platelet count at least 100,000/mm3

- Hemoglobin at least 8.5 g/dL

Hepatic:

- Bilirubin no greater than 1.5 mg/dL

- Transaminases no greater than 4 times upper limit of normal

Renal:

- Creatinine no greater than 1.7 mg/dL

Other:

- 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 serious concurrent infection

- No other medical illness that would preclude study

- Negative pregnancy test

- Not pregnant or nursing

- Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY:

Biologic therapy:

- Not specified

Chemotherapy:

- See Disease Characteristics

- At least 3 weeks since prior chemotherapy (6 weeks for nitrosoureas) and recovered

- No more than 1 prior chemotherapy regimen

Endocrine therapy:

- Must be on stable dose of steroids for at least 5 days

Radiotherapy:

- See Disease Characteristics

- At least 3 months since prior radiotherapy and recovered

- No more than 1 prior course of radiotherapy

Surgery:

- Not specified

Other:

- No other concurrent investigational agents

- At least 10 days since prior anticonvulsant drugs that induce hepatic metabolic
enzymes