Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically confirmed primary brain glioma

- Diffuse astrocytoma

- Gliosarcoma

- Oligodendroglioma

- Oligoastrocytoma

- Progressive disease after radiotherapy

- Measurable or evaluable disease by MRI or CT

PATIENT CHARACTERISTICS:

Age:

- 18 and over

Performance status:

- ECOG 0-2

Hematopoietic:

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

- Platelet count at least 100,000/mm^3

- Hemoglobin at least 9 g/dL

Hepatic:

- Bilirubin no greater than upper limit of normal (ULN)

- SGOT no greater than 2.5 times ULN

Renal:

- Creatinine no greater than 2.0 mg/dL

Cardiovascular:

- No myocardial infarction within the past 6 months

- No congestive heart failure requiring therapy

Other:

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use effective contraception

- No uncontrolled infection

- No other active malignancy

- No other concurrent severe disease

PRIOR CONCURRENT THERAPY:

Chemotherapy:

- At least 4 weeks since prior chemotherapy (6 weeks for nitrosoureas)

- No more than 1 prior adjuvant chemotherapy regimen

- No prior polifeprosan 20 with carmustine implant (Gliadel wafer)

- Study 3 only:

- 1 prior chemotherapy regimen for recurrent disease allowed

- Prior nonplatinum-containing adjuvant chemotherapy allowed

- Prior platinum-containing adjuvant chemotherapy allowed if disease progressed at
least 6 months after last treatment

Endocrine therapy:

- Non-increasing dose of corticosteroids for at least 1 week allowed

Radiotherapy:

- At least 12 weeks since prior radiotherapy

- No prior stereotactic radiosurgery or interstitial brachytherapy unless at least one
lesion outside of irradiated area

Surgery:

- No surgical resection since prior radiotherapy or chemotherapy unless evidence of
disease progression or lesion outside of treatment site

Other:

- Study 1 only: (Study 1 closed as of 03/29/02)

- Must be on anticonvulsants that can induce cytochrome P-450 (phenytoin,
carbamazepine, barbiturates, or primidone)

- Study 2 only: (Study 2 closed as of 03/29/02)

- No concurrent anticonvulsants