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

Life expectancy:

• Not specified

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:

Biologic therapy:

• Not specified

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:

• See Disease Characteristics
• 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