DISEASE CHARACTERISTICS: Histologically proven primary brain glioma Astrocytoma Gliosarcoma Oligodendroglioma Oligoastrocytoma Tumor progression by CT scan or MRI following radiotherapy Measurable or evaluable disease

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-2 Life expectancy: Not specified Hematopoietic: Absolute neutrophil count at least 1500/mm3 Platelet count at least 100,000/mm3 Hemoglobin at least 9 g/dL Hepatic: Bilirubin no greater than 1.5 mg/dL AST no greater than 3 times upper limit of normal No prior Gilbert's syndrome Renal: Creatinine no greater than 2.0 mg/dL Cardiovascular: No history of myocardial infarction within 6 months No congestive heart failure requiring therapy Other: No concurrent active second malignancy No uncontrolled infection No other severe concurrent disease Not pregnant or lactating Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No more than 1 prior adjuvant chemotherapy regimen and 1 for recurrence (Gliadel is considered 1 regimen) At least 4 weeks since prior chemotherapy At least 6 weeks since prior nitrosoureas No prior irinotecan, topotecan, or aminocamptothecin Endocrine therapy: At least 2 weeks on fixed dose of corticosteroids (or no corticosteroids) prior to baseline scan Radiotherapy: At least 8 weeks since prior radiotherapy Surgery: No surgical resection between last radiotherapy or chemotherapy and study therapy, unless unequivocal tumor growth since surgery