Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically or cytologically confirmed solid tumor, including primary brain tumor

- Progressive disease on standard therapy or for which no standard therapy exists

- No symptomatic brain metastases

PATIENT CHARACTERISTICS:

Age:

- 1 to 21

Performance status:

- Lansky 50-100% (age 10 and under)

- Karnofsky 50-100% (over age 10)

Life expectancy:

- At least 8 weeks

Hematopoietic:

- Absolute neutrophil count greater than 1,000/mm3

- Platelet count greater than 100,000/mm3

Hepatic:

- Bilirubin no greater than 1.5 mg/dL

- ALT no greater than 2.5 times upper limit of normal

Renal:

- Glomerular filtration rate at least 30 mL/min

Other:

- No active infection

- No serious uncontrolled medical disorder

- No psychiatric disorder or other disorder that would preclude study

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY:

Biologic therapy:

- At least 6 months since prior allogeneic bone marrow transplantation without evidence
of acute or chronic graft versus host disease

- At least 3 months since prior autologous bone marrow or peripheral blood stem cell
transplantation

- At least 4 weeks since prior immunotherapy and recovered

- No concurrent immunotherapy

Chemotherapy:

- No more than 3 prior chemotherapy regimens

- At least 4 weeks since prior chemotherapy (6 weeks for nitrosoureas or mitomycin) and
recovered

- No other concurrent chemotherapy

Endocrine therapy:

- Concurrent hormone replacement therapy or oral contraceptives allowed

- No other concurrent hormonal therapy

Radiotherapy:

- At least 4 weeks since prior radiotherapy (including for brain metastases) and
recovered

- No concurrent radiotherapy

Surgery:

- Not specified

Other:

- No other concurrent investigational anticancer drugs

- No other concurrent antitumor therapy

- No concurrent anticonvulsants (e.g., phenytoin, phenobarbital, or carbamazepine)
except gabapentin (Neurontin)