Temozolomide and O6-benzylguanine in Treating Children With Solid Tumors

DISEASE CHARACTERISTICS: Histologically confirmed solid tumor refractory to standard therapy and for which no potentially curative therapy exists, including, but not limited to: Rhabdomyosarcoma and other soft tissue sarcomas Ewing's family of tumors Osteosarcoma Neuroblastoma Wilms' tumor Hepatic tumors Germ cell tumors Primary brain tumor Histological confirmation may be waived for brainstem or optic gliomas Measurable or evaluable disease Evidence of progressive disease on prior chemotherapy or radiotherapy or persistent disease after prior surgery PATIENT CHARACTERISTICS: Age: 21 and under Performance status: ECOG 0-2 Life expectancy: At least 8 weeks Hematopoietic: Absolute granulocyte count greater than 1,500/mm^3 Hemoglobin greater than 8 g/dL Platelet count greater than 100,000/mm^3 Hepatic: Bilirubin normal SGPT less than 2 times upper limit of normal No significant hepatic dysfunction Renal: Creatinine normal OR Creatinine clearance at least 60 mL/min Cardiovascular: No significant cardiac dysfunction Pulmonary: No significant pulmonary dysfunction Other: Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception Able to swallow capsules No significant unrelated systemic illness that would preclude study (e.g., serious infections or organ dysfunction) No prior hypersensitivity to dacarbazine, temozolomide, or polyethylene glycol PRIOR CONCURRENT THERAPY: Biologic therapy: At least 1 week since prior colony-stimulating factors (e.g., filgrastim [G- CSF], sargramostim [GM-CSF], or epoetin alfa) At least 4 months since prior myeloablative therapy requiring bone marrow or stem cell transplantation No concurrent anticancer immunotherapy Chemotherapy: See Disease Characteristics At least 3 weeks since prior chemotherapy (4 weeks for nitrosoureas) and recovered Prior temozolomide allowed provided not administered within past 3 months, no severe toxicities experienced during prior course, and not given in combination with other agents designed to inactivate alanine-glyoxylate aminotransferase No other concurrent investigational or standard anticancer chemotherapy Endocrine therapy: Concurrent corticosteroids for control of brain tumor-associated edema allowed provided on stable or decreasing dose for at least 1 week prior to study Radiotherapy: See Disease Characteristics At least 4 weeks since prior limited-field radiotherapy At least 4 months since prior craniospinal irradiation, total body irradiation, or radiotherapy to more than half of the pelvis Recovered from prior radiotherapy No concurrent anticancer radiotherapy Surgery: See Disease Characteristics Other: At least 4 weeks since other prior investigational therapy and recovered No other concurrent anticancer investigational agents