DISEASE CHARACTERISTICS: Histologically confirmed malignant solid tumor that has failed 1 or more conventional treatments or is unlikely to respond to currently available therapies No active CNS metastases

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: Karnofsky 70-100% Life expectancy: At least 3 months Hematopoietic: WBC greater than 3,000/mm3 Absolute neutrophil count at least 1,500/mm3 Platelet count greater than 100,000/mm3 Hemoglobin at least 10 g/dL Hepatic: Bilirubin less than 2.0 mg/dL AST and ALT no greater than 3 times upper limit of normal (ULN) Alkaline phosphate no greater than 3 times ULN (no greater than 5 times ULN if liver metastases present) Renal: Creatinine less than 2.0 mg/dL Cardiovascular: No myocardial infarction within the past 3 months No symptomatic coronary artery disease or heart block No uncontrolled congestive heart failure Pulmonary: No moderate or severe pulmonary dysfunction Other: Not pregnant or nursing Negative pregnancy test Fertile women must use effective contraception Body weight greater than 50 kg No active infection No mental deficits and/or psychiatric disorders that would preclude study No other life-threatening illness No bleeding disorder (except occult blood from gastrointestinal cancer)

PRIOR CONCURRENT THERAPY: Biologic therapy: Prior growth factor treatment allowed if blood counts normal Chemotherapy: At least 3 weeks since prior chemotherapy and recovered At least 6 weeks since prior nitrosoureas or mitomycin and recovered Prior hydroxyurea allowed and recovered Endocrine therapy: At least 2 weeks since prior hormonal therapy Radiotherapy: At least 3 weeks since prior radiotherapy and recovered No prior radiotherapy to greater than 30% of the bone marrow Surgery: At least 2 weeks since any prior major surgery Other: At least 4 weeks since other prior investigational agents and recovered No other concurrent investigational agents without consent of sponsor