Talotrexin in Treating Patients With Advanced or Recurrent Solid Tumors

DISEASE CHARACTERISTICS: * Diagnosis of malignant solid tumor * Metastatic or inoperable disease * No known curative or survival-prolonging palliative therapy exists OR failed these prior therapies * No leukemia * No primary CNS tumor * No third-space fluid collection (i.e., pleural effusion, ascites) * Clinically insignificant small pleural or peritoneal effusions identified by CT scan, MRI, or other diagnostic test allowed * No active\* brain metastases, including the following: * Evidence of cerebral edema by CT scan or MRI * Progression since prior imaging study * Requirement for steroids * Clinical symptoms of/from brain metastases NOTE: \*Treated and/or stable brain metastasis allowed provided patient is asymptomatic PATIENT CHARACTERISTICS: Age * 18 and over Performance status * ECOG 0-2 Life expectancy * At least 2 months Hematopoietic * Absolute neutrophil count ≥ 1,500/mm\^3 * Platelet count ≥ 100,000/mm\^3 * RBC folate ≥ lower limit of normal Hepatic * Bilirubin normal * SGOT and SGPT ≤ 2.5 times upper limit of normal Renal * Creatinine clearance ≥ 50 mL/min Other * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception * No other uncontrolled serious medical or psychiatric illness PRIOR CONCURRENT THERAPY: Biologic therapy * No prior bone marrow transplantation Chemotherapy * More than 3 weeks since prior chemotherapy (6 weeks for nitrosoureas or mitomycin) Endocrine therapy * See Disease Characteristics Radiotherapy * More than 3 weeks since prior radiotherapy * No concurrent radiotherapy Surgery * At least 3 weeks since prior surgery Other * Recovered from prior therapy * More than 3 weeks since prior antifolate therapy