Lometrexol Plus Folic Acid in Treating Patients With Stage IIIB or Stage IV Non-Small Cell Lung Cancer

DISEASE CHARACTERISTICS:

* Histologically confirmed non-small cell lung cancer (NSCLC)

  * Stage IIIB or IV

    * Squamous cell carcinoma
    * Adenocarcinoma
    * Large cell carcinoma
    * Adenosquamous carcinoma
* Progressive disease after receiving 1 cisplatin- or carboplatin-containing regimen for stage IIIB or IV disease
* Measurable disease

  * At least 1 lesion at least 1 cm x 1 cm by CT scan either not in a previously irradiated field or showing clear evidence of disease progression after radiation
* No symptomatic or rapidly increasing, moderate or large amounts of pleural effusion or ascites
* No prior or concurrent CNS metastases (brain or meningeal)

PATIENT CHARACTERISTICS:

Age:

* 18 and over

Performance status:

* Karnofsky 70-100%

Life expectancy:

* At least 3 months

Hematopoietic:

* Absolute neutrophil count at least 1,500/mm\^3\*
* Platelet count at least 100,000/mm\^3\*
* Hemoglobin at least 9.0 g/dL\*
* \*Without transfusions or growth factors in the previous 7 days

Hepatic:

* Bilirubin no greater than 1.5 times upper limit of normal (ULN) (regardless of liver involvement secondary to tumor)
* AST and ALT no greater than 2.5 times ULN (5 times ULN if liver has tumor involvement)

Renal:

* Calculated creatinine clearance at least 60 mL/min using Cockroft and Gault formula

Gastrointestinal:

* No inflammatory bowel disease
* No radiation enteritis
* No malabsorption syndrome
* No inability to absorb folic acid

Other:

* Not pregnant or nursing
* Negative pregnancy test
* Fertile patients must use effective contraception during study
* No known untreated vitamin B12 deficiency
* HIV negative
* No drug abusers
* No prior malignancy within the past 5 years except adequately treated basal cell or squamous cell skin cancer or carcinoma in situ of the cervix
* No severe concurrent disease or major comorbidity that would preclude study participation

PRIOR CONCURRENT THERAPY:

Biologic therapy:

* At least 3 weeks since prior biologic therapy for NSCLC and recovered from acute side effects
* Prior treatment with an experimental vaccine allowed
* No concurrent routine or prophylactic filgrastim (G-CSF), sargramostim (GM- CSF), or epoetin alfa

Chemotherapy:

* See Disease Characteristics
* At least 3 weeks since prior chemotherapy for NSCLC (6 weeks for mitomycin or nitrosourea) and recovered from acute side effects
* Prior adjuvant or neoadjuvant chemotherapy allowed

Endocrine therapy:

* Not specified

Radiotherapy:

* See Disease Characteristics
* Recovered from acute side effects of prior radiotherapy
* No prior radiotherapy to 25% or more of bone marrow
* No prior whole pelvic irradiation

Surgery:

* At least 3 weeks since prior major surgery and recovered

Other:

* At least 3 weeks since prior investigational agent
* No concurrent proguanil, trimethoprim, co-trimoxazole, or pyrimethamine