The PR500 PRISM cell set was grown with either folic acid or 5-methyl tetrahydrofolate (THF) as a folate source and treated with several methotrexate doses. Cells exposed to 5-methyl THF were found to be more resistant to methotrexate indicating that environmental folate source affects folate metabolism and response to antifolate drugs.
Methionine synthase is essential for cancer cell proliferation in physiological folate environments