Microbiologic assay for cytosine arabinoside (NSC-63878): the use of a mutant of streptococcus faecium var. durans resistant to methotrexate (NSC-740) and 6-mercaptopurine (NSC-755).

Cytosine arabinoside has been shown to be effective in the treatment of acute leukemias and lymphomas, especially in combination with other established anticancer agents such as methotrexate, 6-mercaptopurine, and 6-thioguanine. A microbiologic assay capable of detecting cytosine arabinoside in the presence of such anticancer agents in body fluids has been developed using a strain of Streptococcus faecium var. durans resistant to methotrexate and 6-mercaptopurine; the assay can also be used to determine cytosine arabinoside concentrations in the presence of l-thioguanine. In view of the present trend toward drug combinations, including those using tetrahydrouridine, in the chemotherapy for human neoplasms, the proposed assay method will be valuable in cytosine arabinoside distribution studies.