Combined interferon--antimetabolite therapy of murine L1210 leukemia.

To assess the interaction of interferon with estabished chemotherapeutic agents, L1210 murine leukemia in BDF/1 mice was treated with methotrexate, 6-mercaptopurine. Adriamycin, cytosine arabinoside or cyclophosphamide alone or in combination with mouse L-cell (Newcastle disease virus-induced) interferon or with interferon-free tissue culture medium. Also studied was the effect of interferon on the combined 6-mercaptopurine-methotrexate therapy of this tumor. Interferon failed to enhance the response of L1210 leukemia to 6-mercaptopurine, adriamycin, cytosine arabinoside or cyclophosphamide. The addition of interferon to all methotrexate-containing regimens increased mean survival time (P less than 0.05). The increase in survival of host animals treated with 6-mercaptopurine-methotrexate and interferon was sustained though four transfer generations despite evolving resistance to this antimetabolite combination.