The Sensitivity to Chemotherapeutic Agents of a Rat Tumour Grown in Immunosuppressed Mice

The rat Walker 256 tumour was grown in mice that had previously been thymectomized and treated with anti-lymphocyte serum. These rat tumour-bearing mice were used to determine the therapeutic indices of 4 anti-tumour drugs. The agent with the highest index of the four examined was 5-aziridino 2,4-dinitrobenzamide (CB1954), followed by melphalan, aniline mustard and methotrexate, in that order. This rank order is the same as that found when therapeutic indices are determined on the Walker tumour growing in the rat. In this system, therefore, drugs have been ranked correctly in effectiveness against a rat tumour by measuring their effects on the tumour when growing in an immunosuppressed xenogeneic species. The implications for testing the drug sensitivity of individual human tumours before treating the patient are discussed.