Influence of WR 2721 on the efficacy of radiotherapy and chemotherapy of murine tumors.

The effect of WR 2721 on the response of tumors to radiation, antineoplastic alkylating drugs, and DNA binding agents was evaluated and compared to the degree of normal tissue protection provided by WR 2721 against these agents. WR 2721 administered to mice bearing P388 leukemia or Lewis lung carcinoma was found to reduce the radiosensitivity of the leukemia and lung tumor by dose modifying factors of 1.4 and 1.3, respectively. WR 2721 protected bone marrow, intestine, and skin from radiation by factors of 1.9, 1.5, and 1.8. WR 2721 protected mice from the lethality of cyclophosphamide by a factor of only 1.2 whereas protection from melphalan toxicity was more dramatic with a dose modifying factor of 1.6. In chemotherapy studies of established M5076 ovarian tumor, the combination of WR 2721 plus cyclophosphamide was equivalent in activity to cyclophosphamide alone. WR 2721 did not modify the antitumor activity of melphalan in early Lewis lung carcinoma but did decrease the antileukemic effects of this agent by a factor of 2.6 indicating tumor protection greater than host protection in the leukemia. The antitumor activity of the DNA binding agents etoposide (VP16--213) and mitoxantrone against systemic P388 leukemia was not diminished by WR 2721, while a substantial increase in host toxicity was noted for the combinations. The protective effects of WR 2721 against radiation and drug damage were, therefore, not entirely selective for normal tissues. In some cases the degree of tumor protection can be similar to, or greater than, normal tissue protection.