EFFECT OF DRUGS ON CELL AND VIRUS GROWTH IN FRIEND LEUKEMIA AND A TUMOR VARIANT.

Discussion and Summary The results show that neither estradiol nor mitomycin C influence the replication of Friend virus as judged by virus titer in the spleen, although both inhibit development of the leukemia following inoculation of cell-free virus (1,2). The results also show that mitomycin C, TEM, 6MP and urethane inhibited the growth of cellular implants of a transplantable reticulum cell sarcoma variant of Friend leukemia, although none of these substances affected the concentration of virus in either the spleen or tumor. Estradiol occupied an anomalous position in that it inhibited the development of splenomegaly in animals receiving both cell-free virus and tumor transplants, but did not inhibit the growth of the subcutaneous tumor. While these drugs influence the response to Friend virus, it seems likely that their withdrawal, even after complete suppression of the original cellular response, would be followed by recrudescence of leukemia from new foci of neoplasia induced by the large amount of virus in the tissues. Evidence to support this concept has been reported for Maloney virus by Glynn et al (6). The fallacy of using only one parameter in assessing the results of chemotherapy is highlighted. In the case of virus-induced neoplasms, treatment should ideally inhibit the growth of both the neoplastic cells and the virus.