Abstract
Studies were carried out to evaluate further the in vivo effectiveness of reversetranscriptase inhibitors in the therapy of Rauscher viral leukemia. Ethidium bromide, given in multiple doses, was found to be without significant effect on the survival of mice which already had established Rauscher disease as the result of injection with virus 2 weeks earlier. However, the initiation of ethidium bromide treatment immediately after virus did result in the beneficial effect of an increase in the mean survival time of the infected animals. On the other hand, at the virus titers used, 4βNβbenzylβ4βNβdemthylrifampicin showed no significant therapeutic action in either case, even though other studies had suggested that it might be effective for this purpose. A total of 1,000 R of fractionated Xβirradiation given to animals with established leukemia also resulted in increased mean survival times, but the combination of irradiation and ethidium bromide treatment of similar mice resulted in only a marginal improvement over irradiation alone. It is suggested that these reverseβtranscriptase inhibitors, though active against the free virus, may not be effective against the already transformed tumor cell.