An experimental model comparing the antineoplastic and the immunosuppressive effects of some cytostatics

An experimental model evaluating comparatively the antineoplastic and the immunosuppressive effects of some cytostatics (cyclophosphamide and vinblastine) is described in the present paper. Different cytostatic doses were intraperitoneally administered in mice which were 24 hours later grafted with a suspension of human tumoral KB cells. The xenograft acceptance was macroscopically and microscopically recorded 21 days later. By the Reed and Muench method and also by graphical extrapolation the LD50 (lethal dose for 50% animals) and the TD50 (the immunosuppressive dose enabling 50% animals to accept the xenografts) could thus be determined for both cyclophosphamide and vinblastine. The number (percent) of the tumour bearing animals three weeks after grafting was considered as an indicator of the cytostatic dose at which the immunosuppressive effect exceeded the antineoplastic effect. The in vitro effect of the same drugs on the KB cells was tested by inoculating different cytostatic doses in the cell cultures and counting at different time intervals the adherent as well as the nonadherent cells. The in vitro drug toxicity on the KB cell cultures was also determined by the trypan blue exclusion test. Both cyclophosphamide and vinblastine proved to be in vitro highly potent cytostatics i.e. when directly acting on the KB cells. This effect was dose correlated for both the considered drugs. However our in vivo experiments have shown that none of the observed effects when considering the direct action of the cytostatic on the cultured cells could not safely be extrapolated in vivo. Our results have an obvious practical importance when considering the therapeutical approaches in the neoplastic diseases. They demonstrate that the increase in cytostatic dose is not directly correlated to the antineoplastic effect since it reaches a limit at which the immunosuppressive effect highly exceed the tumour growth inhibition effect. The described experimental model could also be used in comparative estimations of the biological effects of different cytostatic drugs possibly referred to a standard immunosuppressive reagent as an antilymphocyte antiserum.