REVERSION OF RESISTANCE TO ADRIAMYCIN BY VANADATE ON 4 FRIEND-CELL SUBLINES

The retention of adriamycin in 5 Friend cell sublines of increasing de gree of resistance was enhanced in vitro by three compounds: verapamil , nigericine and vanadate. Vanadate had the strongest activity, it enh anced also the incorporation in sensitive cells. Its efficacy was incr eased by a pre-incubation with H2O2. The effect of vanadate was then t ested in vivo. When the tumor was transplanted i.p. and the treatment was also i.p., vanadate enhanced the efficacy of adriamycin, but it ha d also an antitumor activity by itself. Vanadate alone had some effica cy on the Friend cells of the lowest degree of resistance, when adriam ycin had no effect. Nevertheless, vanadate had a partial cross resista nce with adriamycin on these cells. When the tumor was transplanted su bcutaneously and the treatment was still i.p., vanadate had no effect whilst adriamycin was still active.