Reversion of resistance to adriamycin by vanadate on 4 friend-cell sublines

The retention of adriamycin in 5 Friend cell sublines of increasing degree of resistance was enhanced in vitro by three compounds: verapamil, nigericine and vanadate. Vanadate had the strongest activity, it enhanced also the incorporation in sensitive cells. Its efficacy was increased by a pre-incubation with H2O2. The effect of vanadate was then tested in vivo. When the tumor was transplanted i.p. and the treatment was also i.p., vanadate enhanced the efficacy of adriamycin, but it had also an antitumor activity by itself. Vanadate alone had some efficacy on the Friend cells of the lowest degree of resistance, when adriamycin had no effect. Nevertheless, vanadate had a partial cross resistance with adriamycin on these cells. When the tumor was transplanted subcutaneously and the treatment was still i.p., vanadate had no effect whilst adriamycin was still active.