Evaluation of an arsenical compound (RM 110, mel Cy, Cymelarsan) against susceptible and drug-resistant Trypanosoma brucei brucei and T.b. evansi.

The trypanocidal activity of an arsenical compound (RM 110; mel Cy; Cymelarsan) was tested in susceptible and drug-resistant stocks of T.b. brucei and T.b. evansi in vitro and in vivo. The trypanosome stocks showed different levels of susceptibility in an in vitro test, their IC50 values ranging from 3-26.9 nM. Mel Cy was 2.2-2.7 times more active against T.b. brucei stocks when compared to another arsenical (mel W; Trimelarsan). The logarithmically transformed IC50 values for both drugs obtained with T.b. brucei stocks correlated significantly. Significant correlations were also found between the log IC50 values of each of the two drugs and diminazene aceturate. In mice, the least susceptible stock was cured with a single i.p. dose of mel Cy which was about 16 times higher than that needed to cure a susceptible stock.