Uptake of diamidine drugs by the P2 nucleoside transporter in melarsen-sensitive and -resistant Trypanosoma brucei brucei

The African trypanosome, Trypanosoma brucei brucei, possesses at least two nucleoside transporter systems designated P1 and P2, the latter being implicated in the selective uptake of melaminophenyl arsenical drugs. Since arsenical-resistant trypanosomes show cross-resistance in vivo to aromatic diamidines, we have investigated whether these drugs are also substrates for the P2 nucleoside transporter. In melarsen-sensitive T. b. brucei, the diamidines, including the commonly used trypanocides, pentamidine and berenil, were found to abrogate lysis induced by the P2 transport of melarsen oxide in vitro. Measurement of [ring-³H]pentamidine transport in melarsen-sensitive T. b. brucei, demonstrated that uptake is carrier-mediated, with a K_m of 0.84 μM and a V_max of 9.35 pmol s^-1 (10⁸ cells)^-1. Pentamidine transport appears to be P2-mediated in these cells, as pentamidine strongly inhibited uptake of [2′,5′,8-³H]adenosine by the P2 transporter, with a K_i of 0.56 μM. Furthermore, [ring-³H]pentamidine transport was blocked by a number of P2 transporter substrates and inhibitors, as well as by other diamidine drugs. Analysis of the uptake of pentamidine and other diamidines in melarsen-resistant trypanosomes in vitro and in vivo, which also show differential levels of resistance to these compounds in vivo, indicated that P2 transport was altered in these cells and that accumulation of these drugs was markedly reduced.