Uptake of pentamidine in Trypanosoma brucei brucei is mediated by the P2 adenosine transporter and at least one novel, unrelated transporter.

Diamidine drugs such as pentamidine and berenil (diminazene aceturate) are vital drugs for the treatment of early stage human African trypanosomiasis and the corresponding veterinary condition, respectively. The action of diamidines on trypanosomes is critically dependent on their efficient uptake by the parasite. We have therefore investigated the mode of uptake of pentamidine by Trypanosoma brucei brucei, using [¹²⁵I]iodopentamidine as a permeant. [¹²⁵I]Iodopentamidine uptake was linear for up to 15 min and inhibited by adenosine with a K_i value of 0.64±0.03 μM, to a maximum of 50–70%. The adenosine-sensitive flux was also inhibited by adenine with a K_i value of 0.44±0.04 μM. Iodopentamidine uptake was saturable, with the adenosine-insensitive flux displaying a K_m of 22±2 μM and a V_max of 2.2±0.9 pmol(10⁷ cells)⁻¹ s⁻¹, whereas the adenosine-sensitive flux was inhibited by much lower iodopentamidine concentrations. These results clearly demonstrate that iodopentamidine is taken up by at least two different T. b. brucei transporters, an adenosine-sensitive pentamidine transporter (ASPT1) and a low-affinity pentamidine transporter (LAPT1). The identity of these transporters was investigated, and their significance for drug uptake and resistance in African trypanosomes is discussed.