Sleeping sickness, caused by Trypanosoma brucei spp., has become resurgent in sub-Saharan Africa. Moreover, there is an alarming increase in treatment failures with melarsoprol, the principal agent used against
late-stage sleeping sickness. In T. brucei, the uptake of melarsoprol as well as diamidines is thought to be
mediated by the P2 aminopurine transporter, and loss of P2 function has been implicated in resistance to these
agents. The trypanosomal gene TbAT1 has been found to encode a P2-type transporter when expressed in yeast.
Here we investigate the role of TbAT1 in drug uptake and drug resistance in T. brucei by genetic knockout of
TbAT1. Tbat1-null trypanosomes were deficient in P2-type adenosine transport and lacked adenosine-sensitive
transport of pentamidine and melaminophenyl arsenicals. However, the null mutants were only slightly
resistant to melaminophenyl arsenicals and pentamidine, while resistance to other diamidines such as diminazene was more pronounced. Nevertheless, the reduction in drug sensitivity might be of clinical significance,
since mice infected with tbat1-null trypanosomes could not be cured with 2 mg of melarsoprol/kg of body weight
for four consecutive days, whereas mice infected with the parental line were all cured by using this protocol.
Two additional pentamidine transporters, HAPT1 and LAPT1, were still present in the null mutant, and
evidence is presented that HAPT1 may be responsible for the residual uptake of melaminophenyl arsenicals.
High-level arsenical resistance therefore appears to involve the loss of more than one transporter.