Overexpression of the putative thiol conjugate transporter TbMRPA causes melarsoprol resistance in Trypanosoma brucei

Summary Melaminophenyl arsenical drugs are a mainstay of chemotherapy against late‐stage African sleeping sickness, but drug resistance is increasingly prevalent. We describe here the characterization of two genes encoding putative metal–thiol conjugate transporters from Trypanosoma brucei. The two proteins, TbMRPA and TbMRPE, were each overexpressed in trypanosomes, with or without co‐expression of two key enzymes in trypanothione biosynthesis, ornithine decarboxylase and gamma‐glutamyl‐cysteine synthetase. Overexpression of gamma‐glutamyl‐cysteine synthetase resulted in a twofold increase in cellular trypanothione, whereas overexpression of ornithine decarboxylase had no effect on the trypanothione level. The overexpression of TbMRPA resulted in a 10‐fold increase in the IC50 of melarsoprol. The overexpression of the trypanothione biosynthetic enzymes alone gave two‐ to fourfold melarsoprol resistance, but did not enhance resistance caused by MRPA. Overexpression of TbMRPE had little effect on susceptibility to melarsoprol but did give two‐ to threefold resistance to suramin.