The role of Trypanosoma brucei MRPA in melarsoprol susceptibility

We previously showed that over-expression of Trypanosoma brucei MRPA, a member of the multidrug resistance protein family in T. brucei, reproducibly resulted in resistance to the anti-trypanosomal drug melarsoprol in vitro. MRPA is predicted to mediate efflux of melarsoprol as a conjugate with trypanothione, a glutathione–spermidine conjugate which is the major small thiol in trypanosomes. Here, we show that depletion of MRPA by RNA interference resulted in moderate hypersensitivity to both melarsoprol and melarsen oxide. Over-expression of MRPA alone is not sufficient to cause melarsoprol resistance in vivo, although it is sufficient in vitro. This discrepancy is not an effect of drug metabolism since over-expression of MRPA alone conferred resistance to melarsoprol and its principle metabolite, melarsen oxide, in vitro. Over-expression of MRPA was not detected in four melarsoprol-resistant trypanosome isolates from sleeping sickness patients.