Received for publication October 4, 2006.
Revised December 11, 2006.
Accepted for publication January 16, 2007.

Loss of the High Affinity Pentamidine Transporter is responsible for high levels of cross-resistance between arsenical and diamidine drugs in African trypanosomes

Abstract

Treatment of many infectious diseases is under threat from drug resistance. Understanding the mechanisms of resistance is as high a priority as the development of new drugs. We have investigated the basis for cross-resistance between the diamidine and melaminophenyl arsenical classes of drugs in African trypanosomes. We induced high levels of pentamidine resistance in a line without the tbat1 gene encoding the P2 transporter previously implicated in drug uptake. We isolated independent clones that displayed very considerable cross-resistance with melarsen oxide but not phenylarsine oxide, and reduced uptake of [³H]-pentamidine. Specifically, the High Affinity Pentamidine Transport (HAPT1) activity was absent in the pentamidine-adapted lines, whereas the Low Affinity Pentamidine Transport (LAPT1) activity was unchanged. The parental tbat1^-/- line was sensitive to lysis by melarsen oxide and this process was inhibited by low concentrations of pentamidine, indicating the involvement of HAPT1. This pentamidine-inhibitable lysis was absent in the adapted line KO-B48. Similarly, uptake of the fluorescent diamidine DAPI was much delayed in live KO-B48 cells and insensitive to competition with up to 10 µM pentamidine. No overexpression of the T. b. brucei ABC-transporter TbMRPA could be detected in KO-B48. We also show that a laboratory line of T. b. gambiense, adapted to high levels of resistance for the melaminophenyl arsenical drug Cymelarsan, had similarly lost TbAT1 and HAPT1 activity while retaining LAPT1 activity. It thus appears that selection for resistance to either pentamidine or arsenical drugs can result in a similar phenotype of reduced drug accumulation, explaining the occurrence of cross-resistance.

Key words: Nucleoside/Nucleotide, MDR/p-Glycoprotein, Fluorescence techniques, Structure/function/mechanism, Antiprotozoal drugs