Abstract
Trypanosoma brucei are unicellular parasites that cause sleeping sickness in humans and nagana in livestock. Trypanosomes salvage purines from their hosts through a variety of transporters, of which adenosine permeases deserve particular attention because of their role in drug sensitivity. T. brucei possess two distinct adenosine transport systems, P1 and P2, the latter of which also mediates cellular uptake of the drugs melarsoprol and pentamidine. Loss or mutation of P2 has been associated with drug resistance and sleeping sickness treatment failures. However, genetic disruption in Trypanosoma brucei brucei of the gene encoding P2, TbAT1, reduced the susceptibility to melarsoprol and pentamidine by only a factor of ∼2. In this study, we show stronger phenotypes of the tbat1 null mutant with respect to its sensitivity toward toxic adenosine analogs. Compared with parental TbAT1+/+ trypanosomes, the tbat1-/- mutant is 77-fold less sensitive to tubercidin and 14-fold less sensitive to cordycepin. Resistance is further increased by the addition of inosine but is reverted by adenine. It is surprising that the tbat1-/- mutant grows faster than TbAT1+/+ trypanosomes and that it overexpresses genes of the TbNT cluster encoding P1-type transporters. These unexpected phenotypes show that there are conditions other than drug pressure under which loss of P2 may confer a selective advantage to bloodstream-form trypanosomes. Overexpression of P1 by trypanosomes after loss of P2 indicates that combinatorial chemotherapy with trypanocidal P1 and P2 substrates may be a promising strategy to prevent drug resistance in sleeping sickness.
- Received December 17, 2004.
- Accepted June 1, 2005.
- The American Society for Pharmacology and Experimental Therapeutics
MolPharm articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|