Abstract
A novel trypanocide, 2,5-bis(4-amidinophenyl)furan (DB75), in its prodrug amidoxime-derivative form, 2,5-bis(4-amidinophenyl)furan-bis-O-methylamidoxime (DB289), is in trials as the first orally administered drug for human African trypanosomiasis. DB75 is a diamidine. Resistance to some diamidines correlates to loss of uptake via the P2 aminopurine transporter. We show here that uptake of DB75 into Trypanosoma brucei also occurs principally via the P2 transporter. Uptake of tritiated DB75 occurred via a high-affinity (Km app, 3.2 μM) carriermediated route that was inhibited by adenosine, adenine, and pentamidine, all known substrates of the P2 transporter. Trypanosomes lacking the TbAT1 gene that encodes the P2 transporter demonstrated an 11-fold reduction in sensitivity to DB75 when measured under controlled in vitro conditions. These knockout cells were also less sensitive to DB75 than wild-type cells in mice. Initial uptake rates of DB75 into the Δtbat1 knockout cell line were greatly reduced compared with rates in wild-type cells. A trypanosome cell line selected in vitro for DB75 resistance was shown to have lost P2-mediated DB75 uptake. The TbAT1 gene was mapped to chromosome V of the T. brucei genome and the DB75-resistant parasites were shown to have deleted both alleles of this gene. Fluorescence microscopy of DB75-treated trypanosomes revealed that DB75 fluorescence localizes rapidly within the DNA-containing organelles of wild-type trypanosomes, whereas no fluorescence was observed in Δtbat1-null parasites or in the parasites selected for resistance to DB75.
Footnotes
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This work was funded by the Bill and Melinda Gates Foundation. C.A.L. and M.L.S. contributed equally to this work
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ABBREVIATIONS: HAT, human African trypanosomiasis; DB75, 2,5-bis(4-amidinophenyl)furan; DB289, 2,5-bis(4-amidinophenyl)furan-bis-O-methylamidoxime; DB75R-CL1, the T. brucei strain selected for resistance to DB75; DAPI, 4′,6-diamidino-2-phenylindole dihydrochloride; melarsoprol, 2-[4-[(4,6-diamino-1,3,5-triazin-2-yl)amino]phenyl]-1,3,2-dithiarsolan-4-yl]methanol; pentamidine, 4-[5-(4-carbamimidoylphenoxy-)pentoxy]benzenecarboximidamide; suramin, 8-[[4-methyl-3-[[3-[[3-[[2-methyl-5-[(4,6,8-trisulfonaphthalen-1-yl) carbamoyl]phenyl]carbamoyl]phenyl]carbamoylamino]benzoyl]amino]benzoyl]amino]naphthalene-1,3,5-trisulfonic acid; eflornithine, 2,5-diamino-2-(difluoromethyl)pentanoic acid; diminazene, 4-[2-(4-carbamimidoylphenyl)iminohydrazinyl]benzenecarboximidamide; PCR, polymerase chain reaction.
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The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material.
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↵1 Current affiliation: Division of Experimental Therapeutics, Walter Reed Army Institute of Research, Silver Spring, Maryland.
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↵2 Current affiliation: Zentrum für Molekulare Biologie Heidelberg, Heidelberg, Germany.
- Received March 27, 2006.
- Accepted August 15, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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