Effects of intermediates of methionine metabolism and nucleoside analogs on S-adenosylmethionine transport by Trypanosoma brucei brucei and a drug-resistant Trypanosoma brucei rhodesiense.

The effects of purine nucleoside analogs, polyamines, and established trypanocidal agents on the uptake of [8-14C]adenosine and S-[methyl-3H]adenosylmethionine (AdoMet) by bloodform trypanosomes of drug-susceptible Trypanosoma brucei brucei and a drug-resistant Trypanosoma brucei rhodesiense clinical isolate were compared. AdoMet uptake was not antagonized by omithine or methionine (500 microM), adenosine (100 microM), or other purine nucleosides, including methylthioadenosine (MTA) at 500 microM. Hydroxyethylthioadenosine (HETA), a trypanocidal analog of methylthioadenosine, and sinefungin, an analog of AdoMet, were competitive with AdoMet transport in both isolates. Dipyridamole, an antagonist of the adenosine P2 transporter, also competed with AdoMet transport in both isolates. The trypanocidal diamidines pentamidine, Berenil, CGP 40215, and the decarboxylated S-adenosylmethionine (dAdoMet) analog MDL 73811 (5'-¿[(Z)-4-amino-2-butenyl]¿methyl-amino¿-5'-deoxyadenosine) competed with P2 adenosine transport but did not inhibit AdoMet transport at 100 microM. Methylglyoxalbis(guanylhydrazone) (MGBG), an analog of dAdoMet, was a strong competitive inhibitor of adenosine transport at 100 microM, but did not inhibit AdoMet transport. The polyamines putrescine, spermine, and spermidine (1 mM) were examined for competition with adenosine and AdoMet transport. Putrescine significantly inhibited P2 adenosine transport in both strains (in the presence of saturating inosine), but AdoMet transport was not affected by these polyamines. P2 adenosine transport in both strains was highly inhibited by melarsen oxide and melamine, its key organic component, whereas AdoMet uptake was not affected by these agents. These findings further characterize distinguishing features of the unique AdoMet transporter in African trypanosomes, and indicate that the P2 adenosine transporter remains functional in melarsen- and diamidine-resistant clinical isolates.