Metabolism and Selective Toxicity of 6-Nitrobenzylthioinosine in Toxoplasma gondii

Abstract

The purine nucleoside analogue NBMPR {nitrobenzylthioinosine or 6-[(4-nitrobenzyl)thio]-9-␤-D-ribo-furanosylpurine} was selectively phosphorylated to its nucleoside 5-monophosphate by Toxoplasma gondii but not mammalian adenosine kinase (EC 2.7.1.20). NBMPR was also cleaved in toxoplasma to its nucleobase, nitrobenzylmercaptopurine. However, nitrobenzylmercaptopurine was not a substrate for either adenosine kinase or hypoxanthine-guanine-xanthine phosphoribosyltransferase (EC 2.4.2.8). Because of this unique and previously unknown metabolism of NBMPR by the parasite, the effect of NBMPR as an antitoxoplasmic agent was tested. NBMPR killed T. gondii grown in human fibroblasts in a dose-dependent manner, with a 50% inhibitory concentration of approximately 10 M and without apparent toxicity to host cells. Doses of up to 100 M had no significant toxic effect on uninfected host cells. The promising antitoxoplasmic effect of NBMPR led to the testing of other 6-substituted 9-␤-D-ribofuranosylpurines, which were shown to be good ligands of the parasite adenosine kinase (M. H. Iltzsch, S. S. Uber, K. O. Tankersley, and M. H. el Kouni, Biochem. Pharmacol. 49: 1501-1512, 1995), as antitoxoplasmic agents. Among the analogues tested, 6-benzylthioinosine, p-nitrobenzyl-6-selenopurine riboside, N 6 -(p-azidobenzyl)adenosine, and N 6 -(p-nitrobenzyl)adenosine, like NBMPR, were selectively toxic to parasite-infected cells. Thus, it appears that the unique characteristics of purine metabolism in T. gondii render certain 6-substituted 9-␤-D-ribofuranosylpurines promising antitoxoplasmic drugs.

Chemotherapeutic Strategies Against Trypanosoma brucei: Drug Targets vs. Drug Targeting

“…Since TgAK is not an essential enzyme [95], it cannot serve as a drug target. Instead it was proposed for targeting of adenosine analogues: the selective phosphorylation of "subversive" adenosine analogues by TgAK but not by the host's AK [96]. NBMPR (nitrobenzylthioinosine) and analogues were shown to be surprisingly good ligands of TgAK but not of mammalian AK [97][98][99].…”

Determination of 6-benzylthioinosine in mouse and human plasma by liquid chromatography–tandem mass spectrometry

“…1) and was originally used in the property studies of adenosine aminohydrolase [1]. In the later 1990s, 6BT was found to be potentially useful in the treatment of toxoplasmosis [2,3] caused by Toxoplasma gondii, an intracellular parasite that infects humans and many other warm-blooded animals [4,5]. Recently, 6BT was identified as a promising differentiation-inducing agent for leukemic cells as less toxic and more efficacious treatment for acute myeloid leukemia (AML) [6].…”

Molecular modeling of the Toxoplasma gondii adenosine kinase inhibitors

“…The parasitic protozoon Toxoplasma gondii is the etiologic agent of toxoplasmosis, a parasitic disease widespread among several warm-blooded animals, including humans (El Kouni et al, 1999). Toxoplasmosis is known to be one of the most prevalent parasitic infections of the central nervous system and causes lethal encephalitis in immunocompromised patients such those with acquired immunodeficiency syndrome (AIDS) (Al Safarjalania et al, 2007).…”

“…Toxoplasmosis is known to be one of the most prevalent parasitic infections of the central nervous system and causes lethal encephalitis in immunocompromised patients such those with acquired immunodeficiency syndrome (AIDS) (Al Safarjalania et al, 2007). In spite of the tragic consequences of toxoplasmosis, the therapy for this disease has not changed in the last 20 years (El Kouni et al, 1999). The current treatment consists on combinations of drugs, such as Pyrimethamine (Daraprim Ò ), trimethoprim-sulfamethoxazole (Bactrin Ò ), Sulfadiazine (Triglobe Ò ), or Clindamycin (Dalacin Ò ) (Ngo et al, 2000).…”

“…Benzyladenosine analogues are known in the literature as subversive substrates, i.e., they are preferentially metabolized to the nucleotide level and become selectively toxic for the parasite, but not for human adenosine kinase (HssAK) (El Kouni et al, 1999;Al Safarjalani et al, 2003;El Kouni 2003). Recently a series of 41 benzyladenosine analogues acting as potent and selective subversive substrates, was described for TgAK (Yadav et al, 2004;Rais et al, 2005;Al Safarjalania et al, 2007) and their binding to TgAK and HssTK were evaluated in enzyme-based assays (Yadav et al, 2004;Rais et al, 2005;Al Safarjalania et al, 2007).…”