Plasmodium falciparum Parasites Are Killed by a Transition State Analogue of Purine Nucleoside Phosphorylase in a Primate Animal Model

Cassera, María B.; Hazleton, Keith Z.; Merino, Emilio F.; Obaldía, Nicanor; Ho, M.; Murkin, Andrew S.; DePinto, R; Gutierrez, Jemy A.; Almo, Steven C.; Evans, Gary B.; Babu, Y.S.; Schramm, Vern L.

doi:10.1371/journal.pone.0026916

Cited by 62 publications

(93 citation statements)

References 44 publications

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“…In P. falciparum , hypoxanthine is the central metabolite, as blocking the production of hypoxanthine formation in vitro or in vivo causes death of the parasites by purine starvation. 4,30 The relative fluxes through purine salvage pathways dictate their essential contributions to cell survival. In some protozoa, including T. vaginalis , alternative purine salvage pathways with specificity overlapping that of PNP make it an ineffective drug target.…”

Section: Protozoan Purine Nucleoside Phosphorylase and Malariamentioning

confidence: 99%

“…4 BCX4945 blocked the growth of P. falciparum strains, including those resistant to other antimalarials, in human erythrocytes cultured with 10 μ M hypoxanthine (sufficient to permit growth; Figure 5A). Addition of isotopically labeled inosine to infected erythrocytes caused robust incorporation into the cellular nucleotide pool.…”

Section: Protozoan Purine Nucleoside Phosphorylase and Malariamentioning

confidence: 99%

“…This treatment causes parasite death in culture and in animal models. 4 DADMe-Immucilin-G is orally available and clears P. falciparum infections in Aotus monkeys, a primate model for human disease. No toxicity has been observed at effective pharmacological doses.…”

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confidence: 99%

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Immucillins in Infectious Diseases

2017

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The Immucillins are chemically stable analogues that mimic the ribocation and leaving-group features of N-ribosyltransferase transition states. Infectious disease agents often rely on ribosyltransferase chemistry in pathways involving precursor synthesis for nucleic acids, salvage of nucleic acid precursors, or synthetic pathways with nucleoside intermediates. Here, we review three infectious agents and the use of the Immucillins to taget enzymes essential to the parasites. First, DADMe-Immucillin-G is a purine nucleoside phosphorylase (PNP) inhibitor that blocks purine salvage and shows clinical potential for treatment for the malaria parasite Plasmodium falciparum, a purine auxotroph requiring hypoxanthine for purine nucleotide synthesis. Inhibition of the PNPs in the host and in parasite cells leads to apurinic starvation and death. Second, Helicobacter pylori, a causative agent of human ulcers, synthesizes menaquinone, an essential electron transfer agent, in a pathway requiring aminofutalosine nucleoside hydrolysis. Inhibitors of the H. pylori methylthioadenosine nucleosidase (MTAN) are powerful antibiotics for this organism. Synthesis of menaquinone by the aminofutalosine pathway does not occur in most bacteria populating the human gut microbiome. Thus, MTAN inhibitors provide high-specificity antibiotics for H. pylori and are not expected to disrupt the normal gut bacterial flora. Third, Immucillin-A was designed as a transition state analogue of the atypical PNP from Trichomonas vaginalis. In antiviral screens, Immucillin-A was shown to act as a prodrug. It is active against filoviruses and flaviviruses. In virus-infected cells, Immucillin-A is converted to the triphosphate, is incorporated into the viral transcript, and functions as an atypical chain-terminator for RNA-dependent RNA polymerases. Immucillin-A has entered clinical trials for use as an antiviral. We also summarize other Immucillins that have been characterized in successful clinical trials for T-cell lymphoma and gout. The human trials support the potential development of the Immucillins in infectious diseases.

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Section: Protozoan Purine Nucleoside Phosphorylase and Malariamentioning

confidence: 99%

Section: Protozoan Purine Nucleoside Phosphorylase and Malariamentioning

confidence: 99%

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Immucillins in Infectious Diseases

2017

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“…An alternative strategy might be to pair a PfENT1 inhibitor with another drug that acts elsewhere in the purine salvage pathway. Schramm and coworkers have shown that transition state analogue inhibitors of the purine salvage pathway enzyme, purine nucleoside phosphorylase, kill malaria parasites (Cassera et al, 2011;Ducati et al, 2013). Targeting two points in the purine metabolic pathway might lead to synergistic effects.…”

Section: Discussionmentioning

confidence: 99%

Substrate and Inhibitor Specificity of thePlasmodium bergheiEquilibrative Nucleoside Transporter Type 1

et al. 2016

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Malaria is a critical public health issue in the tropical world, causing extensive morbidity and mortality. Infection by unicellular, obligate intracellular Plasmodium parasites causes malaria. The emergence of resistance to current antimalarial drugs necessitates the development of novel therapeutics. A potential novel drug target is the purine import transporter. Because Plasmodium parasites are purine auxotrophic, they must import purines from their host to fulfill metabolic requirements. They import purines via equilibrative nucleoside transporter 1 (ENT1) homologs. Recently, we used a yeast-based high-throughput screen to identify inhibitors of the P. falciparum ENT1 (PfENT1) that kill P. falciparum parasites in culture. P. berghei infection of mice is an animal model for human malaria. Because P. berghei ENT1 (PbENT1) shares only 60% amino acid sequence identity with PfENT1, we sought to characterize PbENT1 and its sensitivity to our PfENT1 inhibitors. We expressed PbENT1 in purine auxotrophic yeast and used radiolabeled substrate uptake to characterize its function. We showed that PbENT1 transports both purines and pyrimidines. It preferred nucleosides compared with nucleobases. Inosine (IC 50 5 3.7 mM) and guanosine (IC 50 5 21.3 mM) had the highest affinities. Our recently discovered PfENT1 inhibitors were equally effective against both PbENT1-and PfENT1-mediated purine uptake. The PfENT1 inhibitors are at least 10-fold more potent against PfENT1 than human hENT1. They kill P. berghei parasites in 24-hour ex vivo culture. Thus, the P. berghei murine malaria model may be useful to evaluate the efficacy of PfENT1 inhibitors in vivo and their therapeutic potential for treatment of malaria.

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“…A clinical study reported an immucillin-induced neutropaenia (Gandhi et al, 2005) that may enhance the risk of life-threatening bacterial infections. On the other hand, a more recent analysis showed that these compounds are effective in eradicating a primate model of Plasmodium falciparum infection without noticeable side effects (Cassera et al, 2011). Since higher doses of the immucillins may be required to kill the trypanosomes, which have a distinct life cycle compared with the malaria-causing Plasmodium, compounds with higher selectivity have been devised in order to avoid detrimental effects on the host upon treatment.…”

Section: Introductionmentioning

confidence: 99%

Structures of purine nucleosidase fromTrypanosoma bruceibound to isozyme-specific trypanocidals and a novel metalorganic inhibitor

Giannese

Berg

Veken

et al. 2013

Acta Crystallogr D Biol Cryst

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Sleeping sickness is a deadly disease that primarily affects sub-Saharan Africa and is caused by protozoan parasites of the Trypanosoma genus. Trypanosomes are purine auxotrophs and their uptake pathway has long been appreciated as an attractive target for drug design. Recently, one tight-binding competitive inhibitor of the trypanosomal purine-specific nucleoside hydrolase (IAGNH) showed remarkable trypanocidal activity in a murine model of infection. Here, the enzymatic characterization of T. brucei brucei IAGNH is presented, together with its high-resolution structures in the unliganded form and in complexes with different inhibitors, including the trypanocidal compound UAMC-00363. A description of the crucial contacts that account for the high-affinity inhibition of IAGNH by iminoribitol-based compounds is provided and the molecular mechanism underlying the conformational change necessary for enzymatic catalysis is identified. It is demonstrated for the first time that metalorganic complexes can compete for binding at the active site of nucleoside hydrolase enzymes, mimicking the positively charged transition state of the enzymatic reaction. Moreover, we show that divalent metal ions can act as noncompetitive IAGNH inhibitors, stabilizing a nonproductive conformation of the catalytic loop. These results open a path for rational improvement of the potency and the selectivity of existing compounds and suggest new scaffolds that may be used as blueprints for the design of novel antitrypanosomal compounds.

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Plasmodium falciparum Parasites Are Killed by a Transition State Analogue of Purine Nucleoside Phosphorylase in a Primate Animal Model

Cited by 62 publications

References 44 publications

Immucillins in Infectious Diseases

Immucillins in Infectious Diseases

Substrate and Inhibitor Specificity of thePlasmodium bergheiEquilibrative Nucleoside Transporter Type 1

Structures of purine nucleosidase fromTrypanosoma bruceibound to isozyme-specific trypanocidals and a novel metalorganic inhibitor

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