Identification of highly potent and selective inhibitors of Toxoplasma gondii dihydrofolate reductase

Chio, L. C.; Queener, Sherry F.

doi:10.1128/aac.37.9.1914

Cited by 96 publications

(148 citation statements)

References 14 publications

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“…In the absence of FA both the rat and human enzymes were found to be slightly substrate inhibited above 0.5 and 1 M 7,8-DHF for the rat and human enzymes, respectively, ( Fig. S5) as has been previously reported (20,21). The data were found to be well described by the equation for substrate inhibition detailed by Nakano et al (22).…”

supporting

confidence: 68%

The extremely slow and variable activity of dihydrofolate reductase in human liver and its implications for high folic acid intake

Bailey

Ayling

2009

Proc. Natl. Acad. Sci. U.S.A.

335

291

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Numerous clinical trials using folic acid for prevention of cardiovascular disease, stroke, cognitive decline, and neural tube defects have been completed or are underway. Yet, all functions of folate are performed by tetrahydrofolate and its one-carbon derivatives. Folic acid is a synthetic oxidized form not significantly found in fresh natural foods; to be used it must be converted to tetrahydrofolate by dihydrofolate reductase (DHFR). Increasing evidence suggests that this process may be slow in humans. Here we show, using a sensitive assay we developed, that the reduction of folic acid by DHFR per gram of human liver (n ‫؍‬ 6) obtained from organ donors or directly from surgery is, on average, less than 2% of that in rat liver at physiological pH. Moreover, in contrast to rats, there was almost a 5-fold variation of DHFR activity among the human samples. This limited ability to activate the synthetic vitamer raises issues about clinical trials using high levels of folic acid. The extremely low rate of conversion of folic acid suggests that the benefit of its use in high doses will be limited by saturation of DHFR, especially in individuals possessing lower than average activity. These results are also consistent with the reports of unmetabolized folic acid in plasma and urine.folate ͉ provitamin utilization ͉ unmetabolized folic acid ͉ vitamin supplements ͉ nutrition

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supporting

confidence: 68%

The extremely slow and variable activity of dihydrofolate reductase in human liver and its implications for high folic acid intake

Bailey

Ayling

2009

Proc. Natl. Acad. Sci. U.S.A.

335

291

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“…b Percent survival of parasites was measured by incorporation of [5,[6][7][8][9][10][11][12][13] H]uracil in at least 2 independent experiments of 3 replica each as previously described [19,20,31].…”

Section: Discussionmentioning

confidence: 99%

“…The final concentration of ethanol when the compounds were added to the wells was 2.5%. After an additional 18 hrs incubation the medium was replaced with 1 mL drug free media containing [5,[6][7][8][9][10][11][12][13] H]uracil (5 μCi/mL) and incubated for another 6 hrs after which the media was removed. The fibroblasts were then released from the wells by trypsinization with the addition of 200 μL trypsin/EDTA (2.5X) to each well.…”

Section: Evaluation Of N 6 -Benzyladenosine Analogues As Potential Anmentioning

confidence: 99%

“…Pyrimethamine is currently used in combination with sulfa drugs such as sulfadiazine in toxoplasmic infections [4,5]. This combination therapy targets enzymes of folate metabolism such as dihydrofolate reductase [6][7][8][9]. However, current therapies have been limited due to resistance, host toxicity and side effects.…”

Section: Introductionmentioning

confidence: 99%

“…We have also carried out systematic characterization of the hydrophobic effect and van der Waals interaction employing an induced fit molecular modeling approach to demonstrate the role of additional interaction in enhancing the binding affinity of ligands to T. gondii adenosine kinase in this series. [8][9][10][11][12][13][14] C]Adenosine (55 Ci/mol) and [5,[6][7][8][9][10][11][12][13] H]uracil were purchased from Moravek Biochemicals. RPMI-1640 medium from GIBCO BRL; fetal bovine serum (FBS) from HyClone Laboratories.…”

Section: Introductionmentioning

confidence: 99%

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Synthesis, biological evaluation and molecular modeling studies of N6-benzyladenosine analogues as potential anti-toxoplasma agents

Kim

Sharon

Chu

et al. 2007

Biochemical Pharmacology

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Toxoplasma gondii is an opportunistic pathogen responsible for toxoplasmosis. T. gondii is a purine auxotroph incapable of de novo purine biosynthesis and depends on salvage pathways for its purine requirements. Adenosine kinase (EC.2.7.1.20) is the major enzyme in the salvage of purines in these parasites. 6-Benzylthioinosine and analogues were established as "subversive substrates" for the T. gondii, but not for the human adenosine kinase. Therefore, these compounds act as selective antitoxoplasma agents. In the present study, a series of N 6 -benzyladenosine analogues were synthesized from 6-chloropurine riboside with substituted benzylamines & − solution phase parallel synthesis. These N 6 -benzyladenosine analogues were evaluated for their binding affinity to purified T. gondii adenosine kinase. Furthermore, the anti-toxoplasma efficacy and host toxicity of these compounds were tested in cell culture. Certain substituents on the aromatic ring improved binding affinity to T. gondii adenosine kinase when compared to the unsubstituted N 6 -benzyladenosine. Similarly, varying the type and position of the substituents on the aromatic ring led to different degrees of potency and selectivity as anti-toxoplasma agents. Among the synthesized analogues, N 6 -(2,4-dimethoxybenzyl) adenosine exhibited the most favorable anti-toxoplasma activity without host toxicity. The binding mode of the synthesized N 6 -benzyladenosine analogues were characterized to illustrate the role of additional hydrophobic effect and van der Waals interaction within an active site of T. gondii adenosine kinase by induced fit molecular modeling.

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Molecular modelling of trimethoprim complexes of human wild-type and mutant dihydrofolate reductases: identification of two subsets of binding residues in the antifolate binding site

Pan

Bowen

Southerland

1999

Biopharm. Drug Dispos.

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Computer‐assisted molecular modelling was used to generate structures for the trimethoprim (TMP):NADPH:dihydrofolate reductase (DHFR) ternary complexes for human wild‐type DHFR and for five DHFR mutants (L22R, L22F, F31S, F31W and Q35P). The mutants correspond to DHFR proteins that have been isolated from tissues exposed to chronic or high dose methotrexate (MTX) and show decreased sensitivity to antifolate inhibition. Analysis of the TMP:DHFR interactions suggest the presence of two subsets of TMP binding residues in the DHFR antifolate binding site. One subset of these residues (GLU30, PHE34, ILE60 and VAL115) are common to each DHFR complex studied and are referred to as core residues. The other TMP binding residues vary among the DHFR complexes studied and are referred to as noncore residues. The core residues exhibit a greater number of TMP contacts/residue and form more stable TMP interactions than noncore residues. Additionally, the core and noncore residues make contact with different regions of the TMP structure. Information presented here provides additional insight into the design of new agents for the improved inhibition of wild‐type DHFR and the simultaneous inhibition of both wild‐type and mutant DHFR molecules. Copyright © 1999 John Wiley & Sons, Ltd.

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Identification of highly potent and selective inhibitors of Toxoplasma gondii dihydrofolate reductase

Cited by 96 publications

References 14 publications

The extremely slow and variable activity of dihydrofolate reductase in human liver and its implications for high folic acid intake

The extremely slow and variable activity of dihydrofolate reductase in human liver and its implications for high folic acid intake

Synthesis, biological evaluation and molecular modeling studies of N6-benzyladenosine analogues as potential anti-toxoplasma agents

Molecular modelling of trimethoprim complexes of human wild-type and mutant dihydrofolate reductases: identification of two subsets of binding residues in the antifolate binding site

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