In Vitro Efficacy of New Antifolates against Trimethoprim-Resistant
            <i>Bacillus anthracis</i>

Barrow, Esther W.; Dreier, Jürg; Reinelt, Stefan; Bourne, Philip C.; Barrow, William W.

doi:10.1128/aac.00628-07

Cited by 32 publications

(38 citation statements)

References 22 publications

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“…RAB1 inhibited growth of both Gram-negative (F. tularensis, Y. pestis, and B. abortus) and Gram-positive (B. anthracis, VRE, and S. aureus) organisms, indicating a broad-spectrum profile of activity (Table 3). Despite initial selection of RAB1 (previously BAL17662) for its inhibitory activity against B. anthracis, the present results demonstrate a potent antistaphylococcal profile (3). Among the organisms tested, F. tularensis, B. abortus, B. anthracis, VRS1, and VRS2 have an MIC for TMP of Ն16 g/ml, which is classified as resistant by CLSI (11).…”

Section: Resultsmentioning

confidence: 81%

Inhibition of Antibiotic-Resistant Staphylococcus aureus by the Broad-Spectrum Dihydrofolate Reductase Inhibitor RAB1

Barrow¹,

Bunce

Bourne³

et al. 2010

Antimicrob Agents Chemother

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The bacterial burden on human health is quickly outweighing available therapeutics. Our long-term goal is the development of antimicrobials with the potential for broad-spectrum activity. We previously reported phthalazine-based inhibitors of dihydrofolate reductase (DHFR) with potent activity against Bacillus anthracis, a major component of Project BioShield. The most active molecule, named RAB1, performs well in vitro and, in a cocrystal structure, was found deep within the active site of B. anthracis DHFR. We have now examined the activity of RAB1 against a panel of bacteria relevant to human health and found broad-spectrum applicability, particularly with regard to Gram-positive organisms. RAB1 was most effective against Staphylococcus aureus, including methicillin-and vancomycin-resistant (MRSA/VRSA) strains. We have determined the cocrystal structure of the wild-type and trimethoprim-resistant (Phe 98 Tyr) DHFR enzyme from S. aureus with RAB1, and we found that rotational freedom of the acryloyl linker region allows the phthalazine moiety to occupy two conformations. This freedom in placement also allows either enantiomer of RAB1 to bind to S. aureus, in contrast to the specificity of B. anthracis for the S-enantiomer. Additionally, one of the conformations of RAB1 defines a unique surface cavity that increases the strength of interaction with S. aureus. These observations provide insights into the binding capacity of S. aureus DHFR and highlight atypical features critical for future exploitation in drug development.

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Section: Resultsmentioning

confidence: 81%

Inhibition of Antibiotic-Resistant Staphylococcus aureus by the Broad-Spectrum Dihydrofolate Reductase Inhibitor RAB1

Barrow¹,

Bunce

Bourne³

et al. 2010

Antimicrob Agents Chemother

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“…Previous studies revealed a high selectivity of RAB1 for B. anthracis DHFR over human DHFR (IC 50 ϭ 54 nM versus 110,000 nM) (7). A comparison of binding sites was made using the human DHFR structure complexed with MTX and NADPH (PDB ID code 1U72, RMS deviation ϭ 2.05 Å) (20).…”

Section: Structure Of B Anthracis Dhfr-rab1 Complexmentioning

confidence: 99%

“…We have previously identified dihydrophthalazine TMP derivative inhibitors for this target (7). Variation of the moiety attached to the dihydrophthalazine ring produced 50% inhibitory concentrations (IC 50 s) ranging from 46 to 600 nM (6).…”

mentioning

confidence: 99%

Crystal Structure of Bacillus anthracis Dihydrofolate Reductase with the Dihydrophthalazine-Based Trimethoprim Derivative RAB1 Provides a Structural Explanation of Potency and Selectivity

Bunce

Bourne²,

Berlin

et al. 2009

Antimicrob Agents Chemother

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Bacillus anthracis possesses an innate resistance to the antibiotic trimethoprim due to poor binding to dihydrofolate reductase (DHFR); currently, there are no commercial antibacterials that target this enzyme in B. anthracis. We have previously reported a series of dihydrophthalazine-based trimethoprim derivatives that are inhibitors for this target. In the present work, we have synthesized one compound (RAB1) displaying favorable 50% inhibitory concentration (54 nM) and MIC (<12.8 g/ml) values. RAB1 was cocrystallized with the B. anthracis DHFR in the space group P2 1 2 1 2 1 , and X-ray diffraction data were collected to a 2.3-Å resolution. Binding of RAB1 causes a conformational change of the side chain of Arg58 and Met37 to accommodate the dihydrophthalazine moiety. Unlike the natural substrate or trimethoprim, the dihydrophthalazine group provides a large hydrophobic anchor that embeds within the DHFR active site and accounts for its selective inhibitory activity against B. anthracis.

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“…Based on previous work by Basilea Pharmaceutica 11-14 and Barrow et al, 4 a number of DAP inhibitors were designed, synthesized, and evaluated for their biological activities. The initial modifications were made at R 1 on the dihydrophthalazine ring.…”

Section: Introductionmentioning

confidence: 99%

Modified 2,4-diaminopyrimidine-based dihydrofolate reductase inhibitors as potential drug scaffolds against Bacillus anthracis

Nammalwar

Wakeham

Bourne

et al. 2015

Bioorganic & Medicinal Chemistry

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The current paper describes the synthesis and biological evaluation of dihydrophthalazine-appended 2,4-diaminopyrimidine (DAP) inhibitors (1) oxidized at the methylene bridge linking the DAP ring to the central aromatic ring and (2) modified at the central ring ether groups. Structures 4a-b incorporating an oxidized methylene bridge showed a decrease in activity, while slightly larger alkyl groups (CH2CH3 versus CH3) on the central ring oxygen atoms (R2 and R3) had a minimal impact on the inhibition. Comparison of the potency data for previously reported RAB1 and BN-53 with the most potent of the new derivatives (19b and 20a-b) showed similar values for inhibition of cellular growth and direct enzymatic inhibition (MICs 0.5-2 μg/mL). Compounds 29-34 with larger ester and ether groups containing substituted aromatic rings at R3 exhibited slightly reduced activity (MICs 2-16 μg/mL). One explanation for this attenuated activity could be encroachment of the extended R3 into the neighboring NADPH co-factor. These results indicate that modest additions to the central ring oxygen atoms are well tolerated, while larger modifications have the potential to act as dual-site inhibitors of dihydrofolate reductase (DHFR).

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In Vitro Efficacy of New Antifolates against Trimethoprim-Resistant Bacillus anthracis

Cited by 32 publications

References 22 publications

Inhibition of Antibiotic-Resistant Staphylococcus aureus by the Broad-Spectrum Dihydrofolate Reductase Inhibitor RAB1

Inhibition of Antibiotic-Resistant Staphylococcus aureus by the Broad-Spectrum Dihydrofolate Reductase Inhibitor RAB1

Crystal Structure of Bacillus anthracis Dihydrofolate Reductase with the Dihydrophthalazine-Based Trimethoprim Derivative RAB1 Provides a Structural Explanation of Potency and Selectivity

Modified 2,4-diaminopyrimidine-based dihydrofolate reductase inhibitors as potential drug scaffolds against Bacillus anthracis

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