title: In vitro efficacy of new antifolates against trimethoprim-resistant Bacillus anthracis.
abstract: Bacillus anthracis is innately resistant to trimethoprim (TMP), a synthetic antifolate that selectively inhibits several bacterial dihydrofolate reductases (DHFRs) but not human DHFR. Previously, we were able to confirm that TMP resistance in B. anthracis (MIC > 2,048 microg/ml) is due to the lack of selectivity of TMP for the B. anthracis DHFR (E. W. Barrow, P. C. Bourne, and W. W. Barrow, Antimicrob. Agents Chemother. 48:4643-4649, 2004). In this investigation, 24 2,4-diaminopyrimidine derivatives, representing a class of compounds with dihydrophthalazine side chains, were screened for their in vitro effects on B. anthracis Sterne and their selectivities for the B. anthracis DHFR. MICs were obtained by a colorimetric (Alamar blue) broth microdilution assay. Purified human recombinant DHFR (rDHFR) and B. anthracis rDHFR were used in a validated enzyme assay to determine the 50% inhibitory concentrations (IC(50)s) and the selectivity ratios of the derivatives. The MICs ranged from 12.8 to 128 microg/ml for all but nine compounds, for which the MICs were > or =128 microg/ml. The IC(50) values for B. anthracis rDHFR ranged from 46 to 600 nM, whereas the IC(50) values for human rDHFR were >16,000 nM. This is the first report on the in vitro inhibitory actions of this class of antifolates against TMP-resistant B. anthracis isolates. The selective inhibition of B. anthracis rDHFR and the in vitro activity against B. anthracis demonstrate that members of this class of compounds have the potential to be developed into clinically important therapeutic choices for the treatment of infections caused by TMP-resistant bacteria, such as B. anthracis.
authors: Department of Veterinary Pathobiology, 250 McElroy, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK 74078, USA.
authors: Esther W
authors: EW
authors: Barrow
authors: Jürg
authors: J
authors: Dreier
authors: Stefan
authors: S
authors: Reinelt
authors: Philip C
authors: PC
authors: Bourne
authors: William W
authors: WW
authors: Barrow
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D001408:Bacillus anthracis / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D005493:Folic Acid Antagonists / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D008826:Microbial Sensitivity Tests; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009154:Mutation; D011485:Protein Binding; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship; D013762:Tetrahydrofolate Dehydrogenase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014295:Trimethoprim / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D014296:Trimethoprim Resistance
chemical_list: D000900:Anti-Bacterial Agents; D004791:Enzyme Inhibitors; D005493:Folic Acid Antagonists; D014295:Trimethoprim; D013762:Tetrahydrofolate Dehydrogenase