1 Department of Medicine, Veterans Affairs Medical Center, 800 Irving Avenue, Syracuse, NY 13210; 2 Jacobus Pharmaceutical Company, Princeton, NJ, USA
Keywords: BB-3497, peptide deformylase inhibitors, TB
Sir,
Bacterial peptide deformylase (PDF) belongs to a subfamily of metalloproteases catalysing the removal of the N-terminal formyl group from newly synthesized proteins. PDF is essential in prokaryotes and appears to be conserved throughout the eubacteria. Thus, it may be suitable as a target for new chemotherapeutic agents. Various PDF inhibitors have in vitro activities against several pathogens including Escherichia coli, Haemophilus influenzae and Staphylococcus aureus.13 In view of their wide spectrum of activity, six PDF inhibitors were initially screened against two isolates of Mycobacterium tuberculosis.
BB-84416, BB-3497, BB-83857, BB-83815, BB84518 and BB-83698 were provided by British Biotech Pharmaceuticals Ltd (Oxford, UK). Isoniazid and rifampicin, used as control drugs in these experiments, were obtained from Sigma Chemical Company (St Louis, MI, USA).
Stock solutions of these compounds were diluted in modified 7H10 broth to produce serial two-fold dilutions, 0.0158 mg/L. Isolates were grown at 37°C in modified 7H10 broth (malachite green and agar omitted) with 10% OADC enrichment (oleic acidalbumindextrosecatalase) and 0.05% Tween 80, pH 6.6. The inoculum was prepared by dilution in modified 7H10 broth yielding a final concentration of 2 x 104 cfu/mL (range: 2 x 1037.1 x 104 cfu/mL). The size of the inoculum was measured by titration and counting the duplicate 7H10 agar plates supplemented with 10% OADC. The MIC of a drug was defined as the lowest concentration that yielded no visible turbidity. The incubation time was
14 days.
Statistical analysis was conducted with Minitab 13.2 (College Park, PA, USA). Since the sample sizes were small, non-parametric statistics were used.
Initial testing showed that three of the six compounds had MICs greater than 2 mg/L. The remaining three drugs, BB-3497, BB-84518 and BB-83698 had MICs in the range 0.062 mg/L. Rifampicin, the control drug, had a median MIC of 0.06 mg/L. Expanded testing focused on the three most promising compounds with an additional 17 isolates of M. tuberculosis (Table 1). BB-3497 was the most active PDF inhibitor with a median MIC of 0.25 mg/L. Isoniazid, the control drug for this experiment, had a median MIC of 0.031 mg/L. The difference of 0.22 mg/L was statistically significant (MannWhitney test, P < 0.001), implying that BB-3497 was less potent than isoniazid. Additionally, the MICs of BB-3497 did not correlate with those of isoniazid (r = 0.0032; P = 0.99: Pearsons rank order), implying that there was no relationship between the susceptibility of an isolate to BB-3497 and to isoniazid.
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This study demonstrates that BB-3497 has potent in vitro activity against M. tuberculosis. Further in vivo evaluation of this compound alone or in combination with other agents would define its therapeutic potential.
Acknowledgements
British Biotech Pharmaceuticals provided partial support for these studies.
Footnotes
* Corresponding author. Tel: +1-315-425-4884; Fax: +1-315-425-4871; E-mail: Michael.Cynamon{at}med.va.gov
References
1
.
Clements, J. M., Beckett, R. P., Brown, A. et al. (2001). Antibiotic activity and characterization of BB-3497, a novel peptide deformylase inhibitor. Antimicrobial Agents and Chemotherapy 45, 56370.
2
.
Apfel, C. M., Locher, H., Evers, S. et al. (2001). Peptide deformylase as an antibacterial drug target: target validation and resistance development. Antimicrobial Agents and Chemotherapy 45, 105864.
3
.
Wise, R., Andrews, J. M. & Ashby, J. (2002). In vitro activities of peptide deformylase inhibitors against gram-positive pathogens. Antimicrobial Agents and Chemotherapy 46, 11178.
4
.
Giglione, C., Serero, A., Pierre, M. et al. (2000). Identification of eukaryotic peptide deformylases reveals universality of N-terminal protein processing mechanisms. EMBO Journal 19, 591629.
5 . Saitou, N. & Nei, M. (1987). The neighbor-joining method: a new method for reconstructing phylogenetic trees. Molecular and Biological Evolution 4, 40625.
6 . Nguyen, K. T., Hu, X., Colton, C. et al. (2003). Characterization of a human peptide deformylase: implications for antibacterial drug design. Biochemistry 42, 99528.[CrossRef][ISI][Medline]