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Antimicrobial Agents and Chemotherapy, April 2002, p. 1117-1118, Vol. 46, No. 4
0066-4804/02/$04.00+0 DOI: 10.1128/AAC.46.4.1117-1118.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
In Vitro Activities of Peptide Deformylase Inhibitors against Gram-Positive Pathogens
R. Wise,* J. M. Andrews, and J. Ashby
Department of Microbiology, City Hospital NHS Trust, Birmingham, United Kingdom
Received 14 May 2001/
Returned for modification 25 November 2001/
Accepted 3 January 2002

ABSTRACT
The activities of six peptide deformylase (PDF) inhibitors against
107 respiratory tract pathogens were studied and compared to
those of ciprofloxacin and amoxicillin-clavulanate. Against
Streptococcus pneumoniae, BB-83698 and BB-83815 were the most
active PDF inhibitors (MIC at which 90% of the organisms tested
were inhibited [MIC
90], 0.25 µg/ml). Five of the agents
showed similar activity against
Moraxella catarrhalis (MIC
90,
0.12 µg/ml). All PDF inhibitors were less active against
Haemophilus influenzae; BB-3497 was the most active agent (MIC
90,
2 µg/ml). Five agents were studied against
Chlamydia spp.
and showed activity similar to that of ciprofloxacin (MIC, 0.5
to 4 µg/ml). This study demonstrates that PDF inhibitors
have the potential to be developed for the treatment of respiratory
tract infections.

TEXT
Peptide deformylase (PDF) is a necessary enzyme in bacterial
protein synthesis. Following translation, the
N-formyl group
is hydrolyzed by PDF. The gene encoding PDF (
def) is present
in all pathogenic bacteria but has no mammalian counterpart.
Recently, two novel PDF inhibitors (BB-3497 and VRC 483) were
described (
1; D. Cheu, D. Patel, C. Wu, et al., Abstr. 39th
Intersci. Conf. Antimicrob. Agents Chemother., abstr. 1794,
p. 333, 1999) and shown to be active against a range of gram-positive
pathogens. Here we describe the activities of five new agents
of the same class (including BB-3497) which, unlike VCR 483,
are synthetically derived and were obtained from British Biotech
Pharmaceuticals (Oxford, United Kingdom). Their activities were
compared with those of ciprofloxacin (Bayer Pharmaceuticals,
Basingstoke, United Kingdom) and amoxicillin-clavulanate and
penicillin (GlaxoSmithKine, Worthing, United Kingdom).
A total of 107 organisms (Tables 1 and 2) were tested by methods previously described (2, 3). Briefly, susceptibility was determined by a standard agar plate dilution method with Iso-Sensitest agar (pH 7.2; Unipath, Basingstoke, United Kingdom) supplemented with 5% horse blood (Bradsure Biologicals, Loughborough, United Kingdom) and 20 mg of NAD (Sigma Chemicals, Poole, United Kingdom)/liter. The inoculum was 104 CFU/spot, and incubation was done for 20 h in air and 4 to 6% CO2. The MIC was defined as the lowest concentration of antimicrobial agent at which no more than two colonies were observed. Amoxicillin and clavulanate were combined at a ratio of 2:1, and the MIC for the combination was recorded in terms of the amoxicillin MIC. Chlamydia spp. were studied by the method of Webberly et al. (2). Because of a limited supply of compounds, the highest concentration of the PDF inhibitors used was 16 µg/ml.
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TABLE 2. MIC and minimum lethal concentration (MLC) of ciprofloxacin and five PDF inhibitors for three Chlamydia strains
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Table
1 shows the activities of the six new compounds against
the bacterial strains studied. Eleven strains of
Streptococcus pneumoniae were known to have intermediate susceptibility to
penicillin (MICs,

0.25 and

1 µg/ml), one strain was resistant
to penicillin (MIC, 2 µg/ml), and five had reduced susceptibility
to ciprofloxacin (MIC,

8 µg/ml). The PDF inhibitor activities
ranged from an MIC
90 (MIC at which 90% of the organisms tested
were inhibited) of 0.5 µg/ml for BB-83698 and BB-83815
to an MIC
90 of >8 µg/ml for BB-3497. There was no evidence
of cross-resistance between the PDF inhibitors and penicillin
or ciprofloxacin. Those strains which were more susceptible
to one PDF inhibitor were similarly more susceptible to the
other agents of this class.
Less variation among the new agents tested was seen for Moraxella catarrhalis. For this organism, BB-3497 was as active as the other agents. Generally, all the compounds were as active as ciprofloxacin and amoxicillin-clavulanate.
Against Haemophilus influenzae, there was considerable variation among the PDF inhibitors tested, with BB-3497 being the most active, BB-84518 showing intermediate activity, and the remaining compounds being markedly less active. There was no link between lack of susceptibility to amoxicillin-clavulanate and that to the PDF inhibitors.
In Table 2, the activities of five of the PDF compounds against three strains of Chlamydia spp. are shown and compared with that of ciprofloxacin. Generally, the new agents displayed activities similar to that of the fluoroquinolone, and BB-83857 was the most consistently active compound.
In this study, one agent, BB-3497, whose structure has been described in patent application WO99/39704 (1), was shown to be less potent against respiratory pathogens than the other five compounds studied. The exception was the greater activity of BB-3497 against H. influenzae; whereas the range of MICs of the new compounds against S. pneumoniae and M. catarrhalis was moderately narrow, a far greater degree of activity was noted against H. influenzae. It is not known if this result is related to differences in the avidities of the PDF inhibitors for the target sites or is related to bacterial cell penetration.
An earlier study (1) showed that BB-3497 is active when given orally and is effective in animal models of infection. By increasing the number of agents tested and studying the mode of binding of PDF inhibitors in different bacterial species, it should be possible to improve antibacterial potency against target groups of bacterial pathogens.

ACKNOWLEDGMENTS
We thank J. M. Clements of British Biotech Pharmaceuticals for
advice and financial support.

FOOTNOTES
* Corresponding author. Mailing address: Department of Microbiology, City Hospital NHS Trust, Birmingham, United Kingdom. Phone: 44 121 507 4255. Fax: 44 121 551 7763. E-mail:
r.wise{at}bham.ac.uk.


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2
- Webberly, J. M., R. S. Matthews, J. M. Andrews, and R. Wise. 1987. Commercially available fluorescein-conjugated monoclonal antibody for determining the in vitro activity of antimicrobial agents against Chlamydia trachomatis. Eur. J. Microbiol. 6:587-589.
3
- Wise, R., and J. M. Andrews. 1999. In vitro activity and tentative breakpoints of gemifloxacin, a new fluoroquinolone. J. Antimicrob Chemother. 44:679-688.[Abstract/Free Full Text]
Antimicrobial Agents and Chemotherapy, April 2002, p. 1117-1118, Vol. 46, No. 4
0066-4804/02/$04.00+0 DOI: 10.1128/AAC.46.4.1117-1118.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
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