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Journal of Antimicrobial Chemotherapy (2004) 53, 664-668
© 2004 The British Society for Antimicrobial Chemotherapy

In vitro antibacterial activity of the peptide deformylase inhibitor BB-83698

Denene Lofland1,*, Stacey Difuntorum1, Andrew Waller2, John M. Clements2, Mellany K. Weaver3, James A. Karlowsky3 and Kirk Johnson1

1 Genesoft Pharmaceuticals, Inc., 7300 Shoreline Court, South San Francisco, CA, USA; 2 British Biotech Pharmaceuticals Ltd., Oxford, UK; 3 Focus Technologies, Herndon, VA, USA

Received 2 September 2003; returned 5 November 2003; revised 20 November 2003; accepted 23 December 2003


   Abstract
Top
 Abstract
Introduction
 Materials and methods
 Results
 Discussion
 References
 
Objectives: BB-83698 is a peptide deformylase inhibitor currently in clinical trials in Europe. The purpose of this study was to provide additional susceptibility data from clinical isolates, including drug-resistant strains.

Methods: The in vitro activities of BB-83698 and comparators were determined against 281 streptococci, 154 Staphylococcus aureus, 110 Haemophilus influenzae and 50 Moraxella catarrhalis strains selected for their resistance phenotypes. Broth microdilution MICs and MBCs were determined according to NCCLS guidelines.

Results: The MIC90s were 0.25–0.5 mg/L for S. pneumoniae, including penicillin-, erythromycin-, levofloxacin- and multidrug-resistant strains. The MIC90s for Streptococcus pyogenes and Streptococcus agalactiae were 0.12 mg/L and for viridans streptococci, the MIC90 was 0.5 mg/L. Against S. aureus, including oxacillin- and levofloxacin-resistant strains, and vancomycin-intermediate strains, the MIC90 was 8 mg/L. Against ß-lactamase-negative and -positive H. influenzae, the MIC90s were 32 and 64 mg/L, respectively, and against both ß-lactamase-negative and -positive M. catarrhalis the MIC90 was 0.12 mg/L. In MBC studies, the ratio of MBC/MIC was 1:1 or 2:1 against 31% of S. pneumoniae, 33% of S. aureus, 63% of H. influenzae and 9% of M. catarrhalis.

Conclusions: Although BB-83698 has reduced in vitro activity against H. influenzae, it is a potent antimicrobial with excellent activity against streptococci and Moraxella.

Keywords: antimicrobials, antibiotics, bactericidal, MIC, MBC


   Introduction
Top
 Abstract
 Introduction
Materials and methods
 Results
 Discussion
 References
 
BB-83698 is a member of a novel class of antibiotics. The mechanism of action is through potent inhibition of the bacterial metalloenzyme peptide deformylase (PDF). PDF is essential for bacterial protein maturation. Bacterial translation is initiated by a unique tRNA, formylmethionyl-tRNAfMet. Following translation, PDF removes the N-terminal formyl group and allows further processing by methionine aminopeptidase which removes the methionine group to produce the mature protein.1–3

Whereas other antibiotics have targeted bacterial protein synthesis, this is the first class to target PDF. The gene encoding PDF (def) is ubiquitous in the genome of all sequenced pathogenic bacteria and PDF inhibitors have been shown to be active against many pathogens.1,4,5 Although PDF-like sequences have been identified in human mitochondria, studies suggest human PDF has no function in protein formylation/deformylation.6 BB-83698 is the first compound in this class to enter clinical trials. PDF represents an attractive target for antimicrobial chemotherapy because it is: (i) essential for bacterial growth, (ii) highly conserved among bacteria, (iii) offers selectivity, and (iv) is novel.

The purpose of this study was to profile BB-83698 further for clinical development. This report describes the in vitro activity of BB-83698 against recent clinical isolates including drug-resistant strains. The activity was compared to the activity of other agents such as penicillin, levofloxacin, linezolid and quinupristin/dalfopristin.


   Materials and methods
Top
 Abstract
 Introduction
 Materials and methods
Results
 Discussion
 References
 
Bacterial strains

Strains were selected based upon their phenotypic resistance profiles from the Focus Technologies (Herndon, VA, USA) strain collection. All isolates were collected from patients at US hospitals from January 1999 to March 2002. The activity of BB-83698 was determined for 213 Streptococcus pneumoniae, including penicillin-resistant, erythromycin-resistant, levofloxacin-resistant and multidrug-resistant strains. Multidrug-resistant S. pneumoniae were defined by resistance to three or more of the following agents: penicillin, ceftriaxone, erythromycin, levofloxacin and trimethoprim–sulfamethoxazole. Activity was also determined for 21 Streptococcus pyogenes, 21 Streptococcus agalactiae, 26 viridans streptococci, 154 Staphylococcus aureus (including oxacillin-resistant, levofloxacin-resistant strains and vancomycin-intermediate strains), 110 Haemophilus influenzae (ß-lactamase-negative and -positive) and 50 Moraxella catarrhalis (ß-lactamase-negative and -positive).

Antimicrobial susceptibility testing

Broth microdilution antimicrobial susceptibility testing was carried out in accordance with published NCCLS methods.7 Each isolate was tested over a range of doubling dilution concentrations in frozen microdilution panels prepared by TREK Diagnostics (Cleveland, OH, USA). The quality control (QC) organisms, assayed each day that testing was carried out, were within NCCLS established ranges for comparators. The BB-83698 MIC ranges against QC organisms were: S. pneumoniae ATCC 49619, 0.12–0.25 mg/L; S. aureus ATCC 29213, 4 mg/L; and H. influenzae ATCC 49247, 8 mg/L.

Minimum bactericidal concentrations

Minimum bacterial concentrations (MBCs), defined as the concentrations at which killing of >=99.9% of starting inocula occur, were determined in accordance with published NCCLS methods8 using selected isolates of S. pneumoniae, S. aureus, H. influenzae and M. catarrhalis. To determine an MBC, 10 µL from each clear well on broth microdilution panels was plated on blood agar plates (S. aureus, S. pneumoniae, M. catarrhalis) or chocolate agar plates (H. influenzae) and incubated at 35°C for 48 h (S. aureus) or 72 h (S. pneumoniae, H. influenzae and M. catarrhalis). After incubation, colony counts for each panel well plated were recorded and the 10 µL aliquot of the lowest antimicrobial concentration that demonstrated a kill of >=99.9% relative to the starting inoculum was recorded as the MBC.


   Results
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 Abstract
 Introduction
 Materials and methods
 Results
Discussion
 References
 
The MICs for the isolates tested are shown in Table 1. The table includes the MIC range, MIC50 and MIC90. MBCs for a randomly selected subset of S. pneumoniae, S. aureus, H. influenzae and M. catarrhalis isolates are shown in Table 2.


View this table:
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  		Table 1.. In vitro activity of BB-83698 and comparators
 

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  		Table 2.. MBC versus MIC of BB-83698
 
Streptococci

The MIC90s of BB-83698 for penicillin-susceptible, -intermediate and -resistant S. pneumoniae were, respectively, 0.5, 0.5 and 0.25 mg/L. Similarly, for erythromycin-resistant, levofloxacin-resistant and multidrug-resistant S. pneumoniae, the MIC90 was 0.5 mg/L. BB-83698 MIC90s were comparable to those of levofloxacin, linezolid, quinupristin/dalfopristin and vancomycin for non-susceptible S. pneumoniae and viridans streptococci. BB-83698 was also active against S. pyogenes and S. agalactiae, with an MIC90 of 0.12 mg/L.

S. aureus

There was no difference between the MIC90 of oxacillin-susceptible and oxacillin-resistant S. aureus. The BB-83698 MIC90 of 8 mg/L was lower than that of ampicillin, erythromycin, levofloxacin, oxacillin and tetracycline for oxacillin-resistant strains. Among levofloxacin-resistant strains, quinupristin/dalfopristin and linezolid were the most active (MIC90s 1 and 2 mg/L, respectively) whereas BB-83698 in vitro activity was equivalent to that of vancomycin (MIC90 8 mg/L). Against vancomycin-intermediate S. aureus, the BB-83698 MIC50 was lower than that of all comparators except linezolid, quinupristin/dalfopristin and tetracycline.

H. influenzae

The MIC90s for ß-lactamase-negative and -positive H. influenzae were 32 and 64 mg/L, respectively. Of the 60 ß-lactamase-negative strains, 11 were resistant to ampicillin (BLNAR). The MICs of BB-83698 for the BLNAR strains were 4–16 mg/L.

M. catarrhalis

BB-83698 was one of the most potent agents tested against M. catarrhalis. The MIC90 was 0.12 mg/L against both ß-lactamase producers and non-producers. In this in vitro comparison, erythromycin was as potent as BB-83698 and levofloxacin was the most potent agent against both groups.

Minimum bactericidal concentration

The BB-83698 MBC was one dilution higher than the MIC for five of the 16 (31%) S. pneumoniae tested. No S. pneumoniae isolate had an MBC higher than 8 mg/L. Against S. aureus, BB-83698 MBCs were not more than one dilution higher than the MIC for 33% (four of 12) of the strains. BB-83698 MBCs were no more than one dilution above the MIC against the majority of H. influenzae, 63% (10 of 16). Among M. catarrhalis, BB-83698 MBCs were within one doubling dilution of the MICs for only one of 11 (9%) strains. No isolate had an MBC greater than 2 mg/L.


   Discussion
Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
References
 
Prior studies have shown that, in general, PDF inhibitors have good in vitro activity against Gram-positive pathogens, such as streptococci and staphylococci, as well as the Gram-negative coccobacillus M. catarrhalis. Activity against H. influenzae and Enterobacteriaceae has been variable. A lack of activity is apparently the result of active efflux of PDF inhibitors by AcrAB-type pumps. Reports show PDF inhibitor MICs are higher against wild-type E. coli than against AcrAB efflux pump-deficient strains.1,9

The novel PDF inhibitor BB-83698 was shown to have good in vitro activity against streptococci. This spectrum included S. pyogenes, S. agalactiae, viridans streptococci, and penicillin-susceptible, penicillin-non-susceptible, erythromycin-resistant, levofloxacin-resistant and multidrug-resistant S. pneumoniae. These data are in agreement with previous reports of a lack of cross-resistance between PDF inhibitors and other classes of antimicrobials.1,4

Although MICs were higher against S. aureus than streptococci, BB-83698 showed similar activity among all S. aureus resistance phenotypes tested. H. influenzae was the group least susceptible to BB-83698. The majority of strains were inhibited by >=16 mg/L. In contrast, excellent potency was observed against M. catarrhalis. Of the 50 strains tested, no BB-83698 MIC was greater than 0.25 mg/L.

In addition to the in vitro potency and spectrum, BB-83698 demonstrated an MBC/MIC ratio of 1:1 or 2:1 against almost two-thirds of H. influenzae and approximately one-third of the S. pneumoniae and S. aureus strains tested. Notably, the in vitro anti-pneumococcal activity profile of BB-83698 translates well to the in vivo setting as it has been shown to have bactericidal efficacy against drug-sensitive and -resistant S. pneumoniae in mouse models of infection.10,11

BB-83698 could represent an important therapeutic option, particularly for streptococcal infections. If utilized in settings of H. influenzae infection, then combination with a Gram-negative agent may be warranted. This antimicrobial agent utilizes a mechanism of action distinct from other commercially available antibiotics and no cross-resistance was observed in this study. BB-83698 is currently in clinical trials in Europe.


   Acknowledgements
 
We would like to acknowledge Dr Gary Patou for clinical microbiology support and guidance. This study was presented in part at the Forty-third Interscience Conference on Antimicrobial Agents and Chemotherapy, Chicago, IL, USA, 14–17 September 2003, Abstract E1712.


   Footnotes
 
* Corresponding author. Tel: +1-650-837-1872; Fax: +1-650-827-0475; E-mail: dlofland{at}genesoft.com Back


   References
Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
1 . Clements, J., Beckett, R., Brown, A. et al. (2001). Antibiotic activity and characterization of BB-3497, a novel peptide deformylase inhibitor. Antimicrobial Agents and Chemotherapy 45, 563–70.[Abstract/Free Full Text]

2 . Yuan, Z., Trias, J. & White, R. (2001). Deformylase as a novel antibacterial target. Drug Discovery Today 6, 954–61.[CrossRef][Web of Science][Medline]

3 . Giglione, C., Pierre, M. & Meinnel, T. (2000). Peptide deformylase as a target for new generation, broad spectrum antimicrobial agents. Molecular Microbiology 36, 1197–205.[CrossRef][Web of Science][Medline]

4 . Jones, R. & Rhomberg, P. (2003). Comparative spectrum and activity of NVP-PDF386 (VRC4887), a new peptide deformylase inhibitor. Journal of Antimicrobial Chemotherapy 51, 157–61.[Abstract/Free Full Text]

5 . Wise, R., Andrews, J. & Ashby, J. (2002). In vitro activities of peptide deformylase inhibitors against gram-positive pathogens. Antimicrobial Agents and Chemotherapy 46, 1117–8.[Abstract/Free Full Text]

6 . Nguyen, K., Colton, C., Chakrabarti, R. et al. (2003). Characterization of a human peptide deformylase: implications for antibacterial drug design. Biochemistry 42, 9952–8.[CrossRef][Medline]

7 . National Committee for Clinical Laboratory Standards. (2003). Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow Aerobically—Fifth Edition: Approved Standard M7-A6. NCCLS, Wayne, PA, USA.

8 . National Committee for Clinical Laboratory Standards. (1999). Methods for Determining Bactericidal Activity of Antimicrobial Agents: Approved Standard M26-A. NCCLS, Wayne, PA, USA.

9 . Hackbarth, C., Chen, D., Lewis, J. et al. (2002). N-alkyl urea hydroxamic acids as a new class of peptide deformylase inhibitors with antimicrobial activity. Antimicrobial Agents and Chemotherapy 46, 2752–64.[Abstract/Free Full Text]

10 . Azoulay-Dupuis, E., Mohler, J., Rieux, V. et al. (2001). Efficacy of BB-83698 a novel peptide deformylase inhibitor, in a mouse pneumonia model induced by wild type and antimicrobial-resistant Streptococcus pneumoniae. In Program and Abstracts of the Forty-first Interscience Conference on Antimicrobial Agents and Chemotherapy, Chicago, IL, 1990. Abstract F-354, p. 206. American Society for Microbiology, Washington, DC, USA.

11 . Craig, W. & Andes, D. (2001). In vivo pharmacodynamics of BB-83698, a deformylase inhibitor. In Program and Abstracts of the Forty-first Interscience Conference on Antimicrobial Agents and Chemotherapy, Chicago, IL, 1990. Abstract F-355, p. 206. American Society for Microbiology, Washington, DC, USA.


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