Quality control guidelines for MIC susceptibility testing of NVP PDF-713: a novel peptide deformylase inhibitor.

Background: Compound NVP PDF-713 is a peptide deformylase (PDF) inhibitor which has emerged as a viable clinical candidate combining a complete spectrum of activity against important multi-resistant Gram-positive organisms and the two Gram-negative species most frequently associated with community-acquired respiratory tract infections (Haemophilus influenzae, Moraxella catarrhalis). This report summarizes the results of broth microdilution MIC quality control (QC) investigations for NVP PDF-713. Methods: This study followed the M23-A2 and M7-A6 guidelines established by the National Committee for Clinical Laboratory Standards (NCCLS). The investigation used eight laboratories, four broth media (three manufacturers) and four QC strains. QC strains tested against NVP PDF-713 included: Enterococcus faecalis (EF) ATCC 29212, Staphylococcus aureus (SA) ATCC 29213, Streptococcus pneumoniae (SPN) ATCC 49619 and H. influenzae (HI) ATCC 49247. A total of 320 values were generated per QC organism for NVP PDF-713 and 320 values for each of two control agents (clarithromycin and vancomycin). Results: Proposed three log2 dilution MIC ranges contained 95.6-99.4% of the reported values by all participating centers. The ranges for NVP PDF-713 calculated for routine QC in clinical laboratories were: 2-8 μg/ml for EF, 0.5-2 μg/ml for SA, 0.25-1 μg/ml for SPN and 1-4 μg/ml for HI. Only two laboratories (F, H) produced all MIC values beyond selected QC ranges. Concurrent testing of clarithromycin (HI) and linezolid (EF, SA, SPN) as internal control agents resulted in all MIC results within NCCLS published QC guidelines. The average inoculum concentrations were 3.5 x 10 CFU/ml (range: 3.0 x 10-1.0 x 10 CFU/ml) for all participants. Conclusions: QC ranges for the NVP PDF-713 test using NCCLS methods were established and appear acceptable in preparation for the early phases of clinical trials. These ranges will contribute to overall test accuracy for this first clinically applied agent in the PDF class. I N T R O D U C T I O N Over the past several decades, the development of antimicrobial agents has focused on a limited number of targets including bacterial cell wall synthesis and ribosomal proteins. With a paucity of targets, and the rapidly emerging bacterial resistance, cross-resistance has become common among several antimicrobial classes. To combat the contemporary problems encountered by cross-resistance, antimicrobial agents with novel mechanisms of action must be developed. One such target candidate is peptide deformylase (PDF), which is a required enzyme for prokaryote protein synthesis, but not essential for eukaryote cytoplasmic protein production, thus making an inhibitor of PDF a desirable mechanism of action. Several PDF inhibitors have been described and found to possess potent activity against many antimicrobial-resistant Grampositive cocci, as well as having reasonable activity against Gram-negative bacilli, including Haemophilus spp. and Moraxella catarrhalis. This development has become especially important during the last decade with increasing antimicrobial resistance documented among many clinically significant Gram-positive organisms and community-acquired respiratory tract pathogens. Among numerous PDF inhibitor clinical candidates studied, compound NVP PDF-713 (Novartis, Basel, Switzerland) has emerged as a viable agent combining satisfactory potency and spectrum against key Gram-positive organisms, as well as H. influenzae and M. catarrhalis. To determine the accurate assessment of the susceptibility testing profiles among clinical isolates, quality control (QC) guidelines for NVP PDF-713 are required. C O N C L U S I O N S • Table 1 summarizes all of the proposed MIC ranges for the four QC strains tested. The proposed three log2 dilution MIC ranges for broth microdilution tests with NVP PDF-713 would include 95.6 99.4% of all reported results in this initial study. • NVP PDF-713, a novel clinical candidate PDF inhibitor, has demonstrated excellent in vitro activity against the Gram-positive and Gram-negative organisms most frequently recovered from respiratory tract infections. The QC MIC ranges for NPV PDF713 proposed by these study findings will be important for the accurate development of this compound and other PDF inhibitors as they advance through initial clinical trials worldwide. S E L E C T E D R E F E R E N C E S Apfel CM, Locher H, Evers S, et al. Peptide deformylase as an antimicrobial drug target: Target validation and resistance development. Antimicrobial Agents and Chemotherapy 1999; 45:10581064. Clements JM, Beckett RP, Brown A, et al. Antibiotic activity and characterization of BB-3497, a novel peptide deformylase inhibitor. Antimicrobial Agents and Chemotherapy 2001; 45:563-570. Hackbarth CJ, Chen DZ, Lewis JG, et al. N-alkyl urea hydroxamic acids as a new class of peptide deformylase inhibitors with antibacterial activity. Antimicrobial Agents and Chemotherapy 2002; 46:2752-2764. National Committee for Clinical Laboratory Standards. (2001). Approved guideline M23-A2: Development of in vitro susceptibility testing criteria and quality control parameters, 2 ed. Wayne, PA:NCCLS. National Committee for Clinical Laboratory Standards. (2003). Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically. Document M7-A6. Wayne, PA:NCCLS. National Committee for Clinical Laboratory Standards. (2003). Performance standards for antimicrbial susceptibility testing M100-S13. Wayne, PA:NCCLS. Wise R, Andrews JM, Ashby J. In vitro activities of peptide deformylase inhibitors against Grampositive pathogens. Antimicrobial Agents and Chemotherapy 2002; 46:1117-1118. Table 2. Interand intra-laboratory comparisons of NVP PDF-713 MIC results for S. pneumoniae ATCC 49619. Occurrences by laboratory: NVP PDF-713 A B C D E F G H Total MIC (μg/ml) 0.12 8 8 0.25 4 20 14 31 69 0.5 36 26 22 20 26 1 29 18 178 1 14 18 11 22 65 a. Proposed MIC range that includes 97.5% of reported results. Table 1. Distributions of NVP PDF-713 MIC values for all qualifying results from an eight laboratory study using four control organisms. MIC occurrences by control strain: MIC (μg/ml) H. influenzae S. aureus E. faecalis S. pneumoniae ATCC 49247 ATCC 29213 ATCC 29212 ATCC 49619 0.12 8 0.25 2 69