In Vitro and In Vivo Properties of CUO246, a Novel Bacterial DNA Gyrase/Topoisomerase IV Inhibitor.

CUO246, a novel DNA gyrase/topoisomerase IV inhibitor, is active in vitro against a broad range of Gram-positive, fastidious Gram-negative, and atypical bacterial pathogens and retains activity against quinolone-resistant strains in circulation. The frequency of selection for single step mutants of wild-type S. aureus with reduced susceptibility to CUO246 was <4.64 × 10-9 at 4× and 8× MIC and remained low when using an isogenic QRDR mutant (<5.24 × 10-9 at 4× and 8× MIC). Biochemical assays indicated that CUO246 had potent inhibitory activity against both DNA gyrase (GyrAB) and topoisomerase IV (ParCE). Furthermore, CUO246 showed rapid bactericidal activity in time-kill assays and potent in vivo efficacy against S. aureus in a neutropenic murine thigh infection model. These results suggest that CUO246 may be useful in treating infections by various causative agents of acute skin and skin structure infections, respiratory tract infections, and sexually transmitted infections.

In vivo characterization of the peptide deformylase inhibitor LBM415 in murine infection models.

LBM415 is an antibacterial agent belonging to the peptide deformylase inhibitor class of compounds. It has previously been shown to demonstrate good activity in vitro against a range of pathogens. In this study, the in vivo efficacy of LBM415 was evaluated in various mouse infection models. We investigated activity against a systemic infection model caused by intraperitoneal inoculation of Staphylococcus aureus (methicillin [meticillin] susceptible [MSSA] and methicillin resistant [MRSA]) and Streptococcus pneumoniae (penicillin susceptible [PSSP] and multidrug resistant [MDRSP]), a thigh infection model caused by intramuscular injection of MRSA, and a lung infection produced by intranasal inoculation of PSSP. In the systemic MSSA and MRSA infections, LBM415 was equivalent to linezolid and vancomycin. In the systemic PSSP infection, LBM415 was equivalent to linezolid, whereas against systemic MDRSP infection, the LBM415 50% effective dose (ED50) was 4.8 mg/kg (dosed subcutaneously) and 36.6 mg/kg (dosed orally), compared to 13.2 mg/kg for telithromycin and >60 mg/kg for penicillin V and clarithromycin. In the MRSA thigh infection, LBM415 significantly reduced thigh bacterial levels compared to those of untreated mice, with levels similar to those after treatment with linezolid at the same dose levels. In the pneumonia model, the ED50 to reduce the bacterial lung burden by >4 log10 in 50% of treated animals was 23.3 mg/kg for LBM415, whereas moxifloxacin showed an ED50 of 14.3 mg/kg. In summary, LBM415 showed in vivo efficacy in sepsis and specific organ infection models irrespective of resistance to other antibiotics. Results suggest the potential of peptide deformylase inhibitors as a novel class of therapeutic agents against antibiotic-resistant pathogens.

Biological, biochemical, and molecular characterization of a new clinical Trichophyton rubrum isolate resistant to terbinafine.

We have characterized a new clinical strain of Trichophyton rubrum highly resistant to terbinafine but exhibiting normal susceptibility to drugs with other mechanisms of action. Resistance to terbinafine in this strain is caused by a missense mutation in the squalene epoxidase gene leading to the amino acid substitution F397L.

Amino acid substitution in Trichophyton rubrum squalene epoxidase associated with resistance to terbinafine.

There has only been one clinically confirmed case of terbinafine resistance in dermatophytes, where six sequential Trichophyton rubrum isolates from the same patient were found to be resistant to terbinafine and cross-resistant to other squalene epoxidase (SE) inhibitors. Microsomal SE activity from these resistant isolates was insensitive to terbinafine, suggesting a target-based mechanism of resistance (B. Favre, M. Ghannoum, and N. S. Ryder, Med. Mycol. 42:525-529, 2004). In this study, we have characterized at the molecular level the cause of the resistant phenotype of these clinical isolates. Cloning and sequencing of the SE gene and cDNA from T. rubrum revealed the presence of an intron in the gene and an open reading frame encoding a protein of 489 residues, with an equivalent similarity (57%) to both yeast and mammalian SEs. The nucleotide sequences of SE from two terbinafine-susceptible strains were identical whereas those of terbinafine-resistant strains, serially isolated from the same patient, each contained the same single missense introducing the amino acid substitution L393F. Introduction of the corresponding substitution in the Candida albicans SE gene (L398F) and expression of this gene in Saccharomyces cerevisiae conferred a resistant phenotype to the transformants when compared to those expressing the wild-type sequence. Terbinafine resistance in these T. rubrum clinical isolates appears to be due to a single amino acid substitution in SE.

In vitro analysis of the ability of Trichophyton rubrum to become resistant to terbinafine.

In this study, we have investigated in vitro the resistance frequency and development of resistance to terbinafine of Trichophyton rubrum. Results demonstrated that naturally occurring mutants are rare and that T. rubrum appears to have little capacity to develop resistance to terbinafine even after prolonged exposure.