Pharmacologic Comparison of Clinical Neutral Endopeptidase Inhibitors in a Rat Model of Acute Secretory Diarrhea.

Racecadotril (acetorphan) is a neutral endopeptidase (NEP) inhibitor with known antidiarrheal activity in animals and humans; however, in humans, it suffers from shortcomings that might be improved with newer drugs in this class that have progressed to the clinic for nonenteric disease indications. To identify potentially superior NEP inhibitors with immediate clinical utility for diarrhea treatment, we compared their efficacy and pharmacologic properties in a rat intestinal hypersecretion model. Racecadotril and seven other clinical-stage inhibitors of NEP were obtained or synthesized. Enzyme potency and specificity were compared using purified peptidases. Compounds were orally administered to rats before administration of castor oil to induce diarrhea. Stool weight was recorded over 4 hours. To assess other pharmacologic properties, select compounds were orally administered to normal or castor oil-treated rats, blood and tissue samples collected at multiple time points, and active compound concentrations determined by mass spectroscopy. NEP enzyme activity was measured in tissue homogenates. Three previously untested clinical NEP inhibitors delayed diarrhea onset and reduced total stool output, with little or no effect on intestinal motility assessed by the charcoal meal test. Each was shown to be a potent, highly specific inhibitor of NEP. Each exhibited greater suppression of NEP activity in intestinal and nonintestinal tissues than did racecadotril and sustained this inhibition longer. These results suggest that newer clinical-stage NEP inhibitors originally developed for other indications may be directly repositioned for treatment of acute secretory diarrhea and offer advantages over racecadotril, such as less frequent dosing and potentially improved efficacy.

Novel topoisomerase inhibitors: microbiological characterisation and in vivo efficacy of pyrimidines.

Pyrimidine compounds were identified as inhibitors of DNA topoisomerase IV through high-throughput screening. This study was designed to exemplify the in vitro activity of the pyrimidines against Gram-positive and Gram-negative microorganisms, to reveal the mode of action of these compounds and to demonstrate their in vivo efficacy. Frequencies of resistance to pyrimidines among Staphylococcus aureus and Streptococcus pneumoniae were <10(-10) at four times their minimum inhibitory concentrations (MICs). These compounds exhibited a dual mode of action through inhibition of the ParE subunit of DNA topoisomerase IV as well as the GyrB subunit of DNA gyrase, a homologue of DNA topoisomerase IV. Pyrimidines were shown to have MIC(90) values (MIC that inhibited 90% of the strains tested) of ≤2 mg/L against Gram-positive pathogens, including meticillin-resistant S. aureus, quinolone- and meticillin-resistant S. aureus, vancomycin-resistant enterococci, penicillin-non-susceptible S. pneumoniae and Streptococcus pyogenes, and MIC(90) values of 2- to >16 mg/L and ≤0.5 mg/L against the Gram-negative pathogens Haemophilus influenzae and Moraxella catarrhalis, respectively. The pyrimidines were bactericidal and exhibited a ca. 1000-fold reduction of the bacterial counts at 300 mg/kg in a S. pneumoniae lung infection model. The microbiological properties and in vivo efficacy of pyrimidines underscore their potential as candidates for the treatment of soft-tissue infections and hospital-acquired pneumonia.

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.