Novel FtsZ inhibitor with potent activity against Staphylococcus aureus.

OBJECTIVES: FtsZ is an essential bacterial protein and an unexplored target for the development of antibacterial drugs. The development of a novel inhibitor targeting FtsZ offers a potential opportunity to combat drug resistance. DS01750413, a new derivative of PC190723, is a novel FtsZ inhibitor with improved in vitro and in vivo activity. The objective of this study was to investigate the efficacy of DS01750413 against Staphylococcus spp., including MRSA, in in vitro and in vivo models. METHODS: In vitro activities of DS01750413 and standard-of-care antibiotics were evaluated against clinical isolates of Gram-positive pathogens. The in vivo efficacy was evaluated in a murine systemic infection model caused by MRSA. RESULTS: DS01750413 showed potent in vitro activity against MRSA clinical isolates with MIC ranges of 0.5-1 mg/L and also demonstrated concentration-dependent bactericidal killing. In the murine bacteraemia infection model of MRSA, treatment with DS01750413 resulted in prolonged survival of animals compared with placebo-treated animals and exhibited a significant reduction in the bacterial load in liver, spleen, lungs and kidneys. CONCLUSIONS: DS01750413 showed encouraging in vitro and in vivo activity against MRSA. As a novel chemical class, DS01750413 has the potential to become clinically viable antibiotics to address the drug resistance problem by its unique novel targeting mechanism of action.

Azithromycin Exhibits Activity Against Pseudomonas aeruginosa in Chronic Rat Lung Infection Model.

Pseudomonas aeruginosa forms biofilms in the lungs of chronically infected cystic fibrosis patients, which are tolerant to both the treatment of antibiotics and the host immune system. Normally, antibiotics are less effective against bacteria growing in biofilms; azithromycin has shown a potent efficacy in cystic fibrosis patients chronically infected with P. aeruginosa and improved their lung function. The present study was conducted to evaluate the effect of azithromycin on P. aeruginosa biofilm. We show that azithromycin exhibited a potent activity against P. aeruginosa biofilm, and microscopic observation revealed that azithromycin substantially inhibited the formation of solid surface biofilms. Interestingly, we observed that azithromycin restricted P. aeruginosa biofilm formation by inhibiting the expression of pel genes, which has been previously shown to play an essential role in bacterial attachment to solid-surface biofilm. In a rat model of chronic P. aeruginosa lung infection, we show that azithromycin treatment resulted in the suppression of quorum sensing-regulated virulence factors, significantly improving the clearance of P. aeruginosa biofilms compared to that in the placebo control. We conclude that azithromycin attenuates P. aeruginosa biofilm formation, impairs its ability to produce extracellular biofilm matrix, and increases its sensitivity to the immune system, which may explain the clinical efficacy of azithromycin in cystic fibrosis patients.

DS86760016, a Leucyl-tRNA Synthetase Inhibitor with Activity against Pseudomonas aeruginosa.

DS86760016 is a new leucyl-tRNA-synthetase inhibitor at the preclinical development stage. DS86760016 showed potent activity against extended-spectrum multidrug-resistant Pseudomonas aeruginosa isolated from clinical samples and in vitro biofilms. In a murine catheter-associated urinary tract infection model, DS86760016 treatment resulted in significant eradication of P. aeruginosa from the kidney, bladder, and catheter without developing drug resistance. Our data suggest that DS86760016 has the potential to act as a new drug for the treatment of Pseudomonas infections.

Effect of DS-2969b, a novel GyrB inhibitor, on rat and monkey intestinal microbiota.

DS-2969b, a novel GyrB inhibitor, transiently and reversibly altered the counts of limited intestinal microbiota at around 10 µg/g of faecal levels in rats and monkeys. Considering the high activity of DS-2969b against Clostridium difficile, 10 µg/g of faecal levels would be sufficient for clearing C. difficile from the intestine.

A Phase I, Single-Ascending-Dose Study in Healthy Subjects to Assess the Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of DS-2969b, a Novel GyrB Inhibitor.

DS-2969b is a novel GyrB inhibitor in development for the treatment of Clostridium difficile infection. The aim of this study was to assess the safety, tolerability, pharmacokinetics, and effects on normal gastrointestinal microbiota groups of single daily oral ascending doses of DS-2969b in healthy subjects. The study enrolled 6 sequential ascending dose cohorts (6 mg, 20 mg, 60 mg, 200 mg, 400 mg, and 600 mg). In each cohort, 6 subjects were administered DS-2969b and 2 subjects were administered matching placebo. DS-2969b was safe and well tolerated at all dose levels examined. All adverse events related to DS-2969b were mild to moderate in severity and predominantly related to the gastrointestinal tract. DS-2969a (free form of DS-2969b) plasma concentrations increased with increasing doses; however, both the maximum serum concentration and area under the plasma concentration-time curve generally increased less than dose proportionally. DS-2969a was predominantly eliminated in the urine, with feces as a minor route of elimination. While the overall proportion of DS-2969a eliminated in the feces was low, target fecal levels sufficient for C. difficile eradication were achieved within 24 hours of administration with doses of 60 mg or higher. In exploratory analyses, DS-2969b appeared to reduce bacterial counts in 8 of the 25 groups of normal intestinal microbiota examined, suggesting that DS-2969b has only a mild effect on intestinal microbiota. Data from this study support and encourage further development of DS-2969b as a novel treatment for C. difficile infection.

In Vitro and In Vivo Activities of DS-2969b, a Novel GyrB Inhibitor, and Its Water-Soluble Prodrug, DS11960558, against Methicillin-Resistant Staphylococcus aureus.

DS-2969b is a novel GyrB inhibitor under clinical development. In this study, the in vitro activity of DS-2969b and the in vivo activities of DS-2969b and its water-soluble prodrug, DS11960558, against methicillin-resistant Staphylococcus aureus (MRSA) were evaluated. DS-2969b inhibited the supercoiling activity of S. aureus DNA gyrase and the decatenation activity of its topoisomerase IV. DS-2969b showed antibacterial activity against Gram-positive aerobes but not against Gram-negative aerobes, except for Moraxella catarrhalis and Haemophilus influenzae DS-2969b was active against MRSA with an MIC90 of 0.25 µg/ml, which was 8-fold lower than that of linezolid. The presence of a pulmonary surfactant did not affect the MIC of DS-2969b. DS-2969b showed time-dependent slow killing against MRSA. The frequency of spontaneous resistance development was less than 6.2 × 10-10 in all four S. aureus isolates at 4× MIC of DS-2969b. In a neutropenic MRSA-induced murine muscle infection model, DS-2969b was more efficacious than linezolid by both the subcutaneous and oral routes. DS-2969b and DS11960558 showed efficacy in a neutropenic murine MRSA lung infection model. The pharmacokinetics and pharmacodynamics of DS-2969b and DS11960558 against MRSA were characterized in a neutropenic murine thigh infection model; the percentage of time during the dosing period in which the free drug concentration exceeded the MIC (fTMIC) correlated best with in vivo efficacy, and the static percent fTMIC was 43 to 49%. A sufficient fTMIC was observed in a phase 1 multiple-ascending-dose study of DS-2969b given orally at 400 mg once a day. These results suggest that DS11960558 and DS-2969b have potential for use as intravenous-to-oral step-down therapy for treating MRSA infections with a higher efficacy than linezolid.

In Vitro and In Vivo Activities of DS-2969b, a Novel GyrB Inhibitor, against Clostridium difficile.

DS-2969b is a novel GyrB inhibitor that is currently under clinical development for the treatment of Clostridium difficile infection (CDI). In this study, the in vitro and in vivo activities of DS-2969b were evaluated. DS-2969b inhibited the supercoiling activity of C. difficile DNA gyrase. DS-2969b showed potent in vitro activity against C. difficile clinical isolates with a MIC90 of 0.06 µg/ml, which was 2-, 32-, and 16-fold lower than the MIC90s of fidaxomicin, vancomycin, and metronidazole, respectively. DS-2969b did not select spontaneously resistant mutants of various C. difficile strains at 4× MIC, and the frequency of resistance development was less than 4.8 × 10-9 In a hamster CDI model, 5-day oral administration of DS-2969b conferred complete protection from recurrence and mortality at 0.3 mg/kg of body weight once a day, in contrast to a 50% survival rate with fidaxomicin at 3 mg/kg once a day and 0% with vancomycin at a 50-mg/kg/dose twice a day. Even a single oral administration of 1 mg/kg of DS-2969b in the CDI model exhibited 100% animal survival without recurrence. DS-2969b was also efficacious by 5-day subcutaneous administration in the CDI model. DS-2969b showed similar levels of fecal excretion after intravenous and oral administrations in rats. These data support further development of DS-2969b as a drug for oral and intravenous treatment of CDI.

Phase 1 Study To Assess the Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of Multiple Oral Doses of DS-2969b, a Novel GyrB Inhibitor, in Healthy Subjects.

DS-2969b is a novel GyrB inhibitor in development for the treatment of Clostridium difficile infection (CDI). The aim of this study was to assess the safety, tolerability, pharmacokinetics, and effects on the normal gastrointestinal microbiota of multiple daily oral ascending doses of DS-2969b in healthy subjects. The study enrolled three sequential ascending-dose cohorts (60 mg, 200 mg, and 400 mg). In each cohort, subjects received an oral dose of DS-2969b or placebo (six subjects received DS-2969b, and two received placebo) each morning for 14 days. DS-2969b was safe and well tolerated at all dose levels examined. All adverse events related to DS-2969b were mild and predominantly related to the gastrointestinal tract. DS-2969a (free form of DS-2969b) plasma concentrations increased with increasing doses; however, both the maximum concentration of drug in serum (Cmax) and the area under the concentration-time curve (AUC) increased less than dose proportionally. In all cohorts, sufficient fecal levels of DS-2969a were achieved within 24 h following the administration of the first dose and maintained for at least 17 days. Following treatment with DS-2969b, clear reductions in the populations of Clostridium coccoides and Bifidobacterium groups were observed. However, populations of three other bacterial groups examined (Bacteroides fragilis, Clostridium leptum, and Prevotella) were not affected. Data from this study support and encourage the further development of DS-2969b as a novel treatment for CDI.

In Vitro and In Vivo Activities of DS86760016, a Novel Leucyl-tRNA Synthetase Inhibitor for Gram-Negative Pathogens.

The emergence of multidrug-resistant (MDR) Gram-negative bacilli is a major concern in the treatment of nosocomial infections. Antibacterial agents with novel modes of action can be useful, as these pathogens have become resistant to almost all existing standard-of-care agents. GSK2251052, a leucyl-tRNA synthetase inhibitor, has a novel mode of action against Gram-negative bacteria. However, the phase 2 studies with this drug were terminated due to microbiological failures based on the rapid emergence of drug resistance during the treatment of complicated urinary tract infections. DS86760016 is a novel leucyl-tRNA synthetase inhibitor active against MDR Gram-negative bacteria, such as Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa, with an improved pharmacokinetic profile. DS86760016 showed lower plasma clearance, longer plasma half-life, and higher renal excretion than GSK2251052 did in mice, rats, monkeys and dogs. DS86760016 also showed lower mutant prevention concentrations against P. aeruginosa than did GSK2251052. No resistant bacteria were observed in murine urinary tract infection models at a dose that maintained urinary concentrations above the mutant prevention concentration. DS86760016 also showed a lower risk of resistance development than did GSK2251052 in comparative in vivo studies with murine urinary tract infection models. These results suggest that DS86760016 has potential as a new drug for the treatment of MDR Gram-negative bacterial infections, with a lower risk of drug resistance development than that of GSK2251052.

Identification of the biosynthetic gene cluster of A-500359s in Streptomyces griseus SANK60196.

A-500359s, produced by Streptomyces griseus SANK60196, are inhibitors of bacterial phospho-N-acetylmuramyl-pentapeptide translocase. They are composed of three distinct moieties: a 5'-carbamoyl uridine, an unsaturated hexuronic acid and an aminocaprolactam. Two contiguous cosmids covering a 65-kb region of DNA and encoding 38 open reading frames (ORFs) putatively involved in the biosynthesis of A-500359s were identified. Reverse transcriptase PCR showed that most of the 38 ORFs are highly expressed during A-500359s production, but mutants that do not produce A-500359s did not express these same ORFs. Furthermore, orf21, encoding a putative aminoglycoside 3'-phosphotransferase, was heterologously expressed in Escherichia coli and Streptomyces albus, yielding strains having selective resistance against A-500359B, suggesting that ORF21 phosphorylates the unsaturated hexuronic acid as a mechanism of self-resistance to A-500359s. In total, the data suggest that the cloned region is involved in the resistance, regulation and biosynthesis of A-500359s.

Affinity of Tomopenem (CS-023) for penicillin-binding proteins in Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa.

Tomopenem (formerly CS-023), a novel 1beta-methylcarbapenem, exhibited high affinity for penicillin-binding protein (PBP) 2 in Staphylococcus aureus, PBP 2 in Escherichia coli, and PBPs 2 and 3 in Pseudomonas aeruginosa, which are considered major lethal targets. Morphologically, tomopenem induced spherical forms in E. coli and short filamentation with bulges in P. aeruginosa, which correlated with the drug's PBP profiles. The potential of resistance of these bacteria to tomopenem was comparable to that to imipenem.

Potent in vitro activity of tomopenem (CS-023) against methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa.

Tomopenem (formerly CS-023) is a novel 1beta-methylcarbapenem with broad-spectrum coverage of gram-positive and gram-negative pathogens. Its antibacterial activity against European clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa was compared with those of imipenem and meropenem. The MICs of tomopenem against MRSA and P. aeruginosa at which 90% of the isolates tested were inhibited were 8 and 4 microg/ml, respectively, and were equal to or more than fourfold lower than those of imipenem and meropenem. The antibacterial activity of tomopenem against MRSA was correlated with a higher affinity for the penicillin-binding protein (PBP) 2a. Its activity against laboratory mutants of P. aeruginosa with (i) overproduction of chromosomally coded AmpC beta-lactamase; (ii) overproduction of the multidrug efflux pumps MexAB-OprM, MexCD-OprJ, and MexEF-OprN; (iii) deficiency in OprD; and (iv) various combinations of AmpC overproduction, MexAB-OprM overproduction, and OprD deficiency were tested. The increases in the MIC of tomopenem against each single mutant compared with that against its parent strain were within a fourfold range. Tomopenem exhibited antibacterial activity against all mutants, with an observed MIC range of 0.5 to 8 microg/ml. These results suggest that the antibacterial activity of tomopenem against the clinical isolates of MRSA and P. aeruginosa should be ascribed to its high affinity for PBP 2a and its activity against the mutants of P. aeruginosa, respectively.

In vitro and in vivo antibacterial activities of CS-023 (RO4908463), a novel parenteral carbapenem.

CS-023 (RO4908463, formerly R-115685) is a novel 1beta-methylcarbapenem with 5-substituted pyrrolidin-3-ylthio groups, including an amidine moiety at the C-2 position. Its antibacterial activity was tested against 1,214 clinical isolates of 32 species and was compared with those of imipenem, meropenem, ceftazidime, ceftriaxone, ampicillin, amikacin, and levofloxacin. CS-023 exhibited a broad spectrum of activity against gram-positive and -negative aerobes and anaerobes, including methicillin-resistant Staphylococcus aureus (MRSA), methicillin-resistant Staphylococcus epidermidis, penicillin-resistant Streptococcus pneumoniae (PRSP), beta-lactamase-negative ampicillin-resistant Haemophilus influenzae, and Pseudomonas aeruginosa. CS-023 showed the most potent activity among the compounds tested against P. aeruginosa and MRSA, with MICs at which 90% of isolates tested were inhibited of 4 microg/ml and 8 microg/ml, respectively. CS-023 was stable against hydrolysis by the beta-lactamases from Enterobacter cloacae and Proteus vulgaris. CS-023 also showed potent activity against extended-spectrum beta-lactamase-producing Escherichia coli. The in vivo efficacy of CS-023 was evaluated with a murine systemic infection model induced by 13 strains of gram-positive and -negative pathogens and a lung infection model induced by 2 strains of PRSP (serotypes 6 and 19). Against the systemic infections with PRSP, MRSA, and P. aeruginosa and the lung infections, the efficacy of CS-023 was comparable to those of imipenem/cilastatin and vancomycin (tested against lung infections only) and superior to those of meropenem, ceftriaxone, and ceftazidime (tested against P. aeruginosa infections only). These results suggest that CS-023 has potential for the treatment of nosocomial bacterial infections by gram-positive and -negative pathogens, including MRSA and P. aeruginosa.

Characterization of EvgAS-YdeO-GadE branched regulatory circuit governing glutamate-dependent acid resistance in Escherichia coli.

Escherichia coli prefers growth in neutral pH environments but can withstand extremely acidic conditions (pH 2) for long periods. Of the four E. coli systems that contribute to acid resistance, one, the glutamate-dependent system, is remarkable in its efficacy and regulatory complexity. The resistance mechanism involves the intracellular consumption of protons by the glutamate decarboxylase isozymes GadA and GadB. The antiporter GadC then exports the product, gamma-aminobutyric acid, in exchange for fresh glutamate. A microarray study using overexpressed regulators uncovered evgAS and ydeO as potential regulators of gadE, now known to encode the essential activator of the gadA and gadBC genes. Examination of evgA and ydeO under normal expression conditions revealed that their products do activate gadE expression but only under specific conditions. They were important during exponential growth in acidified minimal medium containing glucose but were unnecessary for gadE expression in stationary-phase cells grown in complex medium. The response regulator EvgA activates gadE directly and indirectly via induction of the AraC-like regulator ydeO. Evidence obtained using gadE-lacZ operon fusions also revealed that GadE was autoinduced. Electrophoretic mobility shift assays indicated that EvgA, YdeO, and GadE bind to different regions upstream of gadE, indicating they all act directly at the gadE promoter. Since GadE controls the expression of numerous genes besides gadA and gadBC, the relevance of these regulatory circuits extends beyond acid resistance.

A motif co-occurrence approach for genome-wide prediction of transcription-factor-binding sites in Escherichia coli.

Various computational approaches have been developed for predicting cis-regulatory DNA elements in prokaryotic genomes. We describe a novel method for predicting transcription-factor-binding sites in Escherichia coli. Our method takes advantage of the principle that transcription factors frequently coregulate gene expression, but without requiring prior knowledge of which groups of genes are coregulated. Using position weight matrices for 49 known transcription factors, we examined spacings between pairs of matrix hits. These pairs were assigned probabilities according to the overrepresentation of their separation distance. The functions of many open reading frames (ORFs) downstream from predicted binding sites are unknown, and may correspond to novel regulon members. For five predictions, knockouts with mutated replacements of the predicted binding sites were created in E. coli MG1655. Quantitative real-time PCR (RT-PCR) indicates that for each of the knockouts, at least one gene immediately downstream exhibits a statistically significant change in mRNA expression. This approach may be useful in analyzing binding sites in a variety of organisms.

Regulatory network of acid resistance genes in Escherichia coli.

Overexpression of the response regulator EvgA confers an acid-resistant phenotype to exponentially growing Escherichia coli. This acid resistance is partially abolished by deletion of ydeP, yhiE or ydeO, genes induced by EvgA overexpression. Microarray analysis identified two classes of operons (genes). The first class contains seven operons induced by EvgA overexpression in the absence of ydeO, an AraC/XylS regulator gene. The second class contains 12 operons induced by YdeO overexpression. Operons in the second class were induced by EvgA overexpression only in the presence of ydeO. EvgA is likely to directly upregulate operons in the first class, and indirectly upregulate operons in the second class via YdeO. Analysis using the motif-finding program alignace identified an 18 bp inverted repeat motif in six upstream regions of all seven operons directly regulated by EvgA. Gel mobility shift assays showed the specific binding of EvgA to the six sequences. Introduction of mutations into the inverted repeats upstream of ydeP and b1500-ydeO resulted in reduction in EvgA-induced ydeP and ydeO expression and acid resistance. These results suggest that EvgA binds to the inverted repeats and upregulates the downstream genes. Overexpression of YdeP, YdeO and YhiE conferred acid resistance to exponentially growing cells, whereas GadX overexpression did not. Microarray analysis also identified several GadX-activated genes. Several genes induced by overexpression of YdeO and GadX overlapped; however, yhiE was induced only by YdeO. The acid resistance induced by YdeO overexpression was abolished by deletion of yhiE, gadC, slp-yhiF, hdeA or hdeD, genes induced by YdeO overexpression, suggesting that several genes orchestrate YdeO-induced acid resistance. We propose a model of the regulatory network of the acid resistance genes.

Escherichia coli gene expression responsive to levels of the response regulator EvgA.

To investigate the function of the EvgA response regulator, we compared the genome-wide transcription profile of EvgA-overexpressing and EvgA-lacking Escherichia coli strains by oligonucleotide microarrays. The microarray measurements allowed the identification of at least 37 EvgA-activated genes, including acid resistance-related genes gadABC and hdeAB, efflux pump genes yhiUV and emrK, and 21 genes with unknown function. EvgA overexpression conferred acid resistance to exponentially growing cells. This acid resistance was abolished by deletion of ydeP, ydeO, or yhiE, which was induced by EvgA overexpression. These results suggest that ydeP, ydeO, and yhiE are novel genes related to acid resistance and that EvgA regulates several acid resistance genes. Furthermore, the deletion of yhiE completely abolished acid resistance in stationary-phase cells, suggesting that YhiE plays a critical role in stationary-phase acid resistance. The multidrug resistance in an acrB deletion mutant caused by EvgA overexpression was completely abolished by deletion of yhiUV, while the emrKY deletion had no effect on the increase in resistance by EvgA overexpression. In addition, EvgA overexpression did not confer resistance in a tolC-deficient strain. These results suggest that YhiUV induced by EvgA overexpression is functionally associated with TolC and contributes to multidrug resistance.