Novel fluorobenzothiazole as a dual inhibitor of gyrase B and topoisomerase IV against Gram-positive pathogens.

Aim: The development of a novel inhibitor targeting gyrase B and topoisomerase IV offers an opportunity to combat multidrug resistance. Methods: We investigated the activity of RBx 10080758 against Gram-positive bacteria in vitro and in vivo. Results: RBx 10080758 showed a potent 50% inhibitory concentration of 0.13 µM and 0.25 µM against gyrase B and topoisomerase IV, respectively, and exhibited strong whole-cell in vitro activity with MIC ranges of 0.015-0.06 and 0.015-0.03 µg/ml against Staphylococcus aureus and Streptococcus pneumoniae, respectively. In a rat thigh infection model with methicillin-resistant S. aureus, RBx 10080758 at 45 mg/kg exhibited a >3 log10 CFU reduction in thigh muscles. Conclusion: RBx 10080758 displayed potent activity against multiple multidrug-resistant Gram-positive bacteria with a dual-targeting mechanism of action.

Potential of the fluoroketolide RBx 14255 against Streptococcus pneumoniae, Neisseria meningitidis and Haemophilus influenzae in an experimental murine meningitis model.

BACKGROUND: RBx 14255 is a fluoroketolide in pre-clinical evaluation with potent activity against MDR Gram-positive pathogens. OBJECTIVES: To investigate the efficacy of RBx 14255 against bacterial meningitis caused by Streptococcus pneumoniae, Neisseria meningitidis or Haemophilus influenzae in an experimental murine meningitis model. METHODS: In vitro activity of RBx 14255 was evaluated against clinical isolates of S. pneumoniae, N. meningitidis and H. influenzae. The in vivo efficacy of RBx 14255 was evaluated against bacterial meningitis, induced with S. pneumoniae 3579 erm(B), S. pneumoniae MA 80 erm(B), N. meningitidis 1852 and H. influenzae B1414 in a murine meningitis model. RESULTS: RBx 14255 showed strong in vitro bactericidal potential against S. pneumoniae, N. meningitidis and H. influenzae with MIC ranges of 0.004-0.1, 0.03-0.5 and 1-4 mg/L, respectively. In a murine meningitis model, a 50 mg/kg dose of RBx 14255, q12h, resulted in significant reduction of bacterial counts in the brain compared with the pretreatment control. The concentration of RBx 14255 in brain tissue correlated well with the efficacy in this mouse model. CONCLUSIONS: RBx 14255 showed superior bactericidal activity in time-kill assays in vitro and in vivo in an experimental murine meningitis model. RBx 14255 could be a promising candidate for future drug development against bacterial meningitis.

Synthesis and evaluation of thiomannosides, potent and orally active FimH inhibitors.

FimH is a type I fimbrial lectin located at the tip of type-1 pili of Gram-negative uropathogenic Escherichia coli (UPEC) guiding its ability to adhere and infect urothelial cells. Accordingly, blocking FimH with small molecule inhibitor is considered as a promising new therapeutic alternative to treat urinary tract infections caused by UPEC. Herein, we report that compounds having the S-glycosidic bond (thiomannosides) had improved metabolic stability and plasma exposures when dosed orally. Especially compound 5h showed the potential to inhibit biofilm formation and also to disrupt the preformed biofilm. And compound 5h showed prophylactic effect in UTI model in mice.

A novel ketolide, RBx 14255, with activity against multidrug-resistant Streptococcus pneumoniae.

We present here the novel ketolide RBx 14255, a semisynthetic macrolide derivative obtained by the derivatization of clarithromycin, for its in vitro and in vivo activities against sensitive and macrolide-resistant Streptococcus pneumoniae. RBx 14255 showed excellent in vitro activity against macrolide-resistant S. pneumoniae, including an in-house-generated telithromycin-resistant strain (S. pneumoniae 3390 NDDR). RBx 14255 also showed potent protein synthesis inhibition against telithromycin-resistant S. pneumoniae 3390 NDDR. The binding affinity of RBx 14255 toward ribosomes was found to be more than that for other tested drugs. The in vivo efficacy of RBx 14255 was determined in murine pulmonary infection induced by intranasal inoculation of S. pneumoniae ATCC 6303 and systemic infection with S. pneumoniae 3390 NDDR strains. The 50% effective dose (ED50) of RBx 14255 against S. pneumoniae ATCC 6303 in a murine pulmonary infection model was 3.12 mg/kg of body weight. In addition, RBx 14255 resulted in 100% survival of mice with systemic infection caused by macrolide-resistant S. pneumoniae 3390 NDDR at 100 mg/kg four times daily (QID) and at 50 mg/kg QID. RBx 14255 showed favorable pharmacokinetic properties that were comparable to those of telithromycin.

Synthesis and antibacterial activity of a novel series of acylides active against community acquired respiratory pathogens.

A novel series of acylides 4 were designed to overcome antibacterial resistance and evaluated for in vitro and in vivo activity. This series of acylides was designed from clarithromycin by changing the substitution on the desosamine nitrogen, followed by conversion to 3-O-acyl and 11,12-carbamate. These compounds showed significantly potent antibacterial activity against not only Gram-positive pathogens, including macrolide-lincosamide-streptogramin B (MLS(B))-resistant and efflux-resistant strains, but also Gram-negative pathogens such as Haemophilus influenzae. These acylides also showed better activity against telithromycin resistant Streptococcus pneumoniae strains.

Activity of a novel series of acylides active against community-acquired respiratory pathogens.

Resistance to macrolides and beta-lactams has increased sharply amongst key respiratory pathogens, leading to major concern. A novel series of acylides was designed to overcome this resistance and was evaluated for in vitro and in vivo activity. This series of acylides was designed starting from clarithromycin by changing the substitution on the desosamine nitrogen, followed by conversion to 3-O-acyl and 11,12-carbamate. Minimum inhibitory concentrations (MICs) of acylides were determined against susceptible as well as macrolide-lincosamide-streptogramin B (MLS(B))--and penicillin-resistant Streptococcus pneumoniae, Streptococcus pyogenes and Moraxella catarrhalis by the agar dilution method. Microbroth MICs for Haemophilus influenzae were determined according to Clinical and Laboratory Standards Institute guidelines. In vivo efficacy was determined by target organ load reduction against S. pneumoniae 3579 (ermB). The bactericidal potential of promising acylides was also determined. MICs of these compounds against S. pneumoniae, S. pyogenes, H. influenzae and M. catarrhalis were in the range of 0.06-2, 0.125-1, 1-16 and 0.015-0.5 microg/mL, respectively, irrespective of their resistance pattern. Mycoplasma pneumoniae and Legionella pneumophila showed MIC ranges of 0.004-0.125 microg/mL and 0.004-0.03 microg/mL, respectively. The acylides also showed better activity against telithromycin-resistant S. pneumoniae strains. Compounds with a 4-furan-2-yl-1H-imidazolyl side chain on the carbamate (RBx 10000296) showed a target organ load reduction of >3 log(10) colony-forming units/mL and concentration-dependent bactericidal potential against S. pneumoniae 994 mefA and H. influenzae strains. This novel and potent series of acylides active against antibiotic-resistant respiratory pathogens should be further investigated.

Novel biaryl oxazolidinones: in vitro and in vivo activities with pharmacokinetics in an animal model.

RBx 1000075 and RBx 1000276, the new investigational oxazolidinones, have an extended spectrum of in vitro activity against Gram-positive pathogens and showed minimum inhibitory concentrations (MICs) lower than comparator drugs. MIC for 90% of the organisms (MIC(90)) values of RBx 1000075, RBx 1000276 and linezolid against the isolates tested were, respectively: methicillin-sensitive Staphylococcus aureus, 0.25, 1 and 4 microg/mL; methicillin-resistant S. aureus (MRSA), 0.5, 2 and 4 microg/mL; methicillin-sensitive Staphylococcus epidermidis, 0.25, 1 and 2 microg/mL; methicillin-resistant S. epidermidis, 0.5, 1 and 2 microg/mL; and enterococci, 0.25, 1 and 4 microg/mL. Against respiratory pathogens, MIC(90) values were: Streptococcus pneumoniae, 0.125, 0.5 and 2 microg/mL; Streptococcus pyogenes, 1, 0.5 and 2 microg/mL; and Moraxella catarrhalis, 0.5, 2 and 4 microg/mL. In vivo efficacies of RBx 1000075 and RBx 1000276 were evaluated in murine systemic infection against S. aureus (MRSA 562) and in a pulmonary infection model against S. pneumoniae ATCC 6303. In murine systemic infection, RBx 1000075 and RBx 1000276 showed efficacy against MRSA 562, exhibiting a 50% effective dose (ED(50)) of 6.25 and 9.92 mg/kg body weight for once-daily administration and 4.96 and 5.56 mg/kg body weight for twice-daily administration, respectively, whereas for linezolid the corresponding ED(50) values were 9.9 and 5.56 mg/kg body weight. In pulmonary infection with S. pneumoniae ATCC 6303, 50% survival was observed with RBx 1000075 at 50mg/kg once daily, whereas 60% survival was observed with RBx 1000276 at 50mg/kg thrice daily. The absolute oral bioavailabilities of RBx 1000075 and RBx 1000276 were 48% and 73%, with half-lives of 13.5 and 3.2h, respectively. RBx 1000075 and RBx 1000276 are promising investigational oxazolidinones against Gram-positive pathogens.

Synthesis and antibacterial activity of potent heterocyclic oxazolidinones and the identification of RBx 8700.

Several potent oxazolidinone antibacterial agents were obtained by systematic modification of the linker between the five-membered heterocycle and the piperazinyl ring of RBx 7644 (Ranbezolid, 1) and its thienyl analogue 2, leading to the identification of an expanded spectrum compound RBx 8700 (6b).

Synthesis and antibacterial activity of novel oxazolidinones with methylene oxygen- and methylene sulfur-linked substituents at C5-position.

Novel oxazolidinone derivatives of the lead compound RBx 8700, containing methylene oxygen- and methylene sulfur-linked substituents at the C5-position, were synthesized. Antibacterial screening of these compounds against a panel of resistant and susceptible Gram-positive and fastidious Gram-negative bacteria gave compounds 2 and 4 as new antibacterial agents.

Characterisation of laboratory-generated vancomycin intermediate resistant Staphylococcus aureus strains.

Vancomycin has been the drug of choice for 30 years for the treatment of methicillin-resistant Staphylococcus aureus (MRSA). Emergence of decreased vancomycin susceptibility in MRSA strains presents a significant clinical problem with few therapeutic options. This study was performed to generate and characterise S. aureus strains with reduced susceptibility to vancomycin. Eighteen S. aureus strains were subjected to serial passaging on vancomycin to generate vancomycin intermediate resistant S. aureus (VISA) strains. Minimum inhibitory concentration (MIC) determination was performed for the parent and the passaged cultures with 13 different antibiotics. The strains were tested by the following five methods: simplified population analysis; CDC method; modified vancomycin agar screen; population analysis profile (PAP); and modified population analysis (PAP-area under the curve (AUC) ratio). Phenotypic changes such as doubling time, synergy with beta-lactam antibiotics and effect on norA efflux pumps were also studied for these strains. The result indicated that 8 VISA mutants (vancomycin MICs, 8-16 microg/mL) were generated in vitro from the 18 S. aureus strains. The CDC and modified agar methods proved to be the most sensitive and specific methods for detection of VISA strains. The PAP for all the VISA strains ranged from 12 microg/mL to > 16 microg/mL, with a PAP-AUC ratio of > 1.3. All mutants showed increased doubling time compared with their parent isolate. Synergism of the vancomycin and beta-lactam combinations was observed for all methicillin-resistant mutants. Upon acquisition of vancomycin resistance, a few mutants showed decreased oxacillin resistance. Two VISA strains were chosen for molecular characterisation of the mecA gene and one mutant showed genotypic changes with deletion of mecA. Loss of norA efflux pumps leading to fluoroquinolone sensitivity was also observed in four mutants.

Synthesis and SAR of novel oxazolidinones: discovery of ranbezolid.

Novel oxazolidinones were synthesized containing a number of substituted five-membered heterocycles attached to the 'piperazinyl-phenyl-oxazolidinone' core of eperezolid. Further, the piperazine ring of the core was replaced by other diamino-heterocycles. These modifications led to several compounds with potent activity against a spectrum of resistant and susceptible gram-positive organisms, along with the identification of ranbezolid (RBx 7644) as a clinical candidate.

In vitro activity of RBx 7644 (ranbezolid) on biofilm producing bacteria.

Biofilm associated infections are becoming more common. Treatment outcome of device related infections cannot be predicted by the results of a standard susceptibility test such as the MIC. Microorganisms involved in device related infections have a slow growth rate and adhere to surfaces. Activity against glass adherent bacteria has been shown to be correlated with treatment outcome in animal models of catheter related infections. Drug efficacy can be predicted if glass adherent staphylococci are killed by low drug concentration. The eradication of bacteria adhering to glass beads and inhibition of biofilm formation by ranbezolid and three other antibiotics (quinupristin/dalfopristin, vancomycin and linezolid) was studied. The results indicated that ranbezolid required only (2-4 x MIC) for total clearance of glass-adherent MRSA 562 and MRSE 879, compared with vancomycin (8 x), quinupristin/dalfopristin (1-4 x) and linezolid (4-16 x MIC). In addition ranbezolid inhibited biofilm formation to a greater extent at sub MIC and MIC level. In conclusion, this study indicated that ranbezolid had potent activity against adherent staphylococci isolates and may prove useful in the prevention and treatment of device related infections caused by staphylococci.