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

Strategies to Improve the Potency of Oxazolidinones towards Bacterial Biofilms

Biofilms are part of the natural lifecycle of bacteria and are known to cause chronic infections that are difficult to treat. Most antibiotics are developed and tested against bacteria in the planktonic state and are ineffective against bacterial biofilms. The oxazolidinones, including the last resort drug linezolid, are one of the main classes of synthetic antibiotics progressed to clinical use in the last 50 years. They have a unique mechanism of action and only develop low levels of resistance in the clinical setting. With the aim of providing insight into strategies to design more potent antibiotic compounds with activity against bacterial biofilms, we review the biofilm activity of clinically approved oxazolidinones and report on structural modifications to oxazolidinones and their delivery systems which lead to enhanced anti-biofilm activity.

In vivo efficacy and pharmacokinetics of bi-aryl oxazolidinone RBx 11760 loaded polylactic acid-polyethylene glycol nanoparticles in mouse hematogenous bronchopneumonia and rat groin abscess caused by Staphylococcus aureus

RBx 11760 is a bi-aryl oxazolidinone antibacterial agent active against Staphylococcus aureus but has poor solubility. Here we have encapsulated RBx 11760 in PLA-PEG NPs with an aim to improve physicochemical, pharmacokinetics and in vivo efficacy. The average size and zeta potential of RBx 11760 loaded NPs were found to be 106.4 nm and -22.2 mV, respectively. The absolute size of nanoparticles by HRTEM was found to be approximately 80 nm. In vitro antibacterial agar well diffusion assay showed clear zone of inhibition of bacterial growth. In pharmacokinetic study, nanoparticle showed 4.6-fold and 7-fold increase in AUC_inf and half-life, respectively, as compared to free drug. RBx 11760 nanoparticle significantly reduced bacterial counts in lungs and improved the survival rate of immunocompromised mice as compared to free drugs. Thus, RBx 11760 loaded nanoparticles have strong potential to be used as nanomedicine against sensitive and drug resistant Staphylococcus aureus infections.

In Vitro and In Vivo Activities of a Bi-Aryl Oxazolidinone, RBx 11760, against Gram-Positive Bacteria

RBx 11760, a bi-aryl oxazolidinone, was investigated for antibacterial activity against Gram-positive bacteria. The MIC₉₀s of RBx 11760 and linezolid against Staphylococcus aureus were 2 and 4 mg/liter, against Staphylococcus epidermidis were 0.5 and 2 mg/liter, and against Enterococcus were 1 and 4 mg/liter, respectively. Similarly, against Streptococcus pneumoniae the MIC₉₀s of RBx 11760 and linezolid were 0.5 and 2 mg/liter, respectively. In time-kill studies, RBx 11760, tedizolid, and linezolid exhibited bacteriostatic effect against all tested strains except S. pneumoniae RBx 11760 showed 2-log₁₀ kill at 4× MIC while tedizolid and linezolid showed 2-log₁₀ and 1.4-log₁₀ kill at 16× MIC, respectively, against methicillin-resistant S. aureus (MRSA) H-29. Against S. pneumoniae 5051, RBx 11760 showed bactericidal activity, with 4.6-log₁₀ kill at 4× MIC compared to 2.42-log₁₀ and 1.95-log₁₀ kill for tedizolid and linezolid, respectively, at 16× MIC. RBx 11760 showed postantibiotic effects (PAE) at 3 h at 4 mg/liter against MRSA H-29, and linezolid showed the same effect at 16 mg/liter. RBx 11760 inhibited biofilm production against methicillin-resistant S. epidermidis (MRSE) ATCC 35984 in a concentration-dependent manner. In a foreign-body model, linezolid and rifampin resulted in no advantage over stasis, while the same dose of RBx 11760 demonstrated a significant killing compared to the initial control against S. aureus (P < 0.05) and MRSE (P < 0.01). The difference in killing was statistically significant for the lower dose of RBx 11760 (P < 0.05) versus the higher dose of linezolid (P > 0.05 [not significant]) in a groin abscess model. In neutropenic mouse thigh infection, RBx 11760 showed stasis at 20 mg/kg of body weight, whereas tedizolid showed the same effect at 40 mg/kg. These data support RBx 11760 as a promising investigational candidate.

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.

Progress in the discovery of treatments for C. difficile infection: A clinical and medicinal chemistry review

Clostridium difficile is an anaerobic, Gram-positive pathogen that causes C. difficile infection, which results in significant morbidity and mortality. The incidence of C. difficile infection in developed countries has become increasingly high due to the emergence of newer epidemic strains, a growing elderly population, extensive use of broad spectrum antibiotics, and limited therapies for this diarrheal disease. Because treatment options currently available for C. difficile infection have some drawbacks, including cost, promotion of resistance, and selectivity problems, new agents are urgently needed to address these challenges. This review article focuses on two parts: the first part summarizes current clinical treatment strategies and agents under clinical development for C. difficile infection; the second part reviews newly reported anti-difficile agents that have been evaluated or reevaluated in the last five years and are in the early stages of drug discovery and development. Antibiotics are divided into natural product inspired and synthetic small molecule compounds that may have the potential to be more efficacious than currently approved treatments. This includes potency, selectivity, reduced cytotoxicity, and novel modes of action to prevent resistance.

Effect of linezolid on clinical severity and pulmonary cytokines in a murine model of influenza A and Staphylococcus aureus coinfection

Excessive inflammation contributes to the severity of post influenza pneumonia caused by methicillin resistant S.aureus (MRSA). Linezolid, vancomycin, and clindamycin are antibiotics used for MRSA infections. Linezolid has immunomodulatory properties. We report on the effects of the three antibiotics on microbial clearance, pulmonary cytokines and clinical course in a murine model of influenza and MRSA coinfection.

METHODS

B6 mice were infected with influenza A virus and 3 days later with MRSA, both intranasally. Treatment with placebo, linezolid, vancomycin or clindamycin started immediately after MRSA infection and continued for 72 hours. Bacterial and viral titers as well as cytokine concentrations in the lungs were assessed 4 and 24 hours after MRSA coinfection. Mice were weighted daily for 13 days.

RESULTS

Coinfected mice had increased pulmonary IL-1β, TNF-α and mKC at 4 and 24 hours, IL-6, IL-10 and IL-12 at 4 hours and IFN-γ at 24 hours after MRSA coinfection (all P<0.05). Compared to placebo, coinfected mice treated with linezolid, vancomycin or clindamycin had decreased pulmonary IL-6 and mKC at 4 hours and IFN-γ at 24 hours after MRSA coinfection (all P<0.05). IL-1β, TNF-α and IL-12 were similar in antibiotic-treated and placebo groups. All antibiotics similarly reduced MRSA without effect on influenza titers. Linezolid-treated mice had less weight loss on days 4-6 after influenza infection compared to placebo (all P<0.05). On all other days weight change was similar among all groups.

CONCLUSIONS

This is the first report comparing the effects of antibiotics on cytokines and clinical outcome in a murine model of influenza and MRSA coinfection. Compared to placebo, antibiotic treatment reduced maximum concentration of IL-6, mKC and IFN-γ in the lungs without any difference among antibiotics. During treatment, only linezolid delayed weight loss compared to placebo.

Recent development of potent analogues of oxazolidinone antibacterial agents

The oxazolidinones are a new and potent class of antimicrobial agents with activity mainly against Gram-positive strains. The commercial success of linezolid, the only FDA-approved oxazolidinone, has prompted many pharmaceutical companies to devote resources to this area of investigation. Until now, four types of chemical modifications of linezolid and oxazolidinone-type antibacterial agents, including modification on each of the A-(oxazolidinone), B-(phenyl), and C-(morpholine) rings as well as the C-5 side chain of the A-ring substructure, have been described. Division into sections according to side chain modification or the type of ring will be used throughout this review, although the process of synthesis usually involves the simultaneous modification of several elements of the linezolid substructure; therefore, assignment into the appropriate section depends on the structure-activity relationships (SAR) studies. This review makes an attempt to summarise the work carried out in the period from 2006 until mid-2012.

Activity of RBx 11760, a novel biaryl oxazolidinone, against Clostridium difficile

OBJECTIVES

RBx 11760, a novel oxazolidinone, was investigated for in vitro and in vivo activity against Clostridium difficile.

METHODS

The in vitro activity of RBx 11760 and three other agents against 50 diverse C. difficile clinical isolates and other obligate anaerobic bacteria was determined. The effect of RBx 11760 on sporulation and toxin production was determined against different C. difficile isolates. We used a hamster infection model to investigate the efficacy of RBx 11760, vancomycin and metronidazole. The mechanism of action of RBx 11760 against C. difficile ATCC 43255 was determined by macromolecular synthesis inhibition.

RESULTS

RBx 11760 MICs were in the range of 0.5-1 mg/L for C. difficile isolates, and it demonstrated concentration-dependent killing of C. difficile ATCC 43255 and C. difficile 6387 up to 2-4× MIC (1-2 mg/L). RBx 11760, at concentrations as low as 0.25-0.5 mg/L, resulted in a significant reduction in de novo toxin production as well as sporulation in different C. difficile isolates. In contrast, vancomycin, metronidazole and linezolid had little or no effect on toxin production and appeared to promote the formation of spores. In the hamster infection model, treatment with RBx 11760 resulted in prolonged survival of animals as compared with vancomycin or metronidazole, which correlated well with the histopathology results. Macromolecular labelling results suggest that RBx 11760 is a potent inhibitor of bacterial protein synthesis.

CONCLUSIONS

RBx 11760 showed excellent in vitro and in vivo activity against C. difficile, and it could be a promising novel candidate for future drug development against C. difficile infection.