Chris Celeri

Bactericidal Activity, Absence of Serum Effect, and Time-Kill Kinetics of Ceftazidime-Avibactam against β-Lactamase-Producing Enterobacteriaceae and Pseudomonas aeruginosa

ABSTRACT Avibactam, a non-β-lactam β-lactamase inhibitor with activity against extended-spectrum β-lactamases (ESBLs), KPC, AmpC, and some OXA enzymes, extends the antibacterial activity of ceftazidime against most ceftazidime-resistant organisms producing these enzymes. In this study, the bactericidal activity of ceftazidime-avibactam against 18 Pseudomonas aeruginosa isolates and 15 Enterobacteriaceae isolates, including wild-type isolates and ESBL, KPC, and/or AmpC producers, was evaluated. Ceftazidime-avibactam MICs (0.016 to 32 μg/ml) were lower than those for ceftazidime alone (0.06 to ≥256 μg/ml) against all isolates except for 2 P. aeruginosa isolates (1 blaVIM-positive isolate and 1 blaOXA-23-positive isolate). The minimum bactericidal concentration/MIC ratios of ceftazidime-avibactam were ≤4 for all isolates, indicating bactericidal activity. Human serum and human serum albumin had a minimal effect on ceftazidime-avibactam MICs. Ceftazidime-avibactam time-kill kinetics were evaluated at low MIC multiples and showed time-dependent reductions in the number of CFU/ml from 0 to 6 h for all strains tested. A ≥3-log10 decrease in the number of CFU/ml was observed at 6 h for all Enterobacteriaceae, and a 2-log10 reduction in the number of CFU/ml was observed at 6 h for 3 of the 6 P. aeruginosa isolates. Regrowth was noted at 24 h for some of the isolates tested in time-kill assays. These data demonstrate the potent bactericidal activity of ceftazidime-avibactam and support the continued clinical development of ceftazidime-avibactam as a new treatment option for infections caused by Enterobacteriaceae and P. aeruginosa, including isolates resistant to ceftazidime by mechanisms dependent on avibactam-sensitive β-lactamases.

Chemical Characterization and Biological Properties of NVC-422, a Novel, Stable N-Chlorotaurine Analog

ABSTRACT During oxidative burst, neutrophils selectively generate HOCl to destroy invading microbial pathogens. Excess HOCl reacts with taurine, a semi-essential amino acid, resulting in the formation of the longer-lived biogenerated broad-spectrum antimicrobial agent, N-chlorotaurine (NCT). In the presence of an excess of HOCl or under moderately acidic conditions, NCT can be further chlorinated, or it can disproportionate to produce N,N-dichlorotaurine (NNDCT). In the present study, 2,2-dimethyltaurine was used to prepare a more stable N-chlorotaurine, namely, N,N-dichloro-2,2-dimethyltaurine (NVC-422). In addition, we report on the chemical characterization, in vitro antimicrobial properties, and cytotoxicity of this compound. NVC-422 was shown effectively to kill all 17 microbial strains tested, including antibiotic-resistant Staphylococcus aureus and Enterococcus faecium. The minimum bactericidal concentration of NVC-422 against Gram-negative and Gram-positive bacteria ranged from 0.12 to 4 μg/ml. The minimum fungicidal concentrations against Candida albicans and Candida glabrata were 32 and 16 μg/ml, respectively. NVC-422 has an in vitro cytotoxicity (50% cytotoxicity = 1,440 μg/ml) similar to that of NNDCT. Moreover, our data showed that this agent possesses rapid, pH-dependent antimicrobial activity. At pH 4, NVC-422 completely killed both Escherichia coli and S. aureus within 5 min at a concentration of 32 μg/ml. Finally, the effect of NVC-422 in the treatment of an E. coli-infected granulating wound rat model was evaluated. Treatment of the infected granulating wound with NVC-422 resulted in significant reduction of the bacterial tissue burden and faster wound healing compared to a saline-treated control. These findings suggest that NVC-422 could have potential application as a topical antimicrobial.

N,N-Dichloroaminosulfonic acids as novel topical antimicrobial agents.

2-Dichloroamino-2-methyl-propane-1-sulfonic acid sodium salt (2a), a stable derivative of endogenous N,N-dichlorotaurine (1), has been identified and is under development as a topical antimicrobial agent. Structure-activity relationships of analogs were explored to achieve optimal antimicrobial activity with minimal mammalian toxicity while maintaining the desired stability. All the analogs synthesized showed antimicrobial activity against Staphylococcus aureus, Escherichia coli, and Candida albicans in the range of 1-128 microg/mL and cytotoxicity against mammalian L929 cells in the range 80-1900 microg/mL.

Quaternary ammonium N,N-dichloroamines as topical, antimicrobial agents

A series of backbone modified and sulfonic acid replacement analogs of our topical, clinical candidate (iii) were synthesized. Their antimicrobial activities and aqueous stabilities at pH 4 and pH 7 were determined, and has led us to identify quaternary ammonium N,N-dichloroamines as a new class of topical antimicrobial agents.

Novel N-chloroheterocyclic antimicrobials.

Antimicrobial compounds with broad-spectrum activity and minimal potential for antibiotic resistance are urgently needed. Toward this end, we prepared and investigated a novel series of N-chloroheterocycles. Of the compounds examined, the N-chloroamine series were found superior over N-chloroamide series in regards to exhibiting high antimicrobial activity, low cytotoxicity, and long-term aqueous stability.

Broad-spectrum virucidal activity of (NVC-422) N,N-dichloro-2,2-dimethyltaurine against viral ocular pathogens in vitro.

PURPOSE Viral conjunctivitis is a highly contagious infection often causing major epidemics. A safe broad-spectrum antiviral agent is needed to treat this unmet medical need. The purpose of this study is to demonstrate that in vitro NVC-422 is a safe, broad-spectrum topical virucidal agent with activity against ophthalmic viral pathogens. METHODS The virucidal activity of NVC-422 against several serotypes of human adenovirus (HAdV), coxsackievirus A24, enterovirus 70, and herpes simplex-virus-1 (HSV-1) was tested in standard in vitro titer reduction assays with or without tears. An in vitro irritancy score for NVC-422 was determined using the MatTek EpiOcular tissue system. RESULTS NVC-422 reduced the viral titer of HAdV-5, HAdV-8, HAdV-19, HAdV-37, and HSV-1 by at least 4 logs after 1 hour incubation at 250 μM. Incubation of coxsackievirus A24 and enterovirus 70 with 2.5 mM NVC-422 for 1 hour reduced the viral titer by 4 logs and 4.5 logs, respectively. The virucidal activity of NVC-422 is maintained in the presence of 10% synthetic tears. In the EpiOcular corneal tissue model, NVC-422 was nonirritating at concentrations up to 41 mM. CONCLUSIONS NVC-422 has potent, rapid in vitro virucidal activity against major causes of conjunctivitis. Its broad-spectrum virucidal activity combined with favorable safety profile validates NVC-422 as a potential new therapeutic agent against viral conjunctivitis.

Structure stability/activity relationships of sulfone stabilized N,N-dichloroamines

Structure stability/activity relationships (SXR) of a new class of N,N-dichloroamine compounds were explored to improve antimicrobial activity against Escherichia coli, Staphylococcus aureus, and Candida albicans while maintaining aqueous solution stability. This study identified a new class of solution-stable and topical antimicrobial agents. These agents are sulfone-stabilized and possess either a quaternary ammonium or sulfonate appendages as a water solubilizing group. Several unique challenges were confronted in the synthesis of these novel compounds which are highlighted in the discussion.