Technologies to address antimicrobial resistance.

Bacterial infections have been traditionally controlled by antibiotics and vaccines, and these approaches have greatly improved health and longevity. However, multiple stakeholders are declaring that the lack of new interventions is putting our ability to prevent and treat bacterial infections at risk. Vaccine and antibiotic approaches still have the potential to address this threat. Innovative vaccine technologies, such as reverse vaccinology, novel adjuvants, and rationally designed bacterial outer membrane vesicles, together with progress in polysaccharide conjugation and antigen design, have the potential to boost the development of vaccines targeting several classes of multidrug-resistant bacteria. Furthermore, new approaches to deliver small-molecule antibacterials into bacteria, such as hijacking active uptake pathways and potentiator approaches, along with a focus on alternative modalities, such as targeting host factors, blocking bacterial virulence factors, monoclonal antibodies, and microbiome interventions, all have potential. Both vaccines and antibacterial approaches are needed to tackle the global challenge of antimicrobial resistance (AMR), and both areas have the underpinning science to address this need. However, a concerted research agenda and rethinking of the value society puts on interventions that save lives, by preventing or treating life-threatening bacterial infections, are needed to bring these ideas to fruition.

A Novel Inhaled Dry-Powder Formulation of Ribavirin Allows for Efficient Lung Delivery in Healthy Participants and Those with Chronic Obstructive Pulmonary Disease in a Phase 1 Study.

Chronic obstructive pulmonary disease (COPD) is an inflammatory lung condition, causing progressive decline in lung function leading to premature death. Acute exacerbations in COPD patients are predominantly associated with respiratory viruses. Ribavirin is a generic broad-spectrum antiviral agent that could be used for treatment of viral respiratory infections in COPD. Using the Particle Replication In Nonwetting Templates (PRINT) technology, which produces dry-powder particles of uniform shape and size, two new inhaled formulations of ribavirin (ribavirin-PRINT-CFI and ribavirin-PRINT-IP) were developed for efficient delivery to the lung and to minimize bystander exposure. Ribavirin-PRINT-CFI was well tolerated in healthy participants after single dosing and ribavirin-PRINT-IP was well tolerated in healthy and COPD participants after single and repeat dosing. Ribavirin-PRINT-CFI was replaced with ribavirin-PRINT-IP since the latter formulation was found to have improved physicochemical properties and it had a higher ratio of active drug to excipient per unit dose. Ribavirin concentrations were measured in lung epithelial lining fluid in both healthy and COPD participants and achieved target concentrations. Both formulations were rapidly absorbed with approximately dose proportional pharmacokinetics in plasma. Exposure to bystanders was negligible based on both the plasma and airborne ribavirin concentrations with the ribavirin-PRINT-IP formulation. Thus, ribavirin-PRINT-IP allowed for an efficient and convenient delivery of ribavirin to the lungs while minimizing systemic exposure. Further clinical investigations would be required to demonstrate ribavirin-PRINT-IP antiviral characteristics and impact on COPD viral-induced exacerbations. (The clinical trials discussed in this study have been registered at ClinicalTrials.gov under identifiers NCT03243760 and NCT03235726.).

Discovery of a novel class of boron-based antibacterials with activity against gram-negative bacteria.

Gram-negative bacteria cause approximately 70% of the infections in intensive care units. A growing number of bacterial isolates responsible for these infections are resistant to currently available antibiotics and to many in development. Most agents under development are modifications of existing drug classes, which only partially overcome existing resistance mechanisms. Therefore, new classes of Gram-negative antibacterials with truly novel modes of action are needed to circumvent these existing resistance mechanisms. We have previously identified a new a way to inhibit an aminoacyl-tRNA synthetase, leucyl-tRNA synthetase (LeuRS), in fungi via the oxaborole tRNA trapping (OBORT) mechanism. Herein, we show how we have modified the OBORT mechanism using a structure-guided approach to develop a new boron-based antibiotic class, the aminomethylbenzoxaboroles, which inhibit bacterial leucyl-tRNA synthetase and have activity against Gram-negative bacteria by largely evading the main efflux mechanisms in Escherichia coli and Pseudomonas aeruginosa. The lead analogue, AN3365, is active against Gram-negative bacteria, including Enterobacteriaceae bearing NDM-1 and KPC carbapenemases, as well as P. aeruginosa. This novel boron-based antibacterial, AN3365, has good mouse pharmacokinetics and was efficacious against E. coli and P. aeruginosa in murine thigh infection models, which suggest that this novel class of antibacterials has the potential to address this unmet medical need.

Discovery of novel P3-oxo inhibitor of hepatitis C virus NS3/4A serine protease.

A novel series of P3 oxo-modified macrocyclic hepatitis C virus NS3/4A serine protease inhibitor was designed, synthesized and biologically evaluated. The hydroxy-substituted inhibitor 10 demonstrated high potency in genotype 1a and 1b replicon and in the panel of HCV protease mutants. Interestingly, the t-butyl carbonate analog 9c, while not the most potent one in this series, exhibited a virtually flat potency profile in the panel of HCV protease mutants, thus providing opportunity for further optimization.

Synthesis and antiviral activity of novel HCV NS3 protease inhibitors with P4 capping groups.

We have synthesized and evaluated a series of novel HCV NS3 protease inhibitors with various P4 capping groups, which include urea, carbamate, methoxy-carboxamide, cyclic carbamate and amide, pyruvic amide, oxamate, oxalamide and cyanoguanidine. Most of these compounds are remarkably potent, exhibiting single-digit to sub-nanomolar activity in the enzyme assay and cell-based replicon assay. Selected compounds were also evaluated in the protease-inhibitor-resistant mutant transient replicon assay, and they were found to show quite different potency profiles against a panel of HCV protease-inhibitor-resistant mutants.

Boron-containing inhibitors of synthetases.

The use of boron in small-molecule pharmaceuticals is increasing. Boron's ubiquitous occurrence in nature and the recent success of a boronic acid drug (Velcade®) in the clinic have alleviated many concerns over its use in pharmaceuticals. In addition, the unique physicochemical properties of boronic acids make them an attractive addition to the medicinal chemists toolbox. This tutorial review will discuss these properties and potential benefits for anyone interested in finding novel enzyme inhibitors. An exceptional class of boronic acids, the oxaboroles, will be highlighted and their properties and uses will be discussed in detail. Finally, the current paradigm for the reaction of boronic acids with enzyme nucleophiles will be summarized.

Synthesis and SAR of novel benzoxaboroles as a new class of ß-lactamase inhibitors.

A new class of benzoxaborole ß-lactamase inhibitors were designed and synthesized. 6-Aryloxy benzoxaborole 22 inhibited AmpC P99 and CMY-2 with K(i) values in the low nanomolar range. Compound 22 restored antibacterial activity of ceftazidime against Enterobacter cloacae P99 expressing AmpC, a class C ß-lactamase enzyme. The SAR around the arylbenzoxaboroles, which included the influence of linker and substitutions was also established.

Synthesis and SAR of acyclic HCV NS3 protease inhibitors with novel P4-benzoxaborole moieties.

We have synthesized and evaluated a new series of acyclic P4-benzoxaborole-based HCV NS3 protease inhibitors. Structure-activity relationships were investigated, leading to the identification of compounds 5g and 17 with low nanomolar potency in the enzymatic and cell-based replicon assay. The linker-truncated compound 5j was found to exhibit improved absorption and oral bioavailability in rats, suggesting that further reduction of molecular weight and polar surface area could result in improved drug-like properties of this novel series.

Design and synthesis of boron-containing PDE4 inhibitors using soft-drug strategy for potential dermatologic anti-inflammatory application.

PDE4 inhibitors are a validated approach as anti-inflammatory agents but are limited by systemic side effects including emesis. We report a soft-drug strategy incorporating a carboxylic ester group into boron-containing PDE4 inhibitors leading to the discovery of a series of benzoxaborole compounds with good potency (for example IC(50)=47 nM of compound 2) and low emetic activity. These compounds are intended for dermatological use further limiting possible systemic side effects.

Synthesis of new acylsulfamoyl benzoxaboroles as potent inhibitors of HCV NS3 protease.

HCV NS3/4A serine protease is essential for the replication of the HCV virus and has been a clinically validated target. A series of HCV NS3/4A protease inhibitors containing a novel acylsulfamoyl benzoxaborole moiety at the P1' region was synthesized and evaluated. The resulting P1-P3 and P2-P4 macrocyclic inhibitors exhibited sub-nanomolar potency in the enzymatic assay and low nanomolar activity in the cell-based replicon assay. The in vivo PK evaluations of selected compounds are also described.

Synthesis and biological evaluations of P4-benzoxaborole-substituted macrocyclic inhibitors of HCV NS3 protease.

We disclose here a series of P4-benzoxaborole-substituted macrocyclic HCV protease inhibitors. These inhibitors are potent against HCV NS3 protease, their anti-HCV replicon potencies are largely impacted by substitutions on benzoxaborole ring system and P2∗ groups. P2∗ 2-thiazole-isoquinoline provides best replicon potency. The in vitro SAR studies and in vivo PK evaluations of selected compounds are described herein.

Novel macrocyclic HCV NS3 protease inhibitors derived from α-amino cyclic boronates.

A novel series of P2-P4 macrocyclic HCV NS3/4A protease inhibitors with α-amino cyclic boronates as warheads at the P1 site was designed and synthesized. When compared to their linear analogs, these macrocyclic inhibitors exhibited a remarkable improvement in cell-based replicon activities, with compounds 9a and 9e reaching sub-micromolar potency in replicon assay. The SAR around α-amino cyclic boronates clearly established the influence of ring size, chirality and of the substitution pattern. Furthermore, X-ray structure of the co-crystal of inhibitor 9a and NS3 protease revealed that Ser-139 in the enzyme active site traps boron in the warhead region of 9a, thus establishing its mode of action.

Synthesis and evaluation of novel alpha-amino cyclic boronates as inhibitors of HCV NS3 protease.

We have designed and synthesized a novel series of alpha-amino cyclic boronates and incorporated them successfully in several acyclic templates at the P1 position. These compounds are inhibitors of the HCV NS3 serine protease, and structural studies show that they inhibit the NS3 protease by trapping the Ser-139 hydroxyl group in the active site. Synthetic methodologies and SARs of this series of compounds are described.

Discovery and structure-activity study of a novel benzoxaborole anti-inflammatory agent (AN2728) for the potential topical treatment of psoriasis and atopic dermatitis.

A series of phenoxy benzoxaboroles were synthesized and screened for their inhibitory activity against PDE4 and cytokine release. 5-(4-Cyanophenoxy)-2,3-dihydro-1-hydroxy-2,1-benzoxaborole (AN2728) showed potent activity both in vitro and in vivo. This compound is now in clinical development for the topical treatment of psoriasis and being pursued for the topical treatment of atopic dermatitis.

Measurement and modeling of exposure to selected air toxics for health effects studies and verification by biomarkers.

The overall aim of our investigation was to quantify the magnitude and range of individual personal exposures to a variety of air toxics and to develop models for exposure prediction on the basis of time-activity diaries. The specific research goals were (1) to use personal monitoring of non-smokers at a range of residential locations and exposures to non-traffic sources to assess daily exposures to a range of air toxics, especially volatile organic compounds (VOCs) including 1,3-butadiene and particulate polycyclic aromatic hydrocarbons (PAHs); (2) to determine microenvironmental concentrations of the same air toxics, taking account of spatial and temporal variations and hot spots; (3) to optimize a model of personal exposure using microenvironmental concentration data and time-activity diaries and to compare modeled exposures with exposures independently estimated from personal monitoring data; (4) to determine the relationships of urinary biomarkers with the environmental exposures to the corresponding air toxic. Personal exposure measurements were made using an actively pumped personal sampler enclosed in a briefcase. Five 24-hour integrated personal samples were collected from 100 volunteers with a range of exposure patterns for analysis of VOCs and 1,3-butadiene concentrations of ambient air. One 24-hour integrated PAH personal exposure sample was collected by each subject concurrently with 24 hours of the personal sampling for VOCs. During the period when personal exposures were being measured, workplace and home concentrations of the same air toxics were being measured simultaneously, as were seasonal levels in other microenvironments that the subjects visit during their daily activities, including street microenvironments, transport microenvironments, indoor environments, and other home environments. Information about subjects' lifestyles and daily activities were recorded by means of questionnaires and activity diaries. VOCs were collected in tubes packed with the adsorbent resins Tenax GR and Carbotrap, and separate tubes for the collection of 1,3-butadiene were packed with Carbopack B and Carbosieve S-III. After sampling, the tubes were analyzed by means of a thermal desorber interfaced with a gas chromatograph-mass spectrometer (GC-MS). Particle-phase PAHs collected onto a quartz-fiber filter were extracted with solvent, purified, and concentrated before being analyzed with a GC-MS. Urinary biomarkers were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS-MS). Both the environmental concentrations and personal exposure concentrations measured in this study are lower than those in the majority of earlier published work, which is consistent with the reported application of abatement measures to the control of air toxics emissions. The environmental concentration data clearly demonstrate the influence of traffic sources and meteorologic conditions leading to higher air toxics concentrations in the winter and during peak-traffic hours. The seasonal effect was also observed in indoor environments, where indoor sources add to the effects of the previously identified outdoor sources. The variability of personal exposure concentrations of VOCs and PAHs mainly reflects the range of activities the subjects engaged in during the five-day period of sampling. A number of generic factors have been identified to influence personal exposure concentrations to VOCs, such as the presence of an integral garage (attached to the home), exposure to environmental tobacco smoke (ETS), use of solvents, and commuting. In the case of the medium- and high-molecular-weight PAHs, traffic and ETS are important contributions to personal exposure. Personal exposure concentrations generally exceed home indoor concentrations, which in turn exceed outdoor concentrations. The home microenvironment is the dominant individual contributor to personal exposure. However, for those subjects with particularly high personal exposures, activities within the home and exposure to ETS play a major role in determining exposure. Correlation analysis and principal components analysis (PCA) have been performed to identify groups of compounds that share common sources, common chemistry, or common transport or meteorologic patterns. We used these methods to identify four main factors determining the makeup of personal exposures: fossil fuel combustion, use of solvents, ETS exposure, and use of consumer products. Concurrent with sampling of the selected air toxics, a total of 500 urine samples were collected, one for each of the 100 subjects on the day after each of the five days on which the briefcases were carried for personal exposure data collection. From the 500 samples, 100 were selected to be analyzed for PAHs and ETS-related urinary biomarkers. Results showed that urinary biomarkers of ETS exposure correlated strongly with the gas-phase markers of ETS and 1,3-butadiene. The urinary ETS biomarkers also correlated strongly with high-molecular-weight PAHs in the personal exposure samples. Five different approaches have been taken to model personal exposure to VOCs and PAHs, using 75% of the measured personal exposure data set to develop the models and 25% as an independent check on the model performance. The best personal exposure model, based on measured microenvironmental concentrations and lifestyle factors, is able to account for about 50% of the variance in measured personal exposure to benzene and a higher proportion of the variance for some other compounds (e.g., 75% of the variance in 3-ethenylpyridine exposure). In the case of the PAHs, the best model for benzo[a]pyrene is able to account for about 35% of the variance among exposures, with a similar result for the rest of the PAH compounds. The models developed were validated by the independent data set for almost all the VOC compounds. The models developed for PAHs explain some of the variance in the independent data set and are good indicators of the sources affecting PAH concentrations but could not be validated statistically, with the exception of the model for pyrene. A proposal for categorizing personal exposures as low or high is also presented, according to exposure thresholds. For both VOCs and PAHs, low exposures are correctly classified for the concentrations predicted by the proposed models, but higher exposures were less successfully classified.

In Vitro penetration of a novel oxaborole antifungal (AN2690) into the human nail plate.

Onychomycosis is a challenging fungal infection to treat topically, likely due to the unique properties of the nail plate. This seemingly impenetrable barrier has high resistance to the passage of antifungal drugs in sufficient concentrations to kill the causative fungi deep in the nail bed. Recently, a new class of antifungal agent was described, termed oxaboroles, which have broad-spectrum activity. These oxaboroles were designed with properties believed to be required to allow for easier transit through the nail plate. Herein, we report (i) the nail penetration results of four oxaboroles that led to the selection of AN2690, (ii) the results of the nail penetration of AN2690 from four vehicles, and (iii) the nail penetration of AN2690 in its chosen vehicle compared to a commercial control, ciclopirox. AN2690 has superior penetration compared to ciclopirox, and achieves levels within and under the nail plate that suggest it has the potential to be an effective topical treatment for onychomycosis.

Discovery of a new boron-containing antifungal agent, 5-fluoro-1,3-dihydro-1-hydroxy-2,1- benzoxaborole (AN2690), for the potential treatment of onychomycosis.

A structure-activity relationship investigation for a more efficacious therapy to treat onychomycosis, a fungal infection of the toe and fingernails, led to the discovery of a boron-containing small molecule, 5-fluoro-1,3-dihydro-1-hydroxy-2,1-benzoxaborole (AN2690), which is currently in clinical trials for onychomycosis topical treatment.

Identification of borinic esters as inhibitors of bacterial cell growth and bacterial methyltransferases, CcrM and MenH.

As bacteria continue to develop resistance toward current antibiotics, we find ourselves in a continual battle to identify new antibacterial agents and targets. We report herein a class of boron-containing compounds termed borinic esters that have broad spectrum antibacterial activity with minimum inhibitory concentrations (MIC) in the low microgram/mL range. These compounds were identified by screening for inhibitors against Caulobacter crescentus CcrM, an essential DNA methyltransferase from gram negative alpha-proteobacteria. In addition, we demonstrate that borinic esters inhibit menaquinone methyltransferase in gram positive bacteria using a new biochemical assay for MenH from Bacillus subtilis. Our data demonstrate the potential for further development of borinic esters as antibacterial agents as well as leads to explore more specific inhibitors against two essential bacterial enzymes.

Lipopolysaccharide inhibits or accelerates biomedical titanium corrosion depending on environmental acidity.

Titanium and its alloys are routinely used as biomedical implants and are usually considered to be corrosion resistant under physiological conditions. However, during inflammation, chemical modifications of the peri-implant environment including acidification occur. In addition certain biomolecules including lipopolysaccharide (LPS), a component of Gram-negative bacterial cell walls and driver of inflammation have been shown to interact strongly with Ti and modify its corrosion resistance. Gram-negative microbes are abundant in biofilms which form on dental implants. The objective was to investigate the influence of LPS on the corrosion properties of relevant biomedical Ti substrates as a function of environmental acidity. Inductively coupled plasma mass spectrometry was used to quantify Ti dissolution following immersion testing in physiological saline for three common biomedical grades of Ti (ASTM Grade 2, Grade 4 and Grade 5). Complementary electrochemical tests including anodic and cathodic polarisation experiments and potentiostatic measurements were also conducted. All three Ti alloys were observed to behave similarly and ion release was sensitive to pH of the immersion solution. However, LPS significantly inhibited Ti release under the most acidic conditions (pH 2), which may develop in localized corrosion sites, but promoted dissolution at pH 4-7, which would be more commonly encountered physiologically. The observed pattern of sensitivity to environmental acidity of the effect of LPS on Ti corrosion has not previously been reported. LPS is found extensively on the surfaces of skin and mucosal penetrating Ti implants and the findings are therefore relevant when considering the chemical stability of Ti implant surfaces in vivo.

The PM10 fraction of road dust in the UK and India: Characterization, source profiles and oxidative potential.

Most studies of road dust composition have sampled a very wide range of particle sizes, but from the perspective of respiratory exposure to resuspended dusts, it is the PM10 fraction which is of most importance. The PM10 fraction of road dust samples was collected at two sites in Birmingham, UK (major highway and road tunnel) and one site in New Delhi, India. Dust loadings were found to be much higher for New Delhi compared to Birmingham, while concentrations of several species were much higher in the case of Birmingham. Detailed chemical source profiles were prepared for both cities and previously generated empirical factors for source attribution to brake wear, tyre wear, and crustal dust were successfully applied to the UK sites. However, 100% of the mass for the Indian site could not be accounted for using these factors. This study highlights the need for generation of local empirical estimation factors for non-exhaust vehicle emissions. A limited number of bulk road dust and brake pad samples were also characterized. Oxidative potential (OP) was also determined for a limited number of PM10 and bulk road dust samples, and Cu was found to be a factor significantly associated with OP in PM10 and bulk road dust.