[Show abstract][Hide abstract] ABSTRACT: The reductively activated nitroaromatic class of antimicrobials, which include nitroimidazole and the more metabolically labile nitrofuran antitubercular agents, have demonstrated some potential for development as therapeutics against dormant TB bacilli. In previous studies, the pharmacokinetic properties of nitrofuranyl isoxazolines were improved by incorporation of the outer ring elements of the antitubercular nitroimidazole OPC-67683. This successfully increased stability of the resulting pentacyclic nitrofuran lead compound Lee1106 (referred to herein as 9a). In the current study, we report the synthesis and antimicrobial properties of 9a and panel of 9a analogs, which were developed to increase oral bioavailability. These hybrid nitrofurans remained potent inhibitors of Mycobacterium tuberculosis with favorable selectivity indices (>150) and a narrow spectrum of activity. In vivo, the pentacyclic nitrofuran compounds showed long half-lives and high volumes of distribution. Based on pharmacokinetic testing and lack of toxicity in vivo,
9a remained the series lead. 9a exerted a lengthy post antibiotic effect and was highly active against nonreplicating M. tuberculosis grown under hypoxia. 9a showed a low potential for cross resistance to current antitubercular agents, and a mechanism of activation distinct from pre-clinical tuberculosis candidates PA-824 and OPC-67683. Together these studies show that 9a is a nanomolar inhibitor of actively growing as well as nonreplicating M. tuberculosis.
[Show abstract][Hide abstract] ABSTRACT: Although the classical antibiotic spectinomycin is a potent bacterial protein synthesis inhibitor, poor antimycobacterial activity limits its clinical application for treating tuberculosis. Using structure-based design, we generated a new semisynthetic series of spectinomycin analogs with selective ribosomal inhibition and excellent narrow-spectrum antitubercular activity. In multiple murine infection models, these spectinamides were well tolerated, significantly reduced lung mycobacterial burden and increased survival. In vitro studies demonstrated a lack of cross resistance with existing tuberculosis therapeutics, activity against multidrug-resistant (MDR) and extensively drug-resistant tuberculosis and an excellent pharmacological profile. Key to their potent antitubercular properties was their structural modification to evade the Rv1258c efflux pump, which is upregulated in MDR strains and is implicated in macrophage-induced drug tolerance. The antitubercular efficacy of spectinamides demonstrates that synthetic modifications to classical antibiotics can overcome the challenge of intrinsic efflux pump-mediated resistance and expands opportunities for target-based tuberculosis drug discovery.
[Show abstract][Hide abstract] ABSTRACT: A series of tetracyclic nitrofuran isoxazoline anti-tuberculosis agents was designed and synthesized to improve the pharmacokinetic properties of an initial lead compound, which had potent anti-tuberculosis activity but suffered from poor solubility, high protein binding and rapid metabolism. In this study, structural modifications were carried on the outer phenyl and piperidine rings to introduce solubilizing and metabolically blocking functional groups. The compounds generated were evaluated for their in vitro antitubercular activity, bacterial spectrum of activity, solubility, permeability, microsomal stability and protein binding. Pharmacokinetic profiles for the most promising candidates were then determined. Compounds with phenyl morpholine and pyridyl morpholine outer rings were found to be the most potent anti-tuberculosis agents in the series. These compounds retained a narrow antibacterial spectrum of activity, with weak anti-Gram positive and no Gram negative activity, as well as good activity against non-replicating Mycobacterium tuberculosis in a low oxygen model. Overall, the addition of solubilizing and metabolically blocked outer rings did improve solubility and decrease protein binding as designed. However, the metabolic stability for compounds in this series was generally lower than desired. The best three compounds selected for in vivo pharmacokinetic testing all showed high oral bioavailability, with one notable compound showing a significantly longer half-life and good tolerability supporting its further advancement.
No preview · Article · Aug 2012 · Bioorganic & medicinal chemistry
[Show abstract][Hide abstract] ABSTRACT: In vivo tuberculosis is exposed to continually changing drug concentrations for which static minimum inhibitory concentration (MIC) testing may be a poor surrogate. While in vitro approaches to determine time-kill curves for antibiotics have been widely applied in assessing antimicrobial activity against fast growing microorganisms, their availability and application for slow-growing microorganisms including Mycobacterium tuberculosis has so far been scarce. Thus, we developed a novel simple in vitro pharmacokinetic/pharmacodynamic (PK/PD) model for establishing time-kill curves and applied it for evaluating the antimicrobial activity of different dosing regimens of isoniazid (INH) against Mycobacterium bovis BCG as a surrogate for virulent M. tuberculosis. In the in vitro model M. bovis BCG was exposed to INH concentration-time profiles as usually encountered during multiple dose therapy with 25, 100 and 300mg/day in humans who are fast or slow INH metabolizers. Bacterial killing was followed over time by determining viable counts and the resulting time-kill data was analyzed using a semi-mechanistic PK/PD model with an adaptive IC(50) function to describe the emergence of insensitive populations of bacteria over the course of treatment. In agreement with previous studies, the time-kill data suggest that AUC(0-24)/MIC is the PK/PD index that is the most explanatory of the antimicrobial effect of INH. The presented in vitro PK/PD model and associated modeling approach were able to characterize the time-kill kinetics of INH in M. bovis BCG, and may in general serve as a potentially valuable, low cost tool for the assessment of antibacterial activity in slow-growing organisms in drug development and applied pharmacotherapy.
[Show abstract][Hide abstract] ABSTRACT: In the course of the development of a potent series of nitrofuranylamide anti-tuberculosis agents, we investigated if the exceptional activity resulted in part from the isoxazoline core and if it possessed any intrinsic anti-tuberculosis activity. This led to the discovery of an isoxazoline ester with appreciable anti-tuberculosis activity. In this study we explored the anti-tuberculosis structure-activity relationship of the isoxazoline ester compound through systematic modification of the 3,5-di-substituted isoxazoline core. Two approaches were used: (i) modification of the potentially metabolically labile ester functionality at the 3 position with acids, amines, amides, reverse amides, alcohols, hydrazides, and 1,3,4-oxadiazoles; (ii) substitution of the distal benzyl piperazine ring in the 5 position of the isoxazoline ring with piperazyl-ureas, piperazyl-carbamates, biaryl systems, piperidines and morpholine. Attempts to replace the ester group at C-3 position of isoxazoline with a variety of bioisosteric head groups led to significant loss of the tuberculosis inhibition indicating that an ester is required for anti-tuberculosis activity. Optimization of the isoxazoline C-5 position produced compounds with improved anti-tuberculosis activity, most notably the piperazyl-urea and piperazyl-carbamate analogs.
Full-text · Article · Feb 2009 · European Journal of Medicinal Chemistry
[Show abstract][Hide abstract] ABSTRACT: The use of NMR spectroscopy in lipid research has been traditionally reserved for the analysis and structural elucidation of discrete lipid molecules. Although NMR analysis of organic molecules provides a plethora of structural information that is normally unattainable by most other techniques, its use for global analysis of mixed lipid pools has been hampered by its relatively low sensitivity and overlapping of signals in the spectrum. However, the last few decades have witnessed great advancements in NMR spectroscopy that generally resulted in greater sensitivity and offered more flexibility in sampling techniques. The method discussed in this chapter describes the use of NMR for global lipidome analysis. This methodology benefits from the quantitative nature of this technique together with the abundance of the structural information it can offer, while partially overcoming the problems of low sensitivity and overlapping signals through isotope-enrichment and the use of multidimensional NMR, respectively. We have applied this method successfully to the mycobacterial lipidome as an example of an organism with a very complex and chemically diverse lipid pool. The same concept is applicable to a wide range of prokaryotes that can grow in the laboratory in well-defined growth media.
No preview · Article · Jan 2009 · Methods in molecular biology (Clifton, N.J.)
[Show abstract][Hide abstract] ABSTRACT: Nitrofuranylamides (NFAs) are nitroaromatic compounds that have recently been discovered and have potent anti-tuberculosis (TB) activity. A foundational study was performed to evaluate whether this class of agents possesses microbiological properties suitable for future antimycobacterial therapy.
Five representative compounds of the NFA series were evaluated by standard microbiological assays to determine MICs, MBCs, activity against anaerobic non-replicating persistent Mycobacterium tuberculosis, post-antibiotic effects (PAEs), antibiotic synergy and the basis for resistance.
The antimicrobial activity of these compounds was restricted to bacteria of the M. tuberculosis complex, and all compounds were highly active against drug-susceptible and -resistant strains of M. tuberculosis, with MICs 0.0004-0.05 mg/L. Moreover, no antagonism was observed with front-line anti-TB drugs. Activity was also retained against dormant bacilli in two in vitro low-oxygen models for M. tuberculosis persistence. A long PAE was observed, which was comparable to that of rifampicin, but superior to isoniazid and ethambutol. Spontaneous NFA-resistant mutants arose at a frequency of 10(-5)-10(-7), comparable to that for isoniazid (10(-5)-10(-6)). Some of these mutants exhibited cross-resistance to one or both of the nitroimidazoles PA-824 and OPC-67683. Cross-resistance was associated with inactivation of the reduced F(420)-deazaflavin cofactor pathway and not with inactivation of the Rv3547, the nitroreductase for PA-824 and OPC-67683.
Based on these studies, NFAs have many useful antimycobacterial properties applicable to TB chemotherapy and probably possess a unique mode of action that results in good activity against active and dormant M. tuberculosis. Therefore, the further development of lead compounds in this series is warranted.
[Show abstract][Hide abstract] ABSTRACT: In order to expand the structure-activity relationship of tetramic acid molecules with structural similarity to the antibiotic reutericyclin, 22 compounds were synthesized and tested against a panel of clinically relevant bacteria. Key structural changes on the tetramic acid core affected antibacterial activity. Various compounds in the N-alkyl 3-acetyltetramic acid series exhibited good activity against Gram-positive bacterial pathogens including Bacillus anthracis, Propionibacterium acnes, Enterococcus faecalis, and both Methicillin-sensitive and -resistant Staphylococcus aureus.
No preview · Article · Apr 2008 · Journal of Medicinal Chemistry
[Show abstract][Hide abstract] ABSTRACT: Mycobacteria, including Mycobacterium tuberculosis, are characterized by a unique cell wall rich in complex lipids, glycolipids, polyketides, and terpenoids. Many of these metabolites have been shown to play important roles in mycobacterial virulence and their inherent resistance to many antibiotics. Here, we report the development of a new simple method for global analysis of these metabolites using two-dimensional (1)H-(13)C heteronuclear single quantum coherence nuclear magnetic resonance. The major advantages of this method are as follows: the small amount of sample and the minimal sample manipulation required; a relatively short procedural time; and the ability to rapidly attain a qualitative and quantitative lipid profile of a mycobacterial sample in which the majority of the clinically relevant lipids can be observed simultaneously. The effectiveness of this method is demonstrated in four different areas of major concern to the mycobacterial research community: i) adaptive changes in cell wall lipids as a result of drug treatment; ii) analysis of gene function; iii) characterization of new mycobacterial species; and iv) analysis of the production of virulence factors in clinical isolates of M. tuberculosis. This method is complementary to mass spectrometry-based lipidomic technologies and provides an urgently needed tool to gain a better understanding of the role of lipids in mycobacteria pathogenesis.
Full-text · Article · Mar 2008 · The Journal of Lipid Research