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Meenakshi Balganesh

Bio: Meenakshi Balganesh is an academic researcher from AstraZeneca. The author has contributed to research in topics: Efflux & Mycobacterium tuberculosis. The author has an hindex of 9, co-authored 13 publications receiving 535 citations.

Papers
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Journal ArticleDOI
TL;DR: It is shown that these four efflux pump KO mutants of M. tuberculosis play a vital role in mediating efflux of different chemical scaffolds and inhibitors of one or several of these efflux pumps could have a significant impact in the treatment of tuberculosis.
Abstract: Active efflux of drugs mediated by efflux pumps that confer drug resistance is one of the mechanisms developed by bacteria to counter the adverse effects of antibiotics and chemicals. To understand these efflux mechanisms in Mycobacterium tuberculosis, we generated knockout (KO) mutants of four efflux pumps of the pathogen belonging to different classes. We measured the MICs and kill values of two different compound classes on the wild type (WT) and the efflux pump (EP) KO mutants in the presence and absence of the efflux inhibitors verapamil and l-phenylalanyl-l-arginyl-β-naphthylamide (PAβN). Among the pumps studied, the efflux pumps belonging to the ABC (ATP-binding cassette) class, encoded by Rv1218c, and the SMR (small multidrug resistance) class, encoded by Rv3065, appear to play important roles in mediating the efflux of different chemical classes and antibiotics. Efflux pumps encoded by Rv0849 and Rv1258c also mediate the efflux of these compounds, but to a lesser extent. Increased killing is observed in WT M. tuberculosis cells by these compounds in the presence of either verapamil or PAβN. The efflux pump KO mutants were more susceptible to these compounds in the presence of efflux inhibitors. We have shown that these four efflux pumps of M. tuberculosis play a vital role in mediating efflux of different chemical scaffolds. Inhibitors of one or several of these efflux pumps could have a significant impact in the treatment of tuberculosis. The identification and characterization of Rv0849, a new efflux pump belonging to the MFS (major facilitator superfamily) class, are reported.

118 citations

01 Jan 2012
TL;DR: In this paper, the authors have shown that four efflux pumps of Mycobacterium tuberculosis play a vital role in mediating efflux of 48 different chemical scaffolds, and that inhibitors of one or several of these pumps could have a significant impact in the treatment for tuberculosis.
Abstract: 31 32 Active efflux of drugs mediated by efflux pumps which confer drug resistance is one of 33 the mechanisms developed by bacteria to counter the adverse effects of antibiotics and 34 chemicals. To understand these efflux mechanisms in Mycobacterium tuberculosis, we 35 generated knock-out (KO) mutants of four efflux pumps of this pathogen, belonging to 36 different classes. We measured the minimal inhibitory concentrations (MICs) and kill 37 values of two different compound classes on the wild-type (WT) and the efflux pump 38 (EP) KO mutants in the presence and absence of the efflux inhibitors verapamil and L39 phenylalanyl-L-arginyl-β-naphthylamide (PAβN). Among the pumps studied, the efflux 40 pumps belonging to the ABC (ATP-binding cassette) class, encoded by Rv1218c and the 41 SMR (small multidrug resistance) class, encoded by Rv3065 appear to play important 42 roles in mediating efflux of different chemical classes and antibiotics. Efflux pumps 43 encoded by Rv0849 and Rv1258c also mediate efflux of these compounds but to lesser 44 extent. Increased kill is observed in WT M. tuberculosis cells by these compounds in the 45 presence of either verapamil or PAβN. The efflux pump KO mutants were more 46 susceptible to these compounds in the presence of efflux inhibitors. We have shown 47 that these four efflux pumps of M. tuberculosis play a vital role in mediating efflux of 48 different chemical scaffolds. Inhibitors of one or several of these efflux pumps could 49 have a significant impact in the treatment for tuberculosis. 50 Identification and characterization of Rv0849, a new efflux pump belonging 51 to the MFS (major facilitator superfamily) class is reported. 52

107 citations

Journal ArticleDOI
TL;DR: Most of the compound classes had significantly better bactericidal activity in the ΔRv 1218c mutant than in the wild-type H37Rv, suggesting the involvement of Rv1218c gene product in effluxing these compounds from M. tuberculosis.
Abstract: Efflux systems are important in determining the efficacy of antibiotics used in the treatment of bacterial infections. In the last decade much attention has been paid to studying the efflux pumps of mycobacteria. New classes of compounds are under investigation for development into potential candidate drugs for the treatment of tuberculosis. Quite often, these have poor bactericidal activities but exhibit excellent target (biochemical) inhibition. Microarray studies conducted in our laboratories for deciphering the mode of action of experimental drugs revealed the presence of putative ABC transporters. Among these transporters, Rv1218c was chosen for studying its physiological relevance in mediating efflux in Mycobacterium tuberculosis. A ΔRv1218c mutant of M. tuberculosis displayed a 4- to 8-fold increase in the inhibitory and bactericidal potency for different classes of compounds. The MICs and MBCs were reversed to wild-type values when the full-length Rv1218c gene was reintroduced into the ΔRv1218c mutant on a multicopy plasmid. Most of the compound classes had significantly better bactericidal activity in the ΔRv1218c mutant than in the wild-type H37Rv, suggesting the involvement of Rv1218c gene product in effluxing these compounds from M. tuberculosis. The implication of these findings on tuberculosis drug discovery is discussed.

77 citations

Journal ArticleDOI
TL;DR: AZD5847, a novel oxazolidinone, demonstrates improved in vitro bactericidal activity against both extracellular and intracellular M. tuberculosis compared to that of linezolid, and appears to function similarly to lineZolid through impairment of the mycobacterial 50S ribosomal subunit.
Abstract: Treatment of tuberculosis (TB) is impaired by the long duration and complexity of therapy and the rising incidence of drug resistance. There is an urgent need for new agents with improved efficacy, safety, and compatibility with combination chemotherapies. Oxazolidinones offer a potential new class of TB drugs, and linezolid-the only currently approved oxazolidinone-has proven highly effective against extensively drug-resistant (XDR) TB in experimental trials. However, widespread use of linezolid is prohibited by its significant toxicities. AZD5847, a novel oxazolidinone, demonstrates improved in vitro bactericidal activity against both extracellular and intracellular M. tuberculosis compared to that of linezolid. Killing kinetics in broth media and in macrophages indicate that the rate and extent of kill obtained with AZD5847 are superior to those obtained with linezolid. Moreover, the efficacy of AZD5847 was additive when tested along with a variety of conventional TB agents, indicating that AZD5847 may function well in combination therapies. AZD5847 appears to function similarly to linezolid through impairment of the mycobacterial 50S ribosomal subunit. Future studies should be undertaken to further characterize the pharmacodynamics and pharmacokinetics of AZD5847 in both in vitro and animal models as well is in human clinical trials.

77 citations

Journal ArticleDOI
TL;DR: Based on pharmacokinetic/pharmacodynamic indexes reported for beta-lactams against other bacterial pathogens, a cumulative percentage of a 24-h period that the drug concentration exceeds the MIC under steady-state pharmacokinetics conditions (%TMIC) of 20 to 40% was achieved in mice using a suitable dosing regimen.
Abstract: Beta-lactams, in combination with beta-lactamase inhibitors, are reported to have activity against Mycobacterium tuberculosis bacteria growing in broth, as well as inside the human macrophage. We tested representative beta-lactams belonging to 3 different classes for activity against replicating M. tuberculosis in broth and nonreplicating M. tuberculosis under hypoxia, as well as against streptomycin-starved M. tuberculosis strain 18b (ss18b) in the presence or absence of clavulanate. Most of the combinations showed bactericidal activity against replicating M. tuberculosis, with up to 200-fold improvement in potency in the presence of clavulanate. None of the combinations, including those containing meropenem, imipenem, and faropenem, killed M. tuberculosis under hypoxia. However, faropenem- and meropenem-containing combinations killed strain ss18b moderately. We tested the bactericidal activities of meropenem-clavulanate and amoxicillin-clavulanate combinations in the acute and chronic aerosol infection models of tuberculosis in BALB/c mice. Based on pharmacokinetic/pharmacodynamic indexes reported for beta-lactams against other bacterial pathogens, a cumulative percentage of a 24-h period that the drug concentration exceeds the MIC under steady-state pharmacokinetic conditions (%TMIC) of 20 to 40% was achieved in mice using a suitable dosing regimen. Both combinations showed marginal reduction in lung CFU compared to the late controls in the acute model, whereas both were inactive in the chronic model.

60 citations


Cited by
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TL;DR: By far the most widespread mechanism of resistance to AGs is the inactivation of these antibiotics by AG-modifying enzymes, and an overview of these mechanisms is provided.
Abstract: Aminoglycoside (AG) antibiotics are used to treat many Gram-negative and some Gram-positive infections and, importantly, multidrug-resistant tuberculosis. Among various bacterial species, resistance to AGs arises through a variety of intrinsic and acquired mechanisms. The bacterial cell wall serves as a natural barrier for small molecules such as AGs and may be further fortified via acquired mutations. Efflux pumps work to expel AGs from bacterial cells, and modifications here too may cause further resistance to AGs. Mutations in the ribosomal target of AGs, while rare, also contribute to resistance. Of growing clinical prominence is resistance caused by ribosome methyltransferases. By far the most widespread mechanism of resistance to AGs is the inactivation of these antibiotics by AG-modifying enzymes. We provide here an overview of these mechanisms by which bacteria become resistant to AGs and discuss their prevalence and potential for clinical relevance.

329 citations

Journal ArticleDOI
TL;DR: The challenges to developing drugs to treat tuberculosis are discussed and how the field has adapted to these difficulties, with an emphasis on drug discovery approaches that might produce more effective agents and treatment regimens.

262 citations

Journal ArticleDOI
TL;DR: Each known mechanism of resistance to INH and ETH is described and its importance in M. tuberculosis clinical isolates is described.
Abstract: Isoniazid (INH) is the cornerstone of tuberculosis (TB) chemotherapy, used for both treatment and prophylaxis of TB. The antimycobacterial activity of INH was discovered in 1952, and almost as soon as its activity was published, the first INH-resistant Mycobacterium tuberculosis strains were reported. INH and its structural analog and second-line anti-TB drug ethionamide (ETH) are pro-drugs. INH is activated by the catalase-peroxidase KatG, while ETH is activated by the monooxygenase EthA. The resulting active species reacts with NAD+ to form an INH-NAD or ETH-NAD adduct, which inhibits the enoyl ACP reductase InhA, leading to mycolic acid biosynthesis inhibition and mycobacterial cell death. The major mechanism of INH resistance is mutation in katG, encoding the activator of INH. One specific KatG variant, S315T, is found in 94% of INH-resistant clinical isolates. The second mechanism of INH resistance is a mutation in the promoter region of inhA (c-15t), which results in inhA overexpression and leads to titration of the drug. Mutations in the inhA open reading frame and promoter region are also the major mechanism of resistance to ETH, found more often in ETH-resistant clinical isolates than mutations in the activator of ETH. Other mechanisms of resistance to INH and ETH include expression changes of the drugs’ activators, redox alteration, drug inactivation, and efflux pump activation. In this article, we describe each known mechanism of resistance to INH and ETH and its importance in M. tuberculosis clinical isolates.

224 citations

Journal ArticleDOI
TL;DR: Mycobacterium tuberculosis (Mtb) relies on a specialized set of metabolic pathways to support growth in macrophages and is subject to a unique form of metabolic constraint induced by the presence of cholesterol, which implicate cyclic-AMP (cAMP) in regulating cholesterol utilization in Mtb.
Abstract: Mycobacterium tuberculosis (Mtb) relies on a specialized set of metabolic pathways to support growth in macrophages. By conducting an extensive, unbiased chemical screen to identify small molecules that inhibit Mtb metabolism within macrophages, we identified a significant number of novel compounds that limit Mtb growth in macrophages and in medium containing cholesterol as the principle carbon source. Based on this observation, we developed a chemical-rescue strategy to identify compounds that target metabolic enzymes involved in cholesterol metabolism. This approach identified two compounds that inhibit the HsaAB enzyme complex, which is required for complete degradation of the cholesterol A/B rings. The strategy also identified an inhibitor of PrpC, the 2-methylcitrate synthase, which is required for assimilation of cholesterol-derived propionyl-CoA into the TCA cycle. These chemical probes represent new classes of inhibitors with novel modes of action, and target metabolic pathways required to support growth of Mtb in its host cell. The screen also revealed a structurally-diverse set of compounds that target additional stage(s) of cholesterol utilization. Mutants resistant to this class of compounds are defective in the bacterial adenylate cyclase Rv1625/Cya. These data implicate cyclic-AMP (cAMP) in regulating cholesterol utilization in Mtb, and are consistent with published reports indicating that propionate metabolism is regulated by cAMP levels. Intriguingly, reversal of the cholesterol-dependent growth inhibition caused by this subset of compounds could be achieved by supplementing the media with acetate, but not with glucose, indicating that Mtb is subject to a unique form of metabolic constraint induced by the presence of cholesterol.

215 citations

Journal ArticleDOI
TL;DR: The current knowledge on drug efflux in M. tuberculosis is described, which shows Mycobacterium tuberculosis presents one of the largest numbers of putativeDrug efflux pumps compared with its genome size andBioinformatics as well as direct and indirect evidence have established relationships among drug Efflux with intrinsic or acquired resistance in M tuberculosis.
Abstract: Tuberculosis remains an important global public health problem, with an estimated prevalence of 14 million individuals with tuberculosis worldwide in 2007. Because antibiotic treatment is one of the main tools for tuberculosis control, knowledge of Mycobacterium tuberculosis drug resistance is an important component for the disease control strategy. Although several gene mutations in specific loci of the M. tuberculosis genome have been reported as the basis for drug resistance, additional resistance mechanisms are now believed to exist. Efflux is a ubiquitous mechanism responsible for intrinsic and acquired drug resistance in prokaryotic and eukaryotic cells. Mycobacterium tuberculosis presents one of the largest numbers of putative drug efflux pumps compared with its genome size. Bioinformatics as well as direct and indirect evidence have established relationships among drug efflux with intrinsic or acquired resistance in M. tuberculosis. This minireview describes the current knowledge on drug efflux in M. tuberculosis.

180 citations