Metabolomics of Central Carbon Metabolism in Mycobacterium tuberculosis

Alkaline arginine promotes the gentamicin-mediated killing of drug-resistant Salmonella by increasing NADH concentration and proton motive force

Introduction

Antimicrobial resistance, especially the development of multidrug-resistant strains, is an urgent public health threat. Antibiotic adjuvants have been shown to improve the treatment of resistant bacterial infections.

Methods

We verified that exogenous L-arginine promoted the killing effect of gentamicin against Salmonella in vitro and in vivo, and measured intracellular ATP, NADH, and PMF of bacteria. Gene expression was determined using real-time quantitative PCR.

Results

This study found that alkaline arginine significantly increased gentamicin, tobramycin, kanamycin, and apramycin-mediated killing of drug-resistant Salmonella, including multidrug-resistant strains. Mechanistic studies showed that exogenous arginine was shown to increase the proton motive force, increasing the uptake of gentamicin and ultimately inducing bacterial cell death. Furthermore, in mouse infection model, arginine effectively improved gentamicin activity against Salmonella typhimurium.

Discussion

These findings confirm that arginine is a highly effective and harmless aminoglycoside adjuvant and provide important evidence for its use in combination with antimicrobial agents to treat drug-resistant bacterial infections.

Serum metabolomic analyses reveal the potential metabolic biomarkers for prediction of amatoxin poisoning

Amatoxin poisoning leads to over 90% of deaths in mushroom poisoning. The objective of present study was to identify the potential metabolic biomarkers for early diagnosis of amatoxin poisoning. Serum samples were collected from 61 patients with amatoxin poisoning and 61 healthy controls. An untargeted metabolomics analysis was performed using the ultra-high-performance liquid chromatography-quadrupole time-of-flight tandem mass spectrometry (UPLC-QTOF-MS/MS). Multivariate statistical analysis revealed that the patients with amatoxin poisoning could be clearly separated from healthy controls on the basis of their metabolic fingerprints. There were 33 differential metabolites including 15 metabolites up-regulated metabolites and 18 down-regulated metabolites in patients with amatoxin poisoning compared to healthy controls. These metabolites mainly enriched in the lipid metabolism and amino acid metabolism pathways, such as Glycerophospholipid metabolism, Sphingolipid metabolism, Phenylalanine tyrosine and typtophan biosynthesis, Tyrosine metabolism, Arginine and proline metabolism, which may serve important roles in the amatoxin poisoning. Among the differential metabolites, a total of 8 significant metabolic markers were identified for discriminating patients with amatoxin poisoning from healthy controls, including Glycochenodeoxycholate-3-sulfate (GCDCA-S), 11-Oxo-androsterone glucuronide, Neomenthol-glucuronide, Dehydroisoandrosterone 3-glucuronide, Glucose 6-phosphate (G6P), Lanthionine ketimine, Glycerophosphocholine (GPC) and Nicotinamide ribotide, which achieved satisfactory diagnostic accuracy (AUC>0.8) in both discovery and validation cohorts. Strikingly, the Pearson's correlation analysis indicated that 11-Oxo-androsterone glucuronide, G6P and GCDCA-S were positively correlated with the liver injury induced by amatoxin poisoning. The findings of the current study may provide insight into the pathological mechanism of amatoxin poisoning and screened out the reliable metabolic biomarkers to contribute the clinical early diagnosis of amatoxin poisoning.

An Insight on the Prospect of Quinazoline and Quinazolinone Derivatives as Anti-tubercular Agents

Multiple potential drugs have been developed based on the heterocyclic molecules for the treatment of different symptoms. Among the existing heterocyclic molecules, quinazoline and quinazolinone derivatives have been found to exhibit extensive pharmacological and biological characteristics. One significant property of these molecules is their potency as anti-tubercular agents. Thus, both quinazoline and quinazolinone derivatives are modified using different functional groups as substituents for investigating their anti-tubercular activities. We present a summary of the reported anti-tubercular drugs, designed using quinazoline and quinazolinone derivatives, in this review.

Exogenous D-ribose promotes gentamicin treatment of several drug-resistant Salmonella

The metabolic microenvironment of bacteria impacts drug efficacy. However, the metabolic mechanisms of drug-resistant Salmonella spp. remain largely unknown. This study characterized the metabolic mechanism of gentamicin-resistant Salmonella Choleraesuis and found that D-ribose increased the gentamicin-mediated killing of this bacteria. Non-targeted metabolomics of homologous gentamicin-susceptible Salmonella Choleraesuis (SCH-S) and gentamicin-resistant S. Choleraesuis (SCH-R) was performed using UHPLC-Q-TOF MS. The metabolic signature of SCH-R included disrupted central carbon metabolism and energy metabolism, along with dysregulated amino acid and nucleotide metabolism, vitamin and cofactor metabolism, and fatty acid synthesis. D-ribose, the most suppressed metabolite in SCH-R, was shown to strengthen gentamicin efficacy against SCH-R and a clinically isolated multidrug-resistant strain. This metabolite had a similar impact on Salmonella. Derby and Salmonella. Typhimurium. D-ribose activates central carbon metabolism including glycolysis, the pentose phosphate pathway (PPP), and the tricarboxylic acid cycle (TCA cycle), increases the abundance of NADH, polarizes the electron transport chain (ETC), and elevates the proton motive force (PMF) of cells, and induces drug uptake and cell death. These findings suggest that central carbon metabolism plays a critical role in the acquisition of gentamicin resistance by Salmonella, and that D-ribose may serve as an antibiotic adjuvant for gentamicin treatment of resistant bacterial infections.

Central carbon metabolism remodeling as a mechanism to develop drug tolerance and drug resistance in Mycobacterium tuberculosis

Suboptimal efficacy of the current antibiotic regimens and frequent emergence of antibiotic-resistant Mycobacterium tuberculosis (Mtb), an etiological agent of tuberculosis (TB), render TB the world’s deadliest infectious disease before the COVID-19 outbreak. Our outdated TB treatment method is designed to eradicate actively replicating populations of Mtb. Unfortunately, accumulating evidence suggests that a small population of Mtb can survive antimycobacterial pressure of antibiotics by entering a “persister” state (slowly replicating or non-replicating and lacking a stably heritable antibiotic resistance, termed drug tolerance). The formation of drug-tolerant Mtb persisters is associated with TB treatment failure and is thought to be an adaptive strategy for eventual development of permanent genetic mutation-mediated drug resistance. Thus, the molecular mechanisms behind persister formation and drug tolerance acquisition are a source of new antibiotic targets to eradicate both Mtb persisters and drug-resistant Mtb. As Mtb persisters are genetically identical to antibiotic susceptible populations, metabolomics has emerged as a vital biochemical tool to differentiate these populations by determining phenotypic shifts and metabolic reprogramming. Metabolomics, which provides detailed insights into the molecular basis of drug tolerance and resistance in Mtb, has unique advantages over other techniques by its ability to identify specific metabolic differences between the two genetically identical populations. This review summarizes the recent advances in our understanding of the metabolic adaptations used by Mtb persisters to achieve intrinsic drug tolerance and facilitate the emergence of drug resistance. These findings present metabolomics as a powerful tool to identify previously unexplored antibiotic targets and improved combinations of drug regimens against drug-resistant TB infection.

Chemical-genetic interaction mapping links carbon metabolism and cell wall structure to tuberculosis drug efficacy

Efforts to improve tuberculosis therapy include optimizing multidrug regimens to take advantage of drug–drug synergies. However, the complex host environment has a profound effect on bacterial metabolic state and drug activity, making predictions of optimal drug combinations difficult. In this study, we leverage a newly developed library of conditional knockdown Mycobacterium tuberculosis mutants in which genetic depletion of essential genes mimics the effect of drug therapy. This tractable system allowed us to assess the effect of growth condition on predicted drug–drug interactions. We found that these interactions can be differentially sensitive to the metabolic state, and select in vitro–defined interactions can be leveraged to accelerate bacterial killing during infection. These findings suggest strategies for optimizing tuberculosis therapy.

Current chemotherapy against Mycobacterium tuberculosis (Mtb), an important human pathogen, requires a multidrug regimen lasting several months. While efforts have been made to optimize therapy by exploiting drug–drug synergies, testing new drug combinations in relevant host environments remains arduous. In particular, host environments profoundly affect the bacterial metabolic state and drug efficacy, limiting the accuracy of predictions based on in vitro assays alone. In this study, we utilized conditional Mtb knockdown mutants of essential genes as an experimentally tractable surrogate for drug treatment and probe the relationship between Mtb carbon metabolism and chemical–genetic interactions (CGIs). We examined the antitubercular drugs isoniazid, rifampicin, and moxifloxacin and found that CGIs are differentially responsive to the metabolic state, defining both environment-independent and -dependent interactions. Specifically, growth on the in vivo–relevant carbon source, cholesterol, reduced rifampicin efficacy by altering mycobacterial cell surface lipid composition. We report that a variety of perturbations in cell wall synthesis pathways restore rifampicin efficacy during growth on cholesterol, and that both environment-independent and cholesterol-dependent in vitro CGIs could be leveraged to enhance bacterial clearance in the mouse infection model. Our findings present an atlas of chemical–genetic–environmental interactions that can be used to optimize drug–drug interactions, as well as provide a framework for understanding in vitro correlates of in vivo efficacy.

Commonalities of Mycobacterium tuberculosis Transcriptomes in Response to Defined Persisting Macrophage Stresses

As the goal of a bacterium is to become bacteria, evolution has imposed continued selections for gene expression. The intracellular pathogen Mycobacterium tuberculosis, the causative agent of tuberculosis, has adopted a fine-tuned response to survive its host's methods to aggressively eradicate invaders. The development of microarrays and later RNA sequencing has led to a better understanding of biological processes controlling the relationship between host and pathogens. In this study, RNA-seq was performed to detail the transcriptomes of M. tuberculosis grown in various conditions related to stresses endured by M. tuberculosis during host infection and to delineate a general stress response incurring during persisting macrophage stresses. M. tuberculosis was subjected to long-term growth, nutrient starvation, hypoxic and acidic environments. The commonalities between these stresses point to M. tuberculosis maneuvering to exploit propionate metabolism for lipid synthesis or to withstand propionate toxicity whilst in the intracellular environment. While nearly all stresses led to a general shutdown of most biological processes, up-regulation of pathways involved in the synthesis of amino acids, cofactors, and lipids were observed only in hypoxic M. tuberculosis. This data reveals genes and gene cohorts that are specifically or exclusively induced during all of these persisting stresses. Such knowledge could be used to design novel drug targets or to define possible M. tuberculosis vulnerabilities for vaccine development. Furthermore, the disruption of specific functions from this gene set will enhance our understanding of the evolutionary forces that have caused the tubercle bacillus to be a highly successful pathogen.

Deciphering the mechanism of action of antitubercular compounds with metabolomics

Tuberculosis (TB), one of the oldest and deadliest bacterial diseases, continues to cause serious global economic, health, and social problems. Current TB treatments are lengthy, expensive, and routinely ineffective against emerging drug resistant strains. Thus, there is an urgent need for the identification and development of novel TB drugs possessing comprehensive and specific mechanisms of action (MoAs). Metabolomics is a valuable approach to elucidating the MoA, toxicity, and potency of promising chemical leads, which is a critical step of the drug discovery process. Recent advances in metabolomics methodologies for deciphering MoAs include high-throughput screening techniques, the integration of multiple omics methods, mass spectrometry imaging, and software for automated analysis. This review describes recently introduced metabolomics methodologies and techniques for drug discovery, highlighting specific applications to the discovery of new antitubercular drugs and the elucidation of their MoAs.

Induced expression of the zwf gene in the presence of glucose contributes to lowering of glucose 6-phosphate level and consequently reduction of growth rate of Mycobacterium smegmatis

In Mycobacterium smegmatis (renamed Mycolicibacterium smegmatis), glucose 6-phosphate (G6P) level is exceptionally high as compared to other bacteria, E. coli for example. Earlier investigations have indicated that G6P protects M. smegmatis (Msm) against oxidative stress-inducing agents. G6P is a glycolytic intermediate formed either directly through the phosphorylation of glucose or indirectly via the gluconeogenic pathway. Its consumption is catalysed by several enzymes, one of which being the NADPH dependent G6P dehydrogenase (G6PDH) encoded by zwf (msmeg_0314). While investigating the extent to which the carbon sources glucose and glycerol influence Msm growth, we observed that intracellular concentration of G6P was lower in the former's presence than the latter. We could correlate this difference with that in the growth rate, which was higher in glycerol than glucose. We also found that lowering of G6P content in glucose-grown cells was triggered by the induced expression of zwf and the resultant increase in G6PDH activity. When we silenced zwf using CRISPR-Cas9 technology, we observed a significant rise in the growth rate of Msm. Therefore, we have found that depletion of G6P in glucose-grown cells due to increased G6PDH activity is at least one reason why the growth rate of Msm in glucose is less than glycerol. However, we could not establish a similar link-up between slow growth in glucose and lowering of G6P level in the case of Mycobacterium tuberculosis (Mtb). Mycobacteria, therefore, may have evolved diverse mechanisms to ensure that they use glycerol preferentially over glucose for their growth.

Understanding Metabolic Regulation Between Host and Pathogens: New Opportunities for the Development of Improved Therapeutic Strategies Against Mycobacterium tuberculosis Infection

Mycobacterium tuberculosis (Mtb) causes chronic granulomatous lung disease in humans. Recently, novel strategies such as host-directed therapeutics and adjunctive therapies that enhance the effect of existing antibiotics have emerged to better control Mtb infection. Recent advances in understanding the metabolic interplay between host immune cells and pathogens have provided new insights into how their interactions ultimately influence disease outcomes and antibiotic-treatment efficacy. In this review, we describe how metabolic cascades in immune environments and relevant metabolites produced from immune cells during Mtb infection play critical roles in the progression of diseases and induction of anti-Mtb protective immunity. In addition, we introduce how metabolic alterations in Mtb itself can lead to the development of persister cells that are resistant to host immunity and can eventually evade antibiotic attacks. Further understanding of the metabolic link between host cells and Mtb may contribute to not only the prevention of Mtb persister development but also the optimization of host anti-Mtb immunity together with enhanced efficacy of existing antibiotics. Overall, this review highlights novel approaches to improve and develop host-mediated therapeutic strategies against Mtb infection by restoring and switching pathogen-favoring metabolic conditions with host-favoring conditions.

A Role for Mycobacterium tuberculosis Sigma Factor C in Copper Nutritional Immunity

Sigma factor C (SigC) contributes to Mycobacterium tuberculosis virulence in various animal models, but the stress response coordinated by this transcription factor was undefined. The results presented here indicate that SigC prevents copper starvation. Whole genome expression studies demonstrate short-term (4-h) induction of sigC, controlled from a tetracycline-inducible promoter, upregulates ctpB and genes in the nonribosomal peptide synthase (nrp) operon. These genes are expressed at higher levels after 48-h sigC induction, but also elevated are genes encoding copper-responsive regulator RicR and RicR-regulated copper toxicity response operon genes rv0846-rv0850, suggesting prolonged sigC induction results in excessive copper uptake. No growth and global transcriptional differences are observed between a sigC null mutant relative to its parent strain in 7H9 medium. In a copper-deficient medium, however, growth of the sigC deletion strain lags the parent, and 40 genes (including those in the nrp operon) are differentially expressed. Copper supplementation reverses the growth defect and silences most transcriptional differences. Together, these data support SigC as a transcriptional regulator of copper acquisition when the metal is scarce. Attenuation of sigC mutants in severe combined immunodeficient mice is consistent with an inability to overcome innate host defenses that sequester copper ions to deprive invading microbes of this essential micronutrient.

M. tuberculosis curli pili (MTP) is associated with alterations in carbon, fatty acid and amino acid metabolism in a THP-1 macrophage infection model

The initial host-pathogen interaction is crucial for the establishment of infection. An improved understanding of the pathophysiology of Mycobacterium tuberculosis (M. tuberculosis) during macrophage infection can aid the development of intervention therapeutics against tuberculosis. M. tuberculosis curli pili (MTP) is a surface located adhesin, involved in the first point-of-contact between pathogen and host. This study aimed to better understand the role of MTP in modulating the intertwined metabolic pathways of M. tuberculosis and its THP-1 macrophage host. Metabolites were extracted from pelleted wet cell mass of THP-1 macrophages infected with M. tuberculosis wild-type V9124 (WT), Δmtp-deletion mutant and the mtp-complemented strains, respectively, via a whole metabolome extraction method using a 1:3:1 ratio of chloroform:methanol:water. Metabolites were detected by two-dimensional gas chromatography time-of-flight mass spectrometry. Significant metabolites were determined through univariate and multivariate statistical tests and online pathway databases. Relative to the WT, a total of nine and ten metabolites were significantly different in the Δmtp and complement strains, respectively. All nine significant metabolites were found in elevated levels in the Δmtp relative to the WT. Additionally, of the ten significant metabolites, eight were detected in lower levels and two were detected in higher levels in the complement relative to the WT. The absence of the MTP adhesin resulted in reduced virulence of M. tuberculosis leading to alterations in metabolites involved in carbon, fatty acid and amino acid metabolism during macrophage infection, suggesting that MTP plays an important role in the modulation of host metabolic activity. These findings support the prominent role of the MTP adhesin as a virulence factor as well as a promising biomarker for possible diagnostic and therapeutic intervention.

RegX3-Mediated Regulation of Methylcitrate Cycle in Mycobacterium smegmatis

Mycobacterium tuberculosis is a global human pathogen that infects macrophages and can establish a latent infection. Emerging evidence has established the nutrients metabolism as a key point to study the pathogenesis of M. tuberculosis and host immunity. It was reported that fatty acids and cholesterol are the major nutrient sources of M. tuberculosis in the period of infection. However, the mechanism by which M. tuberculosis utilizes lipids for maintaining life activities in nutrient-deficiency macrophages is poorly understood. Mycobacterium smegmatis is fast-growing and generally used to study its pathogenic counterpart, M. tuberculosis. In this work, we found that the phosphate sensing regulator RegX3 of M. smegmatis is required for its growing on propionate and surviving in macrophages. We further demonstrated that the expression of prpR and related genes (prpDBC) in methylcitrate cycle could be enhanced by RegX3 in response to the phosphate-starvation condition. The binding sites of the promoter region of prpR for RegX3 and PrpR were investigated. In addition, cell morphology assay showed that RegX3 is responsible for cell morphological elongation, thus promoting the proliferation and survival of M. smegmatis in macrophages. Taken together, our findings revealed a novel transcriptional regulation mechanism of RegX3 on propionate metabolism, and uncovered that the nutrients-sensing regulatory system puts bacteria at metabolic steady state by altering cell morphology. More importantly, since we observed that M. tuberculosis RegX3 also binds to the prpR operon in vitro, the RegX3-mediated regulation might be general in M. tuberculosis and other mycobacteria for nutrient sensing and environmental adaptation.

SAR Analysis of Small Molecules Interfering with Energy-Metabolism in Mycobacterium tuberculosis

Tuberculosis remains the world's top infectious killer: it caused a total of 1.5 million deaths and 10 million people fell ill with TB in 2018. Thanks to TB diagnosis and treatment, mortality has been falling in recent years, with an estimated 58 million saved lives between 2000 and 2018. However, the emergence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) Mtb strains is a major concern that might reverse this progress. Therefore, the development of new drugs acting upon novel mechanisms of action is a high priority in the global health agenda. With the approval of bedaquiline, which targets mycobacterial energy production, and delamanid, which targets cell wall synthesis and energy production, the energy-metabolism in Mtb has received much attention in the last decade as a potential target to investigate and develop new antimycobacterial drugs. In this review, we describe potent anti-mycobacterial agents targeting the energy-metabolism at different steps with a special focus on structure-activity relationship (SAR) studies of the most advanced compound classes.

Synthesis, Structure-Activity Relationship, and Mechanistic Studies of Aminoquinazolinones Displaying Antimycobacterial Activity

Phenotypic whole-cell screening against Mycobacterium tuberculosis (Mtb) in glycerol–alanine–salts supplemented with Tween 80 and iron (GASTE-Fe) media led to the identification of a 2-aminoquinazolinone hit compound, sulfone 1 which was optimized for solubility by replacing the sulfone moiety with a sulfoxide 2. The synthesis and structure–activity relationship (SAR) studies identified several compounds with potent antimycobacterial activity, which were metabolically stable and noncytotoxic. Compound 2 displayed favorable in vitro properties and was therefore selected for in vivo pharmacokinetic (PK) studies where it was found to be extensively metabolized to the sulfone 1. Both derivatives exhibited promising PK parameters; however, when 2 was evaluated for in vivo efficacy in an acute TB infection mouse model, it was found to be inactive. In order to understand the in vitro and in vivo discrepancy, compound 2 was subsequently retested in vitro using different Mtb strains cultured in different media. This revealed that activity was only observed in media containing glycerol and led to the hypothesis that glycerol was not used as a primary carbon source by Mtb in the mouse lungs, as has previously been observed. Support for this hypothesis was provided by spontaneous-resistant mutant generation and whole genome sequencing studies, which revealed mutations mapping to glycerol metabolizing genes indicating that the 2-aminoquinazolinones kill Mtb in vitro via a glycerol-dependent mechanism of action.

Infect and Inject: How Mycobacterium tuberculosis Exploits Its Major Virulence-Associated Type VII Secretion System, ESX-1

Mycobacterium tuberculosis is an ancient master of the art of causing human disease. One important weapon within its fully loaded arsenal is the type VII secretion system. M. tuberculosis has five of them: ESAT-6 secretion systems (ESX) 1 to 5. ESX-1 has long been recognized as a major cause of attenuation of the FDA-licensed vaccine Mycobacterium bovis BCG, but its importance in disease progression and transmission has recently been elucidated in more detail. This review summarizes the recent advances in (i) the understanding of the ESX-1 structure and components, (ii) our knowledge of ESX-1's role in hijacking macrophage function to set a path for infection and dissemination, and (iii) the development of interventions that utilize ESX-1 for diagnosis, drug interventions, host-directed therapies, and vaccines.

Comparative genomics shows differences in the electron transport and carbon metabolic pathways of Mycobacterium africanum relative to Mycobacterium tuberculosis and suggests an adaptation to low oxygen tension

The geographically restricted Mycobacterium africanum lineages (MAF) are primarily found in West Africa, where they account for a significant proportion of tuberculosis. Despite this phenomenon, little is known about the co-evolution of these ancient lineages with West Africans. MAF and M. tuberculosis sensu stricto lineages (MTB) differ in their clinical, in vitro and in vivo characteristics for reasons not fully understood. Therefore, we compared genomes of 289 MAF and 205 MTB clinical isolates from the 6 main human-adapted M. tuberculosis complex lineages, for mutations in their Electron Transport Chain and Central Carbon Metabolic pathway in order to explain these metabolic differences. Furthermore, we determined, in silico, whether each mutation could affect the function of genes encoding enzymes in these pathways. We found more mutations with the potential to affect enzymes in these pathways in MAF lineages compared to MTB lineages. We also found that similar mutations occurred in these pathways between MAF and some MTB lineages. Generally, our findings show further differences between MAF and MTB lineages that may have contributed to the MAF clinical and growth phenotype and indicate potential adaptation of MAF lineages to a distinct ecological niche, which we suggest includes areas characterized by low oxygen tension.

Mycobacterium tuberculosis Metabolism

Mycobacterium tuberculosis is the cause of tuberculosis (TB), a disease which continues to overwhelm health systems in endemic regions despite the existence of effective combination chemotherapy and the widespread use of a neonatal anti-TB vaccine. For a professional pathogen, M. tuberculosis retains a surprisingly large proportion of the metabolic repertoire found in nonpathogenic mycobacteria with very different lifestyles. Moreover, evidence that additional functions were acquired during the early evolution of the M. tuberculosis complex suggests the organism has adapted (and augmented) the metabolic pathways of its environmental ancestor to persistence and propagation within its obligate human host. A better understanding of M. tuberculosis pathogenicity, however, requires the elucidation of metabolic functions under disease-relevant conditions, a challenge complicated by limited knowledge of the microenvironments occupied and nutrients accessed by bacilli during host infection, as well as the reliance in experimental mycobacteriology on a restricted number of experimental models with variable relevance to clinical disease. Here, we consider M. tuberculosis metabolism within the framework of an intimate host-pathogen coevolution. Focusing on recent advances in our understanding of mycobacterial metabolic function, we highlight unusual adaptations or departures from the better-characterized model intracellular pathogens. We also discuss the impact of these mycobacterial "innovations" on the susceptibility of M. tuberculosis to existing and experimental anti-TB drugs, as well as strategies for targeting metabolic pathways. Finally, we offer some perspectives on the key gaps in the current knowledge of fundamental mycobacterial metabolism and the lessons which might be learned from other systems.

Targeting DNA Replication and Repair for the Development of Novel Therapeutics against Tuberculosis

Mycobacterium tuberculosis is the etiological agent of tuberculosis (TB), an infectious disease which results in approximately 10 million incident cases and 1.4 million deaths globally each year, making it the leading cause of mortality from infection. An effective frontline combination chemotherapy exists for TB; however, this regimen requires the administration of four drugs in a 2 month long intensive phase followed by a continuation phase of a further 4 months with two of the original drugs, and is only effective for the treatment of drug-sensitive TB. The emergence and global spread of multidrug-resistant (MDR) as well as extensively drug-resistant (XDR) strains of M. tuberculosis, and the complications posed by co-infection with the human immunodeficiency virus (HIV) and other co-morbidities such as diabetes, have prompted urgent efforts to develop shorter regimens comprising new compounds with novel mechanisms of action. This demands that researchers re-visit cellular pathways and functions that are essential to M. tuberculosis survival and replication in the host but which are inadequately represented amongst the targets of current anti-mycobacterial agents. Here, we consider the DNA replication and repair machinery as a source of new targets for anti-TB drug development. Like most bacteria, M. tuberculosis encodes a complex array of proteins which ensure faithful and accurate replication and repair of the chromosomal DNA. Many of these are essential; so, too, are enzymes in the ancillary pathways of nucleotide biosynthesis, salvage, and re-cycling, suggesting the potential to inhibit replication and repair functions at multiple stages. To this end, we provide an update on the state of chemotherapeutic inhibition of DNA synthesis and related pathways in M. tuberculosis. Given the established links between genotoxicity and mutagenesis, we also consider the potential implications of targeting DNA metabolic pathways implicated in the development of drug resistance in M. tuberculosis, an organism which is unusual in relying exclusively on de novo mutations and chromosomal rearrangements for evolution, including the acquisition of drug resistance. In that context, we conclude by discussing the feasibility of targeting mutagenic pathways in an ancillary, “anti-evolution” strategy aimed at protecting existing and future TB drugs.