A roadmap for drug discovery and its translation to small molecule agents in clinical development for tuberculosis treatment

Design, Synthesis, and Antibacterial Screening of Some Novel Heteroaryl-Based Ciprofloxacin Derivatives as DNA Gyrase and Topoisomerase IV Inhibitors

A novel series of ciprofloxacin hybrids comprising various heterocycle derivatives has been synthesized and structurally elucidated using ¹H NMR, ¹³C NMR, and elementary analyses. Using ciprofloxacin as a reference, compounds 1-21 were screened in vitro against Gram-positive bacterial strains such as Staphylococcus aureus and Bacillus subtilis and Gram-negative strains such as Escherichia coli and Pseudomonas aeruginosa. As a result, many of the compounds examined had antibacterial activity equivalent to ciprofloxacin against test bacteria. Compounds 2-6, oxadiazole derivatives, were found to have antibacterial activity that was 88 to 120% that of ciprofloxacin against Gram-positive and Gram-negative bacteria. The findings showed that none of the compounds tested had antifungal activity against Aspergillus flavus, but did have poor activity against Candida albicans, ranging from 23% to 33% of fluconazole, with compound 3 being the most active (33% of fluconazole). The most potent compounds, 3, 4, 5, and 6, displayed an IC₅₀ of 86, 42, 92, and 180 nM against E. coli DNA gyrase, respectively (novobiocin, IC₅₀ = 170 nM). Compounds 4, 5, and 6 showed IC₅₀ values (1.47, 6.80, and 8.92 µM, respectively) against E. coli topo IV in comparison to novobiocin (IC₅₀ = 11 µM).

Synthesis, evaluation of thymidine phosphorylase and angiogenic inhibitory potential of ciprofloxacin analogues: Repositioning of ciprofloxacin from antibiotic to future anticancer drugs

Over expression of thymidine phosphorylase (TP) in various human tumors compared to normal healthy tissue is associated with progression of cancer and proliferation. The 2-deoxy-d-ribose is the final product of thymidine phosphorylase (TP) catalyzed reaction. Both TP and 2-deoxy-d-ribose are known to promote unwanted angiogenesis in cancerous cells. Discovery of potent inhibitors of thymidine phosphorylase (TP) can offer appropriate approach in cancer treatment. A series of ciprofloxacin 2, 3a-3c, 4a-4d, 5a-5b, 6 and 7 has been synthesized and characterized using spectroscopic techniques. Afterwards, inhibitory potential of synthesized ciprofloxacin 2, 3a-3c, 4a-4d, 5a-5b, 6 and 7 against thymidine phosphorylase enzyme was assessed. Out of these twelve analogs of ciprofloxacin nine analogues 3a-3c, 4a-4c, 5a-5b and 6 showed good inhibitory activity against thymidine phosphorylase. Inhibitory activity as presented by their IC₅₀ values was found in the range of 39.71 ± 1.13 to 161.89 ± 0.95 μM. The 7-deazaxanthine was used as a standard inhibitor with IC₅₀ = 37.82 ± 0.93 μM. Furthermore, the chick chorionic allantoic membrane (CAM) assay was used to investigate anti-angiogenic activity of the most active ciprofloxacin-based inhibitor 3b. To enlighten the important binding interactions of ciprofloxacin derivatives with target enzyme, the structure activity relationship and molecular docking studies of chosen ciprofloxacin analogues was discussed. Docking studies revealed key π-π stacking, π-cation and hydrogen bonding interactions of ciprofloxacin analogues with active site residues of thymidine phosphorylase enzyme.

Synthesis, biological evaluation and computational study of novel isoniazid containing 4H-Pyrimido[2,1-b]benzothiazoles derivatives

Synthesis of novel and potent hit molecules has an eternal demand. It is our continuous study to search novel bioactive hit molecules and as a part of this, a series of novel N'-isonicotinoyl-2-methyl-4-(pyridin-2-yl)-4H-benzo[4,5]thiazolo[3,2-a]pyrimidine-3-carbohydrazide analogs (5a-5n) were synthesized with good yields by the conventional method. The various novel compounds have been characterized and identified by many analytical technique such as IR, ¹H NMR, ¹³C NMR, mass spectral analysis, and elemental analysis. All the synthetic analogs (5a-5n) are evaluated for their in vitro antibacterial and anti-mycobacterial activities against different bacterial strains. Molecular docking and Molecular dynamics studies were helped in revealing the mode of action of these compounds through their interactions with the active site of the Mycobacterium tuberculosis enoyl reductase (InhA) enzyme. The calculated ADMET descriptors for the synthesized compounds validated good pharmacokinetic properties, confirming that these compounds could be used as templates for the development of new Anti-mycobacterial agents.

A metal- and base-free domino protocol for the synthesis of 1,3-benzoselenazines, 1,3-benzothiazines and related scaffolds

Efficient protocols have been described for the synthesis of 1,3-benzoselenazines, 1,3-benzothiazines, 2-aryl thiazin-4-ones and diaryl[b,f][1,5]diazocine-6,12(5H,11H)-diones. These transformations were successfully driven towards the product formation under mild acid catalyzed reaction conditions at room temperature using 2-amino aryl/hetero-aryl alkyl alcohols and amides as substrates. The merits of the present methods also rely on the easy access of rarely explored bioactive scaffolds like 1,3-benzoselenazine derivatives, for which well-documented methods are rarely known in the literature. A broad range of substrates with both electron-rich and electron-deficient groups were well-tolerated under the developed conditions to furnish the desired products in yields up to 98%. The scope of the devised method is not only restricted to the synthesis of 1,3-benzoselenazines, but it was also further extended towards the synthesis of 1,3-benzothiazines, 1,3-benzothiazinones and the corresponding eight membered N-heterocycles such as diaryl[b,f][1,5]diazocine-6,12(5H,11H)-diones.

Carbonic Anhydrase Inhibitors as Novel Drugs against Mycobacterial β-Carbonic Anhydrases: An Update on In Vitro and In Vivo Studies

Mycobacteria cause a variety of diseases, such as tuberculosis, leprosy, and opportunistic diseases in immunocompromised people. The treatment of these diseases is problematic, necessitating the development of novel treatment strategies. Recently, β-carbonic anhydrases (β-CAs) have emerged as potential drug targets in mycobacteria. The genomes of mycobacteria encode for three β-CAs that have been cloned and characterized from Mycobacterium tuberculosis (Mtb) and the crystal structures of two of the enzymes have been determined. Different classes of inhibitor molecules against Mtb β-CAs have subsequently been designed and have been shown to inhibit these mycobacterial enzymes in vitro. The inhibition of these centrally important mycobacterial enzymes leads to reduced growth of mycobacteria, lower virulence, and impaired biofilm formation. Thus, the inhibition of β-CAs could be a novel approach for developing drugs against the severe diseases caused by pathogenic mycobacteria. In the present article, we review the data related to in vitro and in vivo inhibition studies in the field.

Recent advances of imidazole-containing derivatives as anti-tubercular agents

Tuberculosis still remains one of the most common, communicable, and leading deadliest diseases known to mankind throughout the world. Drug-resistance in Mycobacterium tuberculosis which threatens to worsen the global tuberculosis epidemic has caused great concern in recent years. To overcome the resistance, the development of new drugs with novel mechanisms of actions is of great importance. Imidazole-containing derivatives endow with various biological properties, and some of them demonstrated excellent anti-tubercular activity. As the most emblematic example, 4-nitroimidazole delamanid has already received approval for treatment of multidrug-resistant tuberculosis infected patients. Thus, imidazole-containing derivatives have caused great interests in discovery of new anti-tubercular agents. Numerous of imidazole-containing derivatives were synthesized and screened for their in vitro and in vivo anti-mycobacterial activities against both drug-sensitive and drug-resistant Mycobacterium tuberculosis pathogens. This review aims to outline the recent advances of imidazole-containing derivatives as anti-tubercular agents, and summarize the structure-activity relationship of these derivatives. The enriched structure-activity relationship may pave the way for the further rational development of imidazole-containing derivatives as anti-tubercular agents.

Virtual screening of combinatorial library of novel benzenesulfonamides on mycobacterial carbonic anhydrase II

Combinatorial library of novel benzenesulfonamides was docked (Schrodinger Glide) into mycobacterial carbonic anhydrase (mtCA II) and human (hCA II) isoforms with an aim to find drug candidates with selective activity on mtCA II. The predicted selectivity was calculated based on optimized MM-GBSA free energies for ligand enzyme interactions. Selectivity, LogP (o/w) and interaction energy were used to calculate the selection index which determined the subset of best scoring molecules selected for further evaluation. Structure-activity relationship was found for fragment subsets, showing us the possible way regarding how to influence lipophilicity without affecting ligand-enzyme binding properties.

New antimycobacterial agents in the pre-clinical phase or beyond: recent advances in patent literature (2001-2016)

INTRODUCTION

Tuberculosis, an infectious disease, has caused more deaths worldwide than any other single infectious disease, killing more than 1.5 million people each year; equating to 4,100 deaths a day. In the past 60 years, no new drugs have been added to the first line regimen, in spite of the fact that thousands of papers have been published on drugs against tuberculosis and hundreds of drugs have received patents as new potential products. Thus, there is undoubtedly an urgent need for the deployment of new effective drugs against tuberculosis. Areas covered: This review brings to the reader the opportunity to understand the chemical and biological characteristics of all patented anti-tuberculosis drugs in North America, Europe, Japan, and Russia. The 116 patents discussed here concern new molecules in the early or advanced phase of development in the last 16 years. Expert opinion: Of all 116 patents, only one developed drug, bedaquiline, is used, and then, only in specific cases. Another three drugs are in clinical studies. However, many other compounds, for which there are in vitro and in vivo studies, seem to fulfil the requisite criteria to be a new anti-tuberculosis agent. However, why are they not in use? Why were so many studies interrupted? Why is there no more news for many of these drugs?

Perspectives on the Transition From Bacterial Phytopathogen Genomics Studies to Applications Enhancing Disease Management: From Promise to Practice

The advent of genomics has advanced science into a new era, providing a plethora of "toys" for researchers in many related and disparate fields. Genomics has also spawned many new fields, including proteomics and metabolomics, furthering our ability to gain a more comprehensive view of individual organisms and of interacting organisms. Genomic information of both bacterial pathogens and their hosts has provided the critical starting point in understanding the molecular bases of how pathogens disrupt host cells to cause disease. In addition, knowledge of the complete genome sequence of the pathogen provides a potentially broad slate of targets for the development of novel virulence inhibitors that are desperately needed for disease management. Regarding plant bacterial pathogens and disease management, the potential for utilizing genomics resources in the development of durable resistance is enhanced because of developing technologies that enable targeted modification of the host. Here, we summarize the role of genomics studies in furthering efforts to manage bacterial plant diseases and highlight novel genomics-enabled strategies heading down this path.

Legionella pneumophila Carbonic Anhydrases: Underexplored Antibacterial Drug Targets

Carbonic anhydrases (CAs, EC 4.2.1.1) are metalloenzymes which catalyze the hydration of carbon dioxide to bicarbonate and protons. Many pathogenic bacteria encode such enzymes belonging to the α-, β-, and/or γ-CA families. In the last decade, enzymes from some of these pathogens, including Legionella pneumophila, have been cloned and characterized in detail. These enzymes were shown to be efficient catalysts for CO₂ hydration, with k_cat values in the range of (3.4–8.3) × 10⁵ s⁻¹ and k_cat/K_M values of (4.7–8.5) × 10⁷ M⁻¹·s⁻¹. In vitro inhibition studies with various classes of inhibitors, such as anions, sulfonamides and sulfamates, were also reported for the two β-CAs from this pathogen, LpCA1 and LpCA2. Inorganic anions were millimolar inhibitors, whereas diethyldithiocarbamate, sulfamate, sulfamide, phenylboronic acid, and phenylarsonic acid were micromolar ones. The best LpCA1 inhibitors were aminobenzolamide and structurally similar sulfonylated aromatic sulfonamides, as well as acetazolamide and ethoxzolamide (K_Is in the range of 40.3–90.5 nM). The best LpCA2 inhibitors belonged to the same class of sulfonylated sulfonamides, together with acetazolamide, methazolamide, and dichlorophenamide (K_Is in the range of 25.2–88.5 nM). Considering such preliminary results, the two bacterial CAs from this pathogen represent promising yet underexplored targets for obtaining antibacterials devoid of the resistance problems common to most of the clinically used antibiotics, but further studies are needed to validate them in vivo as drug targets.

Toward antituberculosis drugs: in silico screening of synthetic compounds against Mycobacterium tuberculosisl,d-transpeptidase 2

Mycobacterium tuberculosis (Mtb) the main causative agent of tuberculosis, is the main reason why this disease continues to be a global public health threat. It is therefore imperative to find a novel antitubercular drug target that is unique to the structural machinery or is essential to the growth and survival of the bacterium. One such target is the enzyme l,d-transpeptidase 2, also known as Ldt_Mt2, a protein primarily responsible for the catalysis of 3→3 cross-linkages that make up the mycolyl–arabinogalactan–peptidoglycan complex of Mtb. In this study, structure-based pharmacophore screening, molecular docking, and in silico toxicity evaluations were employed in screening compounds from a database of synthetic compounds. Out of the 4.5 million database compounds, 18 structures were identified as high-scoring, high-binding hits with very satisfactory absorption, distribution, metabolism, excretion, and toxicity properties. Two out of the 18 compounds were further subjected to in vitro bioactivity assays, with one exhibiting a good inhibitory activity against the Mtb H37Ra strain.

Novel nicotine analogues with potential anti-mycobacterial activity

Tuberculosis (TB) is the second leading lethal infectious disease in the world after acquired immuno deficiency (AIDs). We have developed a series of twenty-five novel nicotine analogues with de-addiction property and tested them for their activity against Mycobacterium tuberculosis (MTB). In an effort to increase the specificity of action and directing nicotine analogues to target MTB, four promising compounds were further optimized via molecular docking studies against the Dihydrofolate reductase of MTB. After lead optimization, one nicotine analogue [3-(5-(3fluorophenyl)nicotinoyl)-1-methylpyrrolidin-2-one] exhibited minimum inhibitory concentration of 1 μg/mL (2.86 nM) against M. tuberculosis (H37Rv strain), a human pathogenic strain of clinically significant importance. Pharmacokinetic analysis of [3-(5-(3fluorophenyl)nicotinoyl)-1methylpyrrolidin-2-one] with lowest MIC value via oral route in Wistar rats revealed that at a dosage of 5 mg/kg body weight gave a maximum serum drug concentration (Cmax) of 2.86 μg/mL, Tmax of one hour and a half-life (T1/2) of more than 24 h and Volume of distribution (Vd) of 27.36 L. Whereas the parenteral (intra venous) route showed a Cmax of 3.37 μg/mL, Tmax of 0.05 h, T1/2 of 24 h and Vd equivalent to 23.18 L. The acute oral toxicity and repeated oral toxicity studies in female Wistar rats had an LD50>2000 mg/kg body weight. Our data suggests that nicotine derivatives developed in the present study has good metabolic stability with tunable pharmacokinetics (PK) with therapeutic potential to combat MTB. However, further in vivo studies for anti-tuberculosis activity and elucidation of mode of action could result in more promising novel drug for treating MTB. To the best of our knowledge this is the first report revealing the anti-mycobacterial potential of nicotine analogue at potential therapeutic concentrations.

Sulfonamides incorporating fluorine and 1,3,5-triazine moieties are effective inhibitors of three β-class carbonic anhydrases from Mycobacterium tuberculosis

A new series of fluorine containing 1,3,5-triazinyl sulfonamide derivatives obtained from cyanuric fluoride, sulfanilamide/4-aminoethylbenzenesulfonamide followed and incorporating also amin0, amino alcohol and amino acid moieties have been investigated as inhibitors of three β-carbonic anhydrases (CAs, EC 4.2.1.1) from the bacterial pathogen Mycobacterium tuberculosis, mtCA1 (Rv1284), mtCA 2 (Rv3588c) and mtCA 3 (Rv3273). All three enzymes were efficiently inhibited by these sulfonamides with KI values in the nanomolar or submicromolar range, depending on the substitution of one or both fluorine atoms at the 1,3,5-triazine ring. As some of these enzymes are crucial for the life cycle of this bacterium, the class of β-CA inhibitors reported in this study may lead to antimycobacterial agents with a different mechanism of action compared to the clinically used such drugs for which the pathogen developed extensive drug resistance.

Design and synthesis of novel antimicrobials with activity against Gram-positive bacteria and mycobacterial species, including M. tuberculosis

The alarming increase in bacterial resistance over the last decade along with a dramatic decrease in new treatments for infections has led to problems in the healthcare industry. Tuberculosis (TB) is caused mainly by Mycobacterium tuberculosis which is responsible for 1.4 million deaths per year. A world-wide threat with HIV co-infected with multi and extensively drug-resistant strains of TB has emerged. In this regard, herein, novel acrylic acid ethyl ester derivatives were synthesized in simple, efficient routes and evaluated as potential agents against several Mycobacterium species. These were synthesized via a stereospecific process for structure activity relationship (SAR) studies. Minimum inhibitory concentration (MIC) assays indicated that esters 12, 13, and 20 exhibited greater in vitro activity against Mycobacterium smegmatis than rifampin, one of the current, first-line anti-mycobacterial chemotherapeutic agents. Based on these studies the acrylic ester 20 has been developed as a potential lead compound which was found to have an MIC value of 0.4 μg/mL against Mycobacterium tuberculosis. The SAR and biological activity of this series is presented; a Michael-acceptor mechanism appears to be important for potent activity of this series of analogs.

Safety and Efficacy of Delamanid in the Treatment of Multidrug-Resistant Tuberculosis (MDR-TB)

Globally, the incidence of tuberculosis (TB) is declining but the proportion of drug-resistant cases has increased. Strains resistant to both isoniazid and rifampin, and possibly other antibiotics, called multidrug-resistant (MDR), are particularly difficult to treat. Poorer outcomes, including increased mortality, occur in patients infected with MDR strains and the costs associated with treatment of MDR-TB are substantially greater. The recent recognition of MDR-TB and strains with more complex resistance patterns has stimulated the development of new TB medications including fluoroquinolones, oxazolidinones, diarylquinolines, nitroimidazopyrans, ethylenediamines, and benzothiazinones. Bedaquiline, a diarylquinoline, was approved for the treatment of MDR-TB in 2012. Addition of delamanid to WHO-approved treatment improved outcomes for MDR-TB and for extensively drug-resistant TB in a large randomized, controlled phase II clinical trial and is undergoing evaluation in a large international phase III study. This review will focus on MDR-TB and the role of delamanid in its treatment.

Synthesis of Substituted Thioureas and Their Sulfur Heterocyclic Systems ofp-Amino Salicylic Acid as Antimycobacterial Agents

A series of new N,N′-substituted thioureas (2,6, and8) and their sulfur heterocycles as thiobarbituric acids (3,4, and7), 2-thioxothiazoliodin-4-one (10), thiazolidin-4-one (11), 1,2,4-triazol-5-thione (14), and 1,3,4-thiadiazole (15) ofp-Amino salicylic acid (PAS) have been synthesized from treatment with dithiocarbazinate (1,5and12) followed by heterocyclization with dimethyl malonate, chloroacetic acid, and/or trifluoroacetic anhydride. The structures of the newly synthesized compounds were substantiated with IR,H1, andC13NMR spectral data and elementary microanalyses. Thein vitroantitubercular activity of synthesized compounds againstM. tuberculosisstrain H37Rv showed moderate-to-good activity.

Synthesis of New Fluorine Substituted Heterocyclic Nitrogen Systems Derived fromp-Aminosalicylic Acid as Antimycobacterial Agents

Some new fluorine substituted heterocyclic nitrogen systems2–17have been synthesized from ring closure reactions of substitutedp-amino salicylic acids (PAS). The Schiffs base of PAS was cyclized with chloroacetyl chloride and mercaptoacetic acid to give azetidinone2, thiazolidinone3, and spiro-fluoroindolothiazoline-dione10. However, PAS when reacted directly with 4-fluorobenzoyl chloride and 5-oxazolinone yielded derivatives4,5, and7. Aminomethylation of PAS using formaldehyde and piperidine or piperazine formed N-alkyl and N,N′-dialkyl derivatives (11and12respectively) upon fluorinated benzoylation gave compounds13and14. Similarly, treatment of PAS with thiosemicarbazide15and subsequent cyclization with diethyl oxalate yielded the fluorinated heterocycle17. The structures of the fluorinated heterocyclic systems have been established on the basis of elemental analysis,1H NMR,13C NMR, and MS spectral data. Some of the targets exhibited a high inhibition towardsMycobacteriumstrain with favorable logPvalues.

Molecular hybridization of bioactives: synthesis and antitubercular evaluation of novel dibenzofuran embodied homoisoflavonoids via Baylis-Hillman reaction

A novel series of natural product like dibenzofuran embodied homoisoflavonoids [(E)-3-(dibenzo[b,d]furan-2-ylmethylene)chroman-4-ones] designed by molecular hybridization were synthesized in very good yields via a sequence of reactions involving base catalyzed Baylis-Hillmann (BH) reaction of 2-dibenzofuran carboxaldehyde and methyl acrylate; bromination of BH adduct; condensation of resulted allylic bromide with substituted phenols or 2-dibenzofuranol followed by cyclization. Among the all 11 new compounds screened for in vitro antimycobacterial activity against Mycobacterium tuberculosis H37Rv (MTB), (E)-3-(dibenzo[b,d]furan-2-ylmethylene)-6-fluorochroman-4-one (7f) and (E)-3-(dibenzo[b,d] furan-2-ylmethylene)-6-fluorochroman-4-one (7 g) were found to be active with MIC 12.5 μg/mL.

Evaluating our ability to predict the structural disruption of RNA by SNPs

The structure of RiboNucleic Acid (RNA) has the potential to be altered by a Single Nucleotide Polymorphism (SNP). Disease-associated SNPs mapping to non-coding regions of the genome that are transcribed into RiboNucleic Acid (RNA) can potentially affect cellular regulation (and cause disease) by altering the structure of the transcript. We performed a large-scale meta-analysis of Selective 2'-Hydroxyl Acylation analyzed by Primer Extension (SHAPE) data, which probes the structure of RNA. We found that several single point mutations exist that significantly disrupt RNA secondary structure in the five transcripts we analyzed. Thus, every RNA that is transcribed has the potential to be a “RiboSNitch;” where a SNP causes a large conformational change that alters regulatory function. Predicting the SNPs that will have the largest effect on RNA structure remains a contemporary computational challenge. We therefore benchmarked the most popular RNA structure prediction algorithms for their ability to identify mutations that maximally affect structure. We also evaluated metrics for rank ordering the extent of the structural change. Although no single algorithm/metric combination dramatically outperformed the others, small differences in AUC (Area Under the Curve) values reveal that certain approaches do provide better agreement with experiment. The experimental data we analyzed nonetheless show that multiple single point mutations exist in all RNA transcripts that significantly disrupt structure in agreement with the predictions.

Design, synthesis, and structure-activity correlations of novel dibenzo[b,d]furan, dibenzo[b,d]thiophene, and N-methylcarbazole clubbed 1,2,3-triazoles as potent inhibitors of Mycobacterium tuberculosis

A molecular hybridization approach is an emerging structural modification tool to design new molecules with improved pharmacophoric properties. In this study, 1,2,3-triazole-based Mycobacterium tuberculosis inhibitors and synthetic and natural product-based tricyclic (carbazole, dibenzo[b,d]furan, and dibenzo[b,d]thiophene) antimycobacterial agents were integrated in one molecular platform to prepare various novel clubbed 1,2,3-triazole hybrids using click chemistry. Structure-activity correlations and in vitro activity against M. tuberculosis strain H37Rv of new analogues revealed the order: dibenzo[b,d]thiophene > dibenzo[b,d]furan > 9-methyl-9H-carbazole series. Two of the most potent M. tuberculosis inhibitors 13h and 13q with MIC = 0.78 μg/mL (∼1.9 μM) displayed a low cytotoxicity and high selectivity index (50-255) against four different human cancer cell lines. These results together provided the potential importance of molecular hybridization and the development of triazole clubbed dibenzo[b,d]thiophene-based lead candidates to treat mycobacterial infections.

Strategies and challenges involved in the discovery of new chemical entities during early-stage tuberculosis drug discovery

There is an increasing flow of new antituberculosis chemical entities entering the tuberculosis drug development pipeline. Although this is encouraging, the current number of compounds is too low to meet the demanding criteria required for registration, shorten treatment duration, treat drug-resistant infection, and address pediatric tuberculosis cases. More new chemical entities are needed urgently to supplement the pipeline and ensure that more drugs and regimens enter clinical practice. Most drug discovery projects under way exploit enzyme systems deemed essential in a specific Mycobacterium tuberculosis biosynthetic pathway or develop chemical scaffolds identified by phenotypic screening of compound libraries, specific pharmacophores or chemical clusters, and natural products. Because the development of a compound for treating tuberculosis is even longer than for treating other infection indications, the identification of selective, potent, and safe chemical entities early in the drug development process is essential to ensure that the pipeline is filled with new candidates that have the best chance to reach the clinic.

In vitro evaluation of tetrazoles as a novel class of Antimycobacterium tuberculosis agents

PURPOSE

We report here the antimycobacterial activity of some already synthesized tetrazole derivatives containing tetrazole against Mycobacterium tuberculosis strain H37Rv.

METHODS

In vitro evaluation of the antitubercular activity was carried out within the Tuberculosis Antimicrobial Acquisition & Coordinating Facility (TAACF) screening program for the discovery of novel drugs for the treatment of tuberculosis. Under the direction of the US National Institute of Allergy and Infectious Diseases (NIAID), Southern Research Institute that coordinates the overall program. The method of TAACF was followed for evaluation of activity.

RESULTS

This new structural class of compounds showed high activity against the bacilli. The activity depends on the substituent's present in azatidinone core. Compounds having a 4-MeOC6H4 4-N(CH3)2C6H4 group as the substituent on β-lactam ring were active. The highest activity was registered for compounds having 4-MeOC6H4 as substituent.

CONCLUSION

The new compounds showed high potency and promising antitubercular activity and should be regarded as new hits for further development as a novel class of Antimycobacterium tuberculosis agents.

Inhibition of the β-class carbonic anhydrases from Mycobacterium tuberculosis with carboxylic acids

The growth of Mycobacterium tuberculosis is strongly inhibited by weak acids although the mechanism by which these compounds act is not completely understood. A series of substituted benzoic acids, nipecotic acid, ortho- and para-coumaric acid, caffeic acid and ferulic acid were investigated as inhibitors of three β-class carbonic anhydrases (CAs, EC 4.2.1.1) from this pathogen, mtCA 1 (Rv1284), mtCA 2 (Rv3588c) and mtCA 3 (Rv3273). All three enzymes were inhibited with efficacies between the submicromolar to the micromolar one, depending on the scaffold present in the carboxylic acid. mtCA 3 was the isoform mostly inhibited by these compounds (K(I)s in the range of 0.11-0.97 µM); followed by mtCA 2 (K(I)s in the range of 0.59-8.10 µM), whereas against mtCA 1, these carboxylic acids showed inhibition constants in the range of 2.25-7.13 µM. This class of relatively underexplored β-CA inhibitors warrant further in vivo studies, as they may have the potential for developing antimycobacterial agents with a diverse mechanism of action compared to the clinically used drugs for which many strains exhibit multi-drug or extensive multi-drug resistance.

Advances in the Diagnosis, Treatment and Control of HIV Associated Tuberculosis

There has been an increase in the number of published tuberculosis/HIV (TB/HIV) research findings in recent times. The potential impact of these findings on routine care has informed this review which aims at discussing current concepts and practices underpinning TB/HIV care and control. Any HIV infected person with a cough of any duration is currently considered a TB suspect. Preliminary results also show that the diagnostic yield of same day sputum samples (front loading) is comparable to two-day samples. Laboratory diagnosis is shifting from Ziehl-Neelsen (ZN) smear microscopy and solid culture to fluorescent microscopy, molecular tests and liquid culture. Concomitant TB/HIV therapy improves survival and WHO has recommended ART for all TB/HIV patients. Unless CD4 cell counts are less than 50 cells/µl, ART can be deferred until end of intensive phase. Evidence of survival benefit at high CD4 cell counts is still lacking. New TB drugs and treatment shortening studies are underway but so far no new TB drugs has been added to the current arsenal and treatment duration still remains six months or more. WHO has recommended the 31s (intensified TB case finding, isoniazid prophylaxis and infection control) for TB/HIV control in addition to effective therapy, Antiretroviral therapy and TB vaccines. There has been immense progress in TB/HIV research, however optimal management of HIV-Infected TB patients, will require further research and appropriate translation of emerging evidence to policy and practice.

Novel technologies: A weapon against tuberculosis

Tuberculosis (TB) is a leading chronic bacterial infection. Despite potentially curative pharmacotherapies being available for over 50 years, the length of the treatment and the pill burden can hamper patient lifestyle. Low compliance and adherence to administration schedules remain the main reasons for therapeutic failure and contribute to the development of multidrug-resistant strains. The design of novel antibiotics attempts to overcome drug resistance, to shorten the treatment course, and to reduce drug interactions. In this framework, nanotechnology appears as one of the promising approaches for the development of more effective medicines. The present review thoroughly overviews the development of novel microparticulate, encapsulation, and various other carrier-based drug delivery systems for incorporating the principal anti-TB agents. Drug delivery systems have been designed that either target the site of TB or reduce the dosing frequency with the aim of improving patient healthcare.

Bacterial carbonic anhydrases as drug targets: toward novel antibiotics?

Carbonic anhydrases (CAs, EC 4.2.1.1) are metalloenzymes which catalyze the hydration of carbon dioxide to bicarbonate and protons. Many pathogenic bacteria encode such enzymes belonging to the α-, β-, and/or γ-CA families. In the last decade, the α-CAs from Neisseria spp. and Helicobacter pylori as well as the β-class enzymes from Escherichia coli, H. pylori,Mycobacterium tuberculosis, Brucella spp., Streptococcus pneumoniae, Salmonella enterica, and Haemophilus influenzae have been cloned and characterized in detail. For some of these enzymes the X-ray crystal structures were determined, and in vitro and in vivo inhibition studies with various classes of inhibitors, such as anions, sulfonamides and sulfamates reported. Although efficient inhibitors have been reported for many such enzymes, only for Neisseria spp., H. pylori, B. suis, and S. pneumoniae enzymes it has been possible to evidence inhibition of bacterial growth in vivo. Thus, bacterial CAs represent promising targets for obtaining antibacterials devoid of the resistance problems of the clinically used such agents but further studies are needed to validate these and other less investigated enzymes as novel drug targets.

Extensively Drug-Resistant Tuberculosis: A Sign of the Times and an Impetus for Antimicrobial Discovery

Mycobacterium tuberculosis is an extraordinarily successful human pathogen, infecting one-third of the world's population and causing nearly two million deaths each year. In this article, current trends in worldwide tuberculosis (TB) incidence, prevalence, and mortality are discussed along with standard TB treatment regimens, characteristics of first-line and second-line anti-tuberculosis drugs, and mechanisms of antibiotic resistance. The global TB emergency has been further exacerbated by extensively drug-resistant (XDR) TB strains that are resistant to our best antibiotics and very difficult to treat. This review also focuses on the emergence of XDR-TB strains, the global health impact, and existing treatment options and outcomes for XDR-TB disease. Finally, this review briefly describes new anti-tuberculosis drugs currently in Phase II clinical evaluations and the impetus for discovering new antibacterial compounds to target drug-resistant M. tuberculosis and improve tuberculosis therapy.

Tuberculosis research: going forward with a powerful "translational systems biology" approach

Due to the complexity of the immune response to a Mycobacterium tuberculosis infection, identifying new, effective therapies and vaccines to combat it has been a problematic issue. Although many advances have been made in understanding particular mechanisms involved, they have, to date, proved insufficient to provide real breakthroughs in this area of tuberculosis research. The term "Translational Systems Biology" has been formally proposed to describe the use of experimental findings combined with mathematical modeling and/or engineering principles to understand complex biological processes in an integrative fashion for the purpose of enhancing clinical practice. This opinion piece discusses the importance of using a Translational Systems Biology approach for tuberculosis research as a means by which to go forward with the potential for significant breakthroughs to occur.

Carbonic anhydrase inhibitors. Characterization and inhibition studies of the most active beta-carbonic anhydrase from Mycobacterium tuberculosis, Rv3588c

The Rv3588c gene product of Mycobacterium tuberculosis, a beta-carbonic anhydrase (CA, EC 4.2.1.1) denominated here mtCA 2, shows the highest catalytic activity for CO(2) hydration (k(cat) of 9.8 x 10(5)s(-1), and k(cat)/K(m) of 9.3 x 10(7)M(-1)s(-1)) among the three beta-CAs encoded in the genome of this pathogen. A series of sulfonamides/sulfamates was assayed for their interaction with mtCA 2, and some diazenylbenzenesulfonamides were synthesized from sulfanilamide/metanilamide by diazotization followed by coupling with amines or phenols. Several low nanomolar mtCA 2 inhibitors have been detected among which acetazolamide, ethoxzolamide and some 4-diazenylbenzenesulfonamides (K(I)s of 9-59 nM). As the Rv3588c gene was shown to be essential to the growth of M. tuberculosis, inhibition of this enzyme may be relevant for the design of antituberculosis drugs possessing a novel mechanism of action.

Carbonic anhydrase inhibitors. Inhibition of the Rv1284 and Rv3273 beta-carbonic anhydrases from Mycobacterium tuberculosis with diazenylbenzenesulfonamides

A series of diazenylbenzenesulfonamides obtained from sulfanilamide or metanilamide by diazotization followed by coupling with phenols or amines, was tested for the inhibition of the beta-carbonic anhydrases (CAs, EC 4.2.1.1) encoded by the genes Rv1284 and Rv3273 of Mycobacterium tuberculosis. Several low micromolar inhibitors of the two enzymes were detected, with prontosil being the best inhibitor (K(I)s of 126-148nM). Inhibition of pathogenic beta-CAs may lead to the development of antiinfectives with a new mechanism of action, devoid of resistance problems encountered with classical antibiotics.

Mycobacterium tuberculosis: drug resistance and future perspectives

TB is still a global health problem. The selection and spread of multidrug-resistant and extensively drug-resistant Mycobacterium tuberculosis strains represents a threat for global TB control. The reappearance of TB has driven an increased interest in understanding the mechanisms of drug action and drug resistance, which could provide a significant contribution in the development of new antimicrobials. In this article, the authors describe the mode of action and the resistance mechanisms of the principal first- and second-line antitubercular agents, namely isoniazid, ethionamide, ethambutol, D-cycloserine, rifamycins, fluoroquinolones, streptomycin, linezolid and pyrazinamide. A brief outline of the seven drugs in clinical development is reported, showing how the development of new TB drugs is still required.