TMC207: the first compound of a new class of potent anti-tuberculosis drugs

Novel drug combination for Mycobacterium abscessus disease therapy identified in a Drosophila infection model

OBJECTIVES

Mycobacterium abscessus is known to be the most drug-resistant Mycobacterium and accounts for ∼80% of pulmonary infections caused by rapidly growing mycobacteria. This study reports a new Drosophila melanogaster-M. abscessus infection model that can be used as an in vivo efficacy model for anti-M. abscessus drug potency assessment.

METHODS

D. melanogaster were challenged with M. abscessus, and infected flies were fed with a fly medium containing tigecycline, clarithromycin, linezolid, clofazimine, moxifloxacin, amikacin, cefoxitin, dinitrobenzamide or metronidazole at different concentrations (0, 100 and 500 mg/L). The survival rates of infected flies were plotted and bacterial colonization/dissemination in fly bodies was monitored by cfu determination and green fluorescent protein epifluorescence.

RESULTS

The D. melanogaster-M. abscessus model enabled an assessment of the effectiveness of antibiotic treatment. Tigecycline was the best drug for extending the lifespan of M. abscessus-infected Drosophila, followed by clarithromycin and linezolid. Several different combinations of tigecycline, linezolid and clarithromycin were tested to determine the best combination. Tigecycline (25 mg/L) plus linezolid (500 mg/L) was the best drug combination and its efficacy was superior to conventional regimens, not only in prolonging infected fly survival but also against M. abscessus colonization and dissemination.

CONCLUSIONS

This D. melanogaster-M. abscessus infection/curing methodology may be useful for the rapid evaluation of potential drug candidates. In addition, new combinations using tigecycline and linezolid should be considered as possible next-generation combination therapies to be assessed in higher organisms.

Bedaquiline: a novel diarylquinoline for multidrug-resistant tuberculosis

OBJECTIVE

To review the chemistry, pharmacology, microbiology, pharmacokinetics, pharmacodynamics, clinical efficacy, safety, dosage, and administration of bedaquiline, a novel oral diarylquinoline antimycobacterial agent approved by the Food and Drug Administration for the treatment of adults with pulmonary multidrug-resistant tuberculosis (MDR-TB).

DATA SOURCES

A search of PubMed (January 2004-May 2013) and International Pharmaceutical Abstracts (January 2004-May 2013) using the search terms bedaquiline, diarylquinoline, R207910, and TMC207 was performed. Supplementary sources included proceedings of the Union World Conference on Lung Health.

STUDY SELECTION AND DATA EXTRACTION

Preclinical data as well as Phase 1 and 2 studies published in English were evaluated.

DATA SYNTHESIS

Bedaquiline possesses a unique mechanism of action that disrupts the activity of the mycobacterial adenosine triphosphate synthase. Clinical trials have been conducted evaluating the use of bedaquiline in combination with a background regimen for the treatment of adults with pulmonary MDR-TB. Bedaquiline has an excellent in vitro activity against Mycobacterium tuberculosis, including multidrug resistant M tuberculosis; however, its side effect profile limits its use against MDR-TB when no other effective regimen can be provided. Bedaquiline carries Black Box warnings for increased risk of unexplained mortality and QT prolongation. Bedaquiline is metabolized via the CYP3A4 isoenzyme and thus interacts with rifamycins and several antiretrovirals.

CONCLUSIONS

In an era of emerging resistance and given the suboptimal efficacy and toxicity of currently available regimens for MDR-TB, bedaquiline represents a great addition to the existing armamentarium of anti-TB agents particularly in areas of the world where the disease is endemic.

Identification of 1-[4-Benzyloxyphenyl)-but-3-enyl]-1H-azoles as New Class of Antitubercular and Antimicrobial Agents

A series of 1-[(4-benzyloxyphenyl)-but-3-enyl]-1H-azoles has been identified as potent antitubercular agents against Mycobacterium tuberculosis. Synthesis of compounds involved acid catalyzed ring-opening of cyclopropyl ring of phenyl cyclopropyl methanols followed by nucleophilic attack of the azoles on the carbocation intermediates. Several of the compounds 26, 34, and 36 exhibited significant antitubercular activities with MIC value as low as 1.56, 1.56, and 0.61 μg/mL, respectively, comparable to many standard drugs. These compounds were also screened against other strains of bacteria and fungi, and few of them showed good antifungal activity against A. fumigatus, responsible for lung infection.

[New tuberculosis drugs in resistant and multiresistant tuberculosis]

Drug-resistant tuberculosis is a globally emerging problem with a rising incidence. According to the WHO in 2008, 17% of strains of Mycobacterium tuberculosis, in untreated cases were resistant to at least one drug and 3.6% were resistant to rifampicin and isoniazid, which is called multidrug-resistant tuberculosis. The problem is greater in patients previously treated and in some countries, where rates of multidrug resistance reach 60%. Approximately 5% of multidrug-resistant tuberculosis patients are also resistant to any fluoroquinolone and at least one injectable drug, being called extensively drug-resistant tuberculosis. The treatment of these forms of tuberculosis requires the use of second-line drugs, which causes higher cost, higher toxicity and a longer duration of treatment. There is a need for new compounds with efficacy and safety profiles better than those currently used to treat these forms of tuberculosis. In the last decade different drugs have being reassessed and appeared, which are at different stages of development.

Improved synthesis of capuramycin and its analogues

Capuramycin and its congeners are considered to be important lead molecules for the development of a new drug for multidrug-resistant (MDR) Mycobacterium tuberculosis infections. Extensive structure-activity relationship studies of capuramycin to improve the efficacy have been limited because of difficulties in selectively chemically modifying the desired position(s) of the natural product with biologically interesting functional groups. We have developed efficient syntheses of capuramycin and its analogues by using new protecting groups, derived from the chiral (chloro-4-methoxyphenyl)(chlorophenyl)methanols, for the uridine ureido nitrogen and primary alcohol. The chiral nonracemic (2,6-dichloro-4-methoxyphenyl)(2,4-dichlorophenyl)methanol derivative is a useful reagent to resolve rac-3-amino-1,3-dihydro-5-phenyl-2H-1,4-benzodiazepin-2-one, the (S)-configuration isomer of which plays a significant role in improving the mycobactericidal activity of capuramycin.

Anti-mycobacterial activity of marine fungus-derived 4-deoxybostrycin and nigrosporin

4-Deoxybostrycin is a natural anthraquinone compound isolated from the Mangrove endophytic fungus Nigrospora sp. collected from the South China Sea. Nigrosporin is the deoxy-derivative of 4-deoxybostrycin. They were tested against mycobacteria, especially Mycobacterium tuberculosis. In the Kirby-Bauer disk diffusion susceptibility test, they both had inhibition zone sizes of over 25 mm. The results of the absolute concentration susceptibility test suggested that they had inhibitory effects against mycobacteria. Moreover, 4-deoxybostrycin exhibited good inhibition which was even better than that of first line anti-tuberculosis (TB) drugs against some clinical multidrug-resistant (MDR) M. tuberculosis strains. The gene expression profile of M. tuberculosis H37Rv after treatment with 4-deoxybostrycin was compared with untreated bacteria. One hundred and nineteen out of 3,875 genes were significantly different in M. tuberculosis exposed to 4-deoxybostrycin from control. There were 46 functionally known genes which are involved in metabolism, information storage and processing and cellular processes. The differential expressions of six genes were further confirmed by quantitative real-time polymerase chain reaction (qRT-PCR). The present study provides a useful experiment basis for exploitation of correlative new drugs against TB and for finding out new targets of anti-mycobacterial therapy.

Identification of novel imidazo[1,2-a]pyridine inhibitors targeting M. tuberculosis QcrB

Mycobacterium tuberculosis is a major human pathogen and the causative agent for the pulmonary disease, tuberculosis (TB). Current treatment programs to combat TB are under threat due to the emergence of multi-drug and extensively-drug resistant TB. Through the use of high throughput whole cell screening of an extensive compound library a number of imidazo[1,2-a]pyridine (IP) compounds were obtained as potent lead molecules active against M. tuberculosis and Mycobacterium bovis BCG. The IP inhibitors (1-4) demonstrated minimum inhibitory concentrations (MICs) in the range of 0.03 to 5 µM against a panel of M. tuberculosis strains. M. bovis BCG spontaneous resistant mutants were generated against IP 1, 3, and 4 at 5× MIC and subsequent whole genome sequencing identified a single nucleotide polymorphism (937)ACC>(937)GCC (T313A) in qcrB, which encodes the b subunit of the electron transport ubiquinol cytochrome C reductase. This mutation also conferred cross-resistance against IP 1, 3 and 4 demonstrating a common target. Gene dosage experiments confirmed M. bovis BCG QcrB as the target where over-expression in M. bovis BCG led to an increase in MIC from 0.5 to >8 µM for IP 3. An acute murine model of TB infection established bacteriostatic activity of the IP series, which await further detailed characterization.

Safety, tolerability, and pharmacokinetic interactions of the antituberculous agent TMC207 (bedaquiline) with efavirenz in healthy volunteers: AIDS Clinical Trials Group Study A5267

BACKGROUND

Drug-drug interactions complicate management of coinfection with HIV-1 and Mycobacterium tuberculosis. Bedaquiline (formerly TMC207), an investigational agent for the treatment of tuberculosis, is metabolized by cytochrome P450 (CYP) 3A which may be induced by the antiretroviral drug efavirenz.

METHODS

This was a phase 1 pharmacokinetic drug interaction trial. Each healthy volunteer received two 400 mg doses of bedaquiline, the first alone and the second with concomitant steady-state efavirenz. Plasma pharmacokinetic sampling for bedaquiline and its N-monodesmethyl metabolite was performed over 14 days after each bedaquiline dose. Steady-state efavirenz pharmacokinetics were also determined. Efavirenz metabolizer status was based on CYP2B6 composite 516/983 genotype.

RESULTS

Thirty-three of 37 enrolled subjects completed the study. Geometric mean of ratios for bedaquiline with efavirenz versus bedaquiline alone were 0.82 [90% confidence interval (CI): 0.75 to 0.89] for the 14-day area under the concentration-time curve (AUC0-336 h) and 1.00 (90% CI: 0.88 to 1.13) for the maximum concentration (Cmax). For N-monodesmethyl metabolite, the geometric mean of ratios was 1.07 (90% CI: 0.97 to 1.19) for AUC0-336 h and 1.89 (90% CI: 1.66 to 2.15) for C(max). There were no grade 3 or 4 clinical adverse events. One subject developed asymptomatic grade 3 serum transaminase elevation, prompting study drug discontinuation. Efavirenz concentrations stratified by CYP2B6 genotype were similar to historical data.

CONCLUSIONS

Single-dose bedaquiline was well tolerated alone and with steady-state efavirenz. The effect of efavirenz on bedaquiline concentrations is unlikely to be clinically significant.

Antimycobacterial Activities of Novel 5-(1H-1,2,3-Triazolyl)Methyl Oxazolidinones

The antibacterial activities of a series of triazolyl oxazolidinones against Mycobacterium tuberculosis strain in vitro and in vivo in a mice model are presented. Most active compounds were noncytotoxic against VERO cells with acceptable selectivity indexes (SI) as measures of compound tolerability. Structure activity relationships (SARs) revealed that analogs with alkylcarbonyl (IC₉₀: < 0.2 to 0.422 μg/mL) and arylcarbonyl (IC₉₀: < 0.2 to 2.103 μg/mL) groups at the piperazine 4N-position-displayed potent antimycobacterium activities, comparable to the methanesulfonyl (IC₉₀: < 0.2 μg/mL) analog, linezolid (IC₉₀: < 0.2 μg/mL), and isoniazid (IC₉₀: < 0.034 μg/mL). The furanylcarbonyl derivative also displayed potent activity, while the arylsulfonyl analogs were inactive. Of the triazolyl oxazolidinones, the morpholino (PH-27) derivative with medium bioavailability in plasma was most active in vivo, but relatively less efficacious than isoniazid.

Analysis of intracellular expressed proteins of Mycobacterium tuberculosis clinical isolates

Background

Tuberculosis (TB) is the most threatening infectious disease globally. Although progress has been made to reduce global incidence of TB, emergence of multidrug resistant (MDR) TB threatens to undermine these advances. To combat the disease, novel intervention strategies effective against drug resistant and sensitive subpopulations of M. tuberculosis are urgently required as adducts in the present treatment regimen. Using THP-1 cells we have analyzed and compared the global protein expression profile of broth-cultured and intraphagosomally grown drug resistant and sensitive M.tuberculosis clinical isolates.

Results

On comparing the two dimensional (2-DE) gels, many proteins were found to be upregulated/expressed during intracellular state which were identified by matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS). Four proteins (adenosylhomocysteinase, aspartate carbomyltransferase, putatitive thiosulfate sulfurtransferase and universal stress protein) were present in both intracellular MDR and sensitive isolates and three of these belonged to intermediary metabolism and respiration category. Two proteins (alanine dehydrogenase and adenosine kinase) of intracellular MDR isolate and two (glucose-6-phosphate isomerase and ATP synthase epsilon chain) of intracellular sensitive isolate belonged to intermediary metabolism and respiration category. One protein (Peroxidase/Catalase) of intracellular MDR and three (HSPX, 14 kDa antigen and 10 kDa chaperonin) of sensitive isolate belonged to virulence, detoxification and adaptation category. ESAT-6 of intracellular MDR belonged to cell wall and cell processes category. Two proteins (Antigen 85-C and Antigen 85-A) of intracellular sensitive isolate were involved in lipid metabolism while probable peptidyl-prolyl cis-trans isomerase A was involved in information pathways. Four (Rv0635, Rv1827, Rv0036c and Rv2032) of intracellular MDR and two proteins (Rv2896c and Rv2558c) of sensitive isolate were hypothetical proteins which were functionally characterized using bioinformatic tools. Bioinformatic findings revealed that the proteins encoded by Rv0036, Rv2032c, Rv0635, Rv1827 and Rv2896c genes are involved in cellular metabolism and help in intracellular survival.

Conclusions

Mass spectrometry and bioinformatic analysis of both MDR and sensitive isolates of M. tuberculosis during intraphagosomal growth showed that majority of commonly upregulated/expressed proteins belonged to the cellular metabolism and respiration category. Inhibitors of the metabolic enzymes/intermediate can therefore serve as suitable drug targets against drug-resistant and sensitive subpopulations of M. tuberculosis.

Synthesis, characterization, anti-inflammatory and in vitro antimicrobial activity of some novel alkyl/aryl substituted tertiary alcohols

The synthesis of some novel alkyl/aryl substituted tertiary alcohols was accomplished in two steps. The synthetic route involves preparation of Grignard reagents by treating alkyl/aryl bromides with magnesium turnings in dry ether. Then substituted chalcones were reacted with the Grignard reagents to afford alkyl/aryl substituted tertiary alcohols 1-10. The structures of the synthesized compounds were assigned on the basis of FT-IR, 1H-NMR, 13C-NMR and mass spectroscopic data. The in vivo anti-inflammatory activity of the synthesized compounds was evaluated using the carrageenan-induced hind paw edema method and was compared with that of ibuprofen. Some of the newly synthesized compounds showed promising anti-inflammatory activity. The tertiary alcohols 1-10 were also screened for antibacterial activity against ten bacterial strains using seven Gram-positive and three Gram-negative bacteria and for antifungal activity against Aspergillus Flavus, Aspergillus Niger and Aspergillus pterus. Tertiary alcohols 1-10 were found to exhibit good to excellent antimicrobial activities compared to levofloxacin and fluconazole used as standard drugs.

New tuberculosis drugs on the horizon

Tuberculosis (TB) remains a major global health concern whose control has been exacerbated by HIV and the emergence of multidrug-resistant (MDR-TB) and extensively drug-resistant (XDR-TB) strains of Mycobacterium tuberculosis. The demand for new and faster acting TB drugs is thus greater than ever. In the past decade intensive efforts have been made to discover new leads for TB drug development using both target-based and cell-based approaches. Here, we describe the most promising anti-tubercular drug candidates that are in clinical development and introduce some nitro-aromatic compounds that inhibit a new target, DprE1, an essential enzyme involved in a crucial step in mycobacterial cell wall biosynthesis.

Synthesis and antitubercular evaluation of novel dibenzo[b,d]furan and 9-methyl-9H-carbazole derived hexahydro-2H-pyrano[3,2-c]quinolines via Povarov reaction

A series of novel hexahydro-2H-pyrano[3,2-c]quinoline analogues derived from dibenzo[b,d]furan and 9-methyl-9H-carbazole has been synthesized in very good yields through SnCl(2)·2H(2)O catalyzed one-pot Povarov reaction (imino-Diels-Alder reaction). The imines generated in situ from dibenzo[b,d]furan-2-carbaldehyde or 9-methyl-9H-carbazole-3-carbaldehyde and aromatic amines, were reacted with 3,4-dihydro-2H-pyran in a diasteroselective manner in acetonitrile at RT. These synthesized isomeric pyranoquinoline analogues have been evaluated for their in vitro antimycobacterial activity against Mycobacterium tuberculosis H37Rv (MTB) by agar dilution method. Among the 23 compounds screened, 5-(dibenzo[b,d]furan-2-yl)-9-fluoro-3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinoline 4f, 5-(dibenzo[b,d]furan-2-yl)-9-fluoro-3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinoline 5f and 9-fluoro-5-(9-methyl-9H-carbazol-3-yl)-3,4,4a,5,6,10b-hexa hydro-2H-pyrano[3,2-c]quinoline 7f (MIC 3.13 μg/mL) were resulted as most active antitubercular agents.

Time to detection of the growth of Mycobacterium tuberculosis in MGIT 960 for determining the early bactericidal activity of antituberculosis agents

Evaluation of early bactericidal activity (EBA) by the determination of a fall in viable colony-forming units (CFU) of Mycobacterium tuberculosis in sputum is a first step in the clinical study of new antituberculosis agents. The time to detection (TTD) of growth in liquid media is more sensitive and could substitute for CFU counting on solid media. Overnight sputum samples collected during the evaluation of the novel agent TMC207 in comparison to isoniazid and rifampicin were studied. For the determination of CFU, we incubated 10-fold dilutions of homogenized sputum on selective 7H10 agar. The TTD was measured by incubating decontaminated sputum in the BACTEC MGIT 960 system. The fall in bacillary load over 7 days determined by CFU counting closely matched the prolongation of the TTD in the BACTEC MGIT 960 system. The CFU counts correlated significantly with the TTD. While the ranking of agents and different dosages of TMC207 was similar, the highest dose of TMC207 showed markedly better activity when measured by the TTD than CFU counting when compared to the activity of isoniazid. Automated TTD could augment, or, in future, replace, CFU counting to determine sputum bacillary load in EBA clinical trials pending a more formal evaluation of the correlation of the measurements.