Identification of antitubercular benzothiazinone compounds by ligand-based design

1,3-Benzothiazin-4-ones (BTZs) are a novel class of TB drug candidates with potent activity against M. tuberculosis. An in silico ligand-based model based on structure-activity data from 170 BTZ compounds was used to design a new series. Compounds were tested against a panel of mycobacterial strains and were profiled for cytotoxicity, stability, and antiproliferative effects. Several of the compounds showed improved activity against MDR-TB while retaining low toxicity with higher microsomal, metabolic, and plasma stability.     

喹诺酮抗分枝杆菌活性及其构效关系研究进展

随着耐药结核病(尤其是耐多药结核病)发病率的不断上升以及结核病与AIDS病的并发,结核病疫情再度上升,成为全球重大公共卫生问题。作为二线抗结核病药物,氟喹诺酮类药物具有一定优势,它们在临床治疗耐多药结核病以及对不能耐受一线抗结核病药物的患者治疗中扮演着重要角色。本文综述了近年来喹诺酮(包括氟喹诺酮、6-非氟喹诺酮和非经典喹诺酮)在抗分枝杆菌活性及其构效关系方面的研究进展。     

Mechanistic investigation of resistance via drug-inactivating enzymes in Mycobacterium tuberculosis

Abstract

Tuberculosis (TB) is a serious major health concern that has existed from millennia. According to annual WHO report 2016, it is considered as world’s ninth highest killer disease by single infectious agent, ranking above HIV/AIDS. To worsen the scenario the development of multi-drug resistant tuberculosis (MDR-TB) and extremely drug-resistant tuberculosis (XDR-TB) have significantly reduced the success rate of TB treatment. Several efforts are being made to handle pharmacodynamic resistance (MDR and XDR-TB) involving designing of new inhibitors, targeting mutated target or by multi-targeting agents. However, the issue of pharmacokinetic resistance in TB is not being addressed appropriately till date. Pharmacokinetic mode of resistance involves an intrinsic mechanism of bacterial drug resistance via expression of various enzymes and efflux pumps that are responsible for the loss of activity of the therapeutic agents. Mycobacterium tuberculosis is also intrinsically resistant to various approved agents via pharmacokinetic mechanism of resistance. Several bacterial enzymes are encoded that either degrade or modifies the drugs and renders them ineffective. Targeting such inactivating bacterial enzymes provides a novel approach to make the current therapy effective and combat the problem of resistance. This review provides an insight into different bacterial enzymes which are responsible for pharmacokinetic drug resistance in TB. The structure attributes and mechanism of catalysis employed by these enzymes to inactivate drug have also been discussed which may provide basis for developing novel therapeutic agents for resistant TB.     

Biotechnology in the development of new vaccines and diagnostic reagents against tuberculosis

Tuberculosis (TB) is a disease of global concern. About one third of the world population is infected with Mycobacterium tuberculosis. Every year, approximately 8 million people get the disease and 2 million die of TB. The currently available vaccine against TB is the attenuated strain of Mycobacterium bovis, Bacillus Calmette Guerin (BCG), which has failed to provide consistent protection in different parts of the world. The commonly used diagnostic reagent for TB is the purified protein derivative (PPD) of M. tuberculosis, which is nonspecific because of the presence of antigens crossreactive with BCG and environmental mycobacteria. Thus there is a need to identify M. tuberculosis antigens as candidates for new protective vaccines and specific diagnostic reagents against TB. By using the techniques of recombinant DNA, synthetic peptides, antigen-specific antibodies and T cells etc., several major antigens of M. tuberculosis have been identified, e.g. heat shock protein (hsp)60, hsp70, Ag85, ESAT-6 and CFP10 etc. These antigens have shown promise as new candidate vaccines and/or diagnostic reagents against TB. In addition, recent comparisons of the genome sequence of M. tuberculosis with BCG and other mycobacteria have unraveled M. tuberculosis specific regions and genes. Expression and immunological evaluation of these regions and genes can potentially identify most of the antigens of M. tuberculosis important for developing new vaccines and specific diagnostic reagents against TB. Moreover, advances in identification of proper adjuvant and delivery systems can potentially overcome the problem of poor immunogenicity/short-lived immunity associated with protein and peptide based vaccines. In conclusion, the advances in biotechnology are contributing significantly in the process of developing new protective vaccines and diagnostic reagents against TB.     

Novel pyridazino[4,3-b]indoles with dual inhibitory activity against Mycobacterium tuberculosis and monoamine oxidase

Tuberculosis is one of the most common infectious diseases known to man. About 37% of the world's population (about 1.86 billion people) are infected with Mycobacterium tuberculosis. According to the World Health Organization, every year approximately 8 million people develop active tuberculosis and almost 2 million of those die from the disease. The incidence of multidrug-resistant tuberculosis (MDR-TB) is increasing. The present drug regimen for treating tuberculosis has been in existence for 30 years. New drugs that will shorten total treatment duration, improve the treatment of MDR-TB, and address latent tuberculosis are the most urgent need of tuberculosis control programs. A new series of synthetic 3-amino-4-arylpyridazino[4,3-b]indoles (pyridazinoindoles) were identified as inhibitors of Mycobacterium tuberculosis. The design, synthesis, and antimycobacterial activity of these compounds are described. While the most active compounds are still not comparable to the front-line drugs rifampicin and isoniazid, they do show promise. Most of the pyridazinoindoles with appreciable antituberculosis activity also inhibit monoamine oxidase, suggestive of a novel inhibitory effect on mycobacterial redox reactions.     

Synthetic investigational new drugs for the treatment of tuberculosis

Introduction: Tuberculosis (TB) is a major global health concern. And while there are treatments already on the market, there is a demand for new drugs that are effective and safe against Mycobacterium tuberculosis, which reduce the number of drugs and the duration of treatment in both drug-susceptible TB and multidrug-resistant TB (MDR-TB).

Area covered: This review covers promising novel investigational TB drugs that are currently under development. Specifically, the authors review the efficacy of novel agents for the treatment of TB in preclinical, phase I and phase II clinical trials. The authors also review the safety and tolerability profiles of these drugs.

Expert opinion: Bedaquiline and delamanid are the most promising novel drugs for the treatment of MDR-TB, each having high efficacy and tolerability. However, the best regimen for achieving better outcomes and reducing adverse drug reactions remains to be determined, with safety concerns regarding cardiac events due to QT prolongation still to be addressed. Pretomanid is a novel drug that potentially shortens the duration of treatment in both drug-susceptible and drug-resistant TB in combination with moxifloxacin and pyrazinamide. Linezolid shows marked efficacy in the treatment of MDR-TB and extensively drug-resistant TB (XDR-TB), but the drug is known to cause significant adverse drug reactions, including peripheral neuropathy, optic neuropathy and myelosuppression. These adverse reactions must be considered prior to prescribing long-term usage of this drug.     

Promising therapy of XDR-TB/MDR-TB with thioridazine an inhibitor of bacterial efflux pumps

Global rates of pulmonary tuberculosis (TB) continue to increase. Moreover, resistance of the causative organism Mycobacterium tuberculosis to the two most effective anti-TB medications continue to rise. Now, multi-drug resistant TB (MDR-TB) has progressed to extensively drug resistant TB (XDR-TB) - a M. tuberculosis organism that is resistant to the most effective second line drugs available for the treatment of TB. This review provides detailed, significant evidence that supports the use of an old neuroleptic compound, thioridazine (TZ), for the management of MDR-TB and XDR-TB infections and which has been shown to inhibit efflux pumps of bacteria. The argument has been previously presented but no one seems to be listening - and the disease continues unabated when there is a very good probability that the suggested drug will prove to be effective. When the prognosis is poor, available therapy predictably ineffective and death is inevitable, compassionate therapy with TZ should be contemplated. The risks are small and the rewards great.     

Fluoroquinolones for the treatment of pulmonary tuberculosis

Tuberculosis (TB) continues to be a significant problem globally. Treatment includes a multiple drug regimen with isoniazid, rifampicin (rifampin), pyrazinamide and ethambutol. Often, one of these medications needs to be replaced as a result of adverse events or because Mycobacterium tuberculosis develops resistance against one these first-line agents. Fluoroquinolones, particularly the newer ones, possess good in vitro (levofloxacin, gatifloxacin, moxifloxacin) and in vivo (gatifloxacin and moxifloxacin) bactericidal activity against M. tuberculosis, making them attractive agents for the treatment of pulmonary TB.All relevant clinical trials, cohort studies and case reports investigating the clinical efficacy and tolerability of fluoroquinolones when used for the treatment of pulmonary TB were evaluated for this review. Specifically, efficacy and safety in the following indications were investigated: (i) first-line treatment of drug-sensitive pulmonary TB; (ii) first-line treatment for multi-drug resistant (MDR) TB; and (iii) treatment of patients with drug intolerance. Twenty-seven articles met our inclusion criteria; nine articles presented data from randomised, controlled or cohort studies. Seven studies used fluoroquinolones as first-line agents in drug-sensitive TB (1469 patients), 15 studies used fluoroquinolones to treat MDR-TB (1025 patients) and six studies (951 patients) investigated the use of fluoroquinolones in patients intolerant to other TB medications.In patients with susceptible M. tuberculosis strains, substitution with a fluoroquinolone did not have an effect on cure or radiological improvement at 8 weeks or failure at 12 months. Substitution of older fluoroquinolones into a regimen, especially ciprofloxacin, resulted in a higher rate of relapse and a longer time to sputum-culture conversions. The use of fluoroquinolones in patients with MDR-TB is supported by some trials where others show a lack of improvement in efficacy of a regimen.Our review of the literature does not support the use of older fluoroquinolones, especially ciprofloxacin, as substitute agents for drug-sensitive or drug-resistant TB. However, newer fluoroquinolones, such as moxifloxacin, may be a reasonable alternative based on results from one large clinical trial. Fluoroquinolones have an important role as substitute agents for those who are intolerant of first-line TB agents.     

Treatment of multidrug-resistant and extensively drug-resistant tuberculosis: current status and future prospects

Drug resistance in Mycobacterium tuberculosis arises from the man-made selection of mutants that result from spontaneous chromosomal alterations. Preventing the development of drug-resistant TB through a good control program based on directly observed treatment, short-course, is of paramount importance. Established multidrug-resistant (MDR)-TB requires alternative specific chemotherapy, comprising drugs with higher cost and greater toxicity delivered on a programmatic basis. The development of new anti-TB drugs would help to prevent and treat MDR-TB. Notably, moxifloxacin and gatifloxacin are being tested for shortening treatment in Phase III trials, while three novel compounds, TMC-207, OPC-67683 and PA-824 are in Phase II studies for both drug-susceptible and drug-resistant disease. The roles of surgery and immunotherapy in the management of MDR-TB require further evaluation. The recent emergence of extensively drug-resistant TB poses a serious challenge to the global control of TB. In order to combat extensively drug-resistant TB, strengthening of directly observed treatment, short-course and drug-resistance programs, alongside other strategies, including the development of newer diagnostics and drugs, is mandatory.     

结核病疫苗研发面临的挑战

结核病（tuberculosis ,TB）是由结核杆菌（Mycobacterium tuberculosis ,M tb）引起的传染病,每年有近1000万例 TB 新发病例,150万人死于 TB 。卡介苗是唯一能够为婴幼儿提供保护作用的疫苗,但它却不能预防成年人 TB 以及控制 TB 流行。随着耐多药 TB 的播散和 M tb／HIV 双重感染人数的不断上升,在世界范围内控制 TB 的形势变得愈发严峻。新疫苗的研发是 TB 防治的重要内容之一,目前全世界已有至少15种 TB 候选疫苗进入临床试验。此外,适宜的动物模型也将对新型疫苗研发以及宿主抗 TB 免疫机制研究起重要作用。     

Tuberculosis pharmacotherapy: strategies to optimize patient care

Introduction: The treatment of tuberculosis (TB) is a mature discipline, with more than 60 years of clinical experience accrued across the globe. The requisite Multi-drug treatment of drug-susceptible TB, however, lasts 6 months and has never been optimized according to current standards. Multi-drug resistant TB and TB in individuals coinfected with HIV present additional treatment challenges. Objective: This article reviews the role that existing drugs and new compounds could have in shortening or improving treatment for TB. The key to treatment shortening seems to be sterilizing activity, or the ability of drugs to kill mycobacteria that persist after the initial days of multi-drug treatment. Results: Among existing anti-TB drugs, the rifamycins hold the greatest potential for shortening treatment and improving outcomes, in both HIV-infected and HIV-uninfected populations, without dramatic increases in toxicity. Clinical studies underway or being planned, are supported by in vitro , animal and human evidence of increased sterilizing activity - without significant increases in toxicity - at elevated daily doses. Fluoroquinolones also seem to have significant sterilizing activity. At present, at least two class members are being evaluated for treatment shortening with different combinations of first-line drugs. However, in light of apparent rapid selection for fluoroquinolone-resistant mutants, relative frequency of serious adverse events and a perceived need to ‘reserve’ fluoroquinolones for the treatment of drug-resistant TB, their exact role in TB treatment remains to be determined. Other possible improvements may come from inhaled delivery or split dosing (linezolid) of anti-TB drugs for which toxicity (ethionamide) or lack of absorption (aminoglycosides and polypeptides) precludes delivery of maximally effective, oral doses, once daily. New classes of drugs with novel mechanisms of action, nitroimidazopyrans and a diarylquinoline, among others, may soon provide opportunities for improving treatment of drug-resistant TB or shortening treatment of drug-susceptible TB. Conclusion: More potential options for improved TB treatment currently exist than at any other time in the last 30 years. The challenge in TB pharmacotherapy is to devise well-tolerated, efficacious, short-duration regimens that can be used successfully against drug-resistant and drug-resistant TB in a heterogeneous population of patients     

Antimycobacterial plant terpenoids.

Abstract.Tuberculosis (TB), mainly caused by Mycobacterium tuberculosis, is the leading killer among all infectious diseases worldwide and is responsible for more than two million deaths annually. For over thirty years no antitubercular agents with new mechanisms of action have been developed. The recent increase in the number of multi-drug resistant clinical isolates of M. tuberculosis has created an urgent need for the discovery and development of new antituberculosis leads. This review covers recent reports on plant-derived terpenoids that have demonstrated moderate to high activity in in vitro bioassays against M. tuberculosis. In this review, mono-, sesqui-, di- and triterpenes, and sterols, their structural analogs and semisynthetic derivatives will be discussed, with particular emphasis on the structural features essential for antimycobacterial activity.     

Inhibition of Mycobacterium tuberculosis, Mycobacterium bovis, and Mycobacterium avium by novel dideoxy nucleosides

The prevalence of tuberculosis (TB) and mutidrug-resistant tuberculosis (MDR-TB) has been increasing, leading to serious infections, high mortality, and a global health threat. Here, we report the identification of a novel class of dideoxy nucleosides as potent and selective inhibitors of Mycobacterium bovis, Mycobacterium tuberculosis, and drug-resistant Mycobacterium tuberculosis. A series of 5-acetylenic derivatives of 2',3'-dideoxyuridine (3-8) and 3'-fluoro-2',3'-dideoxyuridine (22-27) were synthesized and tested for their antimycobacterial activity against M. bovis, M. tuberculosis, and M. avium. 2',3'-Dideoxyuridine possessing 5-decynyl, 5-dodecynyl, 5-tridecynyl, and 5-tetradecynyl substituents (4-7) exhibited the highest antimycobacterial activity against all three mycobacteria. In contrast, in the 3'-fluoro-2',3'-dideoxyuridine series, a 5-tetradecynyl analogue (26) displayed the most potent activity against these mycobacteria. Among other derivatives, 5-bromo-2',3'-dideoxycytidine (11), 5-methyl-2',3'-dideoxycytidine (12), and 5-chloro-4-thio-2',3'-dideoxyuridine (19) exhibited modest inhibition of M. bovis and M. tuberculosis. In the series of dideoxy derivatives of adenosine, guanosine, and purines, 2-amino-6-mercaptoethyl-9-(2,3-dideoxy-beta-d-glyceropentofuranosyl)purine (32) and 2-amino-4-fluoro-7-(2,3-dideoxy-beta-d-glyceropentofuranosyl)pyrrolo[2,3-d]pyrimidine (35) were the most efficacious against M. bovis and M. tuberculosis, and M. avium, respectively.     

Treatment of multidrug-resistant and extensively drug-resistant tuberculosis: current status and future prospects

Drug resistance in Mycobacterium tuberculosis arises from the man-made selection of mutants that result from spontaneous chromosomal alterations. Preventing the development of drug-resistant TB through a good control program based on directly observed treatment, short-course, is of paramount importance. Established multidrug-resistant (MDR)-TB requires alternative specific chemotherapy, comprising drugs with higher cost and greater toxicity delivered on a programmatic basis. The development of new anti-TB drugs would help to prevent and treat MDR-TB. Notably, moxifloxacin and gatifloxacin are being tested for shortening treatment in Phase III trials, while three novel compounds, TMC-207, OPC-67683 and PA-824 are in Phase II studies for both drug-susceptible and drug-resistant disease. The roles of surgery and immunotherapy in the management of MDR-TB require further evaluation. The recent emergence of extensively drug-resistant TB poses a serious challenge to the global control of TB. In order to combat extensively drug-resistant TB, strengthening of directly observed treatment, short-course and drug-resistance programs, alongside other strategies, including the development of newer diagnostics and drugs, is mandatory.     

Targeting the human macrophage with combinations of drugs and inhibitors of Ca2+ and K+ transport to enhance the killing of intracellular multi-drug resistant Mycobacterium tuberculosis (MDR-TB)--a novel, patentable approach to limit the emergence of XDR-TB

The emergence of resistance in tuberculosis has become a serious problem for the control of this disease. For that reason, new therapeutic strategies that can be implemented in the clinical setting are urgently needed. The design of new compounds active against mycobacteria must take into account that tuberculosis is mainly an intracellular infection of the alveolar macrophage and therefore must maintain activity within the host cells. An alternative therapeutic approach will be described in this review, focusing on the activation of the phagocytic cell and the subsequent killing of the internalized bacteria. This approach explores the combined use of antibiotics and phenothiazines, or Ca(2+) and K(+) flux inhibitors, in the infected macrophage. Targeting the infected macrophage and not the internalized bacteria could overcome the problem of bacterial multi-drug resistance. This will potentially eliminate the appearance of new multi-drug resistant tuberculosis (MDR-TB) cases and subsequently prevent the emergence of extensively-drug resistant tuberculosis (XDR-TB). Patents resulting from this novel and innovative approach could be extremely valuable if they can be implemented in the clinical setting. Other patents will also be discussed such as the treatment of TB using immunomodulator compounds (for example: betaglycans).     

抗结核新药德拉马尼作用机理和化学合成的研究进展

结核分枝杆菌感染导致的结核病仍然是全球重大公共卫生威胁。耐多药结核分枝杆菌感染所致的耐多药结核病则是2035年实现终结结核病的主要障碍之一。德拉马尼是近50年来成功研发并上市的抗结核新药之一。德拉马尼主要依据抑制枝菌酸合成的酶筛选获得,但是,其具体靶标仍然有待研究。本文综述前药德拉马尼的激活途径和基因、转录组效应、作用靶标以及化学合成,为进一步精准确定其药靶提供基础。     

Drug-resistant and multidrug-resistant tubercle bacilli

Drug resistant (DR) and multidrug resistant (MDR) tuberculosis (TB) is a consequence of human activity and did not exist before chemotherapeutic drugs were introduced. Monotherapy with various drugs in sequence or other inadequate drug regimens have strongly contributed to the creation of MDR-TB. Such TB strains are mainly prevalent in regions with weak national TB programmes or poor socio-economic environments. Strains may also spread in some communities such as poorly administered prisons. From these and other sources, MDR-TB may spread in the population from which travellers might transfer strains between countries and continents. Therefore an effective surveillance of the resistance pattern of TB bacilli is a demanding task in all countries. In this review some aspects of epidemiology, diagnosis and mechanisms of DR in TB are discussed. MDR-TB is an important international problem of increasing significance for the whole global community.     

Re-emergence of tuberculosis: strategies and treatment

Tuberculosis (TB) was declared a global emergency by the WHO in 1993. Approximately one third of the world's population is infected with Mycobacterium tuberculosis. Despite the availability of effective chemotherapy, 3.5 million TB deaths occur each year. In addition to this human cost, TB also represents a significant economic burden for developing countries. The worldwide spread of TB is mainly caused by the emergence of multidrug-resistant (MDR) M. tuberculosis strains, thus underlining the need for novel antimycobacterial drugs with improved efficacy. Research in TB chemotherapy, as well as in vaccine development, has entered an intense phase in an attempt to combat this disease.     

Problems of multidrug- and extensively drug-resistant TB

Worldwide, it is thought that in 2010 around 9 million people developed tuberculosis (TB) and around 1.5 million people died from the disease. Standard therapy (6 months of rifampicin and isoniazid, plus pyrazinamide and ethambutol for the first 2 months) is recommended for newly diagnosed active respiratory TB and is effective if taken correctly. However, its effectiveness can be compromised by a number of factors including poor adherence (e.g. because of the long duration of treatment, occurrence of unwanted effects) or inadequate drug levels for other reasons (e.g. drug-drug interactions, poor quality medicines). These factors also contribute to the development of resistance to one or more of the drugs. Multidrug resistant TB (MDR-TB) is defined as TB with resistance to both rifampicin and isoniazid. Patients with MDR-TB are treated with a combination of first-line and second-line drugs based on the results of drug susceptibility testing. The treatment is longer, less effective, less tolerable, and more expensive than standard therapy, and involves the use of injectable drugs. Extensively drug-resistant TB (XDR-TB; defined as TB with resistance to rifampicin and isoniazid, and to at least one fluoroquinolone and one second-line injectable agent such as amikacin or capreomycin) is now emerging. Here we highlight patient groups at increased risk of MDR- and XDR-TB, and discuss how to investigate, manage and treat them.     

Synthesis and evaluation of a pyrazinoic acid prodrug in Mycobacterium tuberculosis

Tuberculosis (TB) is a disease caused mainly by infection of Mycobacterium tuberculosis affecting more than ten million people around the world. Despite TB can be treated, the rise of MDR-TB and XDR-TB cases put the disease in a worrying status. As pyrazinamide-resistant strains exhibit low or none pyrazinamidase activity, it is proposed that the active form of pyrazinamide (PZA) is pyrazinoic acid (POA), although this acid has poor penetration in mycobacteria. In this work, we present a convenient one-pot synthesis of 2-chloroethyl pyrazinoate, and its activity in M. tuberculosis H₃₇Rv (ATCC27294) in MIC assay using the MABA technique. The obtained MIC of the compound was 3.96 g/mL, and discussion about the activity profile of some previously evaluated pyrazinoates is also performed.