Antiinfectives targeting enzymes and the proton motive force

There is a growing need for new antibiotics. Compounds that target the proton motive force (PMF), uncouplers, represent one possible class of compounds that might be developed because they are already used to treat parasitic infections, and there is interest in their use for the treatment of other diseases, such as diabetes. Here, we tested a series of compounds, most with known antiinfective activity, for uncoupler activity. Many cationic amphiphiles tested positive, and some targeted isoprenoid biosynthesis or affected lipid bilayer structure. As an example, we found that clomiphene, a recently discovered undecaprenyl diphosphate synthase inhibitor active against Staphylococcus aureus, is an uncoupler. Using in silico screening, we then found that the anti-glioblastoma multiforme drug lead vacquinol is an inhibitor of Mycobacterium tuberculosis tuberculosinyl adenosine synthase, as well as being an uncoupler. Because vacquinol is also an inhibitor of M. tuberculosis cell growth, we used similarity searches based on the vacquinol structure, finding analogs with potent (∼0.5–2 μg/mL) activity against M. tuberculosis and S. aureus. Our results give a logical explanation of the observation that most new tuberculosis drug leads discovered by phenotypic screens and genome sequencing are highly lipophilic (logP ∼5.7) bases with membrane targets because such species are expected to partition into hydrophobic membranes, inhibiting membrane proteins, in addition to collapsing the PMF. This multiple targeting is expected to be of importance in overcoming the development of drug resistance because targeting membrane physical properties is expected to be less susceptible to the development of resistance.There is a need for new antibiotics, due to the increase in drug resistance (1, 2). For example, some studies report that by 2050, absent major improvements in drug discovery and use, more individuals will die from drug-resistant bacterial infections than from cancer, resulting in a cumulative effect on global gross domestic product of as much as 100 trillion dollars (3, 4). To discover new drugs, new targets, leads, concepts, and implementations are needed (5, 6).Currently, one major cause of death from bacterial infections is tuberculosis (TB) (7), where very highly drug-resistant strains have been found (8). Therapy is lengthy, even with drug-sensitive strains, and requires combination therapies with four drugs. Two recent TB drugs/drug leads (9–11) are TMC207 [bedaquiline (1); Sirturo] and SQ109 (2) (Fig. 1). Bedaquiline (1) targets the Mycobacterium tuberculosis ATP synthase (9) whereas SQ109 (2) has been proposed to target MmpL3 (mycobacterial membrane protein large 3), a trehalose monomycolate transporter essential for cell wall biosynthesis (12). SQ109 (2) is a lipophilic base containing an adamantyl “headgroup” connected via an ethylene diamine “linker” to a geranyl (C₁₀) “side chain,” and in recent work (13), we synthesized a series of 11 analogs of SQ109 (2) finding that the ethanolamine (3) was more potent than was SQ109 (2) against M. tuberculosis H37Rv [0.063 vs. 0.25 μg/mL minimal inhibitory concentration (MIC)], and that at least one protonatable nitrogen in the linker was essential for activity. The latter observation suggested to us that SQ109 (2) and ethanolamine (3) might have activity as uncouplers, collapsing the proton motive force (PMF; ∆P) used to drive ATP synthesis, because we had observed similar uncoupling effects for lipophilic bases, US Food and Drug Administration (FDA)-approved drugs, in trypanosomatid parasites (14, 15). The PMF is given by Mitchell (16, 17): ∆P = ∆ψ − Z∆pH, where ∆ψ is the electrical or membrane potential component of ∆P, ∆pH is the transmembrane pH gradient, and Z is 2.303RT/F where R is the gas constant, T is temperature (in kelvins), and F is the Faraday constant.Open in a separate windowFig. 1.Structures of inhibitors/uncouplers and other compounds of interest. Common or previously used names are indicated.We found with SQ109 and its analogs that the most potent M. tuberculosis cell growth inhibitors investigated did indeed collapse pH gradients and ∆ψ, as also observed with the lipophilic bases amiodarone (4) (14) and dronedarone (5) (15), antiarrhythmia drugs, in trypanosomatid parasites (18), and SQ109 (2) also acts as an uncoupler in Trypanosoma cruzi (19). Amiodarone (4) and dronedarone (5) had little uncoupling activity against host cells. In related work, Li et al. (20) found that other TB drug leads, BM212 (6), THPP-2 (7), Ro 48-8071 (8), the urea AU1235 (9), and the indolecarboxamide 2418 (10), most of which had been proposed to target MmpL3, likewise had activity as uncouplers, collapsing pH gradients, and in some cases were active against the nonreplicative bacteria found under hypoxic conditions. Several of these compounds also have enzyme targets. For example, SQ109 (2), ethanolamine (3), and Ro 48-8071 (8) have been found (13, 20) to inhibit enzymes involved in menaquinone biosynthesis, particularly the prenyl transferase 1,4-dihydroxy-2-naphthoate octaprenyltransferase (MenA) and human oxidosqualene cyclase (OSC) (21), and bedaquiline (1) is a potent ATP synthase inhibitor, indicating the possibility of multitarget activity for such compounds. These results are of interest because they show that several recently discovered M. tuberculosis drug leads can act as uncouplers in addition to targeting one or more enzymes that are essential for bacterial cell growth, with membrane targeting being of particular interest because it might be expected to be less susceptible to the development of resistance than is purely enzyme targeting, and SQ109 (2) does indeed have a low frequency of resistance in M. tuberculosis (∼2.55 × 10⁻¹¹) (22). Targeting membrane lipids is also a reason for the low frequency of resistance found with, for example, amphotericin [which binds to ergosterol in fungi and protozoa (23)], as well as the recently discovered teixobactin, which binds to lipid II/III (24).In other work by Goldman (25), it has been pointed out that most of the new TB drug leads that have been discovered by phenotypic screens and genome sequencing are highly lipophilic (logP ∼ 5.7) bases with membrane targets, which suggested to us the possibility that these drug leads might function by targeting the PMF, as well as membrane proteins. Although targeting the PMF might be expected to be purely mitotoxic, Stock et al. (26) have shown that compounds with logP > 6 have generally low mitotoxicity, which is due, they proposed, to low membrane permeability attributable to accumulation in lipophilic membranes.Perhaps the most well-known uncoupler is 2,4-dinitrophenol (DNP; 11). DNP functions as a protonophore, a proton-translocating molecule, and analogs such as niclosamide (12) and nitazoxanide (13) [active form, tizoxanide (14)] are used clinically: niclosamide (12) to treat tapeworm infections (27) and nitazoxanide (13) to treat infections due to Giardia lamblia (28) and Cryptosporidium parvum. Nitazoxanide (13) has also been in clinical trials for the treatment of Helicobacter pylori and Clostridium difficile infections. Interestingly, SQ109 (2) has similar activity against both organisms (29), and with H. pylori, SQ109 (2) once again has a very low (≈10⁻¹²) frequency of resistance (29). In addition, nitazoxanide (13) has been found to kill both replicating and nonreplicating M. tuberculosis (30–33), and Nathan and coworkers (30, 31) were unable to develop resistant colonies using up to 10¹² cfu, proposing a dual “PMF + unknown target” mechanism of action. Niclosamide (12) has been proposed as a lead for the treatment of type II diabetes (34), and it is also an inhibitor of breast cancer stem-like cells (35) and an inhibitor of Pseudomonas aeruginosa quorum sensing (36). There has also been very recent interest in the development of DNP analogs such as DNP methyl ether (37), for treating diabetes, and of controlled-release DNP formulations (38) as mild hepatic mitochondrial uncouplers for treating hypertriglyceridemia, insulin resistance, hepatic steatosis, and diabetes. Niclosamide (12) and tizoxanide (14) are both FDA-approved, and closantel (15) is an anthelmintic uncoupler in veterinary use, and all could provide leads for new and improved inhibitors that target other pathogens. There has also been considerable renewed interest (39) in the use of pyrazinoic acid (16), which functions, at least in part, as a protonophore uncoupler, for treating TB (39, 40), stimulating our interest in discovering new TB drug leads with uncoupler activity.In this work, we carried out three main types of investigation. First, we investigated the uncoupling effects of 21 compounds (primarily known drugs or drug leads) on uncoupling (∆pH/∆ψ collapse) in bacterial inverted membrane vesicles (IMVs) and in porcine mitochondria. Second, we investigated drug–membrane interactions using differential scanning calorimetry (DSC) and electron paramagnetic resonance (EPR) spectroscopy. Third, we used molecular dynamics (MD) structure-based in silico screening and structure-similarity searches to find prenyl synthase inhibitors with uncoupler activity, leading finally to a consideration of the future prospects for discovering new “enzyme + uncoupler” antiinfective drug leads.     

Bedaquiline as Treatment for Disseminated Nontuberculous Mycobacteria Infection in 2 Patients Co-Infected with HIV

Nontuberculous mycobacteria can cause disseminated infections in immunocompromised patients and are challenging to treat because of antimicrobial resistance and adverse effects of prolonged multidrug treatment. We report successful treatment with bedaquiline, a novel antimycobacterial drug, as part of combination therapy for 2 patients with disseminated nontuberculous mycobacteria co-infected with HIV.     

Global Progress and Challenges in Implementing New Medications for Treating Multidrug-Resistant Tuberculosis

Two new drugs—bedaquiline and delamanid—have recently been approved by stringent regulatory authorities to treat multidrug-resistant tuberculosis (TB) and recommended by the World Health Organization for use under defined programmatic conditions. Introducing the medications in TB programs worldwide has not kept pace with the need for these drugs. In response, the DR-TB STAT (Drug-Resistant TB Scale-up Treatment Action Team) task force was formed in April 2015 to monitor progress and help overcome challenges. Information was collected from multiple sources and assessed monthly. Some progress has been made in introducing bedaquiline: as of October 2015, a total of 1,258 persons were on the medication under programmatic conditions. For delamanid, >100 patients, but few under programmatic conditions, have received the medication. Coordinated global action might help assist making these medications accessible for persons who need them most.     

Selective drug deposition in lungs through pulmonary drug delivery system for effective management of drug-resistant TB

Introduction: The emergence of multidrug-resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB) is a major health issue and continues to be a global health concern. Despite significant advancements in treatment modalities, ~1.6 million deaths worldwide occur due to TB infection. This is because of tuberculosis reservoirs in the alveoli making it a challenge for the formulation scientist to target this.

Area covered: This review recent investigations on the forefront of pulmonary drug delivery for managing MDR-TB and XDR-TB. Novel delivery systems like liposomes, niosomes, employing carbohydrate, and -coated molecules via conjugation to selectively deliver the drugs to the lung TB reservoir via pulmonary administration are discussed.

Expert opinion: Poor patient adherence to treatment due to side effects and extended therapeutic regimen leads to drug-resistant TB. Thus, it is essential to design novel strategies this issue by developing new chemical entities and/or new delivery systems for delivery to the lungs, consequently reducing the side effects, the frequency and the duration of treatment. Delivery of drugs to enhance the efficacy of new/existing anti-TB drugs to overcome the resistance and enhance patient compliance is underway.     

Hearing aid support for patients with DR-TB in Ethiopia

SETTING:Previous and current patients with drug-resistant TB (DR-TB) who had documented treatment-related hearing impairment due to second-line injectable (SLI) use were identified from different DR-TB treatment initiation centres in Ethiopia.OBJECTIVE:To assess selected patients with DR-TB for eligibility for hearing aids and provide hearing aids to 10 eligible patients.DESIGN:This was an observational cohort study. Patients were followed up for 8 months, with hearing assessments conducted at 1, 3 and 8 months to objectively assess hearing capacity.RESULTS:Of 12 patients assessed for hearing aids eligibility, 10 were fitted with hearing aids (type XTM XP P4) and followed up for 8 months. “Formal” improvement was observed only in one patient. However, “general quality of life” appeared to be improved in nine patients.CONCLUSION:Minimal “formal” improvement was observed. However, the study was too small to say whether hearing aids should, or should not, be recommended as a public health measure. This needs a larger better controlled follow-up study. The all-oral DR-TB treatment regimens should be used for all patients with DR-TB in Ethiopia. However, as a proportion of patients with DR-TB are likely to continue receiving SLIs in the foreseeable future, they will require close audiometry assessment and appropriate care.     

基于openFDA对贝达喹啉和德拉马尼药品不良反应的比较分析研究

目的:探索抗耐多药结核病(multidrug resistant tuberculosis,MDR-TB)药物贝达喹啉及德拉马尼不良反应(adverse drug reaction,ADR),从多角度分析两药ADR上报的相关情况,为临床治疗制定相应药学监护策略,为新的研究思路和方向提供线索.方法:利用美国食品药品监督管...     

Combating Tuberculosis Infection: A Forbidding Challenge

After 50 years drought, several drugs are looming from the pipeline to combat tuberculosis. They will serve as a boon to the field that has been burdened with primitive, inadequate treatments and drug-resistant bacterial strains. From the decades, due to lack of interest and resources, the field has suffered a lot. Learning from the flaws, scientists have renovated their approaches to the finding of new antitubercular drugs. The first line drugs take about six months or more for the entire treatment. The second line remedy for resistant-tuberculosis requires daily injections which carry severe side effects. Drug resistance remains a constant menace because patients stop the medication once they start feeling better. So new drugs are required to be explored which are effective against tuberculosis especially drug resistant tuberculosis. These drugs need to work well with other drugs as well as with antivirals used for the treatment of human immunodeficiency virus. It is also very important to be considered that the treatments need to be cheap, as tuberculosis primarily affects people more in the developing countries. Further, new drugs must cure the disease in short span of time than the current six to nine month regimen. Recently a few new and potent drugs such as bedaquiline, delamanid, teixobactin have been evolved which may serve as a nice step forward, with a better outcome. Teixobactin, a new antibiotic has been found to have promising action against resistant strains, is also under consideration.     

State-of-the-art treatment strategies for nontuberculous mycobacteria infections

ABSTRACT

Introduction

Non-tuberculous Mycobacteria (NTM) are a group of organisms whose importance in medicine seems to be increasing in recent times. The increasing number of patients susceptible to these diseases make it necessary to expand our knowledge of therapeutic options and to explore future possibilities for the development of a therapeutic arsenal.     

Current and developing therapies for the treatment of multi drug resistant tuberculosis (MDR-TB) in India

Introduction: India accounts for 25% of the global burden of MDR-TB. In 2016, the India’s Revised National TB Control Programme reported a success rate of 46% among 19,298 MDR-TB patients treated under the programme. This suboptimal treatment outcome warrants an urgent need for newer drugs and newer regimens in the treatment of MDR-TB. India requires new shorter, cheap, safe and effective anti-TB regimen to treat MDR-TB.

Areas covered: We used different search strategies to obtain relevant literature from PubMed, on Indian experiences of developing therapies for the treatment of MDR-TB. Further information from the Central TB Division Government of India on programmatic management of resistant TB was collected.

Expert opinion: In 2016 WHO recommended a shorter MDR-TB regimen of 9–12 months (4–6 Km-Mfx-Pto-Cfz-Z-Hhigh-dose-E /5 Mfx-Cfz-Z-E) may be used instead of longer regimens. Currently, conducting trials involving newer drugs such as bedaquiline, have been proposed. The regimen will be of a shorter duration containing isoniazid, prothionamide, bedaquiline, levofloxacin, ciprofloxacin, ethambutol and pyrazinamide (STREAM regimen). To successfully treat MDR-TB one requires new classes of antibiotic and newer diagnostic tests. This represents an enormous financial and technical challenge to the programme managers and policy makers.