Acceleration of tuberculosis treatment by adjunctive therapy with verapamil as an efflux inhibitor

P-glycoprotein inhibitors as an adjunct therapy for TB

The primary challenge in TB treatment is the emergence of multidrug-resistant TB (MDR-TB). One of the major factors responsible for MDR is the upregulation of efflux pumps. Permeation-glycoprotein (P-gp), an efflux pump, hinders the bioavailability of the administered drugs inside the infected cells. Simultaneously, angiogenesis, the formation of new blood vessels, contributes to drug delivery complexities. TB infection triggers a cascade of events that upregulates the expression of angiogenic factors and P-gp. The combined action of P-gp and angiogenesis foster the emergence of MDR-TB. Understanding these mechanisms is pivotal for developing targeted interventions to overcome MDR in TB. P-gp inhibitors, such as verapamil, and anti-angiogenic drugs, including bevacizumab, have shown improvement in TB drug delivery to granuloma. In this review, we discuss the potential of P-gp inhibitors as an adjunct therapy to shorten TB treatment.

A Dose-Finding Study to Guide Use of Verapamil as an Adjunctive Therapy in Tuberculosis

Induction of mycobacterial efflux pumps is a cause of Mycobacterium tuberculosis (Mtb) drug tolerance, a barrier to shortening antitubercular treatment. Verapamil inhibits Mtb efflux pumps that mediate tolerance to rifampin, a cornerstone of tuberculosis (TB) treatment. Verapamil's mycobacterial efflux pump inhibition also limits Mtb growth in macrophages in the absence of antibiotic treatment. These findings suggest that verapamil could be used as an adjunctive therapy for TB treatment shortening. However, verapamil is rapidly and substantially metabolized when co-administered with rifampin. We determined in a dose-escalation clinical trial of persons with pulmonary TB that rifampin-induced clearance of verapamil can be countered without toxicity by the administration of larger than usual doses of verapamil. An oral dosage of 360 mg sustained-release (SR) verapamil given every 12 hours concomitantly with rifampin achieved median verapamil exposures of 903.1 ng.h/mL (area under the curve (AUC)0-12 h ) in the 18 participants receiving this highest studied verapamil dose; these AUC findings are similar to those in persons receiving daily doses of 240 mg verapamil SR but not rifampin. Moreover, norverapamil:verapamil, R:S verapamil, and R:S norverapamil AUC ratios were all significantly greater than those of historical controls receiving SR verapamil in the absence of rifampin. Thus, rifampin administration favors the less-cardioactive verapamil metabolites and enantiomers that retain similar Mtb efflux inhibitory activity to verapamil, increasing overall benefit. Finally, rifampin exposures were 50% greater after verapamil administration, which may also be advantageous. Our findings suggest that a higher dosage of verapamil can be safely used as adjunctive treatment in rifampin-containing treatment regimens.

Effect of calcium-channel blockers on the risk of active tuberculosis and mortality: systematic review and meta-analysis

Introduction: Recent studies suggest that calcium channel blockers (CCBs) could reduce the risk of active tuberculosis and improve clinical outcomes. We aimed to synthesize the evidence regarding the effect of CCBs on the risk of developing active tuberculosis and mortality. Methods: We systematically searched for observational studies and clinical trials published in six databases until 31 August 2023, following a PECO/PICO strategy. Results: We included eight observational studies, 4,020,830 patients, among whom 241,761 had diabetes mellitus and 30,397 had active tuberculosis. According to our results, CCBs reduce the risk of developing active tuberculosis by 29% (RR 0.71; 95% CI 0.67-0.75) in patients with and without diabetes mellitus. However, CCBs do not show any benefit in terms of tuberculosis-related mortality (RR 1.00; 95% CI 0.98-1.02). For both outcomes, no statistical heterogeneity was found (I2 = 0, p > 0.10). This protective effect of CCBs on the risk of active tuberculosis remained independent of the type of patient (with diabetes mellitus vs. general population) or the class of CCB administered (DHP-CCB vs. non-DHP-CCB) (test for subgroup differences I2 = 0, p > 0.10). However, this beneficial effect was more significant among the general population (RR 0.70; 95% CI 0.66-0.74) compared to patients with diabetes mellitus (RR 0.72; 95% CI 0.61-0.86) and among those patients treated with DHP-CCBs (RR 0.69; 95% CI 0.63-0.74) compared to patients treated with non-DHP-CCBs (RR 0.72; 95% CI 0.67-0.78). Conclusion: CCBs may reduce the risk of active TB in patients with diabetes and the general population. On the contrary, CCBs do not seem to have a protective effect on tuberculosis-related mortality. However, more evidence is still needed. We recommend developing clinical trials to verify these findings, including more diverse populations. Systematic Review Registration: [https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=352129].

In vitro and in vivo evaluation of dual Clofazimine and Verapamil loaded PLGA nanoparticles

Combination therapy may counter the risk caused by efflux pumps mediated resistance developed by mycobacteria with a concomitant increase of the bactericidal effect of anti-TB drugs. In the present study, combination of two drugs in a nanoformulation was prepared. Clofazimine targets type 2 NADH dehydrogenase of the electron transport chain, and Verapamil inhibits various mycobacterial efflux pumps. The nanotechnology approach was adopted to overcome limitations associated with administration of free form of drugs by using poly (D, L-lactic-co-glycolic acid) as a polymer. Nanoparticles were prepared by oil/water single emulsion solvent evaporation procedure and characterized by various techniques. The results thus highlighted that developed nanoparticles were spherical with nano range size (200-450 nm). Fourier transform infrared spectroscopy revealed successful encapsulation of drugs in developed nanoformulations. Drugs in combination showed higher encapsulation efficiency and percentage drug loading capacity as compared to individual drug nanoformulations. Also, reduced toxicity of nanoformulation was observed in hemolysis assay as compared to free drugs. Ex-vivo analysis demonstrated efficient uptake of rhodamine encapsulated nanoparticles by THP-1 cells, while in-vivo results revealed sustained drug release of nanoformulation as compared to free drugs in combination. Therefore, we were able to achieve development of a single nanoformulation encapsulating Clofazimine and Verapamil in combination. Based on these findings, future studies can be designed to explore the potential of co-encapsulated Clofazimine and Verapamil nanoparticles in management of tuberculosis.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12291-022-01062-8.

Mycobacterium tuberculosis Gene Expression Associated With Fluoroquinolone Resistance and Efflux Pump Inhibition

BACKGROUND

We evaluated the relationship between response to efflux pump inhibition in fluoroquinolone-resistant Mycobacterium tuberculosis (Mtb) isolates and differences in gene expression and expression quantitative trait loci (eQTL).

METHODS

We determined ofloxacin minimum inhibitory concentration (MIC) for ofloxacin-resistant and -susceptible Mtb isolates without and with the efflux pump inhibitor verapamil. We performed RNA sequencing (RNA-seq), whole genome sequencing (WGS), and eQTL analysis, focusing on efflux pump, transport, and secretion-associated genes.

RESULTS

Of 42 ofloxacin-resistant Mtb isolates, 27 had adequate WGS coverage and acceptable RNA-seq quality. Of these 27, 7 had >2-fold reduction in ofloxacin MIC with verapamil; 6 had 2-fold reduction, and 14 had <2-fold reduction. Five genes (including Rv0191) had significantly increased expression in the MIC fold change >2 compared to <2 groups. Among regulated genes, 31 eQTLs (without ofloxacin) and 35 eQTLs (with ofloxacin) had significant allele frequency differences between MIC fold change >2 and <2 groups. Of these, Rv1410c, Rv2459, and Rv3756c (without ofloxacin) and Rv0191 and Rv3756c (with ofloxacin) have previously been associated with antituberculosis drug resistance.

CONCLUSIONS

In this first reported eQTL analysis in Mtb, Rv0191 had increased gene expression and significance in eQTL analysis, making it a candidate for functional evaluation of efflux-mediated fluoroquinolone resistance in Mtb.

A dose-finding study to guide use of verapamil as an adjunctive therapy in tuberculosis

Induction of mycobacterial efflux pumps is a cause of Mycobacterium tuberculosis (Mtb) drug tolerance, a barrier to shortening antitubercular treatment. Verapamil inhibits Mtb efflux pumps that mediate tolerance to rifampin, a cornerstone of tuberculosis treatment. Verapamil's mycobacterial efflux pump inhibition also limits Mtb growth in macrophages in the absence of antibiotic treatment. These findings suggest that verapamil could be used as an adjunctive therapy for TB treatment shortening. However, verapamil is rapidly and substantially metabolized when co-administered with rifampin. We determined in a dose-escalation clinical trial that rifampin-induced clearance of verapamil can be countered without toxicity by the administration of larger than usual doses of verapamil. An oral dosage of 360 mg sustained-release (SR) verapamil given every 12 hours concomitantly with rifampin achieved median verapamil exposures of 903.1 ng.h/ml (AUC 0-12h), similar to those in persons receiving daily doses of 240 mg verapamil SR but not rifampin. Norverapamil:verapamil, R:S verapamil and R:S norverapamil AUC ratios were all significantly greater than those of historical controls receiving SR verapamil in the absence of rifampin, suggesting that rifampin administration favors the less-cardioactive verapamil metabolites and enantiomers. Finally, rifampin exposures were significantly greater after verapamil administration. Our findings suggest that a higher dosage of verapamil can be safely used as adjunctive treatment in rifampin-containing treatment regimens.

Advances in immunomodulatory strategies for host-directed therapies in combating tuberculosis

Tuberculosis (TB) maintains its infamous status regarding its detrimental effect on global health, causing the highest mortality by a single infectious agent. The presence of resistance and immune compromising disease favours the disease in maintaining its footing in the health care burden despite various anti-TB drugs used to fight it. Main factors contributing to resistance and difficulty in treating disease include prolonged treatment duration (at least 6 months) and severe toxicity, which further leads to patient non-compliance, and thus a ripple effect leading to therapeutic non-efficacy. The efficacy of new regimens demonstrates that targeting host factors concomitantly with the Mycobacterium tuberculosis (M.tb) strain is urgently required. Due to the huge expenses and time required of up to 20 years for new drug research and development, drug repurposing may be the most economical, circumspective, and conveniently faster journey to embark on. Host-directed therapy (HDT) will dampen the burden of the disease by acting as an immunomodulator, allowing it to defend the body against antibiotic-resistant pathogens whilst minimizing the possibility of developing new resistance to susceptible drugs. Repurposed drugs in TB act as host-directed therapies, acclimatizing the host immune cell to the presence of TB, improving its antimicrobial activity and time taken to get rid of the disease, whilst minimizing inflammation and tissue damage. In this review, we, therefore, explore possible immunomodulatory targets, HDT immunomodulatory agents, and their ability to improve clinical outcomes whilst minimizing the risk of drug resistance, through various pathway targeting and treatment duration reduction.

Protein targets in Mycobacterium tuberculosis and their inhibitors for therapeutic implications: A narrative review

Advancement in the area of anti-tubercular drug development has been full-fledged, yet, a very less number of drug molecules have reached phase II clinical trials, and therefore "End-TB" is still a global challenge. Inhibitors to specific metabolic pathways of Mycobacterium tuberculosis (Mtb) gain importance in strategizing anti-tuberculosis drug discovery. The lead compounds that target DNA replication, protein synthesis, cell wall biosynthesis, bacterial virulence and energy metabolism are emerging as potential chemotherapeutic options against Mtb growth and survival within the host. In recent times, the in silico approaches have become most promising tools in the identification of suitable inhibitors for specific protein targets of Mtb. An update in the fundamental understanding of these inhibitors and the mechanism of interaction may bring hope to future perspectives in novel drug development and delivery approaches. This review provides a collective impression of the small molecules with potential antimycobacterial activities and their target pathways in Mtb such as cell wall biosynthesis, DNA replication, transcription and translation, efflux pumps, antivirulence pathways and general metabolism. The mechanism of interaction of specific inhibitor with their respective protein targets has been discussed. The comprehensive knowledge of such an impactful area of research would essentially reflect in the discovery of novel drug molecules and effective delivery approaches. This narrative review encompasses the knowledge of emerging targets and promising n that could potentially translate in to the anti-TB-drug discovery.

Redefining tuberculosis: an interview with Lalita Ramakrishnan

Professor Lalita Ramakrishnan is at the forefront of modern tuberculosis (TB) research. She has developed vital tools, most notably a robust zebrafish model, to study this disease, leading to seminal discoveries uncovering bacterial and host interactions throughout infection. Her group has harnessed this knowledge to develop new treatments for TB and shape clinical research. By unveiling these complex interactions, they have also improved our understanding of fundamental biology of macrophages and other infectious diseases, such as leprosy.

The human proton pump inhibitors inhibit Mycobacterium tuberculosis rifampicin efflux and macrophage-induced rifampicin tolerance

Tuberculosis treatment requires months-long combination chemotherapy with multiple drugs, with shorter treatments leading to relapses. A major impediment to shortening treatment is that Mycobacterium tuberculosis becomes tolerant to the administered drugs, starting early after infection and within days of infecting macrophages. Multiple lines of evidence suggest that macrophage-induced drug tolerance is mediated by mycobacterial drug efflux pumps. Here, using assays to directly measure drug efflux, we find that M. tuberculosis transports the first-line antitubercular drug rifampicin through a proton gradient-dependent mechanism. We show that verapamil, a known efflux pump inhibitor, which inhibits macrophage-induced rifampicin tolerance, also inhibits M.tuberculosis rifampicin efflux. As with macrophage-induced tolerance, the calcium channel-inhibiting property of verapamil is not required for its inhibition of rifampicin efflux. By testing verapamil analogs, we show that verapamil directly inhibits M. tuberculosis drug efflux pumps through its human P-glycoprotein (PGP)-like inhibitory activity. Screening commonly used drugs with incidental PGP inhibitory activity, we find many inhibit rifampicin efflux, including the proton pump inhibitors (PPIs) such as omeprazole. Like verapamil, the PPIs inhibit macrophage-induced rifampicin tolerance as well as intramacrophage growth, which has also been linked to mycobacterial efflux pump activity. Our assays provide a facile screening platform for M. tuberculosis efflux pump inhibitors that inhibit in vivo drug tolerance and growth.

Gaucher disease protects against tuberculosis

Biallelic mutations in the glucocerebrosidase (GBA1) gene cause Gaucher disease, characterized by lysosomal accumulation of glucosylceramide and glucosylsphingosine in macrophages. Gaucher and other lysosomal diseases occur with high frequency in Ashkenazi Jews. It has been proposed that the underlying mutations confer a selective advantage, in particular conferring protection against tuberculosis. Here, using a zebrafish Gaucher disease model, we find that the mutation GBA1 N370S, predominant among Ashkenazi Jews, increases resistance to tuberculosis through the microbicidal activity of glucosylsphingosine in macrophage lysosomes. Consistent with lysosomal accumulation occurring only in homozygotes, heterozygotes remain susceptible to tuberculosis. Thus, our findings reveal a mechanistic basis for protection against tuberculosis by GBA1 N370S and provide biological plausibility for its selection if the relatively mild deleterious effects in homozygotes were offset by significant protection against tuberculosis, a rampant killer of the young in Europe through the Middle Ages into the 19th century.

The Struggle to End a Millennia-Long Pandemic: Novel Candidate and Repurposed Drugs for the Treatment of Tuberculosis

This article provides an encompassing review of the current pipeline of putative and developed treatments for tuberculosis, including multidrug-resistant strains. The review has organized each compound according to its site of activity. To provide context, mention of drugs within current recommended treatment regimens is made, thereafter followed by discussion on recently developed and upcoming molecules at established and novel targets. The review is designed to provide a clinically applicable understanding of the compounds that are deemed most currently relevant, including those already under clinical study and those that have shown promising pre-clinical results. An extensive review of the efficacy and safety data for key contemporary drugs already incorporated into treatment regimens, such as bedaquiline, pretomanid, and linezolid, is provided. The three levels of the bacterial cell wall (mycolic acid, arabinogalactan, and peptidoglycan layers) are highlighted and important compounds designed to target each layer are delineated. Amongst others, the highly optimistic and potent anti-mycobacterial activity of agents such as BTZ-043, PBTZ 169, and OPC-167832 are emphasized. The evolving spectrum of oxazolidinones, such as sutezolid, delpazolid, and TBI-223, all aiming to exceed the efficacy achieved with linezolid yet offer a safer alternative to the potential toxicity, are reviewed. New and exciting prospective agents with novel mechanisms of impact against TB, including 3-aminomethyl benzoxaboroles and telacebec, are underscored. We describe new diaryloquinolines in development, striving to build on the immense success of bedaquiline. Finally, we discuss some of these compounds that have shown encouraging additive or synergistic benefit when used in combination, providing some promise for the future in treating this ancient scourge.

Antibacterial and Antifungal Alkaloids from Asian Angiosperms: Distribution, Mechanisms of Action, Structure-Activity, and Clinical Potentials

The emergence of multidrug-resistant bacteria and fungi requires the development of antibiotics and antifungal agents. This review identified natural products isolated from Asian angiosperms with antibacterial and/or antifungal activities and analyzed their distribution, molecular weights, solubility, and modes of action. All data in this review were compiled from Google Scholar, PubMed, Science Direct, Web of Science, ChemSpider, PubChem, and a library search from 1979 to 2022. One hundred and forty-one antibacterial and/or antifungal alkaloids were identified during this period, mainly from basal angiosperms. The most active alkaloids are mainly planar, amphiphilic, with a molecular mass between 200 and 400 g/mol, and a polar surface area of about 50 Å2, and target DNA and/or topoisomerase as well as the cytoplasmic membrane. 8-Acetylnorchelerythrine, cryptolepine, 8-hydroxydihydrochelerythrine, 6-methoxydihydrosanguinarine, 2'-nortiliacorinine, pendulamine A and B, rhetsisine, sampangine, tiliacorine, tryptanthrin, tylophorinine, vallesamine, and viroallosecurinine yielded MIC ≤ 1 µg/mL and are candidates for the development of lead molecules.

A multidrug efflux protein in Mycobacterium tuberculosis; tap as a potential drug target for drug repurposing

Tuberculosis (TB) is a serious communicative disease caused by Mycobacterium tuberculosis. Although there are vaccines and drugs available to treat the disease, they are not efficient, moreover, multidrug-resistant TB (MDR-TB) become a major hurdle in its therapy. These MDR strains utilize the multidrug efflux pump as a decisive weapon to fight against antitubercular drugs. Tap membrane protein was observed as a crucial multidrug efflux pump in M. tuberculosis and its critical implication in MDR-MTB development makes it an effective drug target. In the present study, we have utilized various in silico approaches to predict the applicability of FDA-approved ion channel inhibitors and blockers as therapeutic leads against Tuberculosis by targeting multidrug efflux protein; Tap in MTB. Tap protein structure is predicted by Phyre2 server followed by model refinement, validation, physio-chemical catheterization and target prediction. Further, the interaction between Tap protein and ligands were analysed by molecular docking and MD simulation run of 100 ns. Based on implication and compatibility, 18 FDA-approved ion channel inhibitors and blockers are selected as a ligand against the Tap protein and eventually observed five ligands; Glimepiride, Flecainide, Flupiritine, Nimodipine and Amlodipine as promising compounds which have exhibited the significant stable interaction with Tap protein and are proposed to modulate or interfere with its activity. These compounds illustrated the substantial docking score and total binding enthalpy more than -7 kcal/mol and -42 kcal/mol respectively which implies that the selected FDA-approved compounds can spontaneously interact with the Tap protein to modulate its function. This study proposed Tap protein as a prominent drug target in MTB and investigated compounds that show considerable interaction with the Tap protein as potential therapeutic molecules. These interactions may lead to modulating or inhibit the activity of drug efflux protein thereby making MTB susceptible to antitubercular drugs.

Mycobacterial Membranes as Actionable Targets for Lipid-Centric Therapy in Tuberculosis

Infectious diseases remain significant health concerns worldwide, and resistance is particularly common in patients with tuberculosis caused by Mycobacterium tuberculosis. The development of anti-infectives with novel modes of action may help overcome resistance. In this regard, membrane-active agents, which modulate membrane components essential for the survival of pathogens, present attractive antimicrobial agents. Key advantages of membrane-active compounds include their ability to target slow-growing or dormant bacteria and their favorable pharmacokinetics. Here, we comprehensively review recent advances in the development of membrane-active chemotypes that target mycobacterial membranes and discuss clinically relevant membrane-active antibacterial agents that have shown promise in counteracting bacterial infections. We discuss the relationship between the membrane properties and the synthetic requirements within the chemical scaffold, as well as the limitations of current membrane-active chemotypes. This review will lay the chemical groundwork for the development of membrane-active antituberculosis agents and will foster the discovery of more effective antitubercular agents.

Investigation of the effect of the calcium channel blocker, verapamil, on the parasite burden, inflammatory response and angiogenesis in experimental Trichinella spiralis infection in mice

Trichinella spiralis larvae have very special characters that make them able to completely transform the function of the affected muscle cells towards a self-serving environment, offering them nourishment and protection via what is known as “nurse cells”. This setting may be affected by drugs that are used for the treatment of co-morbidities and co-infections as calcium channel blockers, which are widely used in clinical practice. In the present study, the effects of verapamil, ivermectin (IVM), and their combined administration on the parasitic burden, immuno-pathology and angiogenesis were investigated during experimental trichinellosis. Estimation of intestinal adult parasitic stages and muscle larvae was done. VEGF gene expression and CD31 immunohistochemical local expression were measured to investigate angiogenesis, in addition to histopathological examination to explore the extent of inflammation. Although verapamil did not have an effect on the adult worm count during the intestinal phase, it induced an anti-inflammatory effect on intestinal pathology. During the muscle phase, it was very effective in reducing the larval count by 93.78%. IVM effectively reduced the worm count by 85.34%, and the muscle larval count by 97.84%, while combined verapamil and IVM administration resulted in a significant reduction in both adult parasites by 69.5% and larval stages by 99%. Both verapamil and IVM and their combination induced a potent decrease in local CD31 protein expression and VEGF gene expression. The important role of calcium and calcium channels during the pathology of trichinellosis, in addition to the pivotal role of calcium on biological processes such as immunity and angiogenesis, make calcium-channel blockers promising candidates for drug repurposing in the management of helminthic infection.

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Verapamil reduces larval count during the muscle phase of trichinellosis.

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The anti-inflammatory effect of verapamil is more prominent in the muscle phase.

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Verapamil and ivermectin reduce microvessel density in T. spiralis-infected muscles.

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Ivermectin is more potent on reducing VEGF mRNA expression than verapamil.

Critical discussion on drug efflux in Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) can withstand months of antibiotic treatment. An important goal of tuberculosis research is to shorten the treatment to reduce the burden on patients, increase adherence to the drug regimen and thereby slow down the spread of drug resistance. Inhibition of drug efflux pumps by small molecules has been advocated as a promising strategy to attack persistent Mtb and shorten therapy. Although mycobacterial drug efflux pumps have been broadly investigated, mechanistic studies are scarce. In this critical review, we shed light on drug efflux in its larger mechanistic context by considering the intricate interplay between membrane transporters annotated as drug efflux pumps, membrane energetics, efflux inhibitors and cell wall biosynthesis processes. We conclude that a great wealth of data on mycobacterial transporters is insufficient to distinguish by what mechanism they contribute to drug resistance. Recent studies suggest that some drug efflux pumps transport structural lipids of the mycobacterial cell wall and that the action of certain drug efflux inhibitors involves dissipation of the proton motive force, thereby draining the energy source of all active membrane transporters. We propose recommendations on the generation and interpretation of drug efflux data to reduce ambiguities and promote assigning novel roles to mycobacterial membrane transporters.

Nifedipine Potentiates Susceptibility of Salmonella Typhimurium to Different Classes of Antibiotics

The calcium channel blocker nifedipine induces cellular iron export, thereby limiting the availability of the essential nutrient iron for intracellular pathogens, resulting in bacteriostatic activity. To study if nifedipine may exert a synergistic anti-microbial activity when combined with antibiotics, we used the mouse macrophage cell line RAW267.4, infected with the intracellular bacterium Salmonella Typhimurium, and exposed the cells to varying concentrations of nifedipine and/or ampicillin, azithromycin and ceftriaxone. We observed a significant additive effect of nifedipine in combination with various antibiotics, which was not observed when using Salmonella, with defects in iron uptake. Of interest, increasing intracellular iron levels increased the bacterial resistance to treatment with antibiotics or nifedipine or their combination. We further showed that nifedipine increases the expression of the siderophore-binding peptide lipocalin-2 and promotes iron storage within ferritin, where the metal is less accessible for bacteria. Our data provide evidence for an additive effect of nifedipine with conventional antibiotics against Salmonella, which is partly linked to reduced bacterial access to iron.

Flunarizine suppresses Mycobacterium tuberculosis growth via calmodulin-dependent phagosome maturation

Tuberculosis (TB), an infectious bacterial disease caused by Mycobacterium tuberculosis (Mtb), is a major cause of death worldwide. Multidrug-resistant TB remains a public health crisis and thus novel effective treatments, such as host-directed therapies (HDTs), are urgently required to overcome the challenges of TB infection. In this study, we evaluated 4 calcium modulators for their effects on Mtb growth in macrophages. Only flunarizine enhanced the bactericidal ability of macrophages against Mtb, which was induced by an increase in phosphorylated calcium/calmodulin (CaM)-dependent protein kinase II (pCaMKII) levels. We further discovered that the expression of CaM was decreased in Mtb-infected macrophages and restored following flunarizine treatment; this was associated with phagolysosome maturation and acidification. Consistent with these findings, the anti-TB ability of macrophages was reduced following the silencing of CaM or inhibition of CAMKII activity. In conclusion, our results demonstrated that flunarizine enhanced the bactericidal ability of macrophages and clarified its CaM-pCAMKII-dependent mechanism. Therefore, our findings strongly support further studies of this currently approved drug as an HDT candidate for TB therapy.

Mechanism of drug resistance in bacteria: efflux pump modulation for designing of new antibiotic enhancers

Drug resistance has now become a serious concern in the domain of microbial infection. Bacteria are becoming smarter by displaying a variety of mechanisms during drug resistance. It is not only helping bacteria to adapt nicely in adverse environment but it also makes a smart system for better availability of nutritional status for microorganisms. In this domain, pathogenic bacteria are extensively studied and their mechanism for drug resistance is well explored. The common modes in bacterial resistance include degradation of antibiotics by enzymes, antibiotic target modification or inactivation by enzymatic actions, complete replacement of antibiotic targets, quorum sensing (QS) mechanism, and efflux pump-based extrusion of antibiotics. In this review, various mechanisms of drug resistance in bacteria have been highlighted with giving the importance of efflux pumps. This can be explored as a knowledge source for the management of a variety of bacterial infections, related disease and vibrant clue for next-generation drug development.

Understanding the Reciprocal Interplay Between Antibiotics and Host Immune System: How Can We Improve the Anti-Mycobacterial Activity of Current Drugs to Better Control Tuberculosis?

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) infection, remains a global health threat despite recent advances and insights into host-pathogen interactions and the identification of diverse pathways that may be novel therapeutic targets for TB treatment. In addition, the emergence and spread of multidrug-resistant Mtb strains led to a low success rate of TB treatments. Thus, novel strategies involving the host immune system that boost the effectiveness of existing antibiotics have been recently suggested to better control TB. However, the lack of comprehensive understanding of the immunomodulatory effects of anti-TB drugs, including first-line drugs and newly introduced antibiotics, on bystander and effector immune cells curtailed the development of effective therapeutic strategies to combat Mtb infection. In this review, we focus on the influence of host immune-mediated stresses, such as lysosomal activation, metabolic changes, oxidative stress, mitochondrial damage, and immune mediators, on the activities of anti-TB drugs. In addition, we discuss how anti-TB drugs facilitate the generation of Mtb populations that are resistant to host immune response or disrupt host immunity. Thus, further understanding the interplay between anti-TB drugs and host immune responses may enhance effective host antimicrobial activities and prevent Mtb tolerance to antibiotic and immune attacks. Finally, this review highlights novel adjunctive therapeutic approaches against Mtb infection for better disease outcomes, shorter treatment duration, and improved treatment efficacy based on reciprocal interactions between current TB antibiotics and host immune cells.

Something Old, Something New: Ion Channel Blockers as Potential Anti-Tuberculosis Agents

Tuberculosis (TB) remains a challenging global health concern and claims more than a million lives every year. We lack an effective vaccine and understanding of what constitutes protective immunity against TB to inform rational vaccine design. Moreover, treatment of TB requires prolonged use of multi-drug regimens and is complicated by problems of compliance and drug resistance. While most Mycobacterium tuberculosis (Mtb) bacilli are quickly killed by the drugs, the prolonged course of treatment is required to clear persistent drug-tolerant subpopulations. Mtb’s differential sensitivity to drugs is, at least in part, determined by the interaction between the bacilli and different host macrophage populations. Therefore, to design better treatment regimens for TB, we need to understand and modulate the heterogeneity and divergent responses that Mtb bacilli exhibit within macrophages. However, developing drugs de-novo is a long and expensive process. An alternative approach to expedite the development of new TB treatments is to repurpose existing drugs that were developed for other therapeutic purposes if they also possess anti-tuberculosis activity. There is growing interest in the use of immune modulators to supplement current anti-TB drugs by enhancing the host’s antimycobacterial responses. Ion channel blocking agents are among the most promising of the host-directed therapeutics. Some ion channel blockers also interfere with the activity of mycobacterial efflux pumps. In this review, we discuss some of the ion channel blockers that have shown promise as potential anti-TB agents.

Determination of Verapamil Hydrochloride and Norverapamil Hydrochloride in Rat Plasma by Capillary Electrophoresis With End-Column Electrochemiluminescence Detection and Their Pharmacokinetics Study

In this study, we developed a new method for simultaneous determination of verapamil hydrochloride (VerHCl) and its metabolite norverapamil hydrochloride (NorHCl) by using the capillary electrophoresis-electrochemiluminescence. Under optimized experimental conditions, the linear ranges of the VerHCl and NorHCl concentrations were 0.015-10.0 and 0.060-10.0 μg/mL, respectively. The linearity relations were determined using the respective regression equations y = 581.2x + 19.94 and y = 339.4x + 29.16. The respective limits of detection (S/N = 3) were 0.006 and 0.024 μg/mL. The proposed method was used to study the pharmacokinetics of both agents in rat plasma. The maximum concentration (Cmax), half-life time (T1/2) and time to peak (Tmax) were 683.21 ± 74.81 ng/mL, 0.52 ± 0.21 h and 2.49 ± 0.32 h for VerHCl and 698.42 ± 71.45 ng/mL, 1.14 ± 0.26 h and 2.83 ± 0.23 h for NorHCl, respectively, following oral administration of 10 mg/kg VerHCl.

Repurposing Immunomodulatory Drugs to Combat Tuberculosis

Tuberculosis (TB) is an infectious disease caused by an obligate intracellular pathogen, Mycobacterium tuberculosis (M.tb) and is responsible for the maximum number of deaths due to a single infectious agent. Current therapy for TB, Directly Observed Treatment Short-course (DOTS) comprises multiple antibiotics administered in combination for 6 months, which eliminates the bacteria and prevents the emergence of drug-resistance in patients if followed as prescribed. However, due to various limitations viz., severe toxicity, low efficacy and long duration; patients struggle to comply with the prescribed therapy, which leads to the development of drug resistance (DR). The emergence of resistance to various front-line anti-TB drugs urgently require the introduction of new TB drugs, to cure DR patients and to shorten the treatment course for both drug-susceptible and resistant populations of bacteria. However, the development of a novel drug regimen involving 2-3 new and effective drugs will require approximately 20-30 years and huge expenditure, as seen during the discovery of bedaquiline and delamanid. These limitations make the field of drug-repurposing indispensable and repurposing of pre-existing drugs licensed for other diseases has tremendous scope in anti-DR-TB therapy. These repurposed drugs target multiple pathways, thus reducing the risk of development of drug resistance. In this review, we have discussed some of the repurposed drugs that have shown very promising results against TB. The list includes sulfonamides, sulfanilamide, sulfadiazine, clofazimine, linezolid, amoxicillin/clavulanic acid, carbapenems, metformin, verapamil, fluoroquinolones, statins and NSAIDs and their mechanism of action with special emphasis on their immunomodulatory effects on the host to attain both host-directed and pathogen-targeted therapy. We have also focused on the studies involving the synergistic effect of these drugs with existing TB drugs in order to translate their potential as adjunct therapies against TB.

The integrated stress response mediates necrosis in murine Mycobacterium tuberculosis granulomas

The mechanism by which only some individuals infected with Mycobacterium tuberculosis develop necrotic granulomas with progressive disease while others form controlled granulomas that contain the infection remains poorly defined. Mice carrying the sst1-suscepible (sst1S) genotype develop necrotic inflammatory lung lesions, similar to human tuberculosis (TB) granulomas, which are linked to macrophage dysfunction, while their congenic counterpart (B6) mice do not. In this study we report that (a) sst1S macrophages developed aberrant, biphasic responses to TNF characterized by superinduction of stress and type I interferon pathways after prolonged TNF stimulation; (b) the late-stage TNF response was driven via a JNK/IFN-β/protein kinase R (PKR) circuit; and (c) induced the integrated stress response (ISR) via PKR-mediated eIF2α phosphorylation and the subsequent hyperinduction of ATF3 and ISR-target genes Chac1, Trib3, and Ddit4. The administration of ISRIB, a small-molecule inhibitor of the ISR, blocked the development of necrosis in lung granulomas of M. tuberculosis-infected sst1S mice and concomitantly reduced the bacterial burden. Hence, induction of the ISR and the locked-in state of escalating stress driven by the type I IFN pathway in sst1S macrophages play a causal role in the development of necrosis in TB granulomas. Interruption of the aberrant stress response with inhibitors such as ISRIB may offer novel host-directed therapy strategies.

PNA-mediated efflux inhibition as a therapeutic strategy towards overcoming drug resistance in Mycobacterium smegmatis

The emergence of antibiotic-resistant strains of Mycobacterium tuberculosis and the decelerating development of new and effective antibiotics has impaired the treatment of tuberculosis (TB). Efflux pump inhibitors (EPIs) have the potential to improve the efficacy of existing anti-TB drugs although with toxicity limitations. Peptide nucleic acids (PNAs), oligonucleotide mimics, by virtue of their high nucleic acid binding specificity have the capability to overcome this drawback. We, therefore, investigated the efflux pump inhibitory properties of a PNA designed against an efflux pump of Mycobacterium smegmatis. LfrA, an efflux pump found in M. smegmatis, is majorly involved in conferring innate drug resistance to this strain and, therefore, was selected as a target for gene silencing via PNA. qRT-PCR and EtBr assays confirmed the EPI activity of the anti-lfrA PNA. On testing the effect of the anti-lfrA PNA on the bactericidal activity of a fluoroquinolone, norfloxacin, we observed that 5 μM of anti-lfrA PNA in combination with norfloxacin led to an enhanced killing of up to 2.5 log-fold against wild-type and a lab-generated multidrug resistant strain, exemplifying its potential in countering resistance. Improved efficacy was also observed against intra-macrophage mycobacteria, where the drug-PNA combination enhanced bacterial clearance by 1.3 log-fold. Further, no toxicity was observed with PNA concentrations up to 4 times higher than the efficacious anti-lfrA PNA concentration. Thus, PNA, as an adjuvant, presents a novel and viable approach to rejuvenate anti-TB therapeutics.

Are antibacterial effects of non-antibiotic drugs random or purposeful because of a common evolutionary origin of bacterial and mammalian targets?

Purpose

Advances in structural biology, genetics, bioinformatics, etc. resulted in the availability of an enormous pool of information enabling the analysis of the ancestry of pro- and eukaryotic genes and proteins.

Methods

This review summarizes findings of structural and/or functional homologies of pro- and eukaryotic enzymes catalysing analogous biological reactions because of their highly conserved active centres so that non-antibiotics interacted with bacterial targets.

Results

Protease inhibitors such as staurosporine or camostat inhibited bacterial serine/threonine or serine/tyrosine protein kinases, serine/threonine phosphatases, and serine/threonine kinases, to which penicillin-binding-proteins are linked, so that these drugs synergized with β-lactams, reverted aminoglycoside-resistance and attenuated bacterial virulence. Calcium antagonists such as nitrendipine or verapamil blocked not only prokaryotic ion channels but interacted with negatively charged bacterial cell membranes thus disrupting membrane energetics and inducing membrane stress response resulting in inhibition of P-glycoprotein such as bacterial pumps thus improving anti-mycobacterial activities of rifampicin, tetracycline, fluoroquinolones, bedaquilin and imipenem-activity against Acinetobacter spp. Ciclosporine and tacrolimus attenuated bacterial virulence. ACE-inhibitors like captopril interacted with metallo-β-lactamases thus reverting carbapenem-resistance; prokaryotic carbonic anhydrases were inhibited as well resulting in growth impairment. In general, non-antibiotics exerted weak antibacterial activities on their own but synergized with antibiotics, and/or reverted resistance and/or attenuated virulence.

Conclusions

Data summarized in this review support the theory that prokaryotic proteins represent targets for non-antibiotics because of a common evolutionary origin of bacterial- and mammalian targets resulting in highly conserved active centres of both, pro- and eukaryotic proteins with which the non-antibiotics interact and exert antibacterial actions.

Loperamide exerts a direct bactericidal effect against M. tuberculosis, M. bovis, M. terrae and M. smegmatis

Tuberculosis (TB) is caused by Mycobacterium tuberculosis. TB is highly prevalent, characterized by the constant occurrence of drug-resistant cases, and confounded by the incidence of respiratory disease caused by non-tuberculous mycobacteria (NTB). Expanding the spectrum of drugs for the treatment of TB is indispensable. Loperamide, an antidiarrhoeal drug, enhances immune-driven antimycobacterial activity, and we aimed to evaluate its bactericidal activity against M. tuberculosis, Mycobacterium bovis BCG, Mycobacterium terrae and Mycobacterium smegmatis. Loperamide exhibited an inhibitory effect against all mycobacterial species tested, with MICs of 100 and 150 μg ml^-1 . Thus, loperamide is a mycobactericidal drug with potential as adjunctive therapy for TB and NTB infections.

Ion Transport Modulators as Antimycobacterial Agents

There is an urgent need for better and safer therapeutic interventions for tuberculosis (TB). We assessed the effects of FDA-approved ion transport modulators, namely, ambroxol HCl, amiloride HCl, diazoxide, digoxin, furosemide, hydrochlorothiazide (HCTZ), metformin, omeprazole, pantoprazole, phenytoin, verapamil, and drug X and Y on the growth of free and intracellular Mycobacterium bovis BCG. Free and intracellular M. bovis BCG were cultured in the presence or absence of the test drugs for 3 to 9 days and then quantified. For both free and intracellular bacteria, cultures that were exposed to furosemide, phenytoin, or drug Y yielded lower bacteria counts compared to drug-free controls (p < 0.05). The same was observed with diazoxide, HCTZ, verapamil, and drug X, but only for intracellular M. bovis BCG (p < 0.05). To assess the effects of the drugs on bactericidal activity of rifampicin, free and intracellular M. bovis BCG were treated with rifampicin alone or in combination with each of the thirteen test drugs for 3 to 9 days. For extracellular bacteria, higher bacteria clearance rates were observed in cultures exposed to rifampicin in combination with amiloride HCl, diazoxide, digoxin, furosemide, HCTZ, metformin, pantoprazole, phenytoin, drug X, or drug Y than those exposed to rifampicin alone, indicating that rifampicin had a synergistic effect with these test drugs. Rifampicin was also synergistic with ambroxol HCl, diazoxide, digoxin, furosemide, HCTZ, omeprazole, pantoprazole, phenytoin, verapamil, and drug X against intracellular M. bovis BCG. The antimycobacterial properties exhibited by the ion transport modulators in this study make them viable candidates as adjuncts to the current anti-TB regimens.

Mechanisms of Antibiotic Tolerance in Mycobacterium avium Complex: Lessons From Related Mycobacteria

Mycobacterium avium complex (MAC) species are the most commonly isolated nontuberculous mycobacteria to cause pulmonary infections worldwide. The lengthy and complicated therapy required to cure lung disease due to MAC is at least in part due to the phenomenon of antibiotic tolerance. In this review, we will define antibiotic tolerance and contrast it with persistence and antibiotic resistance. We will discuss physiologically relevant stress conditions that induce altered metabolism and antibiotic tolerance in mycobacteria. Next, we will review general molecular mechanisms underlying bacterial antibiotic tolerance, particularly those described for MAC and related mycobacteria, including Mycobacterium tuberculosis, with a focus on genes containing significant sequence homology in MAC. An improved understanding of antibiotic tolerance mechanisms can lay the foundation for novel approaches to target antibiotic-tolerant mycobacteria, with the goal of shortening the duration of curative treatment and improving survival in patients with MAC.

The Impact of Hypertension and Use of Calcium Channel Blockers on Tuberculosis Treatment Outcomes

BACKGROUND

Hypertension induces systemic inflammation, but its impact on the outcome of infectious diseases like tuberculosis (TB) is unknown. Calcium channel blockers (CCB) improve TB treatment outcomes in pre-clinical models, but their effect in patients with TB remain unclear.

METHODS

This retrospective cohort study, including all patients > 18 years receiving treatment for culture-confirmed, drug-sensitive TB from 2000 to 2016 at the National Taiwan University Hospital, assessed the association of hypertension and CCB use with all-cause and infection-related mortality during the first 9 months of TB treatment, as well as sputum-smear microscopy and sputum-culture positivity at 2 and 6 months.

RESULTS

1052 of the 2894 patients (36.4%) had hypertension. Multivariable analysis revealed that hypertension was associated with increased mortality due to all causes (HR 1.57, 95% confidence interval[CI], 1.23-1.99) and infections (HR 1.87, 95%CI, 1.34-2.6), but there was no statistical difference in microbiological outcomes when stratified based on hypertensive group. Dihydropyridine-CCB (DHP-CCB) use was associated with reduced all-cause mortality (HR 0.67, 95%CI: 0.45-0.98) only by univariate Cox regression. There was no association between DHP-CCB use and infection-related mortality (HR 0.78, 95%CI: 0.46-1.34) or microbiological outcomes in univariate or multivariate regression analyses.

CONCLUSIONS

Patients with hypertension have increased all-cause mortality and infection-related mortality during the 9 months following TB treatment initiation. DHP-CCB use may lower all-cause mortality in TB patients with hypertension. The presence of hypertension or the use of CCB did not result in a significant change in microbiological outcomes.

Efflux pump inhibitors as a promising adjunct therapy against drug resistant tuberculosis: a new strategy to revisit mycobacterial targets and repurpose old drugs

INTRODUCTION

In 2018, an estimated 377,000 people developed multidrug-resistant tuberculosis (MDR-TB), urging for new effective treatments. In the last years, it has been accepted that efflux pumps play an important role in the evolution of drug resistance. Strategies are required to mitigate the consequences of the activity of efflux pumps.

AREAS COVERED

Based upon the literature available in PubMed, up to February 2020, on the diversity of efflux pumps in Mycobacterium tuberculosis and their association with drug resistance, studies that identified efflux inhibitors and their effect on restoring the activity of antimicrobials subjected to efflux are reviewed. These support a new strategy for the development of anti-TB drugs, including efflux inhibitors, using in silico drug repurposing.

EXPERT OPINION

The current literature highlights the contribution of efflux pumps in drug resistance in M. tuberculosis and that efflux inhibitors may help to ensure the effectiveness of anti-TB drugs. However, despite the usefulness of efflux inhibitors in in vitro studies, in most cases their application in vivo is restricted due to toxicity. In a time when new drugs are needed to fight MDR-TB and extensively drug-resistant TB, cost-effective strategies to identify safer efflux inhibitors should be implemented in drug discovery programs.

Preclinical Evidence of Nanomedicine Formulation to Target Mycobacterium tuberculosis at Its Bone Marrow Niche

One-third of the world’s population is estimated to be latently infected with Mycobacterium tuberculosis (Mtb). Recently, we found that dormant Mtb hides in bone marrow mesenchymal stem cells (BM-MSCs) post-chemotherapy in mice model and in clinical subjects. It is known that residual Mtb post-chemotherapy may be responsible for increased relapse rates. However, strategies for Mtb clearance post-chemotherapy are lacking. In this study, we engineered and formulated novel bone-homing PEGylated liposome nanoparticles (BTL-NPs) which actively targeted the bone microenvironment leading to Mtb clearance. Targeting of BM-resident Mtb was carried out through bone-homing liposomes tagged with alendronate (Ald). BTL characterization using TEM and DLS showed that the size of bone-homing isoniazid (INH) and rifampicin (RIF) BTLs were 100 ± 16.3 nm and 84 ± 18.4 nm, respectively, with the encapsulation efficiency of 69.5% ± 4.2% and 70.6% ± 4.7%. Further characterization of BTLs, displayed by sustained in vitro release patterns, increased in vivo tissue uptake and enhanced internalization of BTLs in RAW cells and CD271+BM-MSCs. The efficacy of isoniazid (INH)- and rifampicin (RIF)-loaded BTLs were shown using a mice model where the relapse rate of the tuberculosis was decreased significantly in targeted versus non-targeted groups. Our findings suggest that BTLs may play an important role in developing a clinical strategy for the clearance of dormant Mtb post-chemotherapy in BM cells.

Potential anti-TB investigational compounds and drugs with repurposing potential in TB therapy: a conspectus

The latest WHO report estimates about 1.6 million global deaths annually from TB, which is further exacerbated by drug-resistant (DR) TB and comorbidities with diabetes and HIV. Exiguous dosing, incomplete treatment course, and the ability of the tuberculosis bacilli to tolerate and survive current first-line and second-line anti-TB drugs, in either their latent state or active state, has resulted in an increased prevalence of multidrug-resistant (MDR), extensively drug-resistant (XDR), and totally drug-resistant TB (TDR-TB). Although a better understanding of the TB microanatomy, genome, transcriptome, proteome, and metabolome, has resulted in the discovery of a few novel promising anti-TB drug targets and diagnostic biomarkers of late, no new anti-TB drug candidates have been approved for routine therapy in over 50 years, with only bedaquiline, delamanid, and pretomanid recently receiving tentative regulatory approval. Considering this, alternative approaches for identifying possible new anti-TB drug candidates, for effectively eradicating both replicating and non-replicating Mycobacterium tuberculosis, are still urgently required. Subsequently, several antibiotic and non-antibiotic drugs with known treatment indications (TB targeted and non-TB targeted) are now being repurposed and/or derivatized as novel antibiotics for possible use in TB therapy. Insights gathered here reveal that more studies focused on drug-drug interactions between licensed and potential lead anti-TB drug candidates need to be prioritized. This write-up encapsulates the most recent findings regarding investigational compounds with promising anti-TB potential and drugs with repurposing potential in TB therapy.

Host-Directed Therapies and Anti-Virulence Compounds to Address Anti-Microbial Resistant Tuberculosis Infection

Despite global efforts to contain tuberculosis (TB), the disease remains a leading cause of morbidity and mortality worldwide, further exacerbated by the increased resistance to antibiotics displayed by the tubercle bacillus Mycobacterium tuberculosis. In order to treat drug-resistant TB, alternative or complementary approaches to standard anti-TB regimens are being explored. An area of active research is represented by host-directed therapies which aim to modulate the host immune response by mitigating inflammation and by promoting the antimicrobial activity of immune cells. Additionally, compounds that reduce the virulence of M. tuberculosis, for instance by targeting the major virulence factor ESX-1, are being given increased attention by the TB research community. This review article summarizes the current state of the art in the development of these emerging therapies against TB.

Calcium Signaling Commands Phagosome Maturation Process

Phagosome-lysosome (P-L) fusion is one of the central immune-effector responses of host. It is known that phagosome maturation process is associated with numerous signaling cascades and among these, important role of calcium (Ca²⁺) signaling has been realized recently. Ca²⁺ plays key roles in actin rearrangement, activation of NADPH oxidase and protein kinase C (PKC). Involvement of Ca²⁺ in these cellular processes directs phagosomal maturation process. Some of the intracellular pathogens have acquired the strategies to modulate Ca²⁺ associated pathways to block P-L fusion process. In this review we have described the mechanism of Ca²⁺ signals that influence P-L fusion by controlling ROS, actin and PKC signaling cascades. We have also discussed the strategies implemented by the intracellular pathogens to manipulate Ca²⁺ signaling to consequently subvert P-L fusion. A detail study of factors associated in manipulating Ca²⁺ signaling may provide new insights for the development of therapeutic tools for more effective treatment options against infectious diseases.

Emerging opportunities of exploiting mycobacterial electron transport chain pathway for drug-resistant tuberculosis drug discovery

Introduction: Tuberculosis (TB) is a leading infectious disease worldwide whose chemotherapy is challenged by the continued rise of drug resistance. This epidemic urges the need to discover anti-TB drugs with novel modes of action.Areas covered: The mycobacterial electron transport chain (ETC) pathway represents a hub of anti-TB drug targets. Herein, the authors highlight the various targets within the mycobacterial ETC and highlight some of the promising ETC-targeted drugs and clinical candidates that have been discovered or repurposed. Furthermore, recent breakthroughs in the availability of X-ray and/or cryo-EM structures of some targets are discussed, and various opportunities of exploiting these structures for the discovery of new anti-TB drugs are emphasized.Expert opinion: The drug discovery efforts targeting the ETC pathway have led to the FDA approval of bedaquiline, a F_OF₁-ATP synthase inhibitor, and the discovery of Q203, a clinical candidate drug targeting the mycobacterial cytochrome bcc-aa3 supercomplex. Moreover, clofazimine, a proposed prodrug competing with menaquinone for its reduction by mycobacterial NADH dehydrogenase 2, has been repurposed for TB treatment. Recently available structures of the mycobacterial ATP synthase C9 rotary ring and the cytochrome bcc-aa3 supercomplex represent further opportunities for the structure-based drug design (SBDD) of the next-generation of inhibitors against Mycobacterium tuberculosis.

Transcriptomic Signatures Predict Regulators of Drug Synergy and Clinical Regimen Efficacy against Tuberculosis

Multidrug combination therapy is an important strategy for treating tuberculosis, the world’s deadliest bacterial infection. Long treatment durations and growing rates of drug resistance have created an urgent need for new approaches to prioritize effective drug regimens. Hence, we developed a computational model called INDIGO-MTB that identifies synergistic drug regimens from an immense set of possible drug combinations using the pathogen response transcriptome elicited by individual drugs. Although the underlying input data for INDIGO-MTB was generated under in vitro broth culture conditions, the predictions from INDIGO-MTB correlated significantly with in vivo drug regimen efficacy from clinical trials. INDIGO-MTB also identified the transcription factor Rv1353c as a regulator of multiple drug interaction outcomes, which could be targeted for rationally enhancing drug synergy.

The rapid spread of multidrug-resistant strains has created a pressing need for new drug regimens to treat tuberculosis (TB), which kills 1.8 million people each year. Identifying new regimens has been challenging due to the slow growth of the pathogen Mycobacterium tuberculosis (MTB), coupled with the large number of possible drug combinations. Here we present a computational model (INDIGO-MTB) that identified synergistic regimens featuring existing and emerging anti-TB drugs after screening in silico more than 1 million potential drug combinations using MTB drug transcriptomic profiles. INDIGO-MTB further predicted the gene Rv1353c as a key transcriptional regulator of multiple drug interactions, and we confirmed experimentally that Rv1353c upregulation reduces the antagonism of the bedaquiline-streptomycin combination. A retrospective analysis of 57 clinical trials of TB regimens using INDIGO-MTB revealed that synergistic combinations were significantly more efficacious than antagonistic combinations (P value = 1 × 10⁻⁴) based on the percentage of patients with negative sputum cultures after 8 weeks of treatment. Our study establishes a framework for rapid assessment of TB drug combinations and is also applicable to other bacterial pathogens.

Potential impact of efflux pump genes in mediating rifampicin resistance in clinical isolates of Mycobacterium tuberculosis from India

Despite the consideration of chromosomal mutations as the major cause of rifampicin (RIF) resistance in M. tuberculosis, the role of other mechanisms such as efflux pumps cannot be ruled out. We evaluated the role of four efflux pumps viz., MmpL2 (Rv0507), MmpL5 (Rv0676c), Rv0194 and Rv1250 in providing RIF resistance in M. tuberculosis. The real time expression of the efflux pumps was analyzed in 16 RIF resistant and 11 RIF susceptible clinical isolates of M. tuberculosis after exposure to RIF. Expression of efflux pumps in these isolates was also correlated with mutations in the rpoB gene and MICs of RIF in the presence and absence of efflux pump inhibitors. Under RIF stress, Rv0194 was induced in 8/16 (50%) RIF resistant and 2/11 (18%) RIF susceptible isolates; mmpL5 in 7/16 (44%) RIF resistant and 1/11 (9%) RIF susceptible isolates; Rv1250 in 4/16 (25%) RIF resistant and 2/11 (18%) RIF susceptible isolates; and mmpL2 was upregulated in 2/16 (12.5%) RIF resistant and 1/11 (9%) RIF susceptible isolates. This preliminary study did not find any association between Rv0194, MmpL2, MmpL5 and Rv1250 and RIF resistance. However, the overexpression of Rv0194 and mmpL5 in greater number of RIF resistant isolates as compared to RIF susceptible isolates and expression of Rv0194 in wild type (WT) resistant isolates suggests a need for further investigations.

The Contribution of Efflux Pumps in Mycobacterium abscessus Complex Resistance to Clarithromycin

The basis of drug resistance in Mycobacterium abscessus is still poorly understood. Nevertheless, as seen in other microorganisms, the efflux of antimicrobials may also play a role in M. abscessus drug resistance. Here, we investigated the role of efflux pumps in clarithromycin resistance using nine clinical isolates of M. abscessus complex belonging to the T28 erm(41) sequevar responsible for the inducible resistance to clarithromycin. The strains were characterized by drug susceptibility testing in the presence/absence of the efflux inhibitor verapamil and by genetic analysis of drug-resistance-associated genes. Efflux activity was quantified by real-time fluorometry. Efflux pump gene expression was studied by RT-qPCR upon exposure to clarithromycin. Verapamil increased the susceptibility to clarithromycin from 4- to ≥64-fold. The efflux pump genes MAB_3142 and MAB_1409 were found consistently overexpressed. The results obtained demonstrate that the T28 erm(41) polymorphism is not the sole cause of the inducible clarithromycin resistance in M.abscessus subsp. abscessus or bolletii with efflux activity providing a strong contribution to clarithromycin resistance. These data highlight the need for further studies on M. abscessus efflux response to antimicrobial stress in order to implement more effective therapeutic regimens and guidance in the development of new drugs against these bacteria.

TNF Induces Pathogenic Programmed Macrophage Necrosis in Tuberculosis through a Mitochondrial-Lysosomal-Endoplasmic Reticulum Circuit

Necrosis of infected macrophages constitutes a critical pathogenetic event in tuberculosis by releasing mycobacteria into the growth-permissive extracellular environment. In zebrafish infected with Mycobacterium marinum or Mycobacterium tuberculosis, excess tumor necrosis factor triggers programmed necrosis of infected macrophages through the production of mitochondrial reactive oxygen species (ROS) and the participation of cyclophilin D, a component of the mitochondrial permeability transition pore. Here, we show that this necrosis pathway is not mitochondrion-intrinsic but results from an inter-organellar circuit initiating and culminating in the mitochondrion. Mitochondrial ROS induce production of lysosomal ceramide that ultimately activates the cytosolic protein BAX. BAX promotes calcium flow from the endoplasmic reticulum into the mitochondrion through ryanodine receptors, and the resultant mitochondrial calcium overload triggers cyclophilin-D-mediated necrosis. We identify ryanodine receptors and plasma membrane L-type calcium channels as druggable targets to intercept mitochondrial calcium overload and necrosis of mycobacterium-infected zebrafish and human macrophages.

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TNF induces mitochondrial ROS to cause necrosis of mycobacterium-infected macrophages

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Mitochondrial ROS activate lysosomal enzymes that lead to BAX activation

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BAX activates ER ryanodine receptors to cause Ca²⁺ flow into the mitochondrion

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Drugs preventing mitochondrial Ca²⁺ overload prevent pathogenic macrophage necrosis in TB

Non-antibiotic adjunctive therapy: A promising approach to fight tuberculosis

Tuberculosis (TB) is currently a clinical and public health problem. There is a concern about the emergence and development of multidrug-resistant (MDR-TB) and extensively drug-resistant (XDR-TB) species. Additionally, the lack of effective vaccines is another limitation to control the related infections. To overcome these problems various approaches have been pursued such as finding novel drug candidates with a new mechanism of action or repurposing conventional antibiotics. However, these strategies are still far from clinical application. Hence, the use of adjunctive therapy has been suggested for TB. In this paper, we review non-antibiotic adjunctive treatment options for TB. Natural products, vitamins, micronutrients, and trace elementals, as well as non-antibiotic drugs, are examples of agents which have been used as adjunctive therapies. The use of these adjunctive therapies has been shown to improve disease outcomes and reduce the adverse effects of antibiotic drugs. Employing these agents, either alone or in combination with antibiotics, might be considered as a promising approach to control TB infections and achieve better clinical outcomes. However, supportive evidence from randomized controlled trials is still scant and merits further investigations.

Clinical Management of Drug-resistant Mycobacterium tuberculosis Strains: Pathogen-targeted Versus Host-directed Treatment Approaches

Background:

Despite exerted efforts to control and treat Mycobacterium tuberculosis (MTB) strains, Tuberculosis (TB) remains a public health menace. The emergence of complex drug-resistant profiles, such as multi-drug resistant and extensively drug-resistant MTB strains, emphasizes the need for early diagnosis of resistant cases, shorter treatment options, and effective medical interventions.

Objective:

Solutions for better clinical management of drug-resistant cases are either pathogencentered (novel chemotherapy agents) or host-directed approaches (modulating host immune response to prevent MTB invasion and pathogenesis).

Results:

Despite the overall potentiality of several chemotherapy agents, it is feared that their effectiveness could be challenged by sequential pathogen adaptation tactics. On the contrary, host-directed therapy options might offer a long-term conceivable solution.

Conclusion:

This review discusses the main suggestions proposed so far to resolve the clinical challenges associated with drug resistance, in the context of TB. These suggestions include novel drug delivery approaches that could optimize treatment outcome and increase patients’ compliance to the treatment.

Sodium Hyaluronate Nanocomposite Respirable Microparticles to Tackle Antibiotic Resistance with Potential Application in Treatment of Mycobacterial Pulmonary Infections

Tuberculosis resistant cases have been estimated to grow every year. Besides Mycobacterium tuberculosis, other mycobacterial species are responsible for an increasing number of difficult-to-treat infections. To increase efficacy of pulmonary treatment of mycobacterial infections an inhalable antibiotic powder targeting infected alveolar macrophages (AMs) and including an efflux pump inhibitor was developed. Low molecular weight sodium hyaluronate sub-micron particles were efficiently loaded with rifampicin, isoniazid and verapamil, and transformed in highly respirable microparticles (mean volume diameter: 1 μm) by spray drying. These particles were able to regenerate their original size upon contact with aqueous environment with mechanical stirring or sonication. The in vitro drugs release profile from the powder was characterized by a slow release rate, favorable to maintain a high drug level inside AMs. In vitro antimicrobial activity and ex vivo macrophage infection assays employing susceptible and drug resistant strains were carried out. No significant differences were observed when the powder, which did not compromise the AMs viability after a five-day exposure, was compared to the same formulation without verapamil. However, both preparations achieved more than 80% reduction in bacterial viability irrespective of the drug resistance profile. This approach can be considered appropriate to treat mycobacterial respiratory infections, regardless the level of drug resistance.

Reversing resistance to counter antimicrobial resistance in the World Health Organisation's critical priority of most dangerous pathogens

The speed at which bacteria develop antimicrobial resistance far outpace drug discovery and development efforts resulting in untreatable infections. The World Health Organisation recently released a list of pathogens in urgent need for the development of new antimicrobials. The organisms that are listed as the most critical priority are all Gram-negative bacteria resistant to the carbapenem class of antibiotics. Carbapenem resistance in these organisms is typified by intrinsic resistance due to the expression of antibiotic efflux pumps and the permeability barrier presented by the outer membrane, as well as by acquired resistance due to the acquisition of enzymes able to degrade β-lactam antibiotics. In this perspective article we argue the case for reversing resistance by targeting these resistance mechanisms - to increase our arsenal of available antibiotics and drastically reduce antibiotic discovery times - as the most effective way to combat antimicrobial resistance in these high priority pathogens.

A Protein Complex from Human Milk Enhances the Activity of Antibiotics and Drugs against Mycobacterium tuberculosis

Mycobacterium tuberculosis, the causative agent of human tuberculosis (TB), has surpassed HIV/AIDS as the leading cause of death from a single infectious agent. The increasing occurrence of drug-resistant strains has become a major challenge for health care systems and, in some cases, has rendered TB untreatable. However, the development of new TB drugs has been plagued with high failure rates and costs. Alternative strategies to increase the efficacy of current TB treatment regimens include host-directed therapies or agents that make M. tuberculosis more susceptible to existing TB drugs. In this study, we show that HAMLET, an α-lactalbumin-oleic acid complex derived from human milk, has bactericidal activity against M. tuberculosis HAMLET consists of a micellar oleic acid core surrounded by a shell of partially denatured α-lactalbumin molecules and unloads oleic acid into cells upon contact with lipid membranes. At sublethal concentrations, HAMLET potentiated a remarkably broad array of TB drugs and antibiotics against M. tuberculosis For example, the minimal inhibitory concentrations of rifampin, bedaquiline, delamanid, and clarithromycin were decreased by 8- to 16-fold. HAMLET also killed M. tuberculosis and enhanced the efficacy of TB drugs inside macrophages, a natural habitat of M. tuberculosis Previous studies showed that HAMLET is stable after oral delivery in mice and nontoxic in humans and that it is possible to package hydrophobic compounds in the oleic acid core of HAMLET to increase their solubility and metabolic stability. The potential of HAMLET and other liprotides as drug delivery and sensitization agents in TB chemotherapy is discussed here.

Modulatory effects of verapamil in rifampicin activity against Mycobacterium tuberculosis

AIM

To evaluate modulatory effect of verapamil (VP) in rifampicin (RIF) activity and its effect in efflux pumps (EPs) transcript levels in Mycobacterium tuberculosis.

MATERIALS & METHODS

RIF and VP minimal inhibitory concentration, combinatory effect and detection of mutations were determined in 16 isolates. EPs transcript levels were determined in four isolates by real-time PCR after exposure to drugs.

RESULTS

VP showed good combinatory effect among RIF-resistant isolates. This effect was also observed in the relative transcript levels of EPs, mainly after 72 h of exposure, depending on the EP gene, genotype and the resistance profile of the isolate.

CONCLUSION

Additional regulatory mechanisms in the EP activities, as well as, interactions with other drug-specific resistance mechanisms need further investigation in M. tuberculosis.