Comparative in vitro activity of phenothiazines against multidrug-resistant Mycobacterium tuberculosis

Bioenergetic Inhibitors: Antibiotic Efficacy and Mechanisms of Action in Mycobacterium tuberculosis

Development of novel anti-tuberculosis combination regimens that increase efficacy and reduce treatment timelines will improve patient compliance, limit side-effects, reduce costs, and enhance cure rates. Such advancements would significantly improve the global TB burden and reduce drug resistance acquisition. Bioenergetics has received considerable attention in recent years as a fertile area for anti-tuberculosis drug discovery. Targeting the electron transport chain (ETC) and oxidative phosphorylation machinery promises not only to kill growing cells but also metabolically dormant bacilli that are inherently more drug tolerant. Over the last two decades, a broad array of drugs targeting various ETC components have been developed. Here, we provide a focused review of the current state of art of bioenergetic inhibitors of Mtb with an in-depth analysis of the metabolic and bioenergetic disruptions caused by specific target inhibition as well as their synergistic and antagonistic interactions with other drugs. This foundation is then used to explore the reigning theories on the mechanisms of antibiotic-induced cell death and we discuss how bioenergetic inhibitors in particular fail to be adequately described by these models. These discussions lead us to develop a clear roadmap for new lines of investigation to better understand the mechanisms of action of these drugs with complex mechanisms as well as how to leverage that knowledge for the development of novel, rationally-designed combination therapies to cure TB.

Targeting bioenergetics is key to counteracting the drug-tolerant state of biofilm-grown bacteria

Embedded in an extracellular matrix, biofilm-residing bacteria are protected from diverse physicochemical insults. In accordance, in the human host the general recalcitrance of biofilm-grown bacteria hinders successful eradication of chronic, biofilm-associated infections. In this study, we demonstrate that upon addition of promethazine, an FDA approved drug, antibiotic tolerance of in vitro biofilm-grown bacteria can be abolished. We show that following the addition of promethazine, diverse antibiotics are capable of efficiently killing biofilm-residing cells at minimal inhibitory concentrations. Synergistic effects could also be observed in a murine in vivo model system. PMZ was shown to increase membrane potential and interfere with bacterial respiration. Of note, antibiotic killing activity was elevated when PMZ was added to cells grown under environmental conditions that induce low intracellular proton levels. Our results imply that biofilm-grown bacteria avoid antibiotic killing and become tolerant by counteracting intracellular alkalization through the adaptation of metabolic and transport functions. Abrogation of antibiotic tolerance by interfering with the cell’s bioenergetics promises to pave the way for successful eradication of biofilm-associated infections. Repurposing promethazine as a biofilm-sensitizing drug has the potential to accelerate the introduction of new treatments for recalcitrant, biofilm-associated infections into the clinic.

At sub-minimal inhibitory concentrations, phenothiazines have been shown to inhibit virulence as well as the formation of biofilms in a wide range of different bacterial pathogens. In this study, we analyzed the anti-bacterial effect of the FDA-approved drug, promethazine, on biofilm-grown Pseudomonas aeruginosa. We demonstrate that PMZ interferes with bacterial bioenergetics and sensitizes biofilm-grown P. aeruginosa cells to bactericidal activity of several different classes of antibiotics by several orders of magnitude. This effect was most pronounced when cells were grown under environmental conditions that induce low intracellular proton levels. Thus, it seems that a reduced proton efflux in cells that exhibit decreased respiratory activity due to their biofilm mode of growth might explain their general antimicrobial tolerance. The use of PMZ as an antibiotic sensitizer holds promise that targeting tolerance mechanisms of biofilm-grown bacteria could become a practicable way to change the way physicians treat biofilm-associated infections.

Laser-Irradiated Chlorpromazine as a Potent Anti-Biofilm Agent for Coating of Biomedical Devices

Nowadays, antibiotic resistance has become increasingly common, triggering a global health crisis, immediately needing alternative, including repurposed drugs with potent bactericidal effects. We demonstrated that chlorpromazine aqueous solutions exposed to laser radiation exhibited visible activity against various microorganisms. The aim of this study was to investigate the quantitative antimicrobial activity of chlorpromazine in non-irradiated and 4-h laser irradiated form. Also, we examined the effect of both solutions impregnated on a cotton patch, cannula, and urinary catheter against Gram-positive Staphylococcus aureus and Gram-negative Pseudomonas aeruginosa and Escherichia coli. In all experimental versions, the chlorpromazine antimicrobial activity was enhanced by laser exposure. Besides the experimental results, the in silico analyses using molecular docking proved that the improved antimicrobial activity of the irradiated compound was a result of the combined action of the photoproducts on the biological target (s). Our results show that laser radiation could alter the molecular structure of various drugs and their effects, proving to be a promising strategy to halt antibiotic resistance, by repurposing current medicines for new antimicrobial strategies, thereby decreasing the costs and time for the development of more efficient drugs.

Do phenothiazines possess antimicrobial and efflux inhibitory properties?

Antibiotic resistance is a global health concern; the rise of drug-resistant bacterial infections is compromising the medical advances that resulted from the introduction of antibiotics at the beginning of the 20th century. Considering that the presence of mutations within individuals in a bacterial population may allow a subsection to survive and propagate in response to selective pressure, as long as antibiotics are used in the treatment of bacterial infections, development of resistance is an inevitable evolutionary outcome. This, combined with the lack of novel antibiotics being released to the clinical market, means the need to develop alternative strategies to treat these resistant infections is critical. We discuss how the use of antibiotic adjuvants can minimise the appearance and impact of resistance. To this effect, several phenothiazine-derived drugs have been shown to potentiate the activities of antibiotics used to treat infections caused by Gram-positive and Gram-negative bacteria. Outside of their role as antipsychotic medications, we review the evidence to suggest that phenothiazines possess inherent antibacterial and efflux inhibitory properties enabling them to potentially combat drug resistance. We also discuss that understanding their mode of action is essential to facilitate the design of new phenothiazine derivatives or novel agents for use as antibiotic adjuvants.

Chlorpromazine and Amitriptyline Are Substrates and Inhibitors of the AcrB Multidrug Efflux Pump

Efflux is an important mechanism in Gram-negative bacteria conferring multidrug resistance. Inhibition of efflux is an encouraging strategy to restore the antibacterial activity of antibiotics. Chlorpromazine and amitriptyline have been shown to behave as efflux inhibitors. However, their mode of action is poorly understood. Exposure of Salmonella enterica serovar Typhimurium and Escherichia coli to chlorpromazine selected for mutations within genes encoding RamR and MarR, regulators of the multidrug tripartite efflux pump AcrAB-TolC. Further experiments with S. Typhimurium containing AcrB D408A (a nonfunctional efflux pump) and chlorpromazine or amitriptyline resulted in the reversion of the mutant acrB allele to the wild type. Together, this suggests these drugs are AcrB efflux substrates. Subsequent docking studies with AcrB from S. Typhimurium and E. coli, followed by molecular dynamics simulations and free energy calculations showed that chlorpromazine and amitriptyline bind at the hydrophobic trap, a preferred binding site for substrates and inhibitors within the distal binding pocket of AcrB. Based on these simulations, we suggest that chlorpromazine and amitriptyline inhibit AcrB-mediated efflux by interfering with substrate binding. Our findings provide evidence that these drugs are substrates and inhibitors of AcrB, yielding molecular details of their mechanism of action and informing drug discovery of new efflux inhibitors.IMPORTANCE Efflux pumps of the resistance nodulation-cell division (RND) superfamily are major contributors to multidrug resistance for most of the Gram-negative ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) pathogens. The development of inhibitors of these pumps would be highly desirable; however, several issues have thus far hindered all efforts at designing new efflux inhibitory compounds devoid of adverse effects. An alternative route to de novo design relies on the use of marketed drugs, for which side effects on human health have been already assessed. In this work, we provide experimental evidence that the antipsychotic drugs chlorpromazine and amitriptyline are inhibitors of the AcrB transporter, the engine of the major RND efflux pumps in Escherichia coli and Salmonella enterica serovar Typhimurium. Furthermore, in silico calculations have provided a molecular-level picture of the inhibition mechanism, allowing rationalization of experimental data and paving the way for similar studies with other classes of marketed compounds.

Oxidative Phosphorylation—an Update on a New, Essential Target Space for Drug Discovery in Mycobacterium tuberculosis

New drugs with new mechanisms of action are urgently required to tackle the global tuberculosis epidemic. Following the FDA-approval of the ATP synthase inhibitor bedaquiline (Sirturo®), energy metabolism has become the subject of intense focus as a novel pathway to exploit for tuberculosis drug development. This enthusiasm stems from the fact that oxidative phosphorylation (OxPhos) and the maintenance of the transmembrane electrochemical gradient are essential for the viability of replicating and non-replicating Mycobacterium tuberculosis (M. tb), the etiological agent of human tuberculosis (TB). Therefore, new drugs targeting this pathway have the potential to shorten TB treatment, which is one of the major goals of TB drug discovery. This review summarises the latest and key findings regarding the OxPhos pathway in M. tb and provides an overview of the inhibitors targeting various components. We also discuss the potential of new regimens containing these inhibitors, the flexibility of this pathway and, consequently, the complexity in targeting it. Lastly, we discuss opportunities and future directions of this drug target space.

Dos distúrbios psiquiátricos à antibioticoterapia: reposicionamento da clorpromazina como agente antibacteriano

O alarmante aumento na taxa de resistência aos antibióticos põe em check à eficácia da terapia antibacteriana futura. Em contrapartida, as indústrias farmacêuticas negligenciam os investimentos em pesquisa e desenvolvimento de novos fármacos antimicrobianos em virtude de questões financeiras, legais e farmacológicas. Assim sendo, o reposicionamento de agentes disponíveis clinicamente torna-se uma promissora ferramenta para tentar driblar o desinteresse das indústrias. O fármaco antipsicótico clorpromazina (CPZ) destaca-se por possuir uma ampla faixa de atividade antibacteriana, a qual cobre desde patógenos Gram-positivos e Gram-negativos, até as micobactérias. A atividade antibacteriana é independente do perfil de susceptibilidade do microrganismo, sendo ela mantida mesmo em cepas altamente resistentes aos antibióticos. Alguns estudos mostram que mesmo nas concentrações clinicamente disponíveis no plasma (entre 0,1-0,5 μg/mL), a CPZ é capaz de matar Staphylococcus aureus e Mycobacterium tuberculosis dentro dos macrófagos. Em adição, estudos clínicos têm revelado os benefícios do uso da CPZ na terapia de suporte para pacientes com infecções em curso. Em conclusão, a CPZ pode eventualmente ser direcionada ao arsenal terapêutico antimicrobiano, especialmente no manejo das infecções causadas por microrganismos intracelulares com fenótipo multirresistente.

Psychotropics and the Microbiome: a Chamber of Secrets…

The human gut contains trillions of symbiotic bacteria that play a key role in programming different aspects of host physiology in health and disease. Psychotropic medications act on the central nervous system (CNS) and are used in the treatment of various psychiatric disorders. There is increasing emphasis on the bidirectional interaction between drugs and the gut microbiome. An expanding body of evidence supports the notion that microbes can metabolise drugs and vice versa drugs can modify the gut microbiota composition. In this review, we will first give a comprehensive introduction about this bidirectional interaction, then we will take into consideration different classes of psychotropics including antipsychotics, antidepressants, antianxiety drugs, anticonvulsants/mood stabilisers, opioid analgesics, drugs of abuse, alcohol, nicotine and xanthines. The varying effects of these widely used medications on microorganisms are becoming apparent from in vivo and in vitro studies. This has important implications for the future of psychopharmacology pipelines that will routinely need to consider the host microbiome during drug discovery and development.

'Tethering' fragment-based drug discovery to identify inhibitors of the essential respiratory membrane protein type II NADH dehydrogenase

Energy generation is a promising area of drug discovery for both bacterial pathogens and parasites. Type II NADH dehydrogenase (NDH-2), a vital respiratory membrane protein, has attracted attention as a target for the development of new antitubercular and antimalarial agents. To date, however, no potent, specific inhibitors have been identified. Here, we performed a site-directed screening technique, tethering-fragment based drug discovery, against wild-type and mutant forms of NDH-2 containing engineered active-site cysteines. Inhibitory fragments displayed IC₅₀ values between 3 and 110 μM against NDH-2 mutants. Possible binding poses were investigated by in silico modelling, providing a basis for optimisation of fragment binding and improved potency against NDH-2.

Oxidative Phosphorylation as a Target Space for Tuberculosis: Success, Caution, and Future Directions

The emergence and spread of drug-resistant pathogens, and our inability to develop new antimicrobials to combat resistance, have inspired scientists to seek out new targets for drug development. The Mycobacterium tuberculosis complex is a group of obligately aerobic bacteria that have specialized for inhabiting a wide range of intracellular and extracellular environments. Two fundamental features in this adaptation are the flexible utilization of energy sources and continued metabolism in the absence of growth. M. tuberculosis is an obligately aerobic heterotroph that depends on oxidative phosphorylation for growth and survival. However, several studies are redefining the metabolic breadth of the genus. Alternative electron donors and acceptors may provide the maintenance energy for the pathogen to maintain viability in hypoxic, nonreplicating states relevant to latent infection. This hidden metabolic flexibility may ultimately decrease the efficacy of drugs targeted against primary dehydrogenases and terminal oxidases. However, it may also open up opportunities to develop novel antimycobacterials targeting persister cells. In this review, we discuss the progress in understanding the role of energetic targets in mycobacterial physiology and pathogenesis and the opportunities for drug discovery.

Thioridazine enhances sensitivity to carboplatin in human head and neck cancer cells through downregulation of c-FLIP and Mcl-1 expression

Carboplatin is a less toxic analog of cisplatin, but carboplatin also has side effects, including bone marrow suppression. Therefore, to improve the capacity of the anticancer activity of carboplatin, we investigated whether combined treatment with carboplatin and thioridazine, which has antipsychotic and anticancer activities, has a synergistic effect on apoptosis. Combined treatment with carboplatin and thioridazine markedly induced caspase-mediated apoptosis in head and neck squamous cell carcinoma (AMC-HN4) cells. Combined treatment with carboplatin and thioridazine induced downregulation of Mcl-1 and c-FLIP expression. Ectopic expression of Mcl-1 and c-FLIP inhibited carboplatin plus thioridazine-induced apoptosis. We found that augmentation of proteasome activity had a critical role in downregulation of Mcl-1 and c-FLIP expression at the post-translational level in carboplatin plus thioridazine-treated cells. Furthermore, carboplatin plus thioridazine induced upregulation of the expression of proteasome subunit alpha 5 (PSMA5) through mitochondrial reactive oxygen species (ROS)-dependent nuclear factor E2-related factor 2 (Nrf2) activation. In addition, combined treatment with carboplatin and thioridazine markedly induced apoptosis in human breast carcinoma (MDA-MB231) and glioma (U87MG) cells, but not in human normal mesangial cells and normal human umbilical vein cells (EA.hy926). Collectively, our study demonstrates that combined treatment with carboplatin and thioridazine induces apoptosis through proteasomal degradation of Mcl-1 and c-FLIP by upregulation of Nrf2-dependent PSMA5 expression.

Design of new phenothiazine-thiadiazole hybrids via molecular hybridization approach for the development of potent antitubercular agents

A new library of phenothiazine and 1,3,4-thiadiazole hybrid derivatives (5a-u) was designed based on the molecular hybridization approach and the molecules were synthesized in excellent yields using a facile single-step chloro-amine coupling reaction between 2-chloro-1-(10H-phenothiazin-10-yl)ethanones and 2-amino-5-subsituted-1,3,4-thiadiazoles. The compounds were evaluated for their in vitro inhibition activity against Mycobacterium tuberculosis H37Rv (MTB). Compounds 5 g and 5 n were emerged as the most active compounds of the series with MIC of 0.8 μg/mL (∼ 1.9 μM). Also, compounds 5a, 5b, 5c, 5e, 5l and 5m (MIC = 1.6 μg/mL), and compounds 5j, 5k and 5o (MIC = 3.125 μg/mL) showed significant inhibition activity. The structure-activity relationship demonstrated that an alkyl (methyl/n-propyl) or substituted (4-methyl/4-Cl/4-F) phenyl groups on the 1,3,4-thiadiazole ring enhance the inhibition activity of the compounds. The cytotoxicity study revealed that none of the active molecules are toxic to a normal Vero cell line thus proving the lack of general cellular toxicity. Further, the active molecules were subjected to molecular docking studies with target enzymes InhA and CYP121.

SILA-421 activity in vitro against rifampicin-susceptible and rifampicin-resistant Mycobacterium tuberculosis, and in vivo in a murine tuberculosis model

Due to the emergence of multidrug-resistant and extensively drug-resistant tuberculosis (TB), there is an urgent need for new TB drugs or for compounds that improve the efficacy of currently used drugs. In this study, time-kill kinetics of SILA-421 as a single drug and in combination with isoniazid (INH), rifampicin (RIF), moxifloxacin (MXF) or amikacin (AMK) against Mycobacterium tuberculosis were assessed. Therapeutic efficacy in vivo in a mouse TB model was also studied. Further in vitro analysis was performed with a RIF-susceptible and RIF-resistant strains of M. tuberculosis. When used as a single drug, SILA-421 in vitro showed concentration-dependent and time-dependent bactericidal activity. SILA-421 also enhanced the activity of INH and RIF, resulting in synergy in the case of INH. Emergence of INH resistance following exposure to INH can be prevented by the addition SILA-421. SILA-421 had no additional value in combination with MXF or AMK. Furthermore, SILA-421 enhanced the activity of RIF towards a RIF-resistant strain and resulted in complete elimination of RIF-resistant mycobacteria. Unfortunately, in mice with TB induced by a Beijing genotype strain, addition of SILA-421 to an isoniazid-rifampicin-pyrazinamide regimen for 13 weeks did not result in enhanced therapeutic efficacy.

Abnormal immune system development and function in schizophrenia helps reconcile diverse findings and suggests new treatment and prevention strategies

Extensive research implicates disturbed immune function and development in the etiology and pathology of schizophrenia. In addition to reviewing evidence for immunological factors in schizophrenia, this paper discusses how an emerging model of atypical immune function and development helps explain a wide variety of well-established - but puzzling - findings about schizophrenia. A number of theorists have presented hypotheses that early immune system programming, disrupted by pre- and perinatal adversity, often combines with abnormal brain development to produce schizophrenia. The present paper focuses on the hypothesis that disruption of early immune system development produces a latent immune vulnerability that manifests more fully after puberty, when changes in immune function and the thymus leave individuals more susceptible to infections and immune dysfunctions that contribute to schizophrenia. Complementing neurodevelopmental models, this hypothesis integrates findings on many contributing factors to schizophrenia, including prenatal adversity, genes, climate, migration, infections, and stress, among others. It helps explain, for example, why (a) schizophrenia onset is typically delayed until years after prenatal adversity, (b) individual risk factors alone often do not lead to schizophrenia, and (c) schizophrenia prevalence rates actually tend to be higher in economically advantaged countries. Here we discuss how the hypothesis explains 10 key findings, and suggests new, potentially highly cost-effective, strategies for treatment and prevention of schizophrenia. Moreover, while most human research linking immune factors to schizophrenia has been correlational, these strategies provide ethical ways to experimentally test in humans theories about immune function and schizophrenia. This article is part of a Special Issue entitled SI: Neuroimmunology in Health And Disease.

The tuberculosis drug discovery and development pipeline and emerging drug targets

The recent accelerated approval for use in extensively drug-resistant and multidrug-resistant-tuberculosis (MDR-TB) of two first-in-class TB drugs, bedaquiline and delamanid, has reinvigorated the TB drug discovery and development field. However, although several promising clinical development programs are ongoing to evaluate new TB drugs and regimens, the number of novel series represented is few. The global early-development pipeline is also woefully thin. To have a chance of achieving the goal of better, shorter, safer TB drug regimens with utility against drug-sensitive and drug-resistant disease, a robust and diverse global TB drug discovery pipeline is key, including innovative approaches that make use of recently acquired knowledge on the biology of TB. Fortunately, drug discovery for TB has resurged in recent years, generating compounds with varying potential for progression into developable leads. In parallel, advances have been made in understanding TB pathogenesis. It is now possible to apply the lessons learned from recent TB hit generation efforts and newly validated TB drug targets to generate the next wave of TB drug leads. Use of currently underexploited sources of chemical matter and lead-optimization strategies may also improve the efficiency of future TB drug discovery. Novel TB drug regimens with shorter treatment durations must target all subpopulations of Mycobacterium tuberculosis existing in an infection, including those responsible for the protracted TB treatment duration. This review summarizes the current TB drug development pipeline and proposes strategies for generating improved hits and leads in the discovery phase that could help achieve this goal.

Enhancement of in vitro activity of tuberculosis drugs by addition of thioridazine is not reflected by improved in vivo therapeutic efficacy

OBJECTIVES

Assessment of the activity of thioridazine towards Mycobacterium tuberculosis (Mtb), in vitro and in vivo as a single drug and in combination with tuberculosis (TB) drugs.

METHODS

The in vitro activity of thioridazine as single drug or in combination with TB drugs was assessed in terms of MIC and by use of the time-kill kinetics assay. Various Mtb strains among which the Beijing genotype strain BE-1585 were included. In vivo, mice with TB induced by BE-1585 were treated with a TB drug regimen with thioridazine during 13 weeks. Therapeutic efficacy was assessed by the change in mycobacterial load in the lung, spleen and liver during treatment and 13 weeks post-treatment.

RESULTS

In vitro, thioridazine showed a concentration-dependent and time-dependent bactericidal activity towards both actively-replicating and slowly-replicating Mtb. Thioridazine at high concentrations could enhance the activity of isoniazid and rifampicin, and in case of isoniazid resulted in elimination of mycobacteria and prevention of isoniazid-resistant mutants. Thioridazine had no added value in combination with moxifloxacin or amikacin. In mice with TB, thioridazine was poorly tolerated, limiting the maximum tolerated dose (MTD). The addition of thioridazine at the MTD to an isoniazid-rifampicin-pyrazinamide regimen for 13 weeks did not result in enhanced therapeutic efficacy.

CONCLUSIONS

Thioridazine is bactericidal towards Mtb in vitro, irrespective the mycobacterial growth rate and results in enhanced activity of the standard regimen. The in vitro activity of thioridazine in potentiating isoniazid and rifampicin is not reflected by improved therapeutic efficacy in a murine TB-model.

Thioridazine for treatment of tuberculosis: promises and pitfalls

The articles by De Knegt et al. and Singh et al. in a recent issue of this Journal address one of the current debates regarding the potential role of thioridazine in the treatment of tuberculosis. This commentary presents a summary of the available evidence, and, emphasizing the need for further research, asks the question: "How far can we go in repurposing thioridazine?"

Tuberculosis drug discovery and emerging targets

Current tuberculosis (TB) therapies take too long and the regimens are complex and subject to adverse effects and drug-drug interactions with concomitant medications. The emergence of drug-resistant TB strains exacerbates the situation. Drug discovery for TB has resurged in recent years, generating compounds (hits) with varying potential for progression into developable leads. In parallel, advances have been made in understanding TB pathogenesis. It is now possible to apply the lessons learned from recent TB hit generation efforts and newly validated TB drug targets to generate the next wave of TB drug leads. Use of currently underexploited sources of chemical matter and lead-optimization strategies may also improve the efficiency of future TB drug discovery. Novel TB drug regimens with shorter treatment durations must target all subpopulations of Mycobacterium tuberculosis existing in an infection, including those responsible for the protracted TB treatment duration. This review proposes strategies for generating improved hits and leads that could help achieve this goal.

Antipsychotic agent thioridazine sensitizes renal carcinoma Caki cells to TRAIL-induced apoptosis through reactive oxygen species-mediated inhibition of Akt signaling and downregulation of Mcl-1 and c-FLIP(L)

Thioridazine has been known as an antipsychotic agent, but it also has anticancer activity. However, the effect of thioridazine on tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) sensitization has not yet been studied. Here, we investigated the ability of thioridazine to sensitize TRAIL-mediated apoptosis. Combined treatment with thioridazine and TRAIL markedly induced apoptosis in various human carcinoma cells, including renal carcinoma (Caki, ACHN, and A498), breast carcinoma (MDA-MB231), and glioma (U251MG) cells, but not in normal mouse kidney cells (TMCK-1) and human normal mesangial cells. We found that thioridazine downregulated c-FLIP(L) and Mcl-1 expression at the post-translational level via an increase in proteasome activity. The overexpression of c-FLIP(L) and Mcl-1 overcame thioridazine plus TRAIL-induced apoptosis. We further observed that thioridazine inhibited the Akt signaling pathway. In contrast, although other phosphatidylinositol-3-kinase/Akt inhibitors (LY294002 and wortmannin) sensitized TRAIL-mediated apoptosis, c-FLIP(L) and Mcl-1 expressions were not altered. Furthermore, thioridazine increased the production of reactive oxygen species (ROS) in Caki cells, and ROS scavengers (N-acetylcysteine, glutathione ethyl ester, and trolox) inhibited thioridazine plus TRAIL-induced apoptosis, as well as Akt inhibition and the downregulation of c-FLIP(L) and Mcl-1. Collectively, our study demonstrates that thioridazine enhances TRAIL-mediated apoptosis via the ROS-mediated inhibition of Akt signaling and the downregulation of c-FLIP(L) and Mcl-1 at the post-translational level.

Combination approaches to combat multidrug-resistant bacteria

The increasing prevalence of infections caused by multidrug-resistant bacteria is a global health problem that has been exacerbated by the dearth of novel classes of antibiotics entering the clinic over the past 40 years. Herein, we describe recent developments toward combination therapies for the treatment of multidrug-resistant bacterial infections. These efforts include antibiotic-antibiotic combinations, and the development of adjuvants that either directly target resistance mechanisms such as the inhibition of β-lactamase enzymes, or indirectly target resistance by interfering with bacterial signaling pathways such as two-component systems (TCSs). We also discuss screening of libraries of previously approved drugs to identify nonobvious antimicrobial adjuvants.

Why thioridazine in combination with antibiotics cures extensively drug-resistant Mycobacterium tuberculosis infections

Thioridazine (TDZ) in combination with antibiotics to which extensively drug-resistant Mycobacterium tuberculosis (XDR-TB) is initially resistant yields a cure. This is due to the fact that TDZ enhances the killing of intracellular M. tuberculosis by non-killing macrophages, inhibits the genetic expression of efflux pumps of M. tuberculosis that extrude antibiotics prior to reaching their intended targets, and inhibits the activity of existing efflux pumps that contribute to the multidrug-resistant phenotype of M. tuberculosis. The combination of these effects of TDZ probably contributes to the successful recent cures of XDR-TB cases when the phenothiazine TDZ is used in combination with antibiotics to which the patient with XDR-TB was initially unresponsive.

Phenothiazines as anti-tubercular agents: mechanistic insights and clinical implications

INTRODUCTION

Tuberculosis (TB) chemotherapy has been rendered ineffective by the emergence of multi-drug resistant (MDR), extensively drug resistant (XDR) and totally drug resistant strains reinforcing the need for the development of new drugs as a global health priority. Reconsidering phenothiazines for the improvement of TB chemotherapy seems to be a rational option especially in view of their role as inhibitors of type II NADH dehydrogenase, a key component of respiratory chain of Mycobacterium tuberculosis, thus raising the speculation that they can be effective against latent TB as well.

AREAS COVERED

This article offers a detailed description of the chemotherapeutic efficacy of phenothiazine compounds against susceptible, drug resistant and latent TB. Furthermore, their clinical implications and molecular mechanisms of action have been reviewed extensively.

EXPERT OPINION

Phenothiazines are currently being evaluated for the treatment of TB and have been shown to be effective against M. tuberculosis through a number of in vitro, ex vivo and in vivo studies. In addition, recent clinical studies have implicated their role in the treatment of MDR/XDR TB also. Therefore, phenothiazines, particularly thioridazine, hold great potential to be considered as safe and effective antimycobacterial agents in near future.

In vitro antibacterial activity of some antihistaminics belonging to different groups against multi-drug resistant clinical isolates

Antihistaminics are widely used for various indications during microbial infection. Hence, this paper investigates the antimicrobial activities of 10 antihistaminics belonging to both old and new generations using multiresistant Gram-positive and Gram-negative clinical isolates. The bacteriostatic activity of antihistaminics was investigated by determining their MIC both by broth and agar dilution techniques against 29 bacterial strains. Azelastine, cyproheptadine, mequitazine and promethazine were the most active among the tested drugs. Diphenhydramine and cetirizine possessed weaker activity whereas doxylamine, fexofenadine and loratadine were inactive even at the highest tested concentration (1 mg/ml). The MIC of meclozine could not be determined as it precipitated with the used culture media. The MBC values of antihistaminics were almost identical to the corresponding MIC values. The bactericidal activity of antihistaminics was also studied by the viable count technique in sterile saline solution. Evident killing effects were exerted by mequitazine, meclozine, azelastine and cyproheptadine. Moreover, the dynamics of bactericidal activity of azelastine were studied by the viable count technique in nutrient broth. This activity was found to be concentration-dependant. This effect was reduced on increasing the inoculum size while it was increased on raising the pH. The post-antimicrobial effect of 100 μg/ml azelastine was also determined and reached up to 3.36 h.

The antipsychotic thioridazine shows promising therapeutic activity in a mouse model of multidrug-resistant tuberculosis

Multidrug- and extensively drug-resistant tuberculosis have emerged as grave threats to public health worldwide. Very few active drugs are available or likely to become available soon. To address these problems we revisited a classical observation, the applicability of phenothiazines as antimicrobial drugs. Within this pharmacological class we selected thioridazine, which is most efficacious and least toxic, when used as an antipsychotic drug. We tested thioridazine monotherapy in the Balb/c mouse model for its activity to treat both susceptible and multidrug-resistant tuberculosis by a two months daily oral administration of 32 and 70 mg/kg. In addition, we tested its additive value when combined with a standard first-line regimen for susceptible tuberculosis. Thioridazine treatment resulted in a significant reduction of colony-forming-units of the susceptible (−4.4 log CFU, p<0.05) and multidrug-resistant tuberculosis bacilli (−2.4 log CFU, p<0.009) in the lung both at one and two months after infection, compared to controls. Moreover, when thioridazine was added to a regimen containing rifampicin, isoniazid and pyrazinamide for susceptible tuberculosis, a significant synergistic effect was achieved (−6.2 vs −5.9 log CFU, p<0.01). Thioridazine may represent an effective compound for treatment of susceptible and multidrug-resistant tuberculosis. The phenothiazines and their targets represent interesting novel opportunities in the search for antituberculosis drugs.

A unifying hypothesis of schizophrenia: abnormal immune system development may help explain roles of prenatal hazards, post-pubertal onset, stress, genes, climate, infections, and brain dysfunction

We propose a unifying hypothesis of schizophrenia to help reconcile findings from many different disciplines. This hypothesis proposes that schizophrenia often involves pre- or perinatal exposure to adverse factors that produce a latent immune vulnerability. When this vulnerability is manifested, beginning around puberty with changes in immune function and involution of the thymus, individuals become more susceptible to infections and immune dysfunctions that contribute to schizophrenia. Our hypothesis suggests theoretical bridges between different lines of evidence on schizophrenia and offers explanations for many puzzling findings about schizophrenia. For example, the hypothesis helps account for why schizophrenia patients tend to have had increased exposure to neurotropic infections, but most individuals with such exposure do not develop schizophrenia, and why prenatal hardships increase risk for schizophrenia, but the onset of symptoms typically does not occur until after puberty. The hypothesis also explains another paradox: lower socioeconomic status and poor prenatal care increase risk for schizophrenia at the same geographic site, but international comparisons indicate that countries with higher per capita incomes and better prenatal care actually tend to have higher schizophrenia prevalences. As the hypothesis predicts, (1) prenatal adversity, which increases risk for schizophrenia, also impairs post-pubertal immune competence, (2) schizophrenia patients experience elevated morbidity from infectious and auto-immune diseases, (3) genetic and environmental risk factors for schizophrenia increase vulnerability to these diseases, (4) factors that exacerbate schizophrenic symptoms also tend to impair immune function, (5) many anti-psychotic medications combat infection, (6) effects of early infections may not appear until after puberty, when they can produce neurologic and psychiatric symptoms, and (7) immune dysfunctions, such as imbalances of pro- and anti-inflammatory cytokines, may contribute to the onset of psychotic symptoms and the progressive loss of brain tissue in schizophrenia. The disruptive effects of prenatal adversity on the development of the immune system may often combine with adverse effects on prenatal brain development to produce schizophrenia. This paper focuses on the adverse immune system effects, because effects on the brain have been extensively discussed in neurodevelopmental theories of schizophrenia. We propose new tests of scientific predictions. We also point out potential clinical implications of the hypothesis; for example, individuals with schizophrenia may often have underlying infections or immune dysfunctions, such as imbalances in inflammatory cytokines, that contribute to the illness. This possibility could be tested experimentally--e.g., by clinical trials in which patients' exposure to infection is reduced or immune function is normalized.

Effect of the novel antipsychotic drug perospirone on P-glycoprotein function and expression in Caco-2 cells

OBJECTIVE

Perospirone (PER) is a novel atypical antipsychotic drug for the treatment of schizophrenia and other psychotic disorders. The multidrug resistance transporter, P-glycoprotein (Pgp), is involved in the efflux transport of several antipsychotics across the blood-brain barrier (BBB). The aim of the present study was to evaluate the modulating effect of PER on both Pgp activity and expression in Caco-2 cell monolayers.

METHODS

The effects of PER were analyzed by means of rhodamine 123 (Rhd 123) assays, and those of Pgp expression were analyzed by flow cytometry and reverse transcriptase-PCR.

RESULTS

Perospirone at concentrations of 0.01-30 microM, which were found to be non-cytotoxic towards the Caco-2 cells, was observed to inhibit Pgp-mediated efflux transport of Rhd 123 in the cells as well as to down-regulate the cellular Pgp protein and MDR1 mRNA levels in a concentration-dependent manner. In the rhodamine accumulation assays, 30 microM PER produced a 429% increase of the cellular Rhd 123 concentration, which exceeded the inhibitory effect of the well-known Pgp inhibitor verapamil.

CONCLUSION

Our findings provide experimental evidence that PER is an inhibitor of Pgp which interferes directly and indirectly with the function of Pgp.

Nitrate enhances the survival of Mycobacterium tuberculosis during inhibition of respiration

When oxygen is slowly depleted from growing cultures of Mycobacterium tuberculosis, they enter a state of nonreplicating persistence that resembles the dormant state seen with latent tuberculosis. In this hypoxic state, nitrate reductase activity is strongly induced. Nitrate in the medium had no effect on long-term persistence during gradual oxygen depletion (Wayne model) for up to 46 days, but significantly enhanced survival during sudden anaerobiosis. This enhancement required a functional nitrate reductase. Thioridazine is a member of the class of phenothiazines that act, in part, by inhibiting respiration. Thioridazine was toxic to both actively growing and nonreplicating cultures of M. tuberculosis. At a sublethal concentration of thioridazine, nitrate in the medium improved the growth. At lethal concentrations of thioridazine, nitrate increased survival during aerobic incubation as well as in microaerobic cultures that had just entered nonreplicating persistence (NRP-1). In contrast, the survival of anaerobic persistent (NRP-2) cultures exposed to thioridazine was not increased by the addition of nitrate. Nitrate reduction is proposed to play a role during the sudden interruption of aerobic respiration due to causes such as hypoxia, thioridazine, or nitric oxide.

Activity and post antifungal effect of chlorpromazine and trifluopherazine against Aspergillus, Scedosporium and zygomycetes

The phenothiazine compounds chlorpromazine and trifluopherazine are antipsychotic agents that exhibit antimicrobial activity against bacteria, some protozoa and yeasts. Data of activity against filamentous fungi are lacking. The in vitro activity and postantifungal effect (PAFE) of chlorpromazine and trifluopherazine was determined against Aspergillus species, zygomycetes and Scedosporium species. In vitro susceptibility testing was performed with CLSI M38A and the PAFE was determined with previously established methods. Both drugs inhibited the growth of all fungi tested at concentrations of 16 to 64 microg ml(-1). For Aspergillus species the mean PAFE was 3.7 and 4.7 h; for zygomycetes, 3.1 and 3.4 h; for Scedosporium, 4.3 and 5.3 h for chlorpromazine and trifluoroperazine respectively. These are the first drugs shown to induce PAFE against Scedosporium. We show that phenothiazine compounds have in vitro antifungal activity and exhibit PAFE against a broad range of filamentous fungal pathogens. Although the exact mechanism of action is unknown, further studies are needed to explore the clinical usefulness of phenothiazine compounds.

Thioridazine: resurrection as an antimicrobial agent?

The emergence of multiresistant bacterial strains and the continuing burden of infectious disease globally point to the urgent need for novel affordable antimicrobial drugs. Thioridazine is a phenothiazine antipsychotic drug with well-recognized antimicrobial activity, but this property has not been harnessed for clinical use as a result of its central nervous system and cardiac side-effects. The cardiotoxicity of thioridazine has recently been shown to be structurally specific at a molecular level, whereas its antimicrobial properties are shared by a number of phenothiazine analogues. This raises the possibility that its enantiomers or its inactive metabolite, the ring sulphoxide, may act as a lead compound in the future development of antimicrobial drugs to face the new challenges in infectious disease.

Antituberculosis drugs: ten years of research

Tuberculosis is today amongst the worldwide health threats. As resistant strains of Mycobacterium tuberculosis have slowly emerged, treatment failure is too often a fact, especially in countries lacking the necessary health care organisation to provide the long and costly treatment adapted to patients. Because of lack of treatment or lack of adapted treatment, at least two million people will die of tuberculosis this year. Due to this concern, this infectious disease was the focus of renewed scientific interest in the last decade. Regimens were optimized and much was learnt on the mechanisms of action of the antituberculosis drugs used. Moreover, the quest for original drugs overcoming some of the problems of current regimens also became the focus of research programmes and many new series of M. tuberculosis growth inhibitors were reported. This review presents the drugs currently used in antituberculosis treatments and the most advanced compounds undergoing clinical trials. We then provide a description of their mechanism of action along with other series of inhibitors known to act on related biochemical targets. This is followed by other inhibitors of M. tuberculosis growth, including recently reported compounds devoid of a reported mechanism of action.

Enhanced killing of intracellular multidrug-resistant Mycobacterium tuberculosis by compounds that affect the activity of efflux pumps

Whereas human neutrophils are effective and efficient killers of bacteria, macrophages such as those derived from monocytes are almost devoid of killing activity. Nevertheless, monocytes can be transformed into effective killers of mycobacteria or staphylococci when exposed to clinical concentrations of a phenothiazine or to inhibitors of efflux pumps (reserpine and verapamil), or to ouabain, an inhibitor of K(+) transport. Because the rates of multidrug-resistant Mycobacterium tuberculosis (MDR-TB) continue to escalate globally, and because no new effective drug has been made available for almost 40 years, compounds that enhance the killing activity of monocytes against MDR-TB are obviously needed. This review covers the specific characteristics of MDR-TB, identifies a variety of agents that address these characteristics and therefore have potential for managing MDR-TB. Because the mechanism by which these agents enhance the killing of intracellular bacteria is important for the intelligent design of new anti-tubercular agents, the review correlates the mechanisms by which these agents manifest their effects. Lastly, a model is presented which describes the mechanisms by which distinct efflux pumps of the phagosome-lysosome complex are inhibited by agents that are known to inhibit K(+) flux. The model also predicts the existence of a K(+) activated exchange (pump) that is probably located in the membrane that delineates the lysosome. This putative pump, which is immune to inhibitors of K+ flux, is identified as being the cause for the acidification of the lysosome thereby activating its hydrolytic enzymes. Because the non-killer macrophage can be transformed into an effective killer by a variety of compounds that inhibit K(+) transport, perhaps it would be wise to develop drugs that enhance the killing activity of these cells inasmuch as this approach would not be subject to any resistance, as is the eventual case for conventional antibiotics.

Cytokines in schizophrenia and the effects of antipsychotic drugs

Growing evidence suggests that the immune, endocrine, and nervous systems interact with each other through cytokines, hormones, and neurotransmitters. The activation of the cytokine systems may be involved in the neuropathological changes occurring in the central nervous system (CNS) of schizophrenic patients. Numerous studies report that treatment with antipsychotic drugs affects the cytokine network. Hence, it is plausible that the influence of antipsychotics on the cytokine systems may be responsible for their clinical efficacy in schizophrenia. This article reviews current data on the cytokine-modulating potential of antipsychotic drugs. First, basic information on the cytokine networks with special reference to their role in the CNS as well as an up-to-date knowledge of the cytokine alterations in schizophrenia is outlined. Second, the hitherto published studies on the influence of antipsychotics on the cytokine system are reviewed. Third, the possible mechanisms underlying antipsychotics' potential to influence the cytokine networks and the most relevant aspects of this activity are discussed. Finally, limitations of the presented studies and prospects of future research are delineated.

Clinical concentrations of thioridazine kill intracellular multidrug-resistant Mycobacterium tuberculosis

The phenothiazines chlorpromazine (CPZ) and thioridazine (TZ) have equal in vitro activities against antibiotic-sensitive and -resistant Mycobacterium tuberculosis. These compounds have not been used as anti-M. tuberculosis agents because their in vitro activities take place at concentrations which are beyond those that are clinically achievable. In addition, chronic administration of CPZ produces frequent severe side effects. Because CPZ has been shown to enhance the killing of intracellular M. tuberculosis at concentrations in the medium that are clinically relevant, we have investigated whether TZ, a phenothiazine whose negative side effects are less frequent and serious than those associated with CPZ, kills M. tuberculosis organisms that have been phagocytosed by human macrophages, which have nominal killing activities against these bacteria. Both CPZ and TZ killed intracellular antibiotic-sensitive and -resistant M. tuberculosis organisms when they were used at concentrations in the medium well below those present in the plasma of patients treated with these agents. These concentrations in vitro were not toxic to the macrophage, nor did they affect in vitro cellular immune processes. TZ thus appears to be a serious candidate for the management of a freshly diagnosed infection of pulmonary tuberculosis or as an adjunct to conventional antituberculosis therapy if the patient originates from an area known to have a high prevalence of multidrug-resistant M. tuberculosis isolates. Nevertheless, we must await the outcomes of clinical trials to determine whether TZ itself may be safely and effectively used as an antituberculosis agent.

Chlorpromazine has intracellular killing activity against phagocytosed Staphylococcus aureus at clinical concentrations

Chlorpromazine (CPZ) has in vitro antimicrobial activity against Staphylococcus aureus at concentrations that greatly exceed those achieved clinically. It is concentrated by tissues that are rich in macrophages and it is active against phagocytosed mycobacteria when the concentration in the medium is compatible with that achieved clinically. In this report we show that nontoxic concentrations of CPZ below clinical levels have killing activity against S. aureus phagocytosed by human monocyte-derived macrophages that have nominal killing activity against these bacteria. Little or no resistance to the antimicrobial activity of this compound is anticipated to result because of its large number of cellular targets. Therefore, CPZ may have a role in the management of intracellular staphylococcal infections that normally require the use of antibiotics whose potential toxicity exceeds that associated with short-term management with CPZ.

Intracellular activity of clinical concentrations of phenothiazines including thioridiazine against phagocytosed Staphylococcus aureus

The effect of thioridazine (TZ) was studied on the killing activity of human peripheral blood monocyte derived macrophages (HPBMDM) and of human macrophage cell line THP-1 at extracellular concentrations below those achievable clinically. These macrophages have nominal killing activity against bacteria and therefore, would not influence any activity that the compounds may have against intracellular localised Staphylococcus aureus. The results indicated that whereas TZ has an in vitro minimum inhibitory concentration (MIC) against the strains of S. aureus of 18, 0.1 mg/l of TZ in the medium completely inhibits the growth of S. aureus that has been phagocytosed by macrophages. The latter concentration was non-toxic to macrophages, did not cause cellular expression of activation marker CD69 nor induction of CD3+ T cell production of IFN-gamma, but blocked cellular proliferation and down-regulated the production of T cell-derived cytokines (IFN-gamma, IL-5). These results suggest that TZ induces intracellular bactericidal activities independent of the capacity to generate Type 1 responses against S. aureus.

Phenothiazines: potential alternatives for the management of antibiotic resistant infections of tuberculosis and malaria in developing countries

The in vitro and in vivo activity of phenothiazines against antibiotic susceptible and antibiotic resistant Mycobacterium tuberculosis and malaria-causing Plasmodia is reviewed. Given the facts that pulmonary tuberculosis and malaria are the major causes of death in developing countries, that both of these infections continue to escalate in their resistance to antibiotics, that the cost for the management of these infections is beyond that afforded by most developing nations, and lastly, that new and effective agents are not forthcoming from the pharmaceutical industry, the scientific rationale for the potential use of select phenothiazines for the management of these infections is presented.

Phenothiazines: potential management of Creutzfeldt-Jacob disease and its variants

Creutzfeldt-Jakob disease acquired from bovines (nvCJD) has been responsible for nearly 100 deaths in the UK and thousands more may die in the years to come. New variant CJD (nvCJD) is incurable and although clinical diagnosis is becoming more precise, the diagnosis is only certain at autopsy. Phenothiazine derivatives inhibit production of prions, the disease causing agent, in cultured neuroblastoma cells, and an advanced case of nvCJD was recently brought to remission by the use of these agents in combination with an antimalarial. In this review we present direct and circumstantial evidence in support of a model describing the manner by which the intracellular antimicrobial activity of phenothiazines might cause the destruction of intracellular prions.

Naltrexone potentiates anti-HIV-1 activity of antiretroviral drugs in CD4+ lymphocyte cultures

CD4(+) T lymphocytes are the primary cell target for human immunodeficiency virus-1 (HIV-1), and these cells are known to express opioid receptors. Due to the need for new treatment approaches to HIV-1 infection, we sought to determine whether the non-selective opioid receptor antagonist naltrexone would affect HIV-1 expression in CD4(+) lymphocyte cultures and whether naltrexone would alter the antiviral properties of zidovudine (AZT) or indinavir. Activated CD4(+) lymphocytes were infected with a monocytotropic or T-cell tropic HIV-1 isolate, and p24 antigen levels were measured in supernatants of drug-treated or untreated (control) cultures. While naltrexone alone did not affect HIV-1 expression, at a concentration of 10(-12)-10(-10) M naltrexone increased the antiviral activity of AZT and indinavir 2-3-fold. Similar findings with a kappa-opioid receptor (KOR) selective antagonist supported the possible involvement of KOR in naltrexone's potentiation of the antiretroviral drugs. The results of this in vitro study suggest that treatment of alcohol or opiate dependent HIV-1-infected patients with naltrexone is unlikely to interfere with the activity of antiretroviral drugs. Also, based upon naltrexone's safety profile and its synergistic activity in vitro, these findings suggest clinical trials should be considered of naltrexone as an adjunctive therapy of HIV-1 infection.