Phenothiazine Thioridazine Research Articles

Thioridazine as Chemotherapy for Mycobacterium avium Complex Diseases.

Mycobacterium avium-intracellulare complex (MAC) causes an intractable intracellular infection that presents as chronic pulmonary disease. Currently, therapy consists of ethambutol and macrolides and takes several years to complete. The neuroleptic phenothiazine thioridazine kills mycobacteria by inhibiting the electron transport chain. In several experiments with bacterial populations of up to 1012 CFU/ml, we failed to isolate any bacteria resistant to 3 times the MIC of thioridazine, suggesting the absence of resistant mutants at bacterial burdens severalfold higher than those encountered in patients. In the hollow-fiber model of intracellular MAC (HFS-MAC), thioridazine achieved an extracellular half-life of 16.8 h and an intracellular half-life of 19.7 h. Thioridazine concentrations were >28,000-fold higher inside infected macrophages than in the HFS-MAC central compartment (equivalent to plasma). Thioridazine maximal kill was 5.20 ± 0.75 log10 CFU/ml on day 7 (r2 = 0.96) and 7.19 ± 0.31 log10 CFU/ml on day 14 (r2 = 0.99), the highest seen with any drug in the system. Dose fractionation studies revealed that thioridazine efficacy and acquired drug resistance were driven by the peak concentation-to-MIC ratio, with a 50% effective concentration (EC50) of 2.78 ± 0.44 for microbial killing. Acquired drug resistance was encountered by day 21 with suboptimal doses, demonstrating that fluctuating drug concentrations drive evolution faster than static concentrations in mutation frequency studies. However, the thioridazine EC50 changed 16.14-fold when the concentration of fetal bovine serum was changed from 0% to 50%, suggesting that intracellular potency could be heavily curtailed by protein binding. Efficacy in patients will depend on the balance between trapping of the drug in the pulmonary system and the massive intracellular concentrations versus very high protein binding of thioridazine.

Combination therapy with thioridazine and dicloxacillin combats meticillin-resistant Staphylococcus aureus infection in Caenorhabditis elegans

The shortage of drugs active against meticillin-resistant Staphylococcus aureus (MRSA) is a growing clinical problem. In vitro studies indicate that the phenothiazine thioridazine (TZ) might enhance the activity of the β-lactam antibiotic dicloxacillin (DCX) to a level where MRSA is killed, but experiments in simple animal models have not been performed. In the present study, we introduced Caenorhabditis elegans infected by S. aureus as an in vivo model to test the effect of TZ as a helper drug in combination with DCX. Because TZ is an anthelmintic, initial experiments were carried out to define the thresholds of toxicity, determined by larval development, and induction of stress-response markers. No measurable effects were seen at concentrations of less than 64 mg TZ l(-1). Seven different MRSA strains were tested for pathogenicity against C. elegans, and the most virulent strain (ATCC 33591) was selected for further analyses. In a final experiment, full-grown C. elegans were exposed to the test strain for 3 days and subsequently treated with 8 mg DCX l(-1) and 8 mg TZ l(-1) for 2 days. This resulted in a 14-fold reduction in the intestinal MRSA load as compared with untreated controls. Each drug alone resulted in a two- to threefold reduction in MRSA load. In conclusion, C. elegans can be used as a simple model to test synergy between DCX and TZ against MRSA. The previously demonstrated in vitro synergy can be reproduced in vivo.

The Mechanism by which the Phenothiazine Thioridazine Contributes to Cure Problematic Drug-Resistant Forms of Pulmonary Tuberculosis: Recent Patents for “New Use”

At this moment, over half million patients suffer from multi-drug resistant tuberculosis (MDR-TB) according to the data from the WHO. A large majority is terminally ill with essentially incurable pulmonary tuberculosis. This herein mini-review provides the experimental and observational evidence that a specific phenothiazine, thioridazine, will contribute to cure any form of drug-resistant tuberculosis. This antipsychotic agent is no longer under patent protection for its initial use. The reader is informed on the recent developments in patenting this compound for "new use" with a special emphasis on the aspects of drug-resistance. Given that economic motivation can stimulate the use of this drug as an antitubercular agent, future prospects are also discussed.

A comparative Analysis of In Vitro and In Vivo Efficacies of the Enantiomers of Thioridazine and Its Racemate

A long list of chemotherapeutical drugs used in the treatment of the peripheral and the central nervous systems possess anti-microbial activity. Some of these neurotropic compounds are chiral, with the one stereo isomeric form exaggerating reduced neurotropism. This is the case for the levorotatory form of thioridazine. The phenothiazine thioridazine is an interesting compound, characterized by exhibiting a significant growth inhibiting activity on a wide array of micro-organisms. Thioridazine is characterized by another challenging feature, because the compound is concentrated in certain human tissue cells. The present study describes a comparative study of the two enantiomers as well as the racemic form of thioridazine. The study exploits the stereochemical aspect and the in vitro and in vivo potential of these compounds, with a focus on the effects on Gram negative organism Salmonella enterica serover Typhimurium. In summary, the results of this study yielded a significant antibacterial activity of all forms of thioridazine, indicating the levorotatory (–)- form to be superior in terms of both its in vitro and in vivo efficacies.

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.

Latent Tuberculosis: Is There a Role for Thioridazine?

Approximately 1/3 of the world's population is infected with Mycobacterium tuberculosis. In the vast majority of cases this results in latent not active disease. Latent disease is defined as a positive reaction to tuberculin antigens but without any further clinical symptoms. Models have been developed to study latent tuberculosis with the two most prominent being the in vivo murine model and the in vitro Wayne model. In both cases M. tuberculosis undergoes a change in its respiratory profile as it shifts down to a nonreplicating state. However in both the mouse and the Wayne model, dormant M. tuberculosis is sensitive to the phenothiazine thioridazine. This antibiotic has several targets, and the main one is respiration. There is a growing burden of multidrug resistant and extensively drug resistant tuberculosis. Treatment of these cases is expensive with high mortality. We propose that thioridazine alone, or with other antibiotics, be used to treat drug resistant latent tuberculosis. The advantages are that thioridazine is inexpensive, effective against drug resistant tuberculosis, well characterized and unlikely to induce drug resistance. The disadvantages include possible side effects, although these should be rare at the doses and length of time of treatment. Recent patents involving analogs of thioridazine suggest this class of drugs may hold great promise for the future treatment of the most drug resistant strains.

New Patentable Use of an Old Neuroleptic Compound Thioridazine to Combat Tuberculosis: A Gene Regulation Perspective

Use of the old antipsychotic phenothiazine thioridazine (THZ) for therapy of multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis (TB) infection is now being seriously considered. It is reported that THZ primarily acts on enzymes involved in fatty acid metabolism and membrane proteins, particularly efflux pumps, as well as oxidoreductases and proteins involved in aerobic respiration that overlap with a number of conventional antituberculous drugs. It targets the products of the Rv3160c-Rv3161c operon, which are perhaps required for the detoxification of THZ, members of the sigma factor SigB regulon that play a crucial role in protecting the pathogen against cell envelope damage, and Rv2745c, a transcription factor that regulates ATP-dependent proteolysis. Some of these genes have been shown to be essential for the survival or persistence of Mycobacterium tuberculosis in the infected host. Since THZ targets multiple pathways, including those involved in cell wall processes and respiratory chain components, it may serve as a model for multi-target drug development, as well as constitute a highly potent addition to a combination of antituberculous drug regimens. The discussion of some of the patents relevant to thioridazine to combat tuberculosis is also included in the present manuscript.

Uptake of phenothiazines by the harvested chylomicrons ex vivo model: Influence of self-nanoemulsifying formulation design

The aim of this study was to examine the potential of self-nanoemulsifying drug delivery systems (SNEDDS) on the uptake of the lipophilic and poorly water soluble phenothiazines thioridazine and chlorpromazine with the isolated plasma derived chylomicron (CM) ex vivo model. The multi-component delivery systems were optimized by evaluating their ability to self-emulsify when introduced to an aqueous medium under gentle agitation. The uptake of phenothiazines by isolated plasma derived chylomicrons was investigated with short chain triglyceride (SCT) SNEDDS, medium chain triglyceride (MCT) SNEDDS, and long chain triglyceride (LCT) SNEDDS. SNEDDS were also evaluated for their stabilities, dispersibilities, percentage transmittances and by particle size analyses. For thioridazine a 5.6-fold and for chlorpromazine a 3.7-fold higher CM uptake could be observed using a LCT-SNEDDS formulation compared to the drugs without formulation. In contrast, ex vivo uptake by isolated CM was not significantly increased by SNEDDS formulations based on MCT and SCT. Compared with isolated CM, the CM sizes were increased 2.5-fold in LCT-SNEDDS, whereas in MCT-SNEDDS or SCT-SNEDDS only a small, non-significant ( P < 0.05) increase in CM size was observed. These results show that distinct SNEDDS formulations containing phenothiazines are efficiently uptaken by plasma derived chylomicrons ex vivo.

Drug and neurotransmitter receptors. New perspectives with clinical relevance

Our understanding of drug and neurotransmitter receptors has been greatly advanced by receptor binding techniques. The theme of multiple-receptor subtypes with clinical relevance is highlighted by calcium antagonist and benzodiazepine receptors. Numerous drugs may exert therapeutic and untoward effects via calcium channels. Examples include effects of loperamide hydrochloride on diarrhea, the phenothiazine thioridazine hydrochloride on cardiac and ejaculatory function, and the neuromuscular toxicity of aminoglycosides. Elevated numbers of calcium antagonist receptors in hypertrophic cardiomyopathy may be involved in the pathophysiology of this disease. Benzodiazepines act via discrete central and peripheral receptors. At central receptors, benzodiazepines facilitate the inhibitory effects of the neurotransmitter -y-aminobutyric acid. Peripheral benzodiazepine receptors are localized to mitochondria and enriched in several endocrine glands where they are influenced by therapeutic blood levels of benzodiazepines such as diazepam. (<i>JAMA</i>. 1989;261:3126-3129)

Drug and Neurotransmitter Receptors

Our understanding of drug and neurotransmitter receptors has been greatly advanced by receptor binding techniques. The theme of multiple-receptor subtypes with clinical relevance is highlighted by calcium antagonist and benzodiazepine receptors. Numerous drugs may exert therapeutic and untoward effects via calcium channels. Examples include effects of loperamide hydrochloride on diarrhea, the phenothiazine thioridazine hydrochloride on cardiac and ejaculatory function, and the neuromuscular toxicity of aminoglycosides. Elevated numbers of calcium antagonist receptors in hypertrophic cardiomyopathy may be involved in the pathophysiology of this disease. Benzodiazepines act via discrete central and peripheral receptors. At central receptors, benzodiazepines facilitate the inhibitory effects of the neurotransmitter gamma-aminobutyric acid. Peripheral benzodiazepine receptors are localized to mitochondria and enriched in several endocrine glands where they are influenced by therapeutic blood levels of benzodiazepines such as diazepam.

Diltiazem-like effect of thioridazine on the dihydropyridine binding site of the calcium channel of rat myocardial membranes

The phenothiazine thioridazine enhances the binding of [ 3H]-nitrendipine to cardiac membranes and antagonizes the inhibition of [ 3H]-nitrendipine binding by other classes of calcium channel blockers. These effects are similar to those of diltiazem. The increased binding of [ 3H]-nitrendipine in the presence of thioridazine or diltiazem is due to increased binding affinity rather than an increased number of binding sites. Increased affinity is due in part to a decrease in the dissociation rate of nitrendipine in the presence of either thioridazine or diltiazem. Thioridazine also reverses the blocking effect of tiapamil (a phenylalkylamine) on [ 3H]-nitrendipine binding to rat heart membranes, as does diltiazem, suggesting that thioridazine binds to the same site as diltiazem. Thioridazine may have calcium channel blocking effects in the high therapeutic and toxic dose ranges that could be responsible for some of its adverse cardiovascular effects.

Calmodulin, phospholipase, and exocytosis. p-Bromophenacyl bromide inhibits but mepacrine stimulates secretion in rat mast cells.

p-Bromophenacyl bromide (10-50 microM), a reagent that reacts with and inhibits phospholipase A2, completely suppressed exocytotic responses in rat serosal mast cells elicited by A23187. In contrast, mepacrine (0.01-0.1 mM), an antimalarial drug which has likewise been reported to inhibit phospholipase and additionally calmodulin, did not inhibit exocytosis elicited by concanavalin A (con A) or ionophore A23187. Rather, mepacrine (0.1-0.5 mM) alone increased histamine release up to 70%. Light microscopic observations following ruthenium red staining demonstrated the mepacrine-induced response to be exocytosis. Like the response to compound 48/80, that elicited by mepacrine was maximal within 40 s and was inhibited by phosphatidylserine. In the absence of extracellular calcium, secretion elicited by mepacrine and by con A was inhibited by 87 and 90%, respectively, whereas that elicited by 48/80 was unaffected. Incubation of mast cells in the presence of 2 mM EDTA for 2 h inhibited responses to 48/809 by 76% and nearly abolished those to mepacrine and to con A. 5,8,11,14-Eicosatetraynoic acid (50 and 100 microM) inhibited secretion elicited by con A but not that evoked by mepacrine or polymyxin B. The phenothiazines thioridazine (10-50 microM) and chlorpromazine (25-125 microM) inhibited secretory responses to mepacrine, to 48/80 and to con A. Both phenothiazines inhibited secretion elicited by con A more effectively than that elicited by mepacrine or 48/80. The results indicate that mepacrine, like con A, elicits exocytosis in mast cells by drawing on extracellular sources of calcium, but the early events of secretion initiated by these two secretagogues are pharmacologically distinct.(ABSTRACT TRUNCATED AT 250 WORDS)