Phenothiazine drug metabolites: dopamine D2 receptor, alpha 1- and alpha 2-adrenoceptor binding

Polypharmacy-related Shock Symptoms and Complications Associated with Phenothiazine

This report describes a case of shock symptoms in a 72-year-old woman with epilepsy who had been in a state of polypharmacy, taking multiple antipsychotic drugs. After receiving a normal dose of periciazine, she exhibited impaired consciousness, hypothermia, and hypotension and was admitted to hospital. Despite poor response to vasopressors, conservative treatment led to gradual improvement. Subsequent pharmacokinetic analysis showed non-toxic blood concentrations of periciazine, suggesting that even small doses of phenothiazines could result in toxic symptoms. This case highlights the importance of monitoring for adverse reactions when prescribing multiple antipsychotic drugs, particularly in older polypharmacy patients.

Antipsychotics possess anti-glioblastoma activity by disrupting lysosomal function and inhibiting oncogenic signaling by stabilizing PTEN

The repurposing of medications developed for central nervous system (CNS) disorders, possessing favorable safety profiles and blood-brain barrier permeability, represents a promising strategy for identifying new therapies to combat glioblastoma (GBM). In this study, we investigated the anti-GBM activity of specific antipsychotics and antidepressants in vitro and in vivo. Our results demonstrate that these compounds share a common mechanism of action in GBM, disrupting lysosomal function and subsequently inducing lysosomal membrane rupture and cell death. Notably, PTEN intact GBMs possess an increased sensitivity to these compounds. The inhibition of lysosomal function synergized with inhibitors targeting the EGFR-PI3K-Akt pathway, leading to an energetic and antioxidant collapse. These findings provide a foundation for the potential clinical application of CNS drugs in GBM treatment. Additionally, this work offers critical insights into the mechanisms and determinants of cytotoxicity for drugs currently undergoing clinical trials as repurposing agents for various cancers, including Fluoxetine, Sertraline, Thioridazine, Chlorpromazine, and Fluphenazine.

Establishment of LC-MS/MS method for quantifying chlorpromazine metabolites with application to its metabolism in liver and placenta microsomes

Chlorpromazine has sedative and antiemetic pharmacological effects and is widely used in clinic. Its main metabolites include 7-hydroxychlorpromazine, N-monodesmethylchlorpromazine and chlorpromazine sulfoxide, which affect the therapeutic efficacy. To support metabolism research, the quantitative analysis method of 7-hydroxychlorpromazine, N-monodesmethylchlorpromazine and chlorpromazine sulfoxide in microsomal enzymes was established for the first time by LC-MS/MS. This method has been fully validated in rat liver microsomes, and partially verified in human liver microsomes and human placenta microsomes. The intra-day and inter-day accuracy and precision of the analytes were all within ± 15%. The extraction recovery was good, and no matrix effect was detected. This accurate and sensitive method was successfully applied to chlorpromazine metabolism in different microsomal enzymes. In particular, the biotransformation of chlorpromazine in human placenta microsomes was detected for the first time. The metabolites detected in human liver and placenta microsomes presented different formation rates, indicating the wide distribution and different activities of drug-metabolizing enzymes.

Dopamine Dynamics and Neurobiology of Non-Response to Antipsychotics, Relevance for Treatment Resistant Schizophrenia: A Systematic Review and Critical Appraisal

Treatment resistant schizophrenia (TRS) is characterized by a lack of, or suboptimal response to, antipsychotic agents. The biological underpinnings of this clinical condition are still scarcely understood. Since all antipsychotics block dopamine D2 receptors (D2R), dopamine-related mechanisms should be considered the main candidates in the neurobiology of antipsychotic non-response, although other neurotransmitter systems play a role. The aims of this review are: (i) to recapitulate and critically appraise the relevant literature on dopamine-related mechanisms of TRS; (ii) to discuss the methodological limitations of the studies so far conducted and delineate a theoretical framework on dopamine mechanisms of TRS; and (iii) to highlight future perspectives of research and unmet needs. Dopamine-related neurobiological mechanisms of TRS may be multiple and putatively subdivided into three biological points: (1) D2R-related, including increased D2R levels; increased density of D2Rs in the high-affinity state; aberrant D2R dimer or heteromer formation; imbalance between D2R short and long variants; extrastriatal D2Rs; (2) presynaptic dopamine, including low or normal dopamine synthesis and/or release compared to responder patients; and (3) exaggerated postsynaptic D2R-mediated neurotransmission. Future points to be addressed are: (i) a more neurobiologically-oriented phenotypic categorization of TRS; (ii) implementation of neurobiological studies by directly comparing treatment resistant vs. treatment responder patients; (iii) development of a reliable animal model of non-response to antipsychotics.

Contribution of hemodynamic side effects and associated autonomic reflexes to ventricular arrhythmias triggering by torsadogenic hERG blocking drugs

BACKGROUND AND PURPOSES

Several hERG blocking drugs known for their propensity to trigger Torsades de Pointes (TdP) were reported to induce a sympatho-vagal coactivation and to enhance High Frequency heart rate (HFHR) and QT oscillations (HFQT) from telemetric data. The present work aims to characterise the underlying mechanism(s) leading to these autonomic changes.

EXPERIMENTAL APPROACH

Effects of 15 torsadogenic hERG blocking drugs (astemizole, chlorpromazine, cisapride, droperidol, ibutilide, dofetilide, haloperidol, moxifloxacin, pimozide, quinidine, risperidone, sotalol, sertindole, terfenadine, thioridazine) were assessed by telemetry in beagle dogs. Hemodynamic effects on diastolic and systolic arterial pressure were analysed from the first doses causing QTc prolongation and/or HFQT oscillations enhancement. Autonomic control changes were analysed with the High Frequency Autonomic Modulation (HFAM) model.

KEY RESULTS

Except moxifloxacin and quinidine, all torsadogenic hERG blockers induced parasympathetic activation or sympatho-vagal coactivation combined with enhancement of HFQT oscillations. These autonomic effects result from reflex compensatory mechanisms in response to mild hemodynamic side effects. These hemodynamic mechanisms were characterised by transient HR acceleration during HF oscillations. A phenomenon of concealed QT prolongation was unmasked for several torsadogenic hERG blockers under β-adrenoceptors blockade by atenolol. Resulting enhancement of HFQT oscillations was shown to contribute directly to triggering of dofetilide induced ventricular arrhythmias.

CONCLUSIONS AND IMPLICATIONS

This work supports for the first time a contribution of hemodynamic side properties to ventricular arrhythmias triggering by torsadogenic hERG blocking drugs. These hemodynamic side effects may constitute a second component of their arrhythmic profile acting as a trigger alongside their intrinsic arrhythmogenic electrophysiological properties.

Multifaceted effect of chlorpromazine in cancer: implications for cancer treatment

Since its discovery in 1951, chlorpromazine (CPZ) has been one of the most widely used antipsychotic medications for treating schizophrenia and other psychiatric disorders. In addition to its antipsychotic effect, many studies in the last several decades have found that CPZ has a potent antitumorigenic effect. These studies have shown that CPZ affects a number of molecular oncogenic targets through multiple pathways, including the regulation of cell cycle, cancer growth and metastasis, chemo-resistance and stemness of cancer cells. Here we review studies on molecular mechanisms of CPZ’s action on key proteins involved in cancer, including p53, YAP, Ras protein, ion channels, and MAPKs. We discuss common and overlapping signaling pathways of CPZ’s action, its cancer-type specificity, antitumorigenic effects of CPZ reported in animal models and population studies on the rate of cancer in psychiatric patients. We also discuss the potential benefits and limitations of repurposing CPZ for cancer treatment.

Antibacterial properties of phenothiazine derivatives against multidrug-resistant Acinetobacter baumannii strains

AIM

As options to treat recalcitrant bacterial infections which are increasingly limited due to multidrug-resistant strains, searching for new, effective antibacterial compounds is necessary. One strategy is to generate treatment alternatives by drug repurposing.

METHODS AND RESULTS

In this work, phenotypic microarrays were used for the screening of miscellaneous compounds against the growth and biofilm formation of Acinetobacter baumannii, an important emergent multidrug-resistant opportunistic pathogen. The results showed that the phenothiazine derivatives, such as promethazine, trifluoperazine, thioridazine, and chlorpromazine, inhibited the growth of antibiotic-sensitive and multidrug-resistant strains (showing minimal inhibitory concentrations ranging from 0·05 to 0·6 g l^-1 and minimal bactericidal concentrations ranging from 0·1 to 2·5 g l^-1 ). All phenothiazine derivatives were active against biofilm cells (with minimal biofilm eradication concentrations ranging from 0·5 to >3 g l^-1 ). Chlorpromazine promoted reactive oxigen species (ROS) production, and cell membrane and DNA damage. Chlorpromazine showed synergy with antibiotics such as ceftazidime, meropenem, and colistin and was an effective treatment for experimentally infected Galleria mellonella when combined with ceftazidime.

CONCLUSIONS

It was demonstrated that phenothiazine derivatives, especially chlorpromazine, are drugs with attractive antibacterial properties against nosocomial MDR strains of A. baumannii, by generating ROS and cell membrane and DNA damage.

SIGNIFICANCE AND IMPACT OF THE STUDY

The present study indicates that repurposing phenothiazine derivatives for treating recalcitrant infections by A. baumannii could be promising.

How Can Drug Metabolism and Transporter Genetics Inform Psychotropic Prescribing?

Many genetic variants in drug metabolizing enzymes and transporters have been shown to be relevant for treating psychiatric disorders. Associations are strong enough to feature on drug labels and for prescribing guidelines based on such data. A range of commercial tests are available; however, there is variability in included genetic variants, methodology, and interpretation. We herein provide relevant background for understanding clinical associations with specific variants, other factors that are relevant to consider when interpreting such data (such as age, gender, drug-drug interactions), and summarize the data relevant to clinical utility of pharmacogenetic testing in psychiatry and the available prescribing guidelines. We also highlight areas for future research focus in this field.

Retracted: Allosteric Activators of Protein Phosphatase 2A Display Broad Antitumor Activity Mediated by Dephosphorylation of MYBL2

Protein phosphatase 2A (PP2A) enzymes can suppress tumors, but they are often inactivated in human cancers overexpressing inhibitory proteins. Here, we identify a class of small-molecule iHAPs (improved heterocyclic activators of PP2A) that kill leukemia cells by allosterically assembling a specific heterotrimeric PP2A holoenzyme consisting of PPP2R1A (scaffold), PPP2R5E (B56ε, regulatory), and PPP2CA (catalytic) subunits. One compound, iHAP1, activates this complex but does not inhibit dopamine receptor D2, a mediator of neurologic toxicity induced by perphenazine and related neuroleptics. The PP2A complex activated by iHAP1 dephosphorylates the MYBL2 transcription factor on Ser241, causing irreversible arrest of leukemia and other cancer cells in prometaphase. In contrast, SMAPs, a separate class of compounds, activate PP2A holoenzymes containing a different regulatory subunit, do not dephosphorylate MYBL2, and arrest tumor cells in G1 phase. Our findings demonstrate that small molecules can serve as allosteric switches to activate distinct PP2A complexes with unique substrates.

Classification of neuroleptic drugs - lack of relationship to effect on negative symptoms in schizophrenia

There is both pharmacological and clinical support for a classification of the schizophrenic syndrome into negative and positive subtypes. For neuroleptics that act upon both types of symptoms, it appears that lower doses are required for treatment of negative than for positive symptoms. Successful drug treatment of negative symptoms may therefore depend upon the choice of a correct dosage for the individual patient. Due to variation in pharamacokinetic parameters, similar doses of a neuroleptic drug may result in different plasma levels in individual patients, especially after oral medication. Pharmacokinetic variations, if not under proper control, may easily disguise a concentration-dependent relationship, such as the effects of a neuroleptic drug upon negative and positive symptoms. In drug treatment of negative symptoms it may therefore be an advantage to individualize the doses as a function of plasma drug level measurements, when available. No general relationship has been demonstrated between the chemical properties or pharmacodynamics of neuroleptic drugs and their potential to act upon negative symptoms. Also, the drugs which have been demonstrated to have an “energizing” effect have widely different pharmacokinetic properties. A chemical or pharmacological classification of neuroleptics therefore does not seem to give any information about their possible efficacy in treating negative symptoms in schizophrenia.

Confirmation of metabolites of the neuroleptic drug prothipendyl using human liver microsomes, specific CYP enzymes and authentic forensic samples-Benefit for routine drug testing

Metabolism of the tricyclic azaphenothiazine neuroleptic drug prothipendyl was investigated with in vitro studies using human liver microsomes but also specific isoforms of cytochrome P450 (CYP) enzymes. Identification and analysis of metabolites was done by liquid chromatography (LC) coupled with quadrupole time of flight mass spectrometry (LC-QTOF-MS) as well as triple quadrupole mass spectrometry (LC-QQQ-MS). Results of the herein presented study revealed the proof of various demethylated and oxidized metabolites (-CH₂, -C₂H₄, four derivatives of prothipendyl +O and three derivatives of prothipendyl -CH₂+O). Metabolic reactions of prothipendyl were mainly catalyzed by CYP enzymes CYP1A2, CYP2D6, CYP2C19 and CYP3A4. N-demethyl-prothipendyl was predominantly formed by isoforms CYP2C19 and CYP1A2, while particularly the CYP isoenzyme 3A4 was responsible for the formation of prothipendyl sulfoxide. To confirm the formation of previously identified metabolites in vivo, cardiac blood samples that were tested positive for prothipendyl during routine drug testing and serum and urine samples, collected after a voluntary intake of prothipendyl, were analyzed by LC-QQQ-MS. All metabolites of prothipendyl were proven in these authentic specimens. Neither in serum samples nor in urine samples, a prolonged detectability of metabolites in comparison to prothipendyl could be demonstrated.

Acepromazine inhibits hERG potassium ion channels expressed in human embryonic kidney 293 cells

The effects of acepromazine on human ether-à-go-go-related gene (hERG) potassium channels were investigated using whole-cell voltage-clamp technique in human embryonic kidney (HEK293) cells transfected with hERG. The hERG currents were recorded with or without acepromazine, and the steady-state and peak tail currents were analyzed for the evaluating the drug effects. Acepromazine inhibited the hERG currents in a concentration-dependent manner with an IC₅₀ value of 1.5 µM and Hill coefficient of 1.1. Acepromazine blocked hERG currents in a voltage-dependent manner between –40 and +10 mV. Before and after application of acepromazine, the half activation potentials of hERG currents changed to hyperpolarizing direction. Acepromazine blocked both the steady-state hERG currents by depolarizing pulse and the peak tail currents by repolarizing pulse; however, the extent of blocking by acepromazine in the repolarizing pulse was more profound than that in the depolarizing pulse, indicating that acepromazine has a high affinity for the open state of the channels, with a relatively lower affinity for the closed state of hERG channels. A fast application of acepromazine during the tail currents inhibited the open state of hERG channels in a concentration-dependent. The steady-state inactivation of hERG currents shifted to the hyperpolarized direction by acepromazine. These results suggest that acepromazine inhibits the hERG channels probably by an open- and inactivated-channel blocking mechanism. Regarding to the fact that the hERG channels are the potential target of drug-induced long QT syndrome, our results suggest that acepromazine can possibly induce a cardiac arrhythmia through the inhibition of hERG channels.

Molecular mechanisms underlying variations in lung function: a systems genetics analysis

BACKGROUND

Lung function measures reflect the physiological state of the lung, and are essential to the diagnosis of chronic obstructive pulmonary disease (COPD). The SpiroMeta-CHARGE consortium undertook the largest genome-wide association study (GWAS) so far (n=48,201) for forced expiratory volume in 1 s (FEV1) and the ratio of FEV1 to forced vital capacity (FEV1/FVC) in the general population. The lung expression quantitative trait loci (eQTLs) study mapped the genetic architecture of gene expression in lung tissue from 1111 individuals. We used a systems genetics approach to identify single nucleotide polymorphisms (SNPs) associated with lung function that act as eQTLs and change the level of expression of their target genes in lung tissue; termed eSNPs.

METHODS

The SpiroMeta-CHARGE GWAS results were integrated with lung eQTLs to map eSNPs and the genes and pathways underlying the associations in lung tissue. For comparison, a similar analysis was done in peripheral blood. The lung mRNA expression levels of the eSNP-regulated genes were tested for associations with lung function measures in 727 individuals. Additional analyses identified the pleiotropic effects of eSNPs from the published GWAS catalogue, and mapped enrichment in regulatory regions from the ENCODE project. Finally, the Connectivity Map database was used to identify potential therapeutics in silico that could reverse the COPD lung tissue gene signature.

FINDINGS

SNPs associated with lung function measures were more likely to be eQTLs and vice versa. The integration mapped the specific genes underlying the GWAS signals in lung tissue. The eSNP-regulated genes were enriched for developmental and inflammatory pathways; by comparison, SNPs associated with lung function that were eQTLs in blood, but not in lung, were only involved in inflammatory pathways. Lung function eSNPs were enriched for regulatory elements and were over-represented among genes showing differential expression during fetal lung development. An mRNA gene expression signature for COPD was identified in lung tissue and compared with the Connectivity Map. This in-silico drug repurposing approach suggested several compounds that reverse the COPD gene expression signature, including a nicotine receptor antagonist. These findings represent novel therapeutic pathways for COPD.

INTERPRETATION

The system genetics approach identified lung tissue genes driving the variation in lung function and susceptibility to COPD. The identification of these genes and the pathways in which they are enriched is essential to understand the pathophysiology of airway obstruction and to identify novel therapeutic targets and biomarkers for COPD, including drugs that reverse the COPD gene signature in silico.

FUNDING

The research reported in this article was not specifically funded by any agency. See Acknowledgments for a full list of funders of the lung eQTL study and the Spiro-Meta CHARGE GWAS.

Effect of chlorpromazine on rat placenta development

We examined the sequential histopathological changes in the placentas from rats exposed to chlorpromazine. Chlorpromazine was intraperitoneally administered on GD 14 at 50 and 100 mg/kg and the placentas were sampled on GDs 14.5, 15, 17 and 21. The incidence of dams with complete fetal resorption was increased from GD 17 up to 20% at 50 mg/kg and 44.4% at 100 mg/kg. The embryo/fetal weights reduced on GDs 15 and 17 at 50 mg/kg and during GDs 15-21 at 100 mg/kg. The placental weights reduced on GD 17 at 50 mg/kg and during GDs 14.5-21 at 100 mg/kg. Histopathologically, in the labyrinth zone, apoptotic cells were scattered in the trophoblastic septa without inhibition of cell proliferation on GDs 14.5 and 15 at 50 and 100 mg/kg in a dose-dependent manner. A decrease in trophoblasts led to labyrinth zone hypoplasia. In the basal zone, apoptotic cells were scattered on GDs 14.5 and 15 at 100 mg/kg, and most of them appeared to be glycogen cells. A decrease in glycogen cells induced the delayed development of glycogen cell islands and the subsequent remaining glycogen cell islands, and led to the cystic degeneration of glycogen cells. In addition, failure of development of the glycogen cell islands led to the impaired interstitial invasion of the glycogen cells, and then metrial gland hypoplasia occurred.

Main contribution of the cytochrome P450 isoenzyme 1A2 (CYP1A2) to N-demethylation and 5-sulfoxidation of the phenothiazine neuroleptic chlorpromazine in human liver--A comparison with other phenothiazines

The aim of the present study was to identify cytochrome P450 (CYP) isoenzymes involved in the 5-sulfoxidation, mono-N-demethylation and di-N-demethylation of the aliphatic-type phenothiazine neuroleptic chlorpromazine in human liver. Experiments were performed in vitro using cDNA-expressed human CYP isoforms (Supersomes 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, 3A4), liver microsomes from different donors and CYP-selective inhibitors. The obtained results indicate that CYP1A2 is the only CYP isoform that catalyzes the mono-N-demethylation and di-N-demethylation of chlorpromazine (100%) and is the main isoform responsible for chlorpromazine 5-sulfoxidation (64%) at a therapeutic concentration of the drug (10 microM). CYP3A4 contributes to a lesser degree to chlorpromazine 5-sulfoxidation (34%). The role of CYP2B6, CYP2C19 and CYP2D6 in catalyzing of the latter reaction is negligible (0.1-2%). Similar results were obtained at a higher, non-therapeutic concentration of the drug (100 microM); however, the contribution of CYP1A2 to chlorpromazine mono-N-demethylation was noticeably lower (75%), mostly in favour of CYP2C19 and CYP3A4 (about 12% each). The obtained results indicate that the catalysis of chlorpromazine N-demethylation and 5-sulfoxidation in humans exhibits a stricter CYP1A2 preference compared to the previously tested phenothiazines (promazine, perazine, and thioridazine). Hence pharmacokinetic interactions involving chlorpromazine and CYP1A2 substrates and inhibitors are likely to occur. Considering strong dopaminergic D(2), noradrenergic alpha(1) and cholinergic M(1) receptor blocking properties of chlorpromazine and some of its metabolites, as well as their serious side effects, the obtained results may be of pharmacological and clinical importance.

Priapism associated with antipsychotics: role of alpha1 adrenoceptor affinity

Case reports indicate that antipsychotics can cause priapism, a persistent penile erection possibly leading to erectile dysfunction. The mechanism of antipsychotic-induced priapism is thought to be related to blockade of alpha1 adrenergic receptors, but clinical data supporting this hypothesis are lacking. The aim of this study was to investigate if the presence of safety signals for antipsychotics and priapism is associated with their alpha1 affinity. Spontaneous reports of adverse drug reactions contained in the US Adverse Event Reporting System database were used to calculate reporting odds ratios (RORs) of priapism for antipsychotics. In total, 426 cases of priapism with 144 of them attributed to antipsychotics were identified. For antipsychotics with high alpha1 affinity, the adjusted ROR was markedly elevated (ROR = 9.9; 95% CI, 7.9-12.4), whereas a weaker signal was observed for antipsychotics with low/medium alpha1 affinity (ROR = 3.6; 95% CI, 2.4-5.2). Signals were present for chlorpromazine, quetiapine, risperidone, ziprasidone, and aripiprazole. After restricting the analysis to cases with medical intervention or disability, the safety signal remained evident only for antipsychotics with high but not for those with low/medium affinity. The observed pattern of signals indicates a relationship between alpha1 affinities of antipsychotics and the occurrence of priapism.

Collaborative work on evaluation of ovarian toxicity. 16) Effects of 2 or 4 weeks repeated dose studies and fertility study of Chlorpromazine hydrochloride in rats

In order to examine potential ovarian toxicity in 2 weeks or 4 weeks repeated-dose studies and a fertility study, chlorpromazine hydrochloride (CPZ) was administered orally to Crl:CD(SD) female rats at dosage levels of 0, 3, 10 and 30 mg/kg/day. In the repeated-dose studies, ovarian weights were decreased at > or = 10 mg/kg in the 4 weeks study and an increase in large atretic follicles was observed histopathologically at > or = 3 mg/kg and > or = 10 mg/kg in the 2 and 4 weeks studies, respectively. In addition, decreased uterine weights and/or atrophic findings in the uterus and vagina at 30 mg/kg and > or = 10 mg/kg, mucification in the vaginal epithelium and alveolar hyperplasia in the mammary gland at > or = 3 mg/kg and > or = 10 mg/kg were seen in the 2 and 4 weeks studies, respectively. Irregular estrous cycles were seen at > or = 3 mg/kg and > or = 10 mg/kg in the 2 and 4 weeks studies. The no-observed-adverse-effect level (NOAEL) for the 2 and 4 weeks studies was considered to be less than 3 mg/kg and 3 mg/kg, respectively. The fertility study with dosing from 2 weeks before mating to day 6 of gestation showed irregular estrous cycles at > or = 10 mg/kg and prolonged copulatory intervals and a reduced fertility index at 30 mg/kg; the NOAEL was therefore considered to be 3 mg/kg, which was higher than that in the 2 weeks study. These results showed that oral CPZ treatment induced ovarian toxicity with 2 weeks or longer treatment and changed the fertility parameters and was therefore concluded that a 2 weeks administration period is adequate to detect the ovarian toxicity of CPZ.

Further characterization of the discriminative stimulus properties of the atypical antipsychotic drug clozapine in C57BL/6 mice: role of 5-HT(2A) serotonergic and alpha (1) adrenergic antagonism

RATIONALE

The discriminative stimulus properties of the atypical antipsychotic drug (APD) clozapine (CLZ) have recently been studied in C57BL/6 mice, a common background strain for genetic alterations. However, further evaluation is needed to fully characterize CLZ's discriminative cue in this strain of mice.

OBJECTIVES

The objectives of the study were to confirm the previous findings using a shorter pretreatment time and to further characterize the receptor mechanisms mediating the discriminative stimulus properties of CLZ by testing APDs, selective ligands, and N-desmethylclozapine (CLZ's major metabolite) in C57BL/6 mice.

MATERIALS AND METHODS

C57BL/6 male mice were trained to discriminate 2.5 mg/kg CLZ (s.c.) from vehicle in a two-lever drug discrimination task.

RESULTS

Generalization testing with CLZ yielded an ED(50) = 1.19 mg/kg. Substitution testing with APDs showed that the atypical APDs quetiapine, sertindole, zotepine, iloperidone, and melperone fully substituted for CLZ (> or =80% CLZ-appropriate responding), but aripiprazole did not. The typical APDs chlorpromazine and thioridazine substituted for CLZ (fluphenazine and perphenazine did not). The serotonin (5-HT) (2A) antagonist M100907 and the alpha(1)-adrenoceptor antagonist prazosin fully substituted for CLZ. The H(1) histaminergic antagonist pyrilamine, dopamine agonist amphetamine, and the selective serotonin reuptake inhibitor fluoxetine did not substitute for CLZ. While N-desmethylclozapine did not substitute for CLZ when tested alone, N-desmethylclozapine plus a low dose of CLZ combined in an additive manner produced full substitution.

CONCLUSIONS

CLZ's discriminative cue in C57BL/6 mice is a "compound" cue mediated in part by antagonism of 5-HT(2A) and alpha(1) receptors.

Pharmacogenetics, drug-metabolizing enzymes, and clinical practice

The application of pharmacogenetics holds great promise for individualized therapy. However, it has little clinical reality at present, despite many claims. The main problem is that the evidence base supporting genetic testing before therapy is weak. The pharmacology of the drugs subject to inherited variability in metabolism is often complex. Few have simple or single pathways of elimination. Some have active metabolites or enantiomers with different activities and pathways of elimination. Drug dosing is likely to be influenced only if the aggregate molar activity of all active moieties at the site of action is predictably affected by genotype or phenotype. Variation in drug concentration must be significant enough to provide "signal" over and above normal variation, and there must be a genuine concentration-effect relationship. The therapeutic index of the drug will also influence test utility. After considering all of these factors, the benefits of prospective testing need to be weighed against the costs and against other endpoints of effect. It is not surprising that few drugs satisfy these requirements. Drugs (and enzymes) for which there is a reasonable evidence base supporting genotyping or phenotyping include suxamethonium/mivacurium (butyrylcholinesterase), and azathioprine/6-mercaptopurine (thiopurine methyltransferase). Drugs for which there is a potential case for prospective testing include warfarin (CYP2C9), perhexiline (CYP2D6), and perhaps the proton pump inhibitors (CYP2C19). No other drugs have an evidence base that is sufficient to justify prospective testing at present, although some warrant further evaluation. In this review we summarize the current evidence base for pharmacogenetics in relation to drug-metabolizing enzymes.

Electrophoretic separations of twelve phenothiazines and N-demethyl derivatives by using capillary zone electrophoresis and micellar electrokinetic chromatography with non ionic surfactant

We focused our work on the separation of phenothiazines that are important drugs used for the treatment of psychic diseases. For a better understanding of the metabolism of these solutes, we wanted to separate not only a mixture of 12 phenothiazines but also a mixture containing phenothiazines and their N-demethyl metabolites by capillary electrophoresis. Separations in capillary zone electrophoresis were performed using 3 x 10(-2) mol/L H3PO4 (pH 2.5) but the obtained resolutions were not entirely satisfactory especially with regard to phenothiazine -N-demethyl derivative pairs. To improve the obtained results, we have performed separations by using micellar electrokinetic chromatography. In this approach, we used a running electrolyte containing 3 x 10(-2) mol/L H3PO4 electrolyte (pH 2.5) and octaethylene glycol monododecyl ether (C12E8) as neutral surfactant. By introducing 2 x 10(-3) mol/L C12E8 in the electrolyte, 11 out of 12 phenothiazines have been baseline separated. With respect to the separation of a mixture containing 3 phenothiazines and their 3 demethyl derivatives, we obtained an excellent separation by using a running electrolyte prepared with 7.5 x 10(-4) mol/L C12E8 and 3 x 10(-2) mol/L H3PO4.

Simultaneous determination of levomepromazine, midazolam and their major metabolites in human plasma by reversed-phase liquid chromatography

A sensitive and reliable high-performance liquid chromatographic (HPLC) assay is a prerequisite for pharmacokinetic analysis of continuous infusion of levomepromazine adjuvant to midazolam. We developed such a method to determine the levels of levomepromazine, midazolam and their major metabolites (levomepromazinesulfoxide, desmethyl-, didesmethyllevomepromazine, O-desmethyllevomepromazine and alpha-hydroxy-midazolam) simultaneously. Desmethylclomipramine was used as an internal standard (I.S.). The lower limit of quantification of this assay was set for levomepromazine 4.1 microg/l, levomepromazinesulfoxide 4.9 microg/l, O-desmethyllevomepromazine 18.4 microg/l, alpha-hydroxymidazolam 26.6 microg/l, midazolam 23.4 microg/l, didesmethyllevomepromazine 15.8 microg/l, and desmethyllevomepromazine 6.6 microg/l. The between- and within day assay variations were commonly below 5%. The recovery in human plasma for the different analytes varied between 85 and 11%. The accuracy of this assay varied between 95 and 105% for the different concentrations. The linearity of this assay was set between 25 and 800 microg/l (r(2)>0.999 of the regression line). The first results of pharmacokinetic analysis of midazolam indicated that half-life varied between 1.1 and 1.9 h. Pharmacokinetic analysis using a one-compartment model of levomepromazine revealed that the apparent volume of distribution was 4.1+/-2.4 l per kg lean body mass and the metabolic clearance was 309+/-225 l per hour per 70 kg. This assay proved to be robust and reproducible. It can reliably be used for further study of the pharmacokinetics of continuous infusion of levomepromazine.

Identification of the human cytochrome P450 isoforms mediating in vitro N-dealkylation of perphenazine

AIMS

To identify the human cytochrome P450 (CYP) isoforms mediating the N-dealkylation of the antipsychotic drug perphenazine in vitro and estimate the relative contributions of the CYP isoforms involved.

METHODS

cDNA-expressed CYP isoforms were used to identify the isoforms that are able to mediate the N-dealkylation of perphenazine, which is considered a major metabolic pathway for the drug. Using human liver microsomal preparations (HLM), inhibition studies were carried out to establish the relative contributions of the CYP isoforms involved in the N-dealkylation reaction.

RESULTS

CYP isoforms 1A2, 3A4, 2C8, 2C9, 2C18, 2C19 and 2D6 were able to mediate the N-dealkylation of perphenazine. Reaction velocities and their relative abundance in HLM suggested that CYP1A2, 3A4, 2C19 and 2D6 were the most important contributors to N-dealkylation. Apparent Km values of CYP1A2 and CYP2D6 were in the range 1-2 microM, and Km values of CYP2C19 and CYP3A4 were 14 microM and 7.9 microM, respectively. Ketoconazole inhibition of N-dealkylation mediated by a mixed HLM indicated that CYP3A4 accounted for about 40% of perphenazine N-dealkylation at therapeutically relevant concentrations. The contribution of the CYP isoforms 1A2, 2C19 and 2D6 amounted to 20-25% each as measured by the percentage inhibition obtained by addition of furafylline, fluvoxamine or quinidine, respectively. HLM-mediated N-dealkylation of perphenazine accounted for 57% of the total amount of substrate consumed during incubation.

CONCLUSIONS

The present in vitro study suggests that CYP isoforms 1A2, 3A4, 2C19 and 2CD6 are primarily involved in the N-dealkylation of perphenazine. The relatively modest role of CYP2D6 is at variance with in vivo studies, which indicate a greater contribution of this isoform. Alternative metabolic pathways, corresponding to 43% of the HLM-mediated metabolism of the drug, may depend more strongly on CYP2D6.

Long-term treatment with chlorpromazine and haloperidol but not with sulpiride and clozapine markedly elevates neuropeptide Y-like immunoreactivity in the rat hypothalamus

Male Wistar rats were injected intraperitoneally with chlorpromazine (2 or 10 mg/kg), haloperidol (0.5 or 2 mg/kg), sulpiride (50 or 100 mg/kg) or clozapine (10 or 25 mg/kg) once, for 14 or 28 consecutive days. Hypothalamic neuropeptide Y-like (NPY-like) immunoreactivity (NPY-LI) was determined 24 h after the last dose of the neuroleptic and on the eighth day after drug withdrawal following a 1 month administration. A marked increase in the NPY-LI level was observed only after long-term treatment with typical neuroleptics. The dopamine D2 agonist quinpirole antagonized the effects of chlorpromazine and haloperidol, but it did not change NPY-LI concentration by itself. Co-administration of the alpha 1 adrenergic antagonist prazosin with quinpirole to chlorpromazine-pretreated rats attenuated the effect of quinpirole but enhanced an increase in NPY-LI content elicited by chlorpromazine. Neither the dopamine D1 antagonist SCH 23390 (1 mg/kg) nor the dopamine D2 antagonist sulpiride (100 mg/kg) administered i.p. for 14 days by itself altered the hypothalamic NPY-LI level, but in combination they increased it. Our results suggest that NPY in hypothalamus may be involved in the mechanism of action of typical non-selective neuroleptics and that the influence of studied drugs on NPY-LI is at least partly mediated by a simultaneous prolonged blockade of both D1 and D2 dopaminergic receptors.

Metabolism of levomepromazine in man

The phenothiazine drug, levomepromazine (LM), is used in the treatment of psychiatric disorders and as an analgesic. A single 50 or 100 mg dose of LM was given to healthy male volunteers, and urine samples were collected for 24 h. The urine was treated with beta-glucuronidase, purified by solid-phase extraction, and analyzed on a GC-MS system for identification of LM metabolites. Mass spectra suggesting 14 different LM metabolites were obtained from the samples. Our of these, 13 spectra could be ascribed to specific metabolites, 5 of which have not previously been identified. All these 5 metabolites were hydroxylated at the phenothiazine nucleus. Although the applied method did not determine the positions of hydroxyl groups on phenothiazine nuclei. 3 of the 5 metabolites were identified as O-desmethyl 3-hydroxy LM, O-desmethyl 7-hydroxy LM, and N,O-didesmethyl 7-hydroxy LM, based on their chromatographic properties. In addition two metabolites, one being hydroxylated on the phenothiazine nucleus, and one being O-demethylated and hydroxylated on the nucleus, were found. It is suggested that these were 8-hydroxy LM and O-desmethyl 8-hydroxy LM. The concentrations of 3-hydroxy LM (free+conjugated) appeared to be much higher than the concentrations of any other metabolite in the samples.

Effect of levomepromazine and metabolites on debrisoquine hydroxylation in the rat

The influence of the major metabolites of the phenothiazine derivative, levomepromazine (methotrimeprazine), on hydroxylation of debrisoquine was examined in male Sprague-Dawley rats. The metabolic ratio of debrisoquine/4-hydroxy debrisoquine was first determined in rats after oral administration of 10 mg/kg of debrisoquine. Then the same dose of debrisoquine was co-administered with various doses of levomepromazine or one of its metabolites. Levomepromazine and its sulphoxidated, N-demethylated and O-demethylated metabolites caused highly significant and dose-dependent increases in the debrisoquine metabolic ratio. 3-Hydroxy levomepromazine had no significant effect on the metabolism of debrisoquine. This indicates that the non-hydroxylated metabolites of levomepromazine have relatively high affinities for the cytochrome P450 enzyme which converts debrisoquine to 4-hydroxy debrisoquine in the rat. Such metabolites may therefore be responsible for a considerable part of the inhibitory effect of debrisoquine hydroxylation previously reported in patients treated with phenothiazine neuroleptics.

Levomepromazine receptor binding profile in human brain--implications for treatment-resistant schizophrenia

The receptor binding profile of levomepromazine (LMP) in human brain was compared with that of clozapine (CLOZ) and chlorpromazine (CPZ). LMP showed significantly greater binding affinity for both alpha-1 and serotonin-2 binding sites than either CLOZ or CPZ, and significantly greater binding to alpha-2 sites than CPZ. A potent pharmacological effect at these receptor sites may explain the beneficial effect of LMP on psychotic symptoms and akathisia in treatment-resistant schizophrenia recently described in 2 open studies. LMP requires further appraisal as a potentially useful neuroleptic in the management of treatment-resistant schizophrenia.

Antagonism of presynaptic dopamine receptors by phenothiazine drug metabolites

Electrically evoked release of dopamine from the caudate nucleus is reduced by the dopamine receptor agonists, apomorphine and bromocriptine, and facilitated by neuroleptic drugs, which act as dopamine autoreceptor antagonists. The potencies of chlorpromazine, fluphenazine, levomepromazine and their hydroxy-metabolites in modulating electrically evoked release of dopamine were examined by superfusion of rabbit caudate nucleus slices pre-incubated with 3H-dopamine. O-Desmethyl levomepromazine, 3-hydroxy- and 7-hydroxy metabolites of chlorpromazine and levomepromazine facilitated electrically evoked release of 3H-dopamine, having potencies similar to that of the parent compounds. 7-Hydroxy fluphenazine was less active than fluphenazine in this system. These results indicate that phenolic metabolites of chlorpromazine and levomepromazine, but not of fluphenazine, may contribute to effects of the drugs mediated by presynaptic dopamine receptors.

Measurement of blood levels of neuroleptics and metabolites by combined high performance liquid chromatography-radioreceptor assay for D2 and sigma sites

The dopamine (D2) receptor blocking property of antipsychotic medications has been proposed as the mechanism of the therapeutic activity of this class of drugs. This property has also been exploited as a method to quantify therapeutic levels of these drugs in patients. However, the lack of correlation among dosage, blood levels and clinical response has resulted in a contradictory literature on both mechanism and quantification of these drugs. Bioactivity and chemical identity of the commonly prescribed neuroleptic drug fluphenazine and its metabolites in human plasma were determined by a new method which combines the selectivity of chemical methods with the sensitivity and bioassay of the radioreceptor assay (RRA) method. Fluphenazine and its metabolites were separated and identified in human plasma by an ion-pairing reverse phase high performance liquid chromatographic method with electrochemical detection. A volatile buffer system was employed which was compatible with facile sample preparation for post-column analyses, and which provided sharp, symmetrical chromatographic peaks of parent compound and metabolites. Post chromatography, HPLC fractions were assayed by RRA for D2, alpha 1 and sigma receptors. More than one pattern of metabolism of the drug was seen, including biosynthesis of drug metabolites with biological activities at these receptor types. The individual differences with which this occurs may contribute to the variabilities seen in clinical response to neuroleptics, and to difficulties in neuroleptic blood level determinations.

Human metabolism of phenothiazines to sulfoxides determined by a new high performance liquid chromatography--electrochemical detection method

The metabolism of phenothiazine drugs may contribute to both their therapeutic and toxic actions by production of active metabolites in vivo. Idiosyncratic reactions or treatment failure may be a consequence of differing patterns of metabolism in different patients. In this report, a modification of our method for the detection of metabolites of phenothiazines is described, which also permits the simultaneous determination of sulfoxide metabolites in human plasma. Application of this method to human plasma identifies marked individual differences in patterns of phenothiazine metabolism.

Correlation of activity of chlorpromazine and respective hydroxy, dimethoxy and sulphoxide analogues on dopamine, muscarinic, histamine and calmodulin sites of action

1. Chlorpromazine (CPZ) is a unique molecule which has many potential sites of action, as well as a propensity to be transformed into a host of metabolites possessing varying degrees of pharmacological and/or toxic reactions. This investigation examined the rank order of potency of CPZ and eight metabolic derivatives with respect to displacement of 3H-spiperone at central dopamine-2 (DA-2) receptors, 3H-pirenzepine at central muscarinic-1 (M-1) receptors, and inhibition of calmodulin-induced activation of cyclic AMP-dependent phosphodiesterase. 2. The most potent CPZ analogues to displace labelled spiperone from DA-2 receptors in rat striatum were: 3-hydroxy-CPZ, CPZ, 3,7-dihydroxy-CPZ, and 7-hydroxy-CPZ. Intermediate potency was observed with 8-hydroxy-CPZ, 3,7,8-trihydroxy-CPZ, and 7,8-dihydroxy-CPZ. Chlorpromazine sulphoxide and 7,8-dimethoxy-CPZ displayed the least activity at DA-2 receptors. 3. Displacement of labelled pirenzepine from M-1 receptors in rat frontal cortex occurred to the greatest extent with CPZ which was one to two orders of magnitude more potent than noted for 3-hydroxy-CPZ greater than 7-hydroxy-CPZ greater than CPZ-sulphoxide greater than 8-hydroxy-CPZ greater than 7,8-dimethoxy-CPZ. The least potent agents were 3,7-and 7,8-dihydroxy-CPZs and 3,7,8-trihydroxy-CPZ. 4. A partially purified calmodulin-sensitive preparation of cyclic AMP-dependent phosphodiesterase from guinea pig heart was most sensitive to inhibition by 7,8-dihydroxy-CPZ, 7,8-dimethoxy-CPZ, 3-hydroxy-CPZ, 7-hydroxy-CPZ, 8-hydroxy-CPZ and CPZ. Least inhibition occurred with 3,7-dihydroxy-CPZ, 3,7,8-trihydroxy-CPZ and CPZ-sulphoxide. 5. The DA-2 receptors were more sensitive to the active CPZ analogues than were the M-1 receptors while calmodulin-activated phosphodiesterase was the least sensitive preparation. 6. Comparisons of data were made with existing information from other laboratories and in general CPZ, 7-hydroxy-CPZ and 3-hydroxy-CPZ were the most potent compounds across different test conditions.

Muscarinic cholinergic and histamine H1 receptor binding of phenothiazine drug metabolites

In vitro binding affinities of chlorpromazine, fluphenazine, levomepromazine, perphenazine and some of their metabolites for dopamine D2 receptors, alpha 1- and alpha 2 adrenoceptors in rat brain were previously reported from our laboratories. The present study reports the in vitro binding affinities of the same compounds for muscarinic cholinergic receptors and for histamine H1 receptors in rat brain, using 3H-quinuclidinyl benzilate and 3H-mepyramine as radioligands. Chlorpromazine, levomepromazine, and their metabolites had 5-30 times higher binding affinities for muscarinic cholinergic receptors than fluphenazine, perphenazine and their metabolites. Levomepromazine was the most potent and fluphenazine the least potent of the four drugs in histamine H1 receptor binding. 7-Hydroxy levomepromazine, 3-hydroxy levomepromazine and 7-hydroxy fluphenazine had only 10% of the potency of the parent drug in histamine H1 receptor binding, while the 7-hydroxy-metabolites of chlorpromazine and perphenazine had about 75% of the potency of the parent drug in this binding system. Their histamine H1 receptor binding affinities indicate that metabolites may contribute to the sedative effects of chlorpromazine and levomepromazine.

Anti-apomorphine effects of phenothiazine drug metabolites

The potencies in producing muscle relaxation, and in antagonizing apomorphine-induced climbing and hypothermia in mice, were examined for chlorpromazine, levomepromazine and their main metabolites, and for fluphenazine and 7-hydroxy fluphenazine. 3-Hydroxy chlorpromazine was more potent than chlorpromazine in antagonizing apomorphine-induced climbing, while levomepromazine and 3-hydroxy levomepromazine were equipotent in this test. The 3-hydroxy metabolites of chlorpromazine and levomepromazine were more potent than the parent compounds in antagonizing hypothermia, and had significantly weaker muscle relaxant effects than the parent compounds. The 7-hydroxy and N-monodesmethyl metabolites were generally less potent that the parent compounds in antagonizing apomorphine-induced effects. N-Monodesmethyl levomepromazine had a pronounced muscle relaxant effect, like levomepromazine itself. The sulphoxide metabolites of chlorpromazine and levomepromazine were inactive in all tests. Their potencies in these tests indicate that among the metabolites 7-hydroxy chlorpromazine, N-monodesmethyl chlorpromazine and 3-hydroxy levomepromazine, which have all been identified in plasma from patients, may contribute to the antipsychotic effects of the drugs, and furthermore that N-monodesmethyl levomepromazine may contribute to the sedative effects of levomepromazine.