Genetic predictors of therapeutic response to clozapine: current status of research

Indicators of response to clozapine treatment

Since its initial landmark trial against chlorpromazine in 1988, clozapine has been the drug of choice for the treatment of refractory schizophrenia. However, variability in clinical response to clozapine treatment is unequivocal. In an effort to preselect patients who are most likely to benefit from clozapine, a number of patient and disease variables and select genetic differences have been studied for their association with positive treatment response to clozapine. Because of small trial sizes and the heterogeneity of study design, findings have resulted in no generalizable conclusion. Future pharmacogenetic studies hold the promise of antipsychotic treatment personalization.

Clozapine response and pre-treatment EEG-is there some kind of relationship

BACKGROUND

Clozapine has been used widely in the management of treatment-resistant schizophrenia. The present study aims at determining whether pre-treatment electroencephalography (EEG) abnormalities would serve as a marker for response to clozapine treatment.

SUBJECTS AND METHODS

This was a cross-sectional study done in a tertiary care center in Mumbai where patients diagnosed with schizophrenia using DSM-IV criteria and resistant schizophrenia using Kane criteria were assessed using EEG prior to starting clozapine treatment. They were rated for symptomatic improvement using the Positive and Negative Syndrome Scale (PANSS) along with Clinical Global Improvement for Severity (CGI-S). The results were statistically analysed and presented.

RESULTS

55 out of the 80 patients in the study showed baseline EEG abnormalities. The mean duration of illness in the patients were 2.65 years. Slow wave and background EEG abnormalities were common in pre-treatment EEG. 36.4% patients in the study showed clinical response. Patients with negative symptoms and baseline EEG abnormalities showed better response.

CONCLUSIONS

The study was circumscribed and had many limitations due to a small sample size. The relation between pre-treatment EEG abnormalities and clozapine response could not be statistically correlated and it could not be ascertained to be a marker for response to clozapine therapy.

Association between CYP1A2 gene single nucleotide polymorphisms and clinical responses to clozapine in patients with treatment-resistant schizophrenia

OBJECTIVES

Despite clozapine's superior clinical efficacy in treatment-resistant schizophrenia (TRS), its adverse effects, need for periodic leukocyte monitoring, cost and variable clinical outcomes mandate a clinical need to predict its treatment response. Although cytochrome P450 1A2 (CYP1A2) is the principal determinant of metabolism of clozapine, the role of CYP1A2 gene in the clinical response to clozapine is uncertain. Hence, we investigated its association with treatment responses and adverse events of clozapine in TRS.

METHODS

We evaluated four single nucleotide polymorphisms (SNP) in the CYP1A2 gene, clinical responses and serum clozapine levels in 101 consecutive patients with TRS on stable doses of clozapine. We defined clozapine response a priori and investigated allelic and genotypic associations. We assessed the socio-demographic and clinical profiles, premorbid adjustment, traumatic life events, cognition and disability of the participants, using standard assessment schedules for appropriate multivariate analyses.

RESULTS

Our results revealed that CYP1A2 gene SNP (*1C, *1D, *1E and *1F) were not associated with clozapine treatment response, adverse effects, serum clozapine levels or with disability (p values > 0.10).

CONCLUSION

As CYP1A2 gene SNP do not help to predict the clinical response to clozapine, routine screening for them prior to start clozapine is currently unwarranted. We suggest future longitudinal genome-wide association studies investigating clinical and pharmacogenetic variables together.

Outcome definitions and clinical predictors influence pharmacogenetic associations between HTR3A gene polymorphisms and response to clozapine in patients with schizophrenia

RATIONALE

Pharmacogenetics of schizophrenia has not yet delivered anticipated clinical dividends. Clinical heterogeneity of schizophrenia contributes to the poor replication of the findings of pharmacogenetic association studies. Functionally important HTR3A gene single-nucleotide polymorphisms (SNPs) were reported to be associated with response to clozapine.

OBJECTIVE

The aim of this study was to investigate how the association between HTR3A gene SNP and response to clozapine is influenced by various clinical predictors and by differing outcome definitions in patients with treatment-resistant schizophrenia (TRS).

METHODS

We recruited 101 consecutive patients with TRS, on stable doses of clozapine, and evaluated their HTR3A gene SNP (rs1062613 and rs2276302), psychopathology, and serum clozapine levels. We assessed their socio-demographic and clinical profiles, premorbid adjustment, traumatic events, cognition, and disability using standard assessment schedules. We evaluated their response to clozapine, by employing six differing outcome definitions. We employed appropriate multivariate statistics to calculate allelic and genotypic association, accounting for the effects of various clinical variables.

RESULTS

T allele of rs1062613 and G allele of rs2276302 were significantly associated with good clinical response to clozapine (p = 0.02). However, varying outcome definitions make these associations inconsistent. rs1062613 and rs2276302 could explain only 13.8 % variability in the responses to clozapine, while combined clinical predictors and HTR3A pharmacogenetic association model could explain 38 % variability.

CONCLUSIONS

We demonstrated that the results of pharmacogenetic studies in schizophrenia depend heavily on their outcome definitions and that combined clinical and pharmacogenetic models have better predictive values. Future pharmacogenetic studies should employ multiple outcome definitions and should evaluate associated clinical variables.

Early improvement on antipsychotic treatment as a predictor of subsequent response in schizophrenia: analyses from ziprasidone clinical studies

OBJECTIVE

We examine data from short-term placebo-controlled and comparator-controlled clinical trials of ziprasidone in schizophrenia to confirm the predictive capacity of early symptom changes for response. We pose the question of how early is too early to consider "stay or switch" and evaluate the predictive capability of a clinical measure in this regard.

METHODS

We presented two separate pooled analyses of (i) two placebo-controlled and (ii) two active comparator (risperidone and olanzapine) randomized trials of ziprasidone in schizophrenia. Relationship between early changes in Positive and Negative Syndrome Scale (PANSS) total, Brief Psychiatric Rating Scale (BPRS), and Clinical Global Impression-Improvement (CGI-I) scores and treatment outcome was evaluated.

RESULTS

Week 2 improvement was more reliably predictive of subsequent outcome than week 1 improvement using PANSS and BPRS scores with high sensitivity and specificity, whereas CGI-I had much lower specificity. Overall, non-improvement at week 1 or week 2 was highly predictive of non-response using BPRS scores and PANSS but not CGI-I.

CONCLUSIONS

These data, independent of antipsychotic used, confirm prior research showing that early improvement in symptoms is predictive of response. There appears to be an important window of time, beyond week 1, during which important clinical decisions to stay or switch medication may be made.

Factors affecting interindividual differences in clozapine response: a review and case report

OBJECTIVE

Clozapine is the most powerful new‐generation antipsychotic. Although this drug leads to great therapeutic benefits, two types of undesirable conditions frequently occur with its use: side effects and resistance to treatment. Therapeutic drug monitoring of clozapine would be very useful to avoid both these situations. The necessity of monitoring the therapy is the result of a wide interindividual variability in the metabolism of clozapine. In this review, we highlight all the conditions underlying this variability, analyzing them one by one.

METHODS

Relevant literature was identified through a search of MEDLINE and PubMed. In addition, the case of a treatment‐resistant patient with accelerated metabolism of clozapine is reported as representative of utility of therapeutic drug monitoring in terms of clozapine dose adjustment.

RESULTS

Genetic polymorphisms of cytochrome P450 enzymes and of neurotransmitter receptors; drug interactions; interactions of clozapine with other substances such as food and drink; smoking; and nonmodifiable variables such as age, ethnicity, and gender have been examined in relation to the existing scientific literature. The laboratory techniques that clinicians could use to identify these variables and adequate therapies are also reviewed.

Where to position clozapine: re-examining the evidence

OBJECTIVE

To review clozapine's position in treatment algorithms for schizophrenia.

METHOD

Clozapine's status is reviewed in the context of its initial discovery and unique clinical and (or) pharmacological profile, withdrawal and link with hematologic concerns, reintroduction with monitoring guidelines, prototype for atypicality, positioning in treatment algorithms, and current evidence regarding efficacy, effectiveness, and side effects.

RESULTS

The hematologic monitoring implemented with clozapine's reintroduction here in North America has proven successful in preventing clozapine-related deaths secondary to agranulocytosis. While its other side effects are not without concern, present evidence does not link clozapine to increased mortality rates; indeed, it appears better than other antipsychotics in this regard. Moreover, its clinical superiority compared with all other antipsychotics has been confirmed both in efficacy and in effectiveness trials.

CONCLUSIONS

Schizophrenia continues to represent a treatment challenge, with many people demonstrating suboptimal response and poor functional outcome. Clozapine is routinely positioned as a third-line treatment in schizophrenia, but in light of existing evidence this warrants re-examination.

Dopamine receptor D3 genotype association with greater acute positive symptom remission with olanzapine therapy in predominately caucasian patients with chronic schizophrenia or schizoaffective disorder

OBJECTIVE

To test association of dopamine receptor D3 (DRD-3) gene polymorphisms with olanzapine response in genetic samples from a registration phase clinical trial.

METHODS

Eighty-eight acutely ill patients with schizophrenia or schizoaffective disorder were genotyped for ser-9-gly (rs6280) and 23 other polymorphisms within the DRD-3 gene. Allelic association of clinical response (mean baseline- to-endpoint reduction in Positive and Negative Syndrome Scale [PANSS] total and subscores) over 6 weeks of olanzapine treatment was assessed using repeated measures analysis of variance.

RESULTS

Ser-9-gly genotypes were associated with differences in PANSS total score improvement from baseline to 6 weeks (p = 0.021). This association was most notable for improvement in positive symptoms (p = 0.0001), with patients with gly/gly genotype significantly more responsive. More patients with the gly/gly genotype had greater positive symptom remission (endpoint rating of minimal or none on all PANSS positive items, 39.1%) compared with patients with gly/ser and ser/ser genotypes (13.8%; p = 0.033). DRD-3 polymorphisms in disequilibrium with ser-9-gly were also significantly associated with greater positive symptom improvement (p = 0.0009-0.021), and one not in complete linkage disequilibrium, with lesser improvement (p = 0.027).

CONCLUSIONS

Gly/gly DRD-3 genotype predicted statistically and clinically significantly better acute positive symptom reduction compared with other ser-9-gly genotypes in patients treated with olanzapine.

[Refractory schizophrenia]

OBJECTIVE

The aim of the present paper is to review the various aspects of refractory schizophrenia regarding issues such as definitions, clinical aspects, psychobiological correlates, pharmacological and non-pharmacological treatment options and predictors of treatment response.

METHOD

Medline search as well as articles of the authors.

RESULTS AND CONCLUSIONS

Refractory schizophrenia affects at least one third of patients with schizophrenia and the best evidence shows that is monotherapy with clozapine remains the mainstay for the treatment of such condition. Antipsychotic polipharmacy is not supported by current evidence and recent clinical trials have shown that clozapine augmentation with antipsychotics has no benefit over placebo.

Clinical aspects of super-refractory schizophrenia: a 6-month cohort observational study

OBJECTIVE

Approximately 30% of treatment-resistant schizophrenic patients do not fully respond to Clozapine and such patients are termed Clozapine non-responders or super-refractory schizophrenics. The aim of this study was to characterize patients with super-refractory schizophrenia according to demographic and psychopathological variables, as compared with patients with refractory schizophrenia or non-refractory subjects.

METHOD

One hundred two outpatients meeting DSM-IV criteria for schizophrenia were followed-up for 6 months. Subjects were classified into 3 groups: non-refractory (n=25), refractory (n=43) and super-refractory (n=34). Psychopathology was assessed by the Positive and Negative Syndrome Scale, the Schedule for Deficit Syndrome, the Calgary Depression Scale and the Quality of Life Scale. Patients were rated at 2-month intervals.

RESULTS

Higher levels of severity at the disease onset as well as higher severity of positive symptoms were found to be predictive of super-refractoriness.

CONCLUSIONS

The super-refractory schizophrenia patients have psychopathological predictive factors that need studies comparing brain images, genetical features and other clinical comparisons.

Treatment-resistant schizophrenia

This article opens with a brief history of pharmacologic treatment of schizophrenia. It then discusses the definition and treatment of treatment-resistant schizophrenia, with particular attention to clinical, biological and neuroimaging correlates, as well as the best treatment options, including the use of clozapine in patients who meet the definition of treatment-resistant schizophrenia.

Impact of GPCRs in clinical medicine: monogenic diseases, genetic variants and drug targets

By virtue of their large number, widespread distribution and important roles in cell physiology and biochemistry, G-protein-coupled receptors (GPCR) play multiple important roles in clinical medicine. Here, we focus on 3 areas that subsume much of the recent work in this aspect of GPCR biology: (1) monogenic diseases of GPCR; (2) genetic variants of GPCR; and (3) clinically useful pharmacological agonists and antagonists of GPCR. Diseases involving mutations of GPCR are rare, occurring in <1/1000 people, but disorders in which antibodies are directed against GPCR are more common. Genetic variants, especially single nucleotide polymorphisms (SNPs), show substantial heterogeneity in frequency among different GPCRs but have not been evaluated for some GPCR. Many therapeutic agonists and antagonists target GPCR and show inter-subject variability in terms of efficacy and toxicity. For most of those agents, it remains an open question whether genetic variation in primary sequence of the GPCR is an important contributor to such inter-subject variability, although this is an active area of investigation.

Apolipoprotein D is associated with long-term outcome in patients with schizophrenia

Accumulating evidence implicates deficiencies in apolipoprotein D (ApoD) function and arachidonic acid signaling in schizophrenic disorders. We addressed two hypotheses in relation to ApoD: first, polymorphisms in the ApoD gene confer susceptibility to or are markers of disease, and, second, genetic variation in the ApoD is associated with long-term clinical outcome to antipsychotic treatment. We genotyped two single-nucleotide polymorphisms in the ApoD gene in 343 chronic patients with schizophrenia spectrum disorders (ICD-10) and 346 control subjects of Danish origin. We did not find ApoD alleles, genotypes or haplotypes to be associated with disease. However, we did find that long-term clinical outcome was associated with the ApoD polymorphism rs7659 (P = 0.041) following adjustment for lifetime clinical global impression, age at first admission and gender.

Therapeutic Drug Monitoring and Pharmacogenetic Tests as Tools in Pharmacovigilance

Therapeutic drug monitoring (TDM) and pharmacogenetic tests play a major role in minimising adverse drug reactions and enhancing optimal therapeutic response. The response to medication varies greatly between individuals, according to genetic constitution, age, sex, co-morbidities, environmental factors including diet and lifestyle (e.g. smoking and alcohol intake), and drug-related factors such as pharmacokinetic or pharmacodynamic drug-drug interactions. Most adverse drug reactions are type A reactions, i.e. plasma-level dependent, and represent one of the major causes of hospitalisation, in some cases leading to death. However, they may be avoidable to some extent if pharmacokinetic and pharmacogenetic factors are taken into consideration. This article provides a review of the literature and describes how to apply and interpret TDM and certain pharmacogenetic tests and is illustrated by case reports. An algorithm on the use of TDM and pharmacogenetic tests to help characterise adverse drug reactions is also presented. Although, in the scientific community, differences in drug response are increasingly recognised, there is an urgent need to translate this knowledge into clinical recommendations. Databases on drug-drug interactions and the impact of pharmacogenetic polymorphisms and adverse drug reaction information systems will be helpful to guide clinicians in individualised treatment choices.

[Leponex, 10 years after -- a clinical review]

Clozapine was one of the major advances in the treatment of schizophrenia since the introduction of the classic antipsychotic agent chlorpromazine in the 1950s. Over the past 10 years, clozapine has become the reference compound for the development of new antipsychotics, and new drugs have been developed which have also claimed atypical status. The indications of clozapine were recently extended to Psychosis in Parkinson's disease and harmonized in the European Union. This provides the opportunity to update the data on clozapine in the treatment of schizophrenia. In this article we review current clinical evidence in schizophrenia to address the following issues: 1) Efficacy in refractory/positive symptoms: a systematic and critical analysis of 14 double-blind clinical trials in comparison with both standard and novel antipsychotics show consistent findings in favour of clozapine, with all but three of the reports demonstrating superiority. The review of studies allow us to say little about the predictors of treatment response, time to clozapine response and about the impact of clozapine on the quality of patients'life and longer-term outcome. Treatment options for clozapine non-responders are reviewed. 2) Risk of EPS: clozapine is considered to have a minimal risk of EPS and in all studies where a valid methodology was used, a clear superiority over the other neuroleptics is demonstrated. It is pointed out that, if the prevalence and incidence of EPS with clozapine is low, it is not zero. All the studies assessing clozapine treatment for TD have major methodological limitations, so no final conclusion can be drawn. 3) Efficacy for primary and secondary negative symptoms and neurocognitive effects: the data of clinical studies where negative symptoms scales were used favour clozapine in terms of improvement. However most of the studies were carried out in populations with predominantly positive symptoms. With regard to the need to distinguish primary and secondary symptoms, data are conflicting regarding the benefit of clozapine. Due to the lack of studies with a valid methodology, no definitive conclusion can be drawn about the efficacy on clozapine on the deficit syndrome and on neurocognitive disorders. 4) Impact on suicide risk: 4 out of 6 retrospective studies provide evidence for the ability of clozapine therapy to reduce suicidal behaviour. The results of a recent randomized, parallel-group study designed to compare clozapine versus olanzapine in preventing suicide attempts seems to confirm this hypothesis. We also address the tolerability and safety data, especially haematologic, comitial, cardiovascular and metabolic side-effects. The effectiveness of blood monitoring for the management of neutropenia and agranulocytosis demands that the recommendations are strictly followed. The use of clozapine at doses higher than 600 mg daily should follow published recommendations, in order to minimize the risk of seizures; these include anticonvulsant regimens based on blood levels. With regard to the cardiovascular mortality, if clozapine therapy has negligible effects on QT interval, its association with potential fatal myocarditis cannot be excluded in young patients who should be investigated if they develop cardiac symptoms in the first weeks of treatment. Available data support the notion that the frequency of bodyweight gain is high with several new antipsychotics, including clozapine. Potential long term effects of bodyweight gain on mortality and morbidity have to be taken into consideration. The pharmacological mechanisms underlying the "unique clozapine profile" is discussed. Clozapine remains the only antipsychotic with efficacy at relatively low D2 receptor occupancy. The pharmacogenetic and pharmacokinetic aspects are also reviewed. Finally, the place of clozapine in the current treatment of schizophrenia is highlighted to inform the development of guidelines for clinical management.

Advances in pharmacogenomics and individualized drug therapy: exciting challenges that lie ahead

Between the 1930s and 1990s, several dozen predominantly monogenic, high-penetrance disorders involving pharmacogenetics were described, fueling the crusade that gene-drug interactions are quite simple. Then, in 1990, the Human Genome Project was established; in 1995, the term pharmacogenomics was introduced; finally, the complexities of determining an unequivocal phenotype, as well as an unequivocal genotype, have recently become apparent. Since 1965, more than 1000 reviews on this topic have painted an overly optimistic picture-suggesting that the advent of individualized drug therapy used by the practicing physician is fast approaching. For many reasons listed here, however, we emphasize that these high expectations must be tempered. We now realize that the nucleotide sequence of the genome represents only a starting point from which we must proceed to a more difficult stage: knowledge of the function encoded and how this affects the phenotype. To achieve individualized drug therapy, a high level of accuracy and precision is required of any clinical test proposed in human patients. Finally, we suggest that metabonomics, perhaps in combination with proteomics, might complement genomics in eventually helping us to achieve individualized drug therapy.

Integrating pharmacogenetics into society: in search of a model

There has been considerable scientific, corporate and policy interest in the more effective use of genetics in both drug development and delivery. Pharmacogenetics - the study of the relationship between an individual's genetic makeup and response to medicinal drugs - has attracted global interest, but will it live up to its promise? Looking beyond the hype that has accompanied much of the commentary in the area, the future of pharmacogenetics will depend on how competing interests and options are resolved.

Clozapine treatment attenuated somatic and affective signs of nicotine and amphetamine withdrawal in subsets of rats exhibiting hyposensitivity to the initial effects of clozapine

BACKGROUND

Based on the phenomenologic similarity between symptoms of drug withdrawal and the negative symptoms of schizophrenia (e.g., anhedonia), we hypothesized that treatment with clozapine may be effective against nicotine and amphetamine withdrawal.

METHODS

A rate-independent discrete-trial threshold procedure was used to assess brain stimulation reward in rats prepared with electrodes in the lateral hypothalamus. Somatic signs of nicotine withdrawal were also assessed.

RESULTS

Clozapine administration (.75 or 1.5 mg/kg) during nicotine or amphetamine withdrawal did not affect the threshold elevations associated with drug withdrawal. The.75 mg/kg clozapine dose reversed the increased number of somatic signs of nicotine withdrawal. Ten days of clozapine treatment (3 mg/kg/b.i.d.) before exposure to nicotine prevented the threshold elevations in a subset of rats and the increases in somatic signs in all subjects. Fourteen-day pretreatment with clozapine (6 mg/kg/day) decreased the duration of amphetamine withdrawal.

CONCLUSIONS

Correlational analyses indicated that the ability of clozapine to prevent the affective aspects of drug withdrawal depended on low sensitivity to acute clozapine under baseline conditions. The results are consistent with the clinical situation where clozapine is partially effective against the negative symptoms of schizophrenia and more effective in some individuals than others. These results indicate that lack of sensitivity to the initial negative effects of clozapine may predict its a subsequent therapeutic response. Finally, the data suggest that there may be commonalities in the neurosubstrates mediating affective aspects of drug withdrawal and the negative symptoms of schizophrenia.

A perspective on molecular genetic studies of tardive dyskinesia: one clue for individualized antipsychotic drug therapy

Interindividual genetic profile differences related to antipsychotic drug therapy may be determined based on molecular genetic studies of the pathogenesis of schizophrenia and studies of antipsychotic drug responses (therapeutic as well as adverse responses). In the present article, we review molecular genetic studies of tardive dyskinesia (TD), which is a representative adverse response to antipsychotic drugs. Such studies have been performed to explore the gene-associated pharmacokinetic and pharmacodynamic processes of antipsychotic drugs. Positive associations between several genes and TD have been reported. The accumulation of results from such studies will hopefully lead to individualized antipsychotic drug therapies that involve the application of new genomic techniques, including DNA microarrays. Subsequently, antipsychotic drugs may in the future be prescribed for smaller subgroups of patients who have been classified as having a particular genetic profile.

Pharmacogenomics of psychiatric drug treatment

It is the goal of pharmacogenomics in psychiatry to establish predictive relationships between polymorphisms of candidate genes and therapeutic response to drug treatment. Polymorphisms of candidate genes related to drug mechanisms and pathophysiology of illness and defined clinical phenotype are the foundations for pharmacogenomic studies. Pharmacogenomic studies of antipsychotic response have focused on polymorphisms of genes for dopamine and serotonin receptors with most positive results reported for polymorphisms of genes of the 5HT2a and 5HT2c serotonin receptor subtypes. Although the goal of establishing individualized medicine predicated on an individual patient's genetic code has yet to be achieved, the fundamentals are now in place for second-generation investigation and more application to health care.

Clozapine: in prevention of suicide in patients with schizophrenia or schizoaffective disorder

The atypical antipsychotic agent clozapine is associated with a lower propensity for extrapyramidal symptoms than classical antipsychotic agents. The pharmacokinetics of clozapine are affected by wide interpatient variability and a potential for drug interactions. Some studies have shown a relationship between plasma concentrations, duration of treatment and antipsychotic clinical response. Clozapine (mean 274.2 mg/day; n = 490) had a greater preventive effect on suicidality among patients with schizophrenia or schizoaffective disorder at high risk for suicide than olanzapine (mean 16.6 mg/day; n = 490) in a randomised, rater-blinded, multicentre study (p < 0.05; a 22-24% improvement). Other prospective noncomparative trials of the effects of clozapine on suicidal ideation or attempts endorsed these results, while results from retrospective trials are equivocal. Clozapine is commonly associated with sedation, hypersalivation, tachycardia, dizziness, constipation and orthostatic hypotension. Agranulocytosis, diabetes mellitus and weight gain may also occur.