Schizophrenia Clinical Trials Research Articles

The dopamine D3 receptor, a quarter century later.

This review updates the existing knowledge suggesting a role for the D3 receptor in schizophrenia and drug addiction. The D3 receptor is expressed in brain regions controlling reward, emotions, and motivation. Antipsychotics bind invitro to the D3 receptor with similar affinity as to the D2 receptor, and occupancy of D3 receptors invivo by these compounds given acutely at clinical dosage have been demonstrated in Positron Emission Tomography (PET) studies. The D3 receptor modulates glutamatergic pathways from the prefrontal cortex to subcortical areas, either directly by interacting with N-methyl-D-aspartate (NMDA) receptors in the nucleus accumbens, or indirectly by controlling dopamine release from ventral tegmental area neurons. In animals, D3 receptor antagonists reverse behavioral manifestations of NMDA receptor blockade and improve cognitive performances in various paradigms. Two D3 receptor-selective compounds have reached clinical trials in schizophrenia, with negative results seemingly due to insufficient target engagement; the results with a third compound, F17464, have not been disclosed yet. There is converging evidence that D3 receptors do not control the reinforcing effects of drugs of abuse (with the exception of alcohol under low requirement), but rather affects the motivation to take the drugs under high requirement, reactivity to drug-associated cues, and drug-seeking behaviors triggered by stimuli associated with relapse in humans. D3 receptor expression measured by PET is upregulated in humans with various drug addictions. A single administration of the D3 receptor-selective antagonist, GSK598809, in humans transiently alleviated craving in smokers after overnight abstinence. The clinical development of D3-selective compounds will benefit from initial assessment of target engagement through the use of PET.

Review of Recent Clinical Trials in Schizophrenia

Review of Recent Clinical Trials in Schizophrenia

P.3.b.036 - Discrepancies between the PANSS and CGI-S scores at baseline are a marker for subsequent data quality issues in schizophrenia clinical trials

Remission and response were suggested as the most relevant outcome criteria for the treatment of depression. There is still marked uncertainty as to what cut-offs should be used on current depression rating scales. The goal of the present study was to compare the validity of different HAMD, MADRS and BDI cut-offs for response and remission.The naturalistic prospective study was performed in 12 psychiatric hospitals in Germany. All evaluable patients (n = 846) were hospitalized and had to meet DSM-IV criteria for major depressive disorder. Biweekly ratings were assessed using HAMD-21, MADRS and BDI. A CGI-S score of 1 and a CGI-I score of at least 2 was used as the primary comparative measure of remission and response, respectively.A HAMD-21 cut-off ≤ 7 (AUC: 0.92), HAMD-17 cut-of ≤ 6 (AUC: 0.90), MADRS cut-off ≤ 7 (AUC: 0.94) and BDI cut-off ≤ 12 (AUC: 0.83) were associated with a maximum of specificity and sensitivity for defining remission.A minimum decrease of 47% of the HAMD-21 (AUC: 0.90), ≤57% for HAMD-17 (AUC: 0.89), ≤ 46% for MADRS (0.91) and a decrease of 47% for the BDI baseline score (AUC: 0.78) best corresponded CGI response criteria.Our data largely confirmed currently used remission and response criteria in naturalistically treated patients.

Pharmacoeconomic comparison of aripiprazole once-monthly and paliperidone palmitate from a head-to-head clinical trial in schizophrenia: a US analysis.

Schizophrenia presents a substantial clinical and economic burden to the health-care system. In QUAlity of LIfe with AbiliFY Maintena (QUALIFY), a randomized head-to-head study of aripiprazole once-monthly 400 mg (AOM 400) compared with paliperidone palmitate (PP; 78–234 mg/mo), AOM 400 demonstrated greater improvement in health-related quality of life and functioning in patients with stable schizophrenia. The present analysis used health economics assessment data collected during the QUALIFY study to determine the direct medical and pharmacy costs and the cost-effectiveness associated with each treatment over 6 months. Compared with those receiving PP, patients receiving AOM 400 incurred significantly lower direct total costs ($8908±186 vs $9675±190, p=0.005) and treatment costs ($7967±113 vs $8706±116, p<0.001). Effectiveness results in the subset of patients included in the cost analyses were similar to the overall population: mean (95% CI) improvement in Heinrichs-Carpenter Quality of Life Scale total score was greater with AOM 400 (5.97 [3.87; 8.08]) compared with PP (2.85 [0.56; 5.08]). Likewise, Clinical Global Impression–Severity improved more in the AOM 400 group (−0.59 [−0.71; −0.47]) compared with PP group (−0.37 [−0.46; −0.27]). Therefore, the analysis of data from stabilized patients with schizophrenia in the QUALIFY study indicated that AOM 400 is associated with lower health-care costs and greater effectiveness compared with PP and thus represents the economically dominant strategy.

Testing treatment effect in schizophrenia clinical trials with heavy patient dropout using latent class growth mixture models.

By examining the outcome trajectories of the dropout patients with different reasons in the schizophrenia trials, we note that although patients are recruited from the same protocol that have compatible baseline characteristics, they may respond differently even to the same treatment. Some patients show consistent improvement while others only have temporary relief. This creates different patient subpopulations characterized by their response and dropout patterns. At the same time, those who continue to improve seem to be more likely to complete the study while those who only experience temporary relief have a higher chance to drop out. Such phenomenon appears to be quite general in schizophrenia clinical trials. This simultaneous inhomogeneity both in patient response as well as dropout patterns creates a scenario of missing not at random and therefore results in biases when we use the statistical methods based on the missing at random assumption to test treatment efficacy. In this paper, we propose to use the latent class growth mixture model, which is a special case of the latent mixture model, to conduct the statistical analyses in such situation. This model allows us to take the inhomogeneity among subpopulations into consideration to make more accurate inferences on the treatment effect at any visit time. Comparing with the conventional statistical methods such as mixed-effects model for repeated measures, we demonstrate through simulations that the proposed latent mixture model approach gives better control on the Type I error rate in testing treatment effect. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Healthy adolescent performance on the MATRICS Consensus Cognitive Battery (MCCB): Developmental data from two samples of volunteers

The MATRICS Consensus Cognitive Battery (MCCB) fills a significant need for a standardized battery of cognitive tests to use in clinical trials for schizophrenia in adults aged 20–59. A need remains, however, to develop norms for younger individuals, who also show elevated risks for schizophrenia. Toward this end, we assessed performance in healthy adolescents. Baseline MCCB, reading and IQ data were obtained from healthy controls (ages 12–19) participating in two concurrent NIMH-funded studies: North American Prodromal Longitudinal Study phase 2 (NAPLS-2; n=126) and Boston Center for Intervention Development and Applied Research (CIDAR; n=13). All MCCB tests were administered except the Managing Emotions subtest from the Mayer–Salovey–Caruso Emotional Intelligence Test. Data were collected from 8 sites across North America. MCCB scores were presented in four 2-year age cohorts as T-scores for each test and cognitive domain, and analyzed for effects of age and sex. Due to IQ differences between age-grouped subsamples, IQ served as a covariate in analyses. Overall and sex-based raw scores for individual MCCB tests are presented for each age-based cohort. Adolescents generally showed improvement with age in most MCCB cognitive domains, with the clearest linear trends in Attention/Vigilance and Working Memory. These control data show that healthy adolescence is a dynamic period for cognitive development that is marked by substantial improvement in MCCB performance through the 12–19 age range. They also provide healthy comparison raw scores to facilitate clinical evaluations of adolescents, including those at risk for developing psychiatric disorders such as schizophrenia-related conditions.

A Comparison of Frequentist and Bayesian Model Based Approaches for Missing Data Analysis: Case Study with a Schizophrenia Clinical Trial

Missing data are common in clinical trials and could lead to biased estimation of treatment effects. The National Research Council (NRC) report suggests that sensitivity analysis on missing data mechanism should be a mandatory component of the primary reporting of findings from clinical trials, and regulatory agencies are requesting more thorough sensitivity analyses from sponsors. However, recent literature research showed that missing data were almost always inadequately handled. This is partially due to the lack of standard software packages and straightforward implementation platform. With recent availability of flexible Bayesian software packages such as WinBUGS, SAS Proc MCMC, and Stan, it is relatively simple to develop Bayesian methods to address complex missing data problems while incorporating the uncertainty. In this article, we present a case study from the DIA Bayesian Scientific Working Group (BSWG) on Bayesian approaches for missing data analysis. We illustrate how to use Bayesian approaches to fit a few commonly used frequentist missing data models. The properties, advantage, and flexibility of the Bayesian analysis methods will be discussed using a case study based on a schizophrenia clinical trial. Supplementary materials for this article are available online.

Neurocognition and occupational functioning in schizophrenia spectrum disorders: The MATRICS Consensus Cognitive Battery (MCCB) and workplace assessments

The MCCB is widely used in clinical trials of schizophrenia, but its relationship to occupational functioning still needs further elaboration. While previous research has indicated that various domains of neurocognition assessed by individual tests are related to work functioning, these reports preceded the development of the MCCB as the standard neurocognitive test battery in the field. In the current study, the vocational functioning of 131 Norwegian participants with schizophrenia spectrum disorders who were enrolled in a vocational rehabilitation program were assessed on the Vocational Cognitive Rating Scale (VCRS), the Work Behavior Inventory (WBI), and the Complexity Scale (CS) as well as on the MCCB. Significant correlations were found between most MCCB domains and VCRS Total Score. MCCB processing speed and attention were most powerfully related to and predictive of WBI scores. When participants were divided into “low complexity” or “higher complexity” work categories, participants in the “low-complexity” group performed significantly worse than participants in the “higher-complexity” group regarding processing speed, working memory, visual learning and the composite score. The same pattern emerged for participants working sheltered compared to competitive jobs. The VCRS, WBI and CS may be useful in vocational rehabilitation. They bridge an important gap between test- and occupational-setting, providing valuable information about impairments related to occupational functioning. We found the MCCB to be sensitive to occupational functioning as measured by VCRS, WBI and CS, with neurocognition accounting for a small but significant proportion of the variance in these different measures of occupational functioning.

In The News: A roundup of news and information from our community

In <i>The</i> News: A roundup of news and information from our community

Abstract POSTER-BIOL-1336: Investigating the role of phosphodiesterase 10A as a novel target in ovarian cancer

Abstract Cyclic nucleotide phosphodiesterases (PDEs) play major roles regulating cell signaling by hydrolyzing the second messengers cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Phosphodiesterase 10A (PDE10A) is one of 21 PDEs encoded in the human genome. Its predominant expression in the brain striatum has guided intensive investigations on the therapeutic potential of PDE10A in psychiatric and neurological disorders, leading to several PDE10A inhibitors in clinical trials for schizophrenia and Hungtington's disease. Recently, we described for the first time an oncogenic role for PDE10A in colorectal cancer (N. Li et al. 2014 Oncogene 1-11). Our published data showed that PDE10A is overexpressed in colon tumor cells when compared to normal colonocytes, and that pharmacological inhibition or genetic knockdown of PDE10A suppresses colon tumor growth. Here, we are investigating the role of PDE10A in ovarian cancer and its potential as a novel therapeutic target. We detected expression of PDE10A in several ovarian cancer cell lines (SKOV3, SKOV3ip1, A2780, A2780-CP70, OV-90, ES-2 and TOV112D) by western-blotting and quantitative RT-PCR. In addition, our preliminary analysis revealed PDE10A expression in tumors and matched normal tissues from eight patients of ovarian cancer. Finally, we developed novel small molecule compounds targeting PDE10A which potently inhibit growth of all these ovarian cancer cell lines at low micromolar or sub-micromolar concentrations. Future work will focus on i) expanding the cohort of ovarian cancer patient tissues to analyze expression levels of PDE10A by western-blotting, quantitative RT-PCR and immunohistochemistry; ii) genetic silencing of PDE10A by siRNA/shRNA to investigate its role regulating cell proliferation, apoptosis, and cGMP/cAMP cell signaling in ovarian cancer; iii) investigate the signaling pathways suppressed by our novel PDE10A inhibitors. Our studies will determine the potential of using PDE10A as a novel therapeutic target for the treatment and chemoprevention of ovarian cancer. Citation Format: Luciana Madeira da Silva, Kevin Lee, Gary A. Piazza, Lavanya Bachaboina, Rodney P. Rocconi, Jennifer Scalici. Investigating the role of phosphodiesterase 10A as a novel target in ovarian cancer [abstract]. In: Proceedings of the 10th Biennial Ovarian Cancer Research Symposium; Sep 8-9, 2014; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(16 Suppl):Abstract nr POSTER-BIOL-1336.

Effort-Based Decision-Making Paradigms for Clinical Trials in Schizophrenia: Part 2—External Validity and Correlates.

Effort-based decision making has strong conceptual links to the motivational disturbances that define a key subdomain of negative symptoms. However, the extent to which effort-based decision-making performance relates to negative symptoms, and other clinical and functionally important variables has yet to be systematically investigated. In 94 clinically stable outpatients with schizophrenia, we examined the external validity of 5 effort-based paradigms, including the Effort Expenditure for Rewards, Balloon Effort, Grip Strength Effort, Deck Choice Effort, and Perceptual Effort tasks. These tasks covered 3 types of effort: physical, cognitive, and perceptual. Correlations between effort related performance and 6 classes of variables were examined, including: (1) negative symptoms, (2) clinically rated motivation and community role functioning, (3) self-reported motivational traits, (4) neurocognition, (5) other psychiatric symptoms and clinical/demographic characteristics, and (6) subjective valuation of monetary rewards. Effort paradigms showed small to medium relationships to clinical ratings of negative symptoms, motivation, and functioning, with the pattern more consistent for some measures than others. They also showed small to medium relations with neurocognitive functioning, but were generally unrelated to other psychiatric symptoms, self-reported traits, antipsychotic medications, side effects, and subjective valuation of money. There were relatively strong interrelationships among the effort measures. In conjunction with findings from a companion psychometric article, all the paradigms warrant further consideration and development, and 2 show the strongest potential for clinical trial use at this juncture.

Effort-Based Decision-Making Paradigms for Clinical Trials in Schizophrenia: Part 1—Psychometric Characteristics of 5 Paradigms.

Impairments in willingness to exert effort contribute to the motivational deficits characteristic of the negative symptoms of schizophrenia. The current study evaluated the psychometric properties of 5 new or adapted paradigms to determine their suitability for use in clinical trials of schizophrenia. This study included 94 clinically stable participants with schizophrenia and 40 healthy controls. The effort-based decision-making battery was administered twice to the schizophrenia group (baseline, 4-week retest) and once to the control group. The 5 paradigms included 1 that assesses cognitive effort, 1 perceptual effort, and 3 that assess physical effort. Each paradigm was evaluated on (1) patient vs healthy control group differences, (2) test-retest reliability, (3) utility as a repeated measure (ie, practice effects), and (4) tolerability. The 5 paradigms showed varying psychometric strengths and weaknesses. The Effort Expenditure for Rewards Task showed the best reliability and utility as a repeated measure, while the Grip Effort Task had significant patient-control group differences, and superior tolerability and administration duration. The other paradigms showed weaker psychometric characteristics in their current forms. These findings highlight challenges in adapting effort and motivation paradigms for use in clinical trials.

Effort-Based Decision Making: A Novel Approach for Assessing Motivation in Schizophrenia.

Because negative symptoms, including motivational deficits, are a critical unmet need in schizophrenia, there are many ongoing efforts to develop new pharmacological and psychosocial interventions for these impairments. A common challenge of these studies involves how to evaluate and select optimal endpoints. Currently, all studies of negative symptoms in schizophrenia depend on ratings from clinician-conducted interviews. Effort-based decision-making tasks may provide a more objective, and perhaps more sensitive, endpoint for trials of motivational negative symptoms. These tasks assess how much effort a person is willing to exert for a given level of reward. This area has been well-studied with animal models of effort and motivation, and effort-based decision-making tasks have been adapted for use in humans. Very recently, several studies have examined physical and cognitive types of effort-based decision-making tasks in cross-sectional studies of schizophrenia, providing evidence for effort-related impairment in this illness. This article covers the theoretical background on effort-based decision-making tasks to provide a context for the subsequent articles in this theme section. In addition, we review the existing literature of studies using these tasks in schizophrenia, consider some practical challenges in adapting them for use in clinical trials in schizophrenia, and discuss interpretive challenges that are central to these types of tasks.

Relationships between global assessment of functioning and other rating scales in clinical trials for schizophrenia

The relationship between the Global Assessment of Functioning (GAF) with other scales in schizophrenia has rarely been investigated. A systematic literature search was conducted to identify articles that reported the GAF score together with scores in the Positive and Negative Syndrome Scale (PANSS), Clinical Global Impression (CGI) or Brief Psychiatric Rating Scale (BPRS), using MEDLINE, EMBASE and PsycINFO, with keywords of schizophrenia, clinical trial and global assessment of functioning (last search 30 June 2013). Correlational analyses with weighting by the study participant numbers across these rating scales were performed. In 40 clinical trials (n=8000) that reported cross-sectional data on the GAF and PANSS, a significant but modest correlation was noted (Pearson׳s r=−0.401, p<0.0001). Furthermore, a correlation between the GAF and CGI-severity (CGI-S) at study baseline in 38 studies (n=11,315) was robust (r=−0.893, p<0.0001). In longitudinal studies, changes in the GAF scores were negatively correlated with those in the PANSS as well as CGI-S scores (p<0.0001 for both). Data on the BPRS were all statistically significant although relatively scarce. While optimal degree of concordance is undetermined among psychiatric scales that are presumed to be measuring different but overlapping constructs, this study found significant correlations in the GAF and CGI-S or PANSS, both cross-sectionally and longitudinally. The GAF-CGI-S relationship was especially tighter, making it a reliable clinical indicator.

Customising informed consent procedures for people with schizophrenia in India.

There is little information on how the ethical and procedural challenges involved in the informed participation of people with schizophrenia in clinical trials are addressed in low- and middle-income countries (LMICs). The informed consent procedure used in the collaborative community care for people with schizophrenia in India (COPSI) RCT was developed keeping these challenges in mind. We describe the feasibility of conducting the procedure from the trial, researcher and participants perspectives and describe the reasons for people consenting to participate in the trial or refusing to do so. Three sources of information were used to describe the feasibility of the COPSI consent procedure: key process indicators for the trial perspective, data from a specially designed post-interview form for participant's observations and focus group discussion (FGD) with the research interviewers. Categorical data were analysed by calculating frequencies and proportions, while the qualitative data from the FGD, and the reasons for participation or refusal were analysed using a thematic content analysis approach. 434 people with schizophrenia and their primary caregiver(s) were approached for participation in the trial. Consent interviews were conducted with 332, of whom 303 (91%) agreed to participate in the trial. Expectation of improvement was the most common reason for agreeing to participate in the trial, while concerns related to the potential disclosure of the illness, especially for women, were an important reason for refusing consent. The COPSI consent procedure demonstrates preliminary, observational information about the feasibility of customising informed consent procedures for people with schizophrenia LMIC contexts. This and other similar innovations need to be refined and rigorously tested to develop evidence-based guidelines for informed consent procedures in such settings.

The Effects of a Combined Intervention for Cognition in Schizophrenia On Cogstate Schizophrenia Battery

Background Cognitive impairment in schizophrenia is a strong predictor of the functional outcome and no effective treatments are available. MATRICS Consensus Cognitive Battery (MCCB) is approved by the FDA as outcome measure for trials of cognitive-enhancing drugs in schizophrenia. CogState Schizophrenia Battery (CSB) provides a briefer cognition assessment with minimal practice effects and a strong correlation between the CSB and MCCB composite scores. We tested the sensitivity of CSB as a cognitive outcome measure in a clinical trial in schizophrenia, where a cognitive-enhancing drug and cognitive training were combined. Methods 49 participants with schizophrenia were enrolled in a double-blind, placebo-controlled study. Participants were randomised to modafinil (200mg/day) or placebo and underwent a cognitive training program for 10 weekdays. CSB was administered twice at baseline to minimise practice effects, at the last day of the intervention and two weeks after the completion of the intervention. Results There was a significant time effect at the end of the intervention on the CSB composite score (p=0.042). There was no significant treatment effect on CSB composite score at the end of the intervention (p=0.686) or at follow up (p=0.120). Conclusions Multiple administrations of CSB were well tolerated by participants. The significant time effects on the composite score may suggest the operation of practice effects. Several factors could have contributed to the lack of treatment effects on CSB, such as the burden of multiple neuropsychological testing in a relatively brief study, the duration of modafinil treatment and also the intensive nature of cognitive training.

A Flexible Bayesian Approach to Monotone Missing Data in Longitudinal Studies With Nonignorable Missingness With Application to an Acute Schizophrenia Clinical Trial

We develop a Bayesian nonparametric model for a longitudinal response in the presence of nonignorable missing data. Our general approach is to first specify a working model that flexibly models the missingness and full outcome processes jointly. We specify a Dirichlet process mixture of missing at random (MAR) models as a prior on the joint distribution of the working model. This aspect of the model governs the fit of the observed data by modeling the observed data distribution as the marginalization over the missing data in the working model. We then separately specify the conditional distribution of the missing data given the observed data and dropout. This approach allows us to identify the distribution of the missing data using identifying restrictions as a starting point. We propose a framework for introducing sensitivity parameters, allowing us to vary the untestable assumptions about the missing data mechanism smoothly. Informative priors on the space of missing data assumptions can be specified to combine inferences under many different assumptions into a final inference and accurately characterize uncertainty. These methods are motivated by, and applied to, data from a clinical trial assessing the efficacy of a new treatment for acute schizophrenia. Supplementary materials for this article are available online.

Psychometric evaluation of the Work Readiness Questionnaire in schizophrenia.

Unemployment can negatively impact quality of life among patients with schizophrenia. Employment status depends on ability, opportunity, education, and cultural influences. A clinician-rated scale of work readiness, independent of current work status, can be a valuable assessment tool. A series of studies were conducted to create and validate a Work Readiness Questionnaire (WoRQ) for clinicians to assess patient ability to engage in socially useful activity, independent of work availability. Content validity, test-retest and inter-rater reliability, and construct validity were evaluated in three separate studies. Content validity was supported. Cronbach's α was 0.91, in the excellent range. Clinicians endorsed WoRQ concepts, including treatment adherence, physical appearance, social competence, and symptom control. The final readiness decision showed good test-retest reliability and moderate inter-rater reliability. Work readiness was associated with higher function and lower levels of negative symptoms. Low positive and high negative predictive values confirmed the concept validity. The WoRQ has suitable psychometric properties for use in a clinical trial for patients with a broad range of symptom severity. The scale may be applicable to assess therapeutic interventions. It is not intended to assess eligibility for supported work interventions. The WoRQ is suitable for use in schizophrenia clinical trials to assess patient work functional potential.

Circadian rhythms in cognitive functioning among patients with schizophrenia: Impact on signal detection in clinical trials of potential pro-cognitive therapies

ObjectiveCognition is affected by circadian rhythms over the course of a day. Circadian rhythms in cognitive functioning are driven by a variety of both endogenous and exogenous factors. Patients with schizophrenia are known to have disturbed circadian rhythms that can affect their cognitive functioning. We examined the impact of time of day on cognitive test scores from subjects participating in clinical trials of potential pro-cognitive therapies for schizophrenia and then explored how this diurnal variation affected signal detection. MethodBaseline data from 8 separate schizophrenia clinical trials using the MATRICS Consensus Cognitive Battery (MCCB) were aggregated (Total N=2032). The MCCB assessments were divided into five 2-hour time intervals based on the start-time of the assessments (varying from 8:00am to 5:59pm) and then analyzed for differences by time interval. Next, data from two Phase 2 schizophrenia clinical trials of potential pro-cognitive therapies were analyzed to explore the impact of this diurnal variation on placebo separation. ResultsTime of day exerted a significant effect on baseline composite MCCB scores (p=.002). Follow-up comparisons revealed significant differences among multiple temporal epochs. In both Phase 2 clinical trials, subjects whose cognitive functioning was assessed at consistent times of day between their baseline and endpoint visits showed a more robust treatment response as compared to subjects assessed at inconsistent times of day. ConclusionCognitive functioning ebbs and flows over the course of the day. Maintaining consistency in the time of day of cognitive test administrations between visits can help to reduce the noise introduced by circadian rhythms, thereby enhancing signal detection in clinical trials of potential pro-cognitive therapies.

Mapping the binding pocket of a novel, high-affinity, slow dissociating tachykinin NK3 receptor antagonist: Biochemical and electrophysiological characterization

The NK3 receptor is a GPCR that is prominently expressed in limbic areas of the brain, many of which have been implicated in schizophrenia. Phase II clinical trials in schizophrenia with two selective NK3 antagonists (osanetant and talnetant) have demonstrated significant improvement in positive symptoms. The objective of this study was to characterize the properties of a novel dual NK2/NK3 antagonist, RO5328673. [3H]RO5328673 bound to a single saturable site on hNK2, hNK3 and gpNK3 with high-affinity. RO5328673 acted as an insurmountable antagonist at both human and guinea-pig NK3 receptors in the [3H]IP accumulation assay. In binding kinetic analyses, [3H]RO5328673 had fast association and dissociation rates at hNK2 while it had a fast association rate and a remarkably slow dissociation rate at gp and hNK3. In electrophysiological recordings of gp SNpc, RO5328673 inhibited the senktide-induced potentiation of spontaneous activity of dopaminergic neurons with an insurmountable mechanism of action. RO5328673 exhibited in-vivo activity in gerbils, robustly reversing the senktide-induced locomotor activity. The TM2 residue gpNK3-A1142.58 (threonine in all other species) was identified as the critical residue for the RO5328673's slower dissociation kinetics and stronger insurmountable mode of antagonism in the guinea-pig as compared to hNK3-T1392.58. Using site-directed mutagenesis, [3H]RO5328673 binding and rhodopsin-based modeling, the important molecular determinants of the RO5328673-binding pocket of hNK3 were determined. A comparison of the RO5328673-binding pocket with that of osanetant showed that two antagonists have similar contact sides on hNK3 binding crevice except for three mutations V95L1.42, Y247W5.38, V255I5.46, which behaved differently between interacting modes of two antagonists in hNK3.