Evidence of trospium's ability to mitigate cholinergic adverse events related to xanomeline: phase 1 study results

Targeting muscarinic receptors in schizophrenia treatment: Novel antipsychotic xanomeline/trospium chloride

This minireview explores the role of acetylcholine and muscarinic receptors in the pathophysiology of schizophrenia and summarizes the latest data on xanomeline/trospium chloride, a novel antipsychotic approved by the United States Food and Drug Administration in September 2024. Evidence suggests that cholinergic dysfunction, particularly an imbalance in the expression of the M1 and M4 muscarinic receptors, may contribute to the pathophysiology and symptoms of schizophrenia. Xanomeline/trospium chloride combines xanomeline, an M1 and M4 receptor agonist, with trospium chloride, a non-selective peripheral muscarinic receptor antagonist that reduces peripheral cholinergic side effects. Clinical trials have demonstrated significant reductions in the positive and negative symptoms of schizophrenia, with improvements in Positive and Negative Syndrome Scale scores observed as early as two weeks. A post-hoc analysis of one trial revealed cognitive improvements in patients with baseline cognitive impairment. This medication was generally well-tolerated, with mild-to-moderate gastrointestinal symptoms being the most common adverse events. While these results are promising, further research is needed to better understand its effectiveness and safety in real-world clinical practice, and to define its optimal role in managing this complex psychiatric disorder.

Advances in Alzheimer's Therapy: Exploring Neuropathological Mechanisms to Revolutionize the Future Therapeutic Landscape

Alzheimer's disease (AD) is still an excessively complicated neurological disorder that impacts millions of individuals globally. The ideal defensive feature of the central nervous system (CNS) is the intimate junction of endothelial cells, which functions as a biological barrier to safely control molecular transport throughout the brain. The blood-brain barrier (BBB) comprises tightly locked astrocyte cell junctions on CNS blood capillaries. This biological barrier shields the brain from hazardous toxins by preventing the entry of polar medications, cells, and ions. However, it is very challenging to provide any treatment to the brain for neurodegenerative illnesses like Alzheimer's. Different causative mechanisms, such as amyloid-β (Aβ) plaques, tubulin-associated unit (Tau) tangles, and neuroinflammation, cause neuronal dysfunction, leading to dementia and memory loss in the subject. Several treatments are approved for AD therapy, whereas most only help treat related symptoms. Disappointingly, current remedies have not been able to control the progression of AD due to associated side effects. Specific pathogenic mechanisms are involved in the initiation and development of this disease. Therefore, the expected survival of a patient with AD is limited and is approximately ten years. Hence, the pathogenic mechanism behind AD progression must be understood to better comprehend and improve the overall survival rate. This review highlighted the recent insights into AD pathogenesis, molecular mechanisms, advancements in theragnostic techniques, the existing updates of clinical trials, and emerging innovations for AD medicinal development. That has helped researchers develop other strategies to address the shortcomings of traditional medications.

Is muscarinic receptor agonist effective and tolerant for schizophrenia?

BACKGROUND

Several randomized clinical trials (RCTs) have recently examined the efficacy and tolerability of muscarinic receptor agonists in schizophrenia. However, whether therapeutics targeting muscarinic receptors improve symptom management and reduce side effects remains systemically unexplored.

METHODS

Embase, PubMed, and Web of Science were searched from inception until Jan 9, 2025. Altogether, the efficacy and safety outcomes of four RCTs (397 individuals in the muscarinic receptor agonists group, and 374 in the placebo control group) were meta-analyzed. To compare scores of positive and negative syndrome scale (PANSS), response rate, discontinuation rate, and adverse events with muscarinic receptor agonists vs. placebo in patients with schizophrenia, scale changes were pooled as mean difference (MD) for continuous outcomes and risk ratio (RR) for categorical outcomes.

RESULTS

It revealed that muscarinic receptor agonists were superior to placebo in terms of decrease in the total PANSS score (MD, - 9.92; 95% CI, -12.46 to -7.37; I2 = 0%), PANSS positive symptom subscore (MD, - 3.21; 95% CI, -4.02 to -2.40; I2 = 0%), and PANSS negative symptom subscore (MD, -1.79; 95% CI, -2.47 to -1.11; I2 = 48%). According to the study-defined response rate, the pooled muscarinic receptor agonists vs. placebo RR was 2.08 (95% CI, 1.59 to 2.72; I2 = 0%). No significance was found in the discontinuation rate. Muscarinic receptor agonists were associated with a higher risk of nausea (RR = 4.61, 95% CI, 2.65 to 8.02; I2 = 3%), and in particular, xanomeline-trospium was associated with risks of dyspepsia, vomiting, and constipation.

CONCLUSIONS

The findings highlighted an efficacy advantage with tolerated adverse event profiles for muscarinic receptor agonists in schizophrenia.

Does KarXT (xanomeline-trospium) represent a novel approach to schizophrenia management? A GRADE-assessed systematic review and meta-analysis of randomized controlled clinical trials

BACKGROUND

Schizophrenia is a complex psychiatric disorder characterized by positive, negative, and cognitive symptoms. KarXT, a novel combination of xanomeline and trospium, offers potential therapeutic benefits for schizophrenia treatment by targeting muscarinic receptors and avoiding dopamine receptor blockade. We conducted a systematic review and meta-analysis to evaluate the efficacy and safety of KarXT.

METHODS

PubMed, Scopus, Web of Science, and Cochrane databases were systematically searched for relevant randomized controlled trials (RCTs) up to October 2024. Studies involving adult patients with schizophrenia treated with KarXT were included. Furthermore, the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) framework was used to assess evidence quality, and the risk of bias was evaluated using the Cochrane Risk of Bias 2.0 tool.

RESULTS

Four studies with 690 participants were included. KarXT significantly reduced Positive and Negative Syndrome Scale (PANSS) total scores compared to placebo (mean difference (MD): -13.77, 95% confidence interval (CI) [-22.33 to -5.20], P-value = 0.002), with significant improvements in positive and negative subscale scores. It significantly increased the incidence of achieving ≥ 30% PANSS score reduction (risk ratio: 2.15, 95% CI [1.64 to 2.84], P < 0.00001). Moreover, KarXT demonstrated a favorable safety profile, with side effects such as nausea and constipation being mild and transient. Notably, it was not significantly associated with weight gain or extrapyramidal symptoms, which are common with traditional antipsychotics.

CONCLUSIONS

KarXT's distinct mechanism and tolerability highlight its potential to address unmet needs in schizophrenia treatment. Future studies should explore its long-term efficacy, delayed adverse effects, and comparative effectiveness against existing therapies.

CLINICAL TRIAL NUMBER

Not applicable.

Xanomeline-Trospium: A Novel Therapeutic for the Treatment of Schizophrenia

OBJECTIVE

This review describes a novel combination muscarinic agonist and antagonist, xanomeline-trospium, which was recently approved by the Food and Drug Administration (FDA) for schizophrenia. Efficacy and safety evidence from phase II and III clinical trials are reviewed.

DATA SOURCES

The MEDLINE and EMBASE databases were searched in 2024; terms included "xanomeline trospium" OR "xanomelinetrospium" OR "KarXT" OR "Cobenfy" AND "schizophrenia." The search was repeated in January 2025.

CLINICALTRIALS

gov was used to review ongoing or unpublished studies.

STUDY SELECTION AND DATA EXTRACTION

Human subject studies of xanomeline-trospium were included.

DATA SYNTHESIS

In phase III trials, xanomeline-trospium was superior to placebo for acute exacerbation of schizophrenia. EMERGENT-2 and EMERGENT-3 found patients improved by 9.6 and 8.4 points on the Positive and Negative Symptom Scale (PANSS), respectively, compared with placebo (95% confidence interval -13.9 to -5.2, P < 0.001 and -12.4 to -4.3, P < 0.001). Participants in EMERGENT-4, a long-term open-label extension study, who received the intervention in the randomized phases experienced a 9-point decrease in PANSS from the last result.Relevance to Patient Care and Clinical Practice in Comparison to Existing Drugs:Xanomeline-trospium is a novel antipsychotic that is effective for treatment of schizophrenia and may have a favorable adverse effect profile in comparison with other antipsychotics due to its lack of dopamine receptor antagonism. Efficacy for improvement in negative symptoms and cognitive function in schizophrenia is promising.

CONCLUSIONS

Xanomeline-trospium shows promising results for treatment of schizophrenia. Further studies with active comparators, larger sample sizes, and more patients with prominent negative symptoms are needed to corroborate efficacy and determine place in therapy.

Current emerging therapeutic targets and clinical investigational agents for schizophrenia: Challenges and opportunities

Since the first discovery of antipsychotics in the 1950s, targeting dopaminergic drugs has manifested to well manage the positive symptoms of schizophrenia with limited efficacy for the negative and cognitive symptoms. In past decades, extensive efforts have been undertaken towards the development of innovative agents that can effectively stabilize the dopamine and serotonin systems or target to nondopaminergic pathways, leading to various promising drug candidates entering into clinical trials. Notably, the sigma-2, 5-HT2A, and α1A receptor antagonist roluperidone, as well as a fixed-dose combination of the M1/4 receptor agonist KarXT, have been submitted for NDA applications. The dual agonist ulotaront, which targets TAAR1 and 5-HT1A receptors, and the GlyT1 inhibitor iclepertin have advanced into phase 3 clinical trials. Nevertheless, satisfactory therapeutic strategies for schizophrenia remain elusive. This review highlights current clinical endeavors in developing novel chemical small-molecule entities and fixed-dose combinations for the treatment of schizophrenia since 2017, thus facilitating the efficient development of the next generation of antipsychotics.

The Impact of Xanomeline and Trospium Chloride on Cognitive Impairment in Acute Schizophrenia: Replication in Pooled Data From Two Phase 3 Trials

OBJECTIVE

Xanomeline and trospium chloride (formerly known as KarXT), a novel M1/M4 muscarinic receptor agonist, demonstrated efficacy across phase 2 and 3 trials as monotherapy for the treatment of inpatients with acute schizophrenia on the Positive and Negative Syndrome Scale total score primary endpoint. In the phase 2 trial, xanomeline/trospium improved performance on a cognitive outcome measure in the subgroup of participants with clinically significant baseline cognitive impairment. The authors sought to confirm this finding using data from two phase 3 trials.

METHODS

Data were pooled from two 5-week inpatient trials of xanomeline/trospium monotherapy in patients with acute schizophrenia. The statistical analysis plan prespecified comparisons of cognitive composite score changes between xanomeline/trospium and placebo in the full sample and the cognitively impaired (≤1 SD below norms at baseline) subgroup.

RESULTS

There was no significant xanomeline/trospium effect in the full sample (N=357); however, in the impaired subgroup, xanomeline/trospium (N=71) had a significantly greater benefit for cognition compared with placebo (N=66; least squares mean difference=0.31, SE=0.10; d=0.54). The xanomeline/trospium effect size increased significantly with a more stringent baseline impairment threshold (≤-1.5 SD; d=0.80). Improvements in cognition were minimally correlated with concurrent changes in total, positive, and negative symptoms in both treatment groups.

CONCLUSIONS

Participants with acute schizophrenia with prespecified impairments demonstrated significant cognitive improvement with xanomeline/trospium compared with placebo. This result directly confirms earlier findings. This benefit is not attributable to changes in symptoms, despite substantial evidence of efficacy for psychosis. Evaluation of xanomeline/trospium's potential for cognitive enhancement in a well-controlled trial of stable patients with cognitive impairment is warranted.

Methods to address functional unblinding of raters in CNS trials

Treatment-emergent adverse events (TEAEs) associated with the unique properties of a pharmaceutical product may functionally unblind clinician ratings, obscure true medication effects, and affect confidence about clinical trial results. Central nervous system studies are particularly susceptible to functional unblinding because they rely on relatively subjective symptom assessments. Two different methods were used to examine possible functional unblinding in pooled data from three recent five-week, double-blind, placebo-controlled trials of xanomeline and trospium chloride (formerly known as KarXT) in participants with schizophrenia experiencing acute psychosis. Xanomeline/trospium is an M1/M4 muscarinic receptor agonist that may produce cholinergic side effects. First, we compared the scores of remote (site-independent) raters, blinded to TEAEs, who listened to audio recorded, site-based Positive and Negative Syndrome Scale (PANSS) interviews. Second, we conducted a post hoc analysis of participant subgroups with or without reported cholinergic-related TEAEs to ascertain whether cholinergic TEAEs influenced trial outcome. Remote ratings closely replicated 575 available "paired" site-based PANSS total scores at baseline and endpoint (intraclass correlation coefficient = 0.88 and 0.93, respectively). Both site-based and remote PANSS scores yielded significant improvement favouring xanomeline/trospium over placebo (both p < 0.0001) and yielded significantly greater treatment response (≥30% improvement from baseline) than placebo (both p < 0.0001). The significant improvement of PANSS scores favouring xanomeline/trospium over placebo was comparable in magnitude for all subgroups regardless of whether participants reported cholinergic-related TEAEs, or any TEAEs at all (all p < 0.001). In sum, the two different methods used to assess functional unblinding in these studies found no impact of cholinergic TEAEs, or any TEAEs, on the trial results. These methods may have utility across all clinical trials.

Capturing changes in social functioning and positive affect using ecological momentary assessment during a 12-month trial of xanomeline and trospium chloride in schizophrenia

BACKGROUND

Experiential negative symptoms (NS) are determinants of disability in schizophrenia (SCZ). Xanomeline/Trospium Chloride (X/T), an M1/M4 muscarinic receptor agonist, is an approved monotherapy for treatment of schizophrenia, including NS. We used remote ecological momentary assessments (EMA) to track changes in indicators of NS during 12 months of outpatient treatment with X/T.

METHODS

After discontinuing previous medications, 566 outpatients with SCZ received open-label X/T monotherapy for up to 12 months. Participants completed 3 EMA surveys 7 days a week, one week a month. Surveys queried whether participants were home vs. away and alone vs with someone, as well as productive and unproductive activities, and moods. Hierarchical linear modeling (HLM) examined temporal changes and the relationships between the indicators of NS.

RESULTS

500 participants answered one or more EMA surveys and 350 met 33 % adherence criteria, answering a total of 40,464 surveys, with overall adherence among these participants at 66 %. During treatment with X/T, there were significant decreases in surveys at home (p < .001), alone (p < .001), and engaging in unproductive activities (p < .001). There were significant increases in productive activities both home (p < .001) and away (p < .001) and in positive affect (PA) (p < .001). Improvements in PA converged with reduced unproductive activities, particularly when others were present (p < .001).

CONCLUSIONS

Behavioral indicators of NS improved early and were sustained with X/T treatment. Improvements were multidimensional, shifting toward more time with others, away from home, and engaged in productive activities. These improvements were associated with increases in PA, consistent with previous EMA studies of NS.

Xanomeline/Trospium Chloride: First Approval

Xanomeline/trospium chloride (COBENFY™), formerly KarXT, is a first-in-class, oral, fixed-dose muscarinic agonist/antagonist combination being developed for use in schizophrenia and Alzheimer's disease psychosis. Xanomeline is thought to confer efficacy by acting as an agonist at M1 and M4 muscarinic acetylcholine receptors in the brain, and trospium chloride reduces the peripheral cholinergic adverse events associated with xanomeline. Xanomeline/trospium chloride received its first approval on 26 September 2024 in the USA for the treatment of schizophrenia in adults. This article summarizes the milestones in the development of xanomeline/trospium chloride leading to this first approval for schizophrenia.

Overview of Novel Antipsychotic Drugs: State of the Art, New Mechanisms, and Clinical Aspects of Promising Compounds

Antipsychotic medications are a vast class of drugs used for the treatment of psychotic disorders such as schizophrenia. Although numerous compounds have been developed since their introduction in the 1950s, several patients do not adequately respond to current treatments, or they develop adverse reactions that cause treatment discontinuation. Moreover, in the past few decades, discoveries in the pathophysiology of psychotic disorders have opened the way for experimenting with novel compounds that have alternative mechanisms of action, with some of them showing promising results in early trials. The scope of this review was to summarize the novel antipsychotics developed, their current experimental status, and their mechanisms of action. In particular, we analyzed the main classes of investigational antipsychotics, such as monoamine, glutamate, acetylcholine, cannabinoid receptor modulators, enzyme inhibitors, ion channel modulators, and mixed receptor modulators. In addition, the safety profiles and adverse effects of these drugs were carefully evaluated, considering the relevance of these aspects for patients' drug adherence and quality of life, especially in the long-term treatment. Lastly, we tried to understand which compounds have greater potential to be approved by the principal drug regulatory agencies in the next years and if they could be used for diseases other than psychotic disorders.

Efficacy and safety of xanomeline-trospium chloride in schizophrenia: A systematic review and meta-analysis

INTRODUCTION

Schizophrenia is one of the psychiatric illnesses with a higher mortality rate. Xanomeline, an oral muscarinic receptor agonist, combined with Trospium, a pan-muscarinic receptor antagonist, represents a promising new treatment for schizophrenia that has been tested in clinical trials. Herein, we aimed to perform a meta-analysis assessing Xanomeline-Trospium Chloride's (XTC) safety and efficacy for treating schizophrenia.

MATERIALS AND METHODS

MEDLINE, EMBASE, and Cochrane databases were searched for randomized clinical trials testing XTC safety and efficacy in patients with schizophrenia on May 03, 2024. The research protocol was registered with the International Prospective Register of Systematic Reviews (CRD42024547487). Data were examined using the Mantel-Haenszel method and 95% CIs. Heterogeneity was assessed using I2 statistics. R, version 4.3.2, was used for statistical analysis.

RESULTS

3 RCTs and 674 patients were included, of whom 332 (49%) received XTC. The change from baseline in the Positive and Negative Syndrome Scale (PANSS) total score was significantly higher in the XTC arm (MD -13.17; 95% CI -20.16 to -6.18; P = 0.0002; I2 = 100%). Treatment with XTC resulted in improvements across all subscales of the PANSS. Additionally, XTC was associated with the occurrence of cholinergic adverse events, including nausea (18,52% vs. 3,79%; RR 4.37; 95% CI 2.43 to 7.84; P < 0.000001; I2 = 19%) but was not associated with akathisia (MD -0.00; 95% CI -0.13 to 0.13; P = 0.9; I2 = 0%) or body weight gain (MD -0.36; 95% CI -1.18 to 0.46; P = 0.38; I2 = 51%).

CONCLUSION

XTC is effective in improving schizophrenia symptoms. However, it is associated with some bothersome AEs that may undermine its tolerability and lead to increased discontinuation rates, despite its efficacy.

A Clinically Oriented Review of New Antipsychotics for Schizophrenia

BACKGROUND

Currently available antipsychotics, mainly targeting the dopaminergic pathway, fail to address the complexity of schizophrenic symptoms and can lead to burdening adverse events. The need for innovative pharmacological options remains critical and research is now focusing on the development of non-dopaminergic antipsychotics. This review aims to summarize the current literature on the most promising non-dopaminergic new APs (muscarinic agonists, Trace Amine Associated Receptor 1 agonists, Glycine Transporter Type 1 inhibitors and 5-HT2A antagonists) and provide a clinically oriented overview of their efficacy, safety and potential use in schizophrenia.

METHODS

A preliminary search was conducted through the Clinical Trials Database, in order to identify a representative (at late-stage clinical development) for each pharmacological class. The following drugs were selected: bitopertin (GlyT-1 inhibitor), pimavanserin (5-HT2A antagonist), ulotaront (TAAR1 agonist) and xanomeline-trospium (muscarinic agonist). Then, a literature search was conducted through PubMed, in order to retrieve current literature focusing on the efficacy and safety of these drugs.

RESULTS

The clinical development of bitopertin and pimavanserin was halted despite the early promises. Xanomeline-trospium chloride was recently approved by the FDA for the treatment of schizophrenia. Ulotaront showed mixed results, although analysis is ongoing.

CONCLUSION

The findings of our review indicate that research on the treatment of schizophrenia is gaining momentum. However, it is crucial to remain cautious about over-optimism, as many compounds have failed to deliver the expected results. A balanced approach is recommended when dealing with new APs, whether under investigation or approved. In the latter case, clinicians should carefully evaluate the cost-benefit ratio. Since several agents are still being tested, there is hope that additional data may present new therapeutic opportunities.

IUPHAR Review on muscarinic M1 and M4 receptors as drug treatment targets relevant to the molecular pathology of schizophrenia

Cobenfy, a co-formulation of xanomeline and trospium, is the first drug not acting on the dopaminergic system of the CNS approved for the treatment of schizophrenia by the FDA. Xanomeline is a muscarinic M1 and M4 receptor (CHRM1 and CHRM4) agonist whilst trospium is a peripherally active CHRM antagonist that reduces the unwanted peripheral side-effects of xanomeline. Relevant to this exciting development, this review details the human CNS cholinergic systems and how those systems are affected by the molecular pathology of schizophrenia in a way suggesting activating the CHRM1 and 4 would be beneficial in treating the disorder. The CNS distribution of CHRMs is presented along with findings using CHRM knockout mice and mice treated with drugs that activate the CHRM1 and / or M4, these data explain why these CHRMs could be involved in the genesis of the symptoms of schizophrenia. Next, the process leading to the formulation of Cobenfy and the preclinical data on xanomeline are reviewed showing why Cobenfy was expected to be useful in treating schizophrenia. The pipeline of drugs targeting CHRM1 and /or M4 receptors to treat schizophrenia are discussed. Finally, the molecular pathology of two sub-groups within schizophrenia, separated based on the presence or absence of a deficit of cortical CHRM1, are reviewed to show how such approaches could identify new drug targets. In conclusion, the history of the development of Cobenfy highlights how a growing understanding the pathophysiology of schizophrenia will suggest new treatment targets for the disorder and that pharmacologists can synthesise drugs to target these sites.

Efficacy of KarXT on negative symptoms in acute schizophrenia: A post hoc analysis of pooled data from 3 trials

BACKGROUND

Currently approved antipsychotics do not adequately treat negative symptoms (NS), which are a major determinant of functional disability in schizophrenia. KarXT, an M1 /M4 preferring muscarinic receptor agonist, has shown efficacy as a broad-spectrum monotherapy for the treatment of schizophrenia in participants with acute psychosis. Post hoc analyses evaluated the possibility that NS improve independently of positive symptoms with KarXT in a subgroup of participants with moderate-to-severe NS and no predominance of positive symptoms.

METHODS

Data were pooled from the three pivotal trials of KarXT monotherapy in people with schizophrenia with an acute exacerbation of psychosis. All 3 studies used similar 5-week randomized, double-blind, placebo-controlled designs (modified intention-to-treat sample N = 640). PANSS criteria proposed in the literature identified a subset of study participants (n = 64) with prominent NS.

RESULTS

KarXT was significantly better than placebo on PANSS Marder Negative Factor Scores in the full sample (p < .001; Cohen's d = 0.42) and more so in the prominent NS subgroup (p < .001; Cohen's d = 1.18). Further, the KarXT effect in the NS subgroup remained significant after accounting for changes in positive symptoms, depression/anxiety, disorganization, and hostility.

CONCLUSIONS

Participants with prominent NS revealed greater improvement of NS following KarXT therapy than the full sample that persisted after accounting for positive and other symptoms. While these findings must be interpreted with caution, they are consistent with the possibility that NS improvements associated with KarXT are not secondary to improvements in other symptom domains and support further investigation in larger, stable outpatient studies.

Efficacy of xanomeline and trospium chloride in schizophrenia: pooled results from three 5-week, randomized, double-blind, placebo-controlled, EMERGENT trials

In the 5-week, randomized, double-blind, placebo-controlled EMERGENT-1 (NCT03697252), EMERGENT-2 (NCT04659161), and EMERGENT-3 (NCT04738123) trials, xanomeline and trospium chloride (formerly known as KarXT) significantly improved symptoms of schizophrenia and was generally well tolerated. We pooled data from the EMERGENT trials to further characterize the efficacy of xanomeline/trospium and provide sufficient statistical power to analyze responses in participant subgroups. In pooled analyses, xanomeline/trospium significantly improved Positive and Negative Syndrome Scale (PANSS) total score at week 5 versus placebo (least squares mean difference, -9.9; 95% confidence interval, -12.4, -7.3; p < 0.0001; Cohen's d effect size, 0.65). PANSS subscale and Clinical Global Impression-Severity scores also improved significantly with xanomeline/trospium versus placebo. Subgroup analyses consistently favored xanomeline/trospium over placebo regardless of differences in participant age, sex, race, body mass index, and baseline PANSS total score. These results add to existing evidence demonstrating robust and reliable improvements in symptoms with xanomeline/trospium across a broad spectrum of people with schizophrenia.

Muscarinic Receptor Activators as Novel Treatments for Schizophrenia

Achieving optimal treatment outcomes for individuals living with schizophrenia remains challenging, despite 70 years of drug development efforts. Many chemically distinct antipsychotics have been developed over the past 7 decades with improved safety and tolerability but with only slight variation in efficacy. All antipsychotics currently approved for the treatment of schizophrenia act as antagonists or partial agonists at the dopamine D2 receptor. With only a few possible exceptions, antipsychotic drugs have similar and modest efficacy for treating positive symptoms and are relatively ineffective in addressing the negative and cognitive symptoms of the disease. The development of novel treatments focused on targeting muscarinic acetylcholine receptors (mAChRs) has been of interest for more than 25 years following reports that treatment with a dual M1/M4-preferring mAChR agonist resulted in antipsychotic-like effects and procognitive properties in individuals living with Alzheimer's disease and schizophrenia; more recent clinical trials have confirmed these findings. In addition, advances in our understanding of the receptor binding and activation properties of xanomeline at specific mAChRs have the potential to inform future drug design targeting mAChRs.

The potential of muscarinic M1 and M4 receptor activators for the treatment of cognitive impairment associated with schizophrenia

Cognitive impairment is a core symptom of schizophrenia and a major determinant of poor long-term functional outcomes. Despite considerable efforts, we do not yet have any approved pharmacological treatments for cognitive impairment associated with schizophrenia (CIAS). A combination of advances in pre-clinical research and recent clinical trial findings have led to a resurgence of interest in the cognition-enhancing potential of novel muscarinic acetylcholine receptor (mAChR) agonists in schizophrenia. This article provides an overview of the scientific rationale for targeting M1 and M4 mAChRs. We describe the evolution of neuroscience research on these receptors since early drug discovery efforts focused on the mAChR agonist xanomeline. This work has revealed that M1 and M4 mAChRs are highly expressed in brain regions that are implicated in cognition. The functional significance of M1 and M4 mAChRs has been extensively characterized in animal models via use of selective receptor subtype compounds through neuronal and non-neuronal mechanisms. Recent clinical trials of a dual M1/M4 mAChR agonist show promising, replicable evidence of potential pro-cognitive effects in schizophrenia, with several other mAChR agonists in clinical development.

The excitatory-inhibitory balance as a target for the development of novel drugs to treat schizophrenia

The intricate balance between excitation and inhibition (E/I) in the brain plays a crucial role in normative information processing. Dysfunctions in the E/I balance have been implicated in various psychiatric disorders, including schizophrenia (SCZ). In particular, abnormalities in GABAergic signaling, specifically in parvalbumin (PV)-containing interneurons, have been consistently observed in SCZ pathophysiology. PV interneuron function is vital for maintaining an ideal E/I balance, and alterations in PV interneuron-mediated inhibition contribute to circuit deficits observed in SCZ, including hippocampus hyperactivity and midbrain dopamine system overdrive. While current antipsychotic medications primarily target D2 dopamine receptors and are effective primarily in treating positive symptoms, novel therapeutic strategies aiming to restore the E/I balance could potentially mitigate not only positive symptoms but also negative symptoms and cognitive deficits. This could involve, for instance, increasing the inhibitory drive onto excitatory neurons or decreasing the putative enhanced pyramidal neuron activity due to functional loss of PV interneurons. Compounds targeting the glycine site at glutamate NMDA receptors and muscarinic acetylcholine receptors on PV interneurons that can increase PV interneuron drive, as well as drugs that increase the postsynaptic action of GABA, such as positive allosteric modulators of α5-GABA-A receptors, and decrease glutamatergic output, such as mGluR2/3 agonists, represent promising approaches. Preventive strategies aiming at E/I balance also represent a path to reduce the risk of transitioning to SCZ in high-risk individuals. Therefore, compounds with novel mechanisms targeting E/I balance provide optimism for more effective and tailored interventions in the management of SCZ.

Beyond dopamine: Novel strategies for schizophrenia treatment

Despite extensive research efforts aimed at discovering novel antipsychotic compounds, a satisfactory pharmacological strategy for schizophrenia treatment remains elusive. All the currently available drugs act by modulating dopaminergic neurotransmission, leading to insufficient management of the negative and cognitive symptoms of the disorder. Due to these challenges, several attempts have been made to design agents with innovative, non-dopaminergic mechanisms of action. Consequently, a number of promising compounds are currently progressing through phases 2 and 3 of clinical trials. This review aims to examine the rationale behind the most promising of these strategies while simultaneously providing a comprehensive survey of study results. We describe the versatility behind the cholinergic neurotransmission modulation through the activation of M1 and M4 receptors, exemplified by the prospective drug candidate KarXT. Our discussion extends to the innovative approach of activating TAAR1 receptors via ulotaront, along with the promising outcomes of iclepertin, a GlyT-1 inhibitor with the potential to become the first treatment option for cognitive impairment associated with schizophrenia. Finally, we evaluate the 5-HT2A antagonist paradigm, assessing two recently developed serotonergic agents, pimavanserin and roluperidone. We present the latest advancements in developing novel solutions to the complex challenges posed by schizophrenia, offering an additional perspective on the diverse investigated drug candidates.

Treatment of Cognitive Impairment Associated with Schizophrenia Spectrum Disorders: New Evidence, Challenges, and Future Perspectives

Cognitive impairment associated with schizophrenia (CIAS) represents one of the core features of the disorder and has a significant impact on functional and rehabilitation outcomes of people living with schizophrenia spectrum disorders (SSD). The aim of this critical review is to highlight the most recent evidence on effective treatments available for CIAS, to discuss the current challenges in this field, and to present future perspectives that may help to overcome them. Concerning psychopharmacological approaches, among the most indicated strategies for the management and prevention of CIAS is to favor second-generation antipsychotic medications and avoid long-term and high-dose treatments with anticholinergic medications and benzodiazepines. Moreover, non-pharmacological approaches such as cognitive remediation and physical exercise-based programs represent evidence-based interventions in the treatment of CIAS that have shown reliable evidence of effectiveness on both cognitive and functional outcomes. These treatments, however, are still delivered to people accessing mental health services with a diagnosis of CIAS in an uneven manner, even in high-income countries. Academic and clinical partnership and collaboration, as well as advocacy from service users, families, carers, and stakeholders' organizations could help to reduce the bench to bedside gap in the treatment of CIAS. Future perspectives include the development of novel pharmacological agents that could be effective in the treatment of CIAS, the implementation of novel technologies such as telemedicine and virtual reality in the delivery of evidence-based interventions to improve accessibility and engagement, and further research in the field of non-invasive brain stimulation.

Alzheimer's Disease: Combination Therapies and Clinical Trials for Combination Therapy Development

Alzheimer's disease (AD) is a complex multifaceted disease. Recently approved anti-amyloid monoclonal antibodies slow disease progression by approximately 30%, and combination therapy appears necessary to prevent the onset of AD or produce greater slowing of cognitive and functional decline. Combination therapies may address core features, non-specific co-pathology commonly occurring in patients with AD (e.g., inflammation), or non-AD pathologies that may co-occur with AD (e.g., α-synuclein). Combination therapies may be advanced through co-development of more than one new molecular entity or through add-on strategies including an approved agent plus a new molecular entity. Addressing add-on combination therapy is currently urgent since patients on anti-amyloid monoclonal antibodies may be included in clinical trials for experimental agents. Phase 1 information must be generated for each agent in combination drug development. Phase 2 and Phase 3 of add-on therapies may contrast the new molecular entity, the approved agent as standard of care, and the combination. More complex development programs including standard or modified combinatorial designs are required for co-development of two or more new molecular entities. Biomarkers are markedly affected by anti-amyloid monoclonal antibodies, and these effects must be anticipated in add-on trials. Examining target engagement biomarkers and comparing the magnitude and sequence of biomarker changes in those receiving more than one therapy, compared with those on monotherapy, may be informative. Using network-based medicine approaches, computational strategies may identify rational combinations using disease and drug effect network mapping.

What Remains to Be Discovered in Schizophrenia Therapeutics: Contributions by Advancing the Molecular Mechanisms of Drugs for Psychosis and Schizophrenia

Schizophrenia is a frequently debilitating and complex mental disorder affecting approximately 1% of the global population, characterized by symptoms such as hallucinations, delusions, disorganized thoughts and behaviors, cognitive dysfunction, and negative symptoms. Traditional treatment has centered on postsynaptic dopamine antagonists, commonly known as antipsychotic drugs, which aim to alleviate symptoms and improve functioning and the quality of life. Despite the availability of these medications, significant challenges remain in schizophrenia therapeutics, including incomplete symptom relief, treatment resistance, and medication side effects. This opinion article explores advancements in schizophrenia treatment, emphasizing molecular mechanisms, novel drug targets, and innovative delivery methods. One promising approach is novel strategies that target neural networks and circuits rather than single neurotransmitters, acknowledging the complexity of brain region interconnections involved in schizophrenia. Another promising approach is the development of biased agonists, which selectively activate specific signaling pathways downstream of receptors, offering potential for more precise pharmacological interventions with fewer side effects. The concept of molecular polypharmacy, where a single drug targets multiple molecular pathways, is exemplified by KarXT, a novel drug combining xanomeline and trospium to address both psychosis and cognitive dysfunction. This approach represents a comprehensive strategy for schizophrenia treatment, potentially improving outcomes for patients. In conclusion, advancing the molecular understanding of schizophrenia and exploring innovative therapeutic strategies hold promise for addressing the unmet needs in schizophrenia treatment, aiming for more effective and tailored interventions. Future research should focus on these novel approaches to achieve better clinical outcomes and improve the functional level and quality of life for individuals with schizophrenia.

Current Findings and Potential Mechanisms of KarXT (Xanomeline-Trospium) in Schizophrenia Treatment

Standard schizophrenia treatment involves antipsychotic medications that target D2 dopamine receptors. However, these drugs have limitations in addressing all symptoms and can lead to adverse effects such as motor impairments, metabolic effects, sedation, sexual dysfunction, cognitive impairment, and tardive dyskinesia. Recently, KarXT has emerged as a novel drug for schizophrenia. KarXT combines xanomeline, a muscarinic receptor M1 and M4 agonist, with trospium, a nonselective antimuscarinic agent. Of note, xanomeline can readily cross blood-brain barrier (BBB) and, thus, enter into the brain, thereby stimulating muscarinic receptors (M1 and M4). By doing so, xanomeline has been shown to target negative symptoms and potentially improve positive symptoms. Trospium, on the other hand, is not able to cross BBB, thereby not affecting M1 and M4 receptors; instead, it acts as an antimuscarinic agent and, hence, diminishes peripheral activity of muscarinic receptors to minimize side effects probably stemming from xanomeline in other organs. Accordingly, ongoing clinical trials investigating KarXT's efficacy in schizophrenia have demonstrated positive outcomes, including significant improvements in the Positive and Negative Syndrome Scale (PANSS) total score and cognitive function compared with placebo. These findings emphasize the potential of KarXT as a promising treatment for schizophrenia, providing symptom relief while minimizing side effects associated with xanomeline monotherapy. Despite such promising evidence, further research is needed to confirm the efficacy, safety, and tolerability of KarXT in managing schizophrenia. This review article explores the current findings and potential mechanisms of KarXT in the treatment of schizophrenia.

The New Horizon of Antipsychotics beyond the Classic Dopaminergic Hypothesis-The Case of the Xanomeline-Trospium Combination: A Systematic Review

Although the dopamine hypothesis of schizophrenia explains the effects of all the available antipsychotics in clinical use, there is an increasing need for developing new drugs for the treatment of the positive, negative, and cognitive symptoms of chronic psychoses. Xanomeline-trospium (KarXT) is a drug combination that is based on the essential role played by acetylcholine in the regulation of cognitive processes and the interactions between this neurotransmitter and other signaling pathways in the central nervous system, with a potential role in the onset of schizophrenia, Alzheimer's disease, and substance use disorders. A systematic literature review that included four electronic databases (PubMed, Cochrane, Clarivate/Web of Science, and Google Scholar) and the US National Library of Medicine database for clinical trials detected twenty-one sources referring to fourteen studies focused on KarXT, out of which only four have available results. Based on the results of these trials, the short-term efficacy and tolerability of xanomeline-trospium are good, but more data are needed before this drug combination may be recommended for clinical use. However, on a theoretical level, the exploration of KarXT is useful for increasing the interest of researchers in finding new, non-dopaminergic, antipsychotics that could be used either as monotherapy or as add-on drugs.

Efficacy and safety of the muscarinic receptor agonist KarXT (xanomeline-trospium) in schizophrenia (EMERGENT-2) in the USA: results from a randomised, double-blind, placebo-controlled, flexible-dose phase 3 trial

BACKGROUND

New treatments with new mechanisms are urgently needed for people with schizophrenia. Xanomeline is a dual M1 and M4-preferring muscarinic receptor agonist that does not block D2 dopamine receptors, unlike all currently approved treatments for schizophrenia. Xanomeline-trospium (KarXT) combines xanomeline with the peripherally restricted muscarinic receptor antagonist trospium chloride with the goal of ameliorating xanomeline-related adverse events associated with peripheral muscarinic receptors. The EMERGENT-2 trial aimed to assess the efficacy and safety of KarXT in people with schizophrenia experiencing acute psychosis.

METHODS

EMERGENT-2 was a randomised, double-blind, placebo-controlled, flexible-dose, 5-week, inpatient, phase 3 trial in people with schizophrenia. Participants were adults aged 18-65 years with a diagnosis of schizophrenia who had a recent worsening of psychosis warranting hospital admission, a Positive and Negative Syndrome Scale (PANSS) score of 80 or higher, and a Clinical Global Impression-Severity score of 4 or higher. The participants were recruited from 22 inpatient sites in the USA, and were randomly assigned (1:1) to KarXT or placebo twice per day. Participants randomly assigned to KarXT received 50 mg xanomeline and 20 mg trospium twice per day for the first 2 days and then 100 mg xanomeline and 20 mg trospium twice per day for days 3-7. Beginning on day 8, KarXT dosing was flexible with an optional increase to 125 mg xanomeline and 30 mg trospium twice per day and the option to return to 100 mg xanomeline and 20 mg trospium based on tolerability. The primary endpoint was change from baseline to week 5 in PANSS total score. Efficacy analyses used the modified intention-to-treat population (all randomly assigned participants who received at least one trial medication dose and had at least one post-baseline PANSS assessment). Least squares mean change from baseline, SE, and least squares mean difference between the KarXT and placebo groups at week 5, along with the 95% CI and two-sided p values were calculated for the primary and secondary continuous efficacy endpoints. Safety analyses included all participants receiving at least one trial medication dose and used descriptive statistics. This trial is registered with ClinicalTrials.gov (NCT04659161).

FINDINGS

From Dec 16, 2020, to April 13, 2022, of 407 people who were screened, 252 participants meeting enrolment criteria were randomly assigned to the KarXT (n=126) or placebo (n=126). Baseline PANSS total scores were 98·3 (KarXT; n=126) and 97·9 (placebo; n=125). The trial met the primary endpoint with a mean change from baseline to week 5 in PANSS total score that favoured KarXT (-21·2 points, SE 1·7) versus placebo (-11·6 points, 1·6; least squares mean difference -9·6; 95% CI -13·9 to -5·2; p<0·0001, Cohen's d effect size=0·61). All secondary endpoints were also met, and favoured KarXT versus placebo (p<0·05). The most common adverse events with KarXT versus placebo were constipation (27 [21%] vs 13 [10%]), dyspepsia (24 [19%] vs 10 [8%]), headache (17 [14%] vs 15 [12%]), nausea (24 [19%] vs seven [6%]), vomiting (18 [14%] vs one [1%]), hypertension (12 [10%] vs one [1%]), dizziness (11 [9%] vs four [3%]), gastro-oesophageal reflux disease (eight [6%] vs zero [0%]), and diarrhoea (seven [6%] vs four [3%]). Treatment-emergent adverse event rates of extrapyramidal motor symptoms (KarXT, zero [0%] vs placebo, zero [0%]), akathisia (one [1%] vs one [1%]), weight gain (zero [0%] vs one [1%]), and somnolence (six [5%] vs five [4%]) were similar between the KarXT and placebo groups, as were adverse event-related discontinuation rates (nine [7%] vs seven [6%]).

INTERPRETATION

In the EMERGENT-2 trial, KarXT was effective in reducing positive and negative symptoms and was generally well tolerated. These results support the potential for KarXT to represent a new class of effective and well tolerated antipsychotic medicines based on activating muscarinic receptors, not the D2 dopamine receptor-blocking mechanism of all current antipsychotic medications. Results from additional trials, including the identical EMERGENT-3 trial and the 52-week, open-label EMERGENT-4 and EMERGENT-5 trials, will provide additional information on the efficacy and safety of KarXT in people with schizophrenia.

FUNDING

Karuna Therapeutics.

Pharmacological Treatment of Cognitive Impairment Associated With Schizophrenia: State of the Art and Future Perspectives

Cognitive Impairment Associated with Schizophrenia (CIAS) represents one of the core dimensions of Schizophrenia Spectrum Disorders (SSD), with an important negative impact on real-world functional outcomes of people living with SSD. Treatment of CIAS represents a therapeutic goal of considerable importance, and while cognition-oriented evidence-based psychosocial interventions are available, effective pharmacological treatment could represent a game-changer in the lives of people with SSD. The present critical review reports and discusses the evidence regarding the effects of several pharmacological agents that are available in clinical practice or are under study, commenting on both current and future perspectives of CIAS treatment. In particular, the effects on CIAS of antipsychotic medications, anticholinergic medications, benzodiazepines, which are currently commonly used in the treatment of SSD, and of iclepertin, d-serine, luvadaxistat, xanomeline-trospium, ulotaront, anti-inflammatory molecules, and oxytocin, which are undergoing regulatory trials or can be considered as experimental agents, will be reported and discussed. Currently, available pharmacological agents do not appear to provide substantial benefits on CIAS, but accurate management of antipsychotic medications and avoiding treatments that can further exacerbate CIAS represent important strategies. Some molecules that are currently being investigated in Phase 2 and Phase 3 trials have provided very promising preliminary results, but more information is currently required to assess their effectiveness in real-world contexts and to provide clear recommendations regarding their use in clinical practice. The results of ongoing and future studies will reveal whether any of these molecules represents the awaited pharmacological game-changer in the treatment of CIAS.

Recent advances in drug discovery efforts targeting the sigma 1 receptor system: Implications for novel medications designed to reduce excessive drug and food seeking

Psychiatric disorders characterized by uncontrolled reward seeking, such as substance use disorders (SUDs), alcohol use disorder (AUD) and some eating disorders, impose a significant burden on individuals and society. Despite their high prevalence and substantial morbidity and mortality rates, treatment options for these disorders remain limited. Over the past two decades, there has been a gradual accumulation of evidence pointing to the sigma-1 receptor (S1R) system as a promising target for therapeutic interventions designed to treat these disorders. S1R is a chaperone protein that resides in the endoplasmic reticulum, but under certain conditions translocates to the plasma membrane. In the brain, S1Rs are expressed in several regions important for reward, and following translocation, they physically associate with several reward-related GPCRs, including dopamine receptors 1 and 2 (D1R and D2R). Psychostimulants, alcohol, as well as palatable foods, all alter expression of S1R in regions important for motivated behavior, and S1R antagonists generally decrease behavioral responses to these rewards. Recent advances in structural modeling have permitted the development of highly-selective S1R antagonists with favorable pharmacokinetic profiles, thus providing a therapeutic avenue for S1R-based medications. Here, we provide an up-to-date overview of work linking S1R with motivated behavior for drugs of abuse and food, as well as evidence supporting the clinical utility of S1R antagonists to reduce their excessive consumption. We also highlight potential challenges associated with targeting the S1R system, including the need for a more comprehensive understanding of the underlying neurobiology and careful consideration of the pharmacological properties of S1R-based drugs.

Novel Compounds in the Treatment of Schizophrenia-A Selective Review

Schizophrenia is a chronic neuropsychiatric syndrome that significantly impacts daily function and quality of life. All of the available guidelines suggest a combined treatment approach with pharmacologic agents and psychological interventions. However, one in three patients is a non-responder, the effect on negative and cognitive symptoms is limited, and many drug-related adverse effects complicate clinical management. As a result, discovering novel drugs for schizophrenia presents a significant challenge for psychopharmacology. This selective review of the literature aims to outline the current knowledge on the aetiopathogenesis of schizophrenia and to present the recently approved and newly discovered pharmacological substances in treating schizophrenia. We discuss ten novel drugs, three of which have been approved by the FDA (Olanzapine/Samidorphan, Lumateperone, and Pimavanserin). The rest are under clinical trial investigation (Brilaroxazine, Xanomeline/Trospium, Emraclidine, Ulotaront, Sodium Benzoate, Luvadaxistat, and Iclepertin). However, additional basic and clinical research is required not only to improve our understanding of the neurobiology and the potential novel targets in the treatment of schizophrenia, but also to establish more effective therapeutical interventions for the syndrome, including the attenuation of negative and cognitive symptoms and avoiding dopamine blockade-related adverse effects.

The Impact of Muscarinic Antagonism on Psychosis-Relevant Behaviors and Striatal [11C] Raclopride Binding in Tau Mouse Models of Alzheimer's Disease

Psychosis that occurs over the course of Alzheimer's disease (AD) is associated with increased caregiver burden and a more rapid cognitive and functional decline. To find new treatment targets, studies modeling psychotic conditions traditionally employ agents known to induce psychosis, utilizing outcomes with cross-species relevance, such as locomotive activity and sensorimotor gating, in rodents. In AD, increased burdens of tau pathology (a diagnostic hallmark of the disease) and treatment with anticholinergic medications have, separately, been reported to increase the risk of psychosis. Recent evidence suggests that muscarinic antagonists may increase extracellular tau. Preclinical studies in AD models have not previously utilized muscarinic cholinergic antagonists as psychotomimetic agents. In this report, we utilize a human-mutant-tau model (P301L/COMTKO) and an over-expressed non-mutant human tau model (htau) in order to compare the impact of antimuscarinic (scopolamine 10 mg/kg/day) treatment with dopaminergic (reboxetine 20 mg/kg/day) treatment, for 7 days, on locomotion and sensorimotor gating. Scopolamine increased spontaneous locomotion, while reboxetine reduced it; neither treatment impacted sensorimotor gating. In the P301L/COMTKO, scopolamine treatment was associated with decreased muscarinic M4 receptor expression, as quantified with RNA-seq, as well as increased dopamine receptor D2 signaling, as estimated with Micro-PET [11C] raclopride binding. Scopolamine also increased soluble tau in the striatum, an effect that partially mediated the observed increases in locomotion. Studies of muscarinic agonists in preclinical tau models are warranted to determine the impact of treatment-on both tau and behavior-that may have relevance to AD and other tauopathies.

Muscarinic M1 and M4 receptor agonists for schizophrenia: promising candidates for the therapeutic arsenal

INTRODUCTION

Successful phase 3 trials of KarXT in people with schizophrenia herald a new era of treating the disorder with drugs that do not target the dopamine D2 receptor. The active component of KarXT is xanomeline, a muscarinic (CHRM) M1 and M4 agonist, making muscarinic receptors a viable target for treating schizophrenia.

AREAS COVERED

This review covers the process of taking drugs that activate the muscarinic M1 and M4 receptors from conceptualization to the clinic and details the mechanisms by which activating the CHRM1 and 4 can affect the broad spectrum of symptoms experienced by people with schizophrenia.

EXPERT OPINION

Schizophrenia is a syndrome which means drugs that activate muscarinic M1 and M4 receptors, as was the case for antipsychotic drugs acting on the dopamine D2 receptor, will not give optimal outcomes in everyone within the syndrome. Thus, it would be ideal to identify people who are responsive to drugs activating the CHRM1 and 4. Given knowledge of the actions of these receptors, it is possible treatment non-response could be restricted to sub-groups within the syndrome who have deficits in cortical CHRM1 or those with one of the cognitive endophenotypes that may be identifiable by changes in the blood transcriptome.