Pharmacological and Behavioral Profile of N-(4-Fluorophenylmethyl)-N-(1-methylpiperidin-4-yl)-N′-(4-(2-methylpropyloxy)phenylmethyl) Carbamide (2R,3R)-Dihydroxybutanedioate (2:1) (ACP-103), a Novel 5-Hydroxytryptamine2A Receptor Inverse Agonist

New drug treatments for schizophrenia: a review of approaches to target circuit dysfunction

Schizophrenia is a leading cause of global disease burden. Current drug treatments are associated with significant side-effects and have limited efficacy for many patients; highlighting the need to develop new approaches that target other aspects of the neurobiology of schizophrenia. Preclinical, in vivo imaging, post-mortem, genetic and pharmacological studies have highlighted the key role of cortical GABA-glutamatergic microcircuits and their projections to subcortical dopaminergic circuits in the pathoetiology of negative, cognitive and psychotic symptoms. Antipsychotics primarily act downstream of the dopaminergic component of this circuit. However, multiple drugs are currently in development that could target other elements of this circuit to treat schizophrenia. These include drugs for GABA or glutamatergic targets, including glycine transporters, d-amino acid oxidase, sodium channels or potassium channels. Other drugs in development are likely to primarily act on pathways that regulate the dopaminergic system such as muscarinic or trace amine receptors or serotonin 2A receptors, whilst phosphodiesterase 10 A inhibitors are being developed to modulate the downstream consequences of dopaminergic dysfunction. Our review considers where new drugs may act on this circuit and their latest clinical trial evidence in terms of indication, efficacy and side-effects. Limitations of the circuit model, including whether there are neurobiologically distinct subgroups of patients, and future directions are also considered. Several drugs based on the mechanisms reviewed have promising clinical data, with the muscarinic agonist KarXT most advanced. If they are approved for clinical use, they have the potential to revolutionise understanding of the pathophysiology and treatment of schizophrenia.

Advancements in Non-Dopaminergic Treatments for Schizophrenia: A Systematic Review of Pipeline Developments

INTRODUCTION

Conventional antipsychotic drugs that attenuate dopaminergic neural transmission are ineffective in approximately one-third of patients with schizophrenia. This necessitates the development of non-dopaminergic agents.

METHODS

A systematic search was conducted for completed phase II and III trials of compounds for schizophrenia treatment using the US Clinical Trials Registry and the EU Clinical Trials Register. Compounds demonstrating significant superiority over placebo in the primary outcome measure in the latest phase II and III trials were identified. Collateral information on the included compounds was gathered through manual searches in PubMed and press releases.

RESULTS

Sixteen compounds were identified; four compounds (ulotaront, xanomeline/trospium chloride, vabicaserin, and roluperidone) were investigated as monotherapy and the remaining 12 (pimavanserin, bitopertin, BI 425809, encenicline, tropisetron, pregnenolone, D-serine, estradiol, tolcapone, valacyclovir, cannabidiol, and rimonabant) were examined as add-on therapy. Compared to the placebo, ulotaront, xanomeline/trospium chloride, vabicaserin, bitopertin, estradiol, cannabidiol, rimonabant, and D-serine showed efficacy for positive symptoms; roluperidone and pimavanserin were effective for negative symptoms; and encenicline, tropisetron, pregnenolone, tolcapone, BI 425809, and valacyclovir improved cognitive function.

DISCUSSION

Compounds that function differently from existing antipsychotics may offer novel symptom-specific therapeutic strategies for patients with schizophrenia.

Retrospective analyses evaluating the mortality risk associated with pimavanserin or other atypical antipsychotics in patients with Parkinson disease psychosis

Introduction

Parkinson's disease (PD) is associated with increased mortality risk (MR), reflecting progression of motor and nonmotor symptoms. PD psychosis (PDP), a common nonmotor symptom, increases with prolonged disease and elevates the MR of PD even further. Pimavanserin is the only FDA-approved treatment for PDP. This review summarizes real-world evidence around the MR of patients with PDP treated with pimavanserin versus off-label atypical antipsychotics.

Methods

A PubMed search was conducted using the following search terms: pimavanserin AND antipsychotic AND mortality AND Parkinson's disease AND psychosis. Inclusion criteria specified the entry of retrospective, observational, and open-label studies comparing pimavanserin to atypical antipsychotics or untreated controls.

Results

A total of 10 of the 32 articles met inclusion criteria. Among five comparisons of pimavanserin with atypical antipsychotics, two were large (n = 21,719; n = 21,975), representative, Medicare-database studies, which demonstrated comparable or lower all-cause pimavanserin MR. Among three pimavanserin versus control studies, two reported lower or comparable pimavanserin MR and one, long-term care study reported higher MR for pimavanserin versus non-pimavanserin treated patients with unknown PDP status. Two open-label extensions reported pimavanserin mortality rates of 6.45 and 18.8 deaths per 100 patient-years, which are comparable to, or lower than, mortality rates for PD, PDP, and other atypical antipsychotics. Most studies (70 %; 7 of 10) demonstrated pimavanserin's MR was lower than or similar to other atypical antipsychotics or untreated controls.

Conclusions

Pimavanserin did not increase the MR in PDP. Pimavanserin's MR appears to be comparable to or lower than other atypical antipsychotics prescribed for PDP, including quetiapine.

A Brief Historical Overview of Psychedelic Research

Classical serotonergic psychedelics such as lysergic acid diethylamide or the naturally occurring compounds psilocybin and mescaline produce profound changes in mood, thought, intuition, sensory perception, the experience of time and space, and even the experience of self. Research examining psychedelic compounds has had a complex and turbulent evolution. Many cultures throughout the world have used psychedelic plants not only for mystical, ritualistic, or divinatory purposes but also for curing illnesses. Much of the genesis and progress of modern investigations into the effects and underlying mechanisms of action of psychedelics have been intertwined with studies of the neurotransmitter serotonin. Early hypotheses that serotonergic systems mediate psychedelic effects were supported initially by preclinical animal studies and subsequently confirmed by pharmacological studies in healthy humans. The use of psychedelic compounds as putative psychotomimetics that reproduce some features of naturally occurring psychotic disorders met with some limited success. More recent studies are exploring psychedelics as potential psychotherapeutic agents. Recent indications that even 1 or 2 psychedelic treatments produce robust and sustained reductions in clinical symptoms in a variety of psychiatric disorders have prompted an enormous resurgence of interest in the nature and mechanisms contributing to their effects.

Weak links: Advancing target-based drug discovery by identifying the most vulnerable targets

Mycobacterium tuberculosis remains the most common infectious killer worldwide despite decades of antitubercular drug development. Effectively controlling the tuberculosis (TB) pandemic will require innovation in drug discovery. In this review, we provide a brief overview of the two main approaches to discovering new TB drugs-phenotypic screens and target-based drug discovery-and outline some of the limitations of each method. We then explore recent advances in genetic tools that aim to overcome some of these limitations. In particular, we highlight a novel metric to prioritize essential targets, termed vulnerability. Stratifying targets based on their vulnerability presents new opportunities for future target-based drug discovery campaigns.

On the Optimal Diagnosis and the Evolving Role of Pimavanserin in Parkinson's Disease Psychosis

Parkinson's disease (PD) is associated with the development of psychosis (PDP), including hallucinations and delusions, in more than half of the patient population. Optimal PD management must therefore involve considerations about both motor and non-motor symptoms. Often, clinicians fail to diagnosis psychosis in patients with PD and, when it is recognized, treat it suboptimally, despite the availability of multiple interventions. In this paper, we provide a summary of the current guidelines and clinical evidence for treating PDP with antipsychotics. We also provide recommendations for diagnosis and follow-up. Finally, an updated treatment algorithm for PDP that incorporates the use of pimavanserin, the only US FDA-approved drug for the treatment of PDP, was developed by extrapolating from a limited evidence base to bridge to clinical practice using expert opinion and experience. Because pimavanserin is only approved for the treatment of PDP in the US, in other parts of the world other recommendations and algorithms must be considered.

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.

Ligand bias and inverse agonism on 5-HT2A receptor-mediated modulation of G protein activity in post-mortem human brain

BACKGROUND AND PURPOSE

Whereas biased agonism on the 5-HT2A receptor has been ascribed to hallucinogenic properties of psychedelics, no information about biased inverse agonism on this receptor is available. In schizophrenia, increased 5-HT2A receptor constitutive activity has been suggested, highlighting the therapeutic relevance of inverse agonism. This study characterized the modulation of G protein activity promoted by different drugs, commonly considered as 5-HT2A receptor antagonists, in post-mortem human brain cortex.

EXPERIMENTAL APPROACH

Modulation of [35S]GTPγS binding to different subtypes of Gα proteins exerted by different 5-HT2A receptor drugs was determined by scintillation proximity assays in brain from human, WT and 5-HT2A receptor KO mice.

KEY RESULTS

MDL-11,939 was the only drug having no effect on the basal activity of 5-HT2A receptor. Altanserin and pimavanserin decreased basal activation of Gi1, but not Gq/11 proteins. This effect was blocked by MDL-11,939 and absent in 5-HT2A receptor KO mice. Volinanserin showed 5-HT2A receptor-mediated inverse agonism both on Gi1 and Gq/11 proteins. Ketanserin exhibited 5-HT2A receptor partial agonism exclusively on Gq/11 proteins. On the other hand, eplivanserin and nelotanserin displayed inverse agonism on Gq/11 and/or Gi1 proteins, which was insensitive to MDL-11,939 and was present in KO mice suggesting a role for another receptor.

CONCLUSION AND IMPLICATIONS

The results reveal the existence of constitutively active 5-HT2A receptors in human pre-frontal cortex and demonstrate different pharmacological profiles of various 5-HT2A receptor drugs previously considered antagonists. These findings indicate that altanserin and pimavanserin possess biased inverse agonist profile towards 5-HT2A receptor activation of Gi1 proteins.

The effects of treatment with pimavanserin on activities of daily living in patients with Parkinson's disease psychosis: a 16-week, single-arm, open-label study

Background

More than half of patients with Parkinson's disease will experience psychosis symptoms in the form of hallucinations or delusions at some point over the course of their disease. These symptoms can significantly impact patients' health-related quality of life, cognitive abilities, and activities of daily living (ADLs) and function. Clinical assessment of how psychosis impacts these measures is crucial; however, few studies have assessed this sufficiently, in part due to a lack of appropriate scales for comprehensively assessing function.

Objective

The objective was to assess how symptoms of Parkinson's disease psychosis (PDP) impact ADLs and function, cognitive function, and health-related quality of life.

Design

To address this unmet need, we utilized a modified version of the Functional Status Questionnaire (mFSQ) to measure the impact of psychosis on ADLs and function in patients with PDP treated with pimavanserin, a US Food and Drug Administration-approved medication to treat hallucinations and delusions associated with PDP.

Methods

Eligible patients entered a 16-week, single-arm, open-label study of oral pimavanserin (34 mg) taken once daily. The primary endpoint was change from baseline to Week 16 on the mFSQ. Secondary endpoints included the Movement Disorders Society-modified Unified Parkinson's Disease Rating Scale (MDS-UPDRS) I and II; Schwab and England ADL; Clinical Global Impression-Severity of Illness (CGI-S), Clinical Global Impression-Improvement (CGI-I), and Patient Global Impression-Improvement (PGI-I), and were also measured as change from baseline to Week 16 using mixed-effects model for repeated measures (MMRM) and least-squares mean (LSM).

Results

Our results in a proof-of-concept, 16-week, open-label clinical study in 29 patients demonstrated that an improvement in psychosis symptoms following treatment with pimavanserin was associated with improvements in multiple measures of ADLs and function. Notably, a significant improvement was found on the primary endpoint, change from baseline to Week 16 in mFSQ score [LSM [SE] 14.0 [2.50], n = 17; 95% CI (8.8, 19.3); p < 0.0001].

Conclusion

These findings highlight the potential for improvement in function with improvement of psychosis symptoms in patients with PDP and suggest that the mFSQ may be a measurement tool to evaluate the level of improvement in function.

Trial registration

ClinicalTrials.gov Identifier: NCT04292223.

Parkinson disease psychosis: from phenomenology to neurobiological mechanisms

Parkinson disease (PD) psychosis (PDP) is a spectrum of illusions, hallucinations and delusions that are associated with PD throughout its disease course. Psychotic phenomena can manifest from the earliest stages of PD and might follow a continuum from minor hallucinations to structured hallucinations and delusions. Initially, PDP was considered to be a complication associated with dopaminergic drug use. However, subsequent research has provided evidence that PDP arises from the progression of brain alterations caused by PD itself, coupled with the use of dopaminergic drugs. The combined dysfunction of attentional control systems, sensory processing, limbic structures, the default mode network and thalamocortical connections provides a conceptual framework to explain how new incoming stimuli are incorrectly categorized, and how aberrant hierarchical predictive processing can produce false percepts that intrude into the stream of consciousness. The past decade has seen the publication of new data on the phenomenology and neurobiological basis of PDP from the initial stages of the disease, as well as the neurotransmitter systems involved in PDP initiation and progression. In this Review, we discuss the latest clinical, neuroimaging and neurochemical evidence that could aid early identification of psychotic phenomena in PD and inform the discovery of new therapeutic targets and strategies.

Safety Profile of Pimavanserin Therapy in Elderly Patients with Neurodegenerative Disease-Related Neuropsychiatric Symptoms: A Phase 3B Study

Background

Pimavanserin, a 5-HT2A receptor inverse agonist/antagonist, is the only medication approved by the FDA for the treatment of hallucinations and delusions associated with Parkinson's disease psychosis (PDP). Further expanding knowledge of the safety profile of pimavanserin in PDP and neurodegenerative diseases (NDD) such as Alzheimer's disease is of great interest for informing its use in patients with PDP (with or without dementia), given this population is highly sensitive to adverse effects following antipsychotic use.

Objective

This trial evaluated the effects of pimavanserin compared to placebo in frail older adults and elderly patients with neuropsychiatric symptoms related to NDD, such as hallucinations and delusions, to better understand the safety of pimavanserin in this population.

Methods

This was a phase 3b, 8-week treatment (study duration of up to 16 weeks), multicenter, randomized, double-blind, placebo-controlled, two-arm parallel-group trial (NCT03575052). The primary endpoint was safety and tolerability, measured by treatment-emergent adverse events (TEAEs). Secondary safety endpoints were change from baseline in motor and cognitive function; exploratory endpoints included suicidality, sleep quality, and neuropsychiatric symptoms.

Results

Incidences of TEAEs were similar between treatment groups; 29.8% reported ≥1 TEAE (pimavanserin: 30.4%; placebo: 29.3%), and 1.8% reported serious TEAEs (pimavanserin: 2.0%; placebo: 1.5%). Pimavanserin did not impact motor- or cognitive-related function.

Conclusions

Pimavanserin was well tolerated and not associated with motor or cognitive impairment. Together, these findings highlight the manageable and generally favorable safety profile of pimavanserin in patients with NDD, contributing to our knowledge on the safety of pimavanserin as it generalizes to patients with PDP.

Population Pharmacokinetic Modeling and Stochastic Simulations to Support Pediatric Dose Selection of Pimavanserin

Pimavanserin is a selective serotonin-modulating agent with inverse agonist/antagonist activity at the 5-hydroxytryptamine2A (5-HT2A ) receptor. The safety and efficacy of pimavanserin 34 mg once daily were studied in adults with hallucinations and delusions associated with Parkinson's disease psychosis and other neuropsychiatric conditions. This analysis used model-based simulations of pimavanserin steady-state exposures to identify a dose that generated pediatric exposures comparable with adult exposures achieved with 34 mg pimavanserin. A population pharmacokinetics model was developed using pooled plasma drug concentration (ie, actual) data from 13 clinical studies, including a phase 1 study of adolescent pediatric patients (aged 13-17 years) with various psychiatric conditions. Stochastic simulations were performed to predict exposures in a virtual (ie, simulated) group of pediatric patients (aged 5-17 years). Steady-state measures of the area under the plasma concentration-time curve (AUC) and maximum drug concentration (Cmax ) were simulated for relevant age and weight stratifications and compared with simulated exposures in adults (aged 18-49 years). The simulated mean AUC ranged from 47.41 to 54.73 ng d/mL and the mean Cmax ranged from 41.13 to 50.07 ng/mL in adults receiving pimavanserin 34 mg. The simulated mean (SD) Cmax of 56.54 (24.58) ng/mL with pimavanserin 34 mg in patients aged 10-17 years was similar to that in adults. Pimavanserin 20 mg yielded a mean (SD) Cmax of 45.30 (21.31) ng/mL in patients aged 5-9 years and 49.18 (22.91) ng/mL in the pediatric patient weight group of 14-25 kg, which are values close to the Cmax in adults treated with 34 mg. Pimavanserin 20 and 34 mg in pediatric patients aged 5-9 and 10-17 years, respectively, yielded exposures similar to daily pimavanserin 34 mg in adults aged 18-49 years.

μ-opioid receptor agonists and psychedelics: pharmacological opportunities and challenges

Opioid misuse and opioid-involved overdose deaths are a massive public health problem involving the intertwined misuse of prescription opioids for pain management with the emergence of extremely potent fentanyl derivatives, sold as standalone products or adulterants in counterfeit prescription opioids or heroin. The incidence of repeated opioid overdose events indicates a problematic use pattern consistent with the development of the medical condition of opioid use disorder (OUD). Prescription and illicit opioids reduce pain perception by activating µ-opioid receptors (MOR) localized to the central nervous system (CNS). Dysregulation of meso-corticolimbic circuitry that subserves reward and adaptive behaviors is fundamentally involved in the progressive behavioral changes that promote and are consequent to OUD. Although opioid-induced analgesia and the rewarding effects of abused opioids are primarily mediated through MOR activation, serotonin (5-HT) is an important contributor to the pharmacology of opioid abused drugs (including heroin and prescription opioids) and OUD. There is a recent resurgence of interest into psychedelic compounds that act primarily through the 5-HT2A receptor (5-HT 2A R) as a new frontier in combatting such diseases (e.g., depression, anxiety, and substance use disorders). Emerging data suggest that the MOR and 5-HT2AR crosstalk at the cellular level and within key nodes of OUD circuitry, highlighting a major opportunity for novel pharmacological intervention for OUD. There is an important gap in the preclinical profiling of psychedelic 5-HT2AR agonists in OUD models. Further, as these molecules carry risks, additional analyses of the profiles of non-hallucinogenic 5-HT2AR agonists and/or 5-HT2AR positive allosteric modulators may provide a new pathway for 5-HT2AR therapeutics. In this review, we discuss the opportunities and challenges associated with utilizing 5-HT2AR agonists as therapeutics for OUD.

Clinical specificity profile for novel rapid acting antidepressant drugs

Mood disorders are recurrent/chronic diseases with variable clinical remission rates. Available antidepressants are not effective in all patients and often show a relevant response latency, with a range of adverse events, including weight gain and sexual dysfunction. Novel rapid agents were developed with the aim of overcoming at least in part these issues. Novel drugs target glutamate, gamma-aminobutyric acid, orexin, and other receptors, providing a broader range of pharmacodynamic mechanisms, that is, expected to increase the possibility of personalizing treatments on the individual clinical profile. These new drugs were developed with the aim of combining a rapid action, a tolerable profile, and higher effectiveness on specific symptoms, which were relatively poorly targeted by standard antidepressants, such as anhedonia and response to reward, suicidal ideation/behaviours, insomnia, cognitive deficits, and irritability. This review discusses the clinical specificity profile of new antidepressants, namely 4-chlorokynurenine (AV-101), dextromethorphan-bupropion, pregn-4-en-20-yn-3-one (PH-10), pimavanserin, PRAX-114, psilocybin, esmethadone (REL-1017/dextromethadone), seltorexant (JNJ-42847922/MIN-202), and zuranolone (SAGE-217). The main aim is to provide an overview of the efficacy/tolerability of these compounds in patients with mood disorders having different symptom/comorbidity patterns, to help clinicians in the optimization of the risk/benefit ratio when prescribing these drugs.

Pimavanserin treatment increases plasma brain-derived neurotrophic factor levels in rats

Background

Pimavanserin, a serotonin 5HT-2A receptor inverse agonist is the first-line, FDA-approved treatment of hallucinations and delusions associated with Parkinson's Disease psychosis (PDP), which occurs in up to 50% of PD patients. The neurobiological mechanism underlying the therapeutic effectiveness of Pimavanserin in PDP remains unknown. Several earlier studies have shown that treatment with 5HT-2A antagonists and other drugs acting on the serotonergic system such as SSRIs increase Brain derived neurotrophic factor (BDNF) levels in rodents. BDNF is synthesized as the precursor proBDNF, that undergoes cleavage intra or extracellularly to produce a mature BDNF (mBDNF) protein. mBDNF is believed to play a key role in neuroplasticity and neurogenesis. The present study tested the hypothesis that treatment with Pimavanserin is associated with higher and sustained elevations of mBDNF.

Methods

Adult Sprague-Dawley male rats were treated with Pimavanserin, Fluoxetine or vehicle for 4 weeks (chronic) or 2 h (acute). BDNF levels were determined by enzyme-linked Immunosorbent assay (ELISA).

Results

We found significant increases in plasma mBDNF levels in rats following chronic Pimavanserin treatment, but not in Fluoxetine-treated rats. No significant changes in mBDNF levels were found in the prefrontal cortex or hippocampus following Pimavanserin or Fluoxetine treatment.

Conclusion

These findings suggest that increase in mBDNF levels could be a contributing mechanism for the neuroprotective potential of Pimavanserin.

The serotonin transporter sustains human brown adipose tissue thermogenesis

Activation of brown adipose tissue (BAT) in humans is a strategy to treat obesity and metabolic disease. Here we show that the serotonin transporter (SERT), encoded by SLC6A4, prevents serotonin-mediated suppression of human BAT function. RNA sequencing of human primary brown and white adipocytes shows that SLC6A4 is highly expressed in human, but not murine, brown adipocytes and BAT. Serotonin decreases uncoupled respiration and reduces uncoupling protein 1 via the 5-HT2B receptor. SERT inhibition by the selective serotonin reuptake inhibitor (SSRI) sertraline prevents uptake of extracellular serotonin, thereby potentiating serotonin's suppressive effect on brown adipocytes. Furthermore, we see that sertraline reduces BAT activation in healthy volunteers, and SSRI-treated patients demonstrate no 18F-fluorodeoxyglucose uptake by BAT at room temperature, unlike matched controls. Inhibition of BAT thermogenesis may contribute to SSRI-induced weight gain and metabolic dysfunction, and reducing peripheral serotonin action may be an approach to treat obesity and metabolic disease.

Design, Synthesis, Molecular Docking, and Biological Evaluation of Novel Pimavanserin-Based Analogues as Potential Serotonin 5-HT2A Receptor Inverse Agonists

There is concern for important adverse effects with use of second-generation antipsychotics in Parkinson's disease psychosis (PDP) and dementia-related psychosis. Pimavanserin is the only antipsychotic drug authorized for PDP and represents an inverse agonist of 5-HT_2A receptors (5-HT2AR) lacking affinity for dopamine receptors. Therefore, the development of serotonin 5-HT2AR inverse agonists without dopaminergic activity represents a challenge for different neuropsychiatric disorders. Using ligand-based drug design, we discovered a novel structure of pimavanserin analogues (2, 3, and 4). In vitro competition receptor binding and functional G protein coupling assays demonstrated that compounds 2, 3, and 4 showed higher potency than pimavanserin as 5-HT2AR inverse agonists in the human brain cortex and recombinant cells. To assess the effect of molecular substituents for selectivity and inverse agonism at 5-HT2ARs, molecular docking and in silico predicted physicochemical parameters were performed. Docking studies were in agreement with in vitro screenings and the results resembled pimavanserin.

Non-clinical pharmacology and toxicology studies of LPM6690061, a novel 5-hydroxytryptamine (5-HT)2A receptor inverse agonist

LPM6690061 is a novel compound with 5-HT2A receptor antagonist and inverse agonist activities. To support the clinical trial and marketing application of LPM6690061, a series of pharmacology and toxicology studies have been conducted. In vitro and in vivo pharmacology studies showed that LPM6690061 had high inverse agonism and antagonism activities against human 5-HT2A receptors, and demonstrated significant antipsychotic-like effects in two rat models: the DOI-induced head-twitch model and the MK-801-induced hyperactivity model, which was more effective than the control drug pimavanserin. LPM6690061 did not have detectable side effects on the neurobehavioral activities and respiratory function in rats, or on the ECG or blood pressure in dogs at the doses of 2 and 6 mg/kg. The half maximal inhibitory concentration (IC50) of LPM6690061 for inhibiting hERG current was 1.02 μM. Three in vivo toxicology studies were conducted. In the single dose toxicity study in rats and dogs, the maximum tolerated dose of LPM6690061 was 100 mg/kg. In the 4-week repeat dose toxicity study in rats, the main detectable toxic reactions of LPM6690061 included moderate artery wall hypertrophy, minimal to mild mixed cell inflammation and increased macrophages in the lung, which generally recovered after a 4-week drug withdrawal period. In the 4-week repeat dose toxicity study in dogs, no detectable toxicity was observed. The doses of no-observed-adverse-effect-level (NOAEL) in rats and dogs were 10 mg/kg and 20 mg/kg, respectively. In conclusion, both in vitro and in vivo pharmacological and toxicological studies showed that LPM6690061 was a safe and efficacious 5-HT2A receptor antagonist/inverse agonist which supports the clinical development as a novel antipsychotic drug.

Pimavanserin: A Truly Effective Treatment for Parkinson's Disease Psychosis? A Review of Interventions

Parkinson's disease (PD) is the second-most common neurodegenerative disorder with a long-term 60% cumulative prevalence of PD psychosis. Medical treatment is limited to few atypical antipsychotic drugs with low affinity to dopamine D2 receptors. In 2016, pimavanserin, a selective 5-HT2A inverse agonist/antagonist, was approved by the US Food and Drug Administration (FDA) as the only treatment for PD psychosis (PDP). This article provides an overview of the epidemiology, pathophysiology, and treatment options for PDP and illuminates the mode of action and therapy options with pimavanserin and the current study data.

The complex molecular pharmacology of the dopamine D2 receptor: Implications for pramipexole, ropinirole, and rotigotine

With L-DOPA, dopamine agonists such as pramipexole, ropinirole and rotigotine constitute key therapeutic options for the management of motor symptoms of Parkinson's disease. These compounds exert their beneficial effect on motor behaviours by activating dopamine D₂-class receptors and thereby compensating for the declining dopaminergic transmission in the dorsal striatum. Despite a strong similarity in their mechanism of action, these three dopamine agonists present distinct clinical profiles, putatively underpinned by differences in their pharmacological properties. In this context, this review aims at contributing to close the gap between clinical observations and data from molecular neuropharmacology by exploring the properties of pramipexole, ropinirole and rotigotine from both the clinical and molecular perspectives. Indeed, this review first summarizes and compares the clinical features of these three dopamine agonists, and then explores their binding profiles at the different dopamine receptor subtypes. Moreover, the signalling profiles of pramipexole, ropinirole and rotigotine at the D₂ receptor are recapitulated, with a focus on biased signalling and the potential therapeutic implications. Overall, this review aims at providing a unifying framework of interpretation for both clinicians and fundamental pharmacologists interested in a deep understanding of the pharmacological properties of pramipexole, ropinirole and rotigotine.

Pimavanserin reverses multiple measures of anxiety in a rodent model of post-traumatic stress disorder

Pimavanserin is a highly selective 5-HT_2A inverse agonist in current medical use. Prior studies suggest that 5-HT_2A serotonin receptors may play a role in anxiety and emotional memory. Therefore, pimavanserin was tested in a rat model of PTSD to determine whether it might ameliorate PTSD-like symptoms. The lifetime prevalence of PTSD is estimated to be 125% higher in women than men. Consequently, in an effort to create a robust model of PTSD that was more representative of human PTSD prevalence, 20-week old female rats of the emotionally hyperreactive Lewis strain were used for these studies. The rats were single-housed and exposed twice to restraint stress coupled with predator odor or to a sham-stressed condition. Twenty days after the second stress or sham-stress exposure, rats were injected with saline alone or with 0.3 or 1.0 mg/kg pimavanserin, doses that were confirmed to substantially block 5-HT_2A receptor activity in this study without causing any non-specific behavioral or adverse effects. One hour later, rats were tested for anxiety through acoustic startle response, the elevated plus-maze and three parameters of open field behavior. Five days later, blood was sampled for plasma corticosterone. The stressed/saline-injected rats had higher anxiety scores and corticosterone levels than sham-stressed/saline-injected rats. Pimavanserin significantly and generally dose-dependently reversed these persistent stress effects, but had no significant effect on the behavioral measures in normal, non-stressed rats. These results, consistent with a role for the 5-HT_2A receptor, suggest that pimavanserin might have potential to reduce some consequences of traumatic stress.

Back to the Future of Neuropsychopharmacology

Disappointments in translating preclinical findings into clinical efficacy have triggered a number of changes in neuroscience drug discovery ranging from investments diverted to other therapeutic areas to reduced reliance on efficacy claims derived from preclinical models. In this chapter, we argue that there are several existing examples that teach us on what needs to be done to improve the success rate. We advocate the reverse engineering approach that shifts the focus from preclinical efforts to "model" human disease states to pharmacodynamic activity as a common denominator in the journey to translate clinically validated phenomena to preclinical level and then back to humans. Combined with the research rigor, openness, and transparency, this reverse engineering approach is well set to bring new effective and safe medications to patients in need.

Pimavanserin and Parkinson's Disease Psychosis: A Narrative Review

Pimavanserin (PMV) is the first approved drug for treating hallucinations and delusions in Parkinson's disease (PD) psychosis. Psychosis is one of the leading causes of nursing home placement in people with PD. Furthermore, hallucinations are a more frequent cause of institutionalization than motor disability or dementia related to PD. The management of PD psychosis involves antipsychotic medications. Most of the drugs in this class directly block dopamine D2 receptors, leading to significantly worsening motor symptoms in patients with PD. The most commonly used medications for managing PD psychosis are quetiapine, clozapine, and PMV. This literature review aims to study pimavanserin's history, mechanism, clinical trials, and post-marketing experience. PMV is a potent 5-HT2A receptor antagonist/inverse agonist. Moreover, this drug can interact with 5-HT2C receptors. We calculated some physicochemical descriptors and pharmacokinetic properties of PMV. Eight clinical trials of PMV and PD psychosis are registered on ClinicalTrials.gov. Only four of them have complete results already published. Meta-analytic results showed that PMV efficacy is inferior to clozapine. However, PMV has a significantly lower number of side-effects for managing psychosis in PD. Medicare database assessment revealed 35% lower mortality with PMV compared to other atypical antipsychotics. Moreover, sensitive statistical analysis demonstrated that PMV is a protective factor for the risk of falls in individuals with PD.

Positron Emission Tomography (PET) Imaging Tracers for Serotonin Receptors

Serotonin (5-hydroxytryptamine, 5-HT) and 5-HT receptors (5-HTRs) have crucial roles in various neuropsychiatric disorders and neurodegenerative diseases, making them attractive diagnostic and therapeutic targets. Positron emission tomography (PET) is a noninvasive nuclear molecular imaging technique and is an essential tool in clinical diagnosis and drug discovery. In this context, numerous PET ligands have been developed for "visualizing" 5-HTRs in the brain and translated into human use to study disease mechanisms and/or support drug development. Herein, we present a comprehensive repertoire of 5-HTR PET ligands by focusing on their chemotypes and performance in PET imaging studies. Furthermore, this Perspective summarizes recent 5-HTR-focused drug discovery, including biased agonists and allosteric modulators, which would stimulate the development of more potent and subtype-selective 5-HTR PET ligands and thus further our understanding of 5-HTR biology.

Risk of Drug-induced Movement Disorders with Newer Antipsychotic Agents

Background:

The last decade has seen development of numerous novel antipsychotic drugs with unique mechanisms including long-acting formulations for clinical use. A comparative assessment of these new drugs with each other and previous antipsychotics have not been performed with regards to risk for drug-induced movement disorders (DIMD).

Methods:

Medline was searched from January 2010 to February 2022 for primary research articles and review articles in English using the search terms “extrapyramidal” and “tardive” with individual drug names of novel antipsychotics.

Results:

We identified articles describing the risk of DIMD with 6 novel antipsychotics, 4 novel formulations, and 3 experimental antipsychotics. Both short- and long-term data generally showed comparable to lower risk of DIMD with novel antipsychotics and recent long-acting formulations compared to previously marketed antipsychotics.

Discussion:

Several novel antipsychotics, particularly lumateperone and pimavanserin, show promise in being able to treat psychosis while reducing the risk of DIMD. Long-acting paliperidone may reduce risk of DIMD while other long-acting injectable formulations of SGA have similar risk of DIMD compared to oral formulations. New drug targets for treating psychosis without dopamine blockade also show promise.

The Novel Pimavanserin Derivative ST-2300 with Histamine H3 Receptor Affinity Shows Reduced 5-HT2A Binding, but Maintains Antidepressant- and Anxiolytic-like Properties in Mice

The therapy of depression is challenging and still unsatisfactory despite the presence of many antidepressant drugs on the market. Consequently, there is a continuous need to search for new, safer, and more effective antidepressant therapeutics. Previous studies have suggested a potential association of brain histaminergic/serotoninergic signaling and antidepressant- and anxiolytic-like effects. Here, we evaluated the in vivo antidepressant- and anxiolytic-like effects of the newly developed multiple-active ligand ST-2300. ST-2300 was developed from 5-HT_2A/2C inverse agonist pimavanserin (PIM, ACP-103) and incorporates a histamine H₃ receptor (H₃R) antagonist pharmacophore. Despite its parent compound, ST-2300 showed only moderate serotonin 5-HT_2A antagonist/inverse agonist affinity (K_i value of 1302 nM), but excellent H₃R affinity (K_i value of 14 nM). In vivo effects were examined using forced swim test (FST), tail suspension test (TST), and the open field test (OFT) in C57BL/6 mice. Unlike PIM, ST-2300 significantly increased the anxiolytic-like effects in OFT without altering general motor activity. In FST and TST, ST-2300 was able to reduce immobility time similar to fluoxetine (FLX), a recognized antidepressant drug. Importantly, pretreatment with the CNS-penetrant H₃R agonist (R)-α-methylhistamine reversed the antidepressant-like effects of ST-2300 in FST and TST, but failed to reverse the ST-2300-provided anxiolytic effects in OFT. Present findings reveal critical structural features that are useful in a rational multiple-pharmacological approach to target H₃R/5-HT_2A/5-HT_2C.

Hallucinations and delusions associated with Parkinson's disease psychosis: safety of current treatments and future directions

INTRODUCTION

: Over half of Parkinson's disease (PD) patients develop psychotic symptoms, and PD psychosis (PDP) is associated with significant distress to patients, caregiver burden, and impairs quality of life. Pharmacological therapy is limited to atypical antipsychotics.

AREAS COVERED

: This review will summarize efficacy but will focus on the safety of antipsychotics for treating PDP, and in particular the off-target safety issues including cognitive impairment, sleep disturbance, cardiovascular effects, and motor function.

EXPERT OPINION

: Pimavanserin is the only medication approved in the US for treating PDP, however clozapine is also considered efficacious. Despite lack of substantial evidence for efficacy, quetiapine is commonly used to treat PDP. Despite the effectiveness of pimavanserin and clozapine for treating PDP, a need exists for additional pharmacological agents that are effective for PDP while providing an acceptable safety and tolerability profile. Medications to treat PDP should avoid worsening motor function, and also minimize sleep disturbances, cognitive impairment, cardiovascular effects, and other non-motor safety concerns. A neutral effect or reduction in mortality risk associated with PD and PDP would be ideal, and low rate of discontinuation due to AEs is desirable. Lastly, medications that can be used safely in combination with other pharmacological agents is essential.

"Selective" serotonin 5-HT2A receptor antagonists

Blockade of the serotonin 5-HT_2A G protein-coupled receptor (5-HT_2AR) is a fundamental pharmacological characteristic of numerous antipsychotic medications, which are FDA-approved to treat schizophrenia, bipolar disorder, and as adjunctive therapies in major depressive disorder. Meanwhile, activation of the 5-HT_2AR by serotonergic psychedelics may be useful in treating neuropsychiatric indications, including major depressive and substance use disorders. Serotonergic psychedelics and other 5-HT_2AR agonists, however, often bind other receptors, and standard 5-HT_2AR antagonists lack sufficient selectivity to make well-founded mechanistic conclusions about the 5-HT_2AR-dependent effects of these compounds and the general neurobiological function of 5-HT_2ARs. This review discusses the limitations and strengths of currently available "selective" 5-HT_2AR antagonists, the molecular determinants of antagonist selectivity at 5-HT_2ARs, and the utility of molecular pharmacological and computational methods in guiding the discovery of novel unambiguously selective 5-HT_2AR antagonists.

Role of Brain Imaging in Drug Development for Psychiatry

Background:

Over the last decades, many brain imaging studies have contributed to new insights in the pathogenesis of psychiatric disease. However, in spite of these developments, progress in the development of novel therapeutic drugs for prevalent psychiatric health conditions has been limited.

Objective:

In this review, we discuss translational, diagnostic and methodological issues that have hampered drug development in CNS disorders with a particular focus on psychiatry. The role of preclinical models is critically reviewed and opportunities for brain imaging in early stages of drug development using PET and fMRI are discussed. The role of PET and fMRI in drug development is reviewed emphasizing the need to engage in collaborations between industry, academia and phase I units.

Conclusion:

Brain imaging technology has revolutionized the study of psychiatric illnesses, and during the last decade, neuroimaging has provided valuable insights at different levels of analysis and brain organization, such as effective connectivity (anatomical), functional connectivity patterns and neurochemical information that may support both preclinical and clinical drug development. Since there is no unifying pathophysiological theory of individual psychiatric syndromes and since many symptoms cut across diagnostic boundaries, a new theoretical framework has been proposed that may help in defining new targets for treatment and thus enhance drug development in CNS diseases. In addition, it is argued that new proposals for data-mining and mathematical modelling as well as freely available databanks for neural network and neurochemical models of rodents combined with revised psychiatric classification will lead to new validated targets for drug development.

Pimavanserin Exposure-Response Analyses in Patients With Schizophrenia: Results From the Phase 2 ADVANCE Study

PURPOSE/BACKGROUND

Pimavanserin is a selective serotonin 5-HT 2A receptor inverse agonist/antagonist being investigated in patients with negative symptoms of schizophrenia. This analysis aimed to characterize exposure-response relationships of pimavanserin in this population.

METHODS/PROCEDURES

Exposure-response models were developed using data from ADVANCE. Patients with negative symptoms of schizophrenia receiving background antipsychotics were randomized to pimavanserin 20 mg (adjusted to 34 or 10 mg between weeks 2-8 based on efficacy or tolerability) or placebo for 26 weeks. Time-varying pimavanserin exposure measures were predicted for each patient using a population pharmacokinetic model and individual empiric Bayesian parameter estimates. Response measures were the Negative Symptom Assessment 16 (NSA-16, primary end point), Personal and Social Performance scale, negative symptoms component of the Clinical Global Impression of Schizophrenia-Severity Scale, and adverse events.

FINDINGS/RESULTS

A higher pimavanserin exposure was associated with greater improvement in NSA-16 score. For a median area under the pimavanserin plasma concentration-time curve from time 0 to 24 hours of 1465 ng × h/mL for the 34-mg dose, the model predicted a 10.5-point reduction in NSA-16 score. This exposure-response relationship with NSA-16 scores was not influenced by covariates. Similar results were observed with Personal and Social Performance and Clinical Global Impression of Schizophrenia-Severity, but not to the extent as NSA-16. There was no significant exposure-response relationship with anxiety, headache, insomnia, or somnolence.

IMPLICATIONS/CONCLUSIONS

Increasing pimavanserin plasma concentration was associated with improved NSA-16 scores (primary end point) in patients with negative symptoms of schizophrenia. No exposure-response relationship with select adverse events was observed.

Pimavanserin for negative symptoms of schizophrenia: results from the ADVANCE phase 2 randomised, placebo-controlled trial in North America and Europe

BACKGROUND

Negative symptoms of schizophrenia are associated with adverse clinical outcomes, but there are few effective treatments. We aimed to assess the effects of pimavanserin, a selective 5-HT_2A inverse agonist and antagonist, on negative symptoms of schizophrenia.

METHODS

The ADVANCE study was a phase 2, 26-week, randomised, double-blind, placebo-controlled study of pimavanserin in stable outpatients with schizophrenia aged 18-55 years with predominant negative symptoms. Patients were randomly assigned (1:1) across 83 sites (18 in North America and 65 in Europe) to receive pimavanserin or placebo daily, added to an ongoing antipsychotic medication, per a computer-generated schedule (stratification by geographical region). Eligible patients had a score of at least 20 on the sum of seven Positive and Negative Syndrome Scale (PANSS) Marder negative factor items (and scores of ≥4 on at least three or ≥5 on at least two of negative symptom items). The starting dosage of 20 mg of pimavanserin or placebo could be adjusted to 34 mg or 10 mg within the first 8 weeks of the study, after which dosage remained stable until the end of the study. Both pimavanserin and placebo were administered orally once daily as two individual tablets (pimavanserin tablets were either 10 mg or 17 mg). The primary endpoint was change in total score using the 16-item Negative Symptom Assessment (NSA-16) from baseline to week 26. Primary outcomes were analysed in patients who received at least one dose of the study drug and had NSA-16 assessments at baseline and at least once post-baseline (full analysis set). Safety outcomes were analysed in patients who had received at least one dose of the study drug. This trial is registered with ClinicalTrials.gov, NCT02970305, and is complete.

FINDINGS

Between Nov 4, 2016, and April 16, 2019, we randomly assigned 403 patients to pimavanserin (n=201; 131 [65%] male; 187 [93%] White) or placebo (n=202; 137 [68%] male, 186 (92%) White), of whom 400 were included in the efficacy analysis (199 in the pimavanserin group, 201 in the placebo group). Mean age was 37·7 years (SD 9·4) in the pimavanserin group and 36·7 (9·2) years in the placebo group. The change in total NSA-16 score from baseline to week 26 was significantly improved with pimavanserin (least squares mean -10·4 [SE 0·67]) versus placebo (least squares mean -8·5 [0·67]; p=0·043; effect size: 0·211). The number of patients with treatment-emergent adverse events (TEAEs) was similar between groups: 80 (40%) patients experienced TEAEs in the pimavanserin group and 71 (35%) in the placebo group. Most TEAEs were headache (6% [n=13] vs 5% [n=10]) and somnolence (5% [n=11] vs 5% [n=10]). One patient from the placebo group reported severe headache (0·5%), rhinorrhoea (0·5%), cough (0·5%), and influenza (0·5%). In the pimavanserin group, one patient reported severe toothache (0·5%), and two patients had worsening of schizophrenia (1%). Mean change in QTcF interval was higher with pimavanerin (4·5 ms [SD 18·0]) than with placebo (0·0 ms [16·0]).

INTERPRETATION

Stable patients with predominant negative symptoms of schizophrenia showed a reduction in negative symptoms after treatment with pimavanserin. However, given the small effect size, further investigation with optimised dosing is warranted to determine the clinical significance of this effect.

FUNDING

Acadia Pharmaceuticals.

New and emerging treatments for schizophrenia: a narrative review of their pharmacology, efficacy and side effect profile relative to established antipsychotics

Schizophrenia is associated with substantial unmet needs, highlighting the necessity for new treatments. This narrative review compares the pharmacology, clinical trial data and tolerability of novel medications to representative antipsychotics. Cariprazine, brexpiprazole and brilaroxazine are partial dopamine agonists effective in acute relapse. Lumateperone (serotonin and dopamine receptor antagonist) additionally benefits asocial and depressive symptoms. F17464 (D3 antagonist and 5-HT1A partial agonist) has one positive phase II study. Lu AF35700 (dopamine and serotonin receptor antagonist) was tested in treatment-resistance with no positive results. Pimavanserin, roluperidone, ulotaront and xanomeline do not act directly on the D2 receptor at clinical doses. Initial studies indicate pimavanserin and roluperidone improve negative symptoms. Ulotaront and xanomeline showed efficacy for positive and negative symptoms of schizophrenia in phase II trials. BI 409306, BI 425809 and MK-8189 target glutamatergic dysfunction in schizophrenia, though of these only BI 425809 showed efficacy. These medications largely have favourable cardiometabolic side-effect profiles. Overall, the novel pharmacology, clinical trial and tolerability data indicate these compounds are promising new additions to the therapeutic arsenal.

Systematic Review on Parkinson's Disease Medications, Emphasizing on Three Recently Approved Drugs to Control Parkinson's Symptoms

Parkinson's Disease (PD) is a disease that involves neurodegeneration and is characterised by the motor symptoms which include muscle rigidity, tremor, and bradykinesia. Other non-motor symptoms include pain, depression, anxiety, and psychosis. This disease affects up to ten million people worldwide. The pathophysiology behind PD is due to the neurodegeneration of the nigrostriatal pathway. There are many conventional drugs used in the treatment of PD. However, there are limitations associated with conventional drugs. For instance, levodopa is associated with the on-off phenomenon, and it may induce wearing off as time progresses. Therefore, this review aimed to analyze the newly approved drugs by the United States-Food and Drug Administration (US-FDA) from 2016-2019 as the adjuvant therapy for the treatment of PD symptoms in terms of efficacy and safety. The new drugs include safinamide, istradefylline and pimavanserin. From this review, safinamide is considered to be more efficacious and safer as the adjunct therapy to levodopa as compared to istradefylline in controlling the motor symptoms. In Study 016, both safinamide 50 mg (p = 0.0138) and 100 mg (p = 0.0006) have improved the Unified Parkinson's Disease Rating Scale (UPDRS) part III score as compared to placebo. Improvement in Clinical Global Impression-Change (CGI-C), Clinical Global Impression-Severity of Illness (CGI-S) and off time were also seen in both groups of patients following the morning levodopa dose. Pimavanserin also showed favorable effects in ameliorating the symptoms of Parkinson's Disease Psychosis (PDP). A combination of conventional therapy and non-pharmacological treatment is warranted to enhance the well-being of PD patients.

Pimavanserin, a 5-hydroxytryptamine 2A receptor inverse agonist, reverses prepulse inhibition deficits in the nucleus accumbens and ventral hippocampus

Prepulse inhibition (PPI) is disrupted in many neuropsychiatric diseases. Although the inverse agonist of the 5-hydroxytryptamine 2A (5-HT2A) receptors, pimavanserin, alleviates PPI deficits in rodents, the precise mechanisms and critical brain areas in the reversal effect of 5-HT2A receptor inverse agonists remain unclear. The present study aimed to investigate the critical brain areas responsible for the reversal effect of the 5-HT2A receptor inverse agonist on PPI deficits in male mice. The results showed that intraperitoneal administration of pimavanserin was found to improve normal PPI behavior and reverse PPI deficits elicited by the dopamine D1/D2 receptor nonselective agonist, pergolide. Further, local infusion of pimavanserin into the nucleus accumbens and ventral hippocampus reversed PPI deficits, whereas the same manipulation in the medial prefrontal cortex or ventral tegmental area did not reverse PPI deficits. Overall, the nucleus accumbens and ventral hippocampus are the critical brain areas responsible for the reversal effect of 5-HT2A inverse agonists on PPI deficits. Such findings contribute to the extensive exploration of the accurate molecular and neural mechanisms underlying the antipsychotic effects of 5-HT2A receptor inverse agonists, especially the neural circuits modulated by 5-HT2A receptor activity.

A new class of serotonin 5-HT2A /5-HT2C receptor inverse agonists: Synthesis, molecular modeling, in vitro and in vivo pharmacology of novel 2-aminotetralins

BACKGROUND AND PURPOSE

The 5-HT receptor (5-HTR) subtypes 5-HT_2A and 5-HT_2C are important neurotherapeutic targets, though, obtaining selectivity over 5-HT_2B and closely related histamine H₁ Rs is challenging. Here, we delineated molecular determinants of selective binding to 5-HT_2A and 5-HT_2C Rs for novel 4-phenyl-2-dimethylaminotetralins (4-PATs).

EXPERIMENTAL APPROACH

We synthesized 42 novel 4-PATs with halogen or aryl moieties at the C(4)-phenyl meta position. Affinity, function, molecular modeling, and 5-HT_2A R mutagenesis studies were undertaken to understand structure-activity relationships at 5-HT₂ -type and H₁ Rs. Lead 4-PAT-type selective 5-HT_2A /5-HT_2C R inverse agonists were compared to pimavanserin, a selective 5-HT_2A /5-HT_2C R inverse agonist approved to treat psychoses, in the mouse head twitch response, and locomotor activity assays, as models relevant to antipsychotic drug development.

KEY RESULTS

Most 4-PAT diastereomers in the (2S,4R)-configuration bound non-selectively to 5-HT_2A , 5-HT_2C, and H₁ Rs, with >100-fold selectivity over 5-HT_2B Rs, whereas, diastereomers in the (2R,4R)-configuration bound preferentially to 5-HT_2A over 5-HT_2C Rs and had >100-fold selectivity over 5-HT_2B and H₁ Rs. Results suggest that G238^5.42 and V235^5.39 in 5-HT_2A Rs (conserved in 5-HT_2C Rs) are important for high affinity binding, whereas, interactions with T194^5.42 and W158^4.56 determine H₁ R affinity. The 4-PAT (2S,4R)-2k, a potent and selective 5-HT_2A /5-HT_2C R inverse agonist, had activity like pimavanserin in the mouse head-twitch response assay, but was distinct in not suppressing locomotor activity.

CONCLUSIONS AND IMPLICATIONS

We provide evidence that the novel 4-PAT chemotype can yield selective 5-HT_2A /5-HT_2C R inverse agonists for antipsychotic drug development by optimizing ligand-receptor interactions in transmembrane domain 5. We also show that chirality can be exploited to attain selectivity over H₁ Rs which may circumvent sedative effects.

Progress in mechanistically novel treatments for schizophrenia

Currently available pharmacological treatments for schizophrenia derive their activity mainly by directly modulating the D2 receptor. This mode of action can alleviate the positive symptoms of schizophrenia but do not address the negative or cognitive symptoms of the disease and carry a heavy side effect burden that leads to high levels of patient non-compliance. Novel mechanisms to treat the positive symptoms of schizophrenia with improved tolerability, as well as medicines to treat negative and cognitive symptoms are urgently required. Recent efforts to identify small molecules for schizophrenia with non-D2 mechanisms will be highlighted, with a focus on those that have reached clinical development. Finally, the potential for disease modifying treatments for schizophrenia will also be discussed.

Additive effects of mGluR2 positive allosteric modulation, mGluR2 orthosteric stimulation and 5-HT2AR antagonism on dyskinesia and psychosis-like behaviours in the MPTP-lesioned marmoset

PURPOSE

Antagonising serotonin (5-HT) type 2A receptors (5-HT_2AR) is an effective strategy to alleviate both dyskinesia and psychosis in Parkinson's disease (PD). We have recently shown that activation of metabotropic glutamate 2 receptors (mGluR₂), via either orthosteric stimulation or positive allosteric modulation, enhances the anti-dyskinetic and anti-psychotic effects of 5-HT_2AR antagonism. Here, we investigated if greater therapeutic efficacy would be achieved by combining 5-HT_2AR antagonism with concurrent mGluR₂ orthosteric stimulation and mGluR₂ positive allosteric modulation.

METHODS

Five 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmosets exhibiting dyskinesia and psychosis-like behaviours (PLBs) were administered L-3,4-dihydroxyphenylalanine (L-DOPA) in combination with vehicle or the 5-HT_2AR antagonist EMD-281,014. EMD-281,014 was itself administered alone or with the mGluR₂ orthosteric agonist (OA) LY-354,740, the mGluR₂ positive allosteric modulator (PAM) LY-487,379 and combination thereof, after which the severity of dyskinesia, PLBs and parkinsonism was rated.

RESULTS

EMD-281,014 reduced dyskinesia and PLBs by up to 47% and 40%, respectively (both P < 0.001). The addition of LY-354,740, LY-487,379 and LY-354,740/LY-487,379 decreased dyskinesia by 56%, 65% and 77%, while PLBs were diminished by 55%, 63% and 71% (all P < 0.001). All treatment combinations provided anti-dyskinetic and anti-psychotic benefits significantly greater than those conferred by EMD-281,014 alone (all P < 0.05). The combination of EMD-281,014/LY-354,740/LY-487,379 resulted in anti-dyskinetic and anti-psychotic effects significantly greater than those conferred by EMD-281,014 with either LY-354,740 or LY-487,379 (both P < 0.05). No deleterious effects on L-DOPA anti-parkinsonian action were observed.

CONCLUSION

Our results suggest that combining 5-HT_2AR antagonism with mGluR₂ activation results in greater reduction of L-DOPA-induced dyskinesia and PD psychosis. They also indicate that further additive effect can be achieved when a mGluR₂ OA and a mGluR₂ PAM are combined with a 5-HT_2AR antagonist than when a mGluR₂ OA or a mGluR₂ PAM are added to a 5-HT_2AR antagonist.

Multifunctional Arylsulfone and Arylsulfonamide-Based Ligands with Prominent Mood-Modulating Activity and Benign Safety Profile, Targeting Neuropsychiatric Symptoms of Dementia

The current pharmaceutical market lacks therapeutic agents designed to modulate behavioral disturbances associated with dementia. To address this unmet medical need, we designed multifunctional ligands characterized by a nanomolar affinity for clinically relevant targets that are associated with the disease pathology, namely, the 5-HT_2A/6/7 and D₂ receptors. Compounds that exhibited favorable functional efficacy, water solubility, and metabolic stability were selected for more detailed study. Pharmacological profiling revealed that compound 11 exerted pronounced antidepressant activity (MED 0.1 mg/kg), outperforming commonly available antidepressant drugs, while compound 16 elicited a robust anxiolytic activity (MED 1 mg/kg), exceeding comparator anxiolytics. In contrast to the existing psychotropic agents tested, the novel chemotypes did not negatively impact cognition. At a chronic dose regimen (25 days), 11 did not induce significant metabolic or adverse blood pressure disturbances. These promising therapeutic-like activities and benign safety profiles make the novel chemotypes potential treatment options for dementia patients.

Evaluating pimavanserin as a treatment for psychiatric disorders: A pharmacological property in search of an indication

Introduction: Pimavanserin is FDA-approved to treat hallucinations and delusions associated with Parkinson's disease psychosis. As a potent 5-HT_2A inverse agonist/antagonist, it could be efficacious in other psychiatric disorders. Recently, several studies have investigated this potential.Areas covered: The authors review the efficacy and adverse effects of pimavanserin for hallucinations in dementia, major depression, and schizophrenia.Expert opinion: Two controlled studies suggest pimavanserin has potential as a treatment for hallucinations in dementia. In patients with depression who did not respond to antidepressant treatment, pimavanserin augmentation was efficacious in a phase 2 study. Pimavanserin augmentation also alleviated sexual side effects of SSRI and SSNI. However, Acadia Pharmaceuticals stated in a press release that it does not plan further antidepressant trials based on its phase 3 trial, which showed a nonsignificant trend toward an antidepressant effect. Since almost all existing antipsychotics fail to substantially benefit negative symptoms, better treatments are needed. Pimavanserin augmentation of antipsychotics did benefit negative symptoms (effect size≈0.2) but failed to reduce the total PANSS score significantly in two large, well-controlled double-blind studies. Pimavanserin has a good safety profile.

5-HT1A and 5-HT2A Signaling, Desensitization, and Downregulation: Serotonergic Dysfunction and Abnormal Receptor Density in Schizophrenia and the Prodrome

The significant role of serotonin (5-hydroxytryptamine [5-HT]) in the pathogenesis and early development of schizophrenia has been established by contemporary research through the assessment of structural and pharmacological neuroimaging, blood metabolites, cerebrospinal fluid, genome polymorphisms, and other valid indicators of abnormal serotonergic activity in prodromal, ultra-high-risk, and schizophrenic patient groups. A modern approach toward understanding the complex psychophysiology behind schizophrenia will be outlined through the demonstration of 5-HT_1A and 5-HT_2A receptors as key modulators within the spectrum of negative symptoms associated with schizoaffective disorders, including a variety of disturbances in cognition, behavior, mood, social function, perception of reality, and hormonal response to stressors. This paper will review the evidence for attributing the risk of schizophrenia onset to early defects in serotonergic neurotransmission and explore the perspective of selective serotonin receptor inhibitor (SSRI) pharmacotherapy as a method of treatment and intervention for prodromal and ultra-high-risk patients by increasing 5-HT_1A receptor sensitivity levels and modifying the transcription of 5-HT_1A receptor-associated gene expression in these groups.

Comparative pharmacovigilance assessment of mortality with pimavanserin in Parkinson disease-related psychosis

BACKGROUND: Pimavanserin is approved for treatment of Parkinson disease (PD)-related psychosis, but its use has been associated with an increased risk of death during clinical trials, as well as during postmarketing surveillance. Previous reports on the association between pimavanserin and mortality have not taken into account limitations of data sources nor included comparable populations or comparisons to relevant treatment alternatives. OBJECTIVE: To conduct a comparative pharmacovigilance assessment of pimavanserin vs treatment alternatives and by restricting surveillance data to more representative populations. METHODS: This was a retrospective analysis of adverse event case reports submitted to the FDA's Adverse Event Reporting System (FAERS) from 2016 through 2019 quarter 3 (Q3). FAERS data are collected from the full population, were further restricted to only those with PD, and were based on PD medication use. Reports were assessed for exposure to pimavanserin, clozapine, quetiapine, haloperidol, and other atypical antipsychotics. The outcome of interest was all-cause death. A proportional reporting ratio (PRR) and 95% confidence limits were calculated for each 2 by 2 contingency of outcome (death) and exposure (pimavanserin and others). For each outcome/exposure pair, the baseline population was altered to include the full FAERS sample, only reports with PD, reports with PD treated with levodopa, and reports with PD treated with multiple PD medications. The sample was also stratified by time period before April 2018 and after September 2018 to capture periods of public knowledge and federal response. A lower 95% CI (Lower95CI) ≥ 2 for the PRR was considered as the accepted threshold for a drug safety signal. RESULTS: As of 2019 Q3, there were 2,287 reports of death associated with pimavanserin. Compared within the full FAERS base population, pimavanserin yielded a PRR Lower95CI = 2.08 but was smaller when restricted to comparison among only a base population with PD (Lower95CI = 1.09), PD treated with levodopa (Lower95CI = 1.15), or PD treated with multiple PD medications (Lower95CI = 1.63). Metrics for quetiapine, clozapine, and other atypical antipsychotics were similar in magnitude. Stratification by time showed a possible reporting bias associated with pimavanserin, since no safety signal was detected before April 2018; however, a signal was present thereafter. CONCLUSIONS: Compared in context with treatment alternatives for patients with PD, pimavanserin was not associated with excess reports of death in the FAERS data. This information should be used in shared decision making between physicians and PD patients to balance the risks and benefits of pimavanserin and other treatments for PD psychosis. DISCLOSURES: No outside funding supported this study. The authors report no disclosures or conflicts of interest relevant to this study. Armstrong receives research support from the NIA (P30AG047266, R01AG068128) and the Florida Department of Health (grant 20A08). She is the local principal investigator of a Lewy Body Dementia Association Research Center of Excellence. She also receives compensation from the American Academy of Neurology for work as an evidence-based medicine methodology consultant. She is on the level of evidence editorial board for Neurology and related publications (uncompensated), receives publishing royalties for Parkinson's Disease: Improving Patient Care (Oxford University Press, 2014), and has received an honorarium for presenting for Medscape CME in 2018. Okun serves as a consultant for the Parkinson's Foundation and has received research grants from NIH, Parkinson's Foundation, the Michael J. Fox Foundation, the Parkinson Alliance, Smallwood Foundation, the Bachmann-Strauss Foundation, the Tourette Syndrome Association, and the UF Foundation. Okun has participated as a site principal investigator and/or co-investigator for several NIH-, foundation-, and industry-sponsored trials over the years but has not received honoraria. Malaty has participated in research funded by the Parkinson Foundation, Tourette Association, Dystonia Coalition, Abbvie, Boston Scientific, Eli Lilly, Neuroderm, Pfizer, Revance, and Teva. She has received travel compensation and/or honoraria from the Tourette Association of America, NeuroChallenge Foundation and NIH/Neurobiology of Disease in Children, Parkinson Foundation, Medscape, International Association of Parkinsonism and Related Disorders, and Cleveland Clinic, and royalties from Robert Rose publishers. The other authors have no disclosures.

Efficacy results of pimavanserin from a multi-center, open-label extension study in Parkinson's disease psychosis patients

INTRODUCTION

Pimavanserin, a selective 5-HT_2A inverse agonist/antagonist, was approved for hallucinations and delusions associated with Parkinson's disease psychosis (PDP). We present durability of response with pimavanserin in patients with PDP for an additional 4 weeks of treatment.

METHODS

This was an open-label extension (OLE) study in patients previously completing one of three double-blind, placebo-controlled (Core) studies. All patients received pimavanserin 34 mg once daily. Efficacy assessments included the Scale for the Assessment of Positive Symptoms (SAPS) PD and H + D scales, Clinical Global Impression (CGI) Improvement and Severity scales and Caregiver Burden Scale (CBS), through 4 weeks in the OLE. Safety assessments were conducted at each visit.

RESULTS

Of 459 patients, 424 (92.4%) had a Week 4 efficacy assessment. At Week 4 (10 weeks total treatment), SAPS-PD mean (standard deviation) change from OLE baseline was -1.8 (5.5) and for SAPS-H + D was -2.1 (6.2) with pimavanserin 34 mg. Patients receiving placebo during the Core studies had greater improvements (SAPS-PD -2.9 [5.6]; SAPS-H + D -3.5 [6.3]) during the OLE. For participants treated with pimavanserin 8.5 or 17 mg during the Core studies, further improvement was observed during the OLE with pimavanserin 34 mg. The mean change from Core Study baseline for SAPS-PD score was similar among prior pimavanserin 34 mg and prior placebo-treated participants (-7.1 vs. -7.0). The CGI-I response rate (score of 1 or 2) at Week 4 was 51.4%. Adverse events were reported by 215 (46.8%) patients during the first 4 weeks of OLE. The most common AEs were fall (5.9%), hallucination (3.7%), urinary tract infection (2.8%), insomnia (2.4%), and peripheral edema (2.2%) CONCLUSIONS: Patients previously on pimavanserin 34 mg during three blinded core studies had durability of efficacy during the subsequent 4 week OLE SAPS-PD assessment. Patients previously on blinded placebo improved after 4 weeks of OL pimavanserin treatment. These results in over 400 patients from 14 countries support the efficacy of pimavanserin for treating PDP.

Pharmacotherapy of schizophrenia: Mechanisms of antipsychotic accumulation, therapeutic action and failure

Schizophrenia is a multi-dimensional disorder with a complex and mostly unknown etiology, leading to a severe decline in life quality. Antipsychotic drugs (APDs) remain beneficial interventions in the treatment of the disorder, but vary significantly in binding profile, clinical effects and adverse reactions. The present review summarizes the main principles of APD mechanisms of action with a particular focus on recent findings in APD accumulation and its role in the therapeutic efficacy and treatment failure. High and low doses of APDs were shown to be effective in different dimensions of antipsychotic-like behaviour in rodent models. Efficacy of the APDs correlates with high dopamine D2 receptor occupancy, which occurs quickly after drug administration. However, onset and peak of action are delayed up to several days or weeks. APD accumulation via acidic trapping in synaptic vesicles is considered to underlie the time course of APD action. Use-dependent exocytosis, co-release with dopamine and serotonin and inhibition of ion channels impact on the neuronal transmission and determine effects of APDs. Disruption in accumulating properties leads to diminished APD effects. In addition, long-term APD administration at therapeutic doses leads to treatment failure both in animal models and in humans. APD failure was associated with treatment induced neuroadaptations, including a decline in extracellular dopamine levels, dopamine transporter upregulation, and altered neuronal firing. However, enhanced synaptic vesicle release has also been reported. APD loss of efficacy may be reversed through inhibition of the dopamine transporter or switching the administration regimen from continuous to intermittent. Thus, manipulating the accumulation properties of APDs, changes in the administration regimen and doses, or co-administration with dopamine transporter inhibitors may be considered to yield benefits in the development of new effective strategies in the treatment of schizophrenia.

Spotlight on Pimavanserin Tartrate and Its Therapeutic Potential in the Treatment of Major Depressive Disorder: The Evidence to Date

Major depressive disorder (MDD) is widely prevalent and one of the leading causes of disability. Treatment outcomes remain suboptimal with 1 in 3 patients with MDD responding inadequately to commonly used antidepressants. Pimavanserin, an atypical antipsychotic that modulates serotonergic neurotransmission by selectively binding to serotonin receptor (2A and 2C) subtypes and without dopaminergic activity, may have the potential as an adjunctive treatment for MDD. In a phase 2 trial (n=203), addition of pimavanserin, as compared to placebo, to stable treatment with antidepressants was associated with greater reduction in 17-item Hamilton Depression Rating Scale score [HAMD, least square means (95% confidence interval) of -1.7 (-0.03, -3.37), p=0.039]. Furthermore, treatment with pimavanserin was associated with significantly greater improvement in specific symptoms associated with depression such as impaired sexual function, anxiety, sleepiness, and irritability. However, the availability of pimavanserin for clinical care of patients with MDD remains uncertain. Top-line results of phase 3 studies (n=298) that were announced by the sponsor found similar reductions in HAMD (mean baseline-to-week-5 reduction of 9.0 and 8.1, p=0.296) and rates of adverse events (58.1% and 54.7%) with addition of pimavanserin and placebo respectively to stable treatment with antidepressants. Given the potential benefit for specific symptoms such as impaired sexual function, anxiety and sleep/wakefulness disturbances, future studies that enrich for these symptoms may be needed to clarify the utility of adjunctive pimavanserin in treatment of patients with MDD.

Pimavanserin, a 5HT2A receptor inverse agonist, rapidly suppresses Aβ production and related pathology in a mouse model of Alzheimer's disease

Amyloid-β (Aβ) peptide aggregation into soluble oligomers and insoluble plaques is a precipitating event in the pathogenesis of Alzheimer's disease (AD). Given that synaptic activity can regulate Aβ generation, we postulated that 5HT_2A -Rs may regulate Aβ as well. We treated APP/PS1 transgenic mice with the selective 5HT_2A inverse agonists M100907 or Pimavanserin systemically and measured brain interstitial fluid (ISF) Aβ levels in real-time using in vivo microdialysis. Both compounds reduced ISF Aβ levels by almost 50% within hours, but had no effect on Aβ levels in 5HT_2A -R knock-out mice. The Aβ-lowering effects of Pimavanserin were blocked by extracellular-regulated kinase (ERK) and NMDA receptor inhibitors. Chronic administration of Pimavanserin by subcutaneous osmotic pump to aged APP/PS1 mice significantly reduced CSF Aβ levels and Aβ pathology and improved cognitive function in these mice. Pimavanserin is FDA-approved to treat Parkinson's disease psychosis, and also has been shown to reduce psychosis in a variety of other dementia subtypes including Alzheimer's disease. These data demonstrate that Pimavanserin may have disease-modifying benefits in addition to its efficacy against neuropsychiatric symptoms of Alzheimer's disease. Read the Editorial Highlight for this article on page 560.

Effect of the mGlu2 positive allosteric modulator CBiPES on dyskinesia, psychosis-like behaviours and parkinsonism in the MPTP-lesioned marmoset

Advanced Parkinson's disease (PD) is often complicated by the occurrence of dyskinesia, motor fluctuations and psychosis. To this day, few treatment options are available for each of these phenomena, and they are at times not effective or elicit adverse events, leaving some patients short of therapeutic options. We have recently shown that positive allosteric modulation of metabotropic 2 (mGlu₂) receptors with the prototypical positive allosteric modulator (PAM) LY-487,379 is efficacious at alleviating both dyskinesia and psychosis-like behaviours (PLBs), while simultaneously enhancing the anti-parkinsonian action of L-3,4-dihydroxyphenylalanine (L-DOPA), in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmoset. Here, we assessed the effects of CBiPES, a mGlu₂ PAM derived from LY-487,379, but with improved pharmacokinetic properties. Six MPTP-lesioned marmosets with reproducible dyskinesia and PLBs were administered L-DOPA in combination with vehicle or CBiPES (0.1, 1 and 10 mg/kg), after which their behaviour was rated. CBiPES 10 mg/kg reduced global dyskinesia by 60% (P < 0.0001), while peak dose dyskinesia was reduced by 66% (P < 0.001), compared to L-DOPA/vehicle. CBiPES 10 mg/kg also diminished global PLBs by 56% (P < 0.0001), while peak dose PLBs were reduced by 64% (P < 0.001), compared to L-DOPA/vehicle. Lastly, CBiPES enhanced the anti-parkinsonian action of L-DOPA, by reducing global parkinsonian disability by 43% (P < 0.01), compared to L-DOPA/vehicle. Our results provide further evidence that mGlu₂ positive allosteric modulation may be an approach that could be efficacious for the treatment of dyskinesia, psychosis and motor fluctuations in PD.