Extrapyramidal side effects of antipsychotics are linked to their association kinetics at dopamine D2 receptors

A universal cannabinoid CB1 and CB2 receptor TR-FRET kinetic ligand-binding assay

Introduction

The kinetics of ligand binding to G protein-coupled receptors (GPCRs) is an important optimization parameter in drug discovery. Traditional radioligand assays are labor-intensive, preventing their application at the early stages of drug discovery. Fluorescence-based assays offer several advantages, including a possibility to develop a homogeneous format, continuous data collection, and higher throughput. This study sought to develop a fluorescence-based binding assay to investigate ligand-binding kinetics at human cannabinoid type 1 and 2 receptors (CB1R and CB2R).

Methods

We synthesized D77, a novel tracer derived from the non-selective cannabinoid Δ8-THC. Using time-resolved Förster resonance energy transfer (TR-FRET), we developed an assay to study ligand-binding kinetics at physiological temperatures. For CB1R, we truncated the first 90 amino acids of its flexible N-terminal domain to reduce the FRET distance between the terbium cryptate (donor) and the fluorescent ligand (acceptor). The full-length CB2R construct was functional without modification due to its shorter N-terminus. The Motulsky-Mahan competition binding model was used to analyze the binding kinetics of the endocannabinoids and several other non-fluorescent ligands.

Results

The D77 tracer showed nanomolar-range affinity for truncated CB1R (CB1R91-472) and full-length CB2R (CB2R1-360), displaying competitive binding with orthosteric ligands. D77 exhibited rapid dissociation kinetics from both CB1R and CB2R, which were similar to the fastest dissociating reference compounds. This was critical for accurately determining the on- and off-rates of the fastest dissociating compounds. Using D77, we measured the kinetic binding properties of various CB1R and CB2R agonists and antagonists at physiological temperature and sodium ion concentration.

Discussion

The k on values for molecules binding to CB1R varied by three orders of magnitude, from the slowest (HU308) to the fastest (rimonabant). A strong correlation between k on and affinity was observed for compounds binding to CB1R, indicating that the association rate primarily determines their affinity for CB1R. Unlike CB1R, a stronger correlation was found between the dissociation rate constant k off and the affinity for CB2R, suggesting that both k on and k off dictate the overall affinity for CB2R. Exploring the kinetic parameters of cannabinoid drug candidates could help drug development programs targeting these receptors.

Biased signaling in drug discovery and precision medicine

Receptors are crucial for converting chemical and environmental signals into cellular responses, making them prime targets in drug discovery, with about 70% of drugs targeting these receptors. Biased signaling, or functional selectivity, has revolutionized drug development by enabling precise modulation of receptor signaling pathways. This concept is more firmly established in G protein-coupled receptor and has now been applied to other receptor types, including ion channels, receptor tyrosine kinases, and nuclear receptors. Advances in structural biology have further refined our understanding of biased signaling. This targeted approach enhances therapeutic efficacy and potentially reduces side effects. Numerous biased drugs have been developed and approved as therapeutics to treat various diseases, demonstrating their significant therapeutic potential. This review provides a comprehensive overview of biased signaling in drug discovery and disease treatment, highlighting recent advancements and exploring the therapeutic potential of these innovative modulators across various diseases.

Atypical antipsychotics impair the lipid-lowering and pleiotropic effects of simvastatin via activation of the ADMA-NOX-ROS pathway

Patients with schizophrenia receiving atypical antipsychotics have an increased risk of metabolic syndrome; however, the efficacy of statins in mitigating cardiovascular risks in these patients remains unclear. This study examined the effects of typical and atypical antipsychotics on the lipid-lowering efficacy of statins in schizophrenia patients and investigated the underlying mechanisms of simvastatin action in hepatocytes and endothelial cells (ECs). A retrospective analysis revealed that statins were less effective in lowering LDL levels in patients on atypical antipsychotics. In vitro, olanzapine attenuated the beneficial effects of simvastatin in hepatocytes and ECs. Mechanistically, olanzapine downregulated dimethylarginine dimethylaminohydrolase 1 (DDAH1) and/or DDAH2, leading to elevated asymmetric dimethylarginine (ADMA) levels in both cell types. In hepatocytes, olanzapine suppressed low-density lipoprotein receptor (LDLR) expression and reduced LDL binding by activating the NOX-ROS pathway via PPARγ-PCSK9- and LXRα-IDOL-dependent signaling. Inhibition of the NOX-ROS pathway restored LDLR expression, LDL binding, and the lipid-lowering effects of simvastatin. In ECs, olanzapine impaired simvastatin-induced nitric oxide (NO) production and endothelial nitric oxide synthase (eNOS) phosphorylation through NOX-ROS pathway activation. Blocking this pathway reversed eNOS inhibition, restoring the endothelial benefits of simvastatin. Collectively, atypical antipsychotics impair statin efficacy in schizophrenia patients by activating the ADMA-NOX-ROS pathway, which downregulates LDLR in hepatocytes and inhibits eNOS activity in ECs. These findings underscore the need for tailored cardiovascular risk management strategies and identify potential molecular targets to enhance statin effectiveness in patients on atypical antipsychotics.

Antidopaminergic Medications and Clinical Changes in Measures of Huntington's Disease: A Causal Analysis

BACKGROUND

Antidopaminergic medications (ADM) are often used for symptom management of Huntington's disease (HD). Evidence from past research suggests that ADMs are associated with worse clinical outcomes in HD, but their impact on various domains remains underexplored.

OBJECTIVE

We used causal inference analysis to understand the impact of ADM use on measures of clinical progression in HD across multiple domains over 2 years.

METHODS

We used the Enroll-HD database with a new-user design, which compared a cohort that initiated ADM use after the first visit with an unexposed cohort that remained off ADMs. To control for 27 covariates, we used a doubly robust targeted maximum likelihood estimation and conducted two analyses. First, we analyzed ADM treatment 2 years post-baseline and separately for 12 outcome measures. Second, we examined the association of ADM dose with measures of clinical outcomes.

RESULTS

The ADM-exposed group exhibited faster change in measures of clinical outcome compared with the off-ADM group, which was statistically reliable in cognitive and functional outcome measures, and the composite Unified Huntington's Disease Rating Scale (cUHDRS). Motor domain analyses showed faster change in bradykinesia in the ADM-exposed group versus off-ADM but no difference in chorea or total motor score (TMS). Higher ADM doses also showed greater differences compared to the off-ADM group.

CONCLUSIONS

ADM use was associated with more rapid change in clinical measures, particularly in cognitive and functional domains. However, assumptions required to establish causation between ADM use and disease progression may not have been fully met, and further research is warranted. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Haloperidol dopamine receptor occupancy and antagonism correspond to delirium agitation scores and EPS risk: A PBPK-PD modeling analysis

BACKGROUND

Delirium is a severe neuropsychiatric disorder associated with increased morbidity and mortality. Numerous precipitating factors and etiologies merge into the pathophysiology of this condition which can be marked by agitation and psychosis. Judicious use of antipsychotic medications such as intravenous haloperidol reduces these symptoms and distress in critically ill individuals.

AIMS

This study aimed to develop a physiologically-based pharmacokinetic (PBPK) model for the antipsychotic medication haloperidol; estimate plasma and unbound interstitial brain concentrations for repetitive haloperidol administrations used in hyperactive delirium treatment; determine dopamine receptor occupancy and antagonism under these conditions; and correlate these results with Richmond Agitation-Sedation Scale (RASS) scores and the risk of developing extrapyramidal symptoms (EPSs).

METHODS

The PBPK model for single and repetitive administrations of peroral and intravenous haloperidol was developed with PK-Sim software. The pharmacodynamic (PD) model for RASS scores with haloperidol unbound interstitial brain concentration passed as the regressor was developed with the MonolixSuite 2021R platform.

RESULTS

Peak haloperidol plasma and unbound interstitial brain concentrations following a single 2 mg intravenous dose are 32 ± 5 nM and 2.4 ± 0.4 nM. With repetitive administrations, dopamine receptor occupancy is 70%-83% and D2LR antagonism is 1%-10%. Variations in dopamine receptor occupancy correlate with changes in RASS scores in individuals with hyperactive delirium. There is a linear association between the odds ratio of developing EPS and peak D2LR antagonism as functions of dopamine receptor occupancy.

CONCLUSIONS

Haloperidol dopamine receptor occupancy time course and D2LR antagonism parallel RASS score changes and EPS risk, respectively.

Dopamine receptor D2 (DRD2) TaqIA gene polymorphism and acute risperidone-induced changes in body weight, plasma glucose and lipid profile

There are indications that the transient blockade of the dopamine receptor D2 (DRD2) by atypical antipsychotics such as risperidone is related to their metabolic side effects. We, therefore, examined the relationship between TaqIA polymorphism of the DRD2 gene and acute risperidone-induced metabolic changes. We recruited 153 newly diagnosed patients with psychotic disorders (71 males and 82 females) from the Federal Neuropsychiatric Hospital, Yaba, Lagos, Nigeria. Body weight, fasting blood glucose (FBG), triglycerides (TG), total cholesterol (TChol), low-density lipoprotein cholesterol (LDLChol), and high-density lipoprotein cholesterol (LDLChol) were all determined at baseline and the end of 6 weeks of administration of risperidone (2 mg twice daily). DNA was also extracted from peripheral blood, and genotyping was carried out using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). The relationship between the mean changes in the metabolic indices and the DRD2 TaqIA genotype was statistically determined. The frequencies of the A1A1, A1A2, and A2A2 were 0.229, 0.412, and 0.360, respectively. However, the population was not in Hardy-Weinberg equilibrium (χ2 = 4.023, p < 0.01). The mean weight change and the mean changes in FBG, TG, TChol, and LDLChol were significantly (p < 0.05) higher among participants with the A1A1 genotype, followed by the heterozygous (A1A2) participants and lowest among those homozygous for the A2 allele. However, there was no significant difference in the mean change in HDLChol across all genotype groups. The DRD2 TaqIA1 allele is associated with higher risperidone-induced weight gain and metabolic changes among Nigerians.

Post-marketing safety of pimavanserin: a real-world pharmacovigilance study based on the FDA adverse event reporting system (FAERS)

BACKGROUND

Pimavanserin is a new non-dopamine neurotransmitter antipsychotic drug. This study aimed to conduct a post-marketing pharmacovigilance study of pimavanserin, through data mining technology using the FDA Adverse Event Reporting System (FAERS) database.

RESEARCH DESIGN AND METHODS

We analyzed adverse event reports for patients using pimavanserin. Data were classified using systematic organ classification (SOC) and preferred term (PT) of the Medical Dictionary for Regular Activities (MedDRA). Four signal algorithms [reporting odds ratio (ROR), proportional reporting ratio (PRR), multi-item gamma poisson shrinker (MGPS), and bayesian confidence propagation neural network (BCPNN)] were used to detect positive signals, and the median time-to-onset was determined.

RESULTS

Adverse drug events (ADEs) related to pimavanserin (n = 31,852) were analyzed, exhibiting an annual linear upward trend (p = 0.027). The ADEs involved 27 SOCs, but only 'Psychiatric disorders' simultaneously satisfied four algorithms. Overall, 153 PTs simultaneously satisfied four algorithms. Subgroup analysis of differences in the top 30 signal intensity PTs according to sex yielded significant results for seven PTs (p < 0.05). The median time-to-onset was 97 days, the highest proportion occurred within the first 30 days (31.79%).

CONCLUSIONS

Some new PT signals not listed in the label were identified, and some PT signals showed differences according to sex.

Plausible therapeutic effects of melatonin and analogs in the dopamine-associated pathophysiology of bipolar disorder

Bipolar disorder (BD) is a significant neuropsychiatric condition characterized by marked psychological mood disturbances. Despite extensive research on the symptomatology of BD, the mechanisms underlying its development and presentation remain unknown. Consequently, potential treatments are limited, and existing medications often cause significant side effects, leading to treatment discontinuation. Dopamine (DA) has been implicated in behavioral regulation, reward systems, and mood, highlighting the importance of the dopaminergic system in BD. Elevated levels of DA and tyrosine hydroxylase are associated with the onset of manic episodes, whereas reduced levels are linked to the depressive phase. Additionally, endogenous melatonin (MEL) levels are considerably lower in patients with BD. When administered as a treatment, exogenous MEL and MEL agonists improve behavioral characteristics and significantly modulate DA-related pathophysiological pathways in BD, with minimal adverse effects achieved through MEL receptor activation. Moreover, MEL and MEL agonists offer neuroprotection by promoting physiological homeostasis during disruption. The aim of this review is to investigate and propose MEL receptors as potential novel therapeutic targets for BD. This review seeks to analyze the role of MEL and its agonists in modulating dopamine-related pathophysiological pathways, improving behavioral outcomes, and providing neuroprotection with minimal side effects.

Pharmacology, Signaling and Therapeutic Potential of Metabotropic Glutamate Receptor 5 Negative Allosteric Modulators

Metabotropic glutamate receptors are a family of eight class C G protein-coupled receptors regulating higher order brain functions including cognition and motion. Metabotropic glutamate receptors have thus been heavily investigated as potential drug targets for treating neurological disorders. Drug discovery efforts directed toward metabotropic glutamate receptor subtype 5 (mGlu5) have been particularly fruitful, with a wealth of drug candidates and pharmacological tools identified. mGlu5 negative allosteric modulators (NAMs) are promising novel therapeutics for developmental, neuropsychiatric and neurodegenerative disorders (e.g., Alzheimer's Disease, Huntington's Disease, Parkinson's Disease, amyotrophic lateral sclerosis, autism spectrum disorders, substance use disorders, stroke, anxiety and depression) and show promise in ameliorating adverse effects induced by other medications (e.g., L-dopa induced dyskinesia in Parkinson's Disease). However, despite preclinical success, mGlu5 NAMs are yet to reach the market due to poor safety and efficacy profiles in clinical trials. Herein, we review the physiology and signal transduction of mGlu5. We provide a comprehensive critique of therapeutic options with respect to mGlu5 inhibitors, spanning from orthosteric antagonists to NAMs. Finally, we address the challenges associated with drug development and highlight future directions to guide rational drug discovery of safe and effective novel therapeutics.

Glia-related Acute Effects of Risperidone and Haloperidol in Hippocampal Slices and Astrocyte Cultures from Adult Wistar Rats: A Focus on Inflammatory and Trophic Factor Release

Antipsychotics are drugs commonly prescribed to treat a variety of psychiatric conditions. They are classified as typical and atypical, depending on their affinity for dopaminergic and serotonergic receptors. Although neurons have been assumed to be the major mediators of the antipsychotic pharmacological effects, glia, particularly astrocytes, have emerged as important cellular targets for these drugs. In the present study, we investigated the effects of acute treatments with the antipsychotics risperidone and haloperidol of hippocampal slices and astrocyte cultures, focusing on neuron-glia communication and how antipsychotics act in astrocytes. For this, we obtained hippocampal slices and primary astrocyte cultures from 30-day-old Wistar rats and incubated them with risperidone or haloperidol (1 and 10 μM) for 30 min and 24 h, respectively. We evaluated metabolic and enzymatic activities, the glutathione level, the release of inflammatory and trophic factors, as well as the gene expression of signaling proteins. Haloperidol increased glucose metabolism; however, neither of the tested antipsychotics altered the glutathione content or glutamine synthetase and Na+K+-ATPase activities. Haloperidol induced a pro-inflammatory response and risperidone promoted an anti-inflammatory response, while both antipsychotics seemed to decrease trophic support. Haloperidol and risperidone increased Nrf2 and HO-1 gene expression, but only haloperidol upregulated NFκB and AMPK gene expression. Finally, astrocyte cultures confirmed the predominant effect of the tested antipsychotics on glia and their opposite effects on astrocytes. Therefore, antipsychotics cause functional alterations in the hippocampus. This information is important to drive future research for strategies to attenuate antipsychotics-induced neural dysfunction, focusing on glia.

Mapping of c-Fos Expression in Rat Brain Sub/Regions Following Chronic Social Isolation: Effective Treatments of Olanzapine, Clozapine or Fluoxetine

The c-Fos as a marker of cell activation is used to identify brain regions involved in stimuli processing. This review summarizes a pattern of c-Fos immunoreactivity and the overlapping brain sub/regions which may provide hints for the identification of neural circuits that underlie depressive- and anxiety-like behaviors of adult male rats following three and six weeks of chronic social isolation (CSIS), relative to controls, as well as the antipsychotic-like effects of olanzapine (Olz), and clozapine (Clz), and the antidepressant-like effect of fluoxetine (Flx) in CSIS relative to CSIS alone. Additionally, drug-treated controls relative to control rats were also characterized. The overlapping rat brain sub/regions with increased expression of c-Fos immunoreactivity following three or six weeks of CSIS were the retrosplenial granular cortex, c subregion, retrosplenial dysgranular cortex, dorsal dentate gyrus, paraventricular nucleus of the thalamus (posterior part, PVP), lateral/basolateral (LA/BL) complex of the amygdala, caudate putamen, and nucleus accumbens shell. Increased activity of the nucleus accumbens core following exposure of CSIS rats either to Olz, Clz, and Flx treatments was found, whereas these treatments in controls activated the LA/BL complex of the amygdala and PVP. We also outline sub/regions that might represent potential neuroanatomical targets for the aforementioned antipsychotics or antidepressant treatments.

Kinetic analysis of fluorescent ligand binding to cell surface receptors: Insights into conformational changes and allosterism in living cells

Equilibrium binding assays are one of the mainstays of current drug discovery efforts to evaluate the interaction of drugs with receptors in membranes and intact cells. However, in recent years, there has been increased focus on the kinetics of the drug-receptor interaction to gain insight into the lifetime of drug-receptor complexes and the rate of association of a ligand with its receptor. Furthermore, drugs that act on topically distinct sites (allosteric) from those occupied by the endogenous ligand (orthosteric site) can induce conformational changes in the orthosteric binding site leading to changes in the association and/or dissociation rate constants of orthosteric ligands. Conformational changes in the orthosteric ligand binding site can also be induced through interaction with neighbouring accessory proteins and receptor homodimerisation and heterodimerisation. In this review, we provide an overview of the use of fluorescent ligand technologies to interrogate ligand-receptor kinetics in living cells and the novel insights that they can provide into the conformational changes induced by drugs acting on a variety of cell surface receptors including G protein-coupled receptors (GPCRs), receptor tyrosine kinases (RTKs) and cytokine receptors.

The translational value of ligand-receptor binding kinetics in drug discovery

The translation of in vitro potency of a candidate drug, as determined by traditional pharmacology metrics (such as EC50/IC50 and KD/Ki values), to in vivo efficacy and safety is challenging. Residence time, which represents the duration of drug-target interaction, can be part of a more comprehensive understanding of the dynamic nature of drug-target interactions in vivo, thereby enabling better prediction of drug efficacy and safety. As a consequence, a prolonged residence time may help in achieving sustained pharmacological activity, while transient interactions with shorter residence times may be favourable for targets associated with side effects. Therefore, integration of residence time into the early stages of drug discovery and development has yielded a number of clinical candidates with promising in vivo efficacy and safety profiles. Insights from residence time research thus contribute to the translation of in vitro potency to in vivo efficacy and safety. Further research and advances in measuring and optimizing residence time will bring a much-needed addition to the drug discovery process and the development of safer and more effective drugs. In this review, we summarize recent research progress on residence time, highlighting its importance from a translational perspective.

Positive allosteric modulation of a GPCR ternary complex

The activation of a G protein-coupled receptor (GPCR) leads to the formation of a ternary complex between agonist, receptor, and G protein that is characterized by high-affinity binding. Allosteric modulators bind to a distinct binding site from the orthosteric agonist and can modulate both the affinity and the efficacy of orthosteric agonists. The influence allosteric modulators have on the high-affinity active state of the GPCR-G protein ternary complex is unknown due to limitations on attempting to characterize this interaction in recombinant whole cell or membrane-based assays. Here, we use the purified M2 muscarinic acetylcholine receptor reconstituted into nanodiscs to show that, once the agonist-bound high-affinity state is promoted by the G protein, positive allosteric modulators stabilize the ternary complex that, in the presence of nucleotides, leads to an enhanced initial rate of signaling. Our results enhance our understanding of how allosteric modulators influence orthosteric ligand signaling and will aid the design of allosteric therapeutics.

Dysfunction of the NMDA Receptor in the Pathophysiology of Schizophrenia and/or the Pathomechanisms of Treatment-Resistant Schizophrenia

For several decades, the dopamine hypothesis contributed to the discovery of numerous typical and atypical antipsychotics and was the sole hypothesis for the pathophysiology of schizophrenia. However, neither typical nor atypical antipsychotics, other than clozapine, have been effective in addressing negative symptoms and cognitive impairments, which are indices for the prognostic and disability outcomes of schizophrenia. Following the development of atypical antipsychotics, the therapeutic targets for antipsychotics expanded beyond the blockade of dopamine D2 and serotonin 5-HT2A receptors to explore the partial agonism of the D2 receptor and the modulation of new targets, such as D3, 5-HT1A, 5-HT7, and metabotropic glutamate receptors. Despite these efforts, to date, psychiatry has not successfully developed antipsychotics with antipsychotic properties proven to be superior to those of clozapine. The glutamate hypothesis, another hypothesis regarding the pathophysiology/pathomechanism of schizophrenia, was proposed based on clinical findings that N-methyl-D-aspartate glutamate receptor (NMDAR) antagonists, such as phencyclidine and ketamine, induce schizophrenia-like psychotic episodes. Large-scale genome-wide association studies (GWASs) revealed that approximately 30% of the risk genes for schizophrenia (the total number was over one hundred) encode proteins associated with glutamatergic transmission. These findings supported the validation of the glutamate hypothesis, which was inspired by the clinical findings regarding NMDAR antagonists. Additionally, these clinical and genetic findings suggest that schizophrenia is possibly a syndrome with complicated pathomechanisms that are affected by multiple biological and genetic vulnerabilities. The glutamate hypothesis has been the most extensively investigated pathophysiology/pathomechanism hypothesis, other than the dopamine hypothesis. Studies have revealed the possibility that functional abnormalities of the NMDAR play important roles in the pathophysiology/pathomechanism of schizophrenia. However, no antipsychotics derived from the glutamatergic hypothesis have yet been approved for the treatment of schizophrenia or treatment-resistant schizophrenia. Considering the increasing evidence supporting the potential pro-cognitive effects of glutamatergic agents and the lack of sufficient medications to treat the cognitive impairments associated with schizophrenia, these previous setbacks cannot preclude research into potential novel glutamate modulators. Given this background, to emphasize the importance of the dysfunction of the NMDAR in the pathomechanism and/or pathophysiology of schizophrenia, this review introduces the increasing findings on the functional abnormalities in glutamatergic transmission associated with the NMDAR.

Exploring the Relationships Between Antipsychotic Dosage and Voice Characteristics in Relation to Extrapyramidal Symptoms

OBJECTIVE

Extrapyramidal symptoms (EPS) are common side effects of antipsychotic drugs. Despite the growing interest in exploring objective biomarkers for EPS prevention and the potential use of voice in detecting clinical disorders, no studies have demonstrated the relationships between vocal changes and EPS. Therefore, we aimed to determine the associations between voice changes and antipsychotic dosage, and further investigated whether speech characteristics could be used as predictors of EPS.

METHODS

Forty-two patients receiving or expected to receive antipsychotic drugs were recruited. Drug-induced parkinsonism of EPS was evaluated using the Simpson-Angus Scale (SAS). Participants' voice data consisted of 16 neutral sentences and 2 second-long /Ah/utterances. Thirteen voice features were extracted from the obtained voice data. Each voice feature was compared between groups categorized based on SAS total score of below and above "0.6." The associations between antipsychotic dosage and voice characteristics were examined, and vocal trait variations according to the presence of EPS were explored.

RESULTS

Significant associations were observed between specific vocal characteristics and antipsychotic dosage across both datasets of 1-16 sentences and /Ah/utterances. Notably, Mel-Frequency Cepstral Coefficients (MFCC) exhibited noteworthy variations in response to the presence of EPS. Specifically, among the 13 MFCC coefficients, MFCC1 (t=-4.47, p<0.001), MFCC8 (t=-4.49, p<0.001), and MFCC12 (t=-2.21, p=0.029) showed significant group differences in the overall statistical values.

CONCLUSION

Our results suggest that MFCC may serve as a predictor of detecting drug-induced parkinsonism of EPS. Further research should address potential confounding factors impacting the relationship between MFCC and antipsychotic dosage, possibly improving EPS detection and reducing antipsychotic medication side effects.

Know your molecule: pharmacological characterization of drug candidates to enhance efficacy and reduce late-stage attrition

Despite advances in chemical, computational and biological sciences, the rate of attrition of drug candidates in clinical development is still high. A key point in the small-molecule discovery process that could provide opportunities to help address this challenge is the pharmacological characterization of hit and lead compounds, culminating in the selection of a drug candidate. Deeper characterization is increasingly important, because the 'quality' of drug efficacy, at least for G protein-coupled receptors (GPCRs), is now understood to be much more than activation of commonly evaluated pathways such as cAMP signalling, with many more 'efficacies' of ligands that could be harnessed therapeutically. Such characterization is being enabled by novel assays to characterize the complex behaviour of GPCRs, such as biased signalling and allosteric modulation, as well as advances in structural biology, such as cryo-electron microscopy. This article discusses key factors in the assessments of the pharmacology of hit and lead compounds in the context of GPCRs as a target class, highlighting opportunities to identify drug candidates with the potential to address limitations of current therapies and to improve the probability of them succeeding in clinical development.

A novel mucoadhesive paliperidone-nanoemulsion developed using the ultrasonication method in the treatment of schizophrenia

Aim: To develop paliperidone mucoadhesive-nanoemulsion (PLP-NE) to enhance brain bioavailability. To evaluate comparative effects of PLP-NE and CS-PLP-NE in the treatment of schizophrenia, followed by a toxicity study of opt-NE. Material and methods: Oil: oleic acid, surfactant: Tween-80, and co-surfactant: Labrasol were chosen based on the solubility and maximum nanoemulsion area. The ultrasonication technique was applied with the aqueous micro titration method for the development of PLP-NE. The optimization of the method for the excellent PLP-NE was performed using a central composite design based on a five-factor and four-level. Oil (% v/v), S mix (v/v%), ultrasonication intensity in percentage, ultrasonication time in minutes, and temperature (°C) were optimized and used to the independent variables. Results: The parameters i.e., oil (5%), S mix (10%), ultrasonication time (5.0 min), ultrasonication intensity (25%), and temperature (38 °C) were optimized and used as independent and dependent variables for the development of novel PLP-NE. Based on experimental data, the dependent variables, i.e., globule size (53.90 ± 4.01 nm), % transmittance (92.56% ± 1.06%), PDI (0.218 ± 0.007), and zeta potential (-11.60 ± 0.031 mV), were determined. The smooth near about spherical shaped of PLP-NE globules with, refractive index i.e., 1.62 ± 0.021, viscosity: 39 ± 6 cp with the pH: 7.40 ± 0.089, and content of drug (97.98 ± 0.39%) for optimized-PLP-NE. The optimized PLP-NE with oleic acid, Tween-80, and Labrasol was used to improve brain bioavailability with good permeation via the intranasal route. CS-PLP-NE yielded good mucoadhesive property results compared to paliperidone-nanoemulsion, and PLP-S containing a 0.751 minutes retention time with their deuterated-IS (0.806 min) and m/z of 427.2/207.2 with IS (m/z: 431.2/211.2) for PLP and PLP-IS. A calibration curve was plotted with a linear range of 1-2000 ng mL-1 with inter- and intraday accuracy (97.03-99.31%) and precision (1.69-50.05%). The results of AUC(0-24) and C max for PLP were found to be highly significant (p < 0.001) as an improvement of brain bioavailability in rats via intranasal delivery of CS-PLP-NE. Furthermore, the locomotion test, social interaction, and forced swimming test (forced swimming, climbing, and immobility) of a mucoadhesive CS-PLP-NE (intranasally) provided highly significant results with the improvement of behavioral analysis when compared to the PLP-NE and PLP-S studies. Conclusion: CS-PLP-NE (i.n.) showed highly significant results, i.e., p < 0.001 for the improvement of bioavailability of the brain in the treatment of schizophrenia. Optimized-mucoadhesive-CS-based-PLP-NE is safe and shows no toxicity.

Pseudoirreversible inhibition elicits persistent efficacy of a sphingosine 1-phosphate receptor 1 antagonist

Sphingosine 1-phosphate receptor 1 (S1PR1), a G protein-coupled receptor, is required for lymphocyte trafficking, and is a promising therapeutic target in inflammatory diseases. Here, we synthesize a competitive S1PR1 antagonist, KSI-6666, that effectively suppresses pathogenic inflammation. Metadynamics simulations suggest that the interaction of KSI-6666 with a methionine residue Met124 in the ligand-binding pocket of S1PR1 may inhibit the dissociation of KSI-6666 from S1PR1. Consistently, in vitro functional and mutational analyses reveal that KSI-6666 causes pseudoirreversible inhibition of S1PR1, dependent on the Met124 of the protein and substituents on the distal benzene ring of KSI-6666. Moreover, in vivo study suggests that this pseudoirreversible inhibition is responsible for the persistent activity of KSI-6666.

High-throughput kinetics in drug discovery

The importance of a drug's kinetic profile and interplay of structure-kinetic activity with PK/PD has long been appreciated in drug discovery. However, technical challenges have often limited detailed kinetic characterization of compounds to the latter stages of projects. This review highlights the advances that have been made in recent years in techniques, instrumentation, and data analysis to increase the throughput of detailed kinetic and mechanistic characterization, enabling its application earlier in the drug discovery process.

The Use of Ascorbic Acid in Adjunctive Treatment for Schizophrenia-Current State of Knowledge

Schizophrenia is a mental illness characterized by disturbances in the perception of reality, thinking, emotions, and social functioning. This significantly impacts the quality of life of patients and leads to long-term disability. Despite advances in understanding its pathogenesis and treatment, schizophrenia remains a clinical challenge, especially due to the diversity of its symptoms and the complexity of its mechanisms. Schizophrenia is associated with abnormal functioning of the dopaminergic system, disturbances in glutamatergic neurotransmission, and oxidative stress in the brain. In recent years, there has been increasing interest in optimizing the treatment of mental disorders. The potential use of ascorbic acid, or vitamin C, in the therapy of schizophrenia could bring substantial benefits to patients. Ascorbic acid exhibits antioxidant and neuroprotective properties, suggesting its potential efficacy in reducing brain oxidative stress and improving neurotransmission. Additionally, there have been reports of its positive effects on psychotic symptoms and its potential in reducing the side effects of antipsychotic drugs. In this review article, we present the current state of knowledge on the potential use of ascorbic acid in the treatment of schizophrenia as an adjunct to standard pharmacological therapy. We analyze existing clinical studies and the mechanisms of action of vitamin C, suggesting its promising role as an adjunctive therapy in the treatment of schizophrenia. These insights, though not yet widely disseminated, may be significant for the further development of therapeutic strategies for this mental illness.

Oleanolic acid alleviates the extrapyramidal symptoms and cognitive impairment induced by haloperidol through the striatal PKA signaling pathway in mice

Haloperidol, one of the representative typical antipsychotics, is on the market for schizophrenia but shows severe adverse effects such as extrapyramidal symptoms (EPS) or cognitive impairments. Oleanolic acid (OA) is known to be effective for tardive dyskinesia which is induced by long-term treatment with L-DOPA. This study aimed to investigate whether OA could ameliorate EPS or cognitive impairment induced by haloperidol. The balance beam, catalepsy response, rotarod and vacuous chewing movement (VCM) tests were performed to measure EPS and the novel object recognition test was used to estimate haloperidol-induced cognitive impairment. Levels of dopamine and acetylcholine, the phosphorylation levels of c-AMP-dependent protein kinase A (PKA) and its downstream signaling molecules were measured in the striatum. OA significantly attenuated EPS and cognitive impairment induced by haloperidol without affecting its antipsychotic properties. Valbenazine only ameliorated VCM. Also, OA normalised the levels of dopamine and acetylcholine in the striatum which were increased by haloperidol. Furthermore, the increased phosphorylated PKA, extracellular signal-regulated kinase (ERK) and cAMP response element-binding protein (CREB) levels and c-FOS expression level induced by haloperidol were significantly decreased by OA in the striatum. In addition, cataleptic behaviour of haloperidol was reversed by sub-effective dose of H-89 with OA. These results suggest that OA can alleviate EPS and cognitive impairment induced by antipsychotics without interfering with antipsychotic properties via regulating neurotransmitter levels and the PKA signaling pathway in the striatum. Therefore, OA is a potential candidate for treating EPS and cognitive impairment induced by antipsychotics.

Synthesis, computational and experimental pharmacological studies for (thio)ether-triazine 5-HT6R ligands with noticeable action on AChE/BChE and chalcogen-dependent intrinsic activity in search for new class of drugs against Alzheimer's disease

Alzheimer's disease is becoming a growing problem increasing at a tremendous rate. Serotonin 5-HT6 receptors appear to be a particularly attractive target from a therapeutic perspective, due to their involvement not only in cognitive processes, but also in depression and psychosis. In this work, we present the synthesis and broad biological characterization of a new series of 18 compounds with a unique 1,3,5-triazine backbone, as potent 5-HT6 receptor ligands. The main aim of this research is to compare the biological activity of the newly synthesized sulfur derivatives with their oxygen analogues and their N-demethylated O- and S-metabolites obtained for the first time. Most of the new triazines displayed high affinity (Ki < 200 nM) and selectivity towards 5-HT6R, with respect to 5-HT2AR, 5-HT7R, and D2R, in the radioligand binding assays. For selected, active compounds crystallographic studies, functional bioassays, and ADME-Tox profile in vitro were performed. The exciting novelty is that the sulfur derivatives exhibit an agonistic mode of action contrary to all other compounds obtained to date in this chemical class herein and previously reported. Advanced computational studies indicated that this intriguing functional shift might be caused by presence of chalcogen bonds formed only by the sulfur atom. In addition, the N-demethylated derivatives have emerged highly potent antioxidants and, moreover, show a significant improvement in metabolic stability compared to the parent structures. The cholinesterase study present micromolar inhibitory AChE and BChE activity for both 5-HT6 agonist 19 and potent antagonist 5. Finally, the behavioral experiments of compound 19 demonstrated its antidepressant-like properties and slight ability to improve cognitive deficits, without inducing memory impairments by itself. Described pharmacological properties of both compounds (5 and 19) allow to give a design clue for the development of multitarget compounds with 5-HT6 (both agonist and antagonist)/AChE and/or BChE mechanism in the group of 1,3,5-triazine derivatives.

Target immobilization on glass microfiber membranes as a label-free strategy for hit identification

The discovery of novel chemical entities targeting G protein-coupled receptors (GPCRs) is usually guided by their receptor affinity. However, traditional affinity assay methods and hit identification procedures are usually laborious and expensive. In this work, the type-2 vasopressin receptor (V2R) was chosen as a prototypical GPCR. Membrane fragments from cells highly expressing SNAP-V2R were immobilized on the surface of a glass microfiber (GMF) coated with O6-benzylguanine (BG). This was achieved by transferring the benzyl group of BG to the active site of the SNAP-tag through a nucleophilic substitution reaction. As a result, a biofilm called SNAP-V2R@GMF-BG was produced that showed good specificity and stability. The adsorption ratio for each V2R ligand treated with SNAP-V2R@GMF-BG was determined by HPLC and exhibited a good linear correlation with the Ki value determined by displacement assays. Furthermore, a Ki prediction assay was performed by comparing the data with that generated by a homogeneous time-resolved fluorescence (HTRF) assay. SNAP-V2R@GMF-BG was also used to screen hit compounds from natural products. After SNAP-V2R@GMF-BG was incubated with the total extract, the ligand that binds to V2R could be separated and subjected to LC‒MS analysis for identification. Baicalein was screened from Clerodendranthus spicatus and verified as a potential V2R antagonist. This V2R-immobilized GMF platform can help determine the affinity of V2R-binding hit compounds and screen the compounds efficiently and accurately.

Allosteric crosstalk in modular proteins: Function fine-tuning and drug design

Modular proteins are regulatory proteins that carry out more than one function. These proteins upregulate or downregulate a biochemical cascade to establish homeostasis in cells. To switch the function or alter the efficiency (based on cellular needs), these proteins require different facilitators that bind to a site different from the catalytic (active/orthosteric) site, aka 'allosteric site', and fine-tune their function. These facilitators (or effectors) are allosteric modulators. In this Review, we have discussed the allostery, characterized them based on their mechanisms, and discussed how allostery plays an important role in the activity modulation and function fine-tuning of proteins. Recently there is an emergence in the discovery of allosteric drugs. We have also emphasized the role, significance, and future of allostery in therapeutic applications.

Jobelyn® improves motor dysfunctions induced by haloperidol in mice via neuroprotective mechanisms relating to modulation of cAMP response-element binding protein and mitogen-activated protein kinase

The clinical efficacy of haloperidol in the treatment of psychosis has been limited by its tendency to cause parkinsonian-like motor disturbances such as bradykinesia, muscle rigidity and postural instability. Oxidative stress-evoked neuroinflammation has been implicated as the key neuropathological mechanism by which haloperidol induces loss of dopaminergic neurons and motor dysfunctions. This study was therefore designed to evaluate the effect of Jobelyn® (JB), an antioxidant supplement, on haloperidol-induced motor dysfunctions and underlying molecular mechanisms in male Swiss mice. The animals were distributed into 5 groups (n = 8), and treated orally with distilled water (control), haloperidol (1 mg/kg) alone or in combination with each dose of JB (10, 20 and 40 mg/kg), daily for 14 days. Thereafter, changes in motor functions were evaluated on day 14. Brain biomarkers of oxidative stress, proinflammatory cytokines (tumor necrosis factor-alpha and interleukin-6), cAMP response-element binding protein (CREB), mitogen-activated protein kinase (MAPK) and histomorphological changes were also investigated. Haloperidol induces postural instability, catalepsy and impaired locomotor activity, which were ameliorated by JB. Jobelyn® attenuated haloperidol-induced elevated brain levels of MDA, nitrite, proinflammatory cytokines and also boosted neuronal antioxidant profiles (GSH and catalase) of mice. It also restored the deregulated brain activities of CREB and MAPK, and reduced the histomorphological distortions as well as loss of viable neuronal cells in the striatum and prefrontal cortex of haloperidol-treated mice. These findings suggest possible benefits of JB as adjunctive remedy in mitigating parkinsonian-like adverse effects of haloperidol through modulation of CREB/MAPK activities and oxidative/inflammatory pathways.

Extrapyramidal Side Effects with Chronic Atypical Antipsychotic Can Be Predicted by Labeling Pattern of FosB and phosphoThr34-DARPP-32 in Nucleus Accumbens

Extrapyramidal side effects (EPS) can be induced by neuroleptics that regulate the expression of transcription factor FosB and dopaminergic mediator DARPP-32 in the striatum. However, the long-term neurobiological changes in striatal projection neurons resulting from a cumulative dosage of typical and atypical antipsychotics are poorly understood. The present study aimed to determine the differential and long-lasting changes in FosB distribution and DARPP-32 phosphorylation in the striatum and nucleus accumbens (NAc) associated with chronic antipsychotic-induced EPS. Male C57Bl/6J mice received daily injections of Olanzapine (Olz, 15 mg/kg), Clozapine (Clz, 20 mg/kg), or Haloperidol (Hal, 1 mg/kg), for a period of 11 weeks with a 4-day withdrawal period before the last dosage. Catalepsy for detection of EPS, along with open-field and rotarod tests, were assessed as behavioral correlates of motor responses. Additionally, FosB and phosphorylated-DARPP-32 immunohistochemistry were examined in striatal regions after treatment. All antipsychotics produced catalepsy and reduced open-field exploration, such as impaired rota-rod performance after Olz and Hal. The washout period was critical for Clz-induced side effects reduction. Both Olz and Clz increased FosB in NAc Shell-region, and phosphoThr34-DARPP-32 in NAc. Only Clz reduced phosphoThr75-DARPP-32 in the dorsal striatum and showed FosB/phosphoThr34-Darpp-32-ir in the NAc Core region. This study provides evidence that atypical antipsychotics such as Olz and Clz also give rise to EPS effects frequently associated with a cumulative dosage of typical neuroleptics such as Hal. Nevertheless, FosB/phosphoThr34-Darpp-32-ir in the NAc Core region is associated with hypokinetic movements inhibition.

Design, Synthesis, and Application of Fluorescent Ligands Targeting the Intracellular Allosteric Binding Site of the CXC Chemokine Receptor 2

The inhibition of CXC chemokine receptor 2 (CXCR2), a key inflammatory mediator, is a potential strategy in the treatment of several pulmonary diseases and cancers. The complexity of endogenous chemokine interaction with the orthosteric binding site has led to the development of CXCR2 negative allosteric modulators (NAMs) targeting an intracellular pocket near the G protein binding site. Our understanding of NAM binding and mode of action has been limited by the availability of suitable tracer ligands for competition studies, allowing direct ligand binding measurements. Here, we report the rational design, synthesis, and pharmacological evaluation of a series of fluorescent NAMs, based on navarixin (2), which display high affinity and preferential binding for CXCR2 over CXCR1. We demonstrate their application in fluorescence imaging and NanoBRET binding assays, in whole cells or membranes, capable of kinetic and equilibrium analysis of NAM binding, providing a platform to screen for alternative chemophores targeting these receptors.

A Novel Gliotransmitter, L-β-Aminoisobutyric Acid, Contributes to Pathophysiology of Clinical Efficacies and Adverse Reactions of Clozapine

Clozapine is listed as one of the most effective antipsychotics and has been approved for treating treatment-resistant schizophrenia (TRS); however, several type A and B adverse reactions, including weight gain, metabolic complications, cardiotoxicity, convulsions, and discontinuation syndromes, exist. The critical mechanisms of clinical efficacy for schizophrenia, TRS, and adverse reactions of clozapine have not been elucidated. Recently, the GABA isomer L-β-aminoisobutyric acid (L-BAIBA), a protective myokine in the peripheral organs, was identified as a candidate novel transmission modulator in the central nervous system (CNS). L-BAIBA activates adenosine monophosphate-activated protein kinase (AMPK) signalling in both the peripheral organs and CNS. Activated AMPK signalling in peripheral organs is an established major target for treating insulin-resistant diabetes, whereas activated AMPK signalling in the hypothalamus contributes to the pathophysiology of weight gain and metabolic disturbances. Clozapine increases L-BAIBA synthesis in the hypothalamus. In addition, the various functions of L-BAIBA in the CNS have recently been elucidated, including as an activator of GABA-B and group-III metabotropic glutamate (III-mGlu) receptors. Considering the expressions of GABA-B and III-mGlu receptors (localised in the presynaptic regions), the activation of GABA-B and III-mGlu receptors can explain the distinct therapeutic advantages of clozapine in schizophrenia or TRS associated with N-methyl-D-aspartate (NMDA) receptor disturbance compared with other atypical antipsychotics via the inhibition of the persistent tonic hyperactivation of thalamocortical glutamatergic transmission in the prefrontal cortex. L-BAIBA has also been identified as a gliotransmitter, and a detailed exploration of the function of L-BAIBA in tripartite synaptic transmission can further elucidate the pathophysiology of effectiveness for treating TRS and/or specific adverse reactions of clozapine.

Antipsychotic dose, dopamine D2 receptor occupancy and extrapyramidal side-effects: a systematic review and dose-response meta-analysis

Antipsychotic drugs differ in their propensity to cause extrapyramidal side-effects (EPS), but their dose-effects are unclear. Therefore, we conducted a systematic review and dose-response meta-analysis. We searched multiple electronic databases up to 20.02.2023 for fixed-dose studies investigating 16 second-generation antipsychotics and haloperidol (all formulations and administration routes) in adults with acute exacerbations of schizophrenia. The primary outcome was the number of participants receiving antiparkinsonian medication, and if not available, the number of participants with extrapyramidal side-effects (EPS) and the mean scores of EPS rating scales were used as proxies. The effect-size was odds ratio (ORs) compared with placebo. One-stage random-effects dose-response meta-analyses with restricted cubic splines were conducted to estimate the dose-response curves. We also examined the relationship between dopamine D2 receptor (D2R) occupancy and ORs by estimating occupancies from administrated doses. We included data from 110 studies with 382 dose arms (37193 participants). Most studies were short-term with median duration of 6 weeks (range 3-26 weeks). Almost all antipsychotics were associated with dose-dependent EPS with varied degrees and the maximum ORs ranged from OR = 1.57 95%CI [0.97, 2.56] for aripiprazole to OR = 7.56 95%CI [3.16, 18.08] for haloperidol at 30 mg/d. Exceptions were quetiapine and sertindole with negligible risks across all doses. There was very low quality of findings for cariprazine, iloperidone, and zotepine, and no data for clozapine. The D2R occupancy curves showed that the risk increased substantially when D2R occupancy exceeded 75-85%, except for D2R partial agonists that had smaller ORs albeit high D2R occupancies. In conclusion, we found that the risk of EPS increases with rising doses and differs substantially in magnitude among antipsychotics, yet exceptions were quetiapine and sertindole with negligible risks. Our data provided additional insights into the current D2R therapeutic window for EPS.

The antipsychotic medications aripiprazole, brexpiprazole and cariprazine are off-target respiratory chain complex I inhibitors

Antipsychotic drugs are the mainstay of treatment for schizophrenia and provide adjunct therapies for other prevalent psychiatric conditions, including bipolar disorder and major depressive disorder. However, they also induce debilitating extrapyramidal syndromes (EPS), such as Parkinsonism, in a significant minority of patients. The majority of antipsychotic drugs function as dopamine receptor antagonists in the brain while the most recent 'third'-generation, such as aripiprazole, act as partial agonists. Despite showing good clinical efficacy, these newer agents are still associated with EPS in ~ 5 to 15% of patients. However, it is not fully understood how these movement disorders develop. Here, we combine clinically-relevant drug concentrations with mutliscale model systems to show that aripiprazole and its primary active metabolite induce mitochondrial toxicity inducing robust declines in cellular ATP and viability. Aripiprazole, brexpiprazole and cariprazine were shown to directly inhibit respiratory complex I through its ubiquinone-binding channel. Importantly, all three drugs induced mitochondrial toxicity in primary embryonic mouse neurons, with greater bioenergetic inhibition in ventral midbrain neurons than forebrain neurons. Finally, chronic feeding with aripiprazole resulted in structural damage to mitochondria in the brain and thoracic muscle of adult Drosophila melanogaster consistent with locomotor dysfunction. Taken together, we show that antipsychotic drugs acting as partial dopamine receptor agonists exhibit off-target mitochondrial liabilities targeting complex I.

Histone deacetylase 1 regulates haloperidol-induced motor side effects in aged mice

BACKGROUND

Antipsychotic drugs prescribed to elderly patients with neuropsychiatric disorders often experience severe extrapyramidal side effects. Previous studies from our group suggest that changes in histone modifications during aging increase the risk for antipsychotic drug side effects, because co-administration of antipsychotics with class 1 histone deacetylase (HDAC) inhibitors could mitigate the severity of motor side effects in aged mice. However, which HDAC subtype contributes to the age-related sensitivity to antipsychotic drug side effects is unknown.

METHODS

In this study, we overexpressed histone deacetylase type 1(HDAC1) in the striatum of 3-month-old mice and knocked down HDAC 1 in the striatum of 21-month-old mice by microinjection of AAV9-HDAC1-GFP or AAV9-CRISPR/Cas9-HDAC1-GFP vectors. Four weeks after the viral-vector delivery, the typical antipsychotic drug haloperidol was administered daily for 14 days, followed by motor function assessments through the open field, rotarod, and catalepsy behavioral tests.

RESULTS

Young mice with overexpressed HDAC1 showed increased cataleptic behavior induced by haloperidol administration, which is associated with the increased HDAC1 level in the striatum. In contrast, aged mice with HDAC1 knocked down rescued locomotor activity, motor coordination, and decreased cataleptic behavior induced by haloperidol administration, which is associated with decreased HDAC1 level in the striatum.

CONCLUSIONS

Our results suggest that HDAC1 is a critical regulator in haloperidol-induced severe motor side effects in aged mice. Repression of HDAC1 expression in the striatum of aged mice could mitigate typical antipsychotic drug-induced motor side effects.

Dopamine Receptor Ligand Selectivity-An In Silico/In Vitro Insight

Different dopamine receptor (DR) subtypes are involved in pathophysiological conditions such as Parkinson's Disease (PD), schizophrenia and depression. While many DR-targeting drugs have been approved by the U.S. Food and Drug Administration (FDA), only a very small number are truly selective for one of the DR subtypes. Additionally, most of them show promiscuous activity at related G-protein coupled receptors, thus suffering from diverse side-effect profiles. Multiple studies have shown that combined in silico/in vitro approaches are a valuable contribution to drug discovery processes. They can also be applied to divulge the mechanisms behind ligand selectivity. In this study, novel DR ligands were investigated in vitro to assess binding affinities at different DR subtypes. Thus, nine D2R/D3R-selective ligands (micro- to nanomolar binding affinities, D3R-selective profile) were successfully identified. The most promising ligand exerted nanomolar D3R activity (Ki = 2.3 nM) with 263.7-fold D2R/D3R selectivity. Subsequently, ligand selectivity was rationalized in silico based on ligand interaction with a secondary binding pocket, supporting the selectivity data determined in vitro. The developed workflow and identified ligands could aid in the further understanding of the structural motifs responsible for DR subtype selectivity, thus benefitting drug development in D2R/D3R-associated pathologies such as PD.

Enhancement of memory consolidation by an avoidance conditioned stimulus: Modulation by the D3 receptor

Conditioned stimuli (CS) paired with foot-shock can enhance memory consolidation. Because the dopamine D3R has been implicated in mediating various responses to CSs, the current study explored its potential role in modulation of memory consolidation by an avoidance CS. Male Sprague-Dawley rats trained to avoid foot-shocks in a two-way signalled active avoidance task (8 sessions, 30 trials per session, 0.8 mA foot-shock) were pre-treated with the D3R antagonist NGB-2904 (Vehicle, 0.1 or 5 mg/kg) and exposed to the CS immediately after the sample phase of an object recognition memory task. Discrimination ratios were assessed 72 h later. Immediate, but not delayed (6 h), post-sample exposure to the CS enhanced object recognition memory and this effect was dose-dependently blocked by NGB-2904. Control experiments with the beta-noradrenergic receptor antagonist propranolol (10 or 20 mg/kg) and D2R antagonist pimozide (0.2 or 0.6 mg/kg) indicated that NGB-2904 targeted post-training memory consolidation. Exploring the pharmacological selectivity of the D3R effect, it was found that: 1) 5 mg/kg NGB-2904 blocked conditioned memory modulation produced by post-sample exposure to a "weak" CS (one day of avoidance training) and concurrent stimulation of catecholamine activity by 10 mg/kg bupropion; 2) post-sample exposure to a "weak" CS and concurrent administration of the D3R agonist 7-OH-DPAT (1 mg/kg) enhanced consolidation of object memory. Finally, because 5 mg/kg NGB-2904 had no effect on modulation by avoidance training in the presence of foot-shocks, the findings herein support the hypothesis that the D3R plays an important role in modulation of memory consolidation by CSs.

Unique effect of clozapine on adenosine A2A-dopamine D2 receptor heteromerization

The striatal dopamine D2 receptor (D2R) is generally accepted to be involved in positive symptoms of schizophrenia and is a main target for clinically used antipsychotics. D2R are highly expressed in the striatum, where they form heteromers with the adenosine A2A receptor (A2AR). Changes in the density of A2AR-D2R heteromers have been reported in postmortem tissue from patients with schizophrenia, but the degree to which A2R are involved in schizophrenia and the effect of antipsychotic drugs is unknown. Here, we examine the effect of exposure to three prototypical antipsychotic drugs on A2AR-D2R heteromerization in mammalian cells using a NanoBiT assay. After 16 h of exposure, a significant increase in the density of A2AR-D2R heteromers was found with haloperidol and aripiprazole, but not with clozapine. On the other hand, clozapine, but not haloperidol or aripiprazole, was associated with a significant decrease in A2AR-D2R heteromerization after 2 h of treatment. Computational binding models of these compounds revealed distinctive molecular signatures that explain their different influence on heteromerization. The bulky tricyclic moiety of clozapine displaces TM 5 of D2R, inducing a clash with A2AR, while the extended binding mode of haloperidol and aripiprazole stabilizes a specific conformation of the second extracellular loop of D2R that enhances the interaction with A2AR. It is proposed that an increase in A2AR-D2R heteromerization is involved in the extrapyramidal side effects (EPS) of antipsychotics and that the specific clozapine-mediated destabilization of A2AR-D2R heteromerization can explain its low EPS liability.

Antipsychotic treatment effects and structural MRI brain changes in schizophrenia

BACKGROUND

Progressive brain structural MRI changes are described in schizophrenia and have been ascribed to both illness progression and antipsychotic treatment. We investigated treatment effects, in terms of total cumulative antipsychotic dose, efficacy and tolerability, on brain structural changes over the first 24 months of treatment in schizophrenia.

METHODS

A prospective, 24-month, single-site cohort study in 99 minimally treated patients with first-episode schizophrenia, schizophreniform and schizoaffective disorder, and 98 matched healthy controls. We treated the patients according to a fixed protocol with flupenthixol decanoate, a long-acting injectable antipsychotic. We assessed psychopathology, cognition, extrapyramidal symptoms and BMI, and acquired MRI scans at months 0, 12 and 24. We selected global cortical thickness, white matter volume and basal ganglia volume as the regions of interest.

RESULTS

The only significant group × time interaction was for basal ganglia volumes. However, patients, but not controls, displayed cortical thickness reductions and increases in white matter and basal ganglia volumes. Cortical thickness reductions were unrelated to treatment. White matter volume increases were associated with lower cumulative antipsychotic dose, greater improvements in psychopathology and cognition, and more extrapyramidal symptoms. Basal ganglia volume increases were associated with greater improvements in psychopathology, greater increases in BMI and more extrapyramidal symptoms.

CONCLUSIONS

We provide evidence for plasticity in white matter and basal ganglia associated with antipsychotic treatment in schizophrenia, most likely linked to the dopamine blocking actions of these agents. Cortical changes may be more closely related to the neurodevelopmental, non-dopaminergic aspects of the illness.

The Hypothalamic-Pituitary-Gonadal Axis in Men with Schizophrenia

Schizophrenia is a severe mental disorder with a chronic, progressive course. The etiology of this condition is linked to the interactions of multiple genes and environmental factors. The earlier age of onset of schizophrenia, the higher frequency of negative symptoms in the clinical presentation, and the poorer response to antipsychotic treatment in men compared to women suggests the involvement of sex hormones in these processes. This article aims to draw attention to the possible relationship between testosterone and some clinical features in male schizophrenic patients and discuss the complex nature of these phenomena based on data from the literature. PubMed, Web of Science, and Google Scholar databases were searched to select the papers without limiting the time of the publications. Hormone levels in the body are regulated by many organs and systems, and take place through the neuroendocrine, hormonal, neural, and metabolic pathways. Sex hormones play an important role in the development and function of the organism. Besides their impact on secondary sex characteristics, they influence brain development and function, mood, and cognition. In men with schizophrenia, altered testosterone levels were noted. In many cases, evidence from available single studies gave contradictory results. However, it seems that the testosterone level in men affected by schizophrenia may differ depending on the phase of the disease, types of clinical symptoms, and administered therapy. The etiology of testosterone level disturbances may be very complex. Besides the impact of the illness (schizophrenia), stress, and antipsychotic drug-induced hyperprolactinemia, testosterone levels may be influenced by, i.a., obesity, substances of abuse (e.g., ethanol), or liver damage.

Canonical and Non-Canonical Antipsychotics' Dopamine-Related Mechanisms of Present and Next Generation Molecules: A Systematic Review on Translational Highlights for Treatment Response and Treatment-Resistant Schizophrenia

Schizophrenia is a severe psychiatric illness affecting almost 25 million people worldwide and is conceptualized as a disorder of synaptic plasticity and brain connectivity. Antipsychotics are the primary pharmacological treatment after more than sixty years after their introduction in therapy. Two findings hold true for all presently available antipsychotics. First, all antipsychotics occupy the dopamine D2 receptor (D2R) as an antagonist or partial agonist, even if with different affinity; second, D2R occupancy is the necessary and probably the sufficient mechanism for antipsychotic effect despite the complexity of antipsychotics' receptor profile. D2R occupancy is followed by coincident or divergent intracellular mechanisms, implying the contribution of cAMP regulation, β-arrestin recruitment, and phospholipase A activation, to quote some of the mechanisms considered canonical. However, in recent years, novel mechanisms related to dopamine function beyond or together with D2R occupancy have emerged. Among these potentially non-canonical mechanisms, the role of Na²⁺ channels at the dopamine at the presynaptic site, dopamine transporter (DAT) involvement as the main regulator of dopamine concentration at synaptic clefts, and the putative role of antipsychotics as chaperones for intracellular D2R sequestration, should be included. These mechanisms expand the fundamental role of dopamine in schizophrenia therapy and may have relevance to considering putatively new strategies for treatment-resistant schizophrenia (TRS), an extremely severe condition epidemiologically relevant and affecting almost 30% of schizophrenia patients. Here, we performed a critical evaluation of the role of antipsychotics in synaptic plasticity, focusing on their canonical and non-canonical mechanisms of action relevant to the treatment of schizophrenia and their subsequent implication for the pathophysiology and potential therapy of TRS.

Hyperprolactinaemia is common in Chinese premenopausal women with breast diseases

Purpose: Hyperprolactinaemia has been proposed to play a role in breast lesions pathophysiology. Thus far, controversial results have been reported for the relationship between hyperprolactinaemia and breast lesions. Moreover, the prevalence of hyperprolactinaemia in a population with breast lesions is scarcely reported. We aimed to investigate the prevalence of hyperprolactinaemia in Chinese premenopausal women with breast diseases, and explore the associations between hyperprolactinaemia with different clinical characteristics. Methods: This was a retrospective cross-sectional study performed in the department of breast surgery of Qilu hospital of Shandong University. Overall, 1,461 female patients who underwent the serum prolactin (PRL) level assay before breast surgery from January 2019 to December 2020 were included. Patients were divided into two groups: before and after menopause. Data were analyzed using SPSS 18.0 software. Results: The results showed an elevated PRL level in 376 of the 1,461 female patients with breast lesions (25.74%). Furthermore, the proportion of hyperprolactinemia among premenopausal patients with breast disease (35.75%, 340/951) was significantly higher than among postmenopausal patients with breast disease (7.06%, 36/510). In premenopausal patients, the proportion of patients with hyperprolactinaemia and the mean serum PRL level were significantly higher in those diagnosed with fibroepithelial tumours (FETs) and in younger patients (aged < 35 years) than in those with non-neoplastic lesions and in those aged ≥ 35 years (both p < 0.05). Especially, the prolactin level exhibited steady ascending tendency for positive correlation with FET. Conclusion: Hyperprolactinaemia is prevalent in Chinese premenopausal patients with breast diseases, especially in those with FETs, which implies a potential association, to some extent, between the PRL levels in various breast diseases.

Fluphenazine-Induced Neurotoxicity with Acute Almost Transient Parkinsonism and Permanent Memory Loss: Lessons from a Case Report

We report the singular case of a 31-year-old woman who developed very serious Fluphenazine-induced parkinsonism over a few days due to a doubly incongruent drug prescription by indication and dosage having been applied to a healthy subject over one week instead of seven months. Unlike gradual drug-induced parkinsonism, our patient experienced acute extrapyramidal syndrome (EPS), reaching significant motor and sphincter disability in just a few days, followed by a gradual incomplete recovery over more than six months. In fact, after drug discontinuation, hypomimia and slight left hemi-somatic rigidity with bradykinesia remained, as well as stable non-progressive memory disturbances. Despite bio-humoral and instrumental investigations and DaTScan were negative, MRI post-analysis evidenced a 6.5% loss in brain volume. Specifically, irreversible cortical and sub-cortical grey matter reduction and cerebrospinal fluid space enlargement with spared white matter were found. Our observations suggest that the sudden availability of Fluphenazine results in a kind of plateau effect of parkinsonism presentation, partially reversible due to the neurotoxic drug effect on the cortical and sub-cortical grey matter, resulting in asymmetric EPS and stable memory loss, respectively. Our report confirms the debated neurotoxicity of first-generation neuroleptics and the postulated theory of differential susceptibility to the cytotoxic stressors on the central nervous system.

Novel Multimodal Salicylamide Derivative with Antidepressant-like, Anxiolytic-like, Antipsychotic-like, and Anti-Amnesic Activity in Mice

Depression, anxiety, and schizophrenia may coexist in psychiatric patients. Moreover, these disorders are very often associated with cognitive impairments. However, pharmacotherapy of these conditions remains challenging due to limited drug effectiveness or numerous side effects. Therefore, there is an urgent need to develop novel multimodal compounds that can be used to treat depression, anxiety, and schizophrenia, as well as memory deficits. Thus, this study aimed to evaluate the potential antidepressant-like, anxiolytic-like, antipsychotic-like effects, and anti-amnesic properties, of the novel arylpiperazine derivative of salicylamide, JJGW07, with an affinity towards serotonin 5-HT1A, 5-HT2A, and 5-HT7 and dopamine D2 receptors. Firstly, we investigated the compound's affinity for 5-HT6 receptors and its functional activity by using in vitro assays. JJGW07 did not bind to 5-HT6 receptors and showed antagonistic properties for 5-HT1A, 5-HT2A, 5-HT7, and D2 receptors. Based on the receptor profile, we performed behavioral studies in mice to evaluate the antidepressant-like, anxiolytic-like, and antipsychotic-like activity of the tested compound using forced swim and tail suspension tests; four-plate, marble-burying, and elevated plus maze tests; and MK-801- and amphetamine-induced hyperlocomotion tests, respectively. JJGW07 revealed antidepressant-like properties in the tail suspension test, anxiolytic-like effects in the four-plate and marble-burying tests, and antipsychotic-like activity in the MK-801-induced hyperlocomotion test. Importantly, the tested compound did not induce catalepsy and motor impairments or influence locomotor activity in rodents. Finally, to assess the potential procognitive and anti-amnesic properties of JJGW07, we used passive avoidance and object recognition tests in mice. JJGW07 demonstrated positive effects on long-term emotional memory and also ameliorated MK-801-induced emotional memory impairments in mice, but showed no procognitive properties in the case of recognition memory. Our results encourage the search for new compounds among salicylamide derivatives, which could be model structures with multitarget mechanisms of action that could be used in psychiatric disorder therapy.

Identification and Characterization of ML321: A Novel and Highly Selective D2 Dopamine Receptor Antagonist with Efficacy in Animal Models That Predict Atypical Antipsychotic Activity

We have developed and characterized a novel D2R antagonist with exceptional GPCR selectivity - ML321. In functional profiling screens of 168 different GPCRs, ML321 showed little activity beyond potent inhibition of the D2R and to a lesser extent the D3R, demonstrating excellent receptor selectivity. The D2R selectivity of ML321 may be related to the fact that, unlike other monoaminergic ligands, ML321 lacks a positively charged amine group and adopts a unique binding pose within the orthosteric binding site of the D2R. PET imaging studies in non-human primates demonstrated that ML321 penetrates the CNS and occupies the D2R in a dose-dependent manner. Behavioral paradigms in rats demonstrate that ML321 can selectively antagonize a D2R-mediated response (hypothermia) while not affecting a D3R-mediated response (yawning) using the same dose of drug, thus indicating exceptional in vivo selectivity. We also investigated the effects of ML321 in animal models that are predictive of antipsychotic efficacy in humans. We found that ML321 attenuates both amphetamine- and phencyclidine-induced locomotor activity and restored pre-pulse inhibition (PPI) of acoustic startle in a dose-dependent manner. Surprisingly, using doses that were maximally effective in both the locomotor and PPI studies, ML321 was relatively ineffective in promoting catalepsy. Kinetic studies revealed that ML321 exhibits slow-on and fast-off receptor binding rates, similar to those observed with atypical antipsychotics with reduced extrapyramidal side effects. Taken together, these observations suggest that ML321, or a derivative thereof, may exhibit ″atypical″ antipsychotic activity in humans with significantly fewer side effects than observed with the currently FDA-approved D2R antagonists.

Histone deacetylase inhibitors mitigate antipsychotic risperidone-induced motor side effects in aged mice and in a mouse model of Alzheimer's disease

Antipsychotic drugs are still widely prescribed to control various severe neuropsychiatric symptoms in the elderly and dementia patients although they are off-label use in the United States. However, clinical practice shows greater side effects and lower efficacy of antipsychotics for this vulnerable population and the mechanisms surrounding this aged-related sensitivity are not well understood. Our previous studies have shown that aging-induced epigenetic alterations may be involved in the increasing severity of typical antipsychotic haloperidol induced side effects in aged mice. Still, it is unknown if similar epigenetic mechanisms extend to atypical antipsychotics, which are most often prescribed to dementia patients combined with severe neuropsychiatric symptoms. In this study, we report that atypical antipsychotic risperidone also causes increased motor side effect behaviors in aged mice and 5xFAD mice. Histone deacetylase (HDAC) inhibitor Valproic Acid and Entinostat can mitigate the risperidone induced motor side effects. We further showed besides D2R, reduced expression of 5-HT2A, one of the primary atypical antipsychotic targets in the striatum of aged mice that are also mitigated by HDAC inhibitors. Finally, we demonstrate that specific histone acetylation mark H3K27 is hypoacetylated at the 5htr2a and Drd2 promoters in aged mice and can be reversed with HDAC inhibitors. Our work here establishes evidence for a mechanism where aging reduces expression of 5-HT2A and D2R, the key atypical antipsychotic drug targets through epigenetic alteration. HDAC inhibitors can restore 5-HT2A and D2R expression in aged mice and decrease the motor side effects in aged and 5xFAD mice.

Recent advances in dopamine D2 receptor ligands in the treatment of neuropsychiatric disorders

Dopamine is a biologically active amine synthesized in the central and peripheral nervous system. This biogenic monoamine acts by activating five types of dopamine receptors (D_1-5 Rs), which belong to the G protein-coupled receptor family. Antagonists and partial agonists of D₂ Rs are used to treat schizophrenia, Parkinson's disease, depression, and anxiety. The typical pharmacophore with high D₂ R affinity comprises four main areas, namely aromatic moiety, cyclic amine, central linker and aromatic/heteroaromatic lipophilic fragment. From the literature reviewed herein, we can conclude that 4-(2,3-dichlorophenyl), 4-(2-methoxyphenyl)-, 4-(benzo[b]thiophen-4-yl)-1-substituted piperazine, and 4-(6-fluorobenzo[d]isoxazol-3-yl)piperidine moieties are critical for high D₂ R affinity. Four to six atoms chains are optimal for D₂ R affinity with 4-butoxyl as the most pronounced one. The bicyclic aromatic/heteroaromatic systems are most frequently occurring as lipophilic appendages to retain high D₂ R affinity. In this review, we provide a thorough overview of the therapeutic potential of D₂ R modulators in the treatment of the aforementioned disorders. In addition, this review summarizes current knowledge about these diseases, with a focus on the dopaminergic pathway underlying these pathologies. Major attention is paid to the structure, function, and pharmacology of novel D₂ R ligands, which have been developed in the last decade (2010-2021), and belong to the 1,4-disubstituted aromatic cyclic amine group. Due to the abundance of data, allosteric D₂ R ligands and D₂ R modulators from patents are not discussed in this review.

Risk factors, clinical correlates, and social functions of Chinese schizophrenia patients with drug-induced parkinsonism: A cross-sectional analysis of a multicenter, observational, real-world, prospective cohort study

Background: Drug-induced parkinsonism (DIP) is the most prevalent neurological side effect of antipsychotics in the Chinese population. Early prevention, recognition, and treatment of DIP are important for the improvement of treatment outcomes and medication adherence of schizophrenia patients. However, the risk factors of DIP and the impact on the clinical syndromes of schizophrenia remain unknown. Aim: The goal of this study was to explore the risk factors, clinical correlates, and social functions of DIP in Chinese schizophrenia patients. Methods: A cross-sectional analysis of a multicenter, observational, real-world, prospective cohort study of the Chinese schizophrenia population with a baseline assessment was conducted from the year 2012 to 2018. Participants were recruited from four mental health centers in Shanghai and totaled 969 subjects. Sociodemographic data, drug treatment, and clinical variables were compared between the DIP group and the non-DIP group. Variables that correlated with the induction of DIP, and with p≤ 0.1, were included in the binary logistic model for analyzing the risk factors of DIP. First generation antipsychotics (FGA)/second generation antipsychotics (SGA) model and high and low/medium D2 receptor antipsychotics were analyzed respectively to control the bias of co-linearity. All risk factors derived from the a forementioned models and clinical variables with p≤ 0.1 were included in the multivariate analysis of clinical correlates and social function of DIP patients. The Positive and Negative Syndrome Scale (PANSS) model and the personal and social performance (PSP) model were analyzed separately to control for co-linearity bias. Results: Age (OR = 1.03, p< 0.001), high D2 receptor antagonist antipsychotic dose (OR = 1.08, p = 0.032), and valproate dose (OR = 1.01, p = 0.001) were the risk factors of DIP. FGA doses were not a significant contributor to the induction of DIP. Psychiatric symptoms, including more severe negative symptoms (OR = 1.09, p< 0.001), lower cognition status (OR = 1.08, p = 0.033), and lower excited symptoms (OR = 0.91, p = 0.002), were significantly correlated with DIP induction. Social dysfunction, including reduction in socially useful activities (OR = 1.27, p = 0.004), lower self-care capabilities (OR = 1.53, p< 0.001), and milder disturbing and aggressive behavior (OR = 0.65, p< 0.001), were significantly correlated with induction of DIP. Valproate dose was significantly correlated with social dysfunction (OR = 1.01, p = 0.001) and psychiatric symptoms (OR = 1.01, p = 0.004) of DIP patients. Age may be a profound factor that affects not only the induction of DIP but also the severity of psychiatric symptoms (OR = 1.02, p< 0.001) and social functions (OR = 1.02, p< 0.001) of schizophrenia patients with DIP. Conclusion: Age, high D2 receptor antagonist antipsychotic dose, and valproate dose are risk factors for DIP, and DIP is significantly correlated with psychiatric symptoms and social performance of Chinese schizophrenia patients. The rational application or discontinuation of valproate is necessary. Old age is related to psychotic symptoms and social adaption in Chinese schizophrenic patients, and early intervention and treatment of DIP can improve the prognosis and social performance of schizophrenia patients. Clinical Trial Registration: Identifier: NCT02640911.

Non-alcoholic fatty liver disease (NAFLD) and mental illness: Mechanisms linking mood, metabolism and medicines

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease in the world and one of the leading indications for liver transplantation. It is one of the many manifestations of insulin resistance and metabolic syndrome as well as an independent risk factor for cardiovascular disease. There is growing evidence linking the incidence of NAFLD with psychiatric illnesses such as schizophrenia, bipolar disorder and depression mechanistically via genetic, metabolic, inflammatory and environmental factors including smoking and psychiatric medications. Indeed, patients prescribed antipsychotic medications, regardless of diagnosis, have higher incidence of NAFLD than population norms. The mechanistic pharmacology of antipsychotic-associated NAFLD is beginning to emerge. In this review, we aim to discuss the pathophysiology of NAFLD including its risk factors, insulin resistance and systemic inflammation as well as its intersection with psychiatric illnesses.

The Impact of Antipsychotic Treatment on Neurological Soft Signs in Patients with Predominantly Negative Symptoms of Schizophrenia

Schizophrenia is a complex and incompletely elucidated pathology that affects sensorimotor function and also produces numerous therapeutic challenges. The aims of this cross-sectional study were to identify the profile of neurological soft signs (NSS) in patients with predominantly negative symptoms of schizophrenia (PNS) compared with patients with schizophrenia who do not present a predominance of negative symptoms (NPNS) and also to objectify the impact of treatment on the neurological function of these patients. Ninety-nine (n = 99; 56 females and 43 males) patients diagnosed with schizophrenia according to DSM-V were included; these patients were undergoing antipsychotic (4 typical antipsychotics, 86 atypical antipsychotics, and 9 combinations of two atypical antipsychotics) or anticholinergic treatment (24 out of 99) at the time of evaluation, and the PANSS was used to identify the patients with predominantly negative symptoms (n = 39), the Neurological Evaluation Scale (NES) was used for the evaluation of neurological soft signs (NSS), and the SAS was used for the objectification of the extrapyramidal side effects induced by the neuroleptic treatment, which was converted to chlorpromazine equivalents (CPZE). The study's main finding was that, although the daily dose of CPZE did not represent a statistically significant variable, in terms of neurological soft signs, patients with PNS had higher rates of NSS.

Phenothiazines and their Evolving Roles in Clinical Practice: A Narrative Review

Phenothiazines, a diverse class of drugs, can be used to treat multiple mental health and physical conditions. Phenothiazines have been used for decades to treat mental illnesses, including schizophrenia, mania in bipolar disorder, and psychosis. Additionally, these drugs offer relief for physical illnesses, including migraines, hiccups, nausea, and vomiting in both adults and children. Further research is needed to prove the efficacy of phenothiazines in treating physical symptoms. Phenothiazines are dopaminergic antagonists that inhibit D2 receptors with varying potency. High potency phenothiazines such as perphenazine are used to treat various psychiatric conditions such as the positive symptoms of schizophrenia, the symptoms of psychosis, and mania that can occur with bipolar disorder. Low/mid potency phenothiazines such as chlorpromazine antipsychotic drugs that have been used to treat schizophrenia and schizophrenia-like disorders since the 1950s and are utilized in numerous disease states. The present investigation aims to elucidate the effects of phenothiazines in clinical practice.

Development of fluorescent peptide G protein-coupled receptor activation biosensors for NanoBRET characterization of intracellular allosteric modulators

G protein-coupled receptors (GPCRs) are widely therapeutically targeted, and recent advances in allosteric modulator development at these receptors offer further potential for exploitation. Intracellular allosteric modulators (IAM) represent a class of ligands that bind to the receptor-effector interface (e.g., G protein) and inhibit agonist responses noncompetitively. This potentially offers greater selectivity between receptor subtypes compared to classical orthosteric ligands. However, while examples of IAM ligands are well described, a more general methodology for assessing compound interactions at the IAM site is lacking. Here, fluorescent labeled peptides based on the Gα peptide C terminus are developed as novel binding and activation biosensors for the GPCR-IAM site. In TR-FRET binding studies, unlabeled peptides derived from the Gαs subunit were first characterized for their ability to positively modulate agonist affinity at the β₂ -adrenoceptor. On this basis, a tetramethylrhodamine (TMR) labeled tracer was synthesized based on the 19 amino acid Gαs peptide (TMR-Gαs19cha18, where cha = cyclohexylalanine). Using NanoBRET technology to detect binding, TMR-Gαs19cha18 was recruited to Gs coupled β₂ -adrenoceptor and EP₂ receptors in an agonist-dependent manner, but not the Gi-coupled CXCR2 receptor. Moreover, NanoBRET competition binding assays using TMR-Gαs19cha18 enabled direct assessment of the affinity of unlabeled ligands for β₂ -adrenoceptor IAM site. Thus, the NanoBRET platform using fluorescent-labeled G protein peptide mimetics offers novel potential for medium-throughput screens to identify IAMs, applicable across GPCRs coupled to a G protein class. Using the same platform, Gs peptide biosensors also represent useful tools to probe orthosteric agonist efficacy and the dynamics of receptor activation.