A randomized, double-blind, placebo controlled, phase 1 study of the safety, tolerability, pharmacokinetics, and pharmacodynamics of LB-102, a selective dopamine D2/3/5-HT7 inhibitor

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

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

Negative Symptoms in Schizophrenia: An Update on Research Assessment and the Current and Upcoming Treatment Landscape

The negative symptoms of schizophrenia include diminished emotional expression, avolition, alogia, anhedonia, and asociality, and due to their low responsiveness to available treatments, are a primary driver of functional disability in schizophrenia. This narrative review has the aim of providing a comprehensive overview of the current research developments in the treatment of negative symptoms in schizophrenia, and begins by introducing the concepts of primary, secondary, prominent, predominant, and broadly defined negative symptoms. We then compare and contrast commonly used research assessment scales for negative symptoms and review the evidence for the specific utility of widely available off-label and investigational treatments that have been studied for negative symptoms. Mechanism of action/putative treatments included are antipsychotics (D2R antagonists), N-methyl-D-aspartate receptor (NMDAR) and other glutamatergic modulators, serotonin receptor (5-HTR) modulators, anti-inflammatory agents, antidepressants, pro-dopaminergic modulators (non-D2R antagonists), acetylcholine modulators, oxytocin, and phosphodiesterase (PDE) inhibitors. With the caveat that no compounds are definitively proven as gold-standard treatments for broadly defined negative symptoms, the evidence base supports several potentially beneficial off-label and investigational medications for treating negative symptoms in schizophrenia, such as monotherapy with cariprazine, olanzapine, clozapine, and amisulpride, or adjunctive use of memantine, setrons such as ondansetron, minocycline, and antidepressants. These medications are widely available worldwide, generally tolerable and could be considered for an off-label, time-limited trial for a predesignated period of time, after which a decision to switch or stay can be made based on clinical response. Among investigational medications, NMDAR agonists, muscarinic agonists, and LB-102 remain under study. Suggestions for future research include reducing placebo effects by designing studies with a smaller number of high-quality study sites, potentially increasing the use of more precise rating scales for negative symptoms, and focused studies in people with predominant negative symptoms.

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

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

PET clinical study of novel antipsychotic LB-102 demonstrates unexpectedly prolonged dopamine receptor target engagement

Regulation of dopamine activity has important clinical consequences, most notably in schizophrenia. LB-102, N-methyl amisulpride, is a novel dopamine D2/3/5-HT7 inhibitor being developed as a treatment for schizophrenia and other psychiatric disorders. The characteristic that is common to all current antipsychotics is their engagement of D2 dopamine receptors. The goal of this study was to measure the dopamine receptor occupancy of orally administered LB-102 at three different doses (50, 75, and 100 mg as single doses and 50 and 100 mg as multiple doses) and at different timepoints in healthy volunteers using positron emission tomography (PET) with 11C raclopride as a radiotracer. Results of this study (NCT04588129) showed that steady-state once daily oral dosing of 50 mg LB-102 afforded striatal dopamine occupancy (RO) in the desired 60-80% range consistently over the course of 24 h. Contrary to the often observed relationship between RO vs plasma concentrations, maximum dopamine RO significantly lagged maximum plasma concentration and showed little variability under steady state conditions. A similar phenomenon has recently been reported with a non-racemic version of amisulpride [1]. LB-102 was generally safe and well-tolerated at all doses. Results of this study were used to inform dosing in a subsequent Phase 2 clinical study in schizophrenia patients.

Examination of the mechanisms underlying the discriminative stimulus properties of the atypical antipsychotic amisulpride

Amisulpride is an atypical benzamide antipsychotic/antidepressant, whose mechanism of action is thought to depend mainly on dopamine D2/3 receptor activity, but also with some serotonin 5-HT2B/7 effects. The present study examined the role of D2/3 receptors and 5-HT2B/7 receptors in amisulpride's discriminative stimulus. Selective agonists and antagonists of the above receptors were tested in adult, male C57BL/6 mice trained to discriminate 10 mg/kg amisulpride from vehicle in a two-lever drug discrimination assay. After acquisition of the two-lever discrimination, the amisulpride generalization curve yielded an ED50 = 0.56 mg/kg (95% CI = 0.42-0.76 mg/kg). Substitution tests found that the D2/3 antagonist raclopride (62.7% Drug Lever Responding), D2/3 agonist quinpirole (56.6% DLR), 5-HT7 agonist LP-44 (50.1% DLR) and 5-HT7 antagonist SB-269970 (36.7% DLR) produced various degrees of partial substitution for the amisulpride stimulus, whereas the 5-HT2B agonist BW 723C86 (17.9% DLR) and 5-HT2B antagonist SB-204741 (21.1% DLR) yielded negligible amisulpride-like effects. In combination tests with amisulpride, quinpirole decreased percent responding from 98.3% to 57.0% DLR, LP-44 decreased percent responding from 97.6% to 76.7% DLR, and BW 723C86 reduced percent responding from 95.66% to 74.11% DLR. Taken together, the results from stimulus generalization and antagonism studies suggest that amisulpride has a complex discriminative cue that involves mainly mixed D2/3 receptor antagonist/agonist effects and, to a lesser degree, mixed 5-HT7 receptor agonist/antagonist and perhaps 5-HT2B receptor antagonist effects.

A narrative review of non-racemic amisulpride (SEP-4199) for treatment of depressive symptoms in bipolar disorder and LB-102 for treatment of schizophrenia

INTRODUCTION

The challenges posed by treatment-resistant schizophrenia and depressive symptoms have led to ongoing difficulties despite the availability of antipsychotics and antidepressants. This review addresses the potential of amisulpride analogs, particularly SEP-4199, in addressing these challenges through enhanced efficacy and reduced side effects.

AREAS COVERED

This review focuses on the pharmacological profile of amisulpride analogs, exemplified by LB-102 and its derivative SEP-4199. PubMed gathered articles (up to 10 March 2023) on 'amisulpride,' 'schizophrenia,' 'bipolar disorder,' and 'major depressive disorder;' ClinicalTrials.gov tracked SEP-4199 and LB-102 trials. LB-102, a newly identified N-methylated analog of amisulpride, exhibits enhanced lipophilicity at lower doses, as demonstrated in a phase 1 study, indicating significant promise for therapeutic applications. The discovery of SEP-4199, a non-racemic analog composed of R- and S-enantiomers in an 85:15 ratio, is discussed, emphasizing its potential to enhance antidepressant effects while minimizing extrapyramidal side effects via selective D2 receptor binding. Recent phase 2 trials have demonstrated SEP-4199's efficacy in treating depressive symptoms in bipolar disorder I, capitalizing on D2-mediated anti-anhedonic and D3-mediated reward effects.

EXPERT OPINION

The development of SEP-4199 presents a potential breakthrough for managing depressive symptoms in bipolar disorder I. Further exploration of D2 and D3 receptor-mediated effects could lead to improved treatment strategies.