Main Research Findings

1) Usmarapride was found to have disease modifying potential and may act as a promising therapeutic intervention for alleviating cognitive dysfunctional related to Alzheimer’s disease.

2) Treatment with a 5-HT4 receptor agonist such as usmarapride was shown to be a potential treatment for memory dysfunction in patients with major depressive disorder.

Selected Data
1) The study performed by the research team of Nirogi et al evaluated the behavioral, neurochemical, and pharmacological profile of usmarapride (SUVN-D4010), a selective 5-HT4 receptor partial agonist, to determine its therapeutic potential for the treatment of Alzheimer’s disease. A series of complementary in vivo behavioral experiments, neurochemical analyses, pharmacological validation studies, and biochemical assays were performed to assess the compound’s effects on multiple domains of cognition, cholinergic neurotransmission, and amyloid precursor protein processing. Adult Wistar rats, Swiss mice, and C57BL/6J mice were housed under controlled environmental conditions with unrestricted access to food and water. Usmarapride was synthesized in-house, while comparator compounds including scopolamine, MK-801, donepezil, and the selective 5-HT4 receptor antagonist GR-125487 were obtained from commercial or institutional sources [1].
To evaluate episodic memory, the investigators employed the object recognition task (ORT) under several experimental conditions. Animals underwent habituation followed by familiarization with two identical objects before being challenged with either a delayed retention interval or pharmacologically induced cognitive impairment using scopolamine or MK-801. During the choice trial, one familiar object was replaced with a novel object, and the amount of time spent exploring each object was recorded. A discrimination index was calculated to quantify recognition memory performance. Additional experiments examined whether pretreatment with the selective 5-HT4 receptor antagonist GR-125487 blocked the cognitive effects of usmarapride, thereby confirming receptor specificity. Separate ORT studies also evaluated whether co-administration of low-dose usmarapride with donepezil enhanced cognitive performance beyond either treatment alone [1].
Working memory was assessed using the radial arm maze (RAM). Rats were habituated to an eight-arm maze over several days before undergoing testing under scopolamine-induced cognitive impairment. Food pellets were placed at the ends of each arm, and animals were allowed to retrieve rewards while investigators recorded repeated arm entries and omissions. Percentage choice accuracy was calculated from the number of correct arm selections relative to total entries, providing an objective measure of short-term spatial working memory. Usmarapride was administered orally before scopolamine treatment to determine its ability to reverse cholinergic-dependent working memory deficits.
The investigators next examined social recognition memory using the social recognition task (SRT). Adult male rats were exposed to juvenile conspecifics during an initial learning session followed by a second trial after either a 24-hour delay or a brief interval combined with scopolamine administration. During the testing session, animals encountered both the previously familiar juvenile and a novel juvenile, and investigators measured the duration of social investigation directed toward each animal. A discrimination index quantified preference for the novel juvenile. Additional experiments evaluated combination therapy with donepezil and determined whether usmarapride enhanced existing cholinergic treatment. Emotional and associative memory were assessed using the fear conditioning response (FCR) model. Rats received paired tone-foot shock conditioning followed by scopolamine administration, and freezing behavior during later testing without shock served as an indicator of learned associative memory.
To investigate the neurochemical mechanisms underlying the behavioral effects, the researchers measured extracellular acetylcholine concentrations within the frontal cortex using in vivo microdialysis. Guide cannulas were stereotaxically implanted into the frontal cortex of anesthetized rats, after which microdialysis probes continuously perfused artificial cerebrospinal fluid. Baseline dialysate samples were collected before administration of vehicle or usmarapride, followed by serial sample collection for up to four hours after treatment. Acetylcholine concentrations were quantified using tandem mass spectrometry, and area-under-the-curve analyses were performed to assess overall neurotransmitter release. Additional experiments incorporated pretreatment with GR-125487 to determine whether changes in acetylcholine release were mediated specifically through 5-HT4 receptor activation [1].
Finally, the investigators evaluated the potential disease-modifying effects of usmarapride by measuring soluble amyloid precursor protein-alpha (sAPP-α), a product of non-amyloidogenic APP processing associated with neuroprotection. C57BL/6J mice received acute administration of vehicle or usmarapride before sacrifice at predetermined time points. Frontal cortex tissue was isolated, homogenized, and processed for enzyme-linked immunosorbent assay (ELISA) to quantify sAPP-α concentrations. Collectively, these integrated behavioral paradigms, pharmacological validation studies, neurochemical measurements, and biochemical assays provided a comprehensive assessment of the cognitive-enhancing and potential disease-modifying properties of usmarapride in preclinical models of Alzheimer’s disease [1].
2) The study conducted by the research team of Köhler-Forsberg et al used a case-control design to investigate whether cerebral serotonin 4 (5-HT4) receptor binding differs between individuals with untreated major depressive disorder (MDD) and healthy controls, while also determining whether receptor binding is associated with cognitive dysfunction, particularly verbal memory impairment. The investigation included antidepressant-free outpatients experiencing a current moderate-to-severe depressive episode and an age- and sex-matched healthy control group. The primary objective was to compare in vivo cerebral 5-HT4 receptor binding between groups, whereas secondary objectives examined the relationship between receptor availability and multiple cognitive domains within the patient cohort [2].
Initially, 100 patients with MDD were enrolled, although complete positron emission tomography (PET) imaging data were available for 90 participants, who ultimately comprised the patient cohort. Eligible patients were between 18 and 60 years of age and met diagnostic criteria for moderate-to-severe major depressive disorder, defined by a score greater than 17 on the 17-item Hamilton Depression Rating Scale (HAMD-17). Diagnoses were established using the Mini-International Neuropsychiatric Interview and confirmed by a psychiatrist according to the International Classification of Diseases, Tenth Revision. Exclusion criteria included recent antidepressant treatment, previous failure of selective serotonin reuptake inhibitor therapy during the current episode, ongoing psychotherapy, psychotic disorders, significant neurological disease, substance abuse, severe medical illness, pregnancy, contraindications to magnetic resonance imaging (MRI) or PET, and medications known to influence central nervous system function. Ninety-one healthy control participants without a history of psychiatric illness were recruited using the same inclusion and exclusion criteria, with the exception of the absence of depression or other mental illness [2].
All participants underwent high-resolution PET imaging using the selective 5-HT4 receptor radioligand [¹¹C]SB207145 to quantify cerebral serotonin 4 receptor availability. PET data were collected during a 120-minute dynamic acquisition following intravenous administration of the radiotracer. Structural MRI scans were also obtained using 3-Tesla scanners to provide anatomical reference for PET image registration and region-of-interest analysis. PET images underwent motion correction before automatic delineation of brain regions using MRI-based probability maps. Binding potential (BPND) values were calculated using the Simplified Reference Tissue Model with cerebellar gray matter, excluding the vermis, serving as the reference region. In addition to region-based analyses of the neocortex, hippocampus, caudate nucleus, and putamen, exploratory whole-brain voxel- and vertex-based analyses were performed using surface-based PET processing methods to identify localized differences in receptor binding across cortical and subcortical structures.
Only participants with MDD completed an extensive cognitive assessment battery designed to evaluate domains commonly affected in depression. Verbal memory, the primary cognitive outcome, was measured using the 26-item Verbal Affective Memory Test. Secondary assessments included working memory using the Letter-Number Sequencing task from the Wechsler Adult Intelligence Scale, psychomotor speed using a Simple Reaction Time task, emotional processing using the EMOTICOM Emotional Recognition Task, and negative social emotions using the EMOTICOM Moral Emotions Task. These standardized neuropsychological measures allowed investigators to determine whether cerebral 5-HT4 receptor availability was associated with specific cognitive impairments observed during an active depressive episode [2].
Statistical analyses were designed to evaluate both global and regional receptor binding while accounting for multiple interrelated brain measurements. Latent variable models (LVMs) were constructed to generate a global estimate of cerebral 5-HT4 receptor binding based on shared variance across the neocortex, hippocampus, caudate, and putamen. Group comparisons between patients and healthy controls were performed using these latent constructs, while additional models examined relationships between receptor binding and individual cognitive measures within the MDD group. Covariates included age, sex, serotonin transporter genotype (5-HTTLPR), injected radiotracer mass, and MRI scanner type when appropriate.
Post hoc analyses further adjusted for education level, depression severity, and anxiety symptoms to determine whether these factors influenced the observed associations. Exploratory voxel-wise and vertex-wise analyses were performed using permutation testing with correction for multiple comparisons to identify significant regional differences in receptor binding throughout the brain. This comprehensive combination of advanced molecular neuroimaging, structural MRI, standardized cognitive testing, and multilevel statistical modeling enabled investigators to characterize the relationship between cerebral 5-HT4 receptor availability and cognitive dysfunction in untreated major depressive disorder [2].

Discussion

1) The study conducted by Nirogi et al demonstrated that usmarapride (SUVN-D4010) produced robust procognitive effects across multiple behavioral models that assessed episodic, working, social, and emotional memory while simultaneously enhancing cholinergic neurotransmission and promoting non-amyloidogenic processing of amyloid precursor protein. Across nearly all behavioral paradigms, usmarapride consistently improved cognitive performance in both naturally induced memory deficits and pharmacologically impaired models, supporting its potential as both a symptomatic cognitive enhancer and a disease-modifying therapeutic candidate for Alzheimer’s disease. Importantly, many of these effects occurred over a broad dose range and were shown to depend specifically on activation of 5-HT4 receptors through antagonist validation experiments [1].
In the ORT, usmarapride significantly improved episodic memory under multiple experimental conditions. In animals challenged with a 24-hour retention interval, vehicle-treated rats failed to distinguish between familiar and novel objects, demonstrating normal forgetting. In contrast, rats treated with usmarapride at doses ranging from 0.3 to 10 mg/kg spent significantly more time exploring the novel object, indicating successful retention of object memory. Correspondingly, discriminative index values increased significantly, particularly at doses of 1 and 10 mg/kg. Similar improvements were observed in pharmacologically impaired animals. Both scopolamine- and MK-801-treated rats exhibited marked deficits in object recognition, but usmarapride dose-dependently restored recognition memory by increasing exploration of the novel object and improving discrimination indices. The receptor specificity of these effects was confirmed by pretreatment with the selective 5-HT4 receptor antagonist GR-125487, which abolished the memory-enhancing actions of usmarapride. These findings demonstrated that the compound’s procognitive effects were mediated directly through activation of 5-HT4 receptors rather than nonspecific behavioral stimulation [1].

Figure 1: Changes in A) exploration times and B) discrimination index as a measure of time-induced episodic memory deficits in response to treatment with experimental compounds
Combination studies further demonstrated that usmarapride potentiated the cognitive effects of donepezil, the current standard treatment for Alzheimer’s disease. When administered individually at low doses, neither donepezil nor usmarapride significantly improved episodic memory. However, combined treatment produced significantly greater discrimination between familiar and novel objects and yielded higher discrimination index scores than either drug alone. Similar synergistic effects were observed in the SRT, where combined treatment significantly enhanced recognition of novel juvenile animals compared with either monotherapy. These findings suggest that usmarapride may augment existing cholinergic therapies and potentially permit lower therapeutic doses of acetylcholinesterase inhibitors while maintaining cognitive efficacy.
Usmarapride also produced significant improvements in additional domains of cognition. In the radial arm maze, scopolamine markedly impaired working memory by increasing repeated arm entries and reducing percentage choice accuracy. Treatment with usmarapride significantly reversed these deficits at all tested doses, with the greatest improvements observed at 1 and 3 mg/kg. In the social recognition task, both naturally induced time-delay deficits and scopolamine-induced impairments were significantly attenuated by usmarapride, as treated animals consistently spent more time investigating unfamiliar juvenile rats than familiar ones. Discrimination indices increased significantly across multiple doses, demonstrating preservation of social recognition memory. Likewise, in the fear conditioning response model, scopolamine substantially reduced freezing behavior, indicating impaired associative and emotional memory. Usmarapride dose-dependently restored freezing responses toward normal levels, demonstrating improved retention of conditioned fear memory and suggesting efficacy across multiple cognitive domains that are commonly disrupted during Alzheimer’s disease progression [1].
Neurochemical analyses provided mechanistic support for the observed behavioral improvements. In vivo microdialysis demonstrated that usmarapride significantly increased extracellular acetylcholine concentrations within the frontal cortex at doses of 3 and 10 mg/kg. Area-under-the-curve analyses confirmed sustained elevations in acetylcholine release throughout the sampling period. Pretreatment with GR-125487 completely prevented these increases, demonstrating that enhancement of cholinergic neurotransmission resulted specifically from 5-HT4 receptor activation. Because cortical acetylcholine plays a critical role in attention, learning, and memory, these findings provide a neurochemical explanation for the widespread cognitive improvements observed throughout the behavioral studies.
Finally, usmarapride demonstrated evidence of potential disease-modifying activity by significantly increasing sAPP-α concentrations in the frontal cortex. Acute administration of usmarapride produced significant elevations in sAPP-α at both 3 and 10 mg/kg, although the timing of peak responses differed between doses. Since sAPP-α is generated through the non-amyloidogenic processing pathway of amyloid precursor protein and possesses well-established neuroprotective, neurotrophic, and synaptic plasticity-promoting properties, its elevation suggests that usmarapride may shift APP metabolism away from the production of neurotoxic amyloid-β peptides. Collectively, the behavioral, neurochemical, and biochemical findings demonstrate that usmarapride consistently enhances multiple forms of learning and memory through selective 5-HT4 receptor activation, increases cortical acetylcholine release, potentiates the therapeutic effects of donepezil, and promotes neuroprotective APP processing. These combined actions support the compound’s potential to provide both symptomatic cognitive improvement and disease-modifying benefits in Alzheimer’s disease and justify continued clinical development [1].
2) The study by researchers Köhler-Forsberg et al found that individuals with untreated MDD exhibited significantly reduced cerebral 5-HT4 receptor binding compared with healthy control participants, while lower receptor availability was also associated with poorer memory performance among patients. A total of 90 antidepressant-free patients with MDD and 91 healthy controls were included in the final analyses. Although the two groups were well matched for age and sex, patients demonstrated significant impairments across multiple cognitive domains when compared with a separate healthy normative sample. Deficits were observed in verbal memory, working memory, psychomotor speed, emotion recognition, and negative social emotional processing, confirming that untreated depression is accompanied by broad cognitive dysfunction in addition to affective symptoms. Importantly, no significant differences were found in cerebellar tracer uptake between groups, indicating that the observed differences reflected alterations in receptor binding rather than variations in radiotracer delivery or nonspecific uptake [2].
The primary analysis demonstrated a significant reduction in global cerebral 5-HT4 receptor binding among patients with MDD. Latent variable modeling showed that patients exhibited approximately 7% lower receptor binding than healthy controls, with an overall reduction of −7.0%. Regional analyses revealed remarkably consistent findings across all major brain regions examined. Compared with healthy controls, receptor binding was reduced by approximately 7.0% in the neocortex, 7.6% in the hippocampus, 6.2% in the caudate nucleus, and 6.1% in the putamen, with each regional comparison remaining statistically significant after correction for multiple testing. Sensitivity analyses using conventional linear regression produced results nearly identical to those obtained with latent variable modeling, demonstrating the robustness of the findings. These results indicate that reduced 5-HT4 receptor availability represents a widespread neurobiological characteristic of untreated major depressive disorder rather than an isolated abnormality within a single brain region [2].
Exploratory whole-brain analyses further demonstrated that reductions in receptor binding were concentrated primarily within cortical regions involved in emotional regulation and higher cognitive processing. Vertex- and voxel-based imaging analyses identified significantly lower 5-HT4 receptor binding throughout extensive areas of the prefrontal cortex, temporal cortex, parietal cortex, occipital cortex, and isthmus of the cingulate cortex. Additional reductions were observed in the precuneus and precentral gyrus, while no significant differences were detected within subcortical structures beyond those identified in the predefined regional analyses. These imaging findings suggest that depression is associated with widespread cortical alterations in serotonergic signaling, particularly within frontolimbic networks known to support executive functioning, emotional regulation, learning, and memory.
Within the MDD group, investigators next examined whether cerebral 5-HT4 receptor availability was related to symptom severity or cognitive performance. No significant relationship was observed between global receptor binding and depression severity measured using the 17-item Hamilton Depression Rating Scale, indicating that receptor availability was not simply a marker of current depressive symptom intensity. In contrast, a significant positive association was identified between global 5-HT4 receptor binding and verbal memory performance. Patients with higher receptor binding consistently performed better on the Verbal Affective Memory Test, whereas individuals with lower receptor availability exhibited greater impairment in memory function. This association remained significant even after adjusting for education level, depression severity, and anxiety symptoms, demonstrating that the relationship between receptor binding and memory performance was independent of these potential confounding factors [2].
Associations between 5-HT4 receptor binding and other cognitive domains were substantially weaker. Working memory demonstrated a modest positive correlation with receptor binding, but this relationship did not remain significant after correction for multiple comparisons. Likewise, no statistically significant associations were identified between receptor binding and reaction time, emotional recognition bias, or negative social emotions such as guilt and shame. These findings indicate that although cognitive dysfunction in depression affects several domains, alterations in cerebral 5-HT4 receptor availability appear to be most closely linked with verbal learning and memory rather than broader aspects of executive function, emotional processing, or psychomotor performance.
Collectively, the findings demonstrate that untreated major depressive disorder is characterized by a widespread reduction in cerebral serotonin 5-HT4 receptor binding, particularly throughout cortical regions involved in cognition and emotional regulation. While receptor availability was unrelated to the severity of depressive symptoms, lower 5-HT4 receptor binding was consistently associated with poorer verbal memory performance, suggesting that serotonergic dysfunction contributes specifically to the cognitive disturbances frequently observed in depression. These results support the hypothesis that the 5-HT4 receptor represents a promising therapeutic target for addressing cognitive symptoms in major depressive disorder, particularly memory impairment, and provide clinical evidence supporting continued investigation of selective 5-HT4 receptor agonists as novel treatments capable of improving both neurobiological function and cognitive outcomes in affected patients [2].

Disclaimer

**LAB USE ONLY**
*This information is for educational purposes only and does not constitute medical advice. THE PRODUCTS DESCRIBED HEREIN ARE FOR RESEARCH USE ONLY. All clinical research must be conducted with oversight from the appropriate Institutional Review Board (IRB). All preclinical research must be conducted with oversight from the appropriate Institutional Animal Care and Use Committee (IACUC) following the guidelines of the Animal Welfare Act (AWA).

Citations

[1] Nirogi R, Grandhi VR, Medapati R, et al. Usmarapride (SUVN-D4010), a 5-HT4 receptor partial agonist for the potential treatment of Alzheimer’s disease: Behavioural, neurochemical and pharmacological profiling. Eur J Pharmacol. 2023;947:175625. doi:10.1016/j.ejphar.2023.175625

[2] Köhler-Forsberg K, Dam VH, Ozenne B, et al. Serotonin 4 Receptor Brain Binding in Major Depressive Disorder and Association With Memory Dysfunction. JAMA Psychiatry. 2023;80(4):296-304. doi:10.1001/jamapsychiatry.2022.4539

Usmarapride Oxalate is sold for laboratory research use only. Terms of sale apply. Not for human consumption, nor medical, veterinary, or household uses. Please familiarize yourself with our Terms & Conditions prior to ordering.