Therapeutic Potential of Selectively Targeting the α _2C-Adrenoceptor in Cognition, Depression, and Schizophrenia—New Developments and Future Perspective

摘要

α_(2A)- and α_(2C)-adrenoceptors (ARs) are the primary α_(2)-AR subtypes involved in central nervous system (CNS) function. These receptors are implicated in the pathophysiology of psychiatric illness, particularly those associated with affective, psychotic, and cognitive symptoms. Indeed, non-selective α_(2)-AR blockade is proposed to contribute toward antidepressant (e.g., mirtazapine) and atypical antipsychotic (e.g., clozapine) drug action. Both α_(2C)- and α_(2A)-AR share autoreceptor functions to exert negative feedback control on noradrenaline (NA) release, with α_(2C)-AR heteroreceptors regulating non-noradrenergic transmission (e.g., serotonin, dopamine). While the α_(2A)-AR is widely distributed throughout the CNS, α_(2C)-AR expression is more restricted, suggesting the possibility of significant differences in how these two receptor subtypes modulate regional neurotransmission. However, the α_(2C)-AR plays a more prominent role during states of low endogenous NA activity, while the α_(2A)-AR is relatively more engaged during states of high noradrenergic tone. Although augmentation of conventional antidepressant and antipsychotic therapy with non-selective α_(2)-AR antagonists may improve therapeutic outcome, animal studies report distinct yet often opposing roles for the α_(2A)- and α_(2C)-ARs on behavioral markers of mood and cognition, implying that non-selective α_(2)-AR antagonism may compromise therapeutic utility both in terms of efficacy and side-effect liability. Recently, several highly selective α_(2C)-AR antagonists have been identified that have allowed deeper investigation into the function and utility of the α_(2C)-AR. ORM-13070 is a useful positron emission tomography ligand, ORM-10921 has demonstrated antipsychotic, antidepressant, and pro-cognitive actions in animals, while ORM-12741 is in clinical development for the treatment of cognitive dysfunction and neuropsychiatric symptoms in Alzheimer’s disease. This review will emphasize the importance and relevance of the α_(2C)-AR as a neuropsychiatric drug target in major depression, schizophrenia, and associated cognitive deficits. In addition, we will present new prospects and future directions of investigation.