Triple Reuptake Inhibitors as Potential Therapeutics for Depression and Other Disorders: Design Paradigm and Developmental Challenges.

Although first-line antidepressants offer therapeutic benefit, about 35% of depressed patients are not adequately treated, creating a large unmet medical need. These medicines mostly enhance the synaptic levels of serotonin and/or norepinephrine. Evidence from preclinical and clinical studies implicate dopamine hypofunction in the pathophysiology of depression. Triple reuptake inhibitors (TRIs), which elevate dopamine in addition to serotonin and norepinephrine, may demonstrate greater efficacy, with the reversal of anhedonia and improved tolerability. Medicinal chemistry efforts have resulted in more than 10 clinical candidates, although clinical candidates have failed to demonstrate superior efficacy compared to placebo or existing antidepressants. Hence, the successful development of future TRIs for depression will demand strong translational evidence, an optimal dosing regimen, and better tolerability. TRIs also hold therapeutic potential for other indications, with four candidates under clinical development for attention deficit hyperactivity disorder, binge eating disorder, cocaine addiction, obesity, and type 2 diabetes. Clinical studies have indicated a lower abuse potential for TRIs than psychostimulants.