Aripiprazole has functionally selective actions at dopamine D2 receptor-mediated signaling pathways

Area of Science:

• Neuropharmacology
• Molecular Psychiatry
• Drug Discovery

Background:

• Aripiprazole is an atypical antipsychotic with a favorable side-effect profile, potentially linked to its atypical dopamine D(2) receptor interactions.
• The precise mechanism of aripiprazole at the D(2) receptor, whether a partial agonist or a functionally selective ligand, remains debated.
• Understanding these interactions is crucial for elucidating its unique clinical efficacy and safety.

Purpose of the Study:

• To investigate the D(2L) receptor binding properties of aripiprazole.
• To evaluate the effects of aripiprazole on downstream D(2) receptor-mediated functional pathways.
• To differentiate aripiprazole's mechanism from typical D(2) agonists and partial agonists.

Main Methods:

• Assessed aripiprazole's D(2L) receptor binding affinity in the presence of guanosine triphosphate (GTP).
• Measured D(2) receptor-mediated functional effects, including mitogen-activated protein kinase (MAPK) phosphorylation and arachidonic acid (AA) release.
• Quantified D(2) receptor internalization induced by aripiprazole compared to reference compounds.

Main Results:

• Aripiprazole's apparent D(2) affinity was not significantly reduced by GTP, unlike full or partial agonists.
• Aripiprazole exhibited a Hill slope significantly greater than 1.0, distinguishing it from typical agonists.
• Aripiprazole partially activated MAPK and AA pathways differentially and did not induce significant D(2L) receptor internalization.

Conclusions:

• Aripiprazole modulates D(2L)-mediated signaling pathways in a distinct, differential manner.
• The findings support the hypothesis that aripiprazole functions as a functionally selective D(2) ligand.
• This unique pharmacological profile may explain the novel clinical actions and favorable side-effect profile of aripiprazole.