Antipsychotics differ in their ability to internalise human dopamine D2S and human serotonin 5-HT1A receptors in HEK293 cells

Antipsychotic drugs act preferentially via dopamine D2 receptor blockade, but interaction with serotonin 5-HT1A receptors has attracted interest as additional target for antipsychotic treatment. As receptor internalisation is considered crucial for drug action, we tested the propensity of antipsychotics to internalise human (h)D2S receptors and h5-HT1A receptors. Agonist-induced internalisation of hemaglutinin (HA)-tagged hD2S and HA-h5-HT1A receptors expressed in HEK293 cells was increased by coexpression of G-protein coupled receptor kinase 2 and β-arrestin2. At the HA-hD2S receptor, dopamine, quinpirole and bromocriptine behaved as full agonists, while S(−)-3-(3-hydroxyphenyl)-N-n-propylpiperidine [(−)-3PPP] and sarizotan were partial agonists. The typical antipsychotic, haloperidol, and the atypical compounds, olanzapine, nemonapride, ziprasidone and clozapine did not internalise HA-hD2S receptors, whereas aripiprazole potently internalised these receptors (> 50% relative efficacy). Among antipsychotics with combined D2/5-HT1A properties, bifeprunox and (3-exo)-8-benzoyl-N-[[(2S)7-chloro-2,3-dihydro-1,4-benzodioxin-1-yl]methyl]-8-azabicyclo-[3.2.1]octane-3-methanamine (SSR181507) partially internalised HA-hD2S receptors, piperazine, 1-(2,3-dihydro-1,4-benzodioxin-5-yl)-4-[[5-(4-fluorophenyl)-3-pyridinyl]methyl (SLV313) and N-[(2,2-dimethyl-2,3-dihydro-benzofuran-7-yloxy)ethyl]-3-(cyclopent-1-enyl)-benzylamine (F15063) were inactive. At the HA-h5-HT1A receptor, serotonin, (+)-8-hydroxy-2-(di-n-propylamino)tetralin [(+)-8-OH-DPAT] and sarizotan were full agonists, buspirone acted as partial agonist. (−)-Pindolol showed little activity and no internalising properties were manifested for the 5-HT1A receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]-ethyl]-N-(2-pyridinyl)cyclohexanecarboxamide (WAY100635). Most antipsychotics induced HA-h5-HT1A receptor internalisation, with an efficacy rank order: nemonapride > F15063 > SSR181507 > bifeprunox ≈ SLV313 ≈ ziprasidone > aripiprazole and potencies: SLV313 > SSR181507 ≈ F15063 > bifeprunox ≈ nemonapride ≈ aripiprazole > ziprasidone. Interestingly, the internalisation induced by clozapine was only minimal, whereas aripirazole and bifeprunox were more potent for internalisation than for G-protein activation. These different profiles of antipsychotics for receptor internalisation may help to evaluate their potential therapeutic impact in the treatment of schizophrenia.