Agonist and antagonist properties of antipsychotics at human dopamine D4.4 receptors: G-protein activation and K+ channel modulation in transfected cells

Abstract

Interaction at dopamine D4 receptors may improve cognitive function, which is highly impaired in individuals with schizophrenia, but comparative studies of recent antipsychotics in cellular models of D4 receptor activation are lacking. Here, we report the in-vitro profile of over 30 ligands at recombinant hD4.4 receptors. In [35S]GTPgammaS binding experiments using membranes of CHO-hD4.4 cells, apomorphine, preclamol and the selective D4 agonists, ABT724, CP226269, Ro-10-5824 and PD168077, behaved as partial agonists (Emax 20-60% vs. dopamine), whereas L745870 and RBI257, displayed antagonist properties. The 'conventional' antipsychotic, haloperidol and the 'atypicals', clozapine and risperidone, exhibited antagonist properties, while 'third generation' compounds bifeprunox, SLV313 and F15063, acted as partial agonists (10-30%). Aripiprazole and SSR181507 slightly stimulated [35S]GTPgammaS binding at micromolar concentrations. In Xenopus laevis oocytes co-expressing hD4.4 receptors with G-protein-coupled inwardly rectifying potassium (GIRK) channels, apomorphine, preclamol, ABT724, CP226269, and PD168077 stimulated GIRK currents (Emax 70-80%). The 5-HT1A receptor ligands, WAY100635 and flibanserin, also exhibited partial agonist activity (30% and 15%, respectively). Haloperidol, clozapine, olanzapine and nemonapride did not stimulate GIRK currents, whereas aripiprazole, bifeprunox, SLV313 and F15063, but not SSR181507, exhibited partial agonism (Emax 20-35%). In-vitro responses depended on experimental conditions: increasing NaCl concentration (30 mm to 100 mm) reduced agonist efficacy in [35S]GTPgammaS binding, whereas decreasing the amount of hD4.4 cRNA injected into oocytes (from 2.0 to 0.5 ng/oocyte) reduced agonist efficacy of several compounds. These data indicate that, unlike conventional or 'atypical' antipsychotics, several 'third generation' agents display D4 receptor partial agonism that may be sufficient to influence physiological D4 receptor activity in vivo.

Transmembrane Segment Five Serines of the D4 Dopamine Receptor Uniquely Influence the Interactions of Dopamine, Norepinephrine, and Ro10-4548

“…Furthermore, the functional properties of L750,667, PNU101,387G, ABT-724, and Ro10-5824 for the mutant receptors were the same as for the wild-type receptors: they were all antagonists because they did not activate the receptors and prevented activation by the agonist (Ϫ)-quinpirole. Two of the D4-selective ligands used in this study, ABT-724 and Ro10-5824, have been reported to possess partial agonist properties when using either [ 35 S]GTP␥S binding or FLIPR assays as functional end points (Powell et al, 2003;Cowart et al, 2004;Newman-Tancredi et al, 2008). However, using intracellular cAMP accumulation as a functional endpoint we found that ABT-724 and Ro10-5824 lacked agonist properties, but antagonized (Ϫ)-quinpirole activation in wild-type and mutant receptors.…”

Role of dopamine D4 receptors in copulatory behavior: Studies with selective D4 agonists and antagonists in male rats

“…On the other hand, apomorphine modified also other copulatory parameters, e.g. it decreased EL and IF, which were not affected by (e.g., a measure of the activation of G-protein coupled receptors after receptor binding, which is used to study the activation of D 4 receptors Newman-Tancredi et al 2008], and 2) the EC50 of apomorphine (4.3 nM) is lower than that of PD-168,077 (5,6 nM) and of ABT-724 (12,4 nM) in increasing Ca 2+ influx in HEK-293 cells co-transfected with rat/human D 4 receptors and a G protein (Gαq05) (see [Brioni and Moreland, 2006] and references therein). Alternatively, PD-168,077 and ABT-724 may act as dopamine D 4 receptor partial agonists, or the concomitant activation of different dopamine receptor subtypes by apomorphine may produce a higher activation of the targets (see below), which lead to copulation, than the activation of one dopamine receptor subtype only.…”

Multifunctional Pharmacology of Flibanserin: Possible Mechanism of Therapeutic Action in Hypoactive Sexual Desire Disorder

“…These include 5‐HT 2C receptors (antagonistic action), 5‐HT 2B receptors (antagonistic action) (Tables 1 and 2), and DA D4 receptors. For the latter, flibanserin acts as either an antagonist or a weak agonist, depending on the model system used for testing ([18,32,33]; data on file) (Table 2). Affinity of flibanserin for numerous other receptors is low (Tables 3 and 4; Figure 2).…”