F15063, a potential antipsychotic with dopamine D(2)/D(3) antagonist, 5-HT(1A) agonist and D(4) partial agonist properties: (IV) duration of brain D2-like receptor occupancy and antipsychotic-like activity versus plasma concentration in mice

F15063 (N-(2,2-dimethyl-2,3-dihydro-benzofuran-7-yloxy)ethyl]-3-(cyclopent-1-enyl)-benzylamine fumarate salt) is a novel potential antipsychotic with dopamine D₂/D₃ blocking properties and agonist activity at 5-HT_1A and D₄ receptors. The pertinent parameter for pharmacological activity of antipsychotics appears to be central D2-like receptor occupancy. However, its duration is not necessarily correlated with drug plasma levels, on which clinical dosing regimens are often based. Thus, we compared in mice the duration of actions of F15063 and haloperidol to (1) inhibit apomorphine-induced climbing and sniffing (behavioural measures of D2-like receptor antagonism) and (2) occupy D2-like receptors in vivo in the striatum and olfactory tubercles (inhibition of ³H]nemonapride binding). Finally, we measured plasma levels of F15063. D2-like receptor occupancy in the striatum remained elevated at 1, 4 and 8 h postadministration, with both F15063 (ID₅₀: 7.1, 3.6 and 16.5 mg/kg p.o., respectively) and the typical antipsychotic, haloperidol (ID₅₀: 1.4, 0.52 and 0.53 mg/kg p.o., respectively). This was paralleled by a protracted inhibition of apomorphine-induced climbing (ED₅₀: 0.9, 2.8 and 3.6 mg/kg p.o., and 0.21, 0.37 and 0.87 mg/kg p.o., respectively, for F15063 and haloperidol). In contrast, after administration of 10 mg/kg p.o. of F15063, its plasma levels decreased rapidly: 15.2, 2.1 and 0.6 ng/ml, 1, 4 and 8 h after administration, respectively. A similar pattern of results was observed when F15063 and haloperidol were administered i.p. and s.c., respectively. To summarise, the time-course of D2-like receptor occupancy and inhibition of apomorphine-climbing (and sniffing) behaviours was similarly long lasting with F15063 and haloperidol. In addition, the durations of action of F15063 and haloperidol in a behavioural model of antipsychotic-like activity were closely correlated to their occupancy of central D2-like receptors, and much longer than their presence in plasma.