The Antipsychotics Olanzapine, Risperidone, Clozapine, and Haloperidol Are D2-Selective Ex Vivo but Not In Vitro

Abstract

In a recent human [ 11 C]-( + )-PHNO positron emission tomography study, olanzapine, clozapine, and risperidone occupied D2 receptors in striatum (STR), but, despite their similar in vitro D2 and D3 affinities, failed to occupy D3 receptors in globus pallidus. This study had two aims: (1) to characterize the regional D2/D3 pharmacology of in vitro and ex vivo [ 3 H]-( + )-PHNO binding sites in rat brain and (2) to compare, using [ 3 H]-( + )-PHNO autoradiography, the ex vivo and in vitro pharmacology of olanzapine, clozapine, risperidone, and haloperidol. Using the D3-selective drug SB277011, we found that ex vivo and in vitro [ 3 H]-( + )-PHNO binding in STR is exclusively due to D2, whereas that in cerebellar lobes 9 and 10 is exclusively due to D3. Surprisingly, the D3 contribution to [ 3 H]-( + )-PHNO binding in the islands of Calleja, ventral pallidum, substantia nigra, and nucleus accumbens was greater ex vivo than in vitro. Ex vivo, systemically administered olanzapine, risperidone, and haloperidol, at doses occupying B80% D2, did not occupy D3 receptors. Clozapine, which also occupied B80% of D2 receptors ex vivo, occupied a smaller percentage of D3 receptors than predicted by its in vitro pharmacology. Across brain regions, ex vivo occupancy by antipsychotics was inversely related to the D3 contribution to [ 3 H]-( + )-PHNO binding. In contrast, in vitro occupancy was similar across brain regions, independent of the regional D3 contribution. These data indicate that at clinically relevant doses, olanzapine, clozapine, risperidone, and haloperidol are D2-selective ex vivo. This unforeseen finding suggests that their clinical effects cannot be attributed to D3 receptor blockade.

Synthesis and dual D2and 5-HT1Areceptor binding affinities of 5-piperidinyl and 5-piperazinyl-1H-benzo[d]imidazol-2(3H)-ones

“…Reaction of 9 with CDI finally produced 10 in 62% yield. The Suzuki-Miyaura reaction of cyclic vinyl boronate (12) 22 , derived from the vinyl triflates of N-protected tetrahydropyridines, with 10 under a variety of conditions (such as PdCl 2 dppf, KOAc, DMF, 80 C; Pd(PPh 3 ) 4 , toluene, ethanol, Na 2 CO 3 , reflux) were failed; the desired 13 could not be obtained rather the starting 10 was recovered (Scheme 1). The poor solubility of 10 in a variety of solvents is considered to be one of the factors for its lack of reactivity.…”

“…. Samples containing 32 mg of membrane protein, different concentrations of each compound ranging from 0.1 nM to 10 mM were incubated in a final volume of 500 mL of 50 mM Tris-HCl pH 7.4, 5 mM MgSO 4 for 120 min at 37 C. After this incubation time, samples were filtered through Whatman GF/C glass microfiber filters presoaked in polyethylenimine 0.5% for at least 30 min prior to use. The filters were washed twice with 1 mL of ice-cold buffer (50 mM Tris-HCl, pH 7.4).…”

“…The positive symptoms include disorganized thought, delusions and auditory hallucinations, whereas the most characteristic negative symptoms are emotional flattening, poverty of speech and motivational deficits 1 . Although various molecular mechanisms have been proposed to provide antipsychotic activity 2 , antagonism of the dopamine D 2 receptor subtype remains the cornerstone of antipsychotic activity 3,4 . Chlorpromazine (1) and haloperidol (2a), the first-generation antipsychotics or typical antipsychotics, are dopamine antagonists and exhibit robust control of positive symptoms of schizophrenia, for instance hallucinations, agitation and delusions but fail to control the negative symptoms such as blunted affect, emotional withdrawal and cognitive deficits.…”

“…Indeed, numerous mechanistic considerations [12][13][14] and preclinical evidences [15][16][17] support the potential of such a combination. Consequently, adoprazine (3) (SLV-313) and bifeprunox (4), bearing potent D 2 receptor antagonist and 5-HT 1A receptor agonist properties, were developed 18 ( Figure 1). Although compound 4 completed phase III clinical trials, its antipsychotic efficacy was determined to be inferior to that of risperidone and olanzapine 9 and, despite a satisfactory tolerance profile, the US Food and Drug Administration (FDA) did not grant marketing approval.…”

“…This process was repeated three times. The reaction mixture was further stirred at room temperature for 0.5 h. Ethyl acetate (50 mL) was added to the mixture at room temperature, washed with H 2 O (15 mL), brine (10 mL), dried over Na 2 SO 4 …”