[Pharmacological profile and clinical findings of nalmefene (Selincro®) for reducing alcohol consumption in patients with alcohol dependence].

Nalmefene (Selincro®), an opioid receptor modulator, is approved in Japan, the European Union, and other countries for reducing alcohol consumption in patients with alcohol dependence. This article reviews the efficacy and safety of as-needed use of nalmefene in the treatment of alcohol dependence, as well as summarizing its pharmacological properties. Ethanol increases the release of endogenous opioids, such as ß-endorphin, a µ-opioid receptor agonist; and dynorphin, a κ-opioid receptor agonist. Preclinical data suggest that nalmefene acts as an antagonist at the µ-opioid receptor and a partial agonist at the κ-opioid receptor, and reduces ethanol self-administration in ethanol-dependent and ethanol-non-dependent rats. Nalmefene counters alcohol-induced dysregulation of the ß-endorphin/µ-opioid receptor and the dynorphin/κ-opioid receptor systems. In a multicenter, randomized, double-blind, phase 3 study of as-needed use of nalmefene combined with psychosocial support in alcohol-dependent Japanese patients with at least high drinking risk level, compared with placebo, nalmefene 10 mg and 20 mg significantly reduced the number of heavy drinking days and total alcohol consumption at week 12. In the 24-week treatment period, treatment-emergent adverse events occurred in ≥5% of patients in either the nalmefene 10 mg or 20 mg group and at least twice as often as in the placebo group were nausea, dizziness, somnolence, vomiting, insomnia, decreased appetite, constipation, malaise, and palpitations. Most adverse events were mild or moderate in severity. In conclusion, as-needed use of nalmefene provides a new concept for the treatment of alcohol dependence: namely, "reduction of alcohol intake".

Efficacy and safety of brexpiprazole for the treatment of acute schizophrenia in Japan: A 6-week, randomized, double-blind, placebo-controlled study.

AIM: This study aimed to evaluate the efficacy, safety, and tolerability of brexpiprazole compared to placebo in Japanese patients with acute schizophrenia (SCZ). METHODS: We conducted a 6-week, multicenter, double-blind, placebo-controlled, phase 2/3 study in Japan. Patients with acute SCZ were randomized (1:1:1:1) to receive brexpiprazole 1 mg, 2 mg, 4 mg, or placebo once a day. The primary endpoint was the change from baseline to week 6 in Positive and Negative Syndrome Scale (PANSS) total scores. RESULTS: In the 459 patients that were randomized, brexpiprazole 2 mg showed a significant improvement versus placebo (treatment difference: -7.32, P = 0.0124), although brexpiprazole 4 mg showed numerical improvements (treatment difference: -3.86, P = 0.1959), and brexpiprazole 1 mg showed only minimal change (treatment difference: -0.63, P = 0.8330). Treatment-emergent adverse events with an incidence of ≥5% and ≥2 times the rate of placebo in the brexpiprazole groups were vomiting, elevated blood prolactin, diarrhea, nausea, and dental caries. Most treatment-emergent adverse events were mild or moderate in severity. There were no clinically significant changes in electrocardiogram parameters, bodyweight, laboratory values, or vital signs in the brexpiprazole groups. CONCLUSION: Brexpiprazole was efficacious and well tolerated in Japanese adult patients with acute SCZ.

Safety and efficacy from a 6-week double-blind study and a 52-week open-label extension of aripiprazole in adolescents with schizophrenia in Japan.

AIM: The purpose of this study was to evaluate the safety and efficacy of aripiprazole in adolescents with schizophrenia (SCZ) in Japan. METHODS: In a 6-week, randomized, double-blind, dose-comparison study, adolescents (aged 13-17 years) with SCZ were randomized to receive aripiprazole 2, 6-12, or 24-30 mg/day. Patients who completed the 6-week study participated in a 52-week, flexible-dose, open-label extension (OLE) study of aripiprazole (initial dose: 2 mg/day, maintenance dose: 6-24 mg/day, maximum dose: 30 mg/day). RESULTS: In the 6-week study, the percentage of patients completing treatment was: 77.1% (27/35) for 2 mg/day; 80.0% (24/30) for 6-12 mg/day; and 85.4% (35/41) for 24-30 mg/day. The least squares mean change in the Positive and Negative Syndrome Scale (PANSS) total score from baseline to endpoint (primary efficacy endpoint, last observation carried forward) was -19.6 for 2 mg/day, -16.5 for 6-12 mg/day, and - 21.6 for 24-30 mg/day. The most common (≥20% patients in any group) treatment-emergent adverse events (TEAE) were nausea, akathisia, insomnia, and somnolence. Most TEAE were mild or moderate in severity. There were no deaths. In the OLE, 60.3% (41/68) of patients completed treatment, and the PANSS total score decreased by -7.9 from OLE baseline to week 52. The most common (≥20% patients) TEAE were nasopharyngitis and somnolence. Most TEAE were mild or moderate in severity. There were no deaths. CONCLUSION: These study results suggest that aripiprazole would be safe and well tolerated in both short- and long-term treatment for adolescents with SCZ in Japan.

Randomized, double-blind comparison of aripiprazole/sertraline combination and placebo/sertraline combination in patients with major depressive disorder.

AIM: This study compared the efficacy and safety of aripiprazole/sertraline combination (ASC) and placebo/sertraline combination (PSC) in patients with major depressive disorder (MDD) who showed an inadequate response to sertraline 100 mg/day. METHODS: The study comprised a screening period, an 8-week prospective treatment (single-blind sertraline 25-100 mg/day) period, and a 6-week double-blind treatment period. Patients with DSM-5-defined MDD were enrolled. Following the prospective treatment, non-responders were randomly assigned to the ASC group (aripiprazole 3-12 mg/day/sertraline 100 mg/day) or the PSC group (sertraline 100 mg/day). The primary efficacy end-point was the mean change in the Montgomery-Åsberg Depression Rating Scale (MADRS) total score from baseline to 6 weeks. RESULTS: A total of 412 patients were randomly assigned to either the ASC group (n = 209) or the PSC group (n = 203). Mean change in MADRS total score was significantly greater in patients with ASC than PSC (-9.2 vs -7.2; P = 0.0070). Treatment-emergent adverse events (TEAE) that occurred in ≥10% of patients with ASC versus PSC were nasopharyngitis (13.4% vs 11.3%) and akathisia (12.9% vs 3.4%). All TEAE reported in the ASC group were mild or moderate in severity. Rates of discontinuations due to TEAE were low in both the ASC (1.9%) and PSC (1.5%) groups. There were no notable issues in safety assessments in the ASC group compared with the PSC group. CONCLUSION: In patients with MDD who showed an inadequate response to treatment with sertraline 100 mg/day, ASC was efficacious and well tolerated.

Long-term safety and effectiveness of brexpiprazole in Japanese patients with schizophrenia: A 52-week, open-label study.

AIM: This study assessed the long-term safety, tolerability, and maintenance of the therapeutic effect of brexpiprazole in Japanese patients with schizophrenia. METHODS: This 52-week, open-label, flexible-dose (1-4 mg/day) study included patients with schizophrenia who continued treatment from a short-term randomized placebo-controlled fixed-dose (1, 2, or 4 mg/day) trial and de novo patients who switched from other antipsychotics. RESULTS: A total of 282 patients (184 de novo and 98 rolled over from short-term trial) entered the 52-week treatment with brexpiprazole, and 150 (53.2%) patients completed the week-52 assessment. Treatment-emergent adverse events (TEAE) were experienced by 235/281 patients (83.6%), and TEAE reported by ≥10% of all patients were nasopharyngitis (23.1%) and worsening of schizophrenia (22.4%). During the study, most of the TEAE were mild or moderate in severity, and there were no deaths, and no clinically meaningful mean changes in laboratory values, vital signs, or electrocardiogram parameters. Mean scores for the Positive and Negative Syndrome Scale total and Clinical Global Impression-Severity remained stable until week 52. CONCLUSION: Brexpiprazole was generally safe and well tolerated and maintained therapeutic effects in the long-term treatment of Japanese patients with schizophrenia.

An open-label extension long-term study of the safety and efficacy of aripiprazole for irritability in children and adolescents with autistic disorder in Japan.

AIM: The purpose of this study was to evaluate the long-term safety and efficacy of aripiprazole in treating irritability in pediatric patients (6-17 years) with autistic disorder (AD) in Japan. METHODS: In this open-label extension study, patients who had completed a previous randomized, double-blind, placebo-controlled 8-week study were enrolled and were flexibly dosed with aripiprazole (1-15 mg/day) until the new indication of irritability in pediatric autism spectrum disorder was approved in Japan. RESULTS: Seventy (81%) out of 86 enrolled patients completed week-48 assessments. The mean duration of treatment was 694.9 days. The mean daily dose of aripiprazole over the treatment period was 7.2 mg and the mean of the final dose was 8.5 mg. The most common treatment-emergent adverse events (TEAE; ≥20%) included nasopharyngitis, somnolence, influenza, and increased weight. The majority of these TEAE were mild or moderate in severity, and there were no deaths, and no clinically relevant findings in laboratory values except prolactin decrease, vital signs, height, or ECG parameters. At week 48 (observed case), the mean change from baseline in the Irritability subscale score for the Aberrant Behavior Checklist Japanese Version was -6.3 in prior placebo patients and -2.6 in prior aripiprazole patients. CONCLUSION: Aripiprazole was generally safe, well tolerated, and effective in the long-term treatment of irritability associated with AD in Japanese pediatric patients.

Pharmacokinetics and Safety of Brexpiprazole Following Multiple-Dose Administration to Japanese Patients With Schizophrenia.

Brexpiprazole is currently approved in the United States for the treatment of schizophrenia and as adjunctive treatment of major depressive disorder. In Canada, it is approved for the treatment of schizophrenia. This study evaluated the pharmacokinetics (PK) and safety of brexpiprazole in Japanese patients with schizophrenia. This phase 1 study comprised a 14-day multiple-dose administration of brexpiprazole 1, 4, and 6 mg/day (n = 7, 8, and 6, respectively). Plasma concentrations and PK parameters and the influence of CYP2D6 polymorphisms (intermediate metabolizers [IMs] and extensive metabolizers [EMs]) on PK were evaluated. Adverse events (AEs) were recorded. The Cmax and AUC24h of brexpiprazole and its metabolite, DM-3411, showed dose-proportionality. The Cmax and AUC24h of brexpiprazole showed accumulation of about 2.5- to 5.5-fold on day 14, compared with those on day 1. The median tmax and the mean elimination half-life of brexpiprazole were 4-5 and 52-92 hours, respectively, across all doses on day 14. The C24h of brexpiprazole reached steady state after day 10 in all dose groups. The dose-normalized Cmax and AUC24h of brexpiprazole on day 14 were higher in IM patients than in EM patients. AEs were generally mild to moderate, with transient serum prolactin increase being the most common event. No clinically significant changes were observed for other clinical laboratory values. Brexpiprazole was safe and well tolerated in the studied Japanese patients with schizophrenia.

Aripiprazole in the Treatment of Irritability in Children and Adolescents with Autism Spectrum Disorder in Japan: A Randomized, Double-blind, Placebo-controlled Study.

We evaluated the efficacy and safety of aripiprazole in the treatment of irritability in children and adolescents (6-17 years) with autism spectrum disorder (ASD) in a randomized, double-blind, placebo-controlled 8-week study in Japan. Patients received flexibly dosed aripiprazole (1-15 mg/day) or placebo. Ninety-two patients were randomized to placebo (n = 45) or aripiprazole (n = 47). Aripiprazole produced a significant improvement in the mean parent/caregiver-rated Aberrant Behavior Checklist Japanese Version irritability subscale score relative to placebo from week 3 through week 8. Administration of aripiprazole provided significantly greater improvement in the mean clinician-rated Clinical Global Impression-Improvement scores than placebo from week 2 through week 8. All patients randomized to aripiprazole completed the study, and no serious adverse events were reported. Three patients in placebo group discontinued. Aripiprazole was effective and generally safe and well-tolerated in the treatment of irritability associated with ASD in Japanese children and adolescents.

[Pharmacokinetics and safety of aripiprazole long-acting injection, following multiple deltoid administrations in schizophrenia patients in Japan].

Aripiprazole once-monthly (AOM) was previously approved for treatment of schizophrenia as monthly injections in the gluteal muscle. The deltoid muscle provides a more accessible injection site. The present study was conducted in Japanese schizophrenia patients as a 24-week, open-label trial that assessed the pharmacokinetics and safety of 5 sequential doses of AOM 400 mg (AOM 400) once every 4 weeks administered in the deltoid muscle. Patients treated with an oral atypical antipsychotic (other than aripiprazole) continued to receive their pre-study medication up to 14 days after the first AOM 400 injection. The completion rate was 76.5% (n = 13/17). Mean aripiprazole plasma C(min) almost reached steady-state by the fourth AOM 400 injection. After the fifth AOM 400 injection, mean aripiprazole AUC(28d), C(max) and C(min) were 165 µg x h/ml, 331 ng/ml and 201 ng/ml, respectively, which were similar to previously published pharmacokinetic parameters after the fifth gluteal injection of AOM 400. The most common treatment-emergent adverse event (TEAE) was injection site pain (35.3%). Most TEAEs were classified as mild in intensity. In conclusion, the deltoid injection of AOM can be considered an alternative route of administration, as deltoid and gluteal injections are interchangeable in terms of aripiprazole plasma concentrations, with no additional safety issues.

[The therapeutic plasma concentrations of antiparkinson dopamine agonists and their in vitro pharmacology at dopamine receptors].

This review discusses the relationship between therapeutic plasma concentrations of antiparkinson dopamine agonists (rotigotine, pergolide, cabergoline, apomorphine, bromocriptine, ropinirole, pramipexole, and talipexole) and their in vitro pharmacology at dopamine D1, D2 and D3 receptors. A significant correlation was found between therapeutic plasma concentrations of these dopamine agonists and their agonist potencies (EC50) at D2 receptors, although no such correlation existed at D1 or D3 receptors, suggesting that D2 receptors could be the primary and common target for the antiparkinson action of all dopamine agonists. However, D1 receptor stimulation is also important for maintaining swallowing reflex, bladder function and cognition. In particular, continuous D1 and D2 receptor stimulation may be reduced to low levels among Parkinson's disease patients. Our findings revealed therapeutic plasma concentrations of rotigotine were similar to its agonist potencies at both D1 and D2 receptors. Thus, rotigotine may be beneficial for the treatment of Parkinson's disease patients in that this dopamine agonist has the potential of continuous stimulation of both D1 and D2 receptors in the clinical setting.

[Pharmacology of antipsychotics at human dopamine D2 and D3 receptors].

Aripiprazole is a dopamine D/D3 and serotonin 5-HT1A receptor partial agonist which is approved for treatment of schizophrenia. We evaluated the pharmacological properties of aripiprazole, dopamine D2 receptor partial agonists and antipsychotics using forskolin-stimulated cAMP accumulation in cells expressing human dopamine D2 and D3 receptors. In cells expressing high densities of D2 receptor with high sensitivity for dopamine, the maximal agonist effects of partial agonists were higher than in cells expressing low densities of D2 receptor with low sensitivity for dopamine. Aripiprazole's intrinsic activities at D2 and D9 receptors were lower than those observed with partial agonists (terguride, bifeprunox, OPC-4392 and (-)-3-PPP), which demonstrated clinically suboptimal improvement of positive symptoms of schizophrenia patients, and higher than that of SDZ 208-912, which demonstrated incidence of extrapyramidal symptoms similar to haloperidol. Aripiprazole's appropriate intrinsic activities at D2 and D: receptors may contribute to desired results in a clinical profile. Antipsychotics (risperidone, olanzapine, amisulpride, sulpiride and perphenazine) which displayed antidepressive effects in schizophrenia patients behaved as preferential antagonists in cells expressing D2 receptors compared to cells expressing D3 receptors. Preferential antagonism at dopamine D2 receptors may play a role in the antidepressive effects of these antipsychotics.

In vitro pharmacology of aripiprazole, its metabolite and experimental dopamine partial agonists at human dopamine D2 and D3 receptors.

Aripiprazole is the first dopamine D(2)/D(3) receptor partial agonist successfully developed and ultimately approved for treatment of a broad spectrum of psychiatric and neurological disorders. Aripiprazole's dopamine D(2) and serotonin 5-HT(1A) receptor partial agonist activities have been postulated to confer clinical efficacy without marked sedation, and a relatively favorable overall side-effect profile. Using aripiprazole's unique profile as a benchmark for new dopamine partial agonist development may facilitate discovery of new antipsychotics. We conducted an in vitro comparative analysis between aripiprazole, and its human metabolite OPC-14857 (7-(4-[4-(2,3-dichlorophenyl)-1-piperazinyl)butoxy)-2(1H)-quinolinone)); RGH-188 (trans-1-[4-[2-[4-(2,3-dichlorophenyl)piperazine-1-yl]ethyl]cyclohexyl]-3,3-dimethylurea), and its metabolite didesmethyl-RGH-188 (DDM-RGH-188); as well as bifeprunox, sarizotan, N-desmethylclozapine (NDMC; clozapine metabolite), and SDZ 208-912 (N-[(8α)-2-chloro-6-methylergolin-8-yl]-2,2-dimethylpropanamide). In vitro pharmacological assessment included inhibition of forskolin-stimulated cAMP accumulation and the reversal of dopamine-induced inhibition in clonal Chinese hamster ovary cell lines expressing D(2S), D(2L), D(3) Ser-9 and D(3) Gly-9 for human dopamine receptors. All test compounds behaved as dopamine D(2)/D(3) receptor partial agonists. Aripiprazole's intrinsic activity at dopamine D(2S) and D(2L) receptors was similar to that of OPC-14857 and RGH-188; lower than that of dopamine and bifeprunox; and higher than that of DDM-RGH-188, SDZ 208-912, sarizotan, and NDMC. Aripiprazole's intrinsic activity at dopamine D(3) Ser-9 and D(3) Gly-9 receptors was similar to that of OPC-14857 and sarizotan; lower than that of dopamine, bifeprunox, RGH-188 and DDM-RGH-188; and higher than that of SDZ 208-912 and NDMC. A consolidated assessment of these findings may help defining the most appropriate magnitude of intrinsic activity at dopamine D(2)/D(3) receptors for clinical efficacy and safety.

Functional potencies of dopamine agonists and antagonists at human dopamine D2 and D3 receptors.

We measured the functional agonist potencies of dopamine agonists including antiparkinson drugs, and functional antagonist potencies of antipsychotics at human dopamine D(2) and D(3) receptors. In vitro pharmacological assessment included inhibition of forskolin-stimulated cAMP accumulation and the reversal of dopamine-induced inhibition in clonal Chinese hamster ovary cells expressing low and high densities of human dopamine D(2L) and D(2S) receptors (hD(2L)-Low, hD(2L)-High, hD(2S)-Low and hD(2S)-High, respectively) and human dopamine D(3) Ser-9 and D(3) Gly-9 receptors (hD(3)-Ser-9 and hD(3)-Gly-9, respectively). Cabergoline, bromocriptine, pergolide, (±)-7-hydroxy-N,N-di-n-propyl-2-aminotetralin (7-OH-DPAT), talipexole, pramipexole, R-(+)-trans-3,4,4a,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano[4,3-b]-1,4-oxazin-9-olhydrochloride (PD128907) and ropinirole behaved as dopamine D(2) and D(3) receptor full agonists and showed higher potencies in hD(2L)-High and hD(2S)-High compared to hD(2L)-Low and hD(2S)-Low. In hD(3)-Ser-9 and hD(3)-Gly-9 compared to hD(2L)-Low and hD(2S)-Low, dopamine, ropinirole, PD128907, and pramipexole potencies were clearly higher; talipexole and 7-OH-DPAT showed slightly higher potencies; pergolide showed slightly lower potency; and, cabergoline and bromocriptine potencies were lower. Aripiprazole acted as an antagonist in hD(2L)-Low; a low intrinsic activity partial agonist in hD(2S)-Low; a moderate partial agonist in hD(3)-Ser-9 and hD(3)-Gly-9; a robust partial agonist in hD(2L)-High; and a full agonist in hD(2S)-High. Amisulpride, sulpiride and perphenazine behaved as preferential antagonists; and chlorpromazine and asenapine behaved as modest preferential antagonists; whereas fluphenazine, haloperidol, and blonanserin behaved as non-preferential antagonists in hD(2S)-Low and hD(2S)-High compared to hD(3)-Ser-9 and hD(3)-Gly-9. These findings may help to elucidate the basis of therapeutic benefit observed with these drugs, with varying mechanisms of action, in the treatment of Parkinson's disease, depression and schizophrenia.

Receptor reserve-dependent properties of antipsychotics at human dopamine D2 receptors.

Aripiprazole is the first dopamine D(2)/D(3) receptor partial agonist approved for use in the treatment of psychiatric disorders including schizophrenia, bipolar disorder, and unipolar depression in the US. Aripiprazole has demonstrated a relatively favorable side effect profile compared to other commonly prescribed antipsychotics, including a low propensity for treatment-limiting extrapyramidal symptoms, hyperprolactinemia, and body weight gain. In an effort to elucidate aripiprazole's pharmacological activity in relation to clinically relevant fluctuation of dopamine D(2) receptor reserves, we compared the properties of aripiprazole to other antipsychotics, quetiapine, clozapine, olanzapine, ziprasidone, risperidone and haloperidol, a dopamine D(2) receptor partial agonist, bifeprunox, dopamine D(3) receptor modulators, BP897 (N-[4-[4-(2-Methoxyphenyl)-1-piperazinyl]butyl]naphthalene-2-carboxamide) and GR103691 (4'-Acetyl-N-[4-[4-(2-methoxyphenyl)piperazin-1-yl]butyl]biphenyl-4-carboxamide), and a 5-HT(1A) partial agonist, buspirone using forskolin-stimulated cAMP accumulation in clonal Chinese hamster ovary cell lines expressing low and high densities of human dopamine D(2S) receptors (hD(2S)-Low and hD(2S)-High, respectively). In hD(2S)-Low cells lacking receptor reserves for dopamine, all drugs antagonized dopamine responses, and their potencies correlated well with respective affinities. In hD(2S)-High cells possessing receptor reserves, all antipsychotics except aripiprazole antagonized dopamine responses, and their antagonist potencies were less than those in hD(2S)-Low cells treated with the equal dopamine concentration. In contrast, aripiprazole and bifeprunox acted as full agonists. BP897, GR103691 and buspirone acted as partial agonists. These data suggest that the level of receptor reserves influences antagonist potencies and side effects associated with antipsychotics. Aripiprazole's unique receptor reserve dependent properties may account for its favorable tolerability in the clinical setting.

Characterization of aripiprazole partial agonist activity at human dopamine D3 receptors.

Aripiprazole is the first dopamine D2/D3 receptor partial agonist approved for use in the treatment of psychiatric disorders, including schizophrenia, bipolar disorder, and unipolar depression in the US. To explore the functional activity of aripiprazole at dopamine D3 receptors, we established Chinese hamster ovary (CHO) cell lines stably expressing high and low densities of Ser-9 and Gly-9 variants of human dopamine D3 receptors and compared aripiprazole's dopamine D3 pharmacological properties with other marketed and non-approved dopamine D3 receptor modulating agents on inhibition of forskolin-stimulated cAMP accumulation. Maximal cell responses for dopamine were dependent on receptor expression levels, and all cells had similar potency for dopamine responses. Aripiprazole, terguride, bifeprunox, OPC-4392 (7-(3-[4-(2,3-dimethylphenyl)piperazinyl]propoxy)-2(1H)-quinolinone), (-)-3-PPP ((-)-3-(3-hydroxyphenyl)-N-n-propylpiperidine), SDZ 208-912 (N-[(8 alpha)-2-chloro-6-methylergolin-8-yl]-2,2-dimethylpropanamide), BP897 (N-[4-[4-(2-Methoxyphenyl)-1-piperazinyl]butyl]naphthalene-2-carboxamide) and GR103691 (4'-Acetyl-N-[4-[4-(2-methoxyphenyl)piperazin-1-yl]butyl]biphenyl-4-carboxamide) behaved as partial agonists. Aripiprazole's intrinsic activity was similar to that of BP897 and GR103691, lower than that of terguride, bifeprunox, OPC-4392, and (-)-3-PPP, and higher than that of SDZ 208-912. The Gly-9 variant did not differ from the Ser-9 variant with respect to those agonist potencies and intrinsic activities. These compounds blocked the action of dopamine with a maximum effect equal to that of each compound alone. ACR16 (4-(3-Methanesulfonyl-phenyl)-1-propyl-piperidine), quetiapine, clozapine, olanzapine, ziprasidone, risperidone, and haloperidol acted as antagonists. Aripiprazole's unique activity at dopamine D3 receptors may translate into clinically relevant outcomes in patients with a variety of neuropsychiatric disorders.

Differences in agonist/antagonist properties at human dopamine D(2) receptors between aripiprazole, bifeprunox and SDZ 208-912.

Aripiprazole is the first dopamine D(2) receptor partial agonist approved for use in schizophrenia and bipolar disorder. Other partial agonists have failed in various stages of development, either for reasons of poor tolerability or lack of efficacy. We conducted an in vitro comparative analysis between aripiprazole, bifeprunox, SDZ 208-912, OPC-4392 and ACR16 in attempt to correlate specific pharmacological properties with clinical outcome. In vitro pharmacological assessment included inhibition of forskolin-stimulated cAMP accumulation and the reversal of this inhibition produced by dopamine in clonal CHO cell lines expressing high and low densities of human dopamine D(2L) and D(2S) receptors. In cells expressing high receptor densities, all drugs except ACR16 predominantly behaved as agonists. However, in cells expressing low receptor densities, all drugs showed significantly lower maximal effects than dopamine. Aripiprazole's intrinsic activity was lower than that observed with bifeprunox and OPC-4392, and higher than that of SDZ 208-912. Aripiprazole's antagonist activity was greater than that of bifeprunox and OPC-4392, and less than that of SDZ 208-912. In conclusion, our data suggests that aripiprazole's unique intrinsic activity profile may account for its demonstrated clinical efficacy in the treatment of both positive and negative symptoms of schizophrenia, as well as its demonstrated low liability for parkinsonism and hyperprolactinemia. A higher degree of intrinsic activity, and lower relative antagonist activity, such as that observed with bifeprunox and OPC-4392 may translate into a clinically suboptimal improvement of positive symptoms. SDZ 208-912's intrinsic activity may be lower than the optimal level needed to minimize extrapyramidal symptoms.

Dopamine D2 receptor partial agonists display differential or contrasting characteristics in membrane and cell-based assays of dopamine D2 receptor signaling.

Clinical evidence suggests that dopamine D(2) receptor partial agonists must have a sufficiently low intrinsic activity to be effective as antipsychotics. Here, we used dopamine D(2) receptor signaling assays to compare the in vitro functional characteristics of the antipsychotic aripiprazole with other dopamine D(2) receptor partial agonists (7-{3-[4-(2,3-dimethylphenyl)-piperazinyl]propoxy}-2(1H)-quinolinone [OPC-4392], (-)-3-(3-hydroxy-phenyl)-N-n-propylpiperidine [(-)3-PPP] and (+)terguride) and dopamine D(2) receptor antagonists. Aripiprazole and OPC-4392 were inactive in a guanosine-5'-O-(3-[(35)S]thio)-triphosphate ([(35)S]GTPgammaS) binding assay using Chinese Hamster Ovary (CHO) cell membranes expressing cloned human dopamine D(2Long) (hD(2L)) receptors, whereas (-)3-PPP and (+)terguride displayed low intrinsic activity. Aripiprazole also had no effect on [(35)S]GTPgammaS binding to CHO-hD(2L) cells, while OPC-4392, (-)3-PPP and (+)terguride were partial agonists. In contrast, aripiprazole, OPC-4392, (-)3-PPP, and (+)terguride were inactive in a [(35)S]GTPgammaS binding assay using rat striatal membranes. However, at a more downstream level of CHO-hD(2L) cell signalling, these drugs all behaved as dopamine hD(2L) receptor partial agonists, with aripiprazole displaying an intrinsic activity 2 to 3-fold lower (inhibition of forskolin-induced adenosine 3',5'-cyclic monophosphate accumulation) and almost half as high (enhancement of adenosine triphosphate-stimulated [(3)H]arachidonic acid release) as OPC-4392, (-)3-PPP and (+)terguride. Dopamine activity was blocked in each case by (-)raclopride, which was inactive on its own in every assay, as were the antipsychotics haloperidol, olanzapine, ziprasidone and clozapine. Together, these data, whilst preclinical in nature, are consistent with clinical evidence suggesting the favorable antipsychotic profile of aripiprazole, compared with the other clinically ineffective partial agonists, is dependent on its low intrinsic activity at dopamine D(2) receptors. This study also highlights the limitations of using [(35)S]GTPgammaS binding assays to identify dopamine D(2) receptor partial agonists.

In vitro functional characteristics of dopamine D2 receptor partial agonists in second and third messenger-based assays of cloned human dopamine D2Long receptor signalling.

Aripiprazole, (+)terguride, OPC-4392 and (-)3-PPP have been classified as dopamine D(2) receptor partial agonists based largely on their activity in second messenger-based assays of dopamine D(2) receptor signalling. Nevertheless, signal transduction amplification might result in these compounds behaving as dopamine D(2) receptor full agonists at a more downstream level of signalling. We compared the intrinsic activity (E(max), expressed as a percentage of the maximal effect of dopamine) of aripiprazole, (+)terguride, OPC-4392 and (-)3-PPP using second (calcium (Ca(2+)) mobilization) and third (extracellular signal-regulated kinase 2 (ERK2) phosphoprotein expression) messenger readouts of cloned human dopamine D(2long) (hD(2L)) receptor signalling in CHO cells. These compounds were all less potent and displayed lower intrinsic activity in the Ca(2+) assay (aripiprazole = 24.3%, (+)terguride = 56.9%, OPC-4392 = 58.6% and (-)3-PPP = 75.1%), and aripiprazole (E(max) = 54.5%) displayed a substantially lower intrinsic activity than (+)terguride (E(max) = 92.3%), OPC-4392 (E(max) = 93.1%) and (-)3-PPP (E(max) = 101.1%) in the more downstream-based ERK2 phosphoprotein expression assay. These drug effects on Ca(2+) mobilization and ERK2 phosphoprotein expression were mediated through dopamine hD(2L) receptors, as they all were blocked by (-)raclopride, whereas (-)raclopride and other dopamine D(2) receptor antagonists (haloperidol, risperidone, ziprasidone, olanzapine, clozapine and quetiapine) were inactive on their own in both assays. These data are consistent with clinical evidence that only dopamine D(2) receptor partial agonists with a sufficiently low enough intrinsic activity will prove effective against the positive symptoms of schizophrenia, and also highlight the importance of using downstream-based assays in the discovery of novel D(2) receptor partial agonist therapeutics.

In vitro biochemical evidence that the psychotomimetics phencyclidine, ketamine and dizocilpine (MK-801) are inactive at cloned human and rat dopamine D2 receptors.

Dopamine potently increased calcium mobilization in Chinese hamster ovary cells expressing human dopamine D2Long receptors (CHO-D2L cells), and increased guanosine-5'-O-(3-[35S]thio)-triphosphate binding to CHO-D2L cell and rat striatal membranes. These effects of dopamine were blocked by the dopamine D2 receptor antagonist (-)raclopride. In contrast to the findings of a recent controversial study, phencyclidine, ketamine and dizocilpine (MK-801) lacked dopamine D2 receptor full agonist, partial agonist and antagonist activity in these assays, suggesting their psychotomimetic effects, and activity in rodent models of schizophrenia, are associated with N-methyl-d-aspartate receptor blockade rather than a direct interaction with dopamine D2 receptors.