- Email: [email protected]
Is clozapine a dopaminergic drug?
105
P Poster Presentations onist, and YM-436 I I (YM), a novel antagonist for D3 and D4 receptors [I ]. HAL and YM antagonized the mouse climbing behavior induced by apomorphine (EDso = 0.041 and 0.32 mg/kg sc for HAL and YM, respectively). Both antagonists also restored the swimming activity of mice inhibited by apomorphine (EDso= 0.026 and 0.36 mglkg sc for HAL and YM, respectively). Thus haloperidol was 8 to 14 times more potent than YM in these two paradigms. On the other hand, the cataleptogenic activity of haloperidol in rats was 160 times more potent than that of YM (EDso = 0.25 and 40 mg/kg sc for HAL and YM, respectively). These results suggest that D3 and/or D4 receptors are more closely involved in the apomorphine-induced behavioral changes than catalepsy; this is in line with the limbic distribution of D3 and D4 receptors. [ II Hidaka, K et al., J. Neurochern.• 65: 5165 (l995)
I p-9-?1 Dopamine 02 Receptor Change AfterRepeated Treatment with SM-9018, a Novel Neuroleptic Y. Ohno, T. Ishibashi, K. Ikeda, K. Ishida, M, Nakamura. Res. Cent., Sumitomo Pharmaceuticals, Osaka, Japan SM-9018 is a potential atypical neuroleptic agent that has potent blocking activities both for dopamine D2 and 5-HT2 receptors. The present study was conducted to examine the effects of subchronic treatment with SM-9018 on the striatal D2 receptors in rats to evaluate its liability for tardive dyskinesia. Two-weeks treatment of rats with SM-9018, at a dose which blocks D2 receptors (10 mglkglday, p.o.), did not significantly change the density (Bmax) or affinity (Kd) of D2 receptors (labeled by 3H-raclopride), the levels of D2s, D2L or D3 mRNA (measured by RT-PCR) in the striatum. By contrast, haloperidol treatment (3 mglkglday. for 2 weeks) significantly increase the density of striatal D2 receptors while the mRNA levels of D2 receptor family were unchanged. Haloperidol treatment markedly enhanced the incidence of apomorphine-induced stereotyped behaviors and SKF 38393 (a DI agonist)-induced repetitive jaw movement. however, the treatment with SM-9018 did not. These findings suggest that SM-9018 is weaker than haloperidol in inducing up-regulation of striatal D2 receptors and behavioral dopaminergic supersensitivity after its repeated treatments. SM-9018 seems to have low propensity to induce tardive dyskinesia.
IP-9-91 Zotepine Comparison of the Pharmacological Profiles of and Norzotepine DJ . Heal, P.L. Needham. Knoll Pharma ceut icals Research Department, Nottingham, UK
Zotepine (ZOT) is a dibenzothiepine tricyclic antipsychotic which is effective against the positive and negative symptoms of schizophrenia with a low propensity to induce extrapyramidal side-effects (EPS). In this study, the antidopaminergic profile of ZOT has been compared with that of its desmethyl metabolite, norzotepine (NORZ). Affinities for dopamine (DA) receptor subtypes were determined by [3 H)radioligand binding using cloned human receptors expressed in cell-lines. Behavioural tests, conducted using male CD rats, were locomotor activity and stereotype induced by d-amphetamine (2.5 mg/kg sc and 10 rug/kg sc, respectively) and catalepsy. Results are EDso's in mg/kg ip. ZOT and NORZ had similar DA subtype binding profiles with moderate/high affinities for D I, Dz, D3' D4 and lower affinities for Ds : Ki's (nM). D I to n, ZOT = 26,12,3, 9. 99; NORZ = 34, II, 16,31, 109. For comparison also, clozapine (CLOZ) = 121, 209,179,31.340. In the behaviouraltests, ZOT showed little separation between the doses to inhibit the locomotor and stereotype responses to d-amphetamine, whereas NORZ and CLOZ showed 9- and 25-fold separations. respectively. Locomotor activity, ZOT = 0.5, NORZ = 5.0. CLOZ = 4.0; stereotype. ZOT = 0.7, NORZ = 46, CLOZ = 96. These compounds were only weakly cataleptic (ZOT = 13, NORZ = 56, CLOZ = 34) and each showed an excellent separation between the EDso dose to inhibit amphetamine locomotion (predictive of antipsychotic activity) and to induce catalepsy (predictive of EPS): ratios. ZOT = 18, NORZ = I I , CLOZ = 9. These results demonstrate that ZOT and NORZ have similar DA receptor subtype binding profiles and the behavioural tests indicate that both compounds will have a low propensity to induce EPS. In addition, NORZ is similar to CLOZ in showing a marked selectivity to inhibit limbic DA function indicating NORZ may play an important role in the atypical mode of action of ZOT.
IP-9-1 0 I BTS73 947. A Novel 01/05 Antagonist with Predicted Atypical Antipsychotic Activity
P.L. Needham, DJ. Heal, BJ. Sargent, W.R. Buckeu. Knoll
I P-9-S !ls Clozapine a Dopamlnergic Drug?
Pharmaceuticals Research Department. Nottingham, UK.
S.w. Tang, D.M. Helmeste, H. Fang, M. u, C. Widmark, C. Reist.
BTS 73 947 [(+)-1-[1-(2-chlorophenyl)cyclopropyI1-7-hydroxy-6-methoxy-2-methyl-1,2,3,4-tetrahydroisoquinoline J, discovered by Knoll Pharmaceuticals, is a novel antagonist of dopamine (DA) D .-like (D lID 5) receptors. We present its receptor binding profile and actions in behavioural models which are predictive of its antipsychotic and side-effect potential. The in vitro binding profile of BTS 73 947 has been determined using receptors from animal tissues and from cell lines expressing human clones. Behavioural tests, conducted using male CD rats, were locomotor activity and stereotype induced by d-amphetamine sulphate (2.5 mglkg sc and 10 mglkg SC, respectively) and catalepsy. Results are ED 50 ' S in mglkg ip. BTS 73 947 had high affi nity for rat D I-like, but not D z-like. receptors: Ki's (nM) = 0.6 and 1990, respectively. BTS 73 947 similarly had high affinity for human D, and D, (Ki's (nM) 0.6 and 1.0, respectively). but not Dz, D3 or D4 , receptors (Ki's > 250 nM). It did not interact (Ki > 500 nM) with 5HT 1A • 5HT ID • 5HT ZA ' 5HTzc, 5HT, . a " H I. M 1 or M z receptorsand had only weak affinity (Ki = 160 nM) for a z-adrenoceptors. In the behavioural models. BTS 73 947 potently inhibited amphetamine locomotion and stereotype (ED so's's = 0.7 and 2.4, respectively) demonstrating an "" 3.5-fold greater potency against limbic DA function. Its time of peak effect was 4 h and it had a > 6 h duration of action. By comparison. BTS 73 947 was only weakly cataleptic (ED so= 25.4) giving an excellent separation between the ED so dose to inhibit amphetamine locomotion (predictiveof antipsychotic activity) and to induce catalepsy (predictive of extrapyramidal side-effects [EPS]): ratio = 36. These results demonstrate that BTS 73 947 is a selective, high affinity Dj /D, antagonist. The behavioural tests predict that BTS 73 947 will have an atypical profile with potent, long lasting antipsychotic activity and a minimal propensity to produce EPS.
Department of Psychiatry, University of California Irvine, and VA Medical Center, Long Beach CA, USA
Based on its high affinity for cloned dopamine receptors, clozapine was proposed to work as a dopamine D4 antagonist in schizophrenia. This. coupled with the reports of elevated dopamine D4 receptor density in post-mortem schizophrenic brains, propelled much effort to seek a new potent dopamine D4 drug. To validate the site of action of clozapine as a dopamine site "in vivo", we performed ligand displacement studies on rat. calf and human brain tissues. At low concentrations (5 nM). 3H-clozapine was displaced by nanomolar concentrations of atropine and mianserin. The ineffectiveness of ketanserin and sulpiride in competing for 3H-clozapine binding argues against both serotonin Sz and dopaminergic binding sites. This finding supports the clinical observation that antihistaminergic and antimuscarinic actions are observable with low clozapine dosages but therapeutic action is generally not seen. When high dosages are used, plasma levels of clozapine start to reach the low micromolar range. We observed that clozapine, while showing low affinity competition for ' H-YM-9151-2 (I nM) binding, was still unable to displace 3H-Raclopride (6 nM ) in all three brain areas examined. Since -'H-YM-915 1-2 has potential for binding to D4 and sigma sites, clozapine was competed against 3H-YM-9 15 1-2 in three brain areas known to have differing D4 receptor distribution. Micromolar concentrations of clozapine displaced ' H-YM-9151-2 binding equi-potently in the three areas (frontal cortex, cerebellum and striatum). Alternatively. 3H_YM915 1-2 (I nM) binding was almost (80%) completely displaced by sigma ligands in these three brain areas, suggesting that clozapine competition represented sigma rather than dopaminergic binding. Taken together, test results strongly argue against a direct dopamine action of c1ozapine.
=
P Poster Presentations onist, and YM-436 I I (YM), a novel antagonist for D3 and D4 receptors [I ]. HAL and YM antagonized the mouse climbing behavior induced by apomorphine (EDso = 0.041 and 0.32 mg/kg sc for HAL and YM, respectively). Both antagonists also restored the swimming activity of mice inhibited by apomorphine (EDso= 0.026 and 0.36 mglkg sc for HAL and YM, respectively). Thus haloperidol was 8 to 14 times more potent than YM in these two paradigms. On the other hand, the cataleptogenic activity of haloperidol in rats was 160 times more potent than that of YM (EDso = 0.25 and 40 mg/kg sc for HAL and YM, respectively). These results suggest that D3 and/or D4 receptors are more closely involved in the apomorphine-induced behavioral changes than catalepsy; this is in line with the limbic distribution of D3 and D4 receptors. [ II Hidaka, K et al., J. Neurochern.• 65: 5165 (l995)
I p-9-?1 Dopamine 02 Receptor Change AfterRepeated Treatment with SM-9018, a Novel Neuroleptic Y. Ohno, T. Ishibashi, K. Ikeda, K. Ishida, M, Nakamura. Res. Cent., Sumitomo Pharmaceuticals, Osaka, Japan SM-9018 is a potential atypical neuroleptic agent that has potent blocking activities both for dopamine D2 and 5-HT2 receptors. The present study was conducted to examine the effects of subchronic treatment with SM-9018 on the striatal D2 receptors in rats to evaluate its liability for tardive dyskinesia. Two-weeks treatment of rats with SM-9018, at a dose which blocks D2 receptors (10 mglkglday, p.o.), did not significantly change the density (Bmax) or affinity (Kd) of D2 receptors (labeled by 3H-raclopride), the levels of D2s, D2L or D3 mRNA (measured by RT-PCR) in the striatum. By contrast, haloperidol treatment (3 mglkglday. for 2 weeks) significantly increase the density of striatal D2 receptors while the mRNA levels of D2 receptor family were unchanged. Haloperidol treatment markedly enhanced the incidence of apomorphine-induced stereotyped behaviors and SKF 38393 (a DI agonist)-induced repetitive jaw movement. however, the treatment with SM-9018 did not. These findings suggest that SM-9018 is weaker than haloperidol in inducing up-regulation of striatal D2 receptors and behavioral dopaminergic supersensitivity after its repeated treatments. SM-9018 seems to have low propensity to induce tardive dyskinesia.
IP-9-91 Zotepine Comparison of the Pharmacological Profiles of and Norzotepine DJ . Heal, P.L. Needham. Knoll Pharma ceut icals Research Department, Nottingham, UK
Zotepine (ZOT) is a dibenzothiepine tricyclic antipsychotic which is effective against the positive and negative symptoms of schizophrenia with a low propensity to induce extrapyramidal side-effects (EPS). In this study, the antidopaminergic profile of ZOT has been compared with that of its desmethyl metabolite, norzotepine (NORZ). Affinities for dopamine (DA) receptor subtypes were determined by [3 H)radioligand binding using cloned human receptors expressed in cell-lines. Behavioural tests, conducted using male CD rats, were locomotor activity and stereotype induced by d-amphetamine (2.5 mg/kg sc and 10 rug/kg sc, respectively) and catalepsy. Results are EDso's in mg/kg ip. ZOT and NORZ had similar DA subtype binding profiles with moderate/high affinities for D I, Dz, D3' D4 and lower affinities for Ds : Ki's (nM). D I to n, ZOT = 26,12,3, 9. 99; NORZ = 34, II, 16,31, 109. For comparison also, clozapine (CLOZ) = 121, 209,179,31.340. In the behaviouraltests, ZOT showed little separation between the doses to inhibit the locomotor and stereotype responses to d-amphetamine, whereas NORZ and CLOZ showed 9- and 25-fold separations. respectively. Locomotor activity, ZOT = 0.5, NORZ = 5.0. CLOZ = 4.0; stereotype. ZOT = 0.7, NORZ = 46, CLOZ = 96. These compounds were only weakly cataleptic (ZOT = 13, NORZ = 56, CLOZ = 34) and each showed an excellent separation between the EDso dose to inhibit amphetamine locomotion (predictive of antipsychotic activity) and to induce catalepsy (predictive of EPS): ratios. ZOT = 18, NORZ = I I , CLOZ = 9. These results demonstrate that ZOT and NORZ have similar DA receptor subtype binding profiles and the behavioural tests indicate that both compounds will have a low propensity to induce EPS. In addition, NORZ is similar to CLOZ in showing a marked selectivity to inhibit limbic DA function indicating NORZ may play an important role in the atypical mode of action of ZOT.
IP-9-1 0 I BTS73 947. A Novel 01/05 Antagonist with Predicted Atypical Antipsychotic Activity
P.L. Needham, DJ. Heal, BJ. Sargent, W.R. Buckeu. Knoll
I P-9-S !ls Clozapine a Dopamlnergic Drug?
Pharmaceuticals Research Department. Nottingham, UK.
S.w. Tang, D.M. Helmeste, H. Fang, M. u, C. Widmark, C. Reist.
BTS 73 947 [(+)-1-[1-(2-chlorophenyl)cyclopropyI1-7-hydroxy-6-methoxy-2-methyl-1,2,3,4-tetrahydroisoquinoline J, discovered by Knoll Pharmaceuticals, is a novel antagonist of dopamine (DA) D .-like (D lID 5) receptors. We present its receptor binding profile and actions in behavioural models which are predictive of its antipsychotic and side-effect potential. The in vitro binding profile of BTS 73 947 has been determined using receptors from animal tissues and from cell lines expressing human clones. Behavioural tests, conducted using male CD rats, were locomotor activity and stereotype induced by d-amphetamine sulphate (2.5 mglkg sc and 10 mglkg SC, respectively) and catalepsy. Results are ED 50 ' S in mglkg ip. BTS 73 947 had high affi nity for rat D I-like, but not D z-like. receptors: Ki's (nM) = 0.6 and 1990, respectively. BTS 73 947 similarly had high affinity for human D, and D, (Ki's (nM) 0.6 and 1.0, respectively). but not Dz, D3 or D4 , receptors (Ki's > 250 nM). It did not interact (Ki > 500 nM) with 5HT 1A • 5HT ID • 5HT ZA ' 5HTzc, 5HT, . a " H I. M 1 or M z receptorsand had only weak affinity (Ki = 160 nM) for a z-adrenoceptors. In the behavioural models. BTS 73 947 potently inhibited amphetamine locomotion and stereotype (ED so's's = 0.7 and 2.4, respectively) demonstrating an "" 3.5-fold greater potency against limbic DA function. Its time of peak effect was 4 h and it had a > 6 h duration of action. By comparison. BTS 73 947 was only weakly cataleptic (ED so= 25.4) giving an excellent separation between the ED so dose to inhibit amphetamine locomotion (predictiveof antipsychotic activity) and to induce catalepsy (predictive of extrapyramidal side-effects [EPS]): ratio = 36. These results demonstrate that BTS 73 947 is a selective, high affinity Dj /D, antagonist. The behavioural tests predict that BTS 73 947 will have an atypical profile with potent, long lasting antipsychotic activity and a minimal propensity to produce EPS.
Department of Psychiatry, University of California Irvine, and VA Medical Center, Long Beach CA, USA
Based on its high affinity for cloned dopamine receptors, clozapine was proposed to work as a dopamine D4 antagonist in schizophrenia. This. coupled with the reports of elevated dopamine D4 receptor density in post-mortem schizophrenic brains, propelled much effort to seek a new potent dopamine D4 drug. To validate the site of action of clozapine as a dopamine site "in vivo", we performed ligand displacement studies on rat. calf and human brain tissues. At low concentrations (5 nM). 3H-clozapine was displaced by nanomolar concentrations of atropine and mianserin. The ineffectiveness of ketanserin and sulpiride in competing for 3H-clozapine binding argues against both serotonin Sz and dopaminergic binding sites. This finding supports the clinical observation that antihistaminergic and antimuscarinic actions are observable with low clozapine dosages but therapeutic action is generally not seen. When high dosages are used, plasma levels of clozapine start to reach the low micromolar range. We observed that clozapine, while showing low affinity competition for ' H-YM-9151-2 (I nM) binding, was still unable to displace 3H-Raclopride (6 nM ) in all three brain areas examined. Since -'H-YM-915 1-2 has potential for binding to D4 and sigma sites, clozapine was competed against 3H-YM-9 15 1-2 in three brain areas known to have differing D4 receptor distribution. Micromolar concentrations of clozapine displaced ' H-YM-9151-2 binding equi-potently in the three areas (frontal cortex, cerebellum and striatum). Alternatively. 3H_YM915 1-2 (I nM) binding was almost (80%) completely displaced by sigma ligands in these three brain areas, suggesting that clozapine competition represented sigma rather than dopaminergic binding. Taken together, test results strongly argue against a direct dopamine action of c1ozapine.
=