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 inducedby apomorphine (EDso = 0.041 and 0.32 mg/kg sc for HAL and YM,respectively). Both antagonists also restored the swimming activity ofmice inhibited by apomorphine (EDso= 0.026 and 0.36 mglkg sc for HALand YM, respectively). Thus haloperidol was 8 to 14 times more potentthan YM in these two paradigms. On the other hand, the cataleptogenicactivity 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). Theseresults suggest that D3 and/or D4 receptors are more closely involvedin the apomorphine-induced behavioral changes than catalepsy; this is inline 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 AfterRepeatedTreatment withSM-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 presentstudy was conducted to examine the effects of subchronic treatment withSM-9018 on the striatal D2 receptors in rats to evaluate its liability fortardive dyskinesia. Two-weeks treatment of rats with SM-9018, at a dosewhich blocks D2 receptors (10 mglkglday, p.o.), did not significantlychange the density (Bmax) or affinity (Kd) of D2 receptors (labeledby 3H-raclopride), the levels of D2s, D2L or D3 mRNA (measured byRT-PCR) in the striatum. By contrast, haloperidol treatment (3 mglkglday.for 2 weeks) significantly increase the density of striatal D2 receptorswhile the mRNA levels of D2 receptor family were unchanged. Haloperi­dol treatment markedly enhanced the incidence of apomorphine-inducedstereotyped behaviors and SKF 38393 (a DI agonist)-induced repetitivejaw movement. however, the treatment with SM-9018 did not. Thesefindings suggest that SM-9018 is weaker than haloperidol in inducingup-regulation of striatal D2 receptors and behavioral dopaminergic su­persensitivity after its repeated treatments. SM-9018 seems to have lowpropensity to induce tardive dyskinesia.

IP-9-S !ls Clozapine a Dopamlnergic Drug?

S.w. Tang, D.M. Helmeste, H. Fang, M. u, C. Widmark, C. Reist.Department ofPsychiatry, University of California Irvine, and VAMedical Center, Long Beach CA, USA

Based on its high affinity for cloned dopamine receptors, clozapine wasproposed to work as a dopamine D4 antagonist in schizophrenia. This.coupled with the reports of elevated dopamine D4 receptor density inpost-mortem schizophrenic brains, propelled much effort to seek a newpotent dopamine D4 drug. To validate the site of action of clozapine asa dopamine site "in vivo", we performed ligand displacement studieson rat. calf and human brain tissues. At low concentrations (5 nM).3H-clozapine was displaced by nanomolar concentrations of atropine andmianserin. The ineffectiveness of ketanserin and sulpiride in competingfor 3H-clozapine binding argues against both serotonin Sz and dopamin­ergic binding sites. This finding supports the clinical observation thatantihistaminergic and antimuscarinic actions are observable with lowclozapine dosages but therapeutic action is generally not seen. Whenhigh dosages are used, plasma levels of clozapine start to reach thelow micromolar range. We observed that clozapine, while showing lowaffinity competition for ' H-YM-9151-2 (I nM) binding, was still unableto displace 3H-Raclopride (6 nM ) in all three brain areas examined. Since-'H-YM-9151-2 has potential for binding to D4 and sigma sites, clozapinewas competed against 3H-YM-9 15 1-2 in three brain areas known tohave differing D4 receptor distribution. Micromolar concentrations ofclozapine displaced ' H-YM-9151-2 binding equi-potently in the threeareas (frontal cortex, cerebellum and striatum). Alternatively. 3H_YM­9151-2 (I nM) binding was almost (80%) completely displaced by sigmaligands in these three brain areas, suggesting that clozapine competitionrepresented sigma rather than dopaminergic binding. Taken together, testresults strongly argue against a direct dopamine action of c1ozapine.

105

IP-9-91 Comparison of the Pharmacological Profiles ofZotepine andNorzotepine

DJ . Heal, P.L. Needham. Knoll Pharma ceut icals Research Department,Nottingham, UK

Zotepine (ZOT) is a dibenzothiepine tricyclic antipsychotic which iseffective against the positive and negative symptoms of schizophreniawith a low propensity to induce extrapyramidal side-effects (EPS). In thisstudy, the antidopaminergic profile of ZOT has been compared with thatof 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 stereotypeinduced 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 DI, 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. Forcomparison also, clozapine (CLOZ) = 121, 209,179,31.340.

In the behavioural tests, ZOTshowed little separation between the dosesto 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 compoundswere only weakly cataleptic (ZOT = 13, NORZ = 56, CLOZ = 34) andeach showed an excellent separation between the EDso dose to inhibitamphetamine locomotion (predictive of antipsychotic activity) and toinduce catalepsy (predictive of EPS): ratios. ZOT = 18, NORZ = I I ,CLOZ = 9.

These results demonstrate that ZOT and NORZ have similar DAreceptor subtype binding profiles and the behavioural tests indicate thatboth compounds will have a low propensity to induce EPS. In addition,NORZ is similar to CLOZ in showing a marked selectivity to inhibitlimbic DA function indicating NORZ may play an important role in theatypical mode of action of ZOT.

IP-9-1 0 IBTS73 947. A Novel 01/05 Antagonist withPredicted Atypical Antipsychotic Activity

P.L. Needham, DJ. Heal, BJ. Sargent, W.R. Buckeu. KnollPharmaceuticals Research Department. Nottingham, UK.

BTS 73 947 [(+)-1-[1-(2-chlorophenyl)cyclopropyI1-7-hydroxy-6-meth­oxy-2-methyl-1,2,3,4-tetrahydroisoquinolineJ, discovered by Knoll Phar­maceuticals, is a novel antagonist of dopamine (DA) D .-like (D lID5) receptors. We present its receptor binding profile and actions in be­havioural models which are predictive of its antipsychotic and side-effectpotential.

The in vitro binding profile of BTS 73 947 has been determinedusing receptors from animal tissues and from cell lines expressing humanclones. Behavioural tests, conducted using male CD rats, were locomotoractivity and stereotype induced by d-amphetamine sulphate (2.5 mglkgsc and 10 mglkg SC, respectively) and catalepsy. Results are ED 50 ' S inmglkg 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 highaffinity for human D, and D, (Ki's (nM) =0.6 and 1.0, respectively). butnot Dz, D3 or D4 , receptors (Ki's > 250 nM). It did not interact (Ki >500 nM) with 5HT1A• 5HTID • 5HT ZA ' 5HTzc, 5HT, . a " HI. M1 or M zreceptorsand had only weak affinity (Ki = 160 nM) for a z-adrenoceptors.In the behavioural models. BTS 73 947 potently inhibited amphetaminelocomotion and stereotype (ED so's's = 0.7 and 2.4, respectively) demon­strating an "" 3.5-fold greater potency against limbic DA function. Its timeof peak effect was4 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 excellentseparation between the ED so dose to inhibit amphetamine locomotion(predictiveof antipsychotic activity) and to induce catalepsy (predictive ofextrapyramidal side-effects [EPS]): ratio = 36.

These results demonstrate that BTS 73 947 is a selective, high affinityDj /D, antagonist. The behavioural tests predict that BTS 73 947 willhave an atypical profile with potent, long lasting antipsychotic activityand a minimal propensity to produce EPS.