Neuropharmacological Profile of a Novel Potential Atypical Antipsychotic Drug Y-931 (8-fluoro-12-(4-methylpiperazin-1-yl)- 6H-[1]benzothieno[2,3-b][1,5] benzodiazepine maleate) Toshihiko Morimoto, M.S., Kenji Hashimoto, Ph.D., Hiroshi Yasumatsu, Ph.D., Hiroshi Tanaka, Ph.D., Masatake Fujimura, Ph.D., Makoto Kuriyama, M.S, Koreichi Kimura, Ph.D., Shuzo Takehara, M.S., and Keiji Yamagami, Ph.D. The neuropharmacological profile of Y-931, 8-fluoro-12- 931 demonstrated the most potent protective action against (4-methylpiperazin-1-yl)- 6H-[1]benzothieno [2,3- the dizocilpine-induced neurotoxicity (neuronal b][1,5]benzodiazepine maleate, was investigated in vacuolization) in the rat retrosplenial cortex ([Y-931 (ED50; comparison with those of typical and claimed atypical 0.20 mg/kg, p.o.), olanzapine (1.1), clozapine (5.7), antipsychotic drugs. Similar to clozapine and olanzapine, risperidone (6.9), haloperidol (19)). Furthermore, Y-931 Y-931 interacted with multiple neurotransmitter receptors and clozapine, unlike the other antipsychotics used, such as dopaminergic, serotonergic, ␣-adrenergic, reversed the dizocilpine-induced social deficits at the same muscarinic and histaminergic receptors. Y-931, as well as doses at which their neuroprotective action was exhibited. the other antipsychotics, was active in a dose-dependent The present results suggest that Y-931 may be a novel manner in established tests which are indicative of potential potential atypical antipsychotic drug with a low risk of antipsychotic activity such as inhibition of apomorphine- extrapyramidal syndrome (EPS) and the property to induced hyperactivity and suppression of conditioned ameliorate NMDA receptor hypofunction. avoidance responses, however, only Y-931 and clozapine [Neuropsychopharmacology 26:456–467, 2002] were devoid of cataleptogenic potential. In models of N- © 2002 American College of Neuropsychopharmacology. methyl-D-aspartate (NMDA) receptor hypofunction, Y- Published by Elsevier Science Inc. KEY WORDS: Y-931; Dizocilpine ((ϩ)-MK-801); Atypical Schizophrenia is a heterogeneous disease that com- antipsychotic drugs; Schizophrenia; Glutamate; Dopamine prises multiple psychological domains such as positive symptoms, negative symptoms and cognitive dysfunc- From the Drug Discovery Laboratories, Pharmaceutical Research tion. The efficacy of typical antipsychotic drugs, such as Division, Welfide Corporation 7-25, Koyata 3-Chome, Iruma, haloperidol, in treating positive symptoms correlates Saitama, 358-0026, Japan. highly with their affinity for postsynaptic dopamine D Address correspondence to: Dr. Kenji Hashimoto, Welfide Cor- 2 poration, 7-25 Koyata 3-Chome, Iruma, Saitama 358-0026, Japan. receptors, suggesting that the dopamine D2 receptor Tel.: ϩ81-42-963-3121, Fax: ϩ81-42-964-1906. might play a role in the psychotic symptoms of schizo- Received April 12, 2001; revised July 31, 2001; accepted August 7, phrenia. However, a major problem associated with the 2001. Online publication: 8/27/01 at www.acnp.org/citations/Npp use of typical antipsychotic drugs is the production of 082701163. an extrapyramidal syndrome (EPS) as a result of their NEUROPSYCHOPHARMACOLOGY 2002–VOL. 26, NO. 4 © 2002 American College of Neuropsychopharmacology Published by Elsevier Science Inc. 0893-133X/02/$–see front matter 655 Avenue of the Americas, New York, NY 10010 PII S0893-133X(01)00368-2 NEUROPSYCHOPHARMACOLOGY 2002–VOL. 26, NO. 4 Neuropharmacological Profile of Y-931 457 antagonism of dopaminergic projections of the nigros- these neuropathological changes (Sutherland and Hoes- triatal pathway. In addition, their poor efficacy against ing 1993; Maddock 1999). Therefore, determination of negative symptoms and cognitive dysfunction, as well the potential to reverse dizocilpine-induced neuropatho- as the existence of treatment-resistant patients presents logical changes in the rat retrosplenial cortex may pro- more therapeutic limitations on their use. vide a beneficial model for screening and evaluating Clozapine, a prototype of atypical antipsychotic therapeutic agents targeted against the negative symp- drugs, appears to overcome many of the deficiencies as- toms and cognitive dysfunction associated with schizo- sociated with the use of typical antipsychotic drugs. It phrenia (Olney and Farber 1995; Olney et al. 1999). has been shown to be beneficial in approximately 30% In addition, it has been suggested that activity of of patients who do not respond to typical antipsychotic NMDA receptors on cortical glutamatergic efferent pro- therapy, without producing extrapyramidal syndrome jections affects the regulation of various neurotransmit- (EPS) (Kane et al. 1988; Buchanan 1995; Ashby and ter systems involved in a subcortical negative feedback Wang 1996; Meltzer et al. 1999). Despite these advan- loop. For instance, prolonged reductions in cortical ac- tages, the clinical use of clozapine is limited because of tivity of NMDA receptors associated with schizophre- a significant incidence of lethal agranulocytosis (Gro- nia would diminish tonic dopamine release and possi- hmann et al. 1989; Kane and McGlashan 1995; Borison bly lead to large amplitude phasic dopamine activity in 1997). Furthermore, it is known that clozapine also is the midbrain that may drive psychotic symptoms associated with a range of other side effects such as (Carlsson and Carlsson 1990; Grace 1991). It is therefore weight gain, hypersalivation, sedation, cardiovascular suggested that restoration of glutamatergic neurotrans- side effects, lowering of seizure threshold (Miller 2000). mission may possibly contribute to improved therapeu- Although clozapine has triggered the introduction of a tic efficacy against refractory schizophrenia compared number of novel antipsychotic drugs that have also with conventional dopamine antagonists. claimed atypical status during the past decade, it re- In the light of the above observations, we worked on mains controversial whether these newer agents cap- the development of a compound that could suppress ture the clinical uniqueness of clozapine (Kane and Mc- dopaminergic hyperactivity with a low risk of side ef- Glashan 1995; Meltzer et al. 1999; Remington and fects as well as inhibit dizocilpine-induced neuropatho- Kapur 2000). logical changes in the rat retrosplenial cortex. In this pa- Following the domination of the dopamine hypothe- per, we report a novel, potential atypical antipsychotic sis in schizophrenia, several lines of evidence have sug- drug Y-931, 8-fluoro-12-(4-methylpiperazin-1-yl)-6H- gested that a dysfunction in glutamatergic neurotrans- [1]benzothieno [2,3-b][1,5]benzodiazepine maleate, mission might be involved in the pathophysiology of with properties to ameliorate the NMDA receptor hy- schizophrenia (Javitt and Zukin 1991; Olney and Farber pofunction (Figure 1). 1995; Coyle 1996; Tamminga 1998; Aghajanian and Marek 2000). This hypothesis evolves from clinical find- ings that phencyclidine (PCP) and its congener ketamine, MATERIALS AND METHODS which block the N-methyl-D-aspartate (NMDA) receptor Animals ion channel, induce a schizophrenia-like psychosis repre- senting negative and positive symptoms as well as cog- Male Wistar rats (Japan SLC Inc., Shizuoka, Japan), nitive dysfunction in humans (Krystal et al. 1994; Javitt male Lister hooded rats (Seac Yoshitomi, Fukuoka, Ja- and Zukin 1991; Luby et al. 1959). This evidence has led pan) and female Sprague-Dawley rats (Japan Clea Inc., to the extensive use of NMDA receptor antagonists in the Tokyo, Japan) were housed under environmentally con- preclinical research of schizophrenia (Javitt and Zukin trolled conditions (lights on 6:00 A.M. to 6:00 P.M.; 23 Ϯ 1991; Jentsch and Roth 1999; Olney and Farber 1995). Among these approaches, Olney et al. (1989) have dem- onstrated that NMDA receptor antagonists such as PCP and dizocilpine ((ϩ)-MK-801) induce neuropathological changes in the rat retrosplenial cortex, which is a compo- nent of the Papez-like limbic circuit. Interestingly, it has been reported that clozapine, but not haloperidol, blocks the dizocilpine-induced neuropathological changes in the rat retrosplenial cortex at therapeutic doses (Farber et al. 1996; Fujimura et al. 2000; Hashimoto et al. 2000). The retrosplenial cortex has been shown to play a pivotal role in discriminative avoidance learning and spatial mem- Figure 1. Chemical structure of Y-931 (8-fluoro-12-(4- ory processes, thus the cognitive dysfunction produced methylpiperazin-1-yl)-6H-[1]benzothieno [2,3-b][1,5]benzo- by NMDA receptor antagonists may, in part, result from diazepine maleate). 458 T. Morimoto et al. NEUROPSYCHOPHARMACOLOGY 2002–VOL. 26, NO. 4 3ЊC; 55 Ϯ 20% humidity) and had access to food and Radioligand Binding Assays water ad libitum. Details of the animals used for each Each assay was performed in duplicate by incubating experimental procedure are given below. All experi- aliquots of tissue preparation with the tritium ligand in ments were carried out in accordance with the Guide for the assay buffer. The tissues and assay conditions used the Care and Use of Laboratory Animals, Research Laborato- are summarized in Table 1. The striatum, hippocampus ries, Welfide Corporation. and cerebral cortex were dissected from brains of male Wistar rats (7 weeks old, 159–193 g) which were sacri- ficed by decapitation. Choroid plexus was dissected Drugs from porcine brains supplied from Cosmo Bio Co. Ltd. (Tokyo, Japan). The dissected tissues were stored at Y-931, olanzapine, clozapine, haloperidol and risperi- Ϫ