Pharmacological actions of a novel and selective dopamine D₃ receptor antagonist, KCH-1110

1-(2-Ethoxy-phenyl)-4-[3-(3-thiophen-2-yl-isoxazolin-5-yl)-propyl] -piperazine (KCH-1110), has a high affinity for human dopamine D₃ (hD₃) receptor (K_i=1.28nM) with about 90-fold selectivity over the human dopamine D_2L (hD_2L) receptor. Antipsychotic or antidopaminergic activity of KCH-1110 was investigated in the models for the positive symptoms of schizophrenia, apomorphine-induced climbing and cocaine-induced hyperlocomotion, in mice. Intraperitoneal (i.p.) or oral (p.o.) administration of KCH-1110 potently inhibited the apomorphine-induced cage climbing without any rotarod ataxia in mice. Cocaine-induced hyperactivity was also antagonised by KCH-1110. In addition, KCH-1110 attenuated the hypothermia induced by a selective dopamine D₃ agonist, 7-OH-DPAT in mice. KCH-1110 did not induce catalepsy in mice, but at much higher doses only a slight catalepsy response was shown. Although high doses of KCH-1110 significantly enhanced serum prolactin secretion in rats, low dose of KCH-1110 did not increase prolactin levels in rats. The present studies, therefore, suggest that KCH-1110 is a potent and relatively selective dopamine D ₃ receptor antagonist with antipsychotic actions.