(-) S amisulpride binds with high affinity to cloned dopamine D3 and D2 receptors

Amisulpride is a substituted benzamide antipsychotic with nanomolar affinity and high selectivity for dopamine D-2 and dopamine D-3 receptors. The interaction of racemic (+/- )RS amisulpride and its two enantiomers (+)R and (-)S with dopamine D-2 and dopamine D-3 receptors subtypes were compared with that of haloperidol. Binding studies were performed using either [H-3]spiperone or [H-3]nemonapride in baculovirus/Spodoptera frugiperda insect (Sf-9) cell system expressing either the human dopamine recombinant D(2)long (hD(2L)) or the rat dopamine recombinant D-3 (rD(3)) receptors. K-i values at dopamine rD(3) receptors were similar regardless of the radioligand used, whereas at hD(2L) receptors values were higher using [3H]spiperone than [H-3]nemonapride, However, the rank order of compound potency against radiolabeled spiperone or nemonapride both at dopamine hD(2L) and at dopamine rD(3) receptors was similar. (-)S amisulpride displaced [H-3]spiperone or [H-3]nemonapride binding from both dopamine hD(2L) or dopamine rD(3) receptors, being twofold more potent than the racemic form and 38-19-fold more potent than (+)R enantiomer. Both racemic and the (-)S enantiomer exhibited 2-4 ([H-3]spiperone)- and 3-4 ([H-3]nemonapride)-fold higher affinity than haloperidol for dopamine rD(3) receptor, respectively. The (+)R enantiomer has weaker affinity with respect to haloperidol for both dopamine hD(2L) and dopamine rD(3) receptors, Our results show that ( -)S amisulpride is the active enantiomer of amisulpride, showing high affinity for dopamine D-3 and dopamine D-2 receptors