N-(p-isothiocyanatophenethyl)spiperone, a selective and irreversible antagonist of D2 dopamine receptors in brain

N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ), an irreversible and nonselective protein-modifying reagent, has been used extensively in studies involving inactivation of receptors. Here, we present N-(p-isothiocyanatophenethyl)spiperone (NIPS), a novel and highly selective irreversible inactivator of D2 but not D1 receptors. In in vitro studies, NIPS exhibited an apparent Ki of 10 nM for [3H]methylspiperone binding to D2 receptors in rat striatum. Preincubation of the striatal membranes with NIPS followed by extensive washing resulted in up to an 80% reduction of the D2 receptor maximum binding (Bmax). Coincubation with the D2 receptor antagonist domperidone could protect against this reduction. NIPS was additionally shown to irreversibly inactivate D2 receptor binding activity in cultured cells expressing the D2 receptor protein. In in vivo administration studies, using [3H]SCH 23390 and [3H]spiperone to assay D1 and D2 receptors in vitro, 24 hr after injection (s.c.) with 5 to 40 mg/kg of NIPS D2 receptor, Bmax was decreased by 58 to 76%, without a change in D2 receptor affinity. In contrast, there was no effect on D1 receptor Bmax or affinity. There was also a small (24%) reduction in frontal cortex 5-hydroxytryptamine2 receptors by 20 mg/kg of NIPS. However, there was no effect on alpha-1 or alpha-2 adrenergic receptors in the frontal cortex, or on muscarinic cholinergic or 5-hydroxytryptamine1A receptors in the hippocampus. After single doses of either 20 mg/kg of NIPS or 10 mg/kg of EEDQ, the D2 receptor recovery rate was much slower after NIPS (half-time of receptor recovery = 170 hr) than after EEDQ (half-time of receptor recovery = 76.7 hr).(ABSTRACT TRUNCATED AT 250 WORDS)