[3H]4‐(Dimethylamino)‐N‐[4‐(4‐(2‐methoxyphenyl)piperazin‐ 1‐yl)butyl]benzamide, a selective radioligand for dopamine D3 receptors. I. In vitro characterization

Abstract

4‐(Dimethylamino)‐N‐(4‐(4‐(2‐methoxyphenyl)piperazin‐1‐yl)butyl)benzamide (WC‐10), a N‐phenyl piperazine analog, has been shown to have high affinity and selectivity for dopamine D₃ receptors versus dopamine D₂ receptors (Chu et al. [ 2005 ] Bioorg Med Chem 13:77–87). In this study, WC‐10 was radiolabeled with tritium (specific activity = 80 Ci/mmol) and [³H]WC‐10 binding to genetically cloned dopamine D_2L and D₃ receptors was evaluated in vitro. [³H]WC‐10 binds with a 66‐fold higher affinity to human HEK D₃ than HEK D_2L receptors, with a dissociation constant (K_d) of 1.2 nM at HEK D₃ receptors. However, [³H]WC‐10 binds to rat Sf9 rD₃ receptors with a K_d of 3.9 nM, a value that is 3‐fold lower than binding to human HEK D₃ receptors and 40‐fold value higher than binding to rat Sf9 rD_2L receptors. The K_d values obtained from saturation binding experiments were consistent with the results determined from kinetic (k_on and k_off) studies. The pharmacologic profiles of a series of dopaminergic drugs for inhibiting the binding of [³H]WC‐10 to D₃ receptors was in agreement with previously reported data. In vitro autoradiography studies of rat and monkey brains show that [³H]WC‐10 labeled D₃ sites in the striatal region. Synapse 63:717–728, 2009.