MS Binding Assays for D1 and D5 Dopamine Receptors

MS Binding Assays are a label‐free alternative to radioligand binding assays. They provide basically the same capabilities as the latter, but an unlabeled reporter ligand is used instead of a radioligand. The study presented herein describes the development of MS Binding Assays that address D1 and D5 dopamine receptors. A highly sensitive, rapid and robust LC–ESI‐MS/MS quantification method for the selective D1 dopamine receptor antagonist SCH23390 ((5R)‐8‐chloro‐3‐methyl‐5‐phenyl‐1,2,4,5‐tetrahydro‐3‐benzazepin‐7‐ol) was established and validated, using its 8‐bromo analogue SKF83566 as an internal standard. This quantification method proved to be suitable for the characterization of SCH23390 binding to human D1 and D5 receptors. Following the concept of MS Binding Assays, saturation experiments for D1 and D5 receptors were performed, as well as competition experiments for D1 receptors. The results obtained are in good agreement with results from radioligand binding assays and therefore indicate that the established MS Binding Assays addressing D1 and D5 receptors are well‐suited substitutes for radioligand binding assays, the technique that has so far dominated affinity determinations toward these targets. Radioligands—no longer needed! We describe binding assays for D1 and D5 dopamine receptors using LC–MS as detection technique for an unlabeled reporter ligand. Based on a highly sensitive and rapid LC–ESI‐MS/MS quantification method, saturation and competition experiments could be performed. The results indicate that the established MS Binding Assays are an efficient and reliable alternative to conventional radioligand binding assays.