Development of scintillation-proximity assays for alpha adrenoceptors

Binding assays have long been used to determine compound affinity and selectivity for various seven-transmembrane receptors. Over time, the degree of complexity has significantly reduced, whereas the throughput of the various assays has greatly increased. In this article, we detail the development of a filter-binding assay and a scintillation-proximity assay (SPA) designed to quantify a compound's affinity for the three alpha1-adrenoceptor subtypes, alpha1A, alpha1B, and alpha1D. The various components of the assays such as ease of assay performance, robustness, cost, and generation of radioactive waste are compared and contrasted. On the basis of the results, the SPA offers many advantages of high-throughput assay formats over the traditional filter-binding assay. To follow up on the success of the alpha1-adrenoceptor SPA, SPAs for the three alpha2-adrenoceptors were developed and are detailed in this article. Affinity data generated for a select number of alpha2 compounds agree with reported literature values. These assays, like those for alpha1 subtypes, are very amenable to high-throughput screening campaigns. In conclusion, scintillation-proximity assays offer significant advantages over filter-binding assays.