O-10054 Validation of [3H]astemizole binding assay in HEK293 cells expressing HERG K+ channels

A radioligand binding assay for HERG K+ channel was developed to identify compounds with potential cardiotoxicity. Characterization of [3H]astemizole binding assay for HERG channels was performed in HERG-expressing HEK293 cells. Specific binding was 90% using 10 μg membrane protein with 1. 5 nM [3H]astemizole. The estimated Kd and Bmax are 5. 91±0. 81 nM and 6. 36±0. 26 pmol/mg, respectively. The intraassay and interassay variations are 11. 4% and 14. 9%, respectively. Binding affinity for 32 compounds demonstrated similar potency rank order for HERG inhibition reported in the literature. The [3H]astemizole binding data demonstrated a rank order of affinity highly correlated to that of inhibitory potency in the electrophysiological studies in HEK293 (rsp= 0. 92; P