WAY-100635 is a potent dopamine D4 receptor agonist

Rationale and objectives WAY-100635 is a prototypical 5-HT_1A receptor antagonist and has been used widely as a pharmacological probe to investigate the distribution and function of 5-HT_1A receptors. Results from our studies suggested that WAY-100635 was potently inducing effects unrelated to its 5-HT_1A receptor affinity. In the present work, we evaluated the in vitro pharmacology of this compound at two D₂-like receptor subtypes.Method The functional properties and binding affinities of WAY-100635 were evaluated in HEK 293 cells stably expressing dopamine D_2L or D_4.4 receptors.Results Initial screens performed by the NIMH Psychoactive Drug Screening Program indicated that WAY-100635 displayed 940, 370, and 16 nM binding affinities at D_2L, D₃, and D_4.2 receptors, respectively. Subsequent saturation analyses demonstrated that the K _d of [³H]WAY-100635 at D_4.2 receptors was 2.4 nM, only tenfold higher than 5-HT_1A. WAY-100635 and its major metabolite, WAY-100634, were potent agonists in HEK-D_4.4 cells (EC₅₀=9.7±2.2 and 0.65±0.2 nM, respectively). WAY-100635 behaved as a full agonist, and WAY-100634 was a nearly full agonist. In HEK-D_2L cells, WAY-100635 weakly antagonized the effects of 300 nM quinpirole. Subsequent radioligand binding studies confirmed that WAY-100635 possesses high affinity for D_4.4 receptors but binds weakly to D_2L receptors (3.3±0.6 and 420±11 nM, respectively).Conclusions This study demonstrates that WAY-100635 is not a “selective” 5-HT_1A receptor antagonist, as previously reported, and conclusions drawn from studies that employed WAY-100635 as a selective 5-HT_1A antagonist may need to be reevaluated.