WAY-100635 is a potent dopamine D4 receptor agonist

Rationale and objectives WAY-100635 is a prototypical 5-HT1A receptor antagonist and has been used widely as a pharmacological probe to investigate the distribution and function of 5-HT1A receptors. Results from our studies suggested that WAY-100635 was potently inducing effects unrelated to its 5-HT1A receptor affinity. In the present work, we evaluated the in vitro pharmacology of this compound at two D-2-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, D-3, and D-4.2 receptors, respectively. Subsequent saturation analyses demonstrated that the K-d of [H-3]WAY-100635 at D-4.2 receptors was 2.4 nM, only tenfold higher than 5-HT1A. 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-HT1A receptor antagonist, as previously reported, and conclusions drawn from studies that employed WAY-100635 as a selective 5-HT1A antagonist may need to be reevaluated.