l‐Stepholidine is a potent pan‐dopamine receptor antagonist at G protein and β‐arrestin mediated signaling in vitro (662.5)

Dopamine receptors (DARs) are highly validated drug targets in neuropsychiatric disease and, as such, compounds acting on this receptor family are both scientifically and clinically important. The Chinese herbal extract component l‐stepholidine has been reported to exhibit D2 DAR antagonism and D1 DAR agonist‐like activities in a number of in vivo behavioral analyses. Prior studies have further shown complicated mixed pharmacological responses involving both dopamine and serotonin receptors; however, clear in vitro characterization on individual DAR subtype signaling pathways has not been extensively explored. These data are particularly important given the recent discovery of the potential for signaling bias within the DAR family. In this study we present a broad examination of the biological actions and binding activities of l‐stepholidine on all DAR subtypes. l‐Stepholidine demonstrated relatively high binding affinity for all DAR subtypes, but failed to display any agonist response in either G protein‐ (cAMP assays and GTPγS binding), or β‐arrestin‐ (β‐arrestin translocation assays) mediated signaling at any DAR tested. Furthermore, l‐stepholidine was a full antagonist of dopamine mediated signaling at both D1‐ and D2‐like receptors and did not display signaling bias, thereby demonstrating that it acts as a non‐selective pan‐dopamine receptor antagonist in vitro.Grant Funding Source: NIH Intramural Research Program