To characterize the binding/inhibition and potential clinical relevance of ecopipam and relevant metabolites across a wide array of potential off-target receptors, ion channels, enzymes, and transporters.

In vitro screening studies were conducted to evaluate the binding/inhibition of ecopipam, E-G, EBS, and EBS-G to ~98 unique targets at 10 μM concentrations. For any receptor that had at least 50% inhibition, a follow-on study determined the concentration with 50% inhibition (IC₅₀). To understand whether binding/inhibition to each of these targets had potential clinical relevance, the IC₅₀ values were compared to clinical exposures as measured by the free-fraction, steady-state Cmax values (Cmax,ss,free) after dosing with ecopipam using the weight-based dosing paradigm in TS patients. Clinical relevance was determined if the IC₅₀/Cmax,ss,free was less than 10x (a 10-fold “safety margin”). If the ratio was >10x but <15x, then an effect on the receptor binding could not be ruled out.  The clinical relevance of specific targets in the brain was also considered based on the CNS penetration of ecopipam and its metabolites.

Ecopipam, EBS, and E-G demonstrated marked inhibition of D1Rs and ecopipam and EBS also inhibited D5Rs at clinically relevant concentrations expected after steady-state dosing in TS.  EBS-G was not active against any dopamine receptor subtype.  Potential off-target binding/inhibition effects of ecopipam against D_2S, 5HT1A, H₁, and Alpha2C could not be ruled out, but these interactions were above a 10-fold “safety” margin.