TPA-023B has high affinity for α5 subtype with Ki of 1.1 nM of human recombinant GABAA receptor, but over 1500-fold lower for the α4- and α6 containing subtypes (Ki > 1000 nM). In different regions of the CNS,TPA-023B also has a comparable affinity for native rat GABAA receptors (Ki of 0.32-0.99 nM in cerebellum, spinal cord and frontal cortex). TPA-023B antagonizes the ability of chlordiazepoxide to potentiate the GABA EC20-induced current in cells expressing the α1 subtype. More specifically, 3 μM chlordiazepoxide potentiates the GABA EC20 current by 105% and this effect could be reduced to 8% in the presence of 100 nM TPA-023B.

Measured using an in vivo [3H]flumazenil binding assay,TPA-023B gives dose- and time-dependent occupancy of rat brain GABAA receptors, with 50% occupancy corresponding to a respective dose and plasma drug concentration of 0.09 mg/kg and 19 ng/mL. TPA-023B is anxiolytic in rodent and primate (squirrel monkey) models of anxiety (elevated plus maze, fear-potentiated startle,up to doses (10 mg/kg) corresponding to occupancy of greater than 99%.