In Vitro Characterization of A Novel Allosteric Potentiator of the Dopamine D1 Receptor

Allosteric potentiators of the dopamine D1 receptor could be useful for treatment of Parkinson's disease, schizophrenia, depression, ADHD, and narcolepsy. We identified a novel D1 potentiator (“DETQ”)by high‐throughput screening followed by iterative chemical optimization. In a HEK293 cell line expressing the human D1 receptor, agonist‐stimulated cAMP production was measured in the presence of an EC20 concentration of dopamine using homogeneous time resolved fluorescence (HTRF) technology. DETQ potentiated the dopamine response with a mean EC50 of 5.8 nM and mean efficacy corresponding to 95% of the maximum response to dopamine. In the absence of exogenous dopamine (agonist mode), the maximum efficacy of DETQ was 11.6% with an EC50 of 30 nM; based on the initial slopes of the two curves (Ehlert R‐ratio), DETQ was thus 43‐fold less potent as an allosteric agonist than as a potentiator. When concentration‐response curves for dopamine were carried out at multiple DETQ concentrations in the cAMP assay, DETQ shifted the dopamine curve 21‐fold to the left with a KB of 26 nM. In experiments measuring binding of the D1 antagonist 3H‐SCH23390 to the human D1 receptor, 100 nM DETQ caused a 5‐fold leftward shift in the concentration‐inhibition curve for dopamine, indicating adirect effect of DETQ on the D1 receptor. The potency of DETQ in the cAMP assay was about 50‐fold lower at the mouse and rat D1 receptors than at human, rhesus, and dog D1 receptors. DETQ was inactive at concentrations up to atleast 10 uM when tested in agonist and potentiator modes at related receptors, including D2, D5, β1, β2, β3, and 5HT6. DETQ was also inactive in binding and/or functional assays at a largeset of unrelated targets.