Abstract

Abstract ID 90311

Poster Board 475

The D₂ dopamine receptor (D2R) is a G protein-coupled receptor (GPCR) and a validated drug target for the treatment of many neuropsychiatric disorders, including psychosis. All currently available antipsychotics are antagonists of the D2R; however, all of these drugs exhibit polypharmacology resulting in a plethora of off-target side effects including weight gain, dysphoria, and sedation, among others. A highly-selective D2R antagonist might overcome these pitfalls and increase patient compliance with taking antipsychotic medications. Previously, our lab conducted a high-throughput screen to identify D2R-selective antagonists with reduced activity at other GPCRs. This screen identified a promising hit compound that was chemically optimized into the lead drug candidates, NCGC1360 and NCGC1366. These drug leads have relatively high binding affinities at the D2R (∼80 and ∼50 nM, respectively), while displaying >100-fold selectivity over the D3R and >24-fold selectivity over the D4R. A β-arrestin recruitment assay revealed even higher D2R selectivity (>100-fold) of these compounds over the D3R and D4R. In a screen against an array of 46 GPCRs, channels, and transporters using radioligand binding assays, NCGC1360 and NCGC1366 only inhibited radioligand binding to the D2R. A functional screen of 168 GPCRs further determined that NCGC1360 and NCGC1366 were exceptionally selective with each compound completely antagonizing β-arrestin recruitment to the D2R with only minor effects at a few other receptors. Schild-type analyses using dopamine-stimulated β-arrestin recruitment revealed that both compounds are competitive antagonists. A comparative molecular docking study using the active structures of both the D2R and D3R showed that NCGC1366 occupies the orthosteric binding pocket of the D2R with extended contacts with residues in extracellular loop 2 (ECL2). The contacts in ECL2 are not conserved between the D2R and D3R, which may confer D2R selectivity. We thus swapped the ECL2 of the D2R and D3R and found that a D2R mutant with the D3R ECL2 exhibited diminished affinity for NCGC1360 and NCGC1366. Conversely, a D3R mutant with the D2R ECL2 exhibited increased affinity for NCGC1360 and NCGC1366, consistent with the molecular docking study. Pharmacokinetic studies of NCGC1360 in mice revealed a half-life of 1.8 hr in plasma and 1 hr in brain with excellent brain penetration. Finally, NCGC1360 was characterized in animal models that are predicative of antipsychotic efficacy and on-target side effects. NCGC1360 dose-dependently decreased amphetamine-induced hyperlocomotion in mice and also rescued deficits in pre-pulse inhibition induced by amphetamine. Importantly, NCGC1360 did not induce catalepsy up to the highest dose tested (10 mg/kg), suggesting that it would not induce extrapyramidal side effects in patients. Taken together, these studies provide support for continuing the development of this scaffold with preclinical and IND-enabling studies.

Funded by the National Institutes of Health intramural research program.