Efficacy of Hybrid Tetrahydrobenzo[d]thiazole Based Aryl Piperazines D-264 and D-301 at D2 and D3 Receptors

Abstract

In elucidating the role of pharmacodynamic efficacy at D3 receptors in therapeutic effectiveness of dopamine receptor agonists, the influence of study system must be understood. Here two compounds with D3 over D2 selectivity developed in our earlier work, D-264 and D-301, are compared in dopamine receptor-mediated G-protein activation in striatal regions of wild-type and D2 receptor knockout mice and in CHO cells expressing D2 or D3 receptors. In caudate-putamen of D2 knockout mice, D-301 was ~ 3-fold more efficacious than D-264 in activating G-proteins as assessed by [35S]GTP S binding; in nucleus accumbens, D-301 stimulated G-protein activation whereas D-264 did not. In contrast, the two ligands exerted similar efficacy in both regions of wild-type mice, suggesting both ligands activate D2 receptors with similar efficacy. In D2 and D3 receptor-expressing CHO cells, D-264 and D-301 appeared to act in the [35S]GTP S assay as full agonists because they produced maximal stimulation equal to dopamine. Competition for [3H]spiperone binding was then performed to determine Ki/EC50 ratios as an index of receptor reserve for each ligand. Action of D-301, but not D-264, showed receptor reserve in D3 but not in D2 receptor-expressing cells, whereas dopamine showed receptor reserve in both cell lines. G o1 is highly expressed in brain and is important in D2 -like receptor-G protein coupling. Transfection of G o1 in D3- but not D2-expressing CHO cells led to receptor reserve for D-264 without altering receptor expression levels. D-301 and dopamine exhibited receptor reserve in D3-expressing cells both with and without transfection of G o1. Altogether, these results indicate that D-301 has greater intrinsic efficacy to activate D3 receptors than D-264, whereas the two compounds act on D2 receptors with similar intrinsic efficacy. These findings also suggest caution in interpreting Emax values from functional assays in receptor-transfected cell models without accounting for receptor reserve.

Discovery, Optimization, and Characterization of ML417: A Novel and Highly Selective D3 Dopamine Receptor Agonist

“…Further, the positively charged piperazine nitrogen of 20 closest to the anisole moiety was found to interact with Asp110 3.32 (Figure 7B), the highly conserved aspartic acid residue found in TM3 of all biogenic amine GPCRs. 77 Given this observation, it is not surprising that compounds either lacking this nitrogen (50) or with immediately adjacent methyl groups (46 and 48) that could a K i (nM) values for the indicated compounds were determined as described in the Experimental Section. b NA indicates that the inhibition of binding was < 50% in the primary assay conducted using a single 10 μM concentration.…”

“…R f = 0.48 (5% MeOH/ CH 2 Cl 2 ). 1 (50). A mixture of (4-(2-chloroethyl)piperidin-1-yl)(4-methoxyphenyl)methanone (64.9 mg, 0.230 mmol, 1.0 equiv), 4-methoxyphenol (32.0 mg, 0.258 mmol, 1.1 equiv), and potassium carbonate (57.0 mg, 0.412 mmol, 1.8 equiv) in DMF (1 mL) was heated at 55 °C for 19 h, followed by 80 °C for 45 h and then cooled to rt.…”

Advances and challenges in the search for D2 and D3 dopamine receptor-selective compounds

“…However, the fold-selectivity decreased to 22-fold when tested in CHO cells expressing either human D 2 R or D 3 R [107]. In fact, D-264 stimulated [ 35 S]GTPγS binding to brain membranes prepared from wild-type mice, but had no efficacy in membranes from D 2 R KO mice, indicating that D-264 has little efficacy in vivo at the D 3 R, and that its functional effects are probably mediated by activation of the D 2 R, or possibly the D 4 R as it also displays significant affinity for the latter receptor subtype [113]. This study also found that the D 2 R and D 3 R expression levels in the heterologous CHO cells used were 2-fold and 135-fold, respectively, higher than those in rodent striatum, and the expression of the D 3 R was 10 times higher than that of the D 2 R in their cell model.…”

“…This study also found that the D 2 R and D 3 R expression levels in the heterologous CHO cells used were 2-fold and 135-fold, respectively, higher than those in rodent striatum, and the expression of the D 3 R was 10 times higher than that of the D 2 R in their cell model. These factors could lead to artificially inflated D 3 R/D 2 R selectivity values, and the authors proposed the cautious interpretation of their results obtained from a single model system [113]. Treatment with D-264 improved movement in acute MPTP and lactacystin mouse models of PD [104].…”

Current drug treatments targeting dopamine D3 receptor

“…Based on these findings, the chemical scaffold of pramipexole was further used for discovery of selective agonists or partial agonists (Chen et al, 2008;Ghosh et al, 2010;Zhen et al, 2016). Drug design of selective D3R…”