Analogues of Arylamide Phenylpiperazine Ligands To Investigate the Factors Influencing D3 Dopamine Receptor Bitropic Binding and Receptor Subtype Selectivity

Abstract

We have previously reported on the ability of arylamide phenylpiperazines to bind selectively to the D3 versus the D2 dopamine receptor subtype. For these studies, we used LS-3-134 as the prototypic arylamide phenylpiperazine ligand because it binds with high affinity at D3 dopamine receptor (0.17 nM) and exhibits >150-fold D3 vs D2 receptor binding selectivity. Our goal was to investigate how the composition and size of the nonaromatic ring structure at the piperazine position of substituted phenylpiperazine analogues might influence binding affinity at the human D2 and D3 dopamine receptors. Two factors were identified as being important for determining the binding affinity of bitropic arylamide phenylpiperazines at the dopamine D3 receptor subtype. One factor was the strength of the salt bridge between the highly conserved residue Asp with the protonated nitrogen of the nonaromatic ring at the piperazine position. The second factor was the configuration of the unbound ligand in an aqueous solution. These two factors were found to be related to the logarithm of the affinities using a simple correlation model, which could be useful when designing high affinity subtype selective bitropic ligands. While this model is based upon the interaction of arylamide phenylpiperazines with the D2 and D3 D2-like dopamine receptor subtypes, it provides insights into the complexity of the factors that define a bitropic mode of the binding at GPCRs.

Insights From Molecular Dynamics Simulations of a Number of G-Protein Coupled Receptor Targets for the Treatment of Pain and Opioid Use Disorders

“…Calculation of their respective binding energies using MM-PBSA showed that the strength of the electrostatic interaction with the D 3.32 residue generally decreased as the size of the piperazine substituent increased. Umbrella sampling simulations were used to generate a PMF aimed at mimicking the unbinding of the ligand protonated nitrogen from the D 3.32 residue, and the depth of the bound state in the PMF also agreed with the experimental trend except for one of the analogs (Hayatshahi et al, 2018).…”

“…Another recent joint experimental-computational publication also made use of MD simulations to help explain the molecular basis for the binding of bitopic arylamide phenylpiperazine ligands selective for the D3 receptor over D2 (Hayatshahi et al, 2018). Specifically, studies were focused on the prototypic arylamide phenylpiperazine LS-3-134 ligand, which has been found to act as a D3 receptor partial agonist and has also been shown to be 150-fold more selective for the D3 receptor relative to the D2 receptor (Tu et al, 2011).…”

“…Specifically, studies were focused on the prototypic arylamide phenylpiperazine LS-3-134 ligand, which has been found to act as a D3 receptor partial agonist and has also been shown to be 150-fold more selective for the D3 receptor relative to the D2 receptor (Tu et al, 2011). Radioligand binding studies showed that the greatest contribution to the binding energy of the LS-3-134 ligand to the D3 receptor was the phenylpiperazine moiety, but that the arylamide moiety heavily influenced ligand selectivity for the D3 receptor (Hayatshahi et al, 2018). The MD simulations were used to explain the effect that analogs of the piperazine moiety had on the binding affinity.…”

Evaluation of Substituted N-Phenylpiperazine Analogs as D3 vs. D2 Dopamine Receptor Subtype Selective Ligands

“…Since the orthosteric binding site of D2-like dopamine receptors is constructed by conserved amino acid residues in the transmembrane helical spanning regions, it is not surprising that many of the original D2 vs. D1 selective ligands bind nonselectively at the D2 and D3 dopamine receptor subtypes. Ligands that can simultaneously interact with two different regions (an orthosteric and secondary binding site (SBS) on a single GPCR have been described as bitopic ligands [ 20 , 21 , 22 , 23 , 24 ]. The ability of some N -phenylpiperazine benzamides to bind selectively at the D3 dopamine receptor subtype has been attributed to the ability of the N -phenylpiperazine moiety to occupy either the D2 or D3 dopamine orthosteric binding site, while the benzamide moiety interacts with an SBS that is unique to the D3 dopamine receptor subtype [ 21 , 24 ].…”

“…Ligands that can simultaneously interact with two different regions (an orthosteric and secondary binding site (SBS) on a single GPCR have been described as bitopic ligands [ 20 , 21 , 22 , 23 , 24 ]. The ability of some N -phenylpiperazine benzamides to bind selectively at the D3 dopamine receptor subtype has been attributed to the ability of the N -phenylpiperazine moiety to occupy either the D2 or D3 dopamine orthosteric binding site, while the benzamide moiety interacts with an SBS that is unique to the D3 dopamine receptor subtype [ 21 , 24 ]. Consequently, a number of research groups have been able to develop D3 vs. D2 dopamine receptor selective ligands using a substituted N -phenylpiperazine benzamide template to identify ligands that bind selectively and with high affinity at the D3 dopamine receptor subtype [ 25 , 26 , 27 , 28 ].…”