Investigation of the binding and functional properties of extended length D3 dopamine receptor-selective antagonists

Abstract

The D3 dopamine receptor represents an important target in drug addiction in that reducing receptor activity may attenuate the self-administration of drugs and/or disrupt drug or cue-induced relapse. Medicinal chemistry efforts have led to the development of D3 preferring antagonists and partial agonists that are >100-fold selective vs. the closely related D2 receptor, as best exemplified by extended-length 4-phenylpiperazine derivatives. Based on the D3 receptor crystal structure, these molecules are known to dock to two sites on the receptor where the 4-phenylpiperazine moiety binds to the orthosteric site and an extended aryl amide moiety docks to a secondary binding pocket. The bivalent nature of the receptor binding of these compounds is believed to contribute to their D3 selectivity. In this study, we examined if such compounds might also be “bitopic” such that their aryl amide moieties act as allosteric modulators to further enhance the affinities of the full-length molecules for the receptor. First, we deconstructed several extended-length D3-selective ligands into fragments, termed “synthons”, representing either orthosteric or secondary aryl amide pharmacophores and investigated their effects on D3 receptor binding and function. The orthosteric synthons were found to inhibit radioligand binding and to antagonize dopamine activation of the D3 receptor, albeit with lower affinities than the full-length compounds. Notably, the aryl amide-based synthons had no effect on the affinities or potencies of the orthosteric synthons, nor did they have any effect on receptor activation by dopamine. Additionally, pharmacological investigation of the full-length D3-selective antagonists revealed that these compounds interacted with the D3 receptor in a purely competitive manner. Our data further support that the 4-phenylpiperazine D3-selective antagonists are bivalent and that their enhanced affinity for the D3 receptor is due to binding at both the orthosteric site as well as a secondary binding pocket. Importantly, however, their interactions at the secondary site do not allosterically modulate their binding to the orthosteric site.

Highly Selective Dopamine D3 Receptor (D3R) Antagonists and Partial Agonists Based on Eticlopride and the D3R Crystal Structure: New Leads for Opioid Dependence Treatment

“…These new PPs showed moderate binding affinities for both D 3 R and D 2 R receptors with relatively low binding affinities to D 4 R and little or no selectivity, as shown in Table 1. As previously observed, when the alkyl linking chain was extended from the N -phenylpiperazine to N -methyl ( 12a and 12b ) and N - n -butyl analogues ( 13a and 13b ), binding affinities were improved for both D 3 R and D 2 R. 14,22,42 Of this set of synthons, compound 13b demonstrated the highest D 3 R affinity ( K i =0.363 nM) and was the most D 3 R selective (D 2 R/D 3 R=8.1; D 4 R/D 3 R=179).…”

Synthesis and Pharmacological Characterization of Novel trans-Cyclopropylmethyl-Linked Bivalent Ligands That Exhibit Selectivity and Allosteric Pharmacology at the Dopamine D3 Receptor (D3R)

“…It is also noteworthy that these PPs have much lower affinities than the previously reported and privileged 2,3-dichlorophenylpiperazine PP, for which the N- n -butyl-substituted synthon had a K i =1.9 nM. 13 As shown previously with other SPs, 13,15 13a-d showed no or very weak ability to displace [ 3 H]N-methylspiperone (NMS) binding from either the D 2 R or D 3 R. Notably, however, in a separate study, at concentrations over 50 μM, 13b was able to partially inhibit (~20%) [ 3 H]spiperone binding to the D 2 R, a finding that might be consistent with an allosteric interaction. 27 …”

“…12–15 A four-carbon linking chain with or without substituents (e.g. OH or F) or structural rigidity (e.g.…”

Norbenzomorphan Framework as a Novel Scaffold for Generating Sigma 2 Receptor/PGRMC1 Subtype‐Selective Ligands

“…Screening novel norbenzomorphans prepared in our lab led to the discovery of hit compounds with potentially useful medicinal properties. For example, amide 3 is an inhibitor of striatal-enriched protein tyrosine phosphatase (STEP) [2b], an enzyme that is overactive in Alzheimer’s disease (AD) [7], whereas benzylamine 4 is an antagonist of dopamine-3 [8], a target currently being evaluated for treating addiction [9]. …”