Discovery of G Protein-Biased Dopaminergics with a Pyrazolo[1,5-a]pyridine Substructure

Abstract

1,4-Disubstituted aromatic piperazines are privileged structural motifs recognized by aminergic G protein-coupled receptors. Connection of a lipophilic moiety to the arylpiperazine core by an appropriate linker represents a promising concept to increase binding affinity and to fine-tune functional properties. In particular, incorporation of a pyrazolo[1,5-a]pyridine heterocyclic appendage led to a series of high-affinity dopamine receptor partial agonists. Comprehensive pharmacological characterization involving BRET biosensors, binding studies, electrophysiology, and complementation-based assays revealed compounds favoring activation of G proteins (preferably G) over β-arrestin recruitment at dopamine D receptors. The feasibility to design G protein-biased partial agonists as putative novel therapeutics was demonstrated for the representative 2-methoxyphenylpiperazine 16c, which unequivocally displayed antipsychotic activity in vivo. Moreover, combination of the pyrazolo[1,5-a]pyridine appendage with a 5-hydroxy-N-propyl-2-aminotetraline unit led to balanced or G protein-biased dopaminergic ligands depending on the stereochemistry of the headgroup, illustrating the complex structure-functional selectivity relationships at dopamine D receptors.

Biased Receptor Signaling in Drug Discovery

“…Bias activity for dopamine D 2 receptor Ga i1 activation/b-arrestin interaction for 10 agonists measured either by BRET or enzyme complementation. Data are redrawn from Möller et al (2017).…”

“…Ligand-stabilized receptor conformations drive the selection of G protein interactions and these selections can be discerned within G protein subunit families; for instance, studies with bioluminescence resonance energy transfer (BRET) biosensors have shown that oxytocin analogs differentiate between individual G i/o family members (Ga q , Ga i1 , Ga i2 , Ga i3 , Ga oA , Ga oB ; Busnelli et al, 2012). Ligand bias between subunit members of G protein families is increasingly observed with agonists for m-opioid receptors (Ga i1 , Ga oA ; Saidak et al, 2006), dopamine receptors (Ga i1 , Ga i2 , Ga i3 , Ga oA , Ga oB ; Möller et al, 2017), and PTH receptors (Ga s , Ga q/11 , and Ga io ; Appleton et al, 2013). Signaling also results from activation of Gb subunits (activation or deactivation of adenylate cyclase, PLCs, phosphatidylinositol 3-kinase) and Gg subunits (protein kinase D) (Morris and Malbon, 1999;Vanderbeld and Kelly, 2000).…”

“…This is because the concentration-response curves to 16c cannot be fit to the operational model assuming the same affinity differing only in efficacy. The fact that there are divergent EC 50 values for 16c for these two G protein pathways indicates a 158-fold difference in the affinity of an agonist for the dopamine D 2 receptor when the receptor binds to Ga oA versus Ga i2 protein (Möller et al, 2017).…”

“…7, in some cases reversals in the relative potency of agonists are observed with varying assay format assessment of a single pathway, namely b-arrestin activity. Thus, a BRET method versus an enzyme complementation assay for dopamine D 2 receptor/b-arrestin2 interactions (Path-Hunter) indicates differences in the bias of some agonists when comparing G i protein versus b-arrestin interactions (relative to the reference quinpirole) due to the nature of the assay format (Möller et al, 2017). Finally, one experimental strategy that can be employed to expand detection capability is to manipulate assay 288 Kenakin sensitivity.…”

Identification of NQO1 and ferrochelatase as interaction partners for neuroprotective N‐{[2‐(4‐phenyl‐piperazin‐1‐yl)‐ethyl]‐phenyl}‐arylamides

“…The studied compounds consist of an arylpiperazine subunit that is considered to be a privileged chemical structure because it can be found in a variety of pharmacologically interesting compounds capable of interacting with various counterpart cellular targets . Some of the arylpiperazines that are in use in clinics have neuroprotective activity .…”