A conserved intracellular allosteric binding site (IABS) has recently been identified at several G proteincoupled receptors (GPCRs). Starting from vercirnon, an intracellular CÀ C chemokine receptor type 9 (CCR9) antagonist and previous phase III clinical candidate for the treatment of Crohn's disease, we developed a chemical biology toolbox targeting the IABS of CCR9. We first synthesized a fluorescent ligand enabling equilibrium and kinetic binding studies via NanoBRET as well as fluorescence microscopy. Applying this molecular tool in a membrane-based setup and in living cells, we discovered a 4-aminopyrimidine analogue as a new intracellular CCR9 antagonist with improved affinity. To chemically induce CCR9 degradation, we then developed the first PROTAC targeting the IABS of GPCRs. In a proof-of-principle study, we succeeded in showing that our CCR9-PROTAC is able to reduce CCR9 levels, thereby offering an unprecedented approach to modulate GPCR activity.
Dopamine D2 receptors (D2Rs) are major targets in the treatment of psychiatric and neurodegenerative diseases. As with many other G protein-coupled receptors (GPCRs), D2Rs interact within the cellular membrane, leading to a transient receptor homo- or heterodimerization. These interactions are known to alter ligand binding, signaling, and receptor trafficking. Bivalent ligands are ideally suited to target GPCR dimers and are composed of two pharmacophores connected by a spacer element. If properly designed, bivalent ligands are able to engange the two orthosteric binding sites of a GPCR dimer simultaneously. Taking advantage of previously developed ligands for heterodimers of D2R and the neurotensin receptor 1 (NTSR1), we synthesized homobivalent ligands targeting D2R. Employing bioluminescence resonance energy transfer, we found that the bivalent ligands 3b and 4b comprising a 92-atom spacer are able to foster D2R-homodimerization while simultaneously reducing interactions of D2R with NTSR1. Both receptors are coexpressed in the central nervous system and involved in important physiological processes. The newly developed bivalent ligands are excellent tools to further understand the pharmacological consequences of D2R homo- and heterodimerization. Not limited to the dopaminergic system, modifying class A GPCRs’ dynamic equilibrium between monomers, homomers, and heteromers with bivalent ligands may represent a novel pharmacological concept paving the way toward innovative drugs.
Bivalent ligands are composed of two pharmacophores connected by a spacer of variable size. These ligands are able to simultaneously recognize two binding sites, for example in a G protein-coupled receptor heterodimer, resulting in enhanced binding affinity. Taking advantage of previously described heterobivalent dopamine-neurotensin receptor ligands, we demonstrate specific interactions between dopamine D3 (D3R) and neurotensin receptor 1 (NTSR1), two receptors with expression in overlapping brain areas that are associated with neuropsychiatric diseases and addiction. Bivalent ligand binding to D3R-NTSR1 dimers results in picomolar binding affinity and high selectivity compared to the binding to monomeric receptors. Specificity of the ligands for the D3R-NTSR1 receptor pair over D2R-NTSR1 dimers can be achieved by a careful choice of the linker length. Bivalent ligands enhance and stabilize the receptor-receptor interaction leading to NTSR1-controlled internalization of D3R into endosomes via recruitment of β-arrestin, highlighting a potential mechanism for dimer-specific receptor trafficking and signalling.
Eine konservierte intrazelluläre allosterische Bindungsstelle (IABS) wurde kürzlich an mehreren G-Proteingekoppelten Rezeptoren (GPCRs) identifiziert. Ausgehend von Vercirnon, einem intrazellulären Antagonisten am CÀ C-Chemokin-Rezeptor-Typ-9 (CCR9), entwickelten wir molekulare Werkzeuge, die an der IABS von CCR9 angreifen. Zunächst synthetisierten wir fluoreszierende CCR9-Liganden, die Bindungsstudien via NanoBRET sowie Fluoreszenzmikroskopie ermöglichten. Deren Anwendung in zellfreien sowie zellulären Testsystemen erlaubte die Identifizierung eines 4-Aminopyrimidin-Analogons als neuen intrazellulären CCR9-Antagonisten mit verbesserter Affinität. Um den proteasomalen Abbau von CCR9 einzuleiten, entwickelten wir das erste PROTAC, das die IABS von GPCRs als Angriffsort nutzt. In einer Machbarkeitsstudie zeigen wir, dass unser CCR9-PROTAC in der Lage ist, die CCR9-Spiegel zu reduzieren, was einen konzeptionell neuartigen Ansatz zur Modulation der GPCR-Aktivität darstellt.
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