Accelerating GPCR Drug Discovery With Conformation-Stabilizing VHHs

Abstract

The human genome encodes 850 G protein-coupled receptors (GPCRs), half of which are considered potential drug targets. GPCRs transduce extracellular stimuli into a plethora of vital physiological processes. Consequently, GPCRs are an attractive drug target class. This is underlined by the fact that approximately 40% of marketed drugs modulate GPCRs. Intriguingly 60% of non-olfactory GPCRs have no drugs or candidates in clinical development, highlighting the continued potential of GPCRs as drug targets. The discovery of small molecules targeting these GPCRs by conventional high throughput screening (HTS) campaigns is challenging. Although the definition of success varies per company, the success rate of HTS for GPCRs is low compared to other target families (Fujioka and Omori, 2012; Dragovich et al., 2022). Beyond this, GPCR structure determination can be difficult, which often precludes the application of structure-based drug design approaches to arising HTS hits. GPCR structural studies entail the resource-demanding purification of native receptors, which can be challenging as they are inherently unstable when extracted from the lipid matrix. Moreover, GPCRs are flexible molecules that adopt distinct conformations, some of which need to be stabilized if they are to be structurally resolved. The complexity of targeting distinct therapeutically relevant GPCR conformations during the early discovery stages contributes to the high attrition rates for GPCR drug discovery programs. Multiple strategies have been explored in an attempt to stabilize GPCRs in distinct conformations to better understand their pharmacology. This review will focus on the use of camelid-derived immunoglobulin single variable domains (VHHs) that stabilize disease-relevant pharmacological states (termed ConfoBodies by the authors) of GPCRs, as well as GPCR:signal transducer complexes, to accelerate drug discovery. These VHHs are powerful tools for supporting in vitro screening, deconvolution of complex GPCR pharmacology, and structural biology purposes. In order to demonstrate the potential impact of ConfoBodies on translational research, examples are presented of their role in active state screening campaigns and structure-informed rational design to identify de novo chemical space and, subsequently, how such matter can be elaborated into more potent and selective drug candidates with intended pharmacology.

Characterization of a Nanobody-Epitope Tag Interaction and Its Application for Receptor Engineering

“…The expanding collection of Nbs that target GPCRs bodes favorably for these efforts. 37 ■ METHODS Synthesis. Peptides were synthesized using solid-phase synthesis with Fmoc protection of backbone amines.…”

“…Our success in leveraging Nb–epitope interaction for improving the potency of an already high affinity ligand suggests that this approach should be widely useful for basic biomedical research. The expanding collection of Nbs that target GPCRs bodes favorably for these efforts …”

Solid-state NMR study of structural heterogeneity of the apo WT mouse TSPO reconstituted in liposomes

“…This raises the question of the biological significance of such constraints for PK111195 binding site: does the apo form of the mTSPO need a large flexibility to bind so different ligands, such as isoquinoline and porphyrin? Among the biomolecules of medical interest, membrane proteins such as GPCR suffer from spectral crowding induced by conformational plasticity [70] that, for most of them, limits their access for NMR investigation. High-magnetic field and MAS spinning above 60 kHz rotation frequency demonstrated that sensitivity and 1 H resolution can be significantly improved, notably for microcrystalline proteins available in small amounts [71] but also for membrane proteins [41].…”

Intracellular VHHs to monitor and modulate GPCR signaling

“…Methodological hurdles that linger the development of VHHs against GPCR, such as the selection of the antigen ( 90 ), the advantages of synthetic libraries versus libraries from immunized animal ( 40 , 91 , 92 ), the comparison of display methods ( 5 , 38 , 40 ) have been previously reported. Here, we focus on the specificities that make anti-GPCR intra-VHH expression inside the cell and characterization particularly challenging ( Figure 5 ).…”

“…Since anti-GPCR intra-VHHs stabilize selective conformations of the receptor, they have been named “confobodies”, a registered trademark of Confo Therapeutics ( 38 ). They can recognize intracellular regions of the receptor devoted to signal transduction ( Figure 1 ).…”