Endogenous vs Exogenous Allosteric Modulators in GPCRs: A dispute for shuttling CB1 among different membrane microenvironments.

Mariano Stornaiuolo,Romano Silvestri,Giuseppe La Regina,Agostino Bruno,Luciana Marinelli,Sandro Cosconati,Ettore Novellino,Lorenzo Botta

doi:10.1038/srep15453

Mariano Stornaiuolo, Romano Silvestri + Show 6 more

Open Access

https://doi.org/10.1038/srep15453

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Abstract

A Cannabinoid Receptor 1 (CB1) binding site for the selective allosteric modulator ORG27569 is here identified through an integrate approach of consensus pocket prediction, mutagenesis studies and Mass Spectrometry. This unprecedented ORG27569 pocket presents the structural features of a Cholesterol Consensus Motif, a cholesterol interacting region already found in other GPCRs. ORG27569 and cholesterol affects oppositely CB1 affinity for orthosteric ligands. Moreover, the rise in cholesterol intracellular level results in CB1 trafficking to the axonal region of neuronal cells, while, on the contrary, ORG27568 binding induces CB1 enrichment at the soma. This control of receptor migration among functionally different membrane regions of the cell further contributes to downstream signalling and adds a previously unknown mechanism underpinning CB1 modulation by ORG27569 , that goes beyond a mere control of receptor affinity for orthosteric ligands.

Highlights

The endocannabinoid system comprises the GPCR family members cannabinoid receptors Cannabinoid Receptor 1 (CB1) and CB2, their endogenous ligands and the enzymes responsible for the synthesis and degradation of the latters[1]
Few compounds have been identified as exogenous CB1 allosteric modulators including the synthetic “ORG” compounds (ORG27569, ORG29647, ORG27759)[16,17], PSNCBAM-118, RTI-37119 and the natural endogenous modulators lipoxin A420, pregnenolone[21] and cholesterol[22]
With the exception of pocket 4 (P4), which partially overlaps with the orthosteric pocket, the other sites are all lipid exposed (Fig. 1a)

Summary

Introduction

The endocannabinoid system comprises the GPCR family members cannabinoid receptors CB1 and CB2, their endogenous ligands (endocannabinoids) and the enzymes responsible for the synthesis and degradation of the latters[1]. Upon binding to their endogenous partial agonist anandamide or to exogenous ligands like Δ 9-tetrahydrocannabinol, CB1 affects cell proliferation, motility, adhesion and apoptosis and controls a variety of physiological processes spanning from neuronal development to organs functioning[2,3]. The development of functionally selective allosteric modulators is considered a promising avenue to develop new target specific drugs and overcome nowadays obstacles in cannabinoid-based drug discovery such as on- and off-target side effects. Our group embarked in a Structure-Activity-Relationship (SAR) study of ORG2756923 which is an exquisitely selective allosteric modulator for CB123,24

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Conclusion