Positive allosteric modulation of the cannabinoid CB1 receptor potentiates endocannabinoid signalling and changes ERK1/2 phosphorylation kinetics

Abstract

AbstractBackground and PurposeActivation of CB1 by exogenous agonists causes adverse effects in vivo. Positive allosteric modulation may offer improved therapeutic potential and a reduced on‐target adverse effect profile compared with orthosteric agonists, due to reduced desensitisation/tolerance, but this has not been directly tested. This study investigated the ability of PAMs/ago‐PAMs to induce receptor regulation pathways, including desensitisation and receptor internalisation.Experimental ApproachBioluminescence resonance energy transfer (BRET) assays in HEK293 cells were performed to investigate G protein dissociation, ERK1/2 phosphorylation and β‐arrestin 2 translocation, while immunocytochemistry was performed to measure internalisation of CB1 in response to the PAMs ZCZ011, GAT229 and ABD1236 alone and in combination with the orthosteric agonists AEA, 2‐AG, and AMB‐FUBINACA.Key ResultsZCZ011, GAT229 and ABD1236 were allosteric agonists in all pathways tested. The ago‐PAM ZCZ011 induced a biphasic ERK1/2 phosphorylation time course compared to transient activation by orthosteric agonists. In combination with 2‐AG but not AEA or AMB‐FUBINACA, ZCZ011 and ABD1236 caused the transient peak of ERK1/2 phosphorylation to become sustained. All PAMs increased the potency and efficacy of AEA‐induced signalling in all pathways tested; however, no notable potentiation of 2‐AG or AMB‐FUBINACA was observed.Conclusion and ImplicationsAgo‐PAMs can potentiate endocannabinoid CB1 agonism by AEA to a larger extent compared with 2‐AG. However, all compounds were found to be allosteric agonists and induce activation of CB1 in the absence of endocannabinoid, including β‐arrestin 2 recruitment and internalisation. Thus, the spatiotemporal signalling of endogenous cannabinoids will not be retained in vivo.