Project 2 - Molecular pharmacology of cannabinoid receptor probes

Project Summary
The therapeutic potential of the endocannabinoid system has yet to translate into safe and effective
medicines. The translation gap, or “valley of death” separates promising preclinical research from
identification of a newly approved drug. Functional selectivity (or biased agonism) is a recently appreciated
property of CB1 and CB2 receptor signalling. Challenges for clinical translation include the question of what
signalling pathway best predicts therapeutic efficacy. It is, therefore, necessary to establish that candidate
ligands engage the specific signalling pathways necessary for therapeutic benefit, while, ideally,
circumventing those pathways responsible for unwanted side effects. Both biased agonism and allosteric
modulation represent alternative strategies to harness the therapeutic potential of the endocannabinoid
signalling system without the unwanted effects of direct acting CB1 agonists. The signalling pathways
necessary and dispensable for CB1 and CB2 therapeutic efficacy remain poorly understood. Bridging this
gap in knowledge is critical if we are to avoid costly failures in clinical translation. Project 3 will use novel CB1
and CB2 probes that are developed in Project 1 and characterized in vitro in Project 2 to elucidate how CB1
biased agonism, probe specific CB1 positive allosteric modulation and CB2 selective agonism impact in vivo
pharmacology. Aim 1 will define the in vivo pharmacology of functionally selective CB1 probes. We will profile
functionally selective CB1 agonists as well as tight binding (slow Koff) and probe-specific CB1 PAMs (that
exhibit high potency in our preliminary in vivo studies) for cardinal signs of CB1 activation, ability to suppress
neuropathic nociception as well as propensity to induce tolerance and physical dependence. Aim 2 will define
the in vivo pharmacology of CB2 agonists with improved selectivity for CB2 over CB1. We will ascertain
whether in vivo pharmacological profiles and selectivity can be improved by incorporating high affinity CB2
agonism with a lack of CB1 agonism. We will also determine whether in vivo pharmacological profiles can be
enhanced by incorporating CB1 antagonism (neutral, inverse agonism, partial agonism) with high affinity CB2
agonism. This Aim will compare a spectrum of ligands exhibiting these properties for cannabimimetic effects,
anti-allodynic efficacy and tolerance, as well as capacity to induce physical dependence and negative
affective states. This project will validate improved CB1 and CB2 probes, not to develop a medication.
Elucidation of signalling pathways necessary and dispensable for in vivo efficacy and unwanted side effects
will improve cannabinoid-based therapeutics and break down barriers to successful clinical translation.

Grant Number: 5P01DA009158-23
NIH Institute/Center: NIH
Principal Investigator: Laura Bohn