DOI
https://doi.org/10.25772/5SNR-VK95
Defense Date
2019
Document Type
Thesis
Degree Name
Master of Science
Department
Pharmacology & Toxicology
First Advisor
Dana E. Selley
Abstract
Approximately twenty million people in United States have some form of peripheral neuropathy. It has been shown that the CB2 cannabinoid receptor is upregulated when there is peripheral nerve injury and activating the CB2 receptor produces anti-inflammatory effects that translate to a reduction in signs of “neuropathic pain” in animal models. Elevating endogenous cannabinoids by inhibiting degradative enzymes has also been used to reduce neuropathic pain signs in laboratory animal models of pain. We hypothesize that the molecular pharmacology of these two approaches can be leveraged to optimize CB1/CB2 activation to improve non-phyto-cannabinoid treatments for neuropathic pain by: 1) optimizing selectivity and efficacy profiles of synthetic ligands and 2) discovering the relative efficacy of each endocannabinoid for CB1 receptor activation in pain-relevant regions of the CNS. For the first approach, we propose using novel synthetic ligands that act as cannabinoid agonists with selectivity for CB2 > CB1 receptors and that possess moderate to high efficacy at both receptor types. To this end, we characterized five novel compounds that had reversed signs of neuropathic pain in mice and only one of which produced CNS-mediated in vivo effects. In vitro [3H]CP-55,940 competition binding assays using Chinese hamster ovary cells stably expressing either CB1 or CB2 receptors showed that two of these compounds, O-9602 and O-9697, have CB2 receptor selectivity. The efficacy of these compounds to stimulate either CB1 or CB2 receptor-mediated G-protein activation was then evaluated using the [35S]GTPγS assay in these CHO cell models. Compounds O-9598, O-9602, and O-9697 showed high efficacy at both receptors, but the potency of these compounds was higher at the CB2 receptor. Compounds O-9599 and O-9603 had moderate efficacy and potency at CB2 receptors, but low efficacy and potency at CB1 receptors. For the second approach, we propose that blockade of enzymatic degradation of the endocannabinoid that has the highest efficacy for CB1 receptor-mediated G-protein activation in pain-relevant CNS regions would provide optimal therapeutic efficacy in relieving neuropathic pain. Therefore, we determined the relative efficacy of the two major endocannabinoids, 2-AG and AEA, and a putative endocannabinoid, 2-AGE, in CNS regions related to both somatic and affective aspects of pain. Our results showed that in spinal cord and amygdala, AEA was lower in efficacy than 2-AG but had similar efficacy to 2-AGE. In nucleus accumbens and caudate putamen, AEA had lower efficacy than both 2-AG and 2-AGE, but 2-AGE had similar efficacy to 2-AG. In PAG there were no significant differences in efficacy among the three endocannabinoids. In prefrontal cortex, AEA had the lowest efficacy and 2-AGE had lower efficacy than 2-AG. In conclusion, of the five novel cannabinoid agonists that reversed signs of neuropathic pain in mice, two showed selectivity for the CB2 receptor with high efficacy at both the CB1 and CB2 receptors. In most brain regions studied, AEA had lower efficacy than 2-AG, suggesting that inhibiting 2-AG degradation might provide more efficacious analgesia than elevating AEA. Overall, this work provides novel information on pharmacodynamic parameters of novel synthetic ligands and established endocannabinoid ligands, which can be applied in the development of both CB2-prefering synthetic ligands and endocannabinoid modulators for the treatment of neuropathic pain.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
2-25-2020