This study will investigate the mechanisms of cannabinoid tolerance. This objective will be achieved by determining whether cannabinoid tolerance is mediated through agonist-specific mechanisms using a model of chemotherapy-induced neuropathic pain. Our approach will examine tolerance to the anti-allodynic and antinociceptive effects of ?9-THC, CP55,940, and WIN55,212-2, three cannabinoid agonists with distinct signaling and chemical features. Tolerance to ?9-THC antinociception in the tail-flick test was eliminated by pre-treatment of S426A/S430A mutants with SP600125, a selective c-Jun N-terminal kinase (JNK) inhibitor suggesting that JNK (SP600125 inhibitor) and GRK/?arrestin2 (S426/S430A mutation) signaling mechanisms coordinate to mediate tolerance to the antinociceptive effect of ?9-THC. The first objective of this study is to, fully and systematically, test the hypothesis that cannabinoid tolerance is mediated through agonist-specific mechanisms. The second objective is to test the hypothesis that JNK-mediated tolerance for ?9-THC requires the presence of ??arrestin2. The third objective is to test the hypothesis that ??arrestin2 and JNKs can form protein-protein interactions in vivo. The fourth objective is to test the hypothesis that JNKs can directly phosphorylate CB1 when activated by ?9-THC using a technologically innovative chemical-genetic approach. The first three hypotheses will be tested in a clinically relevant model of chemotherapy (cisplatin)-induced model of neuropathic pain. The last hypothesis is equally innovative and will provide important information regarding the molecular mechanism of action that is responsible for JNK-mediated ?9-THC tolerance. The overarching goal of this project is to gain a better understanding of the agonist-specific mechanisms responsible for cannabinoid tolerance that will facilitate the development of long lasting, highly efficacious, and personalized pain therapies.
One of the primary cannabinoids in cannabis, delta-9-tetrahydrocannabinol (?9-THC), has been increasingly used by cancer patients for its analgesic properties as well as for the treatment of nausea secondary to cancer chemotherapy. However, tolerance represents a significant disadvantage for cannabinoid therapies and has been demonstrated clinically in heavy use of cannabis prescribed for cancer pain treatment. Successful completion of this research project will address our novel concept that cannabinoid tolerance occurs through agonist-specific mechanisms, providing novel insight about the mechanisms of cannabinoid tolerance and advancing the knowledge base needed to develop improved and innovative therapeutic strategies.