Cannabinoids are compounds that bind to CB1 (CB1Rs) and CB2 (CB2Rs) cannabinoid receptors. FDA approved cannabinoids like nabilone and dronabinol act similarly to Δ 9-THC, the primary psychoactive constituent found in Cannabis sativa. Effects produced by cannabinoids result from activation of cannabinoid receptors (CBRs) to produce analgesia, reduce nausea from chemotherapeutic drugs used to treat advanced cancer, and stimulate appetite in AIDS patients. While clinical efficacy of cannabinoids has been established in numerous disease states, the therapeutic potential of this drug class is greatly diminished due to concomitant production of adverse effects in response to acute and chronic cannabinoid administration. Based on initial published studies from our laboratory, experiments in this dissertation from three Aims were proposed to investigate two novel molecular scaffolds (selective estrogen receptor modulators and indole quinulidinones) for development of CBR ligands with the primary long-term objective to obtain high affinity, efficacious compounds with fewer adverse effects than those currently available cannabinoids that are used therapeutically.
In Aim one of this dissertation, the cis- (E) and trans- (Z) isomers of tamoxifen (Tam), a selective estrogen receptor modulator (SERM), and subsequent metabolites, 4-hydroxytamoxifen (4OHT) and endoxifen (End), were assessed for affinity and intrinsic activity at CBRs. Results revealed that all SERMs investigated bound CBRs with micromolar affinity and functioned as inverse agonists, producing dose-dependent inhibition of Gi protein signaling. Interestingly, Z-Tam and Z-End also acted as insurmountable antagonists, producing rightward shifts in potency and reduction in efficacy of CP-55,940-induced cAMP inhibition at CB1 and CB 2Rs.
Study of cannabinoid agonists typically reveals “non-biased” signaling, producing CBR coupling to G proteins and recruitment of β-arrestin 2. CBR interaction with G proteins produces desirable therapeutic effects; however, recruitment of β-arrestin 2 results in desensitization, sequestration, and internalization of CBRs, which contributes to tolerance and dependence. As such, development of a G protein biased agonist for CBRs could potentially improve the therapeutic potential for drugs in this class. In Aims 2 and 3 of this dissertation, in vitro and in vivo studies investigated G protein-dependent and -independent signaling produced by two indole quinulidinone (IQD) analogues, PNR-4-20 and PNR-4-02. These experiments provide evidence for the first class of G protein biased agonists at CB1Rs. Specifically, prolonged exposure of intact cells to the G protein biased CB1R agonist PNR-4-20 resulted in less CB1R desensitization and downregulation of CB1Rs than observed with non-biased CB1R agonists, and chronically treated mice exhibited reduced tolerance and dependence.
Collectively, studies in this dissertation reveal promising potential for CBR ligands developed from the novel SERM and IQD molecular scaffolds with reduced toxicity compared to current cannabinoids used therapeutically.
|Advisor:||Prather, Paul L.|
|Commitee:||Fantegrossi, Willam E., Gottschall, Paul E., Paule, Merle G., Prather, Paul L., Wessinger, William D.|
|School:||University of Arkansas for Medical Sciences|
|School Location:||United States -- Arkansas|
|Source:||DAI-B 79/04(E), Dissertation Abstracts International|
|Keywords:||Cannabinoid, G protein biased agonist, Selective estrogen receptor modulator|
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