Role of pregnenolone derivative AEF0117 on the regulation of CB1 signaling that mediates behavioral effects of THC
Cannabis sativa is among the most abused drugs worldwide. THC, its main psychoactive component, represents a risk factor of several mental pathologies, such as cannabis use disorder, addiction, and psychosis. Being a biphasic drug, high doses of THC cause hypoactivity and aversion, whereas low doses of THC cause hyperactivity and reward. THC acts on the type-1 cannabinoid receptor (CB1), one of the most abundant G-protein coupled-receptors (GPCRs) in the brain, whose signaling is biased, meaning that different transducers can carry specific pathway following different conditions. Biased signaling was proven to be extremely relevant in drug discovery and understanding CB1 signaling in pathologic conditions is essential for cannabinoid-based drug development. It is known that different doses of THC bring along different behavioral, cellular, and molecular outcomes. However, the link between those phenomena has never been investigated. Thus, for a therapeutic purpose PREG-like CB1-SSi compounds have been synthetized that share the same PREG therapeutic potential, but cannot be metabolized in downstream steroids. The CB1-SSi studied in the current work is the CB1-SSi lead compound, AEF0117. The first aim of the current work was to understand the intracellular signaling pathways following low, medium, and high doses of THC, leading to three distinct known behavioral outputs in mice, hyperlocomotion, asociability, and hypolocomotion, respectively. The second aim of the thesis was to understand the mechanism of action of AEF0117, and its capability to block the behavioral and molecular effects of THC at low, medium, and high doses. The doctoral dissertation is divided into five main parts. The introduction serves to preface the concepts of the endocannabinoid system, as well as cannabis abuse in humans and the counterpart behavioral outcomes of THC in mice, including hyperlocomotion, asociability, and hypolocomotion. The state of the art of CB1 signaling involving the biased CB1 system is described with particular emphasis on CB1 Signaling Specific Inhibitors (CB1-SSi), in particular the endogenous pregnenolone (PREG), and its synthetic analogue, the lead CB1-SSi compound, AEF0117. The article Zanese*, Tomaselli* et al., 2020 (published in J. Neurosci. Methods) oversees the validation of the high throughput analytical technique (AlphaLISA) of choice in this study for detection of protein phosphorylation in brain tissue lysates. The article Tomaselli et al. (to be submitted), is devoted to the studies of the low dose of THC that causes hyperlocomotion, with the discovering of its related intracellular CB1 signaling pathway, along with the signaling transducer involved in the CB1-rich brain areas relevant for locomotor activity (NAc, Str, CB). The main data revealed that THC via CB1 recruits the β-Arrestin1-PI3K-Akt-GSK3β signaling pathway that lead to hyperlocomotion. Furthermore, both PREG and AEF0117 were able to block the THC-induced hyperlocomotion and altered signaling in mice. The third part of the data represent studies on the effects of THC at medium and high doses that induce asocial behavior and hypolocomotion, respectively. Each dose of THC induced specific alterations in the CB1intracellular signaling pathways in the most CB1-rich brain areas, and the treatment with AEF0117 rescued both behaviors. The general discussion then addresses conclusions and perspectives, highlighting the role of specific CB1 pathways in THC-induced addiction and psychosis, and proposes a mechanism of action for CB1-SSi compounds, including AEF0117.