Contribution à la synthèse et à l'évaluation pharmacologique de nouveaux ligands des récepteurs cannabinoïdes CB1 et CB2
(2005)
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- The discovery of D9-tetrahydrocannabinol, the main psychoactif component of cannabis, in 1964, followed, by the characterization of two subtypes of cannabinoid receptors, named cannabinoid CB1 and CB2 receptors, in the nineties, have stimulated interest in the physiological and pharmacological role of these receptors. Both receptors belong to the seven transmembrane domains receptors coupled to G proteins. The cannabinoid CB1 receptor is mainly localized in the central nervous system, whereas, up to now, the cannabinoid CB2 receptor has mainly been localized peripherally, in the immune cells. At the Pharmaceutical chemistry and Radiopharmacy laboratory at UCL, Martial Kanyonyo, from Professor Didier Lambert's team, developed a new class of cannabinoid ligands which belong to the imidazolidinedione (or hydantoin) family. These compounds, generally substituted at position 5 and alkylated in position N-3 of the hydantoin nucleus, exhibit a hundred nanomolar affinity for cannabinoid CB1 receptor. The aim of this work was to pharmacodynamically characterize new ligands of human and rodent cannabinoid CB1 and CB2 receptors. In this perspective, a first work was to study the structure-activity relations and recognition to human cannabinoid CB1 and CB2 receptors of this new class of cannabinoid compounds by the synthesis of new alkylated hydantoin and thiohydantoin derivatives. The interest for the thiohydantoin compounds was to evaluate the bioisostery oxygen-sulfur. New synthesis methods were followed to: 1°) improve yield obtained in syntheses of alkylated (thio)hydantoin derivatives; 2°) decrease the number of synthesis steps. After synthesis, molecules affinities for human cannabinoid CB1 and CB2 receptors were evaluated by screening. The percentage of inhibition of the specific binding of a high affinity radioligand to the cannabinoid receptors was measured in the presence of a high concentration of the studied compound. Most of the tested compounds exhibit a weak inhibition of the radioligand specific binding to the human cannabinoid CB2 receptors (less than 30%), indicating that these compounds have a poor affinity for this receptor subtype. However, these compounds inhibit up to 90% of the radioligand specific binding to the human cannabinoid CB1 receptors, indicating that these compounds have a high affinity for this receptor subtype. Thus, imidazolidinedione compounds newly synthesized are selective ligands for human cannabinoid CB1 receptors. A second work led to the complete pharmacodynamical characterization of cannabinoid CB1 and CB2 receptors reference radioligands in the three species studied (human, rat, and mouse) and to the one of cannabinoid CB1 and CB2 receptors reference ligands. These ligands have chemical structures different from that of hydantoins. These are D8-THC, D9-THC, HU 210 from classical cannabinoids family; CP 55,940, CP 55,244, CP 55,243, CP 47,947 from non classical cannabinoids family; WIN 55,212-2, WIN 55,212-3 from aminoalkylindoles family; and SR 141716A and SR 144528 from diarylpyrazoles family. Affinity (receptors recognition) and functionality (role of ligands on the interaction between receptor and G proteins) of these various cannabinoid ligands were determined. The interaction between receptors and G proteins, induced by these ligands, is determined by measuring the percentage of [35S]-GTPgS specific binding stimulation to the alpha subunit of G protein. The value obtained for this measure allows to evaluate the G proteins activation degree by the cannabinoid receptors and in this way, their functional state. Thus, we demonstrated which ligands were agonists, partial agonists, inverse agonists and antagonists of cannabinoid receptors CB1 and CB2. In addition to the reference ligands, we also evaluated the three hydantoin derivatives that had the highest percentage of inhibition of radioligand specific binding to the human cannabinoid CB1 receptors. These are DML 20, DML 21, and DML 23. This work allowed to complete the published data in the literature about the different reference cannabinoid ligands. In fact, some of them, the most used, were partially characterized (only their affinity was available), whereas for the others, no information existed. The affinity profiles of these compounds obtained in the three species studied are similar. Ordered by decreasing affinity, all the tested compounds have an affinity for the cannabinoid CB1 receptor: HU 210 > CP 55,940 > D9-THC > WIN-55,212-2 > DML 20 ~ DML 21 ~ DML 23. On the contrary, the affinity of these compounds for the cannabinoid CB2 receptor is weak, except for WIN 55,212-2, and SR 144528. Other results indicate a selectivity of DML 20, DML 21 et DML 23 derivatives for the cannabinoid CB1 receptors. HU 210, CP 55,940, CP 55,244 et CP 47,947 are human cannabinoid CB1 and CB2 receptors agonists, and are rat cannabinoid CB1 receptors agonists, because of their positive intrinsic activity. SR 141716A, and SR 144528 are human cannabinoid CB1 and CB2 receptors inverse agonists, and are rat cannabinoid CB1 receptors inverse agonists, because of their negative intrinsic activity. Natural constitutive components of cannabis (D8-THC et D9-THC) act as partial agonists of rat cannabinoid CB1 receptors (with a partial positive intrinsic activity), and act as inverse agonists of human cannabinoid CB2 receptors. CP 55,243 (less active enantiomer than CP 55,244) is a partial agonist of human cannabinoid CB2 receptors but inverse agonist of human cannabinoid CB1 receptors. WIN 55,212-2, and WIN 55,212-3 (less active enantiomer) have two different behaviours: WIN 55,212-2 is human cannabinoid CB1 and CB2 receptors agonist and rat cannabinoid CB1 receptors agonist, whereas WIN 55,212-3 act as inverse agonists of the same receptors. DML 20, DML 21, and DML 23 are human cannabinoid CB1 and CB2 receptors inverse agonists. However, these compounds are not able to modulate the [35S]-GTPgS specific binding to the alpha subunit of G protein in the rat cannabinoid CB1 receptors: they have no intrinsic activity. But, these compounds competitively inhibit the [35S]-GTPgS specific binding induced by the HU 210 from a membrane preparation of rat cerebellum, indicating that these compounds act as neutral antagonists of rat cannabinoid CB1 receptors. Thus, their rat cannabinoid CB1 receptors antagonist potencies (pKb) were calculated.
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Govaerts, S. (2005). Contribution à la synthèse et à l’évaluation pharmacologique de nouveaux ligands des récepteurs cannabinoïdes CB1 et CB2. https://hdl.handle.net/2078.5/110655