CB2 cannabinoid receptor agonist enantiomers HU-433 and HU-308: An inverse relationship between binding affinity and biological potency

Abstract

Activation of the CB2 receptor is apparently an endogenous protective mechanism. Thus, it restrains inflammation and protects the skeleton against age-related bone loss. However, the endogenous cannabinoids, as well as Δ(9)-tetrahydrocannabinol, the main plant psychoactive constituent, activate both cannabinoid receptors, CB1 and CB2. HU-308 was among the first synthetic, selective CB2 agonists. HU-308 is antiosteoporotic and antiinflammatory. Here we show that the HU-308 enantiomer, designated HU-433, is 3-4 orders of magnitude more potent in osteoblast proliferation and osteoclast differentiation culture systems, as well as in mouse models, for the rescue of ovariectomy-induced bone loss and ear inflammation. HU-433 retains the HU-308 specificity for CB2, as shown by its failure to bind to the CB1 cannabinoid receptor, and has no activity in CB2-deficient cells and animals. Surprisingly, the CB2 binding affinity of HU-433 in terms of [(3)H]CP55,940 displacement and its effect on [(35)S]GTPγS accumulation is substantially lower compared with HU-308. A molecular-modeling analysis suggests that HU-433 and -308 have two different binding conformations within CB2, with one of them possibly responsible for the affinity difference, involving [(35)S]GTPγS and cAMP synthesis. Hence, different ligands may have different orientations relative to the same binding site. This situation questions the usefulness of universal radioligands for comparative binding studies. Moreover, orientation-targeted ligands have promising potential for the pharmacological activation of distinct processes.

Highly Selective, Amine-Derived Cannabinoid Receptor 2 Probes

“…(K i hCB 2 R < 13 nm)w ith at least 86-fold selectivity over hCB 1 R. In line with Mechoulam's report, [31] compounds ent-1, ent-10-Cl and ent-11 showedl ower hCB 2 Ra ffinity than their enantiomers by af actor of ca. 10 (hCB 2 R K i < 121 nm)b ut retained high selectivity over hCB 1 R( hCB 1 R K i > 3.1 mm).…”

“…expectation based on radioligand binding studies, which attested HU-308'sh igher CB 2 Ra ffinity when compared to HU-433. [31] Therefore, ent-1 was included in the presents tudy in order to maximize the chance of identifying irreversible and selective CB 2 Rl igands. Compound ent-1 was accessed by Friedel-Crafts alkylation with ent-8 derived from (1R)-(À)-myrtenol and subsequent elaboration analogous to the sequence shown in Scheme 2( see SupportingI nformation).…”

Antioxidative and Anti-Inflammatory Properties of Cannabidiol

“…In addition, the pinene dimethoxy-dimethylheptyl-CBD derivative HU-308 [(3R, 4S, 6S)-2-[2,6-dimethoxy-4-(2-methyloctan-2-yl)phenyl]-7,7-dimethyl-4-bicyclo[3.1.1]hept-3-enyl]methanol] and its enantiomer HU-433 [(3S, 4R, 6R)-2-[2,6-dimethoxy-4-(2-methyloctan-2-yl)phenyl]-7,7-dimethyl-4bicyclo[3.1.1]hept-3-enyl]methanol] were shown to have specific agonistic activity for the CB2 receptor (Table 2), and consequently, anti-inflammatory activity in cultured calvarial osteoblasts from C57BL/6J mice [125]. However, it has been found that HU-433 exhibits greater anti-inflammatory activity with poorer CB2 receptor binding affinity ( Table 2) [125]. In contrast, HU-308, a CB2 agonist, was found to decrease TNF-α-induced expression of ICAM-1 and VCAM-1 in sinusoidal endothelial cells of human liver tissue [24].…”

“…Table 2. Influence of natural and synthetic CBD derivatives on receptor activation (X: agonist activation or Y: antagonist activation by related CBD derivative; * weak affinity; #: full name is in chapter 4.1) [2,24,72,76,[114][115][116]120,[122][123][124][125][126][127]130]. Natural CB1 CB2 Gpr55 Gpr18 TRPV1 TRPA1 TRPM8 5-HT…”

From Phytocannabinoids to Cannabinoid Receptors and Endocannabinoids: Pleiotropic Physiological and Pathological Roles Through Complex Pharmacology

“…Preclinical studies show that synthetic CB2 agonists rescue ovariectomy-induced bone loss, suggesting that these drugs may improve osteoporosis (805). In women, 17␤-estradiol administration inhibits activity and formation of osteoclasts in vitro and increases CB2 expression, which may underlie the antiresorptive properties of estrogen and postmenopausal osteoporosis (745).…”