Structural determinants of the partial agonist‐inverse agonist properties of 6′‐azidohex‐2′‐yne‐Δ⁸‐tetrahydrocannabinol at cannabinoid receptors

Abstract

We have extended previous investigations of four analogues of Δ8‐tetrahydrocannabinol (Δ8‐THC): 6′‐azidohex‐2′‐yne‐Δ8‐THC (O‐1184), 6′‐azidohex‐cis‐2′‐ene‐Δ8‐THC (O‐1238) and octyl‐2′‐yne‐Δ8‐THC (O‐584) and its 1‐deoxy‐analogue (O‐1315). O‐1184, O‐1238 and O‐584 displaced [3H]‐CP55940 from specific binding sites on Chinese hamster ovary (CHO) cell membranes expressing CB1 or CB2 cannabinoid receptors, with pKi values of 8.28 to 8.45 (CB1) and 8.03 to 8.13 (CB2). The pKi values of O‐1315 were significantly less, 7.63 (CB1) and 7.01 (CB2). All the analogues inhibited forskolin‐stimulated cyclic AMP production by CB1‐transfected CHO cells (pEC50=9.16 to 9.72). Only O‐1238 behaved as a full agonist in this cell line. In mouse vasa deferentia, O‐1238 inhibited electrically‐evoked contractions (pEC50=10.18 and Emax=70.5%). Corresponding values for O‐1184 were 9.08 and 21.1% respectively. At 1 nM, O‐1184 produced surmountable antagonism of the cannabinoid receptor agonist, CP55940. However, at 0.1 nM, O‐1184 did not attenuate CP55940‐induced inhibition of cyclic AMP production by CB1‐transfected CHO cells. In CB2‐transfected CHO cells, cyclic AMP production was inhibited by CP55940 (pEC50=8.59), enhanced by O‐1184 and O‐584 (pEC50=8.20 and 6.86 respectively) and not significantly affected by O‐1238 or O‐1315. At 100 nM, O‐1184 and O‐1238 produced surmountable antagonism of CP55940 in CB2 cells, decreasing the pEC50 of CP55940 from 8.61 to 7.42 (O‐1184) or from 8.54 to 7.44 (O‐1238). These data support the hypothesis that increasing the degree of unsaturation of the aliphatic side‐chain of Δ8‐THC analogues has little effect on CB1 or CB2 receptor affinity but can reduce CB1 receptor efficacy and reverse the direction of responses elicited at CB2 receptors. British Journal of Pharmacology (1999) 128, 735–743; doi:

HU-308: A specific agonist for CB 2 , a peripheral cannabinoid receptor

“…At concentrations up to 10 M, HU-308 had no effect on forskolin-stimulated cyclic AMP production in cells that had not been transfected with cannabinoid receptors (n ϭ 3). These data provide strong evidence that HU-308 shares the ability of established cannabinoid receptor agonists to inhibit cyclic AMP production (19), and they confirm that it interacts significantly more readily with CB 2 than with CB 1 receptors.…”

“…The ability of HU-308 to inhibit forskolinstimulated cyclic AMP production in Chinese hamster ovary (CHO) cells, stably transfected with human CB 1 or CB 2 receptors, was measured by a method we have used previously for the bioassay of other cannabinoids (19). The effect of HU-308 on cyclic AMP production has been expressed in percentage terms and mean values for EC 50 ; maximal effects (E max ) and the SEM or 95% confidence limits of these values have been calculated by nonlinear regression analysis with the equation for a sigmoid concentration-response curve (PRISM software from GraphPad, San Diego) (19).…”

Pharmacological Actions of Cannabinoids

“…Thus, unlike SR141716A (Pertwee et al 1996b), O-2654 does not increase the amplitude of electrically evoked contractions of this preparation. Nor does it share the ability of the CB 1 partial agonist, O-1184, to inhibit these contractions (Ross et al 1999b). O-2050, a sulphonamide analogue of ∆ 8 -THC with an acetylenic side chain also behaves as a neutral CB 1 receptor antagonist in the mouse vas deferens .…”

“…3.2: AM251 (Vásquez et al 2003), AM281 (Cosenza et al 2000;Gifford et al 1997;Izzo et al 2000;Vásquez et al 2003), LY320135 (Felder et al 1998) and AM630 (Sect. 3.2.2) at CB 1 receptors and SR144528 Rinaldi-Carmona et al 1998;Ross et al 1999b), AM630 (New and Wong 2003;Ross et al 1999a) and AM251 (New and Wong 2003) at CB 2 receptors. These effects include SR141716A-and AM281-induced hyperkinesia in rats and/or mice Cosenza et al 2000;Costa and Colleoni 1999) and the attenuation in vitro of CB 1 or CB 2 receptor signalling.…”

“…One cannabinoid receptor ligand that comes close to being a neutral antagonist is 6 -azidohex-2 -yne-∆ 8 -THC (O-1184; Fig. 11 and Table 4), as this behaves as a high-affinity, lowefficacy agonist at CB 1 receptors and as a high-affinity, low-efficacy inverse agonist at CB 2 receptors, and as it produces potent antagonism of R-(+)-WIN55212 and CP55940 in the myenteric plexus-longitudinal muscle preparation of guinea-pig small intestine (Ross et al 1998(Ross et al , 1999b. More recently, an analogue of SR141716A, NESS 0327, has been developed that behaves as a neutral CB 1 receptor antagonist and is markedly more potent and CB 1 -selective than SR141716A (Table 3) .…”