Δ8 - and Δ9 -tetrahydrocannabivarin antagonize cannabinoid receptor agonists both in vitro and in vivo
Previously, we found Δ9 -tetrahydrocannabivarin extracted from cannabis (eΔ9 -THCV) behaves as a CB1 receptor antagonist in vitro (Thomas et al. (2005). We have now investigated if syntheticΔ9 -THCV (O-4394) behaves in this way not only in vitro but also in vivo. To facilitate future structure-activity studies, synthetic Δ8-THCV (O-4395) was also investigated, it being easier to synthesise analogues of Δ8 - than of Δ9 -THCV.
In vitro experiments were performed with vasa deferentia and whole brain membranes obtained from MF1 mice (32 to 44 g) (see Thomas et al., 2005 for descriptions of the methods used in these experiments and to determine Ki and KB values). Nociception was measured 20 min after an injection of Δ9 -tetrahydrocannabinol ( Δ9 -THC), O-4395 or O-4394 by subjecting adult male ICR mice (22 to 30 g) to the tail flick test ( Varvel et al. , 2006). Δ9 -THC was supplied by the National Institute on Drug Abuse (NIDA) and e Δ9 -THCV by GW Pharmaceuticals (Porton Down). For in vitro experiments, WIN55212-2 (WIN) was dissolved in a 1:1 mixture of DMSO and a 0.9% aqueous NaCl solution (saline), while other compounds were dissolved in DMSO. For in vivo experiments, compounds were injected into a tail vein (10 ml kg-1 ) using a 1:1 mixture of ethanol and alkamuls-620 diluted with saline to a final ethanol to alkamuls to saline ratio of 1:1:18.
In the vas deferens, O-4394 and O-4395 (100 nM) produced parallel dextral shifts in the log dose response curve of WIN, when this was first added 30 min after vehicle, O-4394 or O-4395. Mean apparent KB values with 95% confidence limits shown in brackets were 4.8 nM (0.3 & 30.3 nM; n=7) for O-4394 and 3.9 nM (0.7 & 13.3 nM; n=7) for O-4395 . The corresponding K Bof e Δ9 -THCV is 1.5 nM (Thomas et al., 2005). In brain membranes, O-4394 and O-4395 displaced [ 3H]CP55940, their mean K i values with 95% confidence limits shown in brackets being 46.6 nM (31.3 & 69.4 nM; n=5) and 64.4 nM (49.0 & 84.7 nM; n=5) respectively . At 1 µM, O-4394 and O-4395 also produced parallel dextral shifts in the log concentration-response curve of CP55940 for stimulation of [ 35S]GTPγS binding to brain membranes. Mean apparent KB values with 95% confidence limits shown in brackets were 82 nM (54 & 124 nM) for O-4394 and 126 nM (83 & 196 nM) for O-4395 (n=5). Corresponding values for e D9 -THCV are 75.4 (Ki ) and 93.1 nM (KB) (Thomas et al., 2005). Antinociception induced by D9 -THC at 10 mg kg-1 was attenuated by O-4394 and O-4395, injected immediately after Δ9 -THC at 0.3 (O-4395 only) or 3 mg kg-1 (P<0.01; ANOVA + Fisher’s protected least significant difference post hocs; n=6 to 15). O-4394 and O-4395 were not antinociceptive at 3 or 10 mg kg-1 but were at 30 and 56 mg kg-1 (P<0.05; ANOVA + Fisher’s protected least significant difference post hocs; n=6 to 11).
In conclusion, O-4394 and O-4395 exhibited in vitro potency as antagonists of CP55940 or WIN similar to that of e Δ9 -THCV. O-4394 and O-4395 also behaved as cannabinoid receptor antagonists in vivo, as indicated by their ability to antagonize Δ9 -THC.
Thomas, A. et al. (2005) Br. J. Pharmacol., 146, 917-926.
Funded by GW Pharmaceuticals and by NIDA (DA-09789, DA -02396 & DA -03672 )