Structural determinants of the partial agonist-inverse agonist properties of 6 '-azidohex-2 '-yne-Delta(8)-tetrahydrocannabinol at cannabinoid receptors

1 We have extended previous investigations of four analogues of Delta(8)-te trahydrocannabinol (Delta(8)-THC): 6'-azidohex-2'-yne-Delta(8)-THC (O-1184) , 6'-azidohex-cis-2'-ene-Delta(8)-THC (O-1238) and octyl-2'-yne-Delta(8)-TH C (O-584) and its I-deoxy-analogue (O-1315). 2 O-1184, O-1238 and O-584 displaced [H-3]-CP55940 from specific binding si tes on Chinese hamster ovary (CHO) cell membranes expressing CB1 or CB2 can nabinoid receptors, with pK(i) values of 8.28 to 8.45 (CBi) and 8.03 to 8.1 3 (CB2). The pK(i) values of O-1315 were significantly less, 7.63 (CB1) and 7.01 (CB2). 3 All the analogues inhibited forskolin-stimulated cyclic AMP production by CB1-transfected CHO cells(pEC(50) = 9.16 to 9.72). Only O-1238 behaved as a full agonist in this cell line. 4 In mouse vasa deferentia, O-1238 inhibited electrically-evoked contractio ns (pEC(50) = 10.18 and E-max = 70.5%). Corresponding values for O-1184 wer e 9.08 and 21.1% respectively. At 1 nM, O-1184 produced surmountable antago nism of the cannabinoid receptor agonist, CP55940. However, at 0.1 nM, O-11 84 did not attenuate CP55940-induced inhibition of cyclic AMP production by CB(1-)transfected CHO cells. 5 In CB2-transfected CHO cells, cyclic AMP production was inhibited by CP55 940 (pEC(50) = 8.59), enhanced by O-1184 and O-584 (pEC(50) = 8.20 and 6.86 respectively) and not significantly affected by O-1238 or O-1315. 6 At 100 nM, O-1184 and O-1238 produced surmountable antagonism of CP55940 in CB2 cells, decreasing the pEC(50) of CP55940 from 8.61 to 7.42 (O-1184) or from 8.54 to 7.44 (O-1238). 7 These data support the hypothesis that increasing the degree of unsaturat ion of the aliphatic side-chain of Delta(8)-THC analogues has little effect on CB1 or CB2 receptor affinity but can reduce CB1 receptor efficacy and r everse the direction of responses elicited at CB2 receptors.