Fig. (4) Panels A-C show the inhibition by the CB2 selective antagonist AM630 (AM) of the effect of CB2 agonists towards HL-60 cells: 8 (Panel A), 17 (Panel B), and 22 (Panel C). The concentrations of the CB2 agonists were defined according to the peaking doses detected in Figure 3; that of AM630 was chosen among the doses lacking an intrinsic activity and providing an appropriate block of the CB2 receptor. The assays were carried out with 5 min pre-treatment with AM630, followed by a 15 min exposure to CB2 agonist derivatives. On the right side are shown representative western blots of P-ERK expression. Data are expressed as mean percentage of vehicle ± SEM and are the results of five separate experiments. *p < 0.05 vs vehicle; **p < 0.05 vs vehicle; ^#p < 0.05 vs WIN55,212-2; ^§p < 0.05 vs 8, 17, or 22.