Anti-hypersensitive and anti-inflammatory activity of the potent and selective CB2 receptor agonist gsk554418a

Nick Clayton, Jane Hughes, Alex Wilsin, Ged Giblin, Bill Mitchell, Paul Goldsmith, Andy Billinton, Chas Bountra, Iain Chessell. Glaxosmithkline, Harlow Essex, United Kingdom.

The aim of this study was to investigate the effect of the novel, potent and highly selective CB2 receptor agonist (Michel et al., this meeting) GSK554418A (N-(3-chlorophenyl)-1-methyl-7-(4-morpholinylcarbonyl)-1H-pyrrolo[3,2-c]pyridin-4-amine hydrochloride) on the established FCA-induced inflammatory hypersensitivity to pain and potential changes in immune cells. Male Random Hooded rats (180-240g, Bantin and Kingman) were used in all studies. 100 μl of 1 mg/ml Freund’s Complete Adjuvant (FCA) was injected intraplantar into the left hind paw with GSK554418A (0.01-0.1 mg kg-1) dosed orally 23 hrs later. One hr post dose the effect of GSK554418A on the FCA-induced weight bearing deficit was determined (dual channel weight averager: Clayton et al., 1997). To evaluate the contribution of CB2 receptors to the mechanisms of action of GSK554418A, the CB2 receptor selective antagonist AM630 (15 mg kg-1 i.p.) was administered alone or 30 minutes before GSK554418A (1 mg kg-1 p.o.). The effect on FCA-induced hypersensitivity to pain was determined 1 hr post GSK554418A as described above. The effect of GSK554418A on the FCA-induced changes in immune cells was also determined. GSK554418A (1 mg kg-1 p.o.) or celecoxib (10 mg kg-1 p.o) was dosed 23 hrs post FCA and the effect on hypersensitivity was determined 1 hr post dose. Blood samples were taken and the effect on immune cell populations analysed by flow cytometry. Data are presented as mean±s.e.m. Where appropriate geometric mean and 95% confidence intervals for ED50 values were calculated. Statistical analysis was carried out to determine whether there was a significant difference (p<0.05) between the vehicle and drug treated group using ANOVA followed by Fisher LSD. GSK554418A produced a dose related reversal of hypersensitivity (maximum reversal: 96±15% at 0.1 mg kg-1, p<0.05, ED50=0.02 (0.01-.0.03) mg kg-1. The CB2 receptor antagonist (15 mg kg-1 i.p.) alone had no significant effect on the hypersensitivity to pain (7±9%), GSK554418A (1 mg kg-1 p.o.) alone significantly reversed the FCA induced hypersensitivity (81±8, p<0.05) and was significantly reduced by the CB2 receptor antagonist AM630 (28±14%, p<0.05). FCA induced a decrease in circulating T-cell (55%), monocyte (29%) and B-cell (20%) numbers compared to vehicle alone, suggesting that following FCA, the cells migrate from the circulation into inflamed tissues. In contrast, the number of circulating neutrophils increased in response to FCA (374%) indicating increased proliferation or decreased migration. GSK554418A (1 mg kg-1 p.o.) again reduced FCA induced hypersensitivity (114±5%, p<0.05) and decreased circulating cell numbers. The most potent inhibitory effects were on neutrophil (97%) and T-helper cell populations (138%) suggesting that GSK554418A may increase immune cell recruitment to the site of inflammation or inhibit immune cell proliferation. In contrast, celecoxib had no effect on the immune cells but reduced the FCA induced hypersensitivity by 132±16% (p<0.05). In conclusion: GSK554418A reduced the hypersensitivity to pain via CB2 receptors and in part by modulation of the immune cells.

Clayton, N.M et al. (1997) Br J Pharmacol, 120, P78