SELECTIVE REGULATION OF HUMAN NEUTROPHIL FUNCTIONS BY THE CELL ACTIVATION INHIBITOR CI-959

The cell activation inhibitor CI-959 N-1H-tetrazol-5-ylbenzo[b]thiophe ne-2-carboxamide, monosodium salt] was evaluated for its effects on hu man neutrophil functions. CI-959 inhibited spontaneous migration and c hemotaxis toward N-formyl-methionyl-L-leucyl-L-phenylalanine (fMLP) wi th 50% inhibition (IC50) values of 3.6 and 3.1 mu M, respectively. CI- 959 also inhibited superoxide anion generation in response to C5a, fML P, serum-opsonized zymosan (SOZ), concanavalin A (Con A), and calcium ionophore A23187 with IC50 values of 2.5, 4.7, 14.5, 5.4, and 14.8 mu M, respectively. In comparison, CI-959 inhibited myeloperoxidase relea se in response to C5a, fMLP, SOZ, and Con A with IC50 values of 11.6, 16.1, 7.5, and <1.0 mu M, respectively, while inhibiting the response to A23187 by only 5.5% at 100 mu M. At concentrations up to 100 mu M, CI-959 had no effect on the respiratory burst or degranulation in resp onse to L-alpha-1,2-dioctanoylglycerol (DiC(8)) or phorbol 12-myristat e 13-acetate (PMA). In addition, the compound inhibited leukotriene B- 4 release stimulated by fMLP and SOZ (IC50 values 4.0 and 2.5 mu M, re spectively), while having less activity against the A23187-stimulated response (IC50 > 100 mu M). These results demonstrate that CI-959 inhi bits cellular responses to stimuli that mobilize intracellular calcium . For cellular responses to ionophore-mediated calcium influx, only ox ygen radical production was inhibited by CI-959. CI-959 was further ev aluated for its effects on neutrophil stimulus-response coupling. At 1 00 mu M, CI-959 had no effect on human neutrophil phospholipase C or p rotein kinase C. CI-959 inhibited fMLP-stimulated intracellular calciu m mobilization and calcium influx with IC50 values of 16.7 and 3.1 mu M, respectively, and exhibited less potent calmodulin antagonist activ ity (IC50 = 90.5 mu M). These results indicate the CI-959 may exert it s stimulus- and response-specific inhibitory effects on neutrophil fun ctions, in part, through inhibition of calcium-regulated signalling me chanisms.