Immunotoxicologic studies with CI-959, a novel benzothiophene cell activation inhibitor

CI-959 is an orally effective inhibitor of cellular activation in both in vitro and animal models. To assess the effects of CI-959 on immune function, male Fischer 344 rats were evaluated for splenic T- and B-lymphocyte populations, antibody-forming cell response to sheep red blood cells (sRBC), concanavalin A and pokeweed mitogen-induced lymphocyte proliferation, Natural Killer cell activity, and reticuloendothelial system clearance of sRBC. Host resistance was measured in female B6C3F1 mice using Listeria monocytogenes, Streptococcus pneumonia, and B16F10 melanoma models. CI-959 was administered to both species of rodents at 25, 50, and 75 mg/kg/day for 14 days. A vehicle control and two positive controls (cyclophosphamide and dexamethasone) were run concurrently. CI-959 generally did not suppress immunological responses in rats at doses lower than those which also altered body weight gain and reduced spleen and thymus weights. Natural Killer cell activity was significantly reduced at 50 and 75 mg/kg CI-959. At 75 mg/kg rats also exhibited a reduction in ability to make anti-sRBC antibody. The number of T- and B-lymphocytes, proliferative response to mitogens, and macrophage activity of the reticuloendothelial system were not affected by CI-959. CI-959 also did not alter resistance of mice to Listeria monocytogenes, Streptococcus pneumoniae, or B16F10 melanoma cells. Based on these ex vivo and in vivo assays, the rodent immune system does not appear to be a sensitive or toxicologically important target for CI-959.