Effects of SK&F 105685, a novel anti-arthritic agent, on immune function in the dog

SK&F 105685 (N,N-dimethyl-8,8-dipropyl-2-azaspiro[4,5]decane-2-propanamine+ ++ dihydrochloride) is a novel azaspirane with beneficial activity in animal models of autoimmune disease such as adjuvant-induced arthritis and experimental encephalomyelitis in the Lewis rat and lupus-like disease in the MRL mouse. The activity of SK&F 105685 in these models is associated with the induction of non-specific suppressor cell (SC) activity as defined by the ability of cells from drug-treated animals to inhibit the proliferative response of lymphocytes from control animals to concanavalin A. To evaluate the immunotoxicologic potential of SK&F 105685, the effect on immune function of one month of dosing with 1 mg/kg/day of SK&F 105685 was examined in the dog. Differential blood cell counts and ex vivo immune function assays were performed using blood collected before dosing on days 1 (baseline), 15 and 29, of the study. Immune function assays were performed on spleen cells on day 30. Under the conditions of the study, SK&F 105685 displayed pharmacological activity as demonstrated by the induction of splenic SC activity. The drug did not affect the total number or relative percentages of the various white blood cell types present in peripheral blood and did not cause generalized immunosuppression. The ability of peripheral blood lymphocytes or spleen cells to produce IL-2 or proliferate in response to mitogenic stimulation was not affected by drug treatment. SK&F 105685 also failed to affect the candidacidal activity of polymorphonuclear leucocytes and spleen cells indicating that it is unlikely to compromise nonspecific resistance to infection. SK&F 105685 however, was able to inhibit the generation of a specific in vitro antibody response to sheep red blood cells (SRBC) by splenocytes from treated animals. Inhibition of the anti-SRBC antibody response was also observed upon addition of the drug to normal spleen cells. Addition of the drug at different time points during the culture period indicated that SK&F 105685 was interfering with an event(s) occurring during the first 72 h of culture. Taken together, these results suggest that, in a therapeutic setting, SK&F 105685 is unlikely to compromise the immune status of the host as it can down-regulate a specific immune response without causing generalized immunosuppression.