Pleiotropic activities of human interferons are mediated by multiple response pathways.

Among the pleiotropic effects of human interferon are the inhibition of viral replication, the activation of natural killer cells, and the inhibition of cellular growth. Oxyphenbutazone, a nonsteroidal antiinflammatory agent, is a potent inhibitor of the antiviral activity of human alpha and beta interferons as determined by cytopathic effect and vesicular stomatitis virus synthesis and release in human foreskin fibroblasts. The inhibition of interferon activity is dose dependent with maximal inhibition at 25-50 microM and minimal inhibition at 1 microM. In contrast, oxyphenbutazone at concentrations as high as 100 microM has no effect on the activation of natural killer cells by human interferon. Similarly, oxyphenbutazone has no inhibitory effect on interferon-induced antigrowth activity in the human breast carcinoma cell line MDA-MB-231. This cell line is sensitive to oxyphenbutazone inhibition of interferon-induced antiviral activity in vitro. In another human cell line, the vulvar carcinoma A431, oxyphenbutazone apparently augments the antigrowth activity of interferon. Although oxyphenbutazone inhibits the fatty acid cyclooxygenase enzyme in these systems, other inhibitors of cyclooxygenase fail to inactivate the antiviral activity of human interferon. Thus, oxyphenbutazone appears to inhibit the interferon antiviral cascade at a site distinct from prostaglandin biosynthesis. Moreover, the failure to inhibit natural killer cell activation or cellular antigrowth effects of human interferon suggests a pathway different from that associated with the antiviral effect of human interferon.