Saquinavir-NO inhibits IL-6 production in macrophages.

Covalent attachment of the nitric oxide (NO) moiety to the HIV protease inhibitor Saquinavir (Saq) produced a new chemical entity, named Saquinavir-NO, (Saq-NO) with reduced toxicity and potent immunoregulatory influence on T lymphocytes. In this study, we have compared head-to-head the effects of Saq-NO and Saq on mouse and rat peritoneal macrophage cytokine secretion and NO production upon in vitro, ex vivo and in vivo conditions. The results demonstrate that Saq-NO, but not Saq, potently decreased interleukin (IL)-10, IL-6 and nitrite accumulation and increased the levels of IL-1β and tumour necrosis factor (TNF) in supernatants of mouse and rat macrophage cultures in vitro. Treatment of mice with Saq-NO, but not Saq, inhibited ex vivo secretion of IL-6 from macrophages. Consistent with these findings, Saq-NO also reduced blood levels of IL-6 in lipopolysaccharide-treated mice. The observed inhibitory influence of Saq-NO on IL-6 generation in macrophages may be involved in the observed antitumour and immunomodulatory effects of the drug.