Vol. 63, Issue 2, 383-391, February 2003

Sporogen, S14-95, and S-Curvularin, Three Inhibitors of Human Inducible Nitric-Oxide Synthase Expression Isolated from Fungi

Ying Yao, Michael Hausding, Gerhard Erkel, Timm Anke, Ulrich Förstermann, and Hartmut Kleinert

Department of Pharmacology, Johannes Gutenberg University, Mainz, Germany (Y.Y., M.H., U.F., H.K.); and Institute of Biotechnology and Drug Research, Kaiserslautern, Germany (G.E., T.A.)

The induction of human inducible nitric-oxide synthase (iNOS) expression depends (among other factors) on activation of the signal transducer and activator of transcription 1 (STAT1) pathway. Therefore, the STAT1 pathway may be an appropriate target for the development of inhibitors of iNOS expression. HeLa S3 cells transiently transfected with a -activated site (GAS)/interferon-stimulated response element-driven reporter gene construct were used as the primary screening system. Using this system, three novel inhibitors of interferon--dependent gene expression, namely, sporogen, S14-95, and S-curvularin, were isolated from different Penicillium species. These three compounds also inhibited cytokine-induced, GAS-dependent reporter gene expression in stably transfected human A549/8-pGASLuc cells, confirming the data obtained with the above-mentioned screening system. Furthermore, in A549/8 cells, sporogen, S14-95, and S-curvularin inhibited cytokine-induced activity of the human iNOS promoter [a 16-kilobase (kb) fragment in stably transfected A549/8-pNOS2(16)Luc cells], cytokine-induced iNOS mRNA expression, and cytokine-induced nitric oxide (NO) production in a concentration-dependent manner. The proliferation of A549/8 cells, and the activity of the human eNOS promoter (a 3.5-kb fragment in stably transfected ECV-pNOS III-Hu-3500-Luc cells), were only influenced marginally by the three compounds. Sporogen, S14-95, and S-curvularin also inhibited cytokine-induced activation of STAT1 in A549/8 cells. In conclusion, sporogen, S14-95, and S-curvularin represent new transcriptionally based inhibitors of iNOS-dependent NO production, acting on the Janus tyrosine kinase-STAT pathway. These compounds may represent lead structures for the development of drugs inhibiting iNOS-dependent overproduction of NO in pathophysiological situations.