The myxobacterial compounds spirangien A and M522 are potent inhibitors of interleukin-8 expression

Infection and injury induce an immediate immune response which is mediated by numerous cytokines. One of the initial steps in inflammatory response is the attraction of neutrophils by the chemotatic cytokine interleukin-8 (IL-8). Chronic inflammatory diseases like rheumatoid arthritis or COPD are characterized by an aberrant production of proinflammatory cytokines like IL-8. The goal of this project is to find new drug candidates or lead structures to inhibit expression of IL-8 and thereby prevent neutrophil infiltration by chronic inflammatory diseases. We first established a cell based reporter assay for screening. Therefore, HeLa S3 cells were stably transfected with firefly luciferase gene under control of minimal IL-8 promoter. Upon interleukin-1 (IL 1) stimulation, firefly luciferase expression can be detected in cells by luminescence measurement. Screening of HZI compound libraries revealed several compounds which reduce IL-8 reporter expression up to 70 %. In hit validation process, dose dependent effects on reporter gene expression and cell viability were measured. Spirangien A, a natural compound from myxobacteria, showed a significant reduction in firefly luciferase expression. We further analyzed the biological effects of this compound in comparison to its highly related chemical derivate spirangien M522 which contains the core structure of spirangien A. The data presented here show that both variants efficiently reduce the endogenous level of IL-8 mRNA and protein expression in HeLa cells. Detailed analysis of IL-1 dependent signal transduction pathways show that the natural compounds spirangien A and M522 interfere with signaling proteins which are involved in transcriptional regulation of the endogenous IL-8 gene.