Identification of a Novel Inhibitor of LPS-Induced TNF-α Production with Antiproliferative Activity in Monocyte/Macrophages

An isoquinoline derivative, 5-methyl-7,8-dimethoxy-1-phenylpyrazolo[5,4-c]isoquinoline (compound 1), was identified as a novel inhibitor of LPS-induced TNF-α production by cell-based screening. Compound 1 suppressed LPS-induced TNF-α production in RAW264.7 cells and murine peritoneal macrophages in a dose-dependent manner similar to SB203580, known as a specific inhibitor of p38 MAPK. It also inhibited an LPS-induced increase in serum TNF-α in a mouse endotoxic shock model with an ED50 of ∼10 mg/kg. Compound 1 had little effect on the incorporation of [3H]-leucine into the cells, while it suppressed LPS-induced TNF-α mRNA levels in RAW264.7 cells. The results indicate that suppression of TNF-α production was not a result of nonspecific inhibition of de novo translation but was based on the decreased TNF-α mRNA levels. The in vitro kinase assay revealed that compound 1 did not strongly inhibit p38 MAPK activity, its potency being much lower than that of SB203580, suggesting that the TNF-α-suppressive action of compound 1 cannot be attributed to the inhibition of p38 MAPK. Furthermore, in contrast to SB203580, it significantly inhibited the growth of RAW264.7 and THP-1 cells in a cytostatic manner. Compound 1 is likely to have antiinflammatory and antiproliferative effects by acting on some molecule other than p38 MAPK that contributes to both LPS-induced TNF-α production and the cell growth of monocyte/macrophages.