A modulatory effect of novel kojic acid derivatives on cancer cell proliferation and macrophage activation.

We examined whether several newly synthesized derivatives of kojic acid, a compound with known antiinflammatory, anti-proliferative, and anti-oxidative properties, were able to modulate glioma cell proliferation and Toll-like receptor (TLR) 4-mediated functional activation of macrophage-managed tumor microenvironments. Anti-cancer effects on C6 glioma and SYF cells were examined by cell proliferation assays, DNA laddering assays, nuclear staining experiments, and Western blot analysis. The anti-inflammatory activities of the derivatives were assessed by measuring the production of nitric oxide (NO) and cytokine expression in macrophages (RAW264.7 cells) stimulated with the TLR 4 ligand lipopolysacchride (LPS). Among the various derivatives tested, RHS-0110 exhibited the strongest inhibitory activity on the proliferation of C6 glioma cells, with an IC50 value of 4.7 microM. However, the inhibitory effect of this compound was abrogated with respect to the proliferation of SYF cells, a cell line lacking Src, Yes, and Fyn kinases, similar to effects observed with the Src kinase inhibitor PP2. In agreement with these findings, RHS-0110 decreased the expression of Src but not the activation of Yes and Fyn. Based on DNA laddering tests and nucleus staining experiments, the anti-proliferative effects of RHS-0110 appeared to be due to a necrotic pathway. Kojic acid derivatives also suppressed LPS-induced NO production and interleukin (IL)-6 expression in RAW264.7 cells under lowered or non-cytotoxic concentrations of compounds. Because of their anti-proliferative and anti-TLR4-mediated microenvironmental formation features, our results suggest that kojic acid derivatives, including RHS-0110, may be useful as novel anti-cancer drugs.