Decreased helenalin-induced cytotoxicity by flavonoids from Arnica as studied in a human lung carcinoma cell line

The effect of the flavones apigenin, luteolin, hispidulin and eupafolin, and of the flavonols kaempferol, quercetin, 6-methoxykaempferol and patuletin from Amica spp, on the cytotoxicity of the sesquiterpene lactone helenalin was studied in the human lung carcinoma cell line GLC(4) using the microculture tetrazolium (MTT) assay. The tumour cells were exposed to the test compounds for 2 h. Helenalin concentrations around its control IC50 value, 0.5 mu M, were combined with flavonoid concentrations ranging from 0.01 to 20 mu M. At non-toxic concentrations, up to 10 mu M, all flavonoids except kaempferol significantly reduced the helenalin-induced cytotoxicity. Hispidulin and patuletin displayed their modulating effect on helenalin-induced cytotoxicity in the broadest concentration range. The strongest effect was found with 5 and 10 mu M hispidulin, 0.05 mu M quercetin, and 1 mu M patuletin, increasing the IC50 value of helenalin with circa 40%. No dose-dependency was found in the concentration range tested.