Effects of flavonoids on CYP1 expression in RL95-2 endometrial carcinoma cells

RL95-2 endometrial cancer cells were used to study cytochrome P450-mediated chemopreventative mechanisms of four flavonoids found in foods. To investigate enzymatic CYP1 inhibition, intact cells were induced with benzo(a)pyrene or 2,3,7,8-tetrachlorodibenzo-p-dioxin. Quercetin, kaempferol and myricetin inhibited CYP1 activity dose-dependently with IC₅₀s ranging from 2.2 to 4 μM; while amentoflavone was inactive. Further experiments were designed to determine if flavonoids also interacted with the AhR or caused a decrease in CYP1 protein or mRNA expression. CYP1A1 protein expression was inhibited in cells co-treated with TCDD and quercetin, kaempferol or myricetin compared with TCDD alone, but amentoflavone was ineffective. Relatively higher (∼7-fold) basal levels of CYP1B1 protein were not significantly affected by flavonoid treatments. In general, at the message level significant inhibition of induced CYP1A1 or CYP1B1 was not detected following flavonoid cotreatment. Despite the common inhibitory effects of quercetin, kaempferol, and myricetin on induced CYP1A1-dependent activity and protein expression, the mechanisms of CYP1 inhibition in this cell line are complex and dependent on the CYP gene, AhR inducer and the flavonoid.