Growth inhibitory effects of flavonoids in human thyroid cancer cell lines

Previous studies have indicated that flavonoids exhibit antiproliferative p roperties on some hormone-dependent cancer cell. lines, such as breast and prostate cancer. In the present study, the effects of some selected flavono ids, genistein, apigenin, luteolin, chrysin, kaempferol, and biochanin A on human thyroid carcinoma cell lines, UCLA NPA-87-1 (NPA) (papillary carcino ma), UCLA RO-82W-1 (WRO) (follicular carcinoma), and UCLA RO-81A-1 (ARO) (a naplastic carcinoma) have been examined. Among the flavonoids tested, apige nin and luteolin are the most potent inhibitors of these cell lines with IC 50 (concentration at which cell proliferation was inhibited by 50%) values ranging from 21.7 mu M to 32.1 mu M. The cells were viable at these concent rations. Using NPA cells known to be estrogen receptor positive (ER+), it w as shown that no significant [H-3]-E-2 displacement occurred with these fla vonoids at the IC50 concentration. In WRO cells that are known to have an a ntiestrogen binding site (AEBS), biochanin A caused a stronger inhibitory g rowth effect (IC50 = 64.1 mu M) than in NPA and ARO cells. In addition, it was observed that biochanin A has an appreciable binding affinity for the A EBS as indicated by the displacement of [H-3]-tamoxifen from the WRO cells. In summary, flavonoids have potent antiproliferative activity in vitro aga inst various human thyroid cancer cell lines. The inhibitory activity of ce rtain flavonoid compounds may be mediated via the AEBS and/or type II EBS. The observation that ARO cells that lack both the AEBS and the ER are effec tively inhibited by apigenin and luteolin suggest that other mechanisms of action are operative as well. The present study suggests that flavonoids ma y represent a new class of therapeutic agents in the management of thyroid cancer.