Growth-inhibitory effect of quercetin and presence of type II estrogen binding sites in primary human transitional cell carcinomas.

Eight cases of transitional cell carcinoma (TCC) of the bladder were investigated for the presence of estrogen receptors (ER) and Type II estrogen binding sites (Type II EBS). All these tumors specifically expressed type II EBS, while only 3 of 8 cases contained low amounts of ER. All the cases assayed for the presence of both nuclear and cytoplasmic type II EBS revealed the presence of these binding sites in the two compartments. Both cytoplasmic and nuclear receptors were similar to type II EBS described in other tissues relative to their binding specificity for estrogens and quercetin and their sensitivity to reducing agents. Quercetin, 10 microM., was effective in inhibiting in vitro bromodeoxyuridine (BrdUdR) incorporation by TCC cells. Rutin, which bound little if any to type II EBS, did not show any inhibitory effect on in vitro BrdUdR incorporation by tumor cells, suggesting a type II EBS mediated effect of flavonoids. Although the mechanism of the antiproliferative activity of quercetin remains to be fully clarified, the possible therapeutic potential of quercetin and related flavonoids should be considered.