The
antiestrogen tamoxifen is thought to antagonize the effects of
estrogens by competing with them for
estrogen receptor (ER) binding. However, tarnoxifen can also reverse multidrug resistance, synergize with
cisplatin cytotoxicity, and inhibit growth in ER-negative
lung cancer cells. In addition to ERs, rat and human target tissues contain a second binding macromolecule termed the
type II estrogen binding site (
type II EBS). It has been shown that
tamoxifen and
flavonoids, a widely distributed class of natural substances with a variety of
biologic actions, bind to
type II EBS and inhibit the growth of several
tumor cell types. At present, conflicting data about ERs and an absence of data about type II EBSs exist for lung
tumors. We have tested
non-small-cell lung carcinoma cell lines and primary
tumor cells for the presence of ERs and type II EBSs and have evaluated the effects of
tamoxifen and
quercetin (
pentahydroxyflavone) on the growth of these cells. Using a whole-cell assay and nuclear and cytosolic radiobinding experiments with [3H]
estradiol as tracer, we have found that SK-LU1, SW900, ChaGo-K-1, H441, H661, and A549 cells, as well as primary
tumors, bind
estrogen specifically. This binding results mainly from the presence of a large number of type II EBSs, whereas ERs are absent or present at low concentrations. Type II EBSs bound
tamoxifen and
quercetin with similar affinity. Cell counts and a
thymidine incorporation assay showed that both compounds inhibit cell growth in a concentration-dependent manner at concentrations ranging from 10 nM to 1 microM. Neither
ipriflavone, an
isoflavone, nor
rutin, the 3-rhamnosylglucoside of
quercetin, bound type II EBSs or inhibited cell growth. These findings suggest that
tamoxifen and
quercetin could regulate
lung cancer cell growth through a binding interaction with type II EBSs. This mechanism could also be active in vivo, in that we have observed that nuclear and cytosolic type II EBSs were present in all primary
lung cancers tested (n = 12), and that
tamoxifen and
quercetin were effective in inhibiting in vitro
bromodeoxyuridine (
BrdU) incorporation and proliferation-cell
nuclear antigen expression by neoplastic cells in these
cancers.