INTERACTION WITH TYPE-II ESTROGEN-BINDING SITES AND ANTIPROLIFERATIVEACTIVITY OF TAMOXIFEN AND QUERCETIN IN HUMAN NON-SMALL-CELL LUNG-CANCER

The antiestrogen tamoxifen is thought to antagonize the effects of est rogens by competing with them for estrogen receptor (ER) binding. Howe ver, tamoxifen can also reverse multidrug resistance, synergize with c isplatin cytotoxicity, and inhibit growth in ER-negative lung cancer c ells. In addition to ERs, rat and human target tissues contain a secon d binding macromolecule termed the type II estrogen binding site (type II EBS). It has been shown that tamoxifen and flavonoids, a widely di stributed class of natural substances with a variety of biologic actio ns, bind to type LT EBS and inhibit the growth of several tumor cell t ypes. At present, conflicting data about ERs and an absence of data ab out 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 LI EBSs and have evaluated the effects of tamoxifen and q uercetin (pentahydroxyflavone) on the growth of these cells. Using a w hole-cell assay and nuclear and cytosolic radiobinding experiments wit h [H-3]estradiol as tracer, we have found that SK-LU1, SW900, ChaGo-K- 1, H441, H661, and A549 cells, as well as primary tumors, bind estroge n specifically. This binding results mainly from the presence of a lar ge numb ber of type II EBSs, whereas ERs are absent or present at low concentrations. Type II EBSs bound tamoxifen and quercetin with simila r affinity. Cell counts and a thymidine incorporation assay showed tha t both compounds inhibit cell growth in a concentration-dependent mann er at concentrations ranging from 10 nM to 1 mu M Neither ipriflavone, an isoflavone, nor rutin, the 3-rhamnosylglucoside of quercetin, boun d type II EBSs or inhibited cell growth. These findings suggest that t amoxifen 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 ty pe II EBSs were present in all primary lung cancers tested (n = 12), a nd that tamoxifen and quercetin were effective in inhibiting in vitro bromodeoxyuridine (BrdU) incorporation and proliferating-cell nuclear antigen expression by neoplastic cells in these cancers.