Interaction of tamoxifen with cytosolic and nuclear type II estrogen binding sites (type II EBS)

Growth-inhibitory effect of tamoxifen and quercetin and presence of type II estrogen binding sites in human laryngeal cancer cell lines and primary laryngeal tumors

Quercetin and tamoxifen, in a range of concentrations between 0.01 and 5 microM, exert a dose-dependent inhibition on the anchorage-dependent and anchorage-independent cell growth of Hep2 and CO-K3 laryngeal cancer cell lines. Cell cycle analysis revealed that the growth-inhibitory effect was associated with a block of the cells at the G2/M checkpoint of the cell cycle followed by DNA fragmentation. This suggests that the failure of cells to proceed through the G2/M checkpoint can be a trigger for apoptosis. The induction of apoptosis by quercetin and tamoxifen was confirmed immunocytochemically by the in situ nick end labeling (TUNEL) reaction. These compounds also exerted a dose-dependent growth-inhibitory effect on primary tumor cells, as assessed by colony-forming assay and bromodeoxyuridine labeling. Laryngeal cancer cell lines and primary tumor cells expressed Type II estrogen binding sites (Type II EBS) with binding characteristics similar to those of Type II EBS in other tumor cells. Since the affinities of quercetin and tamoxifen for Type II EBS were correlated with their growth-inhibitory potential while ipriflavone neither interacted with these sites nor inhibited cell growth, the possibility exists that the action of these compounds is mediated, at least in part, by the interaction with Type II EBS. In conclusion, our data indicate that quercetin and tamoxifen could be potentially useful in laryngeal cancer treatment.

Tamoxifen synergizes the antiproliferative effect of cisplatin in human ovarian cancer cells: enhancement of DNA platination as a possible mechanism

We investigated the chemosensitizing activity of tamoxifen (TAM) on estrogen receptor negative ovarian cancer cell lines sensitive (A2780 WT) and resistant to cisplatin (CP) (A2780 CP3). Our results showed that the treatment of both cell lines with the association TAM + CP (concentration range 0.01-1 microN and 0.1-1 microgram/ml, respectively) results in a synergistic antiproliferative activity and a complete reversal of the acquired CP-resistant phenotype. We demonstrated that in A2780 cells the addition of TAM to CP treatment is able to significantly enhance at every tested CP dose (P < 0.001) the amount of platinum (Pt) bound to the DNA. Since Pt-DNA levels in the genome are clearly related to the growth inhibitory effect of CP (correlation value = 0.97, P < 0.001) in our experimental model, we hypothesized that TAM could act synergistically with CP and overcome the acquired CP-resistance by enhancing Pt binding to the DNA. We suggest that, from a clinical point of view, TAM may be usefully included in CP-based chemotherapy regimens for ovarian cancer patients since plasma concentrations of the drug capable of in vitro CP resistance modulation are achievable in vivo. A prospective clinical trial to verify the clinical usefulness of combined TAM + CP treatment in ovarian cancer patients refractory to prior Pt-based chemotherapy is now underway in our department.