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 mu N and 0.1-1 mu g/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.