Herceptin down-regulates HER-2/neu and vascular endothelial growth factor expression and enhances taxol-induced cytotoxicity of human Ewing's sarcoma cells in vitro and in vivo

We have previously shown that high levels of HER-2/neu protein were overexpressed in human Ewing's sarcoma cells (TC71, SK-ES1) relative to normal human osteoblasts. The purpose of this study was to determine whether herceptin alone or in combination with chemotherapeutic agents could inhibit the growth of Ewing's sarcoma in vitro and in vivo. Western blot analysis showed that the protein levels of HER-2/neu were decreased following herceptin treatment. Cell growth was also inhibited by herceptin in a dose-dependent manner with an IC₅₀ of 4 mg/mL in TC71 and SK-ES1 cell line, whereas human immunoglobin had no effect. Northern blot and ELISA showed the RNA expression and protein levels of vascular endothelial growth factor were also inhibited by herceptin treatment with no alteration in HIF-1α protein and topoisomerase IIα expression. Furthermore, Ewing's sarcoma tumor growth was significantly delayed by 100 mg/kg herceptin treatment in our Ewing's sarcoma xenograft mouse model. Combining taxol with herceptin resulted in additive cytotoxicity, whereas herceptin-etoposide, doxorubicin, and 9-nitrocamptothecin combinations did not. Taxol-herceptin enhanced growth inhibition in TC71 cells in vitro compared with either agent alone. Ewing's sarcoma growth was also delayed in vivo and mean tumor size was significantly lower in mice treated with herceptin plus taxol than in those receiving taxol or herceptin alone. These data suggest that herceptin in combination with taxol may be a therapeutic option in the treatment of Ewing's sarcoma.