Combined integrin siRNA therapy and radiotherapy of breast cancer.

5175 Objective: Radiation induces the expression of α v β 3 integrin, which is shown to play a key role in tumor angiogenesis and metastasis. We testified the effect of integrin α v β 3 in tumor resistance to irradiation and evaluated the anti-cancer efficacy of combining integrin α v siRNA therapy with irradiation to treat breast cancer. Methods: Wild-type and α v integrin siRNA (10 nM) transfected human breast cancer MDA-MB-435 cells were irradiated with different doses of X-rays, and the radiosensitivity of these cells were evaluated by clonogenic survival assay. To determine whether siRNA treatment against α v β 3 integrin could enhance the efficacy of irradiation, MDA-MB-435 cells were divided into 5 groups: control; non-specific siRNA; α v integrin siRNA; irradiation; combination of siRNA and irradiation. The treatment effect was assessed by cell proliferation assay. Integrin expression levels and the influence of siRNA pre-treatment on cell cycle were measured by flow cytometry. Results: Survival curve showed that MDA-MB-435 cells pre-treated with siRNA (low α v β 3 integrin expression) are more responsive to irradiation than wild-type cells (high α v β 3 integrin expression). The anti-tumor effect of combination therapy is much better than either siRNA or irradiation treatment alone. Flow cytometry showed thatα v β 3 integrin expression increased in the irradiation group while the α v β 3 expression in siRNA or combination group decreased. Furthermore, cell cycle analysis showed that transfection with α v integrin siRNA increased G 2 -M arrest of irradiated cells. Conclusion: Gene silencing with α v integrin siRNA can increase the radiosensitivity of MDA-MB-435 cells. The combination of siRNA treatment and irradiation is more effective than either treatment modality alone.