Apoptosis induction in breast cancer cells after radiotherapy and potential radiosensitizers

Abstract

Background. Today breast cancer is the foremost cancer death type amongst women around the world. At present some of the toughest challenges in the clinic is recurrent, radioresistant breast cancer, and metastatic breast cancer where low cure rates are observed after surgery and radiotherapy. One way to possibly increase survival rates, is combining radiotherapy and systemic therapy that doubles as a radiosensitizer. The aim of this thesis was to identify pathways that increase radiosensitivity in breast cancer cells after combination treatment with external irradiation and anti-cancer drugs, specifically through increased apoptosis.

Method. Three different human breast cancer cell lines were cultured: MCF-7, MDA-MB-453 and HCC-1806. A dose-response study with irradiation was performed on the cells to determine a radiation absorbed dose and time-point after irradiation for the following combination treatment. Lastly, cells were treated with anti-cancer drugs +/– irradiation, and then stained with the fluorescent dyes Annexin V-DyLight 650 (apoptosis marker) and Hoechst 33342 (cell viability marker) whereafter flow cytometry was performed.

Results. A dose and time dependency was observed in the dose-response study. In total, 29 of 31 anti-cancer drugs exhibited a synergistic effect with radiation on any cell line at any concentration. The drugs birinapant (with target IAP) and ganetespib (with target HSP90) showed statistically significant radiosensitizing effects on all three cell lines. Conclusions. Possible radiosensitizing targets for all three cell types included in this study are HSP90 and IAP. In addition, BH3 mimetics are potential radiosensitizing targets for cell lines MDA-MB-453 and HCC-1806, and the DNA repair machinery was a radiosensitizing target for cell line HCC-1806.