High-dose Ionizing Radiation Regulates Gene Expression Changes in the MCF7 Breast Cancer Cell Line

Intraoperative electron radiation therapy (IOERT) is a therapeutic technique which administers a single high dose of ionizing radiation immediately after surgical tumor removal. IOERT induces a strong stress response: both tumor and normal cells activating pro- and antiproliferative cell signaling pathways. Following treatment, several genes and factors are differently modulated, producing an imbalance in cell fate decision. However, the contribution of these genes and pathways in conferring different cell radiosensitivity and radioresistance needs to be further investigated, in particular after high-dose treatments. Despite the documented and great impact of IOERT in breast cancer care, and the trend for dose escalation, very limited data are available regarding gene-expression profiles and cell networks activated by IOERT or high-dose treatment. The aim of the study was to analyze the main pathways activated following high radiation doses in order to select for potential new biomarkers of radiosensitivity or radioresistance, as well as to identify therapeutic targets useful in cancer care.

We performed gene-expression profiling of the MCF7 human breast carcinoma cell line after treatment with 9- and 23-Gy doses (conventionally used during IOERT boost and exclusive treatments, respectively) by cDNA microarrays. Real-Time Quantitative Reverse Transcription PCR (qRT-PCR), immunofluorescence and immunoblot experiments were performed to validate candidate IOERT biomarkers. We also conducted clonogenic tests and cellular senescence assays to monitor for radiation-induced effects.

The analyses highlighted a transcriptome dependent on the dose delivered and a number of specific key genes that may be proposed as new markers of radiosensitivity. Cell and molecular traits observed in MCF7 cells revealed a typical senescent phenotype associated with cell proliferation arrest after treatments with 9- and 23-Gy doses.

In this study, we report genes and cellular networks activated following high-dose IOERT. The selected validated genes were used to design two descriptive models for each dose delivered. We believe that this study could contribute to the understanding over the complex mechanisms which regulate cell radiosensitivity and radioresistance in order to improve personalized radiotherapeutic treatment.