Proton-irradiated breast cells: molecular points of view

Abstract

Breast cancer (BC) is the most common cancer in women, highly heterogeneous at both the clinical and molecular level. Radiation therapy (RT) represents an efficient modality to treat localized tumor in BC care, although the choice of a unique treatment plan for all BC patients, including RT, may not be the best option. Technological advances in RT are evolving with the use of charged particle beams (i.e. protons) which, due to a more localized delivery of the radiation dose, reduce the dose administered to the heart compared with conventional RT. However, few data regarding proton-induced molecular changes are currently available. The aim of this study was to investigate and describe the production of immunological molecules and gene expression profiles induced by proton irradiation. We performed Luminex assay and cDNA microarray analyses to study the biological processes activated following irradiation with proton beams, both in the non-tumorigenic MCF10A cell line and in two tumorigenic BC cell lines, MCF7 and MDA-MB-231. The immunological signatures were dose dependent in MCF10A and MCF7 cell lines, whereas MDA-MB-231 cells show a strong pro-inflammatory profile regardless of the dose delivered. Clonogenic assay revealed different surviving fractions according to the breast cell lines analyzed. We found the involvement of genes related to cell response to proton irradiation and reported specific cell line- and dose-dependent gene signatures, able to drive cell fate after radiation exposure. Our data could represent a useful tool to better understand the molecular mechanisms elicited by proton irradiation and to predict treatment outcome.

Keywords: breast cancer; cDNA microarray; gene signature; proton therapy; radiation.

Fig. 1.

Dose-dependent survival curves of MCF10A, MCF7 and MDA-MB-231 cells after proton irradiation with doses of 0.5, 2, 4, 6 and 9 Gy at the therapeutic middle SOBP.

Fig. 2.

Venn diagram of microarray gene sets of MCF10A cells exposed to 0.5, 2 and 9 Gy of proton irradiation.

Fig. 3.

Venn diagram of microarray gene sets of MCF7 cells exposed to 0.5, 2 and 9 Gy of proton irradiation.

Fig. 4.

Venn diagram of microarray gene sets of MDA-MB-231 cells exposed to 0.5, 2 and 9 Gy of proton irradiation.

Fig. 5.

(A) 27–51 and 70 gene dose-related gene signature of BC cell lines exposed to 0.5, 2 and 9 Gy. (B) Heatmap of the 8 gene signature deregulated in BC cells after all three configuration doses. The individual values contained in a GEP were represented as colors according to their expression with respect to the control. Overall, down- and up-regulated genes after treatments were displayed using blue and red scales, as indicated in the key.