PO-120 Metastatic breast cancer: underlying molecular mechanisms of radiation response

Abstract

IntroductionMetastatic breast cancer (BCa) is an incurable disease with limited therapeutic response. Radiation therapy (RT) is widely used in the management of metastatic BCa, however, efficacy of conventional RT is often not satisfying due to occurrence of resistances. It is suspected that BCa cells with increased invasive potential exhibit intrinsic radiation resistance; however, there is a lack of models that allow investigating the underlying mechanisms. Therefore, the aim of this project is to establish BCa cell lines with increased invasive potential (INV), and to elucidate differences in radio responsiveness compared to parental cell lines.Material and methodsMDA-MB-231, T47D and Au565 were subjected to repetitive migration through an uncoated 8 µm-pore membrane to obtain INV BCa cells. Invasive potential was validated by CytoSelect Invasion Assay (Collagen I or Laminin). Metastatic abilities of INV versus parental cells were assessed in vivo using nude mice. Radiation response was evaluated by clonogenic assay. Deep Profiling Mass Spectrometry assays (MyOmix Dx, USA) was also performed.Results and discussionsWhile MDA-MB-231-INV cells invaded both collagen-I and laminin-coated membranes with a comparable efficiency, T47D-INV and Au565-INV cells showed pronounced invasiveness through Laminin. In in vivo experiments tumours formed by INV cells grew slower at the injection site but, importantly, lead to increased lymph node size, thus confirming increased metastatic potential. After exposure to photon-based ionising radiation MDA-MB-231 parental and INV cells exhibited comparable clonogenic survival. However, while T47D-INV cells display increased clonogenicity, Au565-INV cells revealed lower clonogenic capacities after irradiation, compared to their parental counterparts. Moreover, we identified a number of proteins that were differentially regulated in INV compared to parental BCa cells, demonstrating a close relationship between invasive and migratory capacities and cell death, cell cycle regulation and DNA damage response.ConclusionWe successfully established 3 BCa cell models with increased invasive capacities. Our results demonstrate that enhancement of invasiveness is accompanied by modulation of cell migration, resulting in increased metastatic potential of BCa cells in vivo. The differences in the sensitivity to irradiation in the 3 INV cell lines are pointing to a heterogeneous regulation of radiation response in different BCa subtypes.