Three-Dimensional Triple Negative Breast Cancer Models: A Platform for Radiobiology Studies

Abstract

Breast cancer (BC) is the leading cause of cancer related death and diagnose in women worldwide. (1) Due to its heterogeneous nature, BC is divided into subtypes depending on the expression of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2). Based on these markers, four major subtypes of BC were designated: Luminal A like, Luminal B like, HER2 positive and Basal type (ER-, PR-, HER2-) also known as Triple-negative breast cancer (TNBC). TNBC accounts for 10-15% of new cases in BC and it is associated with a low 5- year survival rate, poor prognosis and high risk of local recurrence. Insensitive to targeted therapies, TNBC standard treatment involves chemotherapy, surgery, radiotherapy and immunotherapy. Radiotherapy, which is one of the conventional treatments, consists in the induction of direct and indirect damage in the DNA, ultimately leading to cell death. Direct effects involve the induction of significant DNA structural damage. At the same time, indirect effects are produced on the cell involving the generation of free radical species which impact biochemical pathways, such as cell growth and division, leading eventually to death of the tumour. However, a significant number of patients develop local reoccurrence normally associated with radioresistance. Recently, extracellular vesicles (EVs), which are a key intercellular communication player, appeared as a possible contributor to TNBC progression and radioresistance. These EVs can transfer a significant amount of different bioactive molecules (proteins, lipids, DNA, mRNAs, and small miRNAs) to other cells possibly impacting the cellular mechanisms as the development of radioresistance mechanisms in radiosensitive cell lines. These results open a window to the discovery of a possible EVs-related radioresistance signature and possible predictive factors of RT response. To develop more effective therapies, it is crucial to understand the signatures and molecular mechanisms underlying cancer radioresistance on a cellular basis while considering the communication axis which is extremely important in the tumour microenvironment. To be able to uncover these mechanisms we propose the development of a 3D spheroid model. These models allow the simulation of cell-cell and cell-extracellular matrix interactions, nutrients and oxygen gradients. The presence of different cell layers - proliferative, quiescent and necrotic - at the spheroid structure, due to the heterogeneous resources and space available provides a more physiologically relevant model than the traditional 2D cultures, which are capable of only providing basic cell interactions and homogeneous conditions.