Abstract
BackgroundThe stromal-epithelial-cell interactions that are responsible for directing normal breast-tissue development and maintenance play a central role in the progression of breast cancer. In the present study, we continued our development of three-dimensional (3-D) cell co-cultures used to study cancerous mammary cell responses to fractionated radiotherapy. In particular, we focused on the role of the reactive stroma in determining the therapeutic ratio for post-surgical treatment.MethodsCancerous human mammary epithelial cells (MRC-7) were cultured in a 3-D collagen matrix with human fibroblasts (MRC-5) stimulated by various concentrations of transforming growth factor beta 1 (TGF-β1). These culture samples were designed to model the post-lumpectomy mammary stroma in the presence of residual cancer cells. We tracked over time the changes in medium stiffness, fibroblast-cell activation (MRC-5 converted to cancer activated fibroblasts (CAFs)), and proliferation of both cell types under a variety of fractionated radiotherapy protocols. Samples were exposed to 6 MV X-rays from a linear accelerator in daily fraction sizes of 90, 180 and 360 cGy over five days in a manner consistent with irradiation exposure during radiotherapy.ResultsWe found in fractionation studies with MRC-5 fibroblasts and CAFs that higher doses per fraction may be more effective early on in deactivating cancer-harboring cellular environments. Higher-dose fraction schemes inhibit contractility in CAFs and prevent differentiation of fibroblasts, thereby metabolically uncoupling tumor cells from their surrounding stroma. However, higher dose fraction appears to increase ECM stiffening.ConclusionsThe findings suggest that dose escalation to the region with residual disease can deactivate the reactive stroma, thus minimizing the cancer promoting features of the cellular environment. Large-fraction irradiation may be used to sterilize residual tumor cells and inhibit activation of intracellular transduction pathways that are promoted during the post-surgical wound-healing period. The higher dose fractions may slow wound healing and increase ECM stiffening that could stimulate proliferation of surviving cancer cells.
Highlights
The stromal-epithelial-cell interactions that are responsible for directing normal breast-tissue development and maintenance play a central role in the progression of breast cancer
We co-cultured cancerous epithelial cells with fibroblast cells in which some of the fibroblasts were prompted by growth factors to differentiate into cancer-associated fibroblasts (CAFs)
Irradiating MRC-5 cells not exposed to growth factor, we found matrix stiffness increased with dose, we believe this may be due to production of reactive oxygen species (ROS) as a result of the absorbed radiation induced cross linking of the collagen matrix [8,9]
Summary
The stromal-epithelial-cell interactions that are responsible for directing normal breast-tissue development and maintenance play a central role in the progression of breast cancer. We focused on the role of the reactive stroma in determining the therapeutic ratio for post-surgical treatment. One primary challenge is the effective application of adjuvant therapies to individuals; for example, to determine the best fractionation schedules for minimizing cancer recurrence using photon radiotherapy in Properties of mesenchymal cells, the extracellular matrix (ECM), and other insoluble proteins surrounding cancer cells facilitate the production and storage of growth factors that modulate the intensity of essential cell signals. CAF phenotype was measured through the expression of α–SMA using immunofluorescence staining Under these conditions fibroblasts are generally called carcinoma associated fibroblasts (CAFs) [3]. These co-culture samples were designed to simulate features of the reactive stroma within a surgical wound containing residual tumor cells. The resulting data provides insights into the effects of different microenvironmental conditions on the therapeutic ratio of fractionated radiotherapy
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