Mammary Tissue-Derived Extracellular Matrix Hydrogels Reveal the Role of the Irradiated Microenvironment in Breast Cancer Recurrence

Radiation therapy (RT) is essential for triple negative breast cancer (TNBC) treatment. However, patients with TNBC continue to experience recurrence after RT. The alteration of extracellular matrix (ECM) of healthy breast tissue induced by radiation and its role on tumor recurrence are still unknown. In this study, we evaluated the structure, molecular composition, and mechanical properties of irradiated murine mammary fat pads (MFPs) and developed ECM hydrogels from decellularized tissues to assess the effects of RT-induced ECM changes on breast cancer cell behavior. Irradiated MFPs were characterized by increased ECM deposition and fiber density compared to unirradiated controls, which may provide a platform for cell invasion and proliferation. Alterations in irradiated ECM components including collagen I, IV, VI, and fibronectin were observed. TNBC cell proliferation was enhanced in irradiated hydrogels. Encapsulated TNBC cell morphology analysis indicated an increase in invasive capacity within irradiated ECM hydrogels. In addition, TNBC cells co-cultured with macrophages in irradiated ECM hydrogels exhibited further increases in cell proliferation. Our study establishes that the ECM in the irradiated microenvironment promotes TNBC invasion and proliferation that is enhanced in the presence of macrophages. This work represents an important step toward elucidating how changes in the ECM after RT contribute to breast cancer recurrence. ### Competing Interest Statement The authors have declared no competing interest.