Breast cancer (BC) and osteoporosis are prevalent in postmenopausal and aging women, and the co-occurrence of these conditions may significantly impact bone health and fracture risk. Bone metastasis (BM) affects approximately 70% of advanced BC patients. Tumor cell (TC) infiltration affects bone microarchitecture via distinct mechanisms, including the formation of osteolytic lesions. Osteolysis is characterized by a reduction in the volume of trabecular bone. 

Notably, osteolytic microenvironments mimic an osteoporotic environment. In osteoporosis, the bone remodeling process becomes pathologically disrupted due to overactive bone resorption and inadequate new bone formation. However, little is known about the impact of preexisting osteoporosis on TC infiltration or BM.

To investigate the co-occurrence of these conditions on bone matrix quality, L4 and L5 of ovariectomized (n = 5) and healthy (n = 5) Sprague-Dawley rats were sectioned into (d = 3.42 ± 0.38 mm, h = 0.66 ± 0.155 mm) and (d = 3.71 ± 0.44 mm, h = 0.65 ± 0.04 mm) slices. Vertebral slices were decellularized and scanned via micro-computed tomography (µCT) to define baseline geometry and mineral density. To evaluate bone resorption, a direct co-culture will be established using 4T1 BC cells (triple negative, Stage IV) and RAW 264.7 cells supplemented with 50 ng/ml RANKL seeded on slices. After 7 days, cell proliferation assays will be performed to quantify TC infiltration and biochemical assays to quantify matrix modifications. It is expected that the osteoporotic bone microenvironment will coincide with increased TC infiltration, greater matrix modification, and altered geometrical and mineral properties.