The exercise-conditioned human serum and skeletal muscle cells secretome induce apoptosis in breast cancer cells.

Abstract

BACKGROUND Regular exercise training provides significant health benefits among cancer survivors and is associated with lower breast cancer mortality and reduced risk of recurrence. Both exercise-induced factors secreted into circulation (exerkines) and bioactive molecules contained in skeletal muscle secretome have been proposed to affect the tumor microenvironment and mediate some of the anti-carcinogenic effects of exercise. This study utilized exercise-conditioned human serum obtained from breast cancer patients during chemotherapy and skeletal myotubes' secretome after mechanical loading to investigate their effects on breast cancer cells in vitro. METHODS Breast cancer patients participated in a 12-week exercise training program during their chemotherapy, and blood serum was collected immediately before and after an exercise session in the 2nd and 12th weeks of training. Skeletal myoblasts were differentiated into myotubes and subjected to mechanical stretching to collect their secretome (stretch medium (SM)). Hormone-sensitive Michigan Cancer Foundation-7 (MCF-7) and triple-negative M.D. Anderson-Metastatic Breast-231 (MDA-MB-231) breast cancer cells were treated with either human serum or with the skeletal myotubes' secretome to examine their metabolic activity, migration, cytotoxicity levels and apoptosis regulation. RESULTS The exercise-conditioned serum obtained from breast cancer patients who were subjected to the 12-week training during chemotherapy resulted in reduced metabolic activity (p < 0.001) and increased lactate dehydrogenase (LDH) activity (cytotoxicity) (p < 0.001) in both MCF-7 and MDA-MB-231 breast cancer cells when compared with the control condition. Moreover, incubation of breast cancer cells with the post-exercise serum induced apoptosis in MCF-7 and MDA-MB-231 cells, as indicated by increase in DNA damage and the percentage of necrotic cells (p < 0.05) when compared to pre-exercise condition. Similarly, a significant decrease (p < 0.001) was observed in the metabolic activity of MCF-7 cells treated with the SM, along with increased cytotoxicity (p < 0.05), compared to the cells cultured with the regular growth media. Comparable though not as profound effects were observed in MDA-MB-231 cells when treated with the SM secretome. Furthermore, the expression of apoptosis-inducing caspase-7 (p < 0.001) and caspase-8 (p < 0.01) proteins was increased, whereas cell survival-regulating factors interleukin-8 (IL-8) (p < 0.001), superoxide dismutase-2 (SOD-2) (p < 0.05), Fas cell surface death receptor (Fas) (p < 0.05), and vascular endothelial growth factor (VEGF) (p < 0.01) were downregulated in the SM-treated MCF-7 cells. In addition, the migrating behavior of MCF-7 cells was diminished, and higher levels of DNA damage were observed in cells treated with either SM or non-stretch media (NSM). CONCLUSION Both exercise-conditioned serum of breast cancer patients and skeletal myotubes secretome after mechanical loading can reduce the metabolic activity, promote cell toxicity and DNA damage, modulate the protein expression of crucial cell survival-regulating factors, and lead to apoptosis in breast cancer cells. These findings suggest that even after cancer diagnosis, exercise may exert beneficial effects additive to chemotherapy against breast cancer prognosis.