The Mechanism Study For The Treatment Of Breast Cancer Bone Metastases Through Mechanical Loading

BackgroundBreast cancer is a serious problem which endangers global women’s health.It is the most common malignancy with a preference to metastasis to bone,and induced several complications.Many meta-analyses revealed that physical activity is associated with reduced incidence and mortality of breast cancer,and improved quality of life in patients.Physical activity reduced developing a variety of cancers.Physical activity has the capacity to improve the sequela during cancer treatment,and increase recovery effect.Mechanical loading is one form of physical treatment which imitates human active physical exercise.Our previous studies suggest that joint loading is a potential physical therapy for osteonecrosis of the femoral head,osteoarthritis and osteoporosis.Ankle loading promotes bone formation and suppress bone resorption,but their effects on bone metastases of breast cancer have not been investigated.ObiectiveUsing a mouse model with 4T1 cells local injection,we investigated a hypothesis that ankle loading suppresses tumor growth and osteolysis by inhibiting bone resorption and enhancing bone formation in bone metastases of breast cancer.MethodsIn this study,bone metastasis of breast cancer was induced by bilateral intra-tibia injection of mouse breast cancer 4T1 cells in BALB/c female mice.Thirty mice were randomized into sham-injected group(sham),model group(model),and loading group.For ankle loading,1 N loads were laterally applied to the bilateral ankle at 5Hz for 5 min/day for 3 weeks.Change in body weight was measured every 5 days.After three weeks,tibias were harvested for micro CT,histomorphometry,immunohistochemical and Western blot to examine bone microstructure,tumor growth,bone resorption and osteoblast formation.ResultsThe results showed that comparison with sham group,body weight decreased after injection with 4T1 cells in model group,but ankle loading significantly restoredrapid loss of body weight.Compared with the sham group,the model group exhibited the lower BV/TV,Tb.Th,Tb.N(all p < 0.01),and higher Tb.Sp(p < 0.001)in tibia.However,compared to the model group,loading significantly increased BV/TV,Tb.Th,Tb.N(all p < 0.05)as well as decreased Tb.Sp(p < 0.001).Otherwise,injection group increased the tumor bearing(p < 0.001),expression of IL-8 and MMP9(both p < 0.001),but ankle loading decreased them.Tumor cell injection activated osteoclast number(p < 0.05),expression of NFATc1(p < 0.05),but loading reduced osteoclast activity and NFATc1 level(p < 0.05).Furthermore,ankle loading significantly increased osteoblast formation(p < 0.05).Western blot shown that compared with control group,loading significantly decreased expression of RANKL,cathepasin K(both p < 0.05),and significantly increased ALP level(p < 0.01).The correlation analysis shown that tumor bearing(TuAr/TAr)was significantly positive correlated with osteoclast number(p < 0.01),but negative correlated with BV/TV,osteoblast number(both p < 0.01).Both IL-8 and MMP9 were positively correlated with NFATc1(both p < 0.01).ConclusionIn summary,these results indicate that ankle loading could be effective in improve osteolysis and tumor growth in tibia with injection of breast cancer cells.This effect might be attributed to suppress osteoclast development and increasing osteoblast formation.The current study suggests that ankle loading might potentially be employed as a potential therapy for bone metastases of breast cancer.