Background  Bone metastasis of breast cancer is one of the current research hotspots. Osteoblasts in the bone microenvironment can promote the survival of tumor cells and form micrometastasis. While, there are few studies on the effect of osteoblast derived exosomes on breast cancer.

  Objective  To investigate the effects of MC3T3-E1 exosomes on the migration and proliferation of breast cancer 4T1 and MDA-MB-231 cells.

  Methods  Exosomes derived from MC3T3-E1 cells were extracted, transmission electron microscopy (TEM), nanopartic tracking analysis (NANOPartic tracking), NTA and Western blot were used to identify exosomes. Transwell and scratch assay were used to detect the effect of MC3T3-E1-derived exosomes on the migration of breast cancer 4T1 and MDA-MB-231 cells. The effects of MC3T3-E1 derived exosomes on the proliferation of breast cancer cells were detected by CCK-8 assay and clonogenesis assay.

  Results  The exosomes derived from MC3T3-E1 cells were characterized by membrane-structured cystic vesicles under transmission electron microscopy. The exosomes derived from MC3T3-E1 cells were 100-200 nm in diameter and expressed exosome related proteins Alix and TSG101. CCK-8 activity test results showed that exosomes derived from MC3T3-E1 cells at a concentration of 20 μg/mL did not affect the vitality of breast cancer cells, while exosomes derived from 30 μg/mL and 50 μg/mL could reduce the vitality of breast cancer cells. Scratch test and Transwell test results showed that 20 μg/mL of exosomes could promote the migration of breast cancer cells (P<0.05). CCk-8 proliferation assay and colony formation assay showed that 20 μg/mL exosomes could promote the proliferation of breast cancer cells (P<0.05).

  Conclusion  Exosomes derived from MC3T3-E1 can promote the migration and proliferation of breast cancer cells, which provides a potential target for therapeutic strategy on bone metastasis of breast cancer.