Role of betulinic acid derivative SH-479 in triple negative breast cancer and bone microenvironment

Breast cancer has a high prevalence in the general population and is often associated with bone metastasis. Specific therapeutic targets are missing for triple negative breast cancer (TNBC), which presents some immunogenic characteristics. Betulinic acid (BA) has been reported to have some anti-tumor properties, and its modified derivative SH-479 was demonstrated to inhibit TNBC bone metastasis. The present study aimed to investigate the effect of the BA derivative SH-479 on breast cancer and bone microenvironment. The effect of BA and its derivative SH-479 on MDA-MB-231 cell proliferation was determined with the MTS method. The cytotoxicity effect of SH-479 was evaluated using the Live and Dead assay. Cell microfilament changes were observed by F-actin staining. The effects of SH-479 on PARP protein expression and cell cycle were detected by western blotting and flow cytometry, respectively. The migratory ability of breast cancer cells treated with SH-479 was determined by migration assay. The effect of SH-479 on osteoclast differentiation induced by breast cancer cells was observed using the osteoclast differentiation assay and tartrate-resistant acid phosphatase staining. The effects of SH-479 on T lymphocytes and bone marrow-derived suppressor cells (MDSCs) in bone marrow from mice were observed by flow cytometry. The results demonstrated that SH-479 significantly inhibited the proliferation of the TNBC cell line MDA-MB-231 at lower concentrations but had no significant effect on normal cells and other types of breast cancer cells for the same concentration. Furthermore, SH-479 significantly interfered with actin microfilaments in breast cancer cells but had no effect on cell apoptosis and cell cycle. In addition, SH-479 inhibited the migratory ability of breast cancer cells and the differentiation of osteoclasts induced by breast cancer cells. In bone marrow immune microenvironment, addition of SH-479 could promote the proliferation of CD4+T lymphocytes and inhibit the proliferation of MDSCs. Taken together, the findings from this study demonstrated that SH-479 inhibited the activity and migratory ability of TNBC cells and the differentiation of osteoclasts induced by TNBC and affected the bone marrow immune microenvironment. SH-479 may therefore inhibit breast cancer metastasis to bones, indicating that SH-479 may be considered as a promising drug to inhibit bone metastasis in patients with breast cancer.