MMP2 and breast cancer: Brucine could inhibit the bone metastasis of breast cancer by regulating the expression of bone metastasis-related factors such as matrix metallopeptidase 2 (MMP-2), chemokine (C-X-C motif) receptor (CXCR4), receptor of NF-κB ligand (RANKL), and osteoclastogenesis inhibitory factor (OPG) (Sun et al., 2017).