Osteoprotegerin (OPG) mediates the anti-carcinogenic effects of normal breast fibroblasts and targets cancer stem cells through inhibition of the β-catenin pathway

Abstract

Normal breast fibroblasts (NBFs) support and maintain the architecture of the organ, and can also suppress tumorigenesis. However, the mechanisms involved are not fully understood. We have shown here that NBFs suppress breast carcinogenesis through secretion of osteoprotegerin (OPG), a soluble decoy receptor for the Receptor Activator of NF-κB ligand (RANKL). Indeed, NBFs and human recombinant OPG (rOPG), suppressed breast cancer cells proliferation and motility through inhibition of the epithelial-to-mesenchymal transition (EMT) process both in vitro and in vivo. Additionally, rOPG inhibited the IL-6/STAT3 and NF-κB pathways as well as the OPG gene, which turned out to be STAT3-regulated. This was confirmed using denosumab, a RANKL-targeted antibody, which also inhibited NF-κB, down-regulated OPG and repressed EMT in breast cancer cells grown in 2D and 3D. Importantly, both rOPG and denosumab targeted cancer stem cells (CSCs). This was mediated through inhibition of the CSC-related pathway β-catenin. Moreover, rOPG reduced tumor growth and inhibited breast CSC biomarkers in orthotopic humanized breast tumors. Therefore, normal mammary fibroblasts can suppress carcinogenesis through OPG, which constitutes great potential as preventive and/or therapeutic molecule for breast carcinomas.

Keywords: Breast cancer; Breast stromal fibroblasts; Cancer stem cells; Denosumab; OPG.