Pharmacological evidence for the bone-autonomous contribution of the NFκB/β-catenin axis to breast cancer related osteolysis

The NFκB signaling pathway is implicated in breast cancer and bone metastasis. However, the bone-autonomous contribution of NFκB to breast cancer-induced osteo lysis is poorly understood. Here, we report that pretreatment of osteoblasts with the sesquiterpene lactone Parthenolide (PTN), a verified NFκB inhibitor, prior to exposure to conditioned medium from human and mouse breast cancer cell lines enhanced osteoblast differentiation and reduced osteoblast ability to stimulate osteoclastogenesis. PTN prevented breast cancer-induced osteoclast formation and reduced the ability of breast cancer cells to prolong osteoclast survival and to inhibit osteoclast apoptosis. In vivo, administration of PTN in immuno-competent mice reduced osteolytic bone loss and skeletal tumour growth following injection of the syngeneic 4T1-BT1 cells and reduced local osteolysis caused by conditioned medium from human and mouse osteotropic breast cancer cell lines. Mechanistic studies revealed that NFκB inhibition by PTN in osteoblasts and osteoclasts was accompanied by a significant increase in β-catenin activation and expression. Collectively, these results raise the possibility that combined targeting of NFκB and β-catenin signalling in the tumour microenvironment may be of value in the treatment of breast cancer related osteolysis.