Immunization With RANKL Inhibits Osteolytic Bone Metastasis in Breast Cancer

Breast cancer cells often metastasize to bone. Accumulating evidence suggests that inhibiting the receptor activator of nuclear factor-κB ligand (RANKL) not only leads to reduced bone metastasis of breast cancer but also has antitumoral effects. Here, we used mutant receptor activator of nuclear factor-κB ligand (RANKLM) as a vaccine for active immunization to induce antibodies for immunotherapy of bone metastatic cancer. We investigated whether anti-RANKL antibodies inhibit osteolytic bone metastasis in vitro and in a murine model. MC3T3 cells stimulated by MDA-MB-231 culture medium secreted growth differentiation factor-15 (GDF-15), which induced the nuclear factor-κB signaling cascade. In addition, RANKLM treatment-induced reduction of intraosseous growth of MDA-MB-231 cells correlated with decreased GDF-15 expression, a reduced number of osteolytic lesions, and slower tumor progression. In addition, vaccination with RANKLM led to significant improvement in overall survival and skeletal metastasis in tumor-bearing mice. Induction of anti-RANKL antibodies by RANKLM decreased GDF-15 production by deactivating nuclear factor-κB signaling, which in turn inhibited metastasis of MDA-MB-231 cells to bone. Taken together, the results demonstrate a role for RANKLM immunization in preventing bone metastasis of breast cancer.