Effects of anti-RANKL and anti-PD-1 antibodies on cancer-induced osteolysis in mice.

OBJECTIVES

Denosumab, an anti-bone resorptive agent composed of the anti-receptor activator of nuclear factor-κB ligand (RANKL) monoclonal antibody, and nivolumab, an immune checkpoint inhibitor composed of the anti-programmed death-1 (PD-1) antibody, are administered to suppress cancer growth. The present study examined the effects of the administration of anti-RANKL antibody alone and in combination with anti-PD-1 antibody on cancer-induced osteolysis in mice.

METHODS

Cells from the mouse breast cancer cell line, 4T1, were injected into the subperiosteal region of mice calvariae, and anti-RANKL antibodies, with or without anti-PD-1 antibodies, were administered. From 0 to 15 days, tumor volume, osteolysis area, and osteoclast distribution were analyzed.

RESULTS

Tumor volume and osteolysis area in the calvariae increased with time and the number of 4T1 cells injected. Administration of anti-RANKL antibody inhibited cancer-induced osteoclast formation and osteolysis but did not suppress tumor growth. Furthermore, the administration of anti-PD-1 antibody, with or without a low dose of anti-RANKL antibody, did not suppress tumor growth or osteolysis. However, an increase in osteoclast-like cells was found, not only in the calvariae, but also in cancer tissues that received anti-PD-1 antibody.

CONCLUSIONS

Inhibition of RANKL function by the anti-RANKL antibody did not affect tumor growth, although it suppressed osteolysis. Interestingly, the anti-PD-1 antibody induced osteoclast-like cells at the tumor sites. Thus, it is postulated that low-dose anti-RANKL and anti-PD-1 antibodies do not have synergistic effects on osteolysis, whereas anti-PD-1 antibody induces the formation of osteoclasts the treated tumor sites.