Inhibition of the RANK/RANKL signaling with osteoprotegerin prevents castration-induced acceleration of bone metastasis in castration-insensitive prostate cancer.

Androgen deprivation therapy (ADT) for patients with metastatic or locally advanced prostate cancer reduces bone mineral density by stimulating receptor activator of nuclear factor kappa-B (RANK) signaling in osteoclasts. The involvement of the RANK/RANKL signaling in ADT-induced acceleration of bone metastasis in castration-insensitive prostate cancer was examined in a murine model using osteoprotegerin (OPG). Male Balb/c nude mice were divided into three groups: the non-castration, castration, and castration + OPG groups. PC-3M-luc-C6 was injected into the left ventricle of the mice. Recombinant OPG was injected intravenously twice weekly in the castration + OPG group. In-vivo imaging system (IVIS®) determined that the prevalence and photon counts of bone metastasis in the castration group were significantly higher than that in the non-castration and castration + OPG groups. The mean number of RANKL-positive osteoblasts and the mean serum RANKL level in the castration group were significantly higher than those in the non-castration group. RANKL-enhanced activation of osteoclasts was attenuated in the castration + OPG group. These results suggest that the mechanisms of RANK/RANKL signaling are involved in the ADT-induced acceleration of bone metastasis in castration-insensitive prostate cancer.