Soluble receptor activator of nuclear factor kappaB Fc diminishes prostate cancer progression in bone

Prostate cancer (CaP) develops metastatic bone lesions that consist of a mixture of osteosclerosis and osteolysis. We have previously demonstrated that targeting receptor activator of nuclear factor kappaB ligand (RANKL) with osteoprotegerin (OPG) prevents the osteolytic activity of CaP and its ability to establish tumor in bone. However, OPG can block tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis, suggesting that the clinical use of OPG may prevent apoptosis of tumors mediated by TRAIL. Thus, methods to block RANKL activity, other than OPG, may be important. Accordingly, we evaluated the ability of soluble murine RANK-Fc (sRANK-Fc) to prevent progression of established CaP in a severe combined immunodeficient mouse implanted with fetal human bone. We first confirmed that sRANK did not block TRAIL-mediated apoptosis of LuCaP cells in vitro and that it did block LuCaP-conditioned media-induced osteoclastogenesis in vitro. Then, LuCaP 35 CaP cells were injected into the marrow space of the bone implanted in the severe combined immunodeficient mice implanted with fetal human bone and allowed to develop into tumors for 6 weeks. Either vehicle or sRANK-Fc was then administered for 6 weeks. sRANK-Fc diminished tumor-induced osteoblastic lesions as demonstrated by radiograph, bone mineral density measurement, and bone histomorphometry. sRANK-Fc also reduced systemic bone remodeling markers, including serum osteocalcin and bone-specific alkaline phosphatase and urine N-telopeptide of collagen. Finally, sRANK-Fc decreased serum prostate-specific antigen levels and tumor volume in the bone, which indicates decreased tumor burden. In contrast, sRANK-Fc had no effect on s.c. implanted LuCaP cells. We conclude that sRANK-Fc is an effective inhibitor of RANKL that diminishes progression of CaP growth in bone through inhibition of bone remodeling.