Bisphosphonates Inhibit Osteosarcoma-Mediated Osteolysis Via Attenuation of Tumor Expression of MCP-1 and RANKL

Abstract

Osteosarcoma is the most common primary malignant tumor of bone and accounts for around 50% of all primary skeletal malignancies. In addition to novel chemotherapies, there is a need for adjuvant therapies designed to inhibit osteosarcoma proliferation and tumor-induced osteolysis to attenuate tumor expansion and metastasis. As such, studies on the efficacy of bisphosphonates on human osteosarcoma are planned after feasibility studies determined that the bisphosphonate zoledronic acid (ZOL) can be safely combined with conventional chemotherapy. However, the molecular mechanisms responsible for, and means of inhibiting, osteosarcoma-induced osteolysis are largely unknown. We establish that osteosarcoma growth directly correlates with tumor-induced osteolysis and activation of osteoclasts in vivo. In vitro, tumor cells were determined to expresses surface, but not soluble, receptor activator of NF-kB ligand (RANKL) and stimulated osteoclastogenesis in a manner directly proportional to their malignant potential. In addition, an aggressive osteosarcoma cell line was shown to secrete monocyte chemoattractant protein-1 (MCP-1), resulting in robust monocyte migration. Because MCP-1 is a key cytokine for monocyte recruitment and surface-bound RANKL strongly supports local osteoclastogenesis, we suggest that high levels of these signaling molecules are associated with the aggressive potential of osteosarcoma. Consistent with these findings, abundant expression of RANKL/MCP-1 was observed in tumor in vivo, and MCP-1 plasma levels strongly correlated with tumor progression and osteolysis. ZOL administration directly attenuates osteosarcoma production of RANKL/MCP-1, reducing tumor-induced bone destruction. In vivo, these findings also correlated with significant reduction in osteosarcoma growth. ZOL attenuates tumor-induced osteolysis, not only through direct inhibition of osteoclasts, but also through direct actions on tumor expression of osteoclast activators. These data provide insight regarding the effect of ZOL on osteosarcoma essential for designing the planned upcoming prospective randomized trials to determine the efficacy of bisphosphonates on osteosarcoma in humans.

Deciphering signaling networks in osteosarcoma pathobiology

“…8 Additional preclinical models also establish RANKL blockade as a way of attenuating osteolytic activity. 15,16 Promising results from the discussed preclinical models regarding RANKL inhibition against OS progression are being evaluated at the clinic and a recent report describes complete metabolic remission of an OS patient with RANK and RANKL overexpression that was treated with combination of sorafenib, a tyrosine kinase inhibitor, and RANKL inhibitor denosumab. 17 …”

MicroRNA-126 enhances the sensitivity of osteosarcoma cells to cisplatin and methotrexate

“…Osteosarcoma, the most common primary malignant tumor, has exhibited a high prevalence in the past 20 years, therefore, the establishment of novel chemotherapy drugs for osteosarcoma is urgently required (5)(6)(7). Approximately 900 novel cases are diagnosed each year in the USA (8,9).…”

Rank ligand as a target in musculoskeletal neoplasms

“…Early cell line work detected RANK is present in the POS-1 [35], the Saos-2 [36], and MOTO [37] osteosarcoma lines and that RANKL can alter downstream kinase signaling and gene expression (implying it may be functional). In contrast, other cell lines (e.g., K7M3) and in human tumor samples suggest that RANKL rather is expressed by the tumor cells themselves and that these may contribute to osteolysis and aggressive behavior of the tumor [34,38,39].…”

“…Similarly, in a mouse osteosarcoma model, a RANK-Fc antagonist of RANKL reduced lung metastases [42]. Additionally, bisophosphonates, which inhibit osteoclast function, was shown to inhibit tumor growth in cell lines and murine models [38,43,44].…”