Novel RANK antagonists for the treatment of bone-resorptive disease: theoretical predictions and experimental validation.

Receptor activator of nuclear factor-κB (RANK) and RANK ligand (RANKL) play a pivotal role in bone metabolism, and selective targeting of RANK signaling has become a promising therapeutic strategy in the management of resorptive bone diseases. Existing antibody-based therapies and novel inhibitors currently in development were designed to target the ligand, rather than the membrane receptor expressed on osteoclast precursors. We describe here an alternative approach to designing small peptides able to specifically bind to the hinge region of membrane RANK responsible for the conformational change upon RANKL association. A nonapeptide generated by this method was validated for its biological activity in vitro and in vivo and served as a lead compound for the generation of a series of peptide RANK antagonists derived from the original sequence. Our study presents a structure- and knowledge-based strategy for the design of novel effective and affordable small peptide inhibitors specifically targeting the receptor RANK and opens a new therapeutic opportunity for the treatment of resorptive bone disease.

A Disintegrin And Metalloproteinase 12 produced by tumour cells accelerates osteosarcoma tumour progression and associated osteolysis.

BACKGROUND: Osteosarcoma is the most common primary malignant bone tumour in children and adolescents for whom the prognosis remains unfavourable despite treatment protocols that combine chemotherapy and surgery. Metalloproteinases decisively contribute to cancer development and promotion by regulating cell growth, angiogenesis or inflammation. However, their role in osteosarcoma remains still unknown. METHODS: A screening of a large panel of metalloproteinases and their inhibitors, carried out in osteolytic (K7M2 and POS-1) or osteoblastic (MOS-J) mouse osteosarcoma models, shows that a member of a family of cell surface metallopeptidases, A Disintegrin And Metalloproteinase 12 (ADAM12), is highly expressed in the K7M2 and POS-1 cell lines and weakly expressed in the MOS-J cell line. To investigate whether ADAM12, involved in several pathologic conditions characterised by abnormal cell growth, plays a role in osteosarcoma tumour growth, ADAM12 was overexpressed in MOS-J and downregulated in K7M2 cells. RESULTS: In vivo experiments demonstrated that ADAM12 favours tumour growth, leading to a significant modification in animal survival. In vitro assays showed that ADAM12 knockdown in K7M2 cells slows cell proliferation. In addition, the study of microarchitectural parameters, assessed by micro-computed tomography (CT) analysis, showed that ADAM12 favours bone osteolysis, as demonstrated both in an ADAM12 overexpressing (MOS-J) and a knockdown (K7M2) model. Histological analysis showed that ADAM12 inhibited osteoblast activity and therefore enhanced bone resorption. CONCLUSIONS: Our study demonstrates that ADAM12 expression not only favours tumour growth but also associates enhanced osteolysis with a significant reduction in animal survival, suggesting that ADAM12 could be a new therapeutic target in osteosarcoma.