The Association of Endothelin-1 Signaling with Bone Alkaline Phosphatase Expression and Protumorigenic Activities in Canine Osteosarcoma.

BACKGROUND: Canine osteosarcoma (OS) is an aggressive sarcoma characterized by pathologic skeletal resorption and pulmonary metastases. A number of negative prognostic factors, including bone alkaline phosphatase, have been identified in dogs with OS, but the underlying biologic factors responsible for such observations have not been thoroughly investigated. Endothelin-1-mediated signaling is active during bone repair, and is responsible for osteoblast migration, survival, proliferation, and bone alkaline phosphatase expression. HYPOTHESIS: The endothelin-1 signaling axis is active in canine OS cells, and this pathway is utilized by malignant osteoblasts for promoting cellular migration, survival, proliferation, and bone alkaline phosphatase activities. ANIMALS: 45 dogs with appendicular OS. METHODS: The expressions of endothelin-1 and endothelin A receptor were studied in OS cell lines and in samples from spontaneously occurring tumors. Activities mediated by endothelin-1 signaling were investigated by characterizing responses in 3 OS cell lines. In 45 dogs with OS, bone alkaline phosphatase concentrations were correlated with primary tumor osteoproductivity. RESULTS: Canine OS cells express endothelin-1 and endothelin A receptor, and this signaling axis mediates OS migration, survival, proliferation, and bone alkaline phosphatase activities. In OS-bearing dogs, circulating bone alkaline phosphatase activities were positively correlated with primary tumor relative bone mineral densities. CONCLUSIONS AND CLINICAL IMPORTANCE: Canine OS cells express endothelin-1 and functional endothelin A receptors, with the potential for a protumorigenic signaling loop. Increases in bone alkaline phosphatase activity are associated with osteoblastic OS lesions, and might be an epiphenomenon of active endothelin-1 signaling or excessive osteoproduction within the localized bone microenvironment.

Cathepsin K expression and activity in canine osteosarcoma.

BACKGROUND: Cathepsin K (CatK) is a lysosomal protease with collagenolytic activity, and its secretion by osteoclasts is responsible for degrading organic bone matrix. People with pathologic bone resorption have higher circulating CatK concentrations. HYPOTHESIS: Canine osteosarcoma (OS) cells will possess CatK, and its secretion will be cytokine inducible. Circulating CatK concentrations will be increased in dogs with OS, and will be a surrogate marker of bone resorption. ANIMALS: Fifty-one dogs with appendicular OS and 18 age- and weight-matched healthy control dogs. METHODS: In a prospective study, expressions of CatK mRNA and protein were investigated in OS cells. The inducible secretion and proteolytic activity of CatK from OS cells was assessed in vitro. Serum CatK concentrations were quantified in normal dogs and dogs with OS and its utility as a bone resorption marker was evaluated in dogs with OS treated with palliative radiation and antiresorptive agents. RESULTS: Canine OS cells contain preformed CatK within cytoplasmic vesicles. In OS cells, TGFß1 induced the secretion of CatK, which degraded bone-derived type I collagen in vitro. CatK concentrations were higher in dogs with OS than healthy dogs (11.3 ± 5.2 pmol/L versus 8.1 ± 5.0 pmol/L, P = .03). In a subset of dogs with OS, pretreatment CatK concentrations gradually decreased after palliative radiation and antiresorptive treatment, from 9.3 ± 3.2 pmol/L to 5.0 ± 3.1 pmol/L, P = .03. CONCLUSIONS AND CLINICAL IMPORTANCE: Canine OS is associated with pathologic bone resorption, and CatK inhibitors might aid in the management of canine OS-related malignant osteolysis.