Osteosarcoma cells in tissue culture: II. Characterization and localization of alkaline phosphatase activity

Although elevated alkaline phosphatase levels in osteosarcoma have been shown to be related to prognosis, the functional significance is unclear. Human osteosarcoma cells in tissue culture retain detectable amounts of alkaline phosphatase activity. In this study the specific activity of that enzyme was compared in 13 osteosarcoma tissue culture lines and 13 normal skin fibroblast lines derived from the same patients. Osteosarcoma cells had significantly higher baseline alkaline phosphatase levels and could be stimulated with hydrocortisone to produce more enzymatic activity than the fibroblast lines. Activity was localized ultracytochemically to the cell membrane and to many small intracellular vesicles in stimulated osteosarcoma cells. These observations aid in the differentiation of osteosarcoma and fibroblast lines in tissue culture and suggest an association between elevated alkaline phosphatase levels and metabolic abnormalities in patients with osteosarcoma.