Neoplastic transformation of osteogenic cells: quantitative morphometric analysis of an in vitro model for osteosarcoma.

Previously we have reported the development of a model in vitro system for the study of osteosarcoma. In this system, when chick periosteal explants are infected with Fujinami sarcoma virus (FSV), osteosarcoma-like tissue is formed. In the present study, a series of histopathologic parameters of neoplastic transformation and osteogenesis were quantitated, at a single cell level, by computer-assisted morphometry. Most significantly, it was found that compared to uninfected (control) cultures, in the FSV-infected (experimental) cultures, the bone to osteoid ratio per unit area was decreased due to a relative decrease in the area of bone and an increase in the area of osteoid. The cellularity of the FSV-infected tissues was significantly increased due to an increase in the number of unlabeled and [3H]thymidine-labeled cells, while the proportion of alkaline phosphatase (AP) positive cells decreased. Double-label immunohistochemistry (with anti-P140gag-fps) and histochemistry for AP activity was performed, to demonstrate production of the oncogene-encoded protein, and osteoblastic differentiation respectively. In an in vitro transformation assay, single cells derived from control, uninfected cultures did not grow, while those derived from FSV-infected cultures formed colonies in semisolid medium. Some of these colonies demonstrated AP staining. Taken together these data show that in this in vitro system (i) neoplastic transformation of osteogenic cells does occur, (ii) changes in osteoid and bone production are related to neoplastic transformation, and (iii) osteosarcoma-like changes can be quantitated at the individual cell level.