Cytotoxic effect of
progesterone on the neoplastic cells was investigated using POS cells, a cell line established from a spontaneous
osteosarcoma in a dog. The
20 alpha-HSD activity of POS cells was 0.85 +/- 0.26
NADPH nmol/min mg
protein, demonstrating that a considerable activity was present in this
tumor cell. When
progesterone was added to the medium and cultured for 48 hr,
progesterone dose-dependently inhibited the cell growth, showing that
progesterone was cytotoxic on this
osteosarcoma cells in vitro. In order to assure the role of
20 alpha-HSD on the cell growth, various concentrations of four types of
steroid derivatives, STZ 20, 23, 25, and 26, potent inhibitors of
20 alpha-HSD, were added to the medium with 0.1 microM
progesterone. Then, the POS cell growth was more strongly inhibited, which may suggest that the cytotoxicity of
progesterone was enhanced by inactivation of
20 alpha-HSD by STZs. From these results, POS
osteosarcoma cells have
20 alpha-HSD, which might play an important role in
tumor cell growth against the cell toxicity of
progesterone.