Differentiation induction of canine osteosarcoma cell lines by retinoids

The effect of two retinoids, all- trans and 9- cis retinoic acid, on the differentiation of three canine osteosarcoma cells (OOS, HOS, and POS) was examined using markers specifically expressed by phenotypic osteoblasts. Both retinoids induced morphologic differentiation in all the canine osteosarcoma cells. Retinoids enhanced cell flattening and spreading, as well as reduction in cell overlapping. Alkaline phosphatase (ALP) activity and ALP staining was enhanced in OOS, and HOS cells, but decreased in POS cells. These results may suggest that OOS and HOS cells have immature osteoblastic properties and POS cells have mature osteoblastic properties. Retinoids decreased osteocalcin production in all the osteosarcoma cells. They induced an increase in production of type I collagen in HOS and POS cells, but a decrease in OOS cells. These results indicate that retinoids induce differentiation of canine osteosarcoma cells, resulting in an altered expression of their malignant phenotype.