Studies on the effect of retinoids on the differentiation of teratocarcinoma stem cells in vitro and in vivo

Previous work has shown that retinoic acid can induce F9 embryonal carcinoma cells to differentiate into extraembryonic endoderm in vitro. We have investigated in detail the structureactivity relationship of various derivatives of retinoic acid, the kinetics of the cellular response, and the nature of the type of endoderm formed. These experiments demonstrate that the carboxylic acid group of retinoic acid is essential for activity, whereas the structure can be modified in the cyclohexenyl ring system with retention of effectiveness. The time course of the response of the cells shows that the amount of differentiation is proportional to the duration of treatment, and suggests that the retinoid facilitates formation of endoderm at each division. Finally, even well-differentiated cultures do not produce alpha-fetoprotein, indicating that the endoderm formed is similar to parietal, but not visceral, endoderm. We have also explored the consequence of in vivo retinoic acid treatment on the tumorigenesis of F9 embryonal carcinoma cells in 129/Sv mice. The presence of retinoic acid in the diet at 100 mg/kg significantly retarded tumor growth and lengthened the survival time of the mice. Histological analysis and assays for biochemical markers of endoderm in the tumor both suggest that the retinoid is inducing differentiation of the embryonal carcinoma cells in vivo.