| Abstract: | The effects of various retinoids on the proliferative capacities and on the synthesis of DNA, RNA, and protein have been investigated in MCF-7 mammary carcinoma cells in culture. Of the various retinoids tested, retinoic acid revealed maximum activity in inhibiting cell proliferation and thymidine incorporation. The degree of inhibition of cell proliferation by the various retinoids paralleled their capacity to inhibit thymidine incorporation, suggesting suppression of DNA synthesis as a primary cause of restriction of cell growth by these compounds. Two nonepithelial human cell lines were tested for sensitivity to retinoids, and showed diminished responses compared with MCF-7 cells. This suggests a correlation between the ability of retinoids to exert control of differentiation and cell proliferation for a given cell type. Reversibility of the effect of retinoid treatment, high cell viability, and lack of retinoid-induced lysosomal enzyme release, as shown in our studies, indicate that cytotoxicity may be excluded as a cause of decreased cell proliferation and inhibition of thymidine incorporation by retinoids. |
