Abstract: Background and purpose: Osteosarcoma, a highly malignant bone tumor, develops rapidly. The current medicines for osteosarcoma present some limitations with serious side effects of long-term use. Isosteviol has the structure of tetracyclic diterpene which is the starting material of many anti-cancer drugs. However, its anti-tumor activity has been rarely reported. This study investigated the effect of isosteviol on proliferation of human osteosarcoma cell line U-2OS. Methods: The effect of isosteviol on U-2OS cell proliferation was assayed by MTT method. Cellular morphologic changes were observed under an inverted phase contrast microscope. The cell condition was observed with Hoechst 33342 and PI staining. Generation of reactive oxygen species and cell membrane potential were detected as well. The cell cycles were analyzed with flow cytometry. The expressions of apoptosis-related proteins Bcl-2 and Bax were measured by Western blot assay. Results: The result indicates that isosteviol suppressed the growth of U-2OS cells in time- and concentration-dependent manner. Isosteviol could cause S phase cell cycle arrest at 24 h and apoptosis at 48 h. With the increased drug concentration, reactive oxygen species increased significantly, and the membrane potential gradually reduced. In addition, isosteviol treatment enhanced the expression of Bax but reduced that of Bcl- 2. Conclusion: The inhibition of isosteviol on cell growth of U-2OS cells was possibly caused by promoting apoptosis through regulating the apoptosis-related protein expressions, such as the enhancement of Bax and reduction of Bcl-2 expression.

Key words: Isosteviol, U-2OS, Growth inhibition, Apoptosis