Abstract: AIM: To study the effects of compound 5F, one of the diterpenoids extracted from Pteris Semipinnata L, on cell cycle and synthesis of DNA and RNA of SPC-A-1 cells.METHODS: Cytotoxicity was determined by MTT test, the cell cycle was analysed by flowcytometry (FCM) and the synthesis of DNA and RNA was observed by the [³H]-TdR and [³H]-UTP incorporation.RESULTS: Compound 5F strongly inhibited the growth of SPC-A-1cells, FCM analysis revealed that 5F could increase the percentage of cells in G2 and S phase and decrease those in G1 phase after 24 h treatment.The assays of [³H]-TdR and [³H]-UTP incorporation into DNA and RNA respectively showed obvious inhibition dose-dependent after exposure to 5F for 24 h.CONCLUSION: Compound 5F obviously inhibits SPC-A-1cells proliferation, arrests SPC-A-1cells in G2 and S phase and inhibits the synthesis of DNA and RNA.

Key words: Pteris Semipinnata L, diterpenoid, SPCA-1, cellcycle, DNA synthesis