[Apoptosis of human nasopharyngeal carcinoma CNE-2Z cells induced by tubeimoside I].

Background & Objective: Tubeimu, Bolbostemma pani- culatum(Maxim.) Franquet (Cucurbitaceae), is a kind of traditional Chinese medicinal herb. Our previous studies revealed that tubeimoside I, a triterpenoid saponin isolated from the tubers of Bolbostemma paniculatum, showed potent antitumor effect. This study was designed to investigate the effect of tubeimoside I on the apoptosis of human nasopharyngeal carcinoma cell line CNE-2Z.

Methods: Cell growth inhibition mediated by tubeimoside I was measured by MTT assay after treatment with tubeimoside I. The effect of tubeimoside I on apoptotic induction in CNE-2Z cells was determined using the fluorescent microscopy, electronic microscopy,DNA agarose gel electrophoresis, and flow cytometry,respectively. Western blot analysis was performed to detect the changes of apoptosis-related genes bcl-2 and bax protein expression.

Results: Tubeimoside I displayed growth inhibitory activity against CNE-2Z cells with IC(50) values of 32.5, 20.7, and 16.7 micromol/L for 24, 48, and 72 hours, and CNE-2Z cells showed typical apoptotic morphological features observed by fluorescent microscopy and electronic microscopy. In CNE-2Z cells occurred typical "Ladder"bands after being exposed to tubeimoside I (10 micromol/L, 24, 48, 72 hours; 30, 40, 50, 60 micromol/L, 12 hours). Sub-G1 peak was found using flow cytometry. When CNE-2Z cells were exposed to tubeimoside I (50 micromol/L, 12 hours), the apoptosis index was 72.8%. The down regulation and phosphorylation of bcl-2 (an inhibitor of apoptosis) were detected at 1 hour after the addition of tubeimoside I. In contrast, the levels of bax appeared to be significantly upregulated at 1, 3, 5, and 24 hours after the addition of tubeimoside I.

Conclusion: Tubeimoside I can induce the apoptosis of CNE-2Z cells, and the induction of apoptosis by tubeimoside I is closely associated with downregulation and phosphorylation of bcl-2 and bax activation.