AIM: To study the mechanisms by which oridonin inhibited HeLa cell growth in vitro. METHODS: Viability oforidonin-induced HeLa cells was measured by MTT assay. Apoptotic cells with condensed nuclei were visualizedby phase contrast microscopy. Nucleosomal DNA fragmentation was assayed by agarose gel electrophoresis.Caspase activity was assayed using fluorometric protease assay. ICAD, Bcl-2, and Bax proteins expression weredetected by Western blot analysis. RESULTS: Oridonin induced oligonucleosomal fragmentation of DNA andincreased caspase-3 activity, on the other hand, reduced the expression of inhibitor of caspase-3-activated DNase(ICAD), a caspase-3 substrate, at 12 h in HeLa cells. Oridonin-induced DNA fragmentation, caspase-3 activationand down-regulation of ICAD expression were effectively inhibited by a caspase-3 inhibitor, z-DEVD-fmk (z-Asp-Glu-Val-Asp-fmk). However, pretreatment with an inhibitor of poly (ADP-ribose) polymerase (PARP), 3, 4-dihydro-5-[4-(1-piperidinyl)butoxy]-1(2H)-isoquinolinone (DPQ), did not suppress oridonin-induced HeLa cell death. Inaddition, oridonin-induced apoptosis was associated with an increase in the expression of the apoptosis inducerBax, and a significant reduction in expression of the apoptosis suppressor Bcl-2 in mitochondria. CONCLUSION:Oridonin induces HeLa cells apoptosis by altering balance of Bcl-2 and Bax protein expression and activation ofcaspase-3/ICAD pathway. AIM: To study the mechanisms by which oridonin inhibited HeLa cell growth in vitro. METHODS: Viability of oridonin-induced HeLa cells was measured by MTT assay. Apoptotic cells with condensed nuclei were visualized by phase contrast microscopy. Nucleosomal DNA fragmentation was assayed by agarose gel electrophoresis .Caspase activity was assayed using fluorometric protease assay. ICAD, Bcl-2, and Bax proteins expression weredetected by Western blot analysis. RESULTS: Oridonin induced oligonucleosomal fragmentation of DNA and increased caspase-3 activity, on the other hand, reduced the expression of inhibitor of caspase-3-activated DNase (ICAD), a caspase-3 substrate, at 12 h in HeLa cells. Oridonin-induced DNA fragmentation, caspase-3 activation and down-regulation of ICAD expression were inhibited by a caspase- However, pretreatment with an inhibitor of poly (ADP-ribose) polymerase (PARP), 3,4-dihydro-5- [4- -piperidinyl) bu inaddition, oridonin-induced apoptosis was associated with an increase in the expression of the apoptosis inducerBax, and a significant reduction in expression of the apoptosis suppressor Bcl-2 in mitochondria. CONCLUSION: Oridonin induces HeLa cells apoptosis by altering balance of Bcl-2 and Bax protein expression and activation of caspase-3 / ICAD pathway.