Aim:To study the caspase-3-independent mechanisms in oridonin-induced MCF-7human breast cancer cell apoptosis in vitro.Methods:The viability of oridonin-treated MCF-7 cells was measured by MTT (thiazole blue) assay.Apoptotic cellswith condensed nuclei were visualized by phase contrast microscopy.Nucleoso-mal DNA fragmentation was assayed by agarose gel electrophoresis.The apoptoticratio was determined by lactate dehydrogenase assay.Cell cycle alternation andmitochondrial membrane potential were measured by flow cytometric analysis.Bax,Bcl-2,caspase-3,caspase-9,heat shock protein (Hsp)90,p53,p-p53,p21,Poly(ADP-ribose) polymerase (PARP),and the inhibitor of caspase-activated DNase(ICAD) protein expressions were detected by Western blot analysis.Results:Oridonin inhibited cell growth in a time-and dose-dependent manner.Cell cyclewas altered through the upregulation of p53 and p21 protein expressions.Pan-caspase inhibitor Z-VAD-fmk and calpain inhibitor Ⅱ both decreased cell deathratio.Nucleosomal DNA fragmentation and the downregulation of ΔΨ_(mit) weredetected in oridonin-induced MCF-7 cell apoptosis,which was involved in apostmitochondrial caspase-9-dependent pathway.Decreased Bcl-2 and Hsp90expression levels and increased Bax and p21 expression levels were positivelycorrelated with elevated levels of phosphorylated p53 phosphorylation.Moreover,PARP was partially cleaved by calpain rather than by capase-3.Conclusion:DNAdamage provoked alternations in the mitochondrial and caspase-9 pathways aswell as p53-mediated cell cycle arrest,but was not related to caspase-3 activity inoridonin-induced MCF-7 cells. Aim: To study the caspase-3-independent mechanisms in oridonin-induced MCF-7 human breast cancer cell apoptosis in vitro. Methods: The viability of oridonin-treated MCF-7 cells was measured by MTT (thiazole blue) assay. nuclei were visualized by phase contrast microscopy. Nucleoso-mal DNA fragmentation was assayed by agarose gel electrophoresis. apoptotic was determined by lactate dehydrogenase assay. Cell cycle alternation and mitochondrial membrane potential were measured by flow cytometric analysis. Bax, Bcl-2, caspase- 3, caspase-9, heat shock protein (Hsp) 90, p53, p-p53, p21, Poly (ADP- ribose) polymerase (PARP), and the inhibitor of caspase-activated DNase (ICAD) protein expressions were detected by Western blot analysis. Results: Oridonin inhibited cell growth in a time-and dose-dependent manner. Cell cycle was altered through the upregulation of p53 and p21 protein expressions. Pan-caspase inhibitor Z-VAD-fmk and calpain inhibitor II both decreased cell deathratio. N ucleosomal DNA fragmentation and the downregulation of ΔΨ_ (mit) were detected in oridonin-induced MCF-7 cell apoptosis, which was involved in apostochondrial caspase-9-dependent pathway. Decreased Bcl-2 and Hsp90 expression levels and increased Bax and p21 expression levels were positively correlated with elevated levels of phosphorylated p53 phosphorylation. Moreover, PARP was partially cleaved by calpain rather than by capase-3.Conclusion: DNAdamage provoked alternations in the mitochondrial and caspase-9 pathways aswell as p53-mediated cell cycle arrest, but was not related to caspase-3 activity inoridonin-induced MCF-7 cells.