Nitidine chloride (NC), a novel benzo[c]phenanthridine alkaloid, induces the growth inhibition of cancer cells. Previously it was demonstrated that SMMC-7721 human hepatocellular carcinoma (HCC) cells are highly susceptible to the antiproliferative effects of NC. However, the specific mechanisms remained unclear. In the present study the pathways of growth inhibition induced by NC in SMMC-7721 cells were investigated. The effects of NC on SMMC-7721 cell proliferation were characterized by MTT and colony formation assays. Additionally, BALB/c nude mice were transplanted with SMMC-7721 cells to verify the inhibition of HCC by NC in vivo. The results showed that NC inhibited the proliferation of SMMC-7721 cells in vitro in a time- and dose-dependent manner and identified efficacy in vivo in a mouse model of HCC. Acridine orange (AO) staining, transmission electron microscopy, Annexin V/PI staining, TUNEL assay and caspase-3 activation assays were used to investigate apoptosis and the cell cycle distribution. Inhibition was mediated in part by cell cycle arrest in G2/M, leading to chromatin condensation, DNA fragmentation and the formation of apoptotic bodies. Apoptosis was also verified by Annexin V/PI staining, TUNEL assay and caspase-3 activation. To assess the levels of the cell cycle and apoptotic regulators, immunohistochemical staining, ELISA, real-time PCR and RNA interference (RNAi) were employed. The apoptotic process triggered by NC involved the upregulation of p53, p21 and Bax, and the downregulation of Bcl-2. These data elucidate a pathway of apoptosis in SMMC‑7721 cells that involves G2/M arrest, upregulation of p53, Bax, caspase-3 and p21, and downregulation of Bcl-2.

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