Proliferation Inhibition And Mechanism Of ICD On Side Population Cells Of Hepatocellular Carcinoma

Side population (SP) cells in hepatocullular carcinoma (HCC) is a cell class with strong multidrug resistance, which is tolerant to many chemotherapeutic drugs. It is valuable to screen drugs targeting SP cells, which may reverse the drug resistance of HCC cells. Isocorydine (ICD) is a potential anti-cancer natural alkaloid. ICD decreased SP percentages of treated human HCC cell lines and thereby increased the sensitivity of HCC cells towards doxorubicin (DXR), a common chemotherapeutic drug. According to DXR efflux and retention assay, ICD treatment increased the up-take of HCC cells to DXR, decreased efflux of DXR and prolonged the residence time that DXR stayed inside cell nuclei, where DXR interfered with DNA replication and thereby inhibited cell growth. BrdU assay indicated that ICD exerted selective inhibitory effect on SP cells compared with nonSP cells. In the beginning, ICD inhibited cell growth of side population cells by inducing G2/M cell cycle arrest; later, ICD caused apoptosis of treated SP cells and nonSP cells. Western blotting showed that ICD activiated caspase-9, caspase-8and caspase-12, upregulated protein expression of anti-apoptosis members of Bcl-2family such as Bax, Bim, Bak and Bid and downregulated protein level of pro-apoptosis member Bcl-2. In vivo experiment confirmed that ICD targeted SP cells by selectively reducing the tumor sizes and weights of xenagraft by HCC SP cells. Programmed cell death4(PDCD4), a tumor suppressor gene closely related to apoptosis, usually expressed preferentially in nonSP cells, and after treatment with ICD, PDCD4was upregulated dramatically in SP cells both in vitro and in vivo. Taken together, ICD may inhibit cell proliferation and kill HCC SP cells by mechanism of upregulating the expression of PDCD4and inducing apoptosis.