Silencing of high mobility group A1 enhances gemcitabine chemosensitivity of lung adenocarcinoma cells.

BACKGROUND: The high mobility group A1 (HMGA1) proteins are architectural transcription factors found to be overexpressed in lung adenocarcinoma. Lentivirus-mediated RNA interference (RNAi) technology is a powerful tool for silencing endogenous or exogenous genes in human cancer cells. Our preliminary study shows that gemcitabine inhibits growth of the human lung cancer cell line SPCA-1 and induces apoptosis, and this effect might link with down-regulation of HMGA1 expression. This study aimed to investigate the chemosensitivity change of the lung adenocarcinoma cells SPCA-1 after HMGA1 inhibition by lentivirus-mediated RNAi. METHODS: We studied a highly malignant lung adenocarcinoma cell line (SPCA-1 cells). Lentiviral short-hairpin RNA (shHMGA1) expression vectors targeting HMGA1 were used for generation of lentiviral particles. After being transfected into the lung adenocarcinoma cell line SPCA-1, the expression of HMGA1 was determined by retrotranscriptase polymerase chain reaction (RT-PCR) and Western blotting. The effect of gemcitabine on proliferation of positive and negative cells was observed by methyl thiazolyl tetrazolium (MTT) assay and clonogenic survival assay. Apoptosis was observed by flow cytometery. Chemosensitivity to gemcitabine was determined by IC50 analysis. Caspase activity was quantitated by a caspase colorimetric protease assay kit. RESULTS: HMGA1-siRNA silenced its target mRNA specifically and effectively in SPCA-1 cells. The apoptotic rates of the scramble control group were (7.43 ± 0.21)%, (11.00 ± 0.20)%, and (14.93 ± 0.31)%, and the apoptotic rates in the silenced group were (9.53 ± 0.42)%, (16.67 ± 0.45)%, and (25.40 ± 0.79)% under exposure to 0.05, 0.5 and 5.0 µg/ml of gemcitabine (P < 0.05). The IC(50) of the silenced group was (0.309 ± 0.003) µg/ml which was significantly lower than in the scramble control group, (0.653 ± 0.003) µg/ml (P < 0.05). It reduced cancer cell proliferation and increased apoptotic cell death after being treated with gemcitabine compared with the scramble control group. HMGA1 silencing resulted in reduction in the phosphorylation of Akt, and promoted the activation of caspases 3, 8 and 9 upon exposure to gemcitabine. CONCLUSIONS: Lentivirus-mediated RNA interference of HMGA1 enhanced chemosensitivity to gemcitabine in lung adenocarcinoma cells. The mechanism may be associated with the PI-3K/Akt signal pathway. HMGA1 may represent a novel therapeutic target in lung cancer.

MDR reversal activity of bromotetrandrine in vitro and in vivo.

The present study was aimed to evaluate the MDR reversal activity of bromotetrandrine (BrTet) in vitro and in vivo. The inhibitory effects of adriamycin (ADM) used alone or in combination with BrTet or Tet on the proliferation of K562 and K562/A02 cells were evaluated by MTT assay. The ADM accumulation and the protein levels of P-glycoprotein (P-gp) were detected by flow cytometry. The mRNA levels of P-gp were determined by RT-PCR. The in vivo effect of BrTet and Tet was investigated by using nude mice grafted with sensitive human leukemia cell line K562 and MDR cell line K562/A02. The results showed that BrTet at 0.25, 0.5 and 1 micromol/L reversed the resistance to ADM in MDR K562/A02 cells in a dose-dependent manner. Flow cytometry suggested that BrTet significantly increased the intracellular accumulation of ADM in K562/A02 cells in a dose-dependent manner. BrTet also inhibited the overexpression of P-gp in K562/A02 cells, and down-regulated mdr1 expression. In nude mice bearing K562 xenografts on the left flank and K562/A02 xenografts on the right flank, intraperitoneal injection of 10 mg/kg BrTet significantly enhanced the antitumor activity of ADM against K562/A02 xenografts with inhibitory rates of 26.1%, while ADM alone inhibited the growth of K562/A02 xenografts only by 5.8%. No enhancement effect by BrTet was seen in K562 xenografts. It is concluded that BrTet shows significant MDR reversal activity in vitro and in vivo. Its activity may be related to the inhibition of P-gp overexpression and the increase intracellular accumulation of anticancer drugs. BrTet may be a promising-MDR modulator for eventual assessment in the clinic.

Tetrandrine: a potent abrogator of G2 checkpoint function in tumor cells and its mechanism.

OBJECTIVE: To assess the ability of tetrandrine (Tet) to enhance the sensitivity to irradiation and its mechanism in cell lines of human breast cancer p53-mutant MCF-7/ADR, p53-wild-type MCF-7 and human colon carcinoma p53-mutant HT-29 as well as in C26 colorectal carcinoma-bearing BALB/c mice. METHODS: MCF-7/ADR, HT-29 and MCF-7 cells were exposed to irradiation in the absence or presence of tetrandrine. The effect of Tet on the cytotoxicity of X-irradiation in these three cells was determined and the effect of tetrandrine on cell cycle arrest induced by irradiation in its absence or presence was studied by flow cytometry. Moreover, mitotic index measurement determined mitosis of cells to enter mitosis. Western blotting was employed to detect cyclin B 1 and Cdc2 proteins in extracts from irradiated or non-irradiated cells of MCF-7/ADR, HT-29 and MCF-7 treated with tetrandrine at various concentrations. Tumor growth delay assay was conducted to determine the radio-sensitization of tetrandrine in vivo. RESULTS: Clonogenic assay showed that tetrandrine markedly enhanced the lethal effect of X-rays on p53-mutant MCF-7/ADR and HT-29 cells and the sensitization enhancement ratio (SER) of tetrandrine was 1.51 and 1.63, but its SER was only 1.1 in p53-wt MCF-7 cells. Irradiated p53-mutant MCF-7/ADR and HT-29 cells were only arrested in G2/M phase while MCF-7 cells were arrested in G1 and G2/M phases. Radiation-induced G2 phase arrests were abrogated by tetrandrine in a concentration-dependent manner in MCF-7/ADR and HT-29 cells, whereas redistribution within MCF-7 cell cycle changed slightly. The proportion of cells in M phase increased from 1.3% to 14.7% in MCF-7/ADR cells, and from 1.5% to 13.2% in HT-29 cells, but 2.4% to 7.1% in MCF-7 cells. Furthermore, the levels of cyclin B 1 and Cdc2 expression decreased after X-irradiation in MCF-7/ADR and HT-29 cells, and the mitotic index was also lower. Tet could reverse the decrease and induce the irradiated cells to enter mitosis (M phase). Endosomatic experiment showed that tetrandrine caused tumor growth delay in irradiated mice. CONCLUSION: Tetrandrine boosts the cell killing activity of irradiation both in vitro and in vivo. Tetrandrine is a potent abrogator for G2 checkpoint control and can sensitize the cells to radiation.