| Rat breast carcinoma cell line SHZ-88 was used to study effects of two kinds of soy isoflavones(daidzein and genistein) on the growth of cancer cells in vitro, and the mechanisms involved in growth inhibition of soy isoflavones on cancer were revealed by testing cell DNA synthesis, cell cycle, cell apoptosis and cAMP/PKA signaling pathway. And the rat small intestinal epithelial cell culture system was established to detect effects of the two kinds of soy isoflavones on this cell in vitro.1. Effects of soy isoflavones on the growth of rat breast carcinoma cell line SHZ-88 in vitroSHZ-88 cell was treated in vitro with daidzein, genistein and estrogen. 3H-TdR incorporation and microculture tetrazolium (MTT) assay were used to study the effects of daidzein, genistein and estrogen on cell proliferation. Results showed that at low concentration ( 100ng/ml), daidzein and genistein had no effect on the proliferation of cancer cell, but estrogen could promote cell DNA synthesis (compared with control, estrogen of Ing/ml, P=0.066; estrogen of 10ng/ml, P=0.026; estrogen of lOOng/ml, P=0.054); meanwhile daidzein and genistein at different concentration did not affect the growth promotion of 10ng/ml estrogen on cell. But at high concentration( daidzein 10 g/ml, genistein 5 g/ml), soy isoflavones could result in a dose-dependent and time-dependent growth inhibition on the proliferation of cancer cell, and the effect of genistein was stronger than that of daidein. The 50% inhibition rate concentration (IC50) of genistein and daidzein were 13.09 0.15 M g/ml and 53.74 0.83 /J g/ml respectively. EGF of 100ng/ml could promote the growth of cancer cell, daidzein at concentration of 50 u g/ml and genistein at concentration of 15 g/ml both could inhibit the effect of EGF, but not completely.2. Effects of soy isoflavones on the cytologic and biochemical characteristics of rat breast carcinoma cell line SHZ-88The effects of soy isoflavones on the cytologic and biochemical characteristics of SHZ-88 cell in vitro were determinated. Daidzein at concentration of 50 M g/ml and genistein at concentration of 15 M g/ml both could prolong the cell population doubling time in the index growth phase (control group 18.3 1.0h, daidzein group 21.9 0.7h, genistein group 33.9 1.0h, P<0.01), decrease cell division index and single cell cloning efficiency (control group 74.2 3.0%, daidzein group 47.4 6.5%, genistein group 33.1 8.0%, P<0.01\ decrease activity of lactate dehydrogenase (LDH), succinate dehydrogenase (SDH) and alkaline phosphatase (AKP) in the cell (compared with control, P<0.01\ but increase the synthesis of total cellular protein (control group 0.32 0.06 mg/1 106cells, daidzein group 0.65 0.18 mg/1 106cells, genistein group 0.68 0.04 mg/1 106cells, P<0.01), and had no effects on the cellular structure within short term (24h). These data suggested us that soy isoflavones could inhibit the growth of SHZ-88 cancer cell, but induce cell differentiation, increase cell protein synthesis by some mechanisms.3. The mechanisms involved in the proliferation inhibition of soy isoflavones on rat breast carcinoma cell line SHZ-88Isotope incorporation, flow cytometry, radioimmunoassay and RT-PCR were used to study the mechanisms of soy isoflavones inhibitory effects on cancer cell proliferation. After cells were treated with isoflavones, cell DNA synthesis, cell cycle and cell apoptosis were analyzed; and the cellular cyclic adenosine monophosphate (cAMP) content, the activity of adenylate cyclase (AC), phosphodiesterase (PDE) and cAMP-dependent protein kinase (PKA) and the expression of cAMP response element binding protein (CREB) mRNA were tested.Results showed that both 50 g/ml of daidzein and 15 g/ml of genistein decreased 3H-TdR incorporation in DNA of rat breast carcinoma cell. Flow cytometry showed that cells were accumulating in the S phase, but cell apoptosis didn't be induced. The concentration of cAMP in the cell treated with daidzein and genistein respectively was increased within 5min (con...
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