[Effects of genistein on colon cancer cells in vitro and in vivo and its mechanism of action].

Objective: To study the effects of genistein on the proliferation, apoptosis induction and expression of related gene proteins of human colon cancer cells in vitro and in vivo, and its mechanisms of action.

Methods: MTT colorimetric assay was used to detect the effects of genistein on the proliferation of human colon adenocarcinoma SW480 cells. Light and transmission electron microscopy were used to study the histological and ultrastructural changes. Flow cytometry was used to determine the effects of genistein on cell cycle and apoptosis. Flow cytometry and immunohistochemistry were used to determine the effects of genistein on apoptosis induction and expression of related gene proteins of colon cancer cells.

Results: The MTT colorimetric assay showed that genistein inhibited the proliferation of SW480 cells in a dose-dependent and time-dependent manner, and the highest inhibition rate was 60.2% after 80 microg/ml genistein treatment for 72 h. The light microscopy revealed that many genistein-treated cancer cells were shrunken, disrupted, or showing cytoplasmic vacuolization. The electron microscopic examination showed cell shrinkage, nuclear fragmentation and pronounced chromatin condensation, sometimes formed crescent chromatin condensation attached to the nuclear membrane. The results of flow cytometry showed that: after SW480 cells were treated with 0, 20, 40, 80 microg/ml genistein for 48 h, the FI values of PCNA were 1.49 +/- 0.02, 1.28 +/- 0.04, 1.14 +/- 0.03, and 0.93 +/- 0.08; the FI values of VEGF were 1.75 +/- 0.02, 1.34 +/- 0.06, 1.32 +/- 0.04, and 1.23 +/- 0.04; the fluorescence index (FI) values of p21 were 1.26 +/- 0.05, 1.36 +/- 0.06, 1.61 +/- 0.03, and 1.73 +/- 0.03, respectively. There were statistically significant differences between the control group and each treatment group (P < 0.05 or P < 0.01). The scores of immunohistochemical staining of PCNA and VEGF proteins were decreased, while p21 increased. There were statistically significant differences between the control group and each treatment group (P < 0.05 or P < 0.01).

Conclusion: Genistein can inhibit the growth of colon cancer cells via apoptosis induction and cell cycle arrest at G(2)/M phase. The anti-tumor mechanisms of genistein may be related with the down-regulation of expression of VEGF and PCNA, and up-regulation of the expression of p21.