Elucidation of the growth inhibitory effects of genistein on human breast cancer cells

Genistein, an abundant flavonoid in soybean, can decrease proliferation of human breast cancer cells, but the explanation remains incomplete. Therefore, the goal of my research was to elucidate how genistein affects the proliferation of cultured human breast cancer cells that are phenotypically dissimilar. More specifically, my research focused on how genistein at pharmacologically relevant concentrations inhibits cell proliferation by affecting relevant components of cell cycle progression, apoptosis, invasiveness, and differentiation.; In my first study, I found that after 48 h of incubation, genistein at ≤10 μm did not affect cell proliferation, cell cycle progression, nor cell size and granularity in either MCF-7 or MDA-MB-231 cells. However, genistein at 25–50 μM decreased cell proliferation and induced cell cycle arrest at the G₂ /M phase in both cell lines but more so in MDA-MB-231 cells. Both cell lines also appeared larger in size and had more intracellular vacuoles, both of which are signs of cell differentiation. Six days later, the majority of MCF-7, but not MDA-MB-231 cells, showed signs of apoptosis. At 100 μM genistein, both cells lines showed morphological signs of apoptosis and differentiation. However, more MCF-7 cells appeared apoptotic while more MDA-MB-231 cells seemed differentiated. At 200–300 μM genistein, both MCF-7 and MDA-MB-231 cells showed morphological signs of apoptosis. In my second study, I confirmed that 50 μM genistein induced apoptosis in MCF-7 but not in MDA-MB-231 cells after 6 d of incubation by evaluating several apoptotic markers, viz., morphological changes, increased proteolytic cleavage of poly(ADP-ribose) polymerase (PARP), and DNA fragmentation. The apoptosis of MCF-7 cells induced by genistein was accompanied by significant increases in p53 and p21 levels after 48 h of incubation. However, MDA-MB-231 cells also had increased p21 levels, suggesting p53-independent regulation of p21 gene expression. No significant changes of the Bax levels were found in either cell line. The Bcl-2 levels in MCF-7 cells decreased slightly at 18–24 h but increased considerably after 48 h. These results suggest that genistein induced apoptosis only in MCF-7 cells that express the wild-type p53 gene and that Bax and Bcl-2 do not play a major role. In my third study, I found that in MDA-MB-231 cells 50 μM genistein reduced NF-κB binding activity and apparently suppressed uPA gene expression as indicated by reduced secretion of uPA protein by the cells into the culture media.; In conclusion, these data suggest that genistein inhibits breast cancer cell proliferation by targeting multiple genes involved in cell cycle progression, apoptosis, invasiveness, and differentiation. The data expand our knowledge on the chemopreventive and chemotherapeutic potential of genistein against breast cancer.