INHIBITION OF MURINE BLADDER TUMORIGENESIS BY SOY ISOFLAVONES VIA ALTERATIONS IN THE CELL-CYCLE, APOPTOSIS, AND ANGIOGENESIS

Soy isoflavones exhibit a number of biological effects, suggesting tha t they may have a role in cancer prevention. Our objectives are to det ermine whether components of soy products or purified soy isoflavones can inhibit the progression of bladder cancer. We compared the in vitr o effects of pure soy isoflavones and soy phytochemical concentrate on growth curves, cell cycle progression, and apoptosis in murine and hu man bladder cancer cell lines. Pure soy isoflavones (genistein, genist in, daidzein, and biochanin A) and soy phytochemical concentrate exhib it dose-dependent growth inhibition of murine (MB49 and MBT-2) and hum an (HT-1376, UM-UC-3, RT-4, J82, and TCCSUP) bladder cancer cell lines , although the degree of inhibition varies among lines. Soy isoflavone s induce a G(2)-M cell cycle arrest in all human and murine lines eval uated by flow cytometry. In addition, some bladder cancer lines show D NA fragmentation consistent with apoptosis. We next evaluated the abil ity of genistein, soy phytochemical concentrate, and soy protein isola te, respectively, to inhibit the growth of transplantable murine bladd er cancer in vivo. C57BL/6 mice were randomly assigned to treatment gr oups (n = 12/ group): (a) AIN-76A diet; (b) AIN-76A diet plus genistei n, i.p., 50 mg/kg body weight/day; (c) AIN-76 diet with soy phytochemi cal concentrate at 0.2% of the diet; (d) AIN-76 diet with soy phytoche mical concentrate at 1.0% of the diet; and (e) AIN-76A diet with soy p rotein isolate, 20% by weight. Mice were inoculated s.c. with 5 x 10(4 ) syngeneic MB49 bladder carcinoma cells, and tumor growth was quantit ated. Neither genistein nor soy products reduced body weight gain. Tum or volumes from mice treated with genistein, dietary soy phytochemical concentrate at 1%, or dietary soy protein isolate were reduced by 40% (P < 0.007), 48% (P < 0.001), or 37% (P < 0.01), respectively, compar ed with controls. We characterized the effects of treatment on several biomarkers in tumor tissue: proliferation index by proliferating cell nuclear antigen staining, apoptotic index by terminal deoxynucleotidy ltransferase-mediated dUTP-biotin nick end labeling staining, and angi ogenesis by microvessel quantitation. Soy products reduced angiogenesi s, increased apoptosis, and slightly reduced proliferation while showi ng no histopathological effects on the normal bladder mucosa. Our data suggest that soy isoflavones can inhibit bladder tumor growth through a combination of direct effects on tumor sells and indirect effects o n the tumor neovasculature. Soy products warrant further investigation in bladder cancer prevention and treatment programs or as antiangioge nic agents.