Positive Health Online

Abstract

ZHOU and colleagues, Nutrition/Metabolism Laboratory, Department of Surgery, Beth Israel-Deaconess Medical Center, Harvard Medical School, Boston, MA 02215 USA characterised the ability of dietary soybean components to inhibit the growth of prostate cancer in mice and alter tumour biomarkers associated with angiogenesis.

Background

Soy isoflavones (genistein or daidzein) or soy phytochemical concentrate inhibit the growth of prostate cancer cells LNCaP, DU 145 and PC-3 in vitro but only at supraphysiologic concentrations i.e., 50% inhibitory concentrations (IC50). G2-M arrest and DNA fragmentation consistent with apoptosis of prostate cancer cells are also observed at concentrations causing growth inhibition. In contrast, the in vitro proliferation of vascular endothelial cells was inhibited by soy phytochemicals at much lower concentrations.

Methodology

The authors evaluated the ability of dietary soy phytochemical concentrate soy protein isolate to inhibit the growth of the LNCaP human prostate cancer in severe combined immune-deficient mice. Mice inoculated with LNCaP cells were randomly assigned to one of six dietary groups based on the AIN-76A formulation for 3 weeks. A 2 x 3 factorial design was used with two protein sources (20% casein vs soy protein) and 3 levels of soy phytochemical concentrate (0, 0.2 and 1.0% of the diet).

Results

Soy components did not alter body weight gain or food intake. Compared with Casein-fed controls, the tumour volumes after 3 weeks were reduced by 11% by soy protein, 19% by 0.2% soy phytochemical concentrate, 28% by soy protein with 0-.2% soy phytochemical concentrate, 30% by 1.0% soy phytochemical concentrate and 40% by soy protein with 1.0% soy protein with 1.0% soy phytochemical concentrate. Histological examination of the tumour tissue showed that consumption of soy products significantly reduced tumour cell proliferation, increased apoptosis and reduced microvessel density . Angiogenic protein insulin-like growth factor-I was reduced in the circulation of mice fed soy protein and phytochemical concentrate.

Conclusion

: These data suggest that dietary soy products may inhibit experimental prostate tumour growth by a combination of direct effects upon tumour cells and by indirect effects upon tumour neovasculature.

References

Zhou JR et al. Soybean phytochemicals inhibit the growth of transplantable human prostate carcinoma and tumor angiogenesis in mice. The Journal of Nutrition 129(9): 1628-35. Sep 1999.

Comment

As researchers attentions become more and more focussed upon the clinical properties of phytonutrients, we will learn much more about their underlying mode of action and how they appear to be able to inhibit cancer growth.