Genistein and resveratrol, alone and in combination, suppress prostate cancer in SV-40 tag rats

Abstract

Background: Chemoprevention utilizing dietary agents is an effective means to slow the development of prostate cancer. We evaluated the potential additive and synergistic effects of genistein and resveratrol for suppressing prostate cancer in the Simian Virus-40 T-antigen (SV-40 Tag) targeted probasin promoter rat model, a transgenic model of spontaneously developing prostate cancer.

Methods: Rats were fed genistein or resveratrol (250 mg/kg AIN-76A diet) alone and in combination, and a low-dose combination (83 mg genistein + 83 mg resveratrol/kg diet). Histopathology and mechanisms of action studies were conducted at 30 and 12 weeks of age, respectively.

Results: Genistein, resveratrol, and the high-dose combination treatments suppressed prostate cancer. The low-dose combination did not elicit protection against prostate cancer and was most likely below the effective dose for causing significant histopathological changes. Total genistein and resveratrol concentrations in the blood reached 2,160 and 211 nM, respectively in rats exposed to the single treatments. Polyphenol treatments decreased cell proliferation and insulin-like growth factor-1 (IGF-1) protein expression in the prostate. In addition, genistein as a single agent induced apoptosis and decreased steroid receptor coactivator-3 (SRC-3) in the ventral prostate (VP).

Conclusions: Genistein and resveratrol, alone and in combination, suppress prostate cancer development in the SV-40 Tag model. Regulation of SRC-3 and growth factor signaling proteins are consistent with these nutritional polyphenols reducing cell proliferation and increasing apoptosis in the prostate.

Figure 1

Cell proliferation as determined by immunohistochemical staining of Ki-67 in ventral and dorsolateral prostate lobes of 12 week old SV-40 Tag rats and non-transgenic rats. SV-40 Tag rats were fed control AIN-76A diet (Cntr), 250 mg genistein/kg diet (Gen), 250 mg resveratrol/kg diet (Res), 83 mg genistein/kg diet + 83 mg resveratrol/kg diet (L-G+R), 250 mg genistein/kg diet + 250 mg resveratrol/kg diet (H-G+R), or non-transgenic rats (NT) were fed control diet starting at birth. Values are presented as total number of Ki-67 staining epithelial cells divided by total number of epithelial cells X 100 ± SEM. Each group contained eight samples. ^aP < 0.05, ^bP < 0.01 and ^cP < 0.001 when compared to control treatment (Cntr) by One-Way ANOVA followed by the Tukey test.

Figure 2

Apoptosis in ventral and dorsolateral prostates of SV-40 Tag and non-transgenic rats. SV-40 Tag rats were fed control AIN-76A diet (Cntr), 250 mg genistein/kg diet (Gen), 250 mg resveratrol/kg diet (Res), 83 mg genistein/kg diet + 83 mg resveratrol/kg diet (L-G+R), 250 mg genistein/kg diet + 250 mg resveratrol/kg diet (H-G+R), or non-transgenic (NT) were rats fed control diet starting at birth. Values are presented as total number of apoptotic epithelial cells divided by total number of epithelial cells X 100 ± SEM. Each group contained eight samples. ^aP < 0.05 compared to control treatment (Cntr) by One-Way ANOVA followed by the Tukey test.

Figure 3

Insulin-like growth factor-1 protein expression in ventral and dorsolateral prostates of 12 week old SV-40 Tag rats. SV-40 Tag rats were fed control AIN-76A diet (Cntr), 250 mg genistein/kg diet (Gen), 250 mg resveratrol/kg diet (Res), 83 mg genistein/kg diet + 83 mg resveratrol/kg diet (L-G+R), or 250 mg genistein/kg diet + 250 mg resveratrol/kg diet (H-G+R), starting at birth. IGF-1 protein expression was determined via ELISA. Each sample was run in triplicate and each group contained eight samples. Values are expressed as mean ± SEM relative to controls. *P < 0.05 when compared to control treatment (Cntr) by One-Way ANOVA followed by the Tukey test.

Figure 4

Androgen receptor and steroid receptor coactivator-3 protein levels as measured by western blot analysis from ventral prostates of 12 week old SV-40 Tag rats. SV-40 Tag rats were fed control AIN-76A diet (Cntr), 250 mg genistein/kg diet (Gen), 250 mg resveratrol/kg diet (Res), 83 mg genistein/kg diet + 83 mg resveratrol/kg diet (L-G+R), 250 mg genistein/kg diet + 250 mg resveratrol/kg diet (H-G+R) starting at birth. Each treatment group contained eight samples. The graph illustrates mean density ± SEM as a percent of the SV-40 Tag control group (Cntr). ^aP < 0.05 and ^bP < 0.01 compared to control treatment (Cntr) by One-Way ANOVA followed by the Tukey test.