Asian women consuming a traditional diet high in soy have a low incidence of breast cancer, yet when they emigrate to the USA the second but not the first generation lose this protection. Accordingly, we hypothesized that early exposure to genistein, a major component of soy, could have a permanent protective effect against breast cancer. Sprague-Dawley CD rats were exposed to genistein from conception to day 21 post-partum in the diet at concentrations of 0, 25 and 250 mg genistein/kg AIN-76A diet. At day 50 post-partum, all animals were treated with 80 mg dimethylbenz[a]anthracene/kg body wt to induce mammary cancers. Dietary genistein resulted in dose-dependent protection against development of mammary tumors (fewer tumors per rat). Analysis of mammary whole mounts showed that 21-and 50-day-old female rats had fewer terminal end buds, terminal ductal structures that were undifferentiated and were most susceptible to carcinogenesis. Bromodeoxyuridine incorporation studies revealed that dietary perinatal genistein resulted in a smaller proliferative compartment for terminal end buds. In rats fed the high genistein dose (250 mg/kg diet) total genistein concentrations in the serum and milk of dams 7 days postpartum were 418 Ϯ 198 and 137 pmol/ml, respectively. Total genistein concentrations in stomach milk, serum and mammary glands of 7-day-old offspring were 4439 Ϯ 1109 and 726 pmol/ml and 440 Ϯ 129 pmol/g, respectively. Total genistein concentrations in the serum and mammary glands of 21-day-old offspring were 1810 Ϯ 135 pmol/ml and 370Ϯ36 pmol/g, respectively. Dietary perinatal genistein did not cause significant toxicity in F 0 and F 1 females. We conclude that genistein in the diet at 'physiological levels' enhances cell differentiation, resulting in programming of mammary gland cells for reduced susceptibility to mammary cancer, with no observed toxicity to the reproductive tract of F 1 females.

We investigated the potential of genistein, the primary isoflavone of soy, to protect against breast and prostate cancers in animal models. For mammary cancer studies, Sprague-Dawley rats were fed AIN-76A diet plus minus 250 mg genistein/kg diet. Dimethylbenz[a]anthracene was administered by gavage at d 50 postpartum to induce mammary tumors. Mammary cancer chemoprevention was demonstrated after prepubertal and combined prepubertal and adult genistein treatments but not after prenatal- or adult-only treatments, demonstrating that the timing of exposure to genistein is important for mammary cancer chemoprevention. The cellular mechanism of action was found to be mammary gland and cell differentiation, as shown by whole-mount analysis and beta-casein expression. An imprinting effect was shown for epidermal growth factor receptor expression in mammary terminal end buds. For prostate cancer studies, we used two models. The first was a chemically (N-methylnitrosourea) induced prostate cancer rat model. Genistein in the diet inhibited the development of invasive adenocarcinomas in a dose-dependent manner. The second model was a transgenic mouse model that resulted in spontaneously developing adenocarcinoma tumor of the prostate. Genistein in the diet reduced the incidence of poorly differentiated prostatic adenocarcinomas in a dose-dependent manner and down-regulated androgen receptor, estrogen receptor-alpha, progesterone receptor, epidermal growth factor receptor, insulin-like growth factor-I, and extracellular signal-regulated kinase-1 but not estrogen receptor-beta and transforming growth factor-alpha mRNA expressions. We conclude that dietary genistein protects against mammary and prostate cancers by regulating specific sex steroid receptors and growth factor signaling pathways.

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The aryl hydrocarbon receptor (AhR) is a transcription factor that mediates the inhibitory effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on prostate growth and also modulates normal prostate development. This is evidenced by AhR null mice (Ahr-/-) having smaller dorsolateral and anterior prostates, even though all prostate lobes remain histologically normal. To test the hypothesis that loss of the AhR increases the rate of prostate carcinogenesis, the incidence of macroscopic prostate tumors was determined in Ahr+/+, Ahr+/- and Ahr-/- C57BL/6J transgenic adenocarcinoma of the mouse prostate (TRAMP) mice at 35, 70, 105, 140, 175 and 210 days of age. From 140 days, prostate tumor incidence was greater in Ahr-/- (60%) and Ahr+/- (43%) mice than in Ahr+/+ mice (16%). Allele quantification did not indicate a loss of the wild-type Ahr allele in heterozygous TRAMP tumors, suggesting that tumor formation in these mice was not due to a loss of Ahr heterozygosity. Prostatic SV40 large T antigen mRNA expression and protein localization were comparable in TRAMP mice of each Ahr genotype. Prostates from all mice of each Ahr genotype were histologically indistinguishable, exhibiting diffuse epithelial hyperplasia by 105 days of age. mRNA expression and protein localization for molecular markers of neuroendocrine differentiation, including chromogranin A and neuropilin-1, were elevated in prostate tumors compared to tumor-free ventral prostates, regardless of Ahr genotype or age. Taken together, these results demonstrate that the Ahr inhibits prostate carcinogenesis in C57BL/6J TRAMP mice by interfering with neuroendocrine differentiation.

Formation of prostatic buds from the urogenital sinus (UGS) to initiate prostate development requires localized action of several morphogenetic factors. This report reveals all-trans-retinoic acid (RA) to be a powerful inducer of mouse prostatic budding that is associated with reciprocal changes in expression of two regulators of budding: sonic hedgehog (Shh) and bone morphogenetic protein 4 (Bmp4). Localization of retinoid signaling and expression of RA synthesis, metabolism, and receptor genes in the UGS on embryonic days 14.5-17.5 implicate RA in the mechanism of bud initiation. In UGS organ culture, RA increased prostatic budding, increased Shh expression, and decreased Bmp4. Prostatic budding was stimulated in the absence of RA by recombinant SHH, by blocking BMP4 signaling with NOGGIN, or by combined treatment with SHH and NOGGIN in UGS organ culture media. These observations suggest that reciprocal changes in hedgehog and BMP signaling by RA may regulate bud initiation. Developmental Dynamics 237:1321-1333, 2008.