No effect of a high-fat diet on promotion of sex hormone-induced prostate and mammary carcinogenesis in the Noble rat model

Obesity, type 2 diabetes, and cancer: the insulin and IGF connection

Epidemiological studies suggest a positive association between obesity and type 2 diabetes mellitus (T2D) with the risk of cancer and cancer-related mortality. Insulin resistance, hyperinsulinemia, increased levels of IGF, elevated levels of steroid and peptide hormones, and inflammatory markers appear to play a role in the connection between these different diseases. Medications, such as metformin and exogenous insulin, used to treat T2D may affect the risk of cancer and cancer-related mortality. Newer therapies targeting the insulin and IGF1 systems are being developed for use in cancer therapy.

A Western-type diet accelerates tumor progression in an autochthonous mouse model of prostate cancer

Epidemiological studies have provided evidence suggesting an important role for diet and obesity in the development of cancer. Specifically, lipid nutrients of the diet have been identified as important regulators of tumor development and progression. In the present study, we have examined the role of dietary fat and cholesterol in the initiation and progression of prostate cancer using the well-characterized TRAMP mouse model. Consumption of a Western-type diet--that is, enriched in both fat and cholesterol--accelerated prostate tumor incidence and tumor burden compared to mice fed a control chow diet. Furthermore, we also show that this diet increased the extent and the histological grade of prostate tumors. These findings were confirmed by the presence of increased levels of protein markers of advanced tumors in prostates obtained from animals fed a Western-type diet compared to those obtained from control animals. Increased lung metastases in animals fed a Western-type diet were also observed. In addition, we found that with a Western diet, animals bearing tumors presented with reduced plasma cholesterol levels compared with animals fed a control diet. Finally, we show that tumors obtained from animals fed a Western-type diet displayed increased expression of the high-density lipoprotein receptor SR-BI and increased angiogenesis. Taken together, our data suggest that dietary fat and cholesterol play an important role in the development of prostate cancer.

Effect of low-fat diet on development of prostate cancer and Akt phosphorylation in the Hi-Myc transgenic mouse model

This study evaluated the effect of dietary fat on prostate cancer development by using the Hi-Myc mouse transgenic prostate cancer model. Hi-Myc mice develop murine prostatic intraepithelial neoplasia (mPIN) as early as 2 to 4 weeks and invasive adenocarcinoma between 6 and 9 months due to the overexpression of human c-Myc in the mouse prostate. Three-week-old male Hi-Myc mice were placed on high-fat (HF; 42% Kcal) or low-fat (LF; 12% Kcal) diets, and equal caloric intake was maintained until euthanasia at 7 months. The number of mice that developed invasive adenocarcinoma at 7 months was 27% less in the LF diet group (12/28) compared with the HF diet group (23/33, P < 0.05). Epithelial cells in mPIN lesions in the LF group had a significantly lower proliferative index compared with epithelial cells in the HF group (21.7% versus 28.9%, P < 0.05). During the mPIN phase of carcinogenesis (4 months), the LF group had higher serum insulin-like growth factor (IGF) binding protein-1 levels (21.0 +/- 8.9 ng/mL versus 3.2 +/- 0.8 ng/mL, P < 0.05) relative to the HF group. Akt (Ser(473)) phosphorylation, Akt kinase activity, and phosphorylation of downstream targets of Akt in prostates were significantly reduced in the LF diet group compared with the HF group. We conclude that dietary fat reduction delays transition from mPIN to invasive cancer in this Myc-driven transgenic mouse model, possibly through suppression of the IGF-Akt pathway and decreased proliferation of mPIN epithelial cells.

Steroid hormones and carcinogenesis of the prostate: the role of estrogens

Androgens have long been known to be the major sex hormones that target the prostate during development, maturation, and carcinogenesis. It is now apparent that estrogens, both those synthesized by the body as well as those from our environment, also target the prostate during all stages of development. Little is known about the mechanisms involved in estrogen stimulation of carcinogenesis and less is known about how to prevent or treat prostate cancer through estrogenic pathways. To better understand how estrogens mediate their carcinogenic effects, the respective roles of estrogen receptor (ER)-alpha and ER-beta must be elucidated in the epithelial and stromal cells that constitute the prostate. Lastly, the significance of ER signaling during various ontogenic periods must be determined. Answers to these questions will further our understanding of the mechanisms of estrogen/ER signaling and will serve as a basis for chemopreventive and/or chemotherapeutic strategies for prostate cancer.

Prostate Development and Carcinogenesis

The process involved in the development and carcinogenesis of the prostate gland is complex. During early prostate development, the androgenic hormone from embryonic testicles is required for ductal formation, growth, and branching morphogenesis of the prostate gland. From this early stage, interactions between the epithelium and mesenchyme become firmly established through paracrine influence (i.e., growth factors) from mesenchyme (stroma), in response to testosterone, acting on epithelium to stimulate its proliferation, morphogenetic differentiation, and function. In return, the epithelium also exerts its paracrine effects on mesenchyme by regulating the differentiation and specific organizational pattern of its stromal smooth muscle. In a normal adult prostate, the maintenance of normal glandular structure and function is dependent not only on the constant presence of testosterone, but also on a normal intact and stable stroma. This chapter will concentrate first on factors involved in the normal development of the prostate gland and then on the aberrant changes in the homeostatic balance arising either from within (i.e., mutations) or outside (i.e., changes in hormonal balance) that result in derangements of the prostate gland. Finally, environmental and genetic factors that lead to prostate carcinogenesis including activation of oncogenes and mutations of tumor suppressor genes are also discussed.