Effective prostate cancer chemopreventive intervention with green tea polyphenols in the TRAMP model depends on the stage of the disease

Abstract

Purpose: We have shown previously that oral feeding of green tea polyphenols (GTP) to transgenic adenocarcinoma of the mouse prostate mice in a purely chemopreventive setting significantly inhibits prostate cancer development. To translate this to a human situation, the present study was designed to identify the stage of prostate cancer that is most vulnerable to chemopreventive intervention by GTP.

Experimental design: GTP infusion (0.1% in drinking water) to transgenic adenocarcinoma of the mouse prostate was initiated at ages representing different stage of the disease: (a) 6 weeks (group 1, normal prostate), (b) 12 weeks (group 2, prostatic intraepithelial neoplasia), (c) 18 weeks (group 3, well-differentiated adenocarcinoma), and (b) 28 weeks (group 4, moderately differentiated adenocarcinoma). At age 32 weeks, subsets of animals were evaluated by magnetic resonance imaging, ultrasound, and prostate weight and for serum insulin-like growth factor (IGF)-I/IGF binding protein-3 and IGF signaling.

Results: Tumor-free survival was extended to 38 weeks (P < 0.001) in group 1, 31 weeks (P < 0.01) in group 2, and 24 weeks (P < 0.05) in group 3 compared with 19 weeks in water-fed controls. Median life expectancy was 68 weeks in group 1, 63 weeks in group 2, 56 weeks in group 3, and 51 weeks in group 4 compared with 42 weeks in the control mice. IGF-I and its downstream targets including phosphatidylinositol 3-kinase, pAkt, and phosphorylated extracellular signal-regulated kinase were significantly inhibited only when intervention was initiated early when prostatic intraepithelial neoplasia lesions were common.

Conclusions: Our studies indicate that chemopreventive potential of GTP decreases with advancing stage of the disease and underscore the need to design appropriate chemoprevention clinical trails.

Fig. 1

Effect of oral feeding of GTP on overall and tumor-free survival. Oral GTP (0.1% in drinking water ad libitum) was initiated in animals at ages representing different stages of the disease as described in the text. A control group that received water alone was run in parallel. A, animals were allowed to remain in the protocol until death to ascertain overall survival by Kaplan-Meier analysis. Survival probability by log-rank test. B, animals were monitored biweekly for tumor development by abdominal pelvic palpation to analyze tumor-free survival. Time in weeks is the start of oral feeding of GTP. Mean ± SD.

Fig. 2

Effect of oral feeding of GTP on prostate cancer development in TRAMP mice. Tumor growth was evaluated by longitudinal MRI analysis and by two- and three-dimensional ultrasound imaging. A, representative MRI of the pelvic region of TRAMP mice at age 32 wk subjected to oral infusion of GTP started at age 6 wk (no cancer), 12 wk (PIN), 18 wk (HGPIN and cancer), and 28 wk (cancer and metastasis). B, mean ± SD tumor volumes in cm³ as evaluated by two-dimensional MRI-based imaging. C, representative ultrasound images of the abdominal region of TRAMP mice subjected to oral infusion of GTP starting at age 6, 12, 18, and 28 wk.

Fig. 3

Effect of oral feeding of GTP in TRAMP on genitourinary apparatus weight recorded at age 32 weeks. Oral GTP (0.1% in drinking water ad libitum) was initiated in animals at ages representing different stages of the disease as described in the text. At age 32 weeks, animals from each group were evaluated for genitourinary weight. A, representative images of the genitourinary apparatus of TRAMP mice subjected to oral infusion of GTP starting at (no cancer), age 12 weeks (PIN), 18 weeks (HGPIN and cancer), and 28 weeks (cancer and metastasis). B, mean ± SD genitourinary weight.

Fig. 4

Effect of oral feeding of GTP in TRAMP on serum IGF-I and IGFBP-3 levels. Oral GTP (0.1% in drinking water ad libitum) was initiated in animals at ages representing different stages of the disease as described in the text. A control group that received water alone was run in parallel. At age 32 wk, blood was collected and serum was separated for (A) IGF-I and (B) IGFBP-3 levels. Mean ± SD.

Fig. 5

Effect of oral feeding of GTP to TRAMP on downstream IGF signaling. Oral GTP (0.1% in drinking water ad libitum) was initiated in animals at ages representing different stages of the disease as described in the text. A, at age 32 wk, the dorsolateral prostate was dissected and tissue lysates were prepared and subjected to immunoblotting for PI3K/p85, pAkt, and phosphorylated ERK. Five samples from each group were analyzed by immunoblotting under identical conditions; however, only two representative bands from each are shown. B, bands for pAkt were subjected to densitometric analysis to ascertain quantitatively the change compared with control. Mean ± SD relative density of five bands from each group normalized to whole Akt.

Fig. 6

Effect of oral feeding of GTP to TRAMP mice on prostate pathology and IGF-I immunostaining. Oral GTP (0.1% in drinking water ad libitum) was initiated in animals at ages representing different stages of the disease as described in the text. At age 32 wk, the dorsolateral prostate was dissected and subjected to pathologic evaluation by routine H&E staining as described in the text and also subjected to IGF-I expression by immunostaining. A, representative photomicrographs of the prostate tissue from control water-fed TRAMP mouse (a) showing poorly differentiated adenocarcinoma also evident in (f), which received GTP starting at age 28 wk. b to e, sections from different GTP-treated groups showing normal pathology in mice that received GTP starting at 6 wk (b) compared with mice that received GTP starting at12 wk (c and d) showing low-grade PIN to HGPIN lesions and 18 wk (e) showing well to moderate differentiation. Magnification, ×200. B, photomicrographs showing sections from each group stained by immunohistochemistry for IGF-I expression. Control water-fed mice (a) and mice that received GTP starting at age 28 wk (f) show high expression for IGF-I. GTP-treated mice (b–e) show comparatively low expression of IGF-I with the degree of inhibition depending on the stage of GTP intervention.