Inositol hexaphosphate inhibits tumor growth, vascularity, and metabolism in TRAMP mice: a multiparametric magnetic resonance study

Abstract

Herein, employing anatomical and dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI), we evaluated noninvasively, the in vivo, chemopreventive efficacy of inositol hexaphosphate (IP6), a major constituent of high-fiber diets, against prostate tumor growth and progression in transgenic adenocarcinoma of the mouse prostate (TRAMP) model. Male TRAMP mice, beginning at 4 weeks of age, were fed with 1%, 2%, or 4% (w/v) IP6 in drinking water or only drinking water till 28 weeks of age and monitored using MRI over the course of study. Longitudinal assessment of prostate volumes by conventional MRI and tumor vascularity by gadolinium-based DCE-MRI showed a profound reduction in tumor size, partly due to antiangiogenic effects by IP6 treatment. As potential mechanisms of IP6 efficacy, decrease in the expression of glucose transporter GLUT-4 protein together with an increase in levels of phospho-AMP-activated kinase (AMPK(Th172)) were observed in prostate tissues of mice from IP6 fed-groups, suggesting that IP6 is interfering with the metabolic events occurring in TRAMP prostate. Investigative metabolomics study using quantitative high-resolution (1)H-NMR on prostate tissue extracts showed that IP6 significantly decreased glucose metabolism and membrane phospholipid synthesis, in addition to causing an increase in myoinositol levels in the prostate. Together, these findings show that oral IP6 supplement blocks growth and angiogenesis of prostate cancer in the TRAMP model in conjunction with metabolic events involved in tumor sustenance. This results in energy deprivation within the tumor, suggesting a practical and translational potential of IP6 treatment in suppressing growth and progression of prostate cancer in humans.

Fig. 1

(A) Effect of IP6 feeding on the weight of LUT organs normalized to body weight. (B) IP6 feeding reduces prostate volume in TRAMP mice as assessed by MRI, performed as a function of time. Error bars indicate ± SEM. (C) Longitudinal assessment of prostate/tumor volume in TRAMP mice using non-invasive proton density-weighted MRI during IP6 feeding over a time period of 24 weeks, starting from 4 weeks till 28 weeks of mice age. Representative coronal PD MRI images (six TRAMP mice per each group were subjected to MRI) of prostate size are presented for untreated control (top panel), 2% IP6-fed (middle) and 4% IP6-fed mice (bottom). The prostate location and size are depictures as yellow ROI (regions of interest) on each image. NS, Not significant

Fig. 2

Inhibitory effect of different doses of IP6 on prostate tumor progression in TRAMP mice. Effect of IP6 feeding on, (A) incidence of low and high grade PIN; (B) adenocarcinoma lesions in dorsolateral prostate of TRAMP mice; (C) tumor grade of dorsolateral prostate in TRAMP mice. (D) Percent area of dorsolateral prostate of positive control and IP6-fed groups having histologically diagnosed PIN, WD, MD, and PD adenocarcinoma characteristics. Error bars indicate ± SEM. NS, Not significant

Fig. 3

Dose dependant effect of IP6 feeding on angiogenesis in prostate of TRAMP mice. (A) Representative DCE-MRI images in axial plane of TRAMP prostate/tumor. There are 4 panes per image: (a) top left, baseline (prior to Gd-injection); (b) top right, 4 min post-; (c) bottom left, 7 min post-; and (d) bottom right, 10 min post-gadolinium injection. The color scale represents incremental increase in signal intensity in the prostate. (B) Quantitative assessment of tumor perfusion and permeability for gadolinium uptake in prostate of TRAMP mice fed with IP6. Quantification of parameters is shown as mean and ± SEM (error bars) in each group. NS, Not significant

Fig. 4

Dose dependant effect of IP6 feeding on biomarkers associated with survival and angiogenesis in dorsolateral prostate of TRAMP mice. IHC staining for (A) VEGF, (B) i-NOS, (C) pP65^Ser536, and (D) pAKT^Ser473. Representative pictographs are depicted at ×400. Columns represent mean and ± SEM (error bars) in each group. NS, Not significant

Fig. 5

Dose dependant effect of IP6 feeding on molecules associated with tumor sustenance and glucose transportation in dorsolateral prostate of TRAMP mice. IHC staining for (A) GLUT-4, (B) pAMPK^Th172 and (C) pACC ^Ser79. Representative pictographs are depicted at ×400. Columns represent mean and ± SEM (error bars) in each group. NS, Not significant.