Gene expression signatures associated with suppression of TRAMP prostate carcinogenesis by a kavalactone-rich Kava fraction

Abstract

Kava (Piper methysticum Forster) extract and its major kavalactones have been shown to block chemically induced lung tumor initiation in mouse models. Here we evaluated the chemopreventive effect of a kavalactone-rich Kava fraction B (KFB), free of flavokavains, on carcinogenesis in a transgenic adenocarcinoma of mouse prostate (TRAMP) model and characterized the prostate gene expression signatures. Male C57BL/6 TRAMP mice were fed AIN93M diet with or without 0.4% KFB from 8 wk of age. Mice were euthanized at 16 or 28 wk. The growth of the dorsolateral prostate (DLP) lobes in KFB-treated TRAMP mice was inhibited by 66% and 58% at the respective endpoint. Anterior and ventral prostate lobes in KFB-treated TRAMP mice were suppressed by 40% and 49% at 28 wk, respectively. KFB consumption decreased cell proliferation biomarker Ki-67 and epithelial lesion severity in TRAMP DLP, without detectable apoptosis enhancement. Real time qRT-PCR detection of mRNA from DLP at 28 wk showed decreased expression of cell cycle regulatory genes congruent with Ki-67 suppression. Microarray profiling of DLP mRNA indicated that "oncogene-like" genes related to angiogenesis and cell proliferation were suppressed by KFB but tumor suppressor, immunity, muscle/neuro, and metabolism-related genes were upregulated by KFB in both TRAMP and WT DLP. TRAMP mice fed KFB diet developed lower incidence of neuroendocrine carcinomas (NECa) (2 out of 14 mice) than those fed the basal diet (8 out of 14 mice, χ² = 5.6, P < 0.025). KFB may, therefore, inhibit not only TRAMP DLP epithelial lesions involving multiple molecular pathways, but also NECa. © 2016 Wiley Periodicals, Inc.

Keywords: Kava kavalactone rich fraction; TRAMP; neuroendocrine carcinoma; prostate epithelial lesions.

Figure 1.

Effects of KFB diet consumption on body weight and select organ weight of TRAMP and WT mice. Mice bearing NECa were excluded. (A) Body weight of 16-wk cohorts; (B) body weight of 28-wk cohorts; (C) relative organ weight by 16 wk; and (D) relative organ weight by 28 wk. Relative liver and kidney weights (mg/g) are normalized by body weight. Number of mice: 16 wk, WT/Basal control diet, n=5; WT/Kava KFB diet, n=3; TRAMP/Basal control diet, n=5; and TRAMP/Kava KFB diet, n=8, respectively; 28 wk, WT/Basal control diet, n=4; WT/Kava KFB diet, n=4; TRAMP/Basal control diet, n=6; and TRAMP/Kava KFB diet, n=12, respectively. Mean±SD, one-way ANOVA followed by the Dunnett’s post hoc test, *: P<0.05; **: P<0.01, ***: P<0.001, ****: P<0.0001.

Figure 2.

Effects of KFB diet consumption on the prostatic lobe weight of TRAMP and WT mice. TRAMP mice bearing NE-Ca were excluded. (A) Relative anterior prostate AP weight by 16wk; (B) relative dorsal-lateral prostate DLP weight by 16 wk; (C) relative ventral prostate VP weight by 16 wk; (D) relative AP weight by 28 wk; (E) relative DLP weight by 28 wk; (F) relative VP weight by 28 wk. Relative weights (mg/g) were normalized by the corresponding body weight. Dashed line indicates the WT baseline; % indicates percentage decrease of the expansion in KFB-treated TRAMP mice. Animal numbers: by 16 wk, WT/Basal control diet, n=5; WT/Kava KFB diet, n=3; TRAMP/Basal control diet, n=5; and TRAMP/Kava KFB diet, n=8, respectively; by 28 wk, WT/Basal control diet, n=4; WT/Kava KFB diet, n=4; TRAMP/Basal control diet, n=6; and TRAMP/Kava KFB diet, n=12, respectively. Mean±SD, one-way ANOVA followed by the Dunnett post hoc test, *: P<0.05; **: P<0.01, ***: P<0.001.

Figure 3.

Effects of KFB diet consumption on SV40-T antigen (T-Ag) expression, lesion severity, and Ki-67 expression in TRAMP mice. (A) Representative photomicrograph of the immunohistochemical analysis of T-Ag expression in TRAMP prostatic lobes (28 wk). The epithelial lesions show T-Ag + nuclei. (B) Mean score of TRAMP prostatic epithelial lesions. The most advanced lesion from each mouse prostatic lobe was scored according to severity and distribution pattern using sections stained with T-Ag. Sections with NE-lesions or without prostatic glands are not included. (C) Representative photomicrograph images of the immunohistochemical analysis of Ki-67 expression in TRAMP prostatic lobes (28 wk). Magnification, 200×. Animal number: by 16 wk, TRAMP/Basal control diet, AP n=5, DLP n=5, VP n=5; TRAMP/Kava KFB diet, AP n=8, DLP n=8,VP n=8; by 28 wk, TRAMP/ Basal control diet, AP n=6, DLP n=5, VP n=5; TRAMP/Kava KFB diet, AP n=11, DLP n=12, VP n=12. Mean±SD, Student’s t-test, *: P<0.05; **: P<0.01.