Abstract 4904: Epigenetic discovery screen identifies SFRP2 as a novel biomarker of high grade prostate cancer

Abstract

Abstract Prostate cancer (CaP) is the most common noncutaneous malignancy and 3rd leading cause of cancer related deaths in men in the Western world. We urgently require CaP-specific biomarkers to distinguish between indolent and aggressive disease and avoid over-treatment. Hyperactivity of Wnt/ β-catenin signaling is an important mechanism of cancer progression, linked to androgen independent growth, development of bone metastases and self-renewal of CaP stem cells. Our aims were to (1) profile Wnt-related gene expression in benign and malignant prostates, (2) investigate hypermethylation of Wnt antagonists and (3) select a novel Wnt-related target for evaluation in low versus high grade CaP. TaqMan Low Density Arrays revealed 14 genes with significantly altered expression between cancer and benign tissue; 12/14 were upregulated in tumors. Only 6/19 human WNT genes were expressed in CaP (WNT3A, WNT4, WNT5B, WNT7B, WNT10A, WNT11); only WNT4 was significantly upregulated in tumors. Overall, the expression profile was highly similar between tumors of high (≥7) and low (≤6) Gleason scores. However, significant differences were observed for DACT1, BTRC, AXIN1 and DLL4. Pharmacological demethylation of PC-3 cells with 5-Aza-CdR reactivated 38 targets (≥2-fold) relative to untreated cells; 40% of these genes inhibit Wnt signalling. Pyrosequencing and QMSP evaluated hypermethylation of Wnt antagonist SFRPs (secreted frizzled related proteins), revealing frequent methylation of SFRP2 in 65% of tumors (48/74; Normalized Index of Methylation (NIM) = 116). Significantly lower frequencies and quantitative levels of methylation were found in benign tissue 9% (7/69; NIM = 0.47, P < 0.0001) and in preinvasive High Grade Prostatic Intraepithelial Neoplasia 30% (6/20, NIM = 7.45, P < 0.0001). Immunohistochemical analysis of tissue microarrays revealed moderate/strong SFRP2 protein expression in the cytoplasm of 84% (172/205) of benign epithelia; while negative/weak SFRP2 staining was noted in most tumor epithelia, particularly Gleason grades 3 & 4, where only 12% (21/171) and 23% (29/124) of cases stained positive, respectively. In contrast, almost half (24/57) of Gleason grade 5 tumors showed moderate/strong SFRP2 expression (P < 0.0001). Microscopic evaluation of these tumors revealed different morphological patterns, corresponding with differential SFRP2 expression. Moderate/strong grade 5 tumors (designated Type A) appeared morphologically solid while negative/weak grade 5 tumors (designated Type B) appeared more diffuse. Furthermore, 80% (4/5 patients) of Type A patients experienced biochemical recurrence, compared with 0% (0/6 patients) of Type B patients (P = 0.015). This is the first report of epigenetic control of Wnt signaling antagonist SFRP2 in CaP. Our data suggest that SFRP2 may be a useful prognostic biomarker in sub-stratifying patients with high grade tumors at increased risk of recurrence. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4904.