Abstract 4904: Epigenetic discovery screen identifies SFRP2 as a novel biomarker of high grade prostate cancer
Authors: Perry Antoinette S. , O'Hurley Gillian , Raheem Omer A. , O'Grady Anthony , Kennedy Anne-Marie , Barrett Ciara , Marignol Laure , Murphy Therese M. , Sullivan Linda , Loftus Barbara , Hewitt Stephen M. , Kay Elaine , Lawler Mark 
Published: February 2011

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 &lt; 0.0001) and in preinvasive High Grade Prostatic Intraepithelial Neoplasia 30% (6/20, NIM = 7.45, P &lt; 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 &lt; 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.