Data from Genetic and Epigenetic <i>SLC18A2</i> Silencing in Prostate Cancer Is an Independent Adverse Predictor of Biochemical Recurrence after Radical Prostatectomy

Abstract

&lt;div&gt;Abstract&lt;p&gt;&lt;b&gt;Purpose:&lt;/b&gt; This study investigates SLC18A2 (vesicular monoamine transporter 2) expression in prostate adenocarcinoma and examines its potential as a predictive marker for prostate cancer patient outcome after radical prostatectomy.&lt;/p&gt;&lt;p&gt;&lt;b&gt;Experimental Design:&lt;/b&gt; Expression and single nucleotide polymorphism microarray analyses identified &lt;i&gt;SLC18A2&lt;/i&gt; as both down-regulated and subject to common loss-of-heterozygosity in prostate cancer. Down-regulated SLC18A2 expression was validated on tissue microarrays containing benign and malignant prostate specimens from an independent patient group (&lt;i&gt;n&lt;/i&gt; = 738). Furthermore, SLC18A2 immunoreactivity in radical prostatectomy tumor specimens (&lt;i&gt;n&lt;/i&gt; = 506) was correlated to clinicopathologic characteristics and recurrence-free survival. The possibility of &lt;i&gt;SLC18A2&lt;/i&gt; silencing by aberrant DNA methylation in prostate cancer cells was investigated by bisulfite sequencing.&lt;/p&gt;&lt;p&gt;&lt;b&gt;Results:&lt;/b&gt; Tissue microarray analysis revealed markedly lower cytoplasmic SLC18A2 staining in cancer compared with nonmalignant prostate tissue samples, confirming RNA expression profiling results. Furthermore, multivariate analysis identified cytoplasmic SLC18A2 immunoreactivity as a novel predictor of biochemical recurrence following prostatectomy (hazard ratio, 0.485; 95% confidence interval, 0.333-0.709; &lt;i&gt;P&lt;/i&gt; &lt; 0.001) independent of prostate-specific antigen, Gleason score, tumor stage, and surgical margin status. &lt;i&gt;SLC18A2&lt;/i&gt; showed loss-of-heterozygosity in 23% of the tumors and was densely hypermethylated in 15 of 17 (88%) prostate cancer samples plus 6 of 6 prostate cancer cell lines. In contrast, &lt;i&gt;SLC18A2&lt;/i&gt; was unmethylated in 4 of 4 adjacent nonmalignant prostate and 3 of 5 benign prostatic hyperplasia tissue samples, whereas 2 of 5 benign prostatic hyperplasia samples had monoallelic hypermethylation. Methylation and histone deacetylase inhibitory agents rescued &lt;i&gt;SLC18A2&lt;/i&gt; expression in three prostate cancer cell lines.&lt;/p&gt;&lt;p&gt;&lt;b&gt;Conclusions:&lt;/b&gt;&lt;i&gt;SLC18A2&lt;/i&gt; silencing by DNA hypermethylation and/or allelic loss is a frequent event in prostate cancer and a novel independent predictor of biochemical recurrence after prostatectomy.&lt;/p&gt;&lt;/div&gt;