Methylated glutathione s-transferase 1 (mGSTP1) as a potential plasma epigenetic marker of prognosis and response to chemotherapy in castrate-resistant prostate cancer (CRPC).

11 Background: GSTP1 is inactivated and displays aberrant CpG island promoter methylation in the majority of prostate cancers (PCs). The aim of this study was to assess whether changes in methylated glutathione s-transferase 1 (mGSTP1) levels are predictive of response to chemotherapy and overall survival (OS). Methods: Plasma samples were collected prospectively from a phase I exploratory cohort of 75 men with castration-resistant prostate cancer (CRPC) (40 treated with chemotherapy) and a phase II independent validation cohort (n=51). Plasma samples were collected at presentation with CRPC and pre- and post-cycle one of chemotherapy (90% Docetaxel). mGSTP1 levels were measured using a methylation-specific head-loop PCR assay from DNA isolated from either (1) immunomagnetic separation of circulating tumor cells (CTCs) or (2) free plasma DNA. The associations between plasma mGSTP1 levels, PSA response (defined by PCWG1 criteria), and OS were tested using non-parametric tests and survival analyses. Results...