Abstract 6023: Plasma methylome landscape across the spectrum of prostate cancer progression, and differentially methylated region (DMR) based biomarkers of hormonal therapy failure in metastatic hormone-sensitive prostate cancer
Authors: Kohli Manish , Wong Jodie , Tian Yijun , Bitaraf Amir , Hanson Claire , Larsen Matt , Lloyd Jennifer , Batten Julia , Agarwal Neeraj , Swami Umang , Maughan Benjamin , Gupta Sumati , Tward Jonathan 
Published: April 2023

Abstract
Background: DNA silencing of gene expression can affect tumorigenesis, treatment outcomes and prognosis. Epigenetic silencing of tumor suppressor genes in prostate cancer detected in plasma at different stages of progression and its effect on clinical outcomes has not been determined. In a cohort study across different stages of prostate cancer (PC) progression, we performed plasma cell-free DNA (cfDNA)-based epigenomic profiling for determining the landscape of methylation and Differentially Methylated Region (DMR) classifiers and the potential impact on clinical outcomes in metastatic hormone-sensitive prostate cancer (mHSPC) state.
Methods: Plasma was collected prospectively in a longitudinal cohort study of 108 PC patients (pts) of which 24 had non-metastatic Local PC; 28 had mHSPC; 56 had mCRPC. cfDNA was used for enzymatic methylation sequencing (EM-seq) of a targeted panel of genes (N=441) implicated in prostate cancer biology. Methylation status at CpG islands of these genes were examined using Twist targeted cfDNA methylation assay. The Bismark program was used for methylation calls. Temporal trends of differentially methylated regions (DMRs) were identified in different states of progression by comparing the methylation status of target genes in localized PC, mHSPC and mCRPC states using a False Discovery Rate (FDR-q-value) of 0.2 or less. DMRs uniquely associated with mHSPC state were identified and determination of genes with DMRs in pts experiencing early failure of androgen deprivation therapy (ADT)-based therapies was performed. Early failure was defined as progression on ADT within 12 months.
Results: We identified 304/441 genes that were differentially methylated between localized PC and advanced PC (mHSPC and mCRPC) (FDR&lt;0.2), of which 237 genes differed between mHSPC and mCRPC (p&lt;0.05) states. mHSPC pts were serially profiles before and after 3 months of ADT-based therapies. All 28 pts experienced a PSA response at 3-months and 112/237 genes showed significant change in methylation status in these serial samples taken before/after 3 months of ADT-based therapies. The median follow up of the cohort was 18 months (range 10-24). 6/28 mHSPC pts experienced early ADT failure (&lt;12 months; median 10 months). 8/112 genes were significantly associated with early failures and included DMRs in RB1, FOXA1, SOX11. GSC, ALDH1L1, SCGB3A1, FLT4, and PTPRN2.
Conclusions. A targeted cfDNA plasma liquid-biopsy based epigenomic profiling of PC cancer related genes was able to capture significant differences in DMRs across different states of cancer progression. Candidate differentially expressed CpG methylome gene biomarkers detected in plasma also identified biomarkers associated with early ADT-based treatment failure in mHSPC.
Citation Format: Manish Kohli, Jodie Wong, Yijun Tian, Amir Bitaraf, Claire Hanson, Matt Larsen, Jennifer Lloyd, Julia Batten, Neeraj Agarwal, Umang Swami, Benjamin Maughan, Sumati Gupta, Jonathan Tward. Plasma methylome landscape across the spectrum of prostate cancer progression, and differentially methylated region (DMR) based biomarkers of hormonal therapy failure in metastatic hormone-sensitive prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6023.