Abstract 2347: Metabolomics profiling of formalin-fixed paraffin-embedded prostate tissues
Authors: Halliday Sophia Rachael , Olsson Linnea T. , Hamilton Alina , Ramamoorthy Sivapriya , Kitchen Jason , Kirk Erin , Farnan Laura , Gerstel Adrian , Troester Melissa A. , Bensen Jannette T. , Wobker Sara E. , Allott Emma 
Published: July 2021

Abstract
The metabolic landscape of the prostate changes with malignant transformation, and metabolomics is a means of identifying diagnostic and prognostic biomarkers for prostate cancer. Epidemiology and registry studies containing archival formalin-fixed paraffin-embedded (FFPE) specimens are a rich resource for this work but this method of tissue preservation presents a challenge due to loss of metabolites. We optimized global metabolic profiling in FFPE tissue and identified metabolites distinguishing tumor from normal prostate tissue, and aggressive from non-aggressive prostate cancer.
For optimization of metabolomics in FFPE tissues, we obtained matched frozen and FFPE tumor tissue from 62 prostate cancer cases who underwent radical prostatectomy (RP) at the University of North Carolina (UNC) hospital, of which 24 also had adjacent normal prostate tissue. To identify metabolites associated with tumor aggressiveness, we obtained matched tumor and normal FFPE tissue from 60 prostate cancer patients (Gleason ≥4+3, n=30; Gleason ≤3+4, n=30) who underwent RP participating in the UNC Health Registry/Cancer Survivorship Cohort. Following log transformation and imputation of missing values with the minimum observed value for each compound, Welch's two-sample t-test was used to identify biochemicals that differed significantly between groups. Random forest analysis evaluated predictive accuracy of metabolites for distinguishing tumor from normal prostate tissue.
We identified 768 compounds of known identity in frozen and 119 in matched FFPE tissues. Therefore, only 15% of the metabolites detected in frozen samples were recovered from corresponding FFPE tissue, with 80% of these common to both FFPE and matched frozen tissues. We found a predictive accuracy of 78% and 67% for frozen and FFPE tissue, respectively, for distinguishing tumor from normal. Of 39 metabolites significantly altered between matched tumor and normal FFPE tissue, 47% belonged to the lipid class, and despite a greater number of significantly altered metabolites in frozen tissue (246), the proportion belonging to the lipid class was similar (50%). Citrate, integral to normal prostate metabolism, and citrulline, involved in nitric oxide synthesis, had significantly lower levels in aggressive versus non-aggressive tumors. Cell membrane phospholipids were found at significantly higher levels in aggressive tumors.
Common patterns of altered metabolites in tumor vs. normal prostate were observed irrespective of tissue preservation method, despite loss of a large proportion of metabolites during the process of FFPE. As such, FFPE studies are feasible particularly when lipid metabolism is of interest as this class appears one of the best preserved in FFPE. This work will pave the way for incorporating metabolomics profiling of FFPE specimens into epidemiology and registry-based studies of prostate cancer.
Citation Format: Sophia Rachael Halliday, Linnea T. Olsson, Alina Hamilton, Sivapriya Ramamoorthy, Jason Kitchen, Erin Kirk, Laura Farnan, Adrian Gerstel, Melissa A. Troester, Jannette T. Bensen, Sara E. Wobker, Emma Allott. Metabolomics profiling of formalin-fixed paraffin-embedded prostate tissues [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2347.