Abstract 2148: Tumor-microenvironment from African-American prostate cancer exhibit methylation of multiple immune modulators
Authors: Sankaran Santosh , Nguyen James , Jennings Tara , Kumar Vinay , Lilly Michael B. , Ittmann Michael M. , Castro Patricia , Song Liankun , Keane Thomas , Chu Weiping , Zi Xiaolin , Yazdanpanah Omid , Kalebasty Arash Rezazadeh , Rahmatpanah Farah 
Published: March 2024

Background: Non-Hispanic Black American patients (BA) with prostate cancer (PCa) tend to fare worse than their Non-Hispanic White American counterparts (WA), even with consideration of socioeconomic disparities. Clinically, BA face diagnosis at younger age with worse clinical outcomes. Stromal cells adjacent to the tumor, including carcinoma-associated fibroblasts (CAFs), play a critical role in tumorigenesis of PCa. Dysfunction in the tumor microenvironment play a crucial role in mediating prostate cancer tumorigenesis and is emerging as a key target for cancer therapy in solid tumors.

Methods: To investigate whether DNA methylation varies in tumor adjacent stroma (TAS) among PCa patients with different geographical ancestries, areas immediate adjacent to tumor (i.e., less than 1mm) removed for methylation analysis. A complete genome-wide DNA methylation of PCa stroma using 17 BA and 15 WA patients who had radical prostatectomy was carried out. Methyl-Captured (mCap) sequencing data was generated for TAS of prostate cancer FFPE tissues. Methylated sites were identified with the MACS2 callpeak function using a band width of 300 bp and a false discovery rate of q &lt; 0.05. A consensus peak set was derived from the aligned reads of BA and WA prostate cancer stroma samples that were sequenced. Pathway analysis was performed using Ingenuity Pathway Analysis (IPA) tools. CAFs from primary tumors of BA and WA was prepared by tissue culture and treated with demethylating agent (i.e., 5-Azacytidine) for 24 hours followed by maintenance of the cells in drug-free medium for 7-10 days and subjected to mCap sequencing.

Results: We found racial disparities in genome-wide DNA methylation in TAS between the two populations in which BA PCa patients had significantly increased in global DNA methylation as compared to their WA counterpart (p value &lt; 0.001). Hypomethylation occurred in CAFs from BA patients treated with 5-Azacytidine. We identified 1041 methylated sites corresponding to 409 unique genes that were differentially methylated in BA vs WA (p value &lt; 0.05). Pathway analysis identified significant association between methylated genes in BA TAS and immune response pathways including IL-13, JACK/STAT, T cell receptors, NF-KB, and PD-1, PDL1 cancer immunotherapy. Evaluation of the methylome profile between patients based on the post-prostatectomy resection margins, negative (R0) vs positive (R1), showed that R0 resections had significantly greater (p value &lt; 0.001) methylation than R1 resections. Further analysis identified 984 sites corresponding to 373 differentially methylated, unique genes (p value &lt; 0.05).

Conclusion: Tumor-adjacent stroma of BA prostate cancer patients has a distinct methylome as compared to WA patients. Differences in immune response pathways suggests a distinct immune response in TAS in men of different races.

Citation Format: Santosh Sankaran, James Nguyen, Tara Jennings, Vinay Kumar, Michael B. Lilly, Michael M. Ittmann, Patricia Castro, Liankun Song, Thomas Keane, Weiping Chu, Xiaolin Zi, Omid Yazdanpanah, Arash Rezazadeh Kalebasty, Farah Rahmatpanah. Tumor-microenvironment from African-American prostate cancer exhibit methylation of multiple immune modulators [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2148.