Abstract 1396: Targeting immune suppressive myeloid cells in prostate cancer recurrence and metastasis
Authors: Mei Shenglin , Zhang Hanyu , Hirz Taghreed , Jeffries Nathan Elias , Wu Shulin , Wu Chin Lee , Dahl Douglas M. , Saylor Philip J. , Sykes David B. 
Published: March 2024

Abstract
Metastatic prostate cancer is a leading cause of cancer-related deaths worldwide and therefore an urgent inadequately addressed clinical problem. We have approached this problem primarily by studying immune cells within the tumor microenvironment rather than the tumor cells themselves. One critical cell subset that seems to be contributing to the aggressive behavior of clinically significant prostate cancers is the immune suppressive myeloid cells (MDSC) within the tumor microenvironment. MDSC have been shown to promote tumor metastases by participating in the formation of pre-metastatic niche, promoting angiogenesis, tumor cell invasion, and mediating immune suppression. Understanding the heterogeneity and function of these myeloid cells is an essential step toward developing effective therapeutic strategies to target them and enhance anti-tumor immune responses that have thus far been so elusive. We utilized previously generated scRNAseq data and combined it with publicly available prostate cancer scRNAseq datasets. The analysis included a total of 96 samples at different disease stages, including healthy prostate tissue, adjacent-normal tissue, low-grade tumors, high-grade tumors, as well as local and bone metastatic tumors. In addition, GeoMx spatial profiling was performed on 24 high-grade prostate cancer patients to assess immune cell spatial infiltration. This meta-analysis provided comprehensive insights into the molecular characteristics of prostate cancer. We characterized multiple MDSC subpopulations and revealed the dynamics of tumor associated macrophages (TAMs) during tumor progression and metastasis. We found that a specific type of TAM, known as APOE+ SPP1+TAM, is significantly enriched in metastatic tumors. They are transcriptionally similar to the TAMs found in the bone metastasis niche of prostate cancer. Moreover, we found APOE+ SPP1+TAMs within primary/localized tumors tumors alone could predict prostate cancer recurrence despite curative-intent local therapy. We validated the accumulation of APOE+ SPP1+TAMs in a prostate cancer mice model. We are currently studying the role of the specific subset of TAMs in tumor metastases by focused analysis of the communication between these TAMs, T cells, and tumors. Additionally, we are exploring the therapeutic potential of blocking APOE+ SPP1+TAMs in a mice model of prostate cancer. Our analyses provide a comprehensive picture of myeloid cell linage across different prostate cancer stages, highlighting the potential for therapeutic targets that disrupt the metastatic process via their effects on tumor associated macrophages.
Citation Format: Shenglin Mei, Hanyu Zhang, Taghreed Hirz, Nathan Elias Jeffries, Shulin Wu, Chin Lee Wu, Douglas M. Dahl, Philip J. Saylor, David B. Sykes. Targeting immune suppressive myeloid cells in prostate cancer recurrence and metastasis [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 1396.