Abstract 4263: Prostate cancer cell-derived small extracellular vesicles regulate monocyte migration via STEAP4 and promote a monocyte transitional state

Abstract Our group has previously shown that prostate cancer (PrCa) -derived small extracellular vesicles (sEVs) are powerful cell communication mediators as they carry an array of proteins that have the ability to change recipient cell functions. Here, we describe a novel pathway of cancer cell-monocyte communication mediated by sEVs. Since sEVs carry cargoes that alter recipient cell phenotypes, we analyzed via proteomic analysis sEVs released from PC3 PrCa cells. Using CRISPR Cas9 methods, we downregulated IFIT3 (Interferon-induced proteins with tetratricopeptide repeats-3, member of the interferon-stimulated gene family) in PC3 PrCa cell (IFIT3KO). We then isolated sEVs from PC3 or IFIT3KO cells by using differential ultracentrifugation followed by iodixanol density gradient. Our proteomic analysis of IFIT3KO sEVs compared to PC3 sEVs shows that IFIT3 downregulation results in a significant upregulation of a metalloreductase, STEAP4 (six-transmembrane-epithelial antigen of the prostate 4), which is increased in PrCa cells and promotes PrCa cell proliferation and survival. STEAP4 is also known to promote an anti-inflammatory response in monocytes and macrophages. We then, investigated whether PrCa sEVs enriched in STEAP4 have a causal effect on monocyte functions and phenotype by using adhesion and migration assays as well as flow cytometry. Our results show that while all PrCa sEVs stimulate the adhesion of healthy donor or non-metastatic PrCa patient monocytes, only PrCa sEVs expressing STEAP4 increase their migration. In parallel, we provide evidence that all PrCa sEVs affect some of the M2 (CD163 or CD204) and M1 (CD80 or HLA DR) polarization markers analyzed in healthy donor monocytes. We show that there is a transitional state induced by PrCa sEVs in healthy donor monocytes, which occurs in a STEAP4-independent manner. This state mimics the non-metastatic PrCa patient monocyte phenotype. In conclusion, we describe a unique pathway whereby PrCa cell sEVs expressing STEAP4 promote monocyte migration with partial changes to their polarization. Funding: This study was supported by NCI P01-CA140043, R01-CA224769, Pennsylvania DOH - Cure award to L. R. L Citation Format: Nicole M. Naranjo, Anna Testa, Santosh K. Yadav, Ulhas P. Naik, Lei Yu, William K. Kelly, Qin Liu, Jianyi Ding, Hushan Yang, Hsin Yao Tang, Cecilia E. Verrillo, Craig D. Hooper, Lucia R. Languino. Prostate cancer cell-derived small extracellular vesicles regulate monocyte migration via STEAP4 and promote a monocyte transitional state 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 (6Suppl): Abstract nr 4263.