Abstract 5097: Single cell analysis reveals upregulation of immune stimulatory pathways in quiescent metastatic castration resistant prostate cancer cells

Abstract Quiescent, or G0 cell cycle phase, cells are common in most prostate cancer (PCa) cases, yet are relatively resistant to many treatments, especially cytotoxic chemotherapy. They also play key roles in tumorigenesis, and dormancy and recurrence after curative intent therapy, but are difficult to identify when viable. To identify characteristics of quiescent prostate cancer cells, we used previously published FACS methods to isolate cancer cells from bone or bone marrow of eight metastatic castration resistant prostate cancer (mCRPC) patient samples and generated single cell RNA sequencing (scRNA-seq) gene expression data of individually sorted cells. We also generated scRNA-seq data from six PCa cell lines and two normal (cancer free) bone marrow samples as positive and negative controls for cell identification. We eliminated a priori any potentially contaminating cells based on tSNE cluster location, expression of a 12 gene panel of PCa markers, and lack of expression of bone marrow markers (PTPRC / CD45, and GYPA / CD235a), leaving 297 high confidence PCa cells. To identify characteristics of G0 cells, we separated the patient PCa cells into quiescent and cycling groups based on expression of MKI67 (Ki67). GSEA analysis of KEGG pathways revealed enrichment of primarily immune related pathways in quiescent cells with the top 3 pathways; “allograft rejection, ” “autoimmune thyroid disease, ” and “intestinal immune network for IgA production.” Similarly, for GSEA analysis using gene ontology (GO) groups, “beta-2-microglobulin binding” was the second most enriched group in quiescent cells. Type 1 HLA genes, were common among multiple pathway groups suggesting potential differences in antigen presentation. In subsequent validation experiments, induction of quiescence in LNCaP, C4-2B, PC3, and RM1 PCa cell lines increased cell surface HLA class 1 or Mhc-1. Overall, these results suggest that antigen presentation is increased in quiescent PCa cells, which may be important for their elimination by the immune system, or useful for future immunotherapy approaches. Citation Format: Kristina G. Ibrahim, Julie Boerner, Steven Zielske, Frank C. Cackowski. Single cell analysis reveals upregulation of immune stimulatory pathways in quiescent metastatic castration resistant prostate cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5097.