Abstract 591: Exploration of immune effects of [177Lu]Lu-PSMA therapy and rationale for combination with immunotherapy

Abstract [177Lu]Lu-PSMA therapy has emerged as a promising option for metastatic prostate cancer (PCa). Many ongoing trials are exploring the combination of [177Lu]Lu-PSMA therapy with immunotherapy, highlighting the urgent need to identify potential biomarkers for this therapeutic approach. This study aims to investigate the immune effects of radionuclide therapy using [177Lu]Lu-PSMA-I&T in PCa.We used the RM1-PGLS cell line (a murine PCa cell line with a castration-resistant phenotype, stably transfected with human PSMA) to establish a syngeneic mouse model. RM1-PGLS tumor-bearing male C57BL/6 mice were treated with either 60 MBq of [177Lu]Lu-PSMA-I&T or 5 Gy of external beam radiotherapy (EBRT). Tumors were harvested on day 7 following treatment, and downstream profiling of immune responses was conducted using the NanoString Pancancer Immune panel.In vivo, immune responses were significantly activated on day 7, with 109 differentially expressed genes (DEGs) upregulated after [177Lu]Lu-PSMA-I&T therapy (accounting for 98.2% of all DEGs). Single sample Gene Set Enrichment Analysis revealed that 24 immune-related pathways (curated from MSigDB) were activated compared to the untreated control. Further analysis also showed significantly higher estimated infiltrations of macrophages, neutrophils, and CD56dim NK cells.Among the observed changes, Cxcl10 emerged as the most significantly upregulated gene for both therapies ([177Lu]Lu-PSMA-I&T: log2 fold change [FC] = 2.1, adjusted p = 0.0059; EBRT: log2FC = 2.3, adjusted p = 0.0025). Protein-protein interaction analysis revealed that Cxcl10 ranked among the top three genes with the highest number of interactions with other genes ([177Lu]Lu-PSMA-I&T: 71 edges, top 1; EBRT: 124 edges, top 3), indicating its critical role in the immune response.To investigate whether RM1-PGLS cells can express and release Cxcl10, we treated the cells with 1.2 MBq/ml of [177Lu]Lu-PSMA-I&T (equivalent to 5 Gy EBRT in vitro) and incubated them for 7 days, with the medium replaced every 2 days. Immunofluorescence images demonstrated a significant increase in Cxcl10 gene expression on day 7 (p < 0.001), while the Cxcl10 protein release peaked on day 2 (p < 0.05) but declined by days 4 and 6, showing no significant difference from baseline. These results suggest that RM1-PGLS cells can express and release Cxcl10 independent of immune cell involvement.Taken together, this study demonstrates that [177Lu]Lu-PSMA-I&T therapy induces a significant immune response characterized by Cxcl10 upregulation and activation of multiple immune pathways. Further studies are warranted to validate the therapeutic potential of these combinations in enhancing anti-tumor immunity and improving clinical outcomes for patients with PCa. Citation Format: Yang-Hong Dai, Gemma Dias, Carsten Kramer, Katherine A. Vallis. Exploration of immune effects of [Lu]Lu-PSMA therapy and rationale for combination with immunotherapy [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 591.