Abstract LB428: Targeting EZH2 to overcome immunotherapy resistance in mCRPC unlocks NSD2-dependent tumor vulnerabilities

Abstract Despite advances in prostate cancer (PCa) diagnosis and treatment, many patients progress to metastatic castration-resistant prostate cancer (mCRPC), for which therapeutic options remain limited. Immunotherapy has emerged as a promising approach, yet clinical trials in mCRPC have shown limited success, partly due to a poor understanding of the mechanisms through which PCa maintains immune evasion and mediates immunosuppression. We previously demonstrated that the epigenetic regulator NSD2 promotes mCRPC progression and that its inhibition increases survival in PCa models. Emerging evidence has established a central role for epigenetic dysregulation in PCa progression and immune escape, supporting the involvement of the EZH2-NSD2 axis as a critical regulator of tumor plasticity and immune suppression and highlighting its potential as a therapeutic target. Thus, the use of EZH2 inhibitors (EZH2i) is becoming a promising avenue for combinatorial immunotherapies strategies and they are being implemented in clinical trials to overcome immunotherapy resistance in mCRPC. In this study, we investigate NSD2 as a predictive marker of response to EZH2 inhibition and assess whether an EZH2i can be integrated into combinatorial immunotherapy strategies to overcome immune resistance in mCRPC. We focused on the tumor immune microenvironment (TIME) in PCa using genetically engineered mouse models (GEMMs), comparing NPp53 mice with NPp53NSD2 mice, which overexpress NSD2, to assess its impact on lineage plasticity and TIME remodeling. We demonstrate that the immune landscape of GEMMs differs according to specific PCa driver alterations. High-dimensional flow cytometry with a 24-antibody panel revealed that NSD2 overexpression in NPp53NSD2 mice correlates with enhanced disease progression and a profoundly immunosuppressive TIME. Importantly, EZH2 inhibition in these mice promoted TIME remodeling toward a more immunogenic state, with increased dendritic cells and CD8⁺/CD4⁺ T cell infiltration. Conversely, NPp53 mice did not exhibit a favorable immune response to EZH2i, displaying instead a more immunosuppressive TIME marked by reduced dendritic cells and increased M2 macrophages. Together, these findings identify NSD2 as a key determinant of the immune response to EZH2 targeting and reveal a previously unrecognized epigenetic vulnerability in mCRPC. Our work supports a stratified epigenetic-immunotherapy approach and provides a strong rationale for leveraging EZH2-NSD2-dependent mechanisms to overcome immune resistance in advanced prostate cancer. Citation Format: Pilar Salamanca Jiménez, Inés Gonzalez-Vazquez, Roderic Espin, Nadia Garcia, Lidia FrancoPujana, MAJM Piulats, Alvaro Aytes. Targeting EZH2 to overcome immunotherapy resistance in mCRPC unlocks NSD2-dependent tumor vulnerabilities [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(8_Suppl):Abstract nr LB428.