Prostate cancer (PCa) is one of the most common malignancies worldwide. Although therapeutic options for early-stage PCa are generally efficient, treatment of advanced disease remains a clinical challenge. Epigenetic mechanisms, such as methylation or histone modifications play an important role, not only in in PCa development and progression, but also in tumor immune-evasion. Enhancer of zeste homolog 2 (EZH2) is the catalytic subunit of the polycomb repressive complex 2 (PRC2), involved in transcriptional repression by histone 3 trimethylation (H3K27me3). EZH2 is known to be involved in PCa progression, however the role it might play in PCa immune evasion mechanisms is rather unexplored. Natural killer (NK) cells are main innate anti-tumor effectors, targeting tumor cells through an array of activating and inhibitory receptors interacting with cell surface ligands on target cells. Here, we showed that inhibiting EZH2 catalytic function could increase PCa sensitivity to NK-mediated killing. PCa patient tissues immunohistochemistry showed an increase in EZH2 and H3K27me3 expression through disease progression. Inhibition of EZH2 in PCa cells resulted in the upregulation of NK cell activating ligands. CUT&RUN revealed H3K27me3 binding at the promoter region of those genes, which was reduced upon treatment. Importantly, epi-drug treatment of PCa tumor cells co-cultured with NK cells led to an increased NK cell-mediated killing. Moreover, we established a PCa patient-derived explant (PDE) organotypic model accounting for tumor heterogeneity and architecture. Remarkably, epi-treatment of PCa-derived PDEs also induced NK ligand upregulation, supporting the results in a patient-derived model. Our findings suggest that EZH2 inhibition can modulate PCa tumor cells rendering them more sensitive to NK cell-mediated killing, in both cell lines and a microtumor model, supporting the design of novel epigenetic-based therapeutic approaches for PCa patients.

This study was funded by EpImmunoPCa_PI143-CI-IPOP-131-2020 and the FCT grant - 022.04809.PTDC; MPC by FCT (CEECINST/00091/2018); FDdR by FCT (UI/BD/154816/2023).