Abstract B014: Therapeutic Reversal of Tumor Cell Plasticity by EHF mRNA Delivery in Prostate Cancer
Prostate cancer is one of the most common cancers and a leading cause of cancer death in men. Tumor cell plasticity is a key driver of prostate cancer progression, metastasis, and resistance to androgen receptor pathway inhibitors (ARPIs), yet no approved therapies directly target this process. ESE3/EHF (EHF) is an epithelial-specific ETS transcription factor highly expressed in normal prostate epithelium and frequently downregulated in aggressive primary tumors, castration-resistant (CRPC) and neuroendocrine (NEPC) prostate cancers. Reduced EHF expression is associated with attenuated androgen receptor (AR) signaling, lineage plasticity and treatment resistance. In human cell lines and murine models with prostate-specific EHF knockout, loss of EHF expression is sufficient to disrupt luminal identity and induce phenotypic plasticity and multilineage transitions, favoring tumor progression. These findings position EHF as a master regulator of epithelial cell identity and a tractable target for therapeutic cell reprogramming. To test this approach, we have developed mRNA- and DNA-based EHF delivery systems formulated in lipid-polymeric nanoparticles (LPNP) for cell cultures and in vivo administration. The activity of EHF-based constructs was evaluated across a translational preclinical platform including human and murine cell lines, cell line- and patient-derived organoids and xenografts, syngeneic murine allografts, and genetically engineered mouse models. Functional assays and drug combination studies were performed to assess cell differentiation and sensitivity to ARPIs. Multiple molecular, phenotypic, and pharmacodynamic endpoints were analyzed. mRNA- and DNA-based EHF delivery led to efficient and sustained EHF expression in human and murine models and reprogrammed tumor cells toward a luminal differentiation state, restoring canonical AR signaling and responsiveness to AR-directed therapies while suppressing phenotypic plasticity and stem-like features. Functionally, EHF delivery in vitro inhibited proliferation, tumor organoid growth, and tumor sphere formation, without affecting normal epithelial cells. Systemic delivery of LPNP-formulated EHF-encoding mRNA by intravenous injection achieved efficient, sustained, and selective intratumoral EHF expression, resulting in significant tumor growth inhibition in subcutaneous human xenografts and murine allograft models without observable toxicity. Intravenous delivery in mice also enabled efficient target engagement in metastatic lesions in bone and visceral organs, leading to a substantial reduction in metastatic burden. These data establish cell lineage reprogramming via EHF restoration as a novel modality to counteract tumor cell plasticity in prostate cancer. With a defined biomarker framework (low EHF expression, plasticity signatures) and compatibility with various delivery platforms, this approach provides a clear path toward clinical translation. This strategy represents a first-in-class opportunity to target tumor plasticity and overcome resistance in advanced prostate cancer. Domenico Albino, Carola Musumeci, Elisa Storelli, Atik Balla, Elisa Federici, Gianluca Civenni, Daniela Impellizzieri, Giada Andrea Cassanmagnago, Marco Bolis, Steve Pascolo, Carlo V. Catapano, Giuseppina MR. Carbone. Therapeutic Reversal of Tumor Cell Plasticity by EHF mRNA Delivery in Prostate Cancer [abstract]. In: Proceedings of AACR Drug Discovery and Development (AACR D3) Conference; 2026 Jul 21-24; Boston, MA. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(14_Suppl):Abstract nr B014.