Abstract 7249: RUNX1T1 as an early driver in treatment-induced neuroendocrine transdifferentiation

Abstract Treatment-induced neuroendocrine prostate cancer (t-NEPC) is a lethal form of castration-resistant variant arising primarily through neuroendocrine (NE) transdifferentiation of prostate adenocarcinoma following androgen deprivation therapy (ADT) and androgen receptor pathway inhibitors (ARPI). Despite its clinical relevance, the early molecular events initiating this transition remain poorly defined. Leveraging the first and only longitudinal patient-derived xenograft (PDX) model capturing adenocarcinoma-to-NEPC transdifferentiation (LTL331/331R), we performed single-cell RNA sequencing (scRNA-seq) across seven key stages spanning pre-castration, post-castration/ transitional phases, and relapsed NEPC.Clustering analysis identified 15 major cell populations and revealed a previously unrecognized intermediate transitional cell state enriched for epithelial-mesenchymal transition (EMT), stemness, metabolic activity, and HDAC-related regulatory signatures, highlighting a unique window of lineage plasticity. Two terminal NEPC subclusters with reciprocal ASCL1/FOXA2 expression patterns reflected intratumoral heterogeneity at relapse.Transcriptional interrogation of the transitional population identified RUNX1T1 as a central regulator emerging early during plasticity. Functional assays revealed that RUNX1T1 overexpression markedly accelerates AR pathway inhibition-induced NE transdifferentiation and confers resistance to ARPI therapy in prostate adenocarcinoma models. Conversely, RUNX1T1 knockdown reduces NE-related pathway expression, suppresses NEPC cell growth, and induces apoptosis. These findings position RUNX1T1 as an essential factor for both NEPC development and progression.Mechanistically, rapid immunoprecipitation and mass spectrometry (RIME) uncovered that RUNX1T1 interacts with multiple repressive epigenetic factors including HDAC-containing complexes and heterochromatin-related genes. These results support a role for RUNX1T1 in mediating transcriptional silencing and regulatory network reprogramming during NEPC development.In summary, this study delineates the temporal evolution of t-NEPC at single-cell resolution, identifies an intermediate transitional state during NE transdifferentiation, and reveals heterogeneity within terminal NEPC. The identification of RUNX1T1 as an early and persistent driver of this trajectory positions RUNX1T1 and its associated repressive complexes as promising candidates for therapeutic intervention. Citation Format: Yuchao Ni, Mingchen Shi, Dong Lin, Yen-Yi Lin, Hui Xue, Xin Dong, Liangliang Liu, Funda Sar, Rebecca Wu, Tunc Morova, Anne Hargert, Robert Bell, Xinyao Pang, Adam Classen, Yu Wang, Junru Chen, Stephan Le Bihan, Wei Dong, Vickie Wang, Ning Xu, Nathan Lack, Martin E. Gleave, Christopher J. Ong, Gang Wang, Hao Zeng, Colin Collins, Yuzhuo Wang. RUNX1T1 as an early driver in treatment-induced neuroendocrine transdifferentiation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 7249.