Abstract B028: Global shRNA screen to identify factors that are involved in MYC/MYCN-dependent growth of prostate cancer

Abstract The androgen receptor (AR) is a key driver of prostate cancer progression, making androgen deprivation therapy and AR signaling inhibitors the standard of care therapies for treating prostate cancer. Although these treatments are effective initially, they often lead to the development of resistance, limiting their long-term efficacy. This acquired resistance is frequently linked to the MYC oncogene family, which, together with reduced AR signaling, is associated with poor clinical prognosis. Among the resistant phenotypes, treatment-induced neuroendocrine prostate cancer (tNEPC) is a particularly aggressive AR-independent subtype characterized by loss of AR signaling and epigenetic reprogramming. These molecular changes promote cell lineage plasticity, creating a permissive environment for MYCN activation, which further drives tumor progression and neuroendocrine differentiation. In summary, MYC proteins pose a major biological challenge, but also offer opportunities to develop new therapeutic approaches. To address these, we generated LNCaP-derived prostate cancer cell lines that constitutively express c-MYC or MYCN. Their sustained proliferation under enzalutamide treatment confirmed the development of a resistant phenotype. In addition, RNA sequencing of MYCN-overexpressing cells revealed transcriptional reprogramming, including the activation of neural lineage markers and epithelial-mesenchymal transition programs consistent with a neuroendocrine-like phenotype. To identify dependency factors, we performed a genome-wide shRNA screen to uncover genes whose knockdown selectively impaired growth of LNCaP cells expressing c-MYC or MYCN under enzalutamide. In c-MYC-expressing cells approximately 80 significantly downregulated genes were identified, many of which had previously been associated with therapeutic resistance. Interestingly, a substantial proportion of these factors were also significantly enriched in RNA processing and metabolic pathways. Both c-MYC and MYCN bind directly to DNA as well as RNA, and recent studies have revealed that MYC proteins play distinct mechanistic roles in transcriptional regulation and RNA metabolism. The newly described RNA-related functions of MYC highlight the importance of RNA regulatory mechanisms as key drivers of MYC-dependent oncogenesis in prostate cancer. Approximately 20 genes were significantly downregulated in MYCN-expressing cells, most of which are involved in RNA splicing. This is an intriguing observation given that MYCN is a well-characterized transcription factor that orchestrates transcriptional reprogramming. The data suggest that MYCN can influence oncogenic processes by modulating RNA splicing mechanisms, revealing an additional level of regulatory complexity in tNEPC. Ongoing validation and integrative analyses, including bulk mRNA-sequencing of patient data, aim to define the roles of these genes, delineate pathways, and identify novel therapeutic targets to overcome MYC-mediated and AR-targeted therapy resistance. Citation Format: Saskia Elena. Haarmann, Martin Eilers, Steffi Herold. Global shRNA screen to identify factors that are involved in MYC/MYCN-dependent growth of prostate cancer abstract. In: Proceedings of the AACR Special Conference in Cancer Research: Innovations in Prostate Cancer Research and Treatment; 2026 Jan 20-22; Philadelphia PA. Philadelphia (PA): AACR; Cancer Res 2026;86 (2Suppl): Abstract nr B028.