Abstract 5863: Double-negative prostate cancer emerges through a mixed basal, club, and hillock cell identity driven by KLF5

Abstract The purpose of this study was to characterize the phenotypes and drivers of therapy-induced lineage plasticity during the development of castration resistant prostate cancer (CRPC). While the majority of localized prostate cancer can be cured with surgery or radiation, metastatic disease is lethal. Therapies targeting the androgen receptor (AR) are initially effective, but eventually men will develop CRPC. About 70-75% of CRPC displays restored AR signaling (ARPC), while the remaining 25-30% display lineage plasticity evidenced by the emergence of AR-negative subtypes including those that display neuroendocrine (NE) markers, or double negative CRPC (DNPC) lacking both AR and NE markers. AR independent manifestations of CRPC represent a clinical challenge because no effective therapies are available and therapeutic targets are largely unknown. We analyzed publicly available bulk and single-cell RNA-seq datasets derived from clinical CRPC specimens to characterize the cellular identity of AR-negative tumors. Using a database of all known transcriptional regulators, we identified potential drivers of these phenotypes. We performed siRNA-mediated knockdown experiments in a model of DNPC to explore the extent to which the candidate regulators maintain AR-negative cell identity and sustain growth of DNPC prostate cancer cells. We identified a subset of CRPC tumors that co-express gene sets defining basal, club, and hillock cells in the benign prostate. This data supports the existence of epithelial cell lineage plasticity manifesting within CRPC tumors, as well as individual CRPC tumor cells, wherein AR-positive tumor cells transform to a phenotype encompassing basal, club, and hillock cell identities. We nominated the stem cell transcription factor KLF5 as a regulator of basal, club, and hillock cell identities in CRPC. In cell line models of DNPC, knock down of KLF5 inhibited cell growth and reduced the expression of genes defining basal, club, and hillock cell identities. This work links a prevalent and poorly-defined subtype of AR-negative CRPC to AR-negative epithelial cell types in benign prostate tissue. Inhibition of KLF5 and its downstream effectors could represent a therapeutic strategy to prevent or delay lineage plasticity and thereby extend patient response to AR-targeted therapies. Citation Format: Samuel Pitzen, Yinjie Qiu, Sarah Munro, Scott Dehm. Double-negative prostate cancer emerges through a mixed basal, club, and hillock cell identity driven by KLF5 abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 5863.