Abstract PR020: Targeting of FOXA1 and FOXA2 by small molecules disables the oncogenic output of castration resistant prostate cancer

Abstract Prostate cancer is among the most prevalent cancer types and advanced castration-resistant prostate cancer (CRPC) remains a lethal disease. It is driven by oncogenic transcription factors, most notably the androgen receptor (AR) which represents to this day the main therapeutic target. That said, more transcription factors have emerged supporting tumor growth in late stages when prostate cancer cells lose AR expression through lineage plasticity. However, targeting this plethora of transcriptional drivers throughout disease progression is a daunting task. Yet, disrupting common enablers upstream of oncogenic transcription factors may provide an opportunity to shut down oncogenic output of prostate cancer cells regardless of their CRPC subtype. Indeed, the pioneer transcription factor FOXA1 is a strong and highly selective Achilles' heel in prostate cancer (www.depmap.org), critical for opening chromatin and enabling AR to exert its oncogenic function. Moreover, its homologue FOXA2 has been shown to be upregulated in AR-negative lineage plasticity prostate cancers as well. That said, effective FOXA1/2 inhibitors are currently not available. Here, we show that the FOXA1 homologue FOXA2 cooperates with the AR-pioneer factor FOXA1 in mediating AR-independent cell proliferation in various prostate cancer subtypes. In AR-negative cells, this colocalization is reinforced and supports the gene transcription of lineage-specific oncogenic transcription factors. Joint loss-of-function of both FOXA1 and FOXA2 leads to the collapse of lineage-specific oncogenic transcription factors. Importantly, using virtual drug screening we identify a non-covalent small molecule capable of directly binding and disrupting the interaction of the conserved forkhead domains with DNA. The inhibitors target both FOXA1 wild-type tumors and tumor characterized by recurrent driver mutations. Mechanistically, the inhibitors bind to a hydrophobic cavity within the N-terminus of the conserved forkhead domains of FOXA1 and FOXA2. Treatment with T and derivatives inhibits specifically the oncogenic transcriptional output programs related to different AR-positive and AR-negative prostate cancer subtypes and effectively blocks tumor growth in culture and after intraperitoneal injection in xenograft models in vivo. In summary, our findings uncover an unexpected collaboration of FOXA1 and FOXA2 in disease progression and a druggable key dependency for AR-positive and -negative CRPC regardless of their specific lineage-specific oncogenic program. Citation Format: Nicolo Formaggio, Jacopo Sgrignani, Gayathri Thillaiyampalam, Claudio Lorenzi, Yanick Uebelhart, Diego Camuzi Cassiano, Andrea Rinaldi, Matteo Pecoraro, Roger Geiger, Raffaella Santoro, Andrea Cavalli, Jean-Philippe Paul. Theurillat. Targeting of FOXA1 and FOXA2 by small molecules disables the oncogenic output of castration resistant 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(2_Suppl):Abstract nr PR020.