Targeting FOXA2/AP-1 axis to overcome lineage plasticity and therapy resistance in castration-resistant prostate cancer - PROJECT SUMMARY Background: Prostate cancer (PCa) can develop resistance to androgen receptor (AR)-targeted therapies and progress to AR-indifferent stages, such as NEPC or DNPC, through lineage plasticity. While several driver transcription factors for AR-indifferent PCa have been identified, the mechanisms by which lineage-specific developmental enhancers regain accessibility to those transcription factors remain unclear. FOXA family proteins are pioneer transcription factors that modulate chromatin accessibility by maintaining an accessible nucleosome state. In AR-driven PCa, FOXA1 is overexpressed and defines AR chromatin binding. In AR-independent PCa, FOXA1 expression decreases, while FOXA2 expression significantly increases. Our preliminary studies indicate that FOXA2 binds to three different classes of lineage-specific enhancers in three major subtypes of AR- indifferent CRPC, suggesting it may function as a pan-plasticity driver. Expressing FOXA2 in luminal PCa cells suppresses FOXA1 and allows FOXA2 to occupy all subclasses of lineage-specific enhancers, potentially driving cells into a highly plastic multilineage transition state. Mechanistically, FOXA2 chromatin binding is stabilized by LSD1-mediated demethylation, and FOXA2 can cooperatively bind to chromatin with JUN and induce the transcriptional reprogramming of AP-1, facilitating the multilineage transition. Objective/Hypothesis: We hypothesize that in response to AR-targeted therapies, FOXA2, in collaboration with AP-1, acts as a pan-plasticity driver by opening multiple classes of developmental enhancers to establish an adaptive multilineage transition state, and that targeting the FOXA2-AP-1 axis can suppress lineage plasticity and thus overcome PCa resistance to AR-targeted therapies. Specific Aims: Aim 1 will determine whether FOXA2 expression drives luminal PCa cells into a multilineage transition state. We will determine FOXA2 chromatin binding to multiple classes developmental enhancers in cell lines and patient-derived AR-independent CRPC models and then will overexpress FOXA2 in luminal PCa cell lines to assess whether FOXA2 can promote an AR-independent multilineage transition. Aim 2 will investigate how FOXA2 rewires AP-1 to drive lineage reprogramming. We will examine the interaction between FOXA2 and JUN on chromatin and then alter AP-1 expression to understand the role of AP-1 reprogramming in the lineage plasticity. Aim 3 will assess the therapeutic potential of inhibitors targeting the FOXA2-AP-1 axis in CRPC PDX models. We will evaluate the efficacy of a small molecule inhibitor targeting AP-1 chromatin binding in combination with a newly designed peptide-based LSD1 inhibitor using a series AR-independent PDX models. Impact: The short-term impact of this study, if successful, is to provide mechanistic insights into the function and molecular activity of FOXA2 in driving PCa lineage plasticity and test a combination approach to target the FOXA2-AP-1 axis in preclinical CRPC models. The long-term impact is to translate this treatment strategy into clinical trials in a well-defined subset of AR-independent PCa patients to improve patient outcomes.
