PROJECT SUMMARY/ABSTRACT Despite advances in the development of highly effective androgen receptor (AR)-directed therapies for the treatment of men with advanced prostate cancer, acquired resistance ultimately ensues. Lineage plasticity has been proposed as one mechanism of therapeutic resistance whereby patients with resistant disease develop AR-negative, androgen signaling-indifferent prostate tumors that lose their luminal identity and display neuroendocrine features (neuroendocrine prostate cancer, NEPC). While NEPC tumors share many genetic alterations with prostate adenocarcinoma, the potential drivers of lineage plasticity remain understudied. Using a novel genetically-engineered mouse model that faithfully recapitulates the transition to NEPC, I have established an organoid-based allograft platform that is amenable to gene editing technologies. Using single-cell based approaches, Furthermore, I have identified a previously undescribed tumor subpopulation with a unique transcriptional regulator that may represent an transition between adenocarcinoma and NEPC. For the proposed studies, I will modulate the expression levels of the identified transcriptional regulator using CRISPR-based gene editing or overexpression strategies in prostate organoids and determine how the transition to NEPC is affected. I will also assess the sensitivity of this tumor subpopulation to clinically-relevant treatment options, including androgen withdrawal and AR-targeted therapy. Finally, I will reveal how targeting epigenetic modifiers changes the composition of tumor subpopulations and reverses the development of therapeutic resistance. Alongside these scientific aims, I will use the period of support to enhance my skillset and develop as an independent researcher. Through a comprehensive plan, including workshops, course work, clinical case conferences, and attendance at seminars and scientific conferences, I plan to develop a deeper understanding of bioinformatics at the single cell level, expand my exposure to critical barriers facing clinicians and prostate cancer patients, and successfully continue my transition to an independent research position. The environment at Weill Cornell Medicine, and among its closely aligned neighboring institutions, is ideal for me to complete the proposed studies and will help foster my continued research and career development success.