Discovery and characterization of a first-in-field transcription factor BRN2 inhibitor for the treatment of neuroendocrine prostate cancer

The increased incidence of treatment-emergent neuroendocrine prostate cancer (NEPC) is particularly alarming as this diagnosis is associated with poor prognosis. Despite initial responses to platinum-based chemotherapy, relapses are common and there is no effective second line therapy for NEPC. We previously identified that neuronal transcription factor BRN2 (POU3F2) is a potent driver of neuroendocrine differentiation and an attractive target for NEPC. Utilizing a combination of in silico modeling and X-ray crystallography followed by structure-based lead optimization, we have developed the first potent, specific and orally bioavailable BRN2 inhibitor (B18-94), which inhibits the interaction between BRN2 and DNA. This loss of BRN2 on the chromatin drastically reduces its transcriptional output resulting in downregulation of several known targets in NEPC such as SOX2, ASCL1 and PEG10 . Additionally, B18-94 reduces specifically cell proliferation specifically in multiple NEPC models with no effect on adenocarcinoma and other BRN2 negative prostate cancer models. Importantly, the consistency in the transcriptomic changes driven by B18-94 and or CRISPR/Cas9 mediated BRN2 knockout confirmed the on-target specificity, with both methods of BRN2 inhibition downregulating pathways involved in cellular plasticity and proliferation. Finally, we have demonstrated that B18-94, the first-in-field POU-domain transcription factor inhibitor, significantly reduced tumor growth in several NEPC xenograft models with no observable toxicity, suggesting potential for therapeutic intervention of NEPC. ### Competing Interest Statement Compound presented in this manuscript are patented. Synthetic derivatives of B18 and B18-14 are covered in a patent filed by the University of British Columbia, BRN2 inhibitors as a therapeutic for treatment resistance, neuroendocrine and small cell cancers, PCT/CA2019/051423. DT, RM, SV and AZ are inventors. Synthetic derivatives of B7 are covered in a patent filed by the University of British Columbia, Transcription factor BRN2 inhibitory compounds for use as therapeutics, 63/236,200. DT, RM and AZ are inventors. All other authors declare no competing interests.