Prostate cancer progression relies on the mitotic kinase citron kinase.

Prostate cancer (PCa) remains the second leading cause of cancer death in men in Western cultures. Deeper understanding of the mechanisms by which PCa cells divide to support tumor growth could help devise strategies to overcome treatment resistance and improve survival. Here, we identified that the mitotic AGC family protein kinase citron kinase (CIT) is a pivotal regulator of PCa growth which mediates PCa cell interphase progression. Increased CIT expression correlated with PCa growth induction and aggressive PCa progression, and CIT was overexpressed in PCa compared to benign prostate tissue. CIT overexpression was controlled by an E2F2-Skp2-p27 signaling axis and conferred resistance to androgen targeted treatment strategies. The effects of CIT relied entirely on its kinase activity. Conversely, CIT silencing inhibited growth of cell lines and xenografts representing different stages of PCa progression and treatment resistance but did not affect benign epithelial prostate cells or non-prostatic normal cells, indicating a potential therapeutic window for CIT inhibition. CIT kinase activity was identified as druggable and was potently inhibited by the multi-kinase inhibitor OTS-167, which decreased proliferation of treatment-resistant PCa cells and patient-derived organoids. Isolation of the in vivo CIT substrates identified proteins involved in diverse cellular functions ranging from proliferation to alternative splicing events that are enriched in treatment-resistant PCa. These findings provide insights into regulation of aggressive PCa cell behavior by CIT and identify CIT as a functionally diverse and druggable driver of PCa progression.