Project Summary/Abstract Precision therapies for aggressive or metastatic cancers, while offering the promise of greater efficacy and less toxicity, rarely achieve durable responses and only modestly extend a patient's life. The major limitation to these approaches is that cancer cells evolve and alternate signaling pathways can compensate for pathways blocked with targeted therapies, i.e. multiple alternative mechanisms to activate the EGFR/RAS/MAPK pathway lead to a "whack-a-mole" approach with serial treatment with different kinase inhibitors. Cyclin-dependent kinases (CDKs) are a conserved family of protein kinases that play a central role in regulating the eukaryotic cell cycle. CDK1 in conjunction with its activating subunit, Cyclin B, plays a critical role in permitting cells to enter mitosis, coordinates the events required for faithful mitotic progression and chromosome segregation. To our knowledge, CDK1/B activity is essential for all cells to proliferate and there are no alternative pathways to bypass the requirement for CDK1. We hypothesize that CDK1 is an ideal therapeutic target in the context of specific oncogenic signaling pathways which result in an abortive cell cycle program, such as cell death or senescence, while non-tumor cells are only transiently arrested. Until now, specific inhibitors of CDK1 have not existed, limiting our ability to discover the underlying mechanisms of CDK1 inhibition as a cancer therapy. Our lab developed a novel engineered mouse, using a chemical-genetic approach, that allows us to inhibit CDK1 selectively and reversibly in normal and oncogene transformed cells, or in the context of transgenic tumor models. Our aims will define the mechanisms through which CDK1 elicits growth arrest and senescence (Aim 1), regulates the unfolded protein response (Aim 2), and how CDK1 inhibition and other therapeutics can be best combined to block tumor growth (Aim 3). We bring together a team with a track record of innovative research in oncogene signaling and cell cycle regulation (Andrei Goga); expertise in chemical biology and analog-sensitive kinases (Kevan Shokat); in vivo studies of senescence (Anil Bhushan) and expertise in mechanisms of regulation of the unfolded protein response (UPR). We hypothesize that CDK1 controls previously unexplored cellular processes which can be exploited for tumor-specific vulnerabilities. Such discoveries will hasten the clinical translation of CDK1 inhibitors for a broad variety of human cancers.