Frontiers in Cell-Cycle-Targeting Therapies: Addressing the Heterogeneity of the Cancer Cell Cycle.

The cell division cycle machinery has been regarded as a promising therapeutic target for several decades. One of the most prominent milestones in the approach to targeting the cancer cell cycle was the development and approval of CDK4/6 inhibitors such as palbociclib, ribociclib, and abemaciclib. These small-molecule therapeutics have exhibited remarkable anti-cancer efficacy and have become primary choices for treating steroid receptor-positive breast cancer at multiple stages. This epoch-making success of cell-cycle-targeting drugs was followed by the development of small molecules to target other cell cycle-regulatory proteins, such as CDK2, CDK1, WEE1 kinase, Aurora kinases, and polo-like kinases, while therapeutic strategies to overcome resistance to CDK4/6 inhibitors have been pursued. In this article, we focus on heterogeneous vulnerabilities of cancers as consequences of various genetic and epigenetic alterations in the cell cycle-regulatory network, and we discuss how next-generation cell-cycle-targeting drugs currently in the developmental pipeline could exploit these heterogeneous vulnerabilities in the cancer cell cycle. We hope to provide a forward-looking perspective on directions for therapeutic cell-cycle targeting in the advent of personalized precision medicine.