Targeting CDK4 and CDK6 in cancer

Abstract

Cyclin-dependent kinase 4 (CDK4) and CDK6 are critical mediators of cellular transition into S phase and are important for the initiation, growth and survival of many cancer types. Pharmacological inhibitors of CDK4/6 have rapidly become a new standard of care for patients with advanced hormone receptor-positive breast cancer. As expected, CDK4/6 inhibitors arrest sensitive tumour cells in the G1 phase of the cell cycle. However, the effects of CDK4/6 inhibition are far more wide-reaching. New insights into their mechanisms of action have triggered identification of new therapeutic opportunities, including the development of novel combination regimens, expanded application to a broader range of cancers and use as supportive care to ameliorate the toxic effects of other therapies. Exploring these new opportunities in the clinic is an urgent priority, which in many cases has not been adequately addressed. Here, we provide a framework for conceptualizing the activity of CDK4/6 inhibitors in cancer and explain how this framework might shape the future clinical development of these agents. We also discuss the biological underpinnings of CDK4/6 inhibitor resistance, an increasingly common challenge in clinical oncology. Dysregulation of cyclin-dependent kinase 4 (CDK4) and CDK6, regulators of the cell cycle, favours the growth and survival of several cancer types. Owing to this, CDK4 and CDK6 inhibitors were developed and are currently approved for the treatment of advanced hormone receptor-positive breast cancer. This Review describes how we are only now beginning to fully understand their mechanisms of action and provides a new framework for conceptualizing their activity, which might enable expansion of the clinical opportunities of these agents.