When Kinases Meet PROTACs

Small molecule drugs targeting kinases have revolutionized treatment options for millions of patients worldwide, especially in oncology. These targeted treatments have less side effects because they inhibit a specific dysfunctional kinase usually with relatively narrow selectivity. However, kinase inhibitors do have well‐established liabilities, most prominently the emergence of drug resistance. Moreover, the majority of kinases are multidomain and multifunctional proteins that in addition to their enzymatic activity have scaffolding and other roles, and inhibitors seldom address these alternative functions. Recently, small molecule mediated targeted protein degradation emerged as a new pharmacological strategy. The majority of small molecule degraders are bispecific molecules called proteolysis targeting chimeras (PROTACs), and their mechanism of action is based on simultaneous recruitment of the target of interest and an E3 ligase, resulting in target polyubiquitination and eventual destruction by the proteasome. Over the last couple of years, PROTAC strategy has been developed and validated for a range of targets, including kinases. Here, we introduce the targeted protein degradation strategy, provide an overview of representative kinase PROTACs, and describe design rationales, efficacy and specificity. We also discuss their potential advantages, as well as comment on some of the limitations of this emerging pharmacological modality.