The assumption that blocking a kinase's enzymatic activity is the best way to disable a cancer driver is being systematically dismantled. For the subset of adults whose cancers are fueled by dysregulated cell-cycle machinery — breast cancer, certain lung and blood cancers among them — a new generation of molecular tools may eventually offer far more selective and durable control than the inhibitors now in clinical use.

This comprehensive review in MedComm maps the expanded biology of cyclin-dependent kinase (CDK) / cyclin complexes, cataloguing their roles well beyond cell division: transcriptional elongation, DNA damage surveillance, chromatin remodeling, metabolic reprogramming, and modulation of anti-tumor immune responses. The authors dissect how specific pairings — CDK7/cyclin H, CDK8/cyclin C, CDK9/cyclin T1, and others — govern oncogenic transcription programs in ways that enzymatic inhibition alone fails to resolve. They then survey an emerging pharmacological toolkit: proteolysis-targeting chimeras (PROTACs) that recruit E3 ubiquitin ligases to degrade specific CDK or cyclin proteins; HSP90-mediated targeting chimeras that exploit chaperone biology; hydrophobic tagging that mimics misfolding signals; molecular glues that redirect protein–protein interactions; and autophagy-tethering compounds (ATTECs) that shunt targets to lysosomal destruction. Alongside degraders, the review highlights chemical inducers of proximity and transcriptional modulators that rewire CDK complex activity without eliminating the proteins.

The clinical validation provided by CDK4/6 inhibitors (palbociclib, ribociclib, abemaciclib) across HR-positive breast cancer established proof-of-concept that CDKs are genuinely druggable — but resistance, driven partly by CDK2 and CDK1 compensation, is routine. This review represents an incremental but important contribution: it synthesizes scattered mechanistic findings and an accelerating body of chemical-biology work into a single framework that should accelerate rational drug design. Key limitations are inherent to the review format — most proximity-based strategies cited remain preclinical, and translating selective degradation from cell lines to heterogeneous human tumors is notoriously difficult. Nevertheless, for researchers and clinicians tracking the oncology pipeline, the pivot from inhibition to targeted degradation of CDK/cyclin complexes is a genuine strategic inflection point.