Disrupting the CCND1–CDK4 Protein-Protein Interaction: Emerging Strategies to Target Cyclin D–Dependent Kinase Assembly in Cancer

Abstract

Cyclin D1 (CCND1)–CDK4 complex formation is a gatekeeping event for G1 progression and a central vulnerability in many cancers, as underscored by the clinical impact of ATP-competitive CDK4/6 inhibitors. Yet catalytic-site inhibition does not fully address the biology of CDK4, which operates across multiple assembly and regulatory states and can be modulated by partner proteins and cellular context. These features motivate an alternative strategy: direct disruption of the CCND1–CDK4 protein–protein interaction (PPI) to prevent (or destabilize) productive complex formation. In this review, we synthesize the structural and mechanistic basis of CCND1–CDK4 assembly, highlight how endogenous regulators—particularly INK4 family inhibitors—provide biological proof-of-principle for antagonizing cyclin–CDK interfaces, and evaluate engineered approaches aimed at interface blockade. We compare peptide-and peptidomimetic modalities (including constrained/stapled peptides), intracellular biologics such as intrabodies, and emerging structure-guided and computational discovery efforts, emphasizing what constitutes convincing evidence of true PPI disruption versus indirect loss of kinase signaling. Finally, we discuss translational considerations—delivery, selectivity, pharmacodynamic biomarkers, and resistance—and propose a practical validation framework to accelerate the development of bona fide CCND1–CDK4 PPI disruptors.