Intracellular protein binders for imaging, control and future therapeutics.

Intracellular protein dysregulation underlies many cancers, neurodegenerative disorders and infectious diseases, yet a substantial fraction of the human proteome remains inaccessible to conventional small-molecule drugs or extracellular antibodies. Genetically encoded intracellular binders, including nanobodies, DARPins, affibodies and de novo-designed scaffolds, provide modular platforms for selective recognition, visualization and functional modulation of endogenous proteins in living cells. These binders can engage extended protein surfaces and conformational epitopes and are increasingly applied in preclinical models to inhibit oncogenic signalling, degrade pathogenic proteins, rewire cellular pathways and engineer programmable cell therapies. Here we outline the structural diversity, discovery strategies and design principles of intracellular binders and summarize their emerging applications in imaging, biosensing and targeted protein control. We further discuss recent advances in computationally assisted binder design and optimization. Finally, we examine key translational challenges, including cellular stability, delivery technologies and immunogenicity, that will shape the clinical development of intracellular binder-based therapeutics.