Targeting the Elongin BC-BC-Box Interface: Structural Insights, Peptidic Disruptors and Emerging Small-Molecule...

Protein-protein interactions (PPIs) that orchestrate ubiquitin-dependent signaling have long challenged drug discovery because their interfaces are typically large and hydrophobic. The heterodimeric adaptor Elongin BC (ELOB/ELOC) defies this stereotype: its BC-box-binding groove is a deep, rigid pocket that anchors dozens of cellular and viral partners to cullin-RING ligases and to transcriptional machinery. Recent structural and chemical-biology breakthroughs have converted this once "undruggable" site into a tractable target. A sub-nanomolar peptide derived from the chromatin factor EPOP has been shown to displace native BC-box proteins, trigger apoptosis in multiple cancer lines, and unveil a transcriptomic signature that converges on MYC and cell-cycle control. Parallel fragment screens and crystallography have mapped adjacent hot spots suitable for small-molecule growth, while functional genomics highlights Elongin BC as a pan-cancer dependency and an unexpected regulator of the SARS-CoV-2 co-receptor TMPRSS2. This review synthesizes the structural principles of BC-box recognition, the current state of peptide and fragment-based inhibitors, and the biological consequences of disrupting the Elongin BC hub. We discuss therapeutic prospects in oncology and virology, outline key challenges-delivery, selectivity, and resistance-and propose future directions ranging from stapled-peptide optimization to covalent fragment tethering and PROTAC strategies. Together, these advances position Elongin BC inhibition at the forefront of next-generation PPI drug discovery, offering a unified approach to modulate ubiquitin signaling, epigenetic regulation, and viral entry through a single conserved pocket.