E3 Ligase Ligands for PROTACs: How They Were Found and How to Discover New Ones

Tasuku Ishida, Alessio Ciulli (Lead / Corresponding author)

Research output: Contribution to journalArticlepeer-review

113 Citations (Scopus)
187 Downloads (Pure)


Bifunctional degrader molecules, also called proteolysis-targeting chimeras (PROTACs), are a new modality of chemical tools and potential therapeutics to understand and treat human disease. A required PROTAC component is a ligand binding to an E3 ubiquitin ligase, which is then joined to another ligand binding to a protein to be degraded via the ubiquitin–proteasome system. The advent of nonpeptidic small-molecule E3 ligase ligands, notably for von Hippel–Lindau (VHL) and cereblon (CRBN), revolutionized the field and ushered in the design of drug-like PROTACs with potent and selective degradation activity. A first wave of PROTAC drugs are now undergoing clinical development in cancer, and the field is seeking to extend the repertoire of chemistries that allow hijacking new E3 ligases to improve the scope of targeted protein degradation. Here, we briefly review how traditional E3 ligase ligands were discovered, and then outline approaches and ligands that have been recently used to discover new E3 ligases for PROTACs. We will then take an outlook at current and future strategies undertaken that invoke either target-based screening or phenotypic-based approaches, including the use of DNA-encoded libraries (DELs), display technologies and cyclic peptides, smaller molecular glue degraders, and covalent warhead ligands. These approaches are ripe for expanding the chemical space of PROTACs and usher in the advent of other emerging bifunctional modalities of proximity-based pharmacology.

Original languageEnglish
Pages (from-to)484-502
Number of pages19
JournalSLAS Discovery
Issue number4
Early online date3 Nov 2020
Publication statusPublished - 1 Apr 2021


  • E3 ubiquitin ligase
  • binding ligands
  • molecular glues
  • targeted protein degradation

ASJC Scopus subject areas

  • Biotechnology
  • Analytical Chemistry
  • Biochemistry
  • Molecular Medicine


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