1. Academic Validation
  2. Impact of Target Warhead and Linkage Vector on Inducing Protein Degradation: Comparison of Bromodomain and Extra-Terminal (BET) Degraders Derived from Triazolodiazepine (JQ1) and Tetrahydroquinoline (I-BET726) BET Inhibitor Scaffolds

Impact of Target Warhead and Linkage Vector on Inducing Protein Degradation: Comparison of Bromodomain and Extra-Terminal (BET) Degraders Derived from Triazolodiazepine (JQ1) and Tetrahydroquinoline (I-BET726) BET Inhibitor Scaffolds

  • J Med Chem. 2018 Jan 25;61(2):504-513. doi: 10.1021/acs.jmedchem.6b01912.
Kwok-Ho Chan 1 Michael Zengerle 1 Andrea Testa 1 Alessio Ciulli 1
Affiliations

Affiliation

  • 1 Division of Biological Chemistry and Drug Discovery, School of Life Sciences, University of Dundee , Dow Street, Dundee, DD1 5EH, Scotland, U.K.
Abstract

The design of proteolysis-targeting chimeras (PROTACs) is a powerful small-molecule approach for inducing protein degradation. PROTACs conjugate a target warhead to an E3 ubiquitin ligase ligand via a linker. Here we examined the impact of derivatizing two different BET bromodomain inhibitors, triazolodiazepine JQ1 and the more potent tetrahydroquinoline I-BET726, via distinct exit vectors, using different polyethylene glycol linkers to VHL ligand VH032. Triazolodiazepine PROTACs exhibited positive cooperativities of ternary complex formation and were more potent degraders than tetrahydroquinoline compounds, which showed negative cooperativities instead. Marked dependency on linker length was observed for BET-degrading and cMyc-driven antiproliferative activities in acute myeloid leukemia cell lines. This work exemplifies as a cautionary tale how a more potent inhibitor does not necessarily generate more potent PROTACs and underscores the key roles played by the conjugation. The provided insights and framework for structure-activity relationships of bivalent degraders are anticipated to have wide future applicability.

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