A “Click Chemistry Platform” for the Rapid Synthesis of Bispecific Molecules for Inducing Protein Degradation

Proteolysis
targeting chimeras (PROTACs) are bispecific molecules containing a
target protein binder and an ubiquitin ligase binder connected by
a linker. By recruiting an ubiquitin ligase to a target protein, PROTACs
promote ubiquitination and proteasomal degradation of the target protein.
The generation of effective PROTACs depends on the nature of the protein/ligase
ligand pair, linkage site, linker length, and linker composition,
all of which have been difficult to address in a systematic way. Herein,
we describe a “click chemistry” approach for the synthesis
of PROTACs. We demonstrate the utility of this approach with the bromodomain
and extraterminal domain-4 (BRD4) ligand JQ-1 (3) and
ligase binders targeting cereblon (CRBN) and Von Hippel–Lindau
(VHL) proteins. An AlphaScreen proximity assay was used to determine
the ability of PROTACs to form the ternary ligase–PROTAC–target
protein complex and a MSD assay to measure cellular degradation of
the target protein promoted by PROTACs.