Discovery of a Small-Molecule Degrader of Bromodomain and Extra-Terminal (BET) Proteins with Picomolar Cellular Potencies and Capable of Achieving Tumor Regression

The
bromodomain and extra-terminal (BET) family proteins, consisting
of BRD2, BRD3, BRD4, and testis-specific BRDT members, are epigenetic
“readers” and play a key role in the regulation of gene
transcription. BET proteins are considered to be attractive therapeutic
targets for cancer and other human diseases. Recently, heterobifunctional
small-molecule BET degraders have been designed based upon the proteolysis
targeting chimera (PROTAC) concept to induce BET protein degradation.
Herein, we present our design, synthesis, and evaluation of a new
class of PROTAC BET degraders. One of the most promising compounds, 23, effectively degrades BRD4 protein at concentrations as
low as 30 pM in the RS4;11 leukemia cell line, achieves an IC50 value of 51 pM in inhibition of RS4;11 cell growth and induces
rapid tumor regression in vivo against RS4;11 xenograft tumors. These
data establish that compound 23 (BETd-260/ZBC260) is
a highly potent and efficacious BET
degrader.