Physachenolide C is a Potent, Selective BET Inhibitor
Christopher J. Zerio, Jared Sivinski, E. M. Kithsiri Wijeratne, Ya-Ming Xu, Duc T. Ngo, Andrew J. Ambrose, Luis Villa-Celis, Niloofar Ghadirian, Michael W. Clarkson, Donna D. Zhang, Nancy C. Horton, A. A. Leslie Gunatilaka, Raimund Fromme, Eli Chapman
Abstract
A pulldown using a biotinylated natural product of interest in the 17β-hydroxywithanolide (17-BHW) class, physachenolide C (PCC), identified the bromodomain and extra-terminal domain (BET) family of proteins (BRD2, BRD3, and BRD4), readers of acetyl-lysine modifications and regulators of gene transcription, as potential cellular targets. BROMOscan bromodomain profiling and biochemical assays support PCC as a BET inhibitor with increased selectivity for bromodomain (BD)-1 of BRD3 and BRD4, and X-ray crystallography and NMR studies uncovered specific contacts that underlie the potency and selectivity of PCC toward BRD3-BD1 over BRD3-BD2. PCC also displays characteristics of a molecular glue, facilitating proteasome-mediated degradation of BRD3 and BRD4. Finally, PCC is more potent than other withanolide analogues and gold-standard pan-BET inhibitor (+)-JQ1 in cytotoxicity assays across five prostate cancer (PC) cell lines regardless of androgen receptor (AR)-signaling status.