GSK973 is a highly selective and orally bioavailable inhibitor that targets the second bromodomains (BD2s) of the BET family. It exhibits a pIC 50 of 7.8 and a pK d of 8.7 specifically for BRD4 BD2. Additionally, GSK973 demonstrates a remarkable selectivity of 1600-fold for BRD4 BD2 over BRD4 BD1. Moreover, it displays good potency against BRD2 BD2, BRD3 BD2, and BRDT BD2, with pIC 50 ranging from 7.4 to 7.8 and pK d ranging from 8.3 to 8.5.
dBRD4-BD1 is a selective BRD4 bromodomain inhibitor. dBRD4-BD1 can selectively degrade BRD4 (DC50 = 280 nM). Notably, dBRD4-BD1 upregulates BRD2 3, a result not observed with degraders using pan-BET ligands. Designing BRD4 selectivity up front enables analysis of BRD4 biology without wider BET-inhibition and simplifies designing BRD4-selective heterobifunctional molecules, such as degraders with new E3 recruiting ligands or for additional probes beyond degraders.