Given our interest in evaluating domain-specific BET protein inhibition in inflammatory liver disease, we first selected a panel of inhibitors based on their diverse selectivity profile. As representative pan-BET inhibitors, we selected (+)-JQ1 and I-BET151. I-BET151 is a well-characterized pre-clinical candidate with a slight pan-D1 bias, whereas (+)-JQ1 shows less preference. In addition, we selected a well-characterized pan-D2 inhibitor developed by Gilan et al., iBETBD2. For BRD4-D1 inhibition, we chose iBRD4(D1) (henceforth referred to as 1), and a new analog, 2, developed to address the cytotoxicity of UMN627, and two commercial inhibitors, ZL0590 and ZL0454, developed by Zhou and co-workers (Figure ). Finally, we selected DW34, hereafter referred to as 3, which is a pan-D1 biased inhibitor with additional BRD4-D2 activity. Based on the use of several literature-reported compounds with diverse BET affinity and selectivity profiles, we conducted an initial comparative binding study using the same protein constructs and assay conditions. In these experiments, we used an AlphaScreen competitive inhibition assay, using BRD4-D1 and two representative D2 bromodomains for BRD4 and BRD2. These proteins were chosen to provide a preliminary assessment of intra-BET protein selectivity and D1/D2 selectivity.