The BET family of proteins consists of BRD2, BRD3, BRD4, and BRDt. Each protein contains two distinct bromodomains (BD1 and BD2). BET family bromodomain inhibitors under clinical development for oncology bind to each of the eight bromodomains with similar affinities. We hypothesized that it may be possible to achieve an improved therapeutic index by selectively targeting subsets of the BET bromodomains. Both BD1 and BD2 are highly conserved across family members (>70% identity), whereas BD1 and BD2 from the same protein exhibit a larger degree of divergence (∼40% identity), suggesting selectivity between BD1 and BD2 of all family members would be more straightforward to achieve. Exploiting the Asp144/His437 and Ile146/Val439 sequence differences (BRD4 BD1/BD2 numbering) allowed the identification of compound 27 demonstrating greater than 100-fold selectivity for BRD4 BD2 over BRD4 BD1. Further optimization to improve BD2 selectivity and oral bioavailability resulted in the clinical development compound 46 (ABBV-744).

中文翻译：

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N-乙基-4- [2-（4-氟-2,6-二甲基-苯氧基）-5-（1-羟基-1-甲基-乙基）苯基] -6-甲基-7-氧代-1H的发现-吡咯并[2,3-c]吡啶-2-甲酰胺（ABBV-744），一种对第二个溴结构域具有选择性的BET溴结构域抑制剂。

BET蛋白质家族由BRD2，BRD3，BRD4和BRDt组成。每种蛋白质均包含两个不同的溴结构域（BD1和BD2）。在肿瘤学方面正在临床研究中的BET家族溴结构域抑制剂以相似的亲和力与八个溴结构域的每一个结合。我们假设有可能通过选择性地靶向BET溴结构域的子集来实现更高的治疗指数。BD1和BD2在家族成员中都是高度保守的（> 70％一致性），而同一蛋白质的BD1和BD2则表现出较大的差异（〜40％一致性），这表明所有家族成员的BD1和BD2之间的选择性都很高。更容易实现。利用Asp144 / His437和Ile146 / Val439序列差异（BRD4 BD1 / BD2编号）可以鉴定出化合物27，与BRD4 BD1相比，其对BRD4 BD2的选择性高100倍以上。进一步优化以改善BD2选择性和口服生物利用度导致了临床开发化合物46（ABBV-744）。