Bromodomain and extra-terminal (BET) family is a well-known member of bromodomain family. Proteins of this family include BRD2, BRD3, BRD4 and a testis-specific protein, BRDT. BET proteins act as important epigenetic “readers” and play a vital role in regulating gene transcription. Thus, they are becoming hot targets for cancer research. It is necessary to find out a potent and selective BET inhibitor. However, the process is quite complicated.

First of all, Yujun Zhao, et al., have synthesized and purified a series of structurally similar compounds. The analogues share similar structure, and may possess common bioactivity on their target BET proteins.

Next, these compounds are determined for their affinities to BET proteins. Among them, the most-promising inhibitor, CF53 (compound 28), emerges. CF53 is a highly potent, selective and orally active inhibitor of BET protein. It exhibits a K_i of <1 nM, K_d of 2.2 nM, an IC₅₀ of 2 nM for BRD4 BD1. What’s more, CF53 exhibits >50-fold selectivity for BET bromodomains over CECR2 and EP300 and >20-fold over CREBBP.

Then, the authors evaluated CF53 for its anti-tumor activity in vitro. CF53 potently inhibits the growth of MOLM-13 acute leukemia and MDA-MB-231 breast cancer cell lines. IC₅₀s are 7 and 85 nM, respectively.

Lastly, in vivo, CF53 is administrated at doses of 25 and 50 mg/kg via oral route. As expected, CF53 dramatically prevents tumor growth in MDA-MB-231 xenograft tumor model and in RS4;11 model.

All in all, CF53 is a highly potent, selective, and orally active BET inhibitor. It needs further study for anti-cancer research and preclinical development.