BET bromodomain inhibitor 1 is an orally active, selective bromodomain and extra-terminal (BET) bromodomain inhibitor with an IC50 of 2.6 nM for BRD4. BET bromodomain inhibitor 1 binds to BRD2(2), BRD3(2), BRD4(1), BRD4(2), and BRDT(2) with high affinities (Kd values of 1.3 nM, 1.0 nM, 3.0 nM, 1.6 nM, 2.1 nM, respectively). bromodomain inhibitor 1 has anti-cancer activity.