GSK973 is a highly selective, orally bioavailable inhibitor of the BD2s (second bromodomains) of the BET family, with a pIC 50 of 7.8 and a pK d of 8.7 for BRD4 BD2. GSK973 displays a 1600-fold selectivity for BRD4 BD2 over BRD4 BD1. GSK973 shows good potency against BRD2 BD2, BRD3 BD2, and BRDT BD2 (pIC 50 =7.4~7.8; pK d =8.3~8.5).