BRD4 is a member of the bromodomain and extra terminal(BET) familyof proteins, and is a desirable drug target because of its conservedtandem bromodomain and its role in cancer epigenetic.50 BRD4 is inhibited by the selective small molecule GSK1210151A(I-BET151), which provides an effective treatment for MLL-fusion leukemia.51 Here, we performed HDX-MS of BRD4 with and withoutbound I-BET151 to gain a further understanding of the molecular detailsof the interaction. The gene discussed is KMT2A; the disease is leukemia.