H3B-120 is primarily utilized in the field of medicinal chemistry and drug development. It serves as a potent and selective inhibitor of the histone methyltransferase enzyme DOT1L, which plays a crucial role in the regulation of gene expression. By inhibiting DOT1L, H3B-120 is used in research to study the effects of epigenetic modifications on cancer progression, particularly in leukemias such as mixed lineage leukemia (MLL). Its application extends to preclinical studies where it helps in understanding the therapeutic potential of targeting DOT1L for the treatment of cancers driven by MLL gene rearrangements. Additionally, H3B-120 is employed in the development of novel epigenetic therapies, providing insights into the design of more effective and specific inhibitors for clinical use.