GSK126 is primarily used in research settings as a potent and selective inhibitor of the enzyme EZH2 (enhancer of zeste homolog 2), which is a histone methyltransferase. By inhibiting EZH2, GSK126 reduces the methylation of histone H3 at lysine 27 (H3K27me3), a modification associated with gene silencing. This activity makes it a valuable tool in studies of epigenetic regulation, particularly in cancers where EZH2 is overexpressed or mutated, such as certain lymphomas and solid tumors. It is widely applied in preclinical studies to evaluate the therapeutic potential of targeting epigenetic pathways. Researchers use GSK126 to investigate how epigenetic changes influence cell proliferation, differentiation, and apoptosis. Its selectivity allows for precise modulation of EZH2 activity without significant off-target effects on other methyltransferases, enhancing its utility in mechanistic studies. GSK126 has also been used in combination therapies to assess synergistic effects with other anticancer agents, supporting the development of new treatment strategies in oncology.