MK-5108 (VX-689) is a potent and selective inhibitor of Aurora A kinase, an enzyme involved in the regulation of mitosis. Its primary application lies in cancer research, particularly in studying cell cycle progression and mitotic spindle formation. Due to its ability to selectively inhibit Aurora A without significant activity against Aurora B, it is used as a tool compound to dissect the distinct roles of Aurora kinases in tumor cell proliferation and survival. In preclinical studies, MK-5108 has demonstrated anti-tumor activity in various cancer cell lines, especially those with elevated Aurora A expression, such as certain breast, ovarian, and pancreatic cancers. It induces G2/M phase arrest and leads to the formation of monopolar spindles, resulting in apoptosis of rapidly dividing cells. This makes it valuable in evaluating the therapeutic potential of Aurora A inhibition in oncology drug development. Additionally, MK-5108 is used in combination studies with other chemotherapeutic agents to assess synergistic effects and overcome drug resistance. Its selectivity profile supports its use in validating Aurora A as a target in xenograft models and in pharmacodynamic studies where target modulation needs to be clearly attributed to Aurora A inhibition.