CSN5i-3 is primarily used in research settings to study the role of the COP9 signalosome (CSN) complex in cellular processes. It acts as an inhibitor of CSN5, a key subunit of the CSN complex, which is involved in regulating protein degradation pathways, particularly those mediated by the ubiquitin-proteasome system. By inhibiting CSN5, researchers can investigate its impact on cell cycle regulation, DNA damage response, and cancer progression. This compound is particularly valuable in understanding the mechanisms of diseases where CSN5 is dysregulated, such as certain types of cancers, and in exploring potential therapeutic targets for drug development.