A High-Throughput Screening Platform for the Discovery of Noncovalent Inhibitors of the ISG15–UBA7 Interaction

Abstract Patients with metastatic breast cancer have a dismal five-year survival rate of 28% because these cancers develop resistance to multiple treatment modalities; thus, novel therapies are desperately needed. Interferon signaling gene signatures and the expression of interferon stimulated gene 15 (ISG15) have been linked to resistance to chemotherapy, radiotherapy, immunotherapy, and targeted therapy in patients, but there are no therapies that target ISG15 or the enzymatic machinery that enables its covalent conjugation to substrate proteins, such as its activating E1 enzyme UBA7. In this pilot study, we established an AlphaLISA-based high-throughput assay to identify inhibitors of the ISG15–UBA7 interaction. The assay demonstrated strong performance characteristics for high-throughput screening with a Z′ factor of 0.69, indicating excellent robustness and sensitivity. Screening a library of 880 compounds yielded three hits that inhibited the ISG15–UBA7 interaction. Two of these compounds were also found to reduce ISGylation in cell-based assays. Overall, these findings highlight the utility of AlphaLISA as a scalable platform for high-throughput screening of drug-like inhibitors targeting the ISGylation pathway.