“Targeting Asparagine Synthetase: Structural and Cellular Mechanisms of the Small-Molecule Inhibitor ASX-173”
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Date and Time
4:00 PM – 5:30 PM Wednesday, December 17th, 2025
Location
Hybrid（CryoEM building and Zoom）
Speaker
Yuichiro H. Takagi, Ph.D.
Associate Professor
Scientific advisor for cryo-EM
Department of Biochemistry and Molecular Biology
Indiana University School of Medicine
Abstract
Targeting asparagine metabolism is a promising strategy for treating asparaginase-resistant acute lymphoblastic leukemia (ALL), sarcoma, and potentially other solid tumors. Here, we characterize the molecular mechanism by which a cell-penetrable small molecule, ASX-173, inhibits human asparagine synthetase (ASNS), the enzyme that catalyzes intracellular asparagine biosynthesis. ASX-173 reduces cellular asparagine levels, induces the integrated stress response (ISR), and reduces cell growth in HEK-293A cells. A cryo-EM structure reveals that ASX-173 engages a unique, hydrophobic pocket formed by AMP, Mg2+, and pyrophosphate in the C-terminal synthetase domain of ASNS, thereby enabling multivalent, high-affinity binding. Based on in vitro kinetic and thermal shift assays, we find that ASX-173 binds to the ASNS/Mg2+/ATP complex and is therefore a rare example of an uncompetitive enzyme inhibitor with potential therapeutic use. These findings provide a structural and mechanistic basis for targeting ASNS with small molecules, which have application in treating cancer and other human diseases.