ASAH1 is a lysosomal ceramidase that hydrolyzes sphingolipid ceramides into sphingosine and free fatty acids. Ceramides, sphingosine, and its phosphorylated form sphingosine-1-phosphate are bioactive lipids that mediate cellular signaling pathways regulating several biological processes including cell proliferation, apoptosis, and differentiation. ASAH1 is implicated in fibrosis and cancers . We used the crystal structure of human ASAH1 (PDB ID 5U7Z, ) to define the binding site (Figure ).