Discovery of structurally-diverse inhibitor scaffolds by high-throughput screening of a fragment library with dimethylarginine dimethylaminohydrolase.

Potent and selective inhibitors of the enzyme dimethylarginine dimethylaminohydrolase (DDAH) are useful as molecular probes to better understand cellular regulation of nitric oxide. Inhibitors are also potential therapeutic agents for treatment of pathological states associated with the inappropriate overproduction of nitric oxide, such as septic shock, selected types of cancer, and other conditions. Inhibitors with structures dissimilar to substrate may overcome limitations inherent to substrate analogs. Therefore, to identify structurally-diverse inhibitor scaffolds, high-throughput screening (HTS) of a 4000-member library of fragment-sized molecules was completed using the Pseudomonas aeruginosa DDAH and human DDAH-1 isoforms. Use of a substrate concentration equal to its K(M) value during the primary screen allowed for the detection of inhibitors with different modes of inhibition. A series of validation tests were designed and implemented in the identification of four inhibitors of human DDAH-1 that were unknown prior to the screen. Two inhibitors share a 4-halopyridine scaffold and act as quiescent affinity labels that selectively and covalently modify the active-site Cys residue. Two inhibitors are benzimidazole-like compounds that reversibly and competitively inhibit human DDAH-1 with Ligand Efficiency values ≥0.3 kcal/mol/heavy (non-hydrogen) atom, indicating their suitability for further development. Both inhibitor scaffolds have available sites to derivatize for further optimization. Therefore, use of this fragment-based HTS approach is demonstrated to successfully identify two novel scaffolds for development of DDAH-1 inhibitors.