Project Summary/Abstract Recently, it was found that the enzyme ornithine aminotransferase (OAT) is overexpressed in hepatocellular carcinoma (HCC), the most common primary malignancy of the liver and the 2nd leading cause of cancer-related death in men (6th in women) worldwide. There are relatively few molecules known to inhibit the activity of OAT, and those that have been reported focus on their ability to increase the concentration of ornithine as a potential treatment for acute ammonia intoxications and hepatogenic encephalopathy. The objective of this proposal is to use computer modeling, based on the known crystal structures of human OAT and other PLP-dependent enzymes with our previously-active inactivators bound, to assist in the design of new inactivators of OAT that are selective against other related enzymes to lower the potential of side effects from off-target inhibition. Modifications to our earlier compounds will be made to improve on potency and pharmacokinetic properties. The mechanisms of those compounds that selectively inactivate OAT will be investigated. X-ray crystal structures of the inactivators bound to OAT will be obtained by our collaborator, Dr. Dali Liu, to assist in further structural modifications. Compounds that are potent and selective inactivators of OAT will be tested by Dr. Wenan Qiang against several cancer cell lines also found to overexpress OAT and carry out PDX studies with the most effective compounds. He also will corroborate that the compounds inhibit secretion of alpha-fetoprotein, a biomarker for HCC, and that OAT is the target. The goal is to identify one or more compounds that are selective inhibitors/inactivators of OAT that suppress the growth of HCC, and other cancers that overexpress OAT, in animals. These compounds would be first-in-class treatments for HCC, a cancer that is highly resistant to both standard cancer chemotherapy and radiation therapy, and the prognosis for recovery is very poor, as well as other OAT-expressing cancers.