Suppression of Hepatocellular Carcinoma by Inhibition of Overexpressed Ornithine Aminotransferase

Abstract

Hepatocellular carcinoma is the second leading cause of cancer death worldwide. DNA microarray analysis identified the ornithine aminotransferase (OAT) gene as a prominent gene overexpressed in hepatocellular carcinoma (HCC) from Psammomys obesus. In vitro studies demonstrated inactivation of OAT by gabaculine (1), a neurotoxic natural product, which suppressed in vitro proliferation of two HCC cell lines. Alpha-fetoprotein (AFP) secretion, a biomarker for HCC, was suppressed by gabaculine in both cell lines, but not significantly. Because of the active site similarity between GABA aminotransferase (GABA-AT) and OAT, a library of 24 GABA-AT inhibitors was screened to identify a more selective inhibitor of OAT. (1S,3S)-3-Amino-4-(hexafluoropropan-2-ylidene)cyclopentane-1-carboxylic acid (2) was found to be an inactivator of OAT that only weakly inhibits GABA-AT, Laspartate aminotransferase, and L-alanine aminotransferase. In vitro administration of 2 significantly suppressed AFP secretion in both Hep3B and HepG2 HCC cells; in vivo, 2 significantly suppressed AFP serum levels and tumor growth in HCC-harboring mice, even at 0.1 mg/kg. Overexpression of the OAT gene in HCC and the ability to block the growth of HCC by OAT inhibitors support the role of OAT as a potential therapeutic target to inhibit HCC growth. This is the first demonstration of suppression of HCC by an OAT inactivator.

Selective Targeting by a Mechanism-Based Inactivator against Pyridoxal 5′-Phosphate-Dependent Enzymes: Mechanisms of Inactivation and Alternative Turnover

“…OAT is overexpressed in HCC cells, and its inhibition was shown to suppress their growth. 8 GABA-AT (EC 2.6.1.19) catalyzes the transfer of the amino group of GABA to α -ketoglutarate, producing succinic semialdehyde and L-glutamate (Scheme 1C). GABA is the principal inhibitory neuro-transmitter in mammalian cells, 9 and abnormally low levels of GABA in the brain have been associated with several neurological disorders, such as epilepsy, and several neuro-degenerative diseases, such as Parkinson’s, Huntington’s, and Alzheimer’s diseases.…”

“…In this study, we investigated the mechanism by which (1 R ,3 S ,4 S )-3-amino-4-fluorocyclopentane-1-carboxylic acid (FCP), a known inactivator of GABA-AT 11 and OAT, 8 inactivates OAT, and the effects of FCP on the PLP-dependent, off-target enzyme Asp-AT. Our study serves as a proof of principle that new OAT inactivators could be developed from GABA analogues, without targeting other off-target, PLP-dependent enzymes.…”

Ornithine Aminotransferase, an Important Glutamate-Metabolizing Enzyme at the Crossroads of Multiple Metabolic Pathways

“…However, a study conducted by Wang et al [123] has shown, at least for rapidly proliferating cancer cells, that OAT is needed to establish spindle formation; OAT was found to be over-expressed in some cancers, especially in HCC cells [234]. OAT inhibition could thus be beneficial in treating HCC or other cancers [34,235]. Currently, one major obstacle to the development of a drug that inhibits OAT is the fear it may give rise to toxic hyperornithinemia as observed in GA.…”

Ornithine aminotransferase promoted the proliferation and metastasis of non‐small cell lung cancer via upregulation of miR‐21

“…As mentioned earlier, OAT has been reported by Zigmond et al (2015) to be overexpressed in hepatocellular carcinoma, but its functional role in liver cancer was not further investigated. In the current study, we reported the OAT inhibitor significantly suppressed AFP serum levels and tumor growth in hepatocellular carcinoma-harboring mice (Zigmond et al, 2015). These previous findings demonstrated the potential application of OAT inhibitors in the treatment of hepatocellular carcinoma.…”