L-Asparaginase and inhibitors of glutamine synthetase disclose glutamine addiction of β-catenin-mutated human hepatocellular carcinoma cells

• Published in: Current cancer drug targets Vol. 11; no. 8; p. 929
• Main Authors: Tardito, S, Chiu, M, Uggeri, J, Zerbini, A, Da Ros, F, Dall'Asta, V, Missale, G, Bussolati, O
• Format: Journal Article
• Language: English
• Published: Netherlands 01.10.2011
• Subjects: Antineoplastic Agents - metabolism; Antineoplastic Agents - pharmacology; Apoptosis - drug effects; Asparaginase - metabolism; Asparaginase - pharmacology; Autophagy - drug effects; beta Catenin - genetics; beta Catenin - metabolism; Carcinoma, Hepatocellular - drug therapy; Carcinoma, Hepatocellular - metabolism; Carcinoma, Hepatocellular - pathology; Cell Line, Tumor; Cell Proliferation - drug effects; Drug Resistance, Neoplasm; Enzyme Inhibitors - pharmacology; Eukaryotic Initiation Factor-2B - metabolism; Gene Silencing; Glutamate-Ammonia Ligase - antagonists & inhibitors; Glutamate-Ammonia Ligase - genetics; Glutamate-Ammonia Ligase - metabolism; Glutamine - metabolism; Humans; Liver Neoplasms - drug therapy; Liver Neoplasms - metabolism; Liver Neoplasms - pathology; Molecular Targeted Therapy; Mutant Proteins - genetics; Mutant Proteins - metabolism; Neoplasm Proteins - antagonists & inhibitors; Neoplasm Proteins - genetics; Neoplasm Proteins - metabolism; Phosphorylation - drug effects; Protein Processing, Post-Translational - drug effects; Recombinant Proteins - antagonists & inhibitors; Recombinant Proteins - metabolism
• ISSN: 1873-5576
• DOI: 10.2174/156800911797264725

Selected oncogenic mutations support unregulated growth enhancing glutamine availability but increasing the dependence of tumor cells on the amino acid. Data from literature indicate that a subset of HepatoCellular Carcinomas (HCC) is characterized by mutations of β-catenin and overexpression of Glutamine Synthetase (GS). To assess if this phenotype may constitute an example of glutamine addiction, we treated four human HCC lines with the enzyme L-Asparaginase (ASNase), a glutaminolytic drug. ASNase had a significant antiproliferative effect only in the β-catenin mutated HepG2 cells, which were partially rescued by the anaplerotic intermediates pyruvate and α-ketoglutarate. The enzyme severely depleted cell glutamine, caused eIF2α phosphorylation, inhibited mTOR activity, and increased autophagy in both HepG2 and in the β-catenin wild type cell line Huh-7. When used with ASNase, the GS inhibitor methionine sulfoximine (MSO) emptied cell glutamine pool, arresting proliferation in ASNase-insensitive Huh-7 cells and activating caspase-3 and apoptosis in HepG2 cells. Compared with Huh-7 cells, HepG2 cells accumulated much higher levels of glutamine and MSO, due to the higher expression and activity of SNAT2, a concentrative transporter for neutral amino acids, but were much more sensitive to glutamine withdrawal from the medium. In the presence of ASNase, MSO caused a paradoxical maintenance of rapamycin-sensitive mTOR activity in both HepG2 and Huh-7 cells. β-catenin silencing lowered ASNase sensitivity of HepG2 cells and of Huh-6 cells, another β-catenin-mutated cell line, which also exhibited high sensitivity to ASNase. Thus, β-catenin mutated HCC cells are more sensitive to glutamine depletion and accumulate higher levels of GS inhibitors. These results indicate that glutamine deprivation may constitute a targeted therapy for β-catenin-mutated HCC cells addicted to the amino acid.