Inhibition of the Polyamine Synthesis Pathway Is Synthetically Lethal with Loss of Argininosuccinate Synthase 1

Our plain-English summary of Inhibition of the Polyamine Synthesis Pathway Is Synthetically Lethal with Loss of Argininosuccinate Synthase 1, by M. Locke, E. Ghazaly, M.O. Freitas, et al (Cell Reports, 2016).

The study

• Authors: M. Locke, E. Ghazaly, M.O. Freitas, M. Mitsinga, L. Lattanzio, C. Lo Nigro, A. Nagano, J. Wang, C. Chelala, P. Szlosarek, S.A. Martin
• Journal: Cell Reports
• Published: 2016;16(6):1604-1613
• Cited by: 51 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Argininosuccinate synthase 1 (ASS1) is the rate-limiting enzyme for arginine biosynthesis. ASS1 expression is lost in a range of tumor types, including 50% of malignant pleural mesotheliomas. Starving ASS1-deficient cells of arginine with arginine blockers such as ADI-PEG20 can induce selective lethality and has shown great promise in the clinical setting. We have generated a model of ADI-PEG20 resistance in mesothelioma cells. This resistance is mediated through re-expression of ASS1 via demethylation of the ASS1 promoter. Through coordinated transcriptomic and metabolomic profiling, we have shown that ASS1-deficient cells have decreased levels of acetylated polyamine metabolites, together with a compensatory increase in the expression of polyamine biosynthetic enzymes. Upon arginine deprivation, polyamine metabolites are decreased in the ASS1-deficient cells and in plasma isolated from ASS1-deficient mesothelioma patients. We identify a synthetic lethal dependence between ASS1 deficiency and polyamine metabolism, which could potentially be exploited for the treatment of ASS1-negative cancers.

Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.

In plain English

This laboratory study, with analysis of patient blood samples, examined malignant pleural mesothelioma cells lacking ASS1, an enzyme used to make the amino acid arginine. It did not study asbestos exposure. The authors grew ASS1-deficient Ju77 cells in the arginine-depleting drug ADI-PEG20 until a resistant line (Ju77R) emerged. That line had switched ASS1 back on, with a 20-fold increase in ASS1 mRNA and reduced promoter methylation. Compared with the resistant cells, the ASS1-deficient cells had lower levels of acetylated polyamines and higher expression of polyamine-making enzymes. In plasma from ASS1-deficient mesothelioma patients, the polyamine putrescine fell significantly after ADI-PEG20 treatment in 17 patients with stable disease or partial response. It did not fall in 6 control patients or in 11 patients with mixed response or progressive disease. DFMO, a polyamine-blocking drug tested only in cell lines, reduced viability more in ASS1-deficient than ASS1-proficient cells. Combining DFMO with ADI-PEG20 was synergistic at the specific concentrations tested. The authors concluded that their data suggest this increased polyamine gene activity drives growth of ASS1-deficient cells and can be exploited clinically with polyamine inhibitors.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory (cell line) study of a drug-resistance model, using genetic, gene-expression and metabolite profiling, plus analysis of plasma samples from patients in a randomized phase II trial (ADAM)
• Who was studied: Malignant pleural mesothelioma (MPM) cell lines: Ju77 and its ADI-PEG20-sensitive (Ju77S) and resistant (Ju77R) forms, MSTO-211H, H28 and H226, plus two other ASS1-negative cell lines (2591 and T24). Plasma from ASS1-deficient mesothelioma patients in the ADAM trial at St. Bartholomew's Hospital: 6 controls receiving best supportive care alone, 17 with stable disease or partial response, and 11 with mixed response or progressive disease after ADI-PEG20 plus best supportive care
• Exposure: No asbestos exposure was studied. The treatments studied were the arginine-depleting drug ADI-PEG20 and the polyamine synthesis (ODC1) inhibitor DFMO, alone and combined. DFMO was tested only in cell lines
• Main results:
  • Resistant Ju77R cells had a 20-fold increase in ASS1 mRNA compared with sensitive Ju77S cells
  • Compared with Ju77S cells, Ju77R cells had decreased ASS1 promoter methylation at six of seven CpG sites, with an overall 5% reduction
  • Knocking down c-Myc did not change ASS1 levels. The authors attributed ASS1 re-expression to promoter demethylation rather than c-Myc
  • The acetylated polyamines N1-acetylspermidine and N1-acetylspermine were significantly lower in ASS1-deficient Ju77S cells than in ASS1-proficient Ju77R cells
  • After ADI-PEG20 treatment, putrescine and spermine levels fell significantly in Ju77S cells but not in Ju77R cells (p < 0.05)
  • All ASS1-deficient cell lines tested showed a significant fall in spermine on arginine depletion (p < 0.0005)
  • In patient plasma, putrescine fell significantly only in ASS1-deficient patients with stable disease or partial response (n = 17) after ADI-PEG20 and best supportive care (p < 0.0002). There was no decrease in controls (n = 6) or in patients with mixed response or progressive disease (n = 11)
  • Microarrays identified 234 genes with a greater than 2-fold difference between Ju77S and Ju77R cells (adjusted p < 0.05). Several polyamine-synthesis enzymes, including ODC1, AMD1, SMS, SMOX and AGMAT, were increased in ASS1-deficient Ju77S cells
  • In cell lines, ASS1-deficient cells were more sensitive to DFMO than ASS1-proficient cells (p < 0.0005)
  • Adding polyamines, but not arginine, reversed the effect of DFMO on cell viability
  • DFMO combined with ADI-PEG20 was synergistic at specific concentrations. Combination index values were 0.368 and 0.499 in Ju77S cells and 0.418 and 0.581 in Ju77R cells; values below 1 indicate synergism
• The authors' conclusion: The authors concluded that their data suggest the increase in polyamine metabolic gene expression drives proliferation in ASS1-deficient cells and can be exploited clinically through polyamine inhibitors such as DFMO
• Limitations the authors state:
  • The authors stated that studies of tumor tissue and/or plasma from patients undergoing arginine deprivation are needed to assess the clinical relevance of the findings
  • The authors stated that further studies are required to establish the potential of the therapeutic strategy

Topics

Medical terms in this study, explained in our Lexicon: Pleural Mesothelioma, Pegargiminase (ADI-PEG20), Mesothelioma.

Related studies

• Metabolic response to pegylated arginine deiminase in mesothelioma with promoter methylation of argininosuccinate synthetase — P.W. Szlosarek, P. Luong, et al. (2013)
• Phase 1 Dose-Escalation Study of Pegylated Arginine Deiminase, Cisplatin, and Pemetrexed in Patients With Argininosuccinate Synthetase 1-Deficient Thoracic Cancers — E. Beddowes, J. Spicer, et al. (2017)
• A role for macrophages under cytokine control in mediating resistance to ADI-PEG20 (pegargiminase) in ASS1-deficient mesothelioma — M.M. Phillips, I. Pavlyk, et al. (2023)
• BAP1 Loss Is Associated with Higher ASS1 Expression in Epithelioid Mesothelioma: Implications for Therapeutic Stratification — S.E. Barnett, J. Kenyani, et al. (2023)
• Targeting polyamine as a novel therapy in xenograft models of malignant pleural mesothelioma — S.K. Lam, S. Yan, et al. (2020)
• Loss of Argininosuccinate Synthetase-1 (ASS1) Occurs in Esophageal Adenocarcinoma and Represents a Promising Biomarker for Therapy with Pegargiminase — K. Knipper, S.I. Lyu, et al. (2025)

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