Nutritional stress and arginine auxotrophy confer high sensitivity to chloroquine toxicity in mesothelioma cells

Our plain-English summary of Nutritional stress and arginine auxotrophy confer high sensitivity to chloroquine toxicity in mesothelioma cells, by S. Battisti, D. Valente, L. Albonici, et al (American Journal of Respiratory Cell and Molecular Biology, 2012).

The study

• Authors: S. Battisti, D. Valente, L. Albonici, R. Bei, A. Modesti, C. Palumbo
• Journal: American Journal of Respiratory Cell and Molecular Biology
• Published: 2012;46(4):498-506
• Cited by: 21 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The correlation between cell sensitivity to autophagy inhibitors, such as chloroquine (CQ), and the expression/activity of molecules involved in the control and execution of autophagy is well documented. However, tumor cells with comparable autophagic potentials may display variable degrees of autophagy addiction, due to the differential expression of molecular determinants, which are still scarcely defined. In this study, we investigated the effects of CQ on growth, death, and autophagic activity of malignant mesothelioma cell lines cultured in standard versus nutritional stress conditions partially mimicking those found in the tumor microenvironment. We report that, in each cell line, the toxic effects of CQ were amplified by nutritional stress and paralleled by autophagy inhibition. Still, the cell lines displayed different levels of sensitivity to CQ toxicity, which did not correlate with their relative degrees of constitutive and nutritional stress-induced autophagy, nor with the relative magnitude of the autophagy inhibition induced by the drug. Thus, we tested the hypothesis that the cell lines' sensitivity to CQ was related to their variable dependence on recycling of intracellular constituents by autophagy. In fact, the cell line with the highest sensitivity to the toxic effects of CQ was auxotrophic for arginine, due to the deficient expression of the enzyme argininosuccinate synthetase (ASS). Furthermore, overexpression of ASS in these cells reduced their sensitivity to CQ toxicity. Based on these results, the assessment of ASS expression in malignant mesothelioma tissues may allow the identification of subgroups of tumors with an increased sensitivity to the toxic effects of this drug.

In plain English

This was a laboratory study of human cancer cells grown in dishes. It did not study people, and it did not study asbestos exposure. The authors tested the drug chloroquine on five cell lines of pleural malignant mesothelioma. They grew the cells in normal conditions (10% serum) and in low-nutrient conditions (1% serum) meant to partly imitate conditions inside a tumor. Chloroquine slowed the growth of every cell line. All lines were more sensitive under nutrient stress: the chloroquine concentration needed to halve growth fell eightfold for the line Mero 48a and 2.3- to 3.1-fold for the others. Mero 48a was the most sensitive line. It was the only line lacking the enzyme argininosuccinate synthetase (ASS), which cells use to make the amino acid arginine. How sensitive a line was did not match its level of autophagy, a recycling process inside cells that chloroquine blocks. When the authors added ASS back into Mero 48a cells, the cells became less sensitive to chloroquine. The authors concluded that testing mesothelioma tissue for ASS might help identify tumors more sensitive to this drug.

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 (in vitro) experiment on cultured human cancer cell lines, including genetically modified (transfected) clones
• Who was studied: Five human pleural malignant mesothelioma cell lines (H-Meso-1, Mero 25, Mero 48a, MM-B1, MM-F1), representing epithelioid, biphasic and sarcomatoid types, with HeLa cervical carcinoma cells as a control. Three lines (Mero 48a, MM-B1, Mero 25) were studied further. No human subjects.
• Exposure: The drug chloroquine (and, for comparison, cisplatin and pemetrexed), given to cells grown in 10% serum (standard) or 1% serum (nutritional stress). No asbestos or fiber exposure was studied.
• Main results:
  • All cell lines were more sensitive to chloroquine under nutritional stress. Measured at 50% growth inhibition, Mero 48a showed an eightfold sensitization and the other cell lines 2.3- to 3.1-fold.
  • After 72 hours at the lowest chloroquine concentration tested, in low-serum conditions, Mero 48a cultures contained about 40% dead cells.
  • Cell lines with similar levels of baseline and stress-induced autophagy differed in their sensitivity to chloroquine.
  • The enzyme ASS was found in every mesothelioma cell line except Mero 48a, the line most sensitive to chloroquine.
  • Mero 48a clones given the ASS gene were more resistant to chloroquine than clones given an empty vector. At 50% growth inhibition, the mean resistance index was 1.9 in 10% serum and 5.2 in 1% serum.
  • Of the three lines studied further, Mero 48a cells were the least sensitive to the standard drugs cisplatin and pemetrexed.
• The authors' conclusion: The authors concluded that chloroquine has significant toxic effects on mesothelioma cells, that nutritional stress amplifies these effects, and that assessing ASS expression in mesothelioma tissue may help identify tumor subgroups more sensitive to the drug.
• Limitations the authors state:
  • The authors cautioned that judging autophagy from p62 levels alone is uncertain.
  • Under low serum, the control (mock-transfected) clones were more sensitive to chloroquine than the original Mero 48a cells. The authors suggested the transfection and selection procedures may have favored more autophagy-dependent clones.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma.

Medical terms in this study, explained in our Lexicon: Mesothelioma, Malignant Mesothelioma, Tumor Microenvironment.

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