Growth suppressive effect of pegylated arginase in malignant pleural mesothelioma xenografts

Our plain-English summary of Growth suppressive effect of pegylated arginase in malignant pleural mesothelioma xenografts, by S.K. Lam, Y.Y. Li, S. Xu, et al (Respiratory Research, 2017).

The study

• Authors: S.K. Lam, Y.Y. Li, S. Xu, L.L. Leung, K.P. U, Y.F. Zheng, P.N. Cheng, J.C. Ho
• Journal: Respiratory Research
• Published: 2017;18(1):80
• Cited by: 23 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Malignant pleural mesothelioma (MPM) is a difficult-to-treat global disease. Pegylated arginase (BCT-100) has recently shown anti-tumor effects in hepatocellular carcinoma, acute myeloid leukemia and melanoma. This study aims to investigate the effects of PEG-BCT-100 in MPM.

Methods: A panel of 5 mesothelioma cell lines (H28, 211H, H226, H2052 and H2452) was used to study the in vitro effects of BCT-100 by crystal violet staining. The in vivo effects of BCT-100 were studied using 211H and H226 nude mice xenografts. Protein expression (argininosuccinate synthetase, ornithine transcarbamylase, cleaved PARP, cleaved caspase 3, cyclins (A2, D3, E1 and H), CDK4 and Ki67) and arginine concentration were evaluated by Western blot and ELISA respectively. Cellular localization of BCT-100 was detected by immunohistochemistry and immunoflorescence. TUNEL assay was used to identify cellular apoptotic events.

Results: Argininosuccinate synthetase was expressed in H28, H226, and H2452 cells as well as 211H and H266 xenografts. Ornithine transcarbamylase was undetectable in all cell lines and xenograft models. BCT-100 reduced in vitro cell viability (IC50 values at 13-24 mU/ml, 72 h) across different cell lines and suppressed tumor growth in both 211H and H226 xenograft models. BCT-100 (60 mg/kg) significantly suppressed tumor growth (p < 0.01) with prolonged median survival (p < 0.01) in both xenograft models. Combining BCT-100 with pemetrexed or cisplatin conferred no additional benefits over single agents. Serum and intratumoral arginine levels were effectively decreased by BCT-100, associated with cytosolic accumulation of BCT-100 within tumor cells. Apoptosis (PARP cleavage in 211H xenografts; Bcl-2 downregulation, and cleavage of PARP and caspase 3 in H226 xenografts; positive TUNEL staining in both) and G1 arrest (downregulation of cyclin A2, D3, E1 and CDK4 in 211H xenografts; suppression of cyclin A2, E1, H and CDK4 in H226 xenografts) were evident with BCT-100 treatment. Furthermore, proliferative factor Ki67 was downregulated in BCT-100 treatments arms.

Conclusions: BCT-100 suppressed tumor growth with prolonged median survival partially mediated by intratumoral arginine depletion resulting in apoptosis and G1 arrest in mesothelioma xenograft models. The findings provide scientific evidence to support further clinical development of BCT-100 in treatment of MPM.

In plain English

This laboratory and animal study tested BCT-100, an enzyme drug that breaks down the amino acid arginine, against malignant pleural mesothelioma; it did not study asbestos exposure. The authors treated five human mesothelioma cell lines and grew two (211H and H226) as tumors in nude mice. BCT-100 reduced cell-line viability (IC50, the concentration halving viability, 13.0 to 22.4 mU/ml at 72 hours). At 60 mg/kg, tumor volume relative to controls was 41.4% after 20 days (211H) and 44.4% after 35 days (H226). Median time from treatment start to humane endpoints (mice were killed at 600 mm3 tumor volume) rose from 22 to 38 days (211H) and 36.5 to 50.5 days (H226). Adding pemetrexed gave no extra benefit. BCT-100 plus cisplatin, tested only in 211H mice, gave no benefit, and liver cirrhosis was seen in all those mice. BCT-100 lowered arginine in blood and tumors. Tumors showed cell-death markers and protein changes the authors took as indirect evidence of G1 cell-cycle arrest. The authors concluded the effects were partially mediated by arginine depletion inside tumors. No sarcomatoid tumor model could be grown in mice.

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 study of human mesothelioma cell lines plus an animal experiment using tumor xenografts in nude mice
• Who was studied: Five human mesothelioma cell lines: H28 (sarcomatoid), 211H (biphasic), H226 (epithelioid), H2052 (sarcomatoid) and H2452 (epithelioid). Tumors from 211H and H226 cells were grown in female nude mice; the article states 18 nude mice. Xenografts from H28, H2052 and H2452 could not be established. The work was done at the University of Hong Kong.
• Exposure: Treatment with pegylated arginase BCT-100 (20 and 60 mg/kg twice a week in mice), alone or combined with pemetrexed (150 mg/kg twice a week) or cisplatin (2.5 mg/kg once a week). Control mice received PBS. No asbestos exposure was studied.
• Main results:
  • In the cell lines, BCT-100 reduced viability in a dose-dependent way. After 72 h the IC50 values were 14.3 (H28), 13.0 (211H), 22.4 (H226), 20.8 (H2052) and 18.6 (H2452) mU/ml.
  • In 211H xenografts after 20 days of treatment, tumor volume relative to the control group was 70.5% (20 mg/kg) and 41.4% (60 mg/kg, p less than 0.01).
  • In H226 xenografts after 35 days of treatment, tumor volume relative to the control group was 65.5% (20 mg/kg, p less than 0.01) and 44.4% (60 mg/kg, p less than 0.001).
  • Survival in the mice was defined as the time from the start of treatment until humane endpoints were reached. Mice were sacrificed when tumor volume reached 600 mm3.
  • Median survival (to humane endpoint) in the 211H model increased from 22 days in the control arm to 38 days with 60 mg/kg BCT-100 (p less than 0.01).
  • Median survival (to humane endpoint) in the H226 model increased from 36.5 days in the control group to 50.5 days with 60 mg/kg BCT-100 (p less than 0.01).
  • In the cell lines, combining BCT-100 with cisplatin or pemetrexed showed no synergism. In mice, BCT-100 plus pemetrexed showed no synergistic effect in either the 211H or the H226 model.
  • BCT-100 plus cisplatin was tested only in the 211H mouse model. It gave no beneficial effect, and liver cirrhosis was observed in all mice in the BCT-100/cisplatin arms, so this combination was not pursued in the H226 model.
  • Serum arginine was 98 μM in control mice. In 211H mice it fell to 24 (20 mg/kg) and 14 (60 mg/kg) μM. In H226 mice it fell to 14 and 13 μM.
  • Arginine inside the tumors fell in a dose-dependent way. In 211H tumors it went from 9.7 (control) to 5.3 (20 mg/kg) and 3.4 (60 mg/kg) nmole/mg protein. In H226 tumors it went from 9.1 to 6.2 and 4.3 nmole/mg protein.
  • In the cell lines, ASS1 was highly expressed in H28 and H2452, moderately expressed in H226, and not detectable in 211H and H2052. All cell lines were OTC negative.
  • In both xenograft models, BCT-100-treated tumors showed protein changes and TUNEL staining indicating apoptosis (cell death).
  • G1 cell-cycle arrest was inferred indirectly from changes in cell-cycle proteins (cyclins and CDK4). Ki67, a growth marker, was lower in BCT-100-treated tumors in both models.
• The authors' conclusion: The authors concluded that BCT-100 suppressed tumor growth and prolonged median survival in the mesothelioma xenograft models. In the abstract they describe this as partially mediated by arginine depletion inside tumors, leading to apoptosis and G1 arrest. The closing Conclusion section omits the word 'partially'. They wrote that the findings support further clinical development of BCT-100 for MPM.
• Limitations the authors state:
  • No sarcomatoid mesothelioma xenograft model could be developed, so the effect of BCT-100 on that subtype in mice was not assessed.
  • Experiments using primary cultures from patients' tumors, which would better mimic the tumor environment, were not feasible because MPM is rare in Hong Kong (about 20 new cases per year).

Topics

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

Medical terms in this study, explained in our Lexicon: Pleural Mesothelioma, Carcinoma, Mesothelioma, Immunohistochemistry, Median Overall Survival, Pemetrexed (Alimta), Cisplatin, Apoptosis.

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• Combination of onconase and dihydroartemisinin synergistically suppresses growth and angiogenesis of non-small-cell lung carcinoma and malignant mesothelioma — R. Shen, J. Li, et al. (2016)
• A Redox-Inactive Derivative of Tocotrienol Suppresses Tumor Growth of Mesothelioma Cells in a Xenograft Model — A. Sato, T. Arai, et al. (2019)
• Disulfiram suppresses growth of the malignant pleural mesothelioma cells in part by inducing apoptosis — V.T. Cheriyan, Y. Wang, et al. (2014)

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