Inhibition of autophagy initiation potentiates chemosensitivity in mesothelioma

Our plain-English summary of Inhibition of autophagy initiation potentiates chemosensitivity in mesothelioma, by C. Follo, Y. Cheng, W.G. Richards, et al (Molecular Carcinogenesis, 2018).

The study

• Authors: C. Follo, Y. Cheng, W.G. Richards, R. Bueno, V.C. Broaddus
• Journal: Molecular Carcinogenesis
• Published: 2018;57(3):319-332
• Cited by: 30 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The benefits of inhibiting autophagy in cancer are still controversial, with differences in outcome based on the type of tumor, the context and the particular stage of inhibition. Here, we investigated the impact of inhibiting autophagy at different stages on chemosensitivity using 3-dimensional (3D) models of mesothelioma, including ex vivo human tumor fragment spheroids. As shown by LC3B accumulation, we successfully inhibited autophagy using either an early stage ULK1/2 inhibitor (MRT 68921) or a late stage inhibitor (hydroxychloroquine). We found that inhibition of autophagy at the early stage, but not at late stage, potentiated chemosensitivity. This effect was seen only in those spheroids with high autophagy and active initiation at steady state. Inhibition of autophagy alone, at either early or late stage, did not cause cell death, showing that the inhibitors were non-toxic and that mesothelioma did not depend on autophagy at baseline, at least over 24 h. Using ATG13 puncta analysis, we found that autophagy initiation identified tumors that are more chemosensitive at baseline and after autophagy inhibition. Our results highlight a potential role of autophagy initiation in supporting mesothelioma cells during chemotherapy. Our work also highlights the importance of testing the inhibition of different stages in order to uncover the role of autophagy and the potential of its modulation in the treatment of cancer.

© 2017 Wiley Periodicals, Inc.

In plain English

This laboratory study tested whether blocking autophagy, a process cells use to recycle their own contents, changed how mesothelioma cells responded to chemotherapy. It did not study asbestos exposure. The authors used clusters grown from two mesothelioma cell lines (M28, with high autophagy, and REN, with low autophagy). They also used tumor fragments from 10 patients with malignant pleural mesothelioma who had not had chemotherapy. Samples were treated for 24 hours with carboplatin plus pemetrexed, with or without one of two drugs: MRT 68921, which blocks an early stage of autophagy, or hydroxychloroquine, which blocks a late stage. MRT 68921 increased chemotherapy-related cell death in M28 and in tumor samples with high autophagy, but not in low-autophagy samples. Hydroxychloroquine did not increase cell death. Neither drug alone caused cell death in the cell-line clusters. Across 28 tumor samples, a marker of early autophagy (ATG13) correlated with response to chemotherapy. The authors concluded that early-stage inhibition enhanced chemosensitivity. They noted that only 24-hour treatment and one chemotherapy combination were studied.

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 using 3-dimensional models of mesothelioma: multicellular spheroids grown from cell lines, and ex vivo tumor fragment spheroids made from surgically removed human tumors
• Who was studied: Two human mesothelioma cell lines (M28 and REN). Tumor fragment spheroids from patients with malignant pleural mesothelioma who had surgery at Brigham and Women's Hospital in Boston without prior chemotherapy: 10 tumors for the inhibitor experiments, and 28 in total (including 18 used earlier) for the correlation analysis. Dates are not given.
• Exposure: No asbestos exposure was studied. Samples were exposed for 24 h to carboplatin (200 µM) plus pemetrexed (10 µM), given together with an autophagy inhibitor or a vehicle control. The inhibitors were MRT 68921 (1 µM, blocks the early initiation stage) and hydroxychloroquine (20 µM, blocks the late stages).
• Main results:
  • In the cell-line spheroids, MRT 68921 inhibited autophagic flux in M28 (high autophagy) but not in REN (low autophagy). Hydroxychloroquine inhibited autophagy in both.
  • In the cell-line spheroids, adding MRT 68921 to chemotherapy increased chemosensitivity in M28 but had no evident effect in REN. Hydroxychloroquine did not alter chemosensitivity in either cell line.
  • In the cell-line spheroids, inhibiting autophagy alone, at either the early or the late stage, did not cause cell death.
  • Of the 10 tumor fragment spheroids, 5 had high autophagy and 5 had low autophagy.
  • In tumor fragment spheroids, MRT 68921 potentiated chemosensitivity specifically in those with high autophagy. MRT 68921 by itself did not cause cell death.
  • Hydroxychloroquine was tested in 6 tumor fragment spheroids. It did not increase cell death, either with chemotherapy or alone, and it significantly decreased chemosensitivity in one tumor with high autophagy.
  • Across 28 tumor fragment spheroids, the percentage of ATG13-positive mesothelioma cells correlated with the chemotherapy-induced increase in cleaved caspase 3-positive cells (Spearman rank correlation 0.82, P less than 0.0001).
• The authors' conclusion: The authors concluded that inhibiting autophagy at the early stage (initiation) enhances chemosensitivity in mesothelioma, while late-stage inhibition did not.
• Limitations the authors state:
  • Autophagy was inhibited for only 24 h; longer inhibition may have a different effect.
  • MRT 68921 may not be similarly useful in other tumors or models.
  • Only one chemotherapy combination, carboplatin plus pemetrexed, was used.
  • The results come from 3D settings and may not apply directly to studies in 2D.
  • Because tumor tissue was limited, hydroxychloroquine was tested in only 6 tumor fragment spheroids.

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, Chemotherapy.

Related studies

• Autophagy facilitates the release of immunogenic signals following chemotherapy in 3D models of mesothelioma — C. Follo, Y. Cheng, et al. (2019)
• Autophagy in 3D In Vitro and Ex Vivo Cancer Models — C. Follo, D. Barbone, et al. (2019)
• Pro-oxidant activity of sulforaphane and cisplatin potentiates apoptosis and simultaneously promotes autophagy in malignant mesothelioma cells — Y.J. Lee, S.H. Lee (2017)
• Berberine induces mitochondrial‑mediated apoptosis and protective autophagy in human malignant pleural mesothelioma NCI‑H2452 cells — Z. Yao, Y. Wan, et al. (2018)
• Inhibition of autophagy sensitizes malignant pleural mesothelioma cells to dual PI3K/mTOR inhibitors — N. Echeverry, G. Ziltener, et al. (2015)
• Cisplatin and resveratrol induce apoptosis and autophagy following oxidative stress in malignant mesothelioma cells — Y.J. Lee, G.J. Lee, et al. (2016)

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