Autophagy Correlates with the Therapeutic Responsiveness of Malignant Pleural Mesothelioma in 3D Models

Our plain-English summary of Autophagy Correlates with the Therapeutic Responsiveness of Malignant Pleural Mesothelioma in 3D Models, by D. Barbone, C. Follo, N. Echeverry, et al (PloS One, 2015).

The study

• Authors: D. Barbone, C. Follo, N. Echeverry, V.H. Gerbaudo, A. Klabatsa, R. Bueno, E. Felley-Bosco, V.C. Broaddus
• Journal: PloS One
• Published: 2015;10(8):e0134825
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant pleural mesothelioma is a highly chemoresistant solid tumor. We have studied this apoptotic resistance using in vitro and ex vivo three-dimensional models, which acquire a high level of chemoresistance that can be reduced by PI3K/mTOR inhibitors. Here, we investigate the activity of GDC-0980, a novel dual PI3K/mTOR inhibitor, which has been proposed to be effective in mesothelioma. In this work, we aimed to identify mechanisms and markers of efficacy for GDC-0980 by utilizing 3D models of mesothelioma, both in vitro multicellular spheroids and ex vivo tumor fragment spheroids grown from patient tumor samples. We found that a subset of mesothelioma spheroids is sensitive to GDC-0980 alone and to its combination with chemotherapy. Unexpectedly, this sensitivity did not correlate with the activation of the Akt/mTOR pathway. Instead, sensitivity to GDC-0980 correlated with the presence of constitutive ATG13 puncta, a feature of autophagy, a cellular program that supports cells under stress. In tumor fragment spheroids grown from 21 tumors, we also found a subset (n = 11) that was sensitive to GDC-0980, a sensitivity that also correlated with the presence of ATG13 puncta. Interference with autophagy by siRNA of ATG7, an essential autophagic protein, increased the response to chemotherapy, but only in the sensitive multicellular spheroids. In the spheroids resistant to GDC-0980, autophagy appeared to play no role. In summary, we show that GDC-0980 is effective in mesothelioma 3D models that display ATG13 puncta, and that blockade of autophagy increases their response to chemotherapy. For the first time, we show a role for autophagy in the response to chemotherapy of 3D models of mesothelioma and propose ATG13 as a potential biomarker of the therapeutic responsiveness of mesothelioma.

In plain English

This was a laboratory study of mesothelioma tissue. It did not study asbestos exposure. The authors tested GDC-0980, an experimental drug that blocks the PI3K and mTOR pathways, on malignant pleural mesothelioma grown as three-dimensional clusters ("spheroids"). The spheroids came from six cell lines and from surgically removed tumors of 21 patients in Boston. The drug was given alone or with chemotherapy (cisplatin plus pemetrexed) or bortezomib. Three cell lines (M28, SARC, VAMT) and 11 of the 21 tumors responded to the drug. Three cell lines and 10 tumors did not. The drug had little to no effect on normal mesothelial cells. In the tumor samples, response did not match the level of an Akt pathway marker (p = 0.6713). Instead, the extra cell death when GDC-0980 was added to cisplatin plus pemetrexed correlated with the percentage of tumor cells showing clumps ("puncta") of a protein called ATG13 (R = 0.72). ATG13 puncta are a sign of autophagy, a process that helps cells survive stress. Blocking autophagy with ATG7 siRNA increased the response to chemotherapy only in the sensitive M28 spheroids. The authors proposed ATG13 puncta as a promising marker for identifying such tumors. They noted that ATG5 siRNA could not fully block autophagy.

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 and ex vivo) study using three-dimensional mesothelioma models: multicellular spheroids grown from cell lines and tumor fragment spheroids grown from patient tumor samples
• Who was studied: Six human mesothelioma cell lines (M28, REN, SARC, VAMT, JMN, MSTO-211H), normal human mesothelial cells, and tumor fragment spheroids from 21 tumor samples (11 epithelioid, 10 biphasic) obtained from extrapleural pneumonectomy or pleurectomy at Brigham and Women's Hospital, Boston
• Exposure: No asbestos exposure was studied. The exposures were the drug GDC-0980 (1 μM), alone or combined with cisplatin (200 μM) plus pemetrexed (10 μM) or with bortezomib (25 nM), plus siRNA blocking of the autophagy proteins ATG5 and ATG7
• Main results:
  • Among the six cell lines grown as spheroids, M28, SARC and VAMT were sensitive to GDC-0980; REN, JMN and MSTO-211H were resistant
  • Of the 21 tumor fragment spheroids, 11 responded significantly to GDC-0980 and 10 did not
  • GDC-0980 had little to no activity in normal mesothelial cells
  • In multicellular spheroids from cell lines, the sensitive spheroids had higher P-Akt than the resistant ones. In tumor fragment spheroids, response did not correlate with P-Akt levels (p = 0.6713, 11 sensitive vs 10 resistant)
  • GDC-0980 increased autophagy only in the sensitive spheroids
  • Among cell-line spheroids, only the GDC-0980-sensitive ones showed ATG13 puncta. All sensitive tumor fragment spheroids had more than 10% of cells with ATG13 puncta; the resistant ones showed little to no ATG13 staining
  • In the tumor fragment spheroids, the response to GDC-0980, measured as the additional apoptosis when GDC-0980 was added to cisplatin plus pemetrexed, showed a linear correlation with the percentage of cells with ATG13 puncta (R = 0.72)
  • Blocking autophagy with ATG7 siRNA increased the response to GDC-0980 and to chemotherapy only in M28 spheroids, not in REN spheroids
• The authors' conclusion: The authors concluded that autophagy is a possible therapeutic target in a subset of mesotheliomas. They proposed the presence of ATG13 puncta as a promising autophagy marker to identify these tumors.
• Limitations the authors state:
  • The authors did not know whether the lack of an increase in autophagy in resistant tumors means those tumors were not stressed or that their autophagy is defective
  • ATG5 siRNA did not completely block autophagy in M28 and REN spheroids
  • The authors noted that autophagy cannot currently be measured confidently in fixed or in vivo tumor tissue

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, Mesothelioma, Chemotherapy, Biomarker.

Related studies

• Inhibition of autophagy sensitizes malignant pleural mesothelioma cells to dual PI3K/mTOR inhibitors — N. Echeverry, G. Ziltener, et al. (2015)
• Autophagy initiation correlates with the autophagic flux in 3D models of mesothelioma and with patient outcome — C. Follo, D. Barbone, et al. (2016)
• 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)
• Inhibition of autophagy potentiates pemetrexed and simvastatin-induced apoptotic cell death in malignant mesothelioma and non-small cell lung cancer cells — K.E. Hwang, Y.S. Kim, et al. (2015)
• MET and PI3K/mTOR as a potential combinatorial therapeutic target in malignant pleural mesothelioma — R. Kanteti, I. Dhanasingh, et al. (2014)

Browse more research in PloS One, or return to medical research.