SAHA overcomes FLIP-mediated inhibition of SMAC mimetic-induced apoptosis in mesothelioma

Our plain-English summary of SAHA overcomes FLIP-mediated inhibition of SMAC mimetic-induced apoptosis in mesothelioma, by N. Crawford, I. Stasik, C. Holohan, et al (Cell Death & Disease, 2013).

The study

• Authors: N. Crawford, I. Stasik, C. Holohan, J. Majkut, M. McGrath, P.G. Johnston, G. Chessari, G.A. Ward, D.J. Waugh, D.A. Fennell, D.B. Longley
• Journal: Cell Death & Disease
• Published: 2013;4(7):e733
• Cited by: 19 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant pleural mesothelioma (MPM) is a highly pro-inflammatory malignancy that is rapidly fatal and increasing in incidence. Cytokine signaling within the pro-inflammatory tumor microenvironment makes a critical contribution to the development of MPM and its resistance to conventional chemotherapy approaches. SMAC mimetic compounds (SMCs) are a promising class of anticancer drug that are dependent on tumor necrosis factor alpha (TNFα) signaling for their activity. As circulating TNFα expression is significantly elevated in MPM patients, we examined the sensitivity of MPM cell line models to SMCs. Surprisingly, all MPM cell lines assessed were highly resistant to SMCs either alone or when incubated in the presence of clinically relevant levels of TNFα. Further analyses revealed that MPM cells were sensitized to SMC-induced apoptosis by siRNA-mediated downregulation of the caspase 8 inhibitor FLIP, an antiapoptotic protein overexpressed in several cancer types including MPM. We have previously reported that FLIP expression is potently downregulated in MPM cells in response to the histone deacetylase inhibitor (HDACi) Vorinostat (SAHA). In this study, we demonstrate that SAHA sensitizes MPM cells to SMCs in a manner dependent on its ability to downregulate FLIP. Although treatment with SMC in the presence of TNFα promoted interaction between caspase 8 and the necrosis-promoting RIPK1, the cell death induced by combined treatment with SAHA and SMC was apoptotic and mediated by caspase 8. These results indicate that FLIP is a major inhibitor of SMC-mediated apoptosis in MPM, but that this inhibition can be overcome by the HDACi SAHA.

In plain English

This was a laboratory study of four human malignant pleural mesothelioma cell lines (REN, MM98, H28 and JU77). No patients were studied, and asbestos was not tested. The authors treated the cells with AT-IAP, an experimental drug of the type called SMAC mimetics. They gave it alone or with the inflammatory signal TNF-alpha at 10 ng/ml. None of the cell lines was sensitive to AT-IAP at concentrations up to 10 micromolar, with or without TNF-alpha. Lowering the level of a protein called FLIP made the cells more sensitive to AT-IAP combined with TNF-alpha. The drug SAHA (vorinostat) lowered FLIP in three of the four lines but not in JU77. In those three lines it increased cell death from AT-IAP with TNF-alpha. In REN cells, this effect was blocked when FLIP was overexpressed or when caspase 8 was reduced, and further tests in REN cells indicated that the cell death was apoptotic. The authors concluded that SAHA, or a similar drug, combined with a SMAC mimetic could be a promising approach for treating mesothelioma. Two authors worked for Astex Pharmaceuticals, which makes AT-IAP, and one consulted for Merck, which makes vorinostat.

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) study of human mesothelioma cell lines
• Who was studied: Four malignant pleural mesothelioma cell lines: REN, MM98, H28 (NCI-H28) and JU77. No human subjects.
• Exposure: No asbestos exposure was studied. The cells were treated with the SMAC mimetic AT-IAP (from Astex Pharmaceuticals), TNF-alpha (10 ng/ml in most experiments), the HDAC inhibitor SAHA (vorinostat) and cisplatin. Levels of FLIP and other proteins were lowered using siRNA.
• Main results:
  • None of the four mesothelioma cell lines was sensitive to AT-IAP at concentrations up to 10 micromolar, either alone or together with TNF-alpha.
  • Lowering the IAP proteins one at a time moderately increased sensitivity only in REN cells cocultured with TNF-alpha. It did not sensitize the other three lines.
  • In REN cells cocultured with TNF-alpha, lowering FLIP increased cell death from AT-IAP. The effect was strongest when both forms of FLIP were lowered together, and results were similar in MM98 cells.
  • In H28 and JU77 cells, lowering the long form FLIP(L), but not the short form FLIP(S), significantly increased cell death from AT-IAP with TNF-alpha.
  • Cisplatin lowered FLIP(S) in some cell lines but had little effect on FLIP(L).
  • SAHA lowered both forms of FLIP in REN, MM98 and H28 cells but not in JU77 cells. Cell death from AT-IAP with TNF-alpha was significantly increased in the three lines where FLIP fell, and not increased in JU77.
  • In REN cells, overexpressing either form of FLIP blocked the cell-killing effect of SAHA combined with AT-IAP and TNF-alpha.
  • In REN cells, the caspase inhibitor z-VAD-fmk blocked the cell death, but the necroptosis inhibitor Nec-1 did not, indicating the death was apoptotic. Lowering caspase 8 in REN cells completely abolished it.
• The authors' conclusion: The authors concluded that combining SAHA (or a similar HDAC inhibitor) with a SMAC mimetic could be a promising therapeutic approach for mesothelioma. They also suggested that circulating TNF-alpha could be a candidate biomarker for sensitivity to the combination.

Topics

Medical terms in this study, explained in our Lexicon: Apoptosis, Mesothelioma, Pleural Mesothelioma, Cytokine, Tumor Microenvironment, Chemotherapy, Necrosis.

Related studies

• Vorinostat/SAHA-induced apoptosis in malignant mesothelioma is FLIP/caspase 8-dependent and HR23B-independent — J.L. Hurwitz, I. Stasik, et al. (2012)
• Mechanisms of neuroblastoma cell growth inhibition by CARP-1 functional mimetics — M. Muthu, V.T. Cheriyan, et al. (2014)
• Vorinostat eliminates multicellular resistance of mesothelioma 3D spheroids via restoration of Noxa expression — D. Barbone, P. Cheung, et al. (2012)
• Histone deacetylase inhibitors in malignant pleural mesothelioma: preclinical rationale and clinical trials — P.K. Paik, L.M. Krug (2010)
• Death receptor 5 and cellular FLICE-inhibitory protein regulate pemetrexed-induced apoptosis in human lung cancer cells — L. Su, G. Liu, et al. (2011)
• Dual HDAC and PI3K Inhibitor CUDC-907 Inhibits Growth of Pleural Mesothelioma: The Impact of Cisplatin Sensitivity and Myc Expression — L. Hegedüs, S. Qaisieh, et al. (2025)

Browse more research in Cell Death & Disease, or return to medical research.