Vorinostat/SAHA-induced apoptosis in malignant mesothelioma is FLIP/caspase 8-dependent and HR23B-independent

Our plain-English summary of Vorinostat/SAHA-induced apoptosis in malignant mesothelioma is FLIP/caspase 8-dependent and HR23B-independent, by J.L. Hurwitz, I. Stasik, E.M. Kerr, et al (European Journal of Cancer, 2012).

The study

• Authors: J.L. Hurwitz, I. Stasik, E.M. Kerr, C. Holohan, K.M. Redmond, K.M. McLaughlin, S. Busacca, D. Barbone, V.C. Broaddus, S.G. Gray, K.J. O'Byrne, P.G. Johnston, D.A. Fennell, D.B. Longley
• Journal: European Journal of Cancer
• Published: 2012;48(7):1096-107
• Cited by: 41 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Introduction: Malignant pleural mesothelioma (MPM) is a rapidly fatal malignancy that is increasing in incidence. The caspase 8 inhibitor FLIP is an anti-apoptotic protein over-expressed in several cancer types including MPM. The histone deacetylase (HDAC) inhibitor Vorinostat (SAHA) is currently being evaluated in relapsed mesothelioma. We examined the roles of FLIP and caspase 8 in regulating SAHA-induced apoptosis in MPM.

Methods: The mechanism of SAHA-induced apoptosis was assessed in 7 MPM cell lines and in a multicellular spheroid model. SiRNA and overexpression approaches were used, and cell death was assessed by flow cytometry, Western blotting and clonogenic assays.

Results: RNAi-mediated FLIP silencing resulted in caspase 8-dependent apoptosis in MPM cell line models. SAHA potently down-regulated FLIP protein expression in all 7 MPM cell lines and in a multicellular spheroid model of MPM. In 6/7 MPM cell lines, SAHA treatment resulted in significant levels of apoptosis induction. Moreover, this apoptosis was caspase 8-dependent in all six sensitive cell lines. SAHA-induced apoptosis was also inhibited by stable FLIP overexpression. In contrast, down-regulation of HR23B, a candidate predictive biomarker for HDAC inhibitors, significantly inhibited SAHA-induced apoptosis in only 1/6 SAHA-sensitive MPM cell lines. Analysis of MPM patient samples demonstrated significant inter-patient variations in FLIP and caspase 8 expressions. In addition, SAHA enhanced cisplatin-induced apoptosis in a FLIP-dependent manner.

Conclusions: These results indicate that FLIP is a major target for SAHA in MPM and identifies FLIP, caspase 8 and associated signalling molecules as candidate biomarkers for SAHA in this disease.

Copyright © 2011 Elsevier Ltd. All rights reserved.

In plain English

This was a laboratory study of the drug vorinostat (also called SAHA) in malignant pleural mesothelioma. It did not study asbestos exposure. The authors used seven mesothelioma cell lines, a three-dimensional "spheroid" model grown from one line (Ren), and tissue from 20 patients collected at surgery in Leicester: 5 benign samples and 15 mesothelioma samples. Switching off the protein FLIP caused cell death through caspase 8 in three cell lines. SAHA lowered FLIP in the cell lines and in the spheroids. After 24 hours at 5 micromolar, five cell lines were sensitive to SAHA-induced cell death, one (MM98) was less sensitive and one (H2591) was resistant. Cells made to produce extra FLIP died less after SAHA. Silencing caspase 8 significantly reduced SAHA-induced death in six lines. Silencing HR23B, a proposed predictor of response, significantly reduced death in only one of six lines (Ren). Patient tumours had higher but variable FLIP and procaspase 8 levels than benign tissue. In each cell line, SAHA plus cisplatin increased cell death compared with either drug alone. The authors concluded that FLIP and caspase 8 may be useful markers of response to SAHA.

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 using mesothelioma cell lines and a multicellular spheroid model, plus protein analysis of patient tumour samples
• Who was studied: Seven malignant pleural mesothelioma cell lines (Ren, NCI-H28, ONE58, MSTO-211H, H2461, H2591, MM98). Also anonymised tissue from 20 patients who had no treatment before surgery, collected at debulking surgery at Glenfield Hospital, Leicester. These were 5 benign mesothelial samples and biphasic (n = 5), sarcomatoid (n = 4) and epithelial (n = 6) mesothelioma samples.
• Exposure: No asbestos exposure was studied. The treatments were the drug vorinostat/SAHA (1, 5 or 10 micromolar), cisplatin (7.5 micromolar), recombinant TRAIL, and gene silencing of FLIP, caspase 8, FADD and HR23B.
• Main results:
  • Silencing FLIP caused caspase 8 activation and PARP cleavage (a sign of cell death) in the Ren, ONE58 and NCI-H28 cell lines. When caspase 8 was also silenced, this cell death was blocked.
  • After 24 hours of 5 micromolar SAHA, five cell lines were sensitive to cell death (Ren, ONE58, NCI-H28, MSTO, H2461), MM98 was less sensitive, and H2591 was resistant.
  • In spheroids grown from Ren cells, SAHA lowered FLIP and activated caspase 3. The effect increased with dose.
  • In Ren cells engineered to overproduce either form of FLIP, SAHA-induced cell death was significantly inhibited.
  • Silencing caspase 8 significantly reduced SAHA-induced cell death: P less than 0.01 in Ren, ONE58 and NCI-H28, and P less than 0.05 in MSTO, MM98 and H2461. H2591 was resistant to SAHA.
  • Of the six SAHA-sensitive cell lines, silencing HR23B significantly reduced SAHA-induced cell death only in Ren.
  • In patient samples, FLIP and procaspase 8 levels were higher overall in mesothelioma than in benign tissue, but they varied among the mesothelioma samples.
  • In each cell line, SAHA combined with cisplatin significantly increased cell death compared with either drug alone. Overproduction of either form of FLIP significantly inhibited the cell death from the combination.
• The authors' conclusion: The authors concluded that FLIP and caspase 8 are key determinants of sensitivity to vorinostat/SAHA in mesothelioma and may be useful biomarkers of response to this drug.

Topics

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

Medical terms in this study, explained in our Lexicon: Apoptosis, Malignant Mesothelioma, Pleural Mesothelioma, Mesothelioma, Biomarker, Cisplatin.

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