Expression profiling stratifies mesothelioma tumors and signifies deregulation of spindle checkpoint pathway and microtubule network with therapeutic implications

Our plain-English summary of Expression profiling stratifies mesothelioma tumors and signifies deregulation of spindle checkpoint pathway and microtubule network with therapeutic implications, by M.B. Suraokar, M.I. Nunez, L. Diao, et al (Annals of Oncology, 2014).

The study

• Authors: M.B. Suraokar, M.I. Nunez, L. Diao, C.W. Chow, D. Kim, C. Behrens, H. Lin, S. Lee, G. Raso, C. Moran, D. Rice, R. Mehran, J.J. Lee, H.I. Pass, J. Wang, A.A. Momin, B.P. James, A. Corvalan, K. Coombes, A. Tsao, I.I. Wistuba
• Journal: Annals of Oncology
• Published: 2014;25(6):1184-92
• Cited by: 49 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Malignant pleural mesothelioma (MPM) is a lethal neoplasm exhibiting resistance to most treatment regimens and requires effective therapeutic options. Though an effective strategy in many cancer, targeted therapy is relatively unexplored in MPM because the therapeutically important oncogenic pathways and networks in MPM are largely unknown.

Materials And Methods: We carried out gene expression microarray profiling of 53 surgically resected MPMs tumors along with paired normal tissue. We also carried out whole transcriptomic sequence (RNA-seq) analysis on eight tumor specimens. Taqman-based quantitative Reverse-transcription polymerase chain reaction (qRT-PCR), western analysis and immunohistochemistry (IHC) analysis of mitotic arrest deficient-like 1 (MAD2L1) was carried out on tissue specimens. Cell viability assays of MPM cell lines were carried out to assess sensitivity to specific small molecule inhibitors.

Results: Bioinformatics analysis of the microarray data followed by pathway analysis revealed that the mitotic spindle assembly checkpoint (MSAC) pathway was most significantly altered in MPM tumors with upregulation of 18 component genes, including MAD2L1 gene. We validated the microarray data for MAD2L1 expression using quantitative qRT-PCR and western blot analysis on tissue lysates. Additionally, we analyzed expression of the MAD2L1 protein by IHC using an independent tissue microarray set of 80 MPM tissue samples. Robust clustering of gene expression data revealed three novel subgroups of tumors, with unique expression profiles, and showed differential expression of MSAC pathway genes. Network analysis of the microarray data showed the cytoskeleton/spindle microtubules network was the second-most significantly affected network. We also demonstrate that a nontaxane small molecule inhibitor, epothilone B, targeting the microtubules have great efficacy in decreasing viability of 14 MPM cell lines.

Conclusions: Overall, our findings show that MPM tumors have significant deregulation of the MSAC pathway and the microtubule network, it can be classified into three novel molecular subgroups of potential therapeutic importance and epothilone B is a promising therapeutic agent for MPM.

© The Author 2014. Published by Oxford University Press on behalf of the European Society for Medical Oncology. All rights reserved. For permissions, please email: [email protected].

In plain English

This was a laboratory study of malignant pleural mesothelioma (MPM) tumors. It did not examine asbestos exposure. The authors measured gene expression in 53 surgically removed tumors (35 epitheloid, 12 biphasic and 6 sarcomatoid) and compared them with 38 paired non-tumor tissue samples. The most significantly altered pathway was the mitotic spindle assembly checkpoint, a set of genes that checks cell division. Eighteen of its component genes were expressed at higher levels in tumors. The tumors fell into three molecular subgroups. These partly overlapped with tumor type but were not significantly associated with features such as overall survival. One checkpoint gene, MAD2L1, was 3.09-fold higher in tumors. In a separate set of 80 tumors, higher MAD2L1 protein in cell nuclei was associated with shorter overall survival in a simple analysis (P = 0.043), but not after adjusting for gender, stage and lymph node status. In 14 mesothelioma cell lines grown in the laboratory, not in patients, the drug epothilone B inhibited the cells at a median IC50 of 1.5 nM, compared with 416 nM for paclitaxel. The authors concluded that epothilone B is a promising therapeutic agent for MPM.

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 surgically resected tumor tissue (gene expression microarrays, RNA sequencing, qPCR, western blot, immunohistochemistry) plus drug testing in mesothelioma cell lines
• Who was studied: 53 surgically resected malignant pleural mesothelioma tumors (35 epitheloid, 12 biphasic, 6 sarcomatoid) with 38 paired nontumor tissues. There was also an independent set of 80 tumors on tissue microarrays, and 14 MPM cell lines. Where and when patients were treated is not stated in the text.
• Exposure: Not studied: the article does not report patients' asbestos exposure, fiber types or occupations.
• Main results:
  • The mitotic spindle assembly checkpoint (MSAC) pathway was the most significantly deregulated pathway. Eighteen of its component genes, including MAD2L1, were upregulated (expressed at higher levels) in MPM tumors.
  • Cluster analysis defined three molecular subgroups. Subgroup 1 held 19 of the 35 epitheloid tumors, subgroup 2 held 7 of 12 biphasic tumors and subgroup 3 held 4 of 6 sarcomatoid tumors.
  • The authors found no significant association between subgroup membership and clinico-pathological features such as overall survival.
  • On the microarray, the MAD2L1 transcript was 3.09-fold higher in tumors than in paired normal tissue.
  • By RT-qPCR, 23 MPM tumor samples had significantly higher MAD2L1 expression than their paired controls. The text gives P = 0.036; the figure legend gives P = 0.0036.
  • By western blot, tumors (80 cases) showed a 2.7-fold increase in mean MAD2L1 protein compared with normal samples (54 cases), with P less than 0.0001.
  • In the independent set of 80 tumors, cytoplasmic MAD2L1 was significantly higher in epitheloid tumors than in the other two histotypes.
  • Tumors with lymph node metastasis had higher cytoplasmic MAD2L1 (mean score 57.1) than tumors without metastasis (mean score 33.2).
  • In univariate analysis, higher nuclear MAD2L1 was associated with lower overall survival in all MPM patients.
  • In multivariate analysis adjusting for gender, pathological stage and lymph node status, MAD2L1 was not significantly associated with survival.
  • RNA sequencing of eight subgroup 3 tumors found no mutations in MSAC pathway genes.
  • In 14 MPM cell lines, epothilone B inhibited proliferation with IC50 values from 0.01 to 27 nM (median 1.5 nM).
  • In the same cell lines, paclitaxel IC50 values ranged from 4 to 25285 nM (median 416 nM).
  • Inhibitors of five MSAC-related kinases were not effective in the cell lines.
  • Etoposide was relatively ineffective overall (median IC50 1928 nM) but was effective against two sarcomatoid cell lines (DM3 IC50 1.6 nM, Mero-14 IC50 247 nM).
• The authors' conclusion: The authors concluded that MPM tumors show significant deregulation of the MSAC pathway and the microtubule network, that the tumors can be classified into three molecular subgroups of potential therapeutic importance, and that epothilone B is a promising therapeutic agent for MPM.
• Limitations the authors state:
  • The activity of MAD2L1 depends on phosphorylation, and no commercial antibodies were available to detect its phosphorylated form.
  • The authors state that further functional studies in cell lines are needed to explore whether higher nuclear MAD2L1 leads to a more or less aggressive phenotype.

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: Mesothelioma, Pleural Mesothelioma, Neoplasm, Targeted Therapy, Immunohistochemistry.

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