Splicing modulation as novel therapeutic strategy against diffuse malignant peritoneal mesothelioma

Our plain-English summary of Splicing modulation as novel therapeutic strategy against diffuse malignant peritoneal mesothelioma, by R. Sciarrillo, A. Wojtuszkiewicz, B. El Hassouni, et al (EBioMedicine, 2019).

The study

• Authors: R. Sciarrillo, A. Wojtuszkiewicz, B. El Hassouni, N. Funel, P. Gandellini, T. Lagerweij, S. Buonamici, M. Blijlevens, E.A. Zeeuw van der Laan, N. Zaffaroni, M. Deraco, S. Kusamura, T. Würdinger, G.J. Peters, C.F.M. Molthoff, G. Jansen, G.J.L. Kaspers, J. Cloos, E. Giovannetti
• Journal: EBioMedicine
• Published: 2019;39:215-225
• Cited by: 56 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Introduction: Therapeutic options for diffuse malignant peritoneal mesothelioma (DMPM) are limited to surgery and locoregional chemotherapy. Despite improvements in survival rates, patients eventually succumb to disease progression. We investigated splicing deregulation both as molecular prognostic factor and potential novel target in DMPM, while we tested modulators of SF3b complex for antitumor activity.

Methods: Tissue-microarrays of 64 DMPM specimens were subjected to immunohistochemical assessment of SF3B1 expression and correlation to clinical outcome. Two primary cell cultures were used for gene expression profiling and in vitro screening of SF3b modulators. Drug-induced splicing alterations affecting downstream cellular pathways were detected through RNA sequencing. Ultimately, we established bioluminescent orthotopic mouse models to test the efficacy of splicing modulation in vivo.

Results: Spliceosomal genes are differentially upregulated in DMPM cells compared to normal tissues and high expression of SF3B1 correlated with poor clinical outcome in univariate and multivariate analysis. SF3b modulators (Pladienolide-B, E7107, Meayamycin-B) showed potent cytotoxic activity in vitro with IC50 values in the low nanomolar range. Differential splicing analysis of Pladienolide-B-treated cells revealed abundant alterations of transcripts involved in cell cycle, apoptosis and other oncogenic pathways. This was validated by RT-PCR and functional assays. E7107 demonstrated remarkable in vivo antitumor efficacy, with significant improvement of survival rates compared to vehicle-treated controls.

Conclusions: SF3B1 emerged as a novel potential prognostic factor in DMPM. Splicing modulators markedly impair cancer cell viability, resulting also in potent antitumor activity in vivo. Our data designate splicing as a promising therapeutic target in DMPM.

Copyright © 2018 The Authors. Published by Elsevier B.V. All rights reserved.

In plain English

This laboratory study examined diffuse malignant peritoneal mesothelioma (DMPM), a cancer of the abdominal lining. It tested experimental drugs that interfere with RNA splicing through a protein complex called SF3b. The study did not look at asbestos exposure. The authors measured the splicing protein SF3B1 in tumor tissue from 64 DMPM patients treated in Milan between 1995 and 2013. Higher SF3B1 levels were associated with shorter overall and progression-free survival, and SF3B1 kept its independent prognostic value in a multivariate analysis. In two patient-derived tumor cell cultures, the drugs Pladienolide-B, E7107 and Meayamycin-B cut cell growth by half at concentrations between 0.34 and 1.57 nanomolar. Pladienolide-B altered 2804 splicing events in 1304 genes, raised the share of dying cells to 35% and 81% in the two cultures, and reduced cell migration. In mice with implanted tumors (6 per group), E7107 lowered the tumor signal and lengthened survival compared with control mice. Three treated mice were free of tumor cells at the end. The authors concluded that SF3B1 may be a prognostic factor that needs validation studies, and that splicing-modulating drugs may be applicable to future DMPM treatment.

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 combining analysis of patient tumor tissue against survival, experiments on patient-derived cell cultures, and an animal (mouse) experiment
• Who was studied: Tumor tissue from 64 DMPM patients treated with cytoreductive surgery and hyperthermic intraperitoneal chemotherapy at the National Cancer Institute of Milan, August 1995 to October 2013; two primary epithelioid DMPM cell cultures (MesoII and STO); nude female mice with implanted tumors, 6 animals per treatment arm
• Exposure: No asbestos exposure was studied. The exposures were three experimental drugs that modulate the SF3b splicing complex: Pladienolide-B, E7107 and Meayamycin-B. In mice, E7107 was given into the abdomen four times (two doses of 5 mg/kg and two of 2.5 mg/kg).
• Main results:
  • Compared with three normal mesothelium tissues, the two DMPM cell cultures had 4042 genes expressed differently: 2217 higher and 1825 lower. Splicing-related pathways were overrepresented among the genes expressed more highly.
  • In the 64 patients, high SF3B1 protein levels were significantly correlated with shorter overall and progression-free survival in univariate analysis.
  • Multivariate analysis that included established predictors of treatment outcome confirmed SF3B1 as an independent prognostic factor in the patients.
  • In the cell cultures, the drug concentrations that inhibited 50% of cell growth (MesoII and STO respectively) were:
• Pladienolide-B: 1.57 plus or minus 0.29 nM and 0.82 plus or minus 0.1 nM
• E7107: 1.27 plus or minus 0.04 nM and 0.34 plus or minus 0.08 nM
• Meayamycin-B: 1.19 plus or minus 0.43 nM and 1.00 plus or minus 0.3 nM
  • In MesoII and STO cells, treatment with 30 nM Pladienolide-B produced 2804 significant alternative splicing events affecting 1304 genes.
  • After 48 hours of Pladienolide-B, cell death (apoptosis) rose with dose, reaching 35% in MesoII cells and 81% in STO cells.
  • In a 24-hour wound-healing assay, Pladienolide-B significantly inhibited migration of the DMPM cells compared with untreated controls.
  • In mice, the tumor light signal was significantly lower in E7107-treated animals than in untreated controls from Day 8 (P = 0.0011).
  • E7107-treated mice survived significantly longer than vehicle-treated control mice. Control animals were sacrificed at humane end-points after about 50 days.
  • Of the 6 E7107-treated mice, 3 were clear of tumor cells at the end of the experiment. Two died from disease progression, and one died from infection with no tumor found at post-mortem.
• The authors' conclusion: The authors concluded that their data assign a new prognostic role to SF3B1, which prompts validation studies. They also concluded that their laboratory and animal data support the idea that drugs modulating splicing may be applicable to future clinical practice in DMPM.
• Limitations the authors state:
  • The authors noted the limitation of comparing normal mesothelium tissues with primary tumor cells in the gene expression analysis.
  • The authors stated that whether giving the drug into the abdomen reduces side effects, especially nervous-system effects, was not investigated in this study.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma, Peritoneal mesothelioma.

Medical terms in this study, explained in our Lexicon: Peritoneal Mesothelioma, Chemotherapy, Disease Progression, Multivariate Analysis, Apoptosis.

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