An RNAi-based screen reveals PLK1, CDK1 and NDC80 as potential therapeutic targets in malignant pleural mesothelioma

Our plain-English summary of An RNAi-based screen reveals PLK1, CDK1 and NDC80 as potential therapeutic targets in malignant pleural mesothelioma, by A. Linton, Y.Y. Cheng, K. Griggs, et al (British Journal of Cancer, 2014).

The study

• Authors: A. Linton, Y.Y. Cheng, K. Griggs, L. Schedlich, M.B. Kirschner, S. Gattani, S. Srikaran, S. Chuan-Hao Kao, B.C. McCaughan, S. Klebe, N. van Zandwijk, G. Reid
• Journal: British Journal of Cancer
• Published: 2014;110(2):510-9
• Cited by: 40 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Malignant pleural mesothelioma (MPM) is an aggressive tumour originating in the thoracic mesothelium. Prognosis remains poor with 9- to 12-month median survival, and new targets for treatments are desperately needed.

Methods: Utilising an RNA interference (RNAi)-based screen of 40 genes overexpressed in tumours, including genes involved in the control of cell cycle, DNA replication and repair, we investigated potential therapeutic targets for MPM. Following in vitro characterisation of the effects of target silencing on MPM cells, candidates were assessed in tumour samples from 154 patients.

Results: Gene knockdown in MPM cell lines identified growth inhibition following knockdown of NDC80, CDK1 and PLK1. Target knockdown induced cell-cycle arrest and increased apoptosis. Using small-molecule inhibitors specific for these three proteins also led to growth inhibition of MPM cell lines, and Roscovitine (inhibitor of CDK1) sensitised cells to cisplatin. Protein expression was also measured in tumour samples, with markedly variable levels of CDK1 and PLK1 noted. PLK1 expression in over 10% of cells correlated significantly with a poor prognosis.

Conclusion: These results suggest that RNAi-based screening has utility in identifying new targets for MPM, and that inhibition of NDC80, CDK1 and PLK1 may hold promise for treatment of this disease.

In plain English

This was a laboratory study with an added analysis of patient tumour samples. It looked for possible new drug targets in malignant pleural mesothelioma. Using a technique called RNA interference, the authors switched off, one at a time, 40 genes previously reported to be overexpressed (produced at higher levels) in mesothelioma, in mesothelioma cell lines grown in the laboratory. Switching off seven genes cut growth by more than half. The authors focused on three of them, CDK1, NDC80 and PLK1, because drugs that block them already exist. Silencing these genes stalled cell division and increased cell death, and drugs blocking each one slowed cell-line growth. The CDK1 blocker roscovitine made two cell lines 2.5- to 4-fold more sensitive to the chemotherapy drug cisplatin. In tumour tissue from 154 Sydney surgical patients, those with PLK1 in 10% or more of tumour cells had a median survival of 5.0 months, against 15.5 months for the rest. This link held after allowing for age, sex and tumour type. CDK1 levels were not linked to survival. The authors concluded that the three genes are potential treatment targets. The study did not examine asbestos exposure.

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: an RNA interference screen in mesothelioma cell lines followed by drug tests, combined with a retrospective cohort analysis of patient tumour tissue
• Who was studied: Human mesothelioma cell lines H28, H226, H2452, MSTO-211H and MM05. Tumour samples from 154 patients with malignant pleural mesothelioma treated surgically in Sydney, Australia: 80 who had extrapleural pneumonectomy (EPP) between 1994 and 2004 and 74 who had pleurectomy/decortication (P/D) between 1991 and 2009, according to the Results section
• Exposure: No asbestos exposure was studied. The interventions were laboratory silencing of 40 cell-cycle and DNA replication/repair genes previously reported to be overexpressed in mesothelioma, and small-molecule inhibitors of CDK1 (roscovitine), NDC80 (INH1) and PLK1 (BI 2536), alone and combined with cisplatin or gemcitabine. Tumour levels of PLK1 and CDK1 protein were measured in patients.
• Main results:
  • In the initial screen, silencing with both test siRNAs cut growth by more than 50% for seven genes: BIRC5, CDK1, CHEK1, NDC80, PLK1, RRM1 and RRM2
  • Five days after transfection, silencing reduced cell growth by these amounts: CDK1 by 20% (MM05) to 80% (MSTO-211H); NDC80 by 25% (MM05) to 80% (MSTO-211H); PLK1 by 48% (MM05, H28, H2452) to 80% (MSTO-211H)
  • Silencing CDK1 or PLK1 doubled the share of cells stalled at the G2/M stage of cell division. Silencing all three targets increased early cell death (apoptosis) in H28 and MSTO-211H cells
  • Roscovitine and INH1 inhibited growth of all mesothelioma cell lines tested. The PLK1 inhibitor BI 2536 was cytotoxic at low nanomolar concentrations
  • Roscovitine increased cisplatin sensitivity 3.3-fold in MSTO-211H cells and 2.5- to 4-fold in H226 cells. INH1 gave a two-fold sensitisation in MSTO-211H cells but had no effect in H226 cells. BI 2536 had no effect on cisplatin toxicity in either line
  • In the 154 patients, median overall survival was 14.2 months, and 90% had died at the time of analysis. Median PLK1 expression was 3.05% of tumour cells (range 0 to 42.5%); 12% of patients had PLK1 expression over 10%. Median CDK1 expression was 16.0%
  • Median survival was 15.5 months for patients with PLK1 below 10% and 5.0 months for patients with PLK1 at 10% or above (P = 0.004). CDK1 expression was not linked to survival (15.7 vs 11.5 months, P = 0.388)
  • After adjusting for age, sex and histologic subtype, PLK1 at 10% or above remained linked to poorer survival: hazard ratio 2.05 (95% CI 1.21 to 3.46; P = 0.007)
• The authors' conclusion: The authors concluded that RNAi screening can uncover new treatment targets for mesothelioma. They identified PLK1, CDK1 and NDC80 as targets with roles in mesothelioma cell growth and PLK1 expression as an independent prognostic factor. They stated that further evaluation in animal (xenograft) models is warranted.
• Limitations the authors state:
  • NDC80 levels could not be measured in patient tumour samples because no suitable antibodies were available
  • The authors stated it is uncertain whether the level of PLK1 overexpression predicts how patients will respond to PLK1 inhibitors

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, Mesothelium, Prognosis, Median Survival, Apoptosis, Cisplatin.

Related studies

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• Abrogating G₂/M checkpoint through WEE1 inhibition in combination with chemotherapy as a promising therapeutic approach for mesothelioma — P. Indovina, E. Marcelli, et al. (2014)
• Extracellular signal-regulated kinase 5: a potential therapeutic target for malignant mesotheliomas — A. Shukla, J.M. Miller, et al. (2013)
• Data mining analysis of the PP2A cell cycle axis in mesothelioma patients — R. Pippa, S. Boffo, et al. (2020)
• Gli as a novel therapeutic target in malignant pleural mesothelioma — H. Li, N. Lui, et al. (2013)
• miR-193a-3p is a potential tumor suppressor in malignant pleural mesothelioma — M. Williams, M.B. Kirschner, et al. (2015)

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