ZDHHC8 knockdown enhances radiosensitivity and suppresses tumor growth in a mesothelioma mouse model

Our plain-English summary of ZDHHC8 knockdown enhances radiosensitivity and suppresses tumor growth in a mesothelioma mouse model, by H. Sudo, A.B. Tsuji, A. Sugyo, et al (Cancer Science, 2012).

The study

• Authors: H. Sudo, A.B. Tsuji, A. Sugyo, Y. Ogawa, M. Sagara, T. Saga
• Journal: Cancer Science
• Published: 2012;103(2):203-9
• Cited by: 31 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Mesothelioma is an aggressive tumor caused by asbestos exposure, the incidence of which is predicted to increase globally. The prognosis of patients with mesothelioma undergoing conventional therapy is poor. Radiation therapy for mesothelioma is of limited use because of the intrinsic radioresistance of tumor cells compared with surrounding normal tissue. Thus, a novel molecular-targeted radiosensitizing agent that enhances the radiosensitivity of mesothelioma cells is required to improve the therapeutic efficacy of radiation therapy. ZDHHC8 knockdown reduces cell survival and induces an impaired G(2) /M checkpoint after X-irradiation in HEK293 cells. In the present study, we further analyzed the effect of the combination of ZDHHC8 knockdown and X-irradiation and assessed its therapeutic efficacy in mesothelioma models. SiRNA-induced ZDHHC8 knockdown in 211H and H2052 mesothelioma cells significantly reduced cell survival after X-irradiation. In 211H cells treated with ZDHHC8 siRNA and X-irradiation, the G(2) /M checkpoint was impaired and there was an increase in the number of cells with micronuclei, as well as apoptotic cells, in vitro. In 211H tumor-bearing mice, ZDHHC8 siRNA and X-irradiation significantly suppressed tumor growth, whereas ZDHHC8 siRNA alone did not. Immunohistochemical analysis showed decreased cell proliferation and induction of apoptosis in tumors treated with ZDHHC8 siRNA and X-irradiation, but not with ZDHHC8 siRNA alone. These results suggest that ZDHHC8 knockdown with X-irradiation induces chromosomal instability and apoptosis through the impaired G(2) /M checkpoint. In conclusion, the combination of ZDHHC8 siRNA and X-irradiation has the potential to improve the therapeutic efficacy of radiation therapy for malignant mesothelioma.

© 2011 Japanese Cancer Association.

In plain English

This laboratory and mouse study from Japan did not involve people or asbestos. The authors tested whether lowering expression of the ZDHHC8 gene with a small RNA (siRNA) made human mesothelioma cells more sensitive to X-rays. In 211H cells, where the siRNA cut the gene's messenger RNA to 14.3% of the control level, survival was significantly lower at all X-ray doses, with a threefold drop at 4 Gy. H2052 cells showed reduced survival at 4, 6 and 8 Gy. No significant differences appeared in H28 or H2452 mesothelioma cells or MeT-5A mesothelial cells, possibly due to weaker knockdown, the authors said. In treated 211H cells, the normal pause in cell division after radiation was largely missing, the rise in cells with micronuclei, a chromosome-breakage marker, was about twice that in controls, and signs of programmed cell death increased. In mice with 211H tumors (five per group), siRNA plus 15 Gy X-rays significantly slowed tumor growth; siRNA alone did not. The authors concluded the combination has potential to improve radiation therapy for malignant mesothelioma. They noted that tumor-targeted siRNA carriers still need development.

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 experiments on human cell lines plus an animal experiment (human tumor cells implanted under the skin of mice)
• Who was studied: Four human malignant mesothelioma cell lines (211H, H28, H2052, H2452) and one mesothelial cell line (MeT-5A), obtained from the American Type Culture Collection. Also nude mice carrying 211H tumors, which the authors call a sarcomatoid mesothelioma model, with five mice per treatment group.
• Exposure: No asbestos exposure was studied. The cells were treated with siRNA to reduce expression of the ZDHHC8 gene, then X-irradiated with 2, 4, 6 or 8 Gy. The mouse tumors were injected with siRNA and X-irradiated with 15 Gy 72 hours later.
• Main results:
  • In 211H cells, ZDHHC8 mRNA was reduced to 14.3 ± 2.7% (siRNA #1) and 23.3 ± 6.0% (siRNA #2) of the level in mock control cells.
  • 211H cells treated with ZDHHC8 siRNA had significantly reduced survival at all X-ray doses compared with control cells (P < 0.01). At 4 Gy the surviving fraction decreased threefold.
  • Survival of H2052 mesothelioma cells treated with ZDHHC8 siRNA was significantly reduced after 4, 6 and 8 Gy. There were no significant differences for the H28 and H2452 mesothelioma cell lines or the MeT-5A mesothelial cell line.
  • In 211H cells, 8 hours after 4 Gy, the share of cells paused at the G2/M checkpoint rose to 61.0 ± 4.9% in mock control cells and 53.3 ± 5.1% in negative siRNA cells. In ZDHHC8 siRNA cells it rose only to 18.8 ± 4.3%.
  • After X-irradiation, the increase in micronucleus formation (a marker of chromosome breakage) in ZDHHC8 siRNA 211H cells was approximately twofold higher than in mock control or negative siRNA cells (P < 0.01).
  • In ZDHHC8 siRNA cells, levels of activated caspase-3 (an apoptosis marker) increased 1.7-fold compared with non-irradiated cells, peaking 8 hours after X-irradiation (P < 0.01).
  • In mice, ZDHHC8 siRNA plus X-irradiation significantly suppressed tumor growth compared with the other treatments, from 10 days after irradiation onward (P < 0.01). Tumors treated with ZDHHC8 siRNA alone did not differ significantly from tumors treated with negative siRNA.
  • After X-irradiation, proliferating (Ki-67-positive) cells were 28.1 ± 2.8% in ZDHHC8 siRNA-treated tumors and 38.5 ± 4.1% in negative siRNA-treated tumors (P < 0.05).
  • After X-irradiation, apoptotic cells were 9.7 ± 1.5% in ZDHHC8 siRNA-treated tumors and 2.4 ± 1.0% in negative siRNA-treated tumors (P < 0.01).
• The authors' conclusion: The authors concluded that combining ZDHHC8 siRNA with X-irradiation has the potential to improve the effectiveness of radiation therapy for malignant mesothelioma.
• Limitations the authors state:
  • The lack of effect in H28, H2452 and MeT-5A cells may be due to insufficient knockdown of the gene.
  • Cell cycle distribution after X-irradiation could not be analyzed in the mouse tumors.
  • Other types of cell death besides apoptosis may also have occurred, which needs further study.
  • Before clinical use, specific and effective carriers to deliver siRNA to tumor tissue must be developed.

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Asbestos Exposure, Prognosis, Micronuclei, Apoptosis, Malignant Mesothelioma.

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