Downregulation of thymidylate synthase by RNAi molecules enhances the antitumor effect of pemetrexed in an orthotopic malignant mesothelioma xenograft mouse model

Our plain-English summary of Downregulation of thymidylate synthase by RNAi molecules enhances the antitumor effect of pemetrexed in an orthotopic malignant mesothelioma xenograft mouse model, by A.S. Abu Lila, C. Kato, M. Fukushima, et al (International Journal of Oncology, 2016).

The study

• Authors: A.S. Abu Lila, C. Kato, M. Fukushima, C.L. Huang, H. Wada, T. Ishida
• Journal: International Journal of Oncology
• Published: 2016;48(4):1399-407
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Malignant pleural mesothelioma (MPM) is an incurable cancer with an increasing incidence. Currently, pemetrexed (PMX)-based chemotherapy is the mainstay of chemotherapy for MPM, however, the outcome of PMX-based chemotherapy in patients with MPM is dismal. RNA interference (RNAi) technology has been considered as an effective tool to substantially enhance the therapeutic efficacy of chemotherapeutic agents in many preclinical and clinical settings. In this study, therefore, we investigated whether non-viral anti-thymidylate synthase RNAi embedded liposome (TS shRNA lipoplex) would effectively guide the downregulation of TS in human malignant mesothelioma MSTO-211H cells. Consequently, it enhanced the antitumor effect of PMX both in vitro and in vivo. TS shRNA effectively enhanced the in vitro cell growth inhibition upon treatment with PMX via downregulating TS expression in the MSTO-211H cell line. In in vivo orthotopic tumor model, the combined treatment of PMX and TS shRNA lipoplex efficiently combated the progression of orthotopic thoracic tumors and as a result prolonged mouse survival, compared to each single treatment. Our findings emphasize the pivotal relevance of RNAi as an effective tool for increasing the therapeutic efficacy of PMX, a cornerstone in the treatment regimens of MPM, and thereby, raising the possibility for the development of a novel therapeutic strategy, combination therapy of TS-shRNA and PMX, that can surpass many of the currently applied, but less effective, therapeutic regimens against lethal MPM.

In plain English

This laboratory study tested whether silencing the thymidylate synthase (TS) gene with a chemically synthesized short hairpin RNA (shRNA) would increase the effect of pemetrexed (PMX) against human malignant pleural mesothelioma MSTO-211H cells, in culture and in mice. The introduction notes that MPM is most often caused by asbestos exposure. In culture, TS shRNA transfection lowered TS mRNA by more than 90% (p less than 0.001) compared with untransfected cells, and the combination of TS shRNA with PMX gave an IC50 of 2.74 plus or minus 0.20 ng/ml versus 38.82 plus or minus 1.70 ng/ml for PMX alone (p less than 0.05). In nude mice given intrapleural MSTO-211H-Luc cells, the combination of intrapleural TS shRNA lipoplex and intraperitoneal PMX reduced tumour bioluminescence compared with other treated groups (p less than 0.001); mean survival time was greater than 39 days (ILS greater than 75.0%) versus 22.5 days for controls, with 3 of 6 mice surviving beyond 45 days. The authors concluded the combination shows therapeutic promise 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 experimental study: in vitro cell-culture experiments plus an in vivo orthotopic xenograft mouse model
• Who was studied: Human malignant pleural mesothelioma cell line MSTO-211H (luciferase-expressing) and 5-week-old male BALB/c nu/nu mice (6 per treatment group; 5 mice in the distribution study), Tokushima University, Japan
• Exposure: Anti-thymidylate synthase shRNA delivered in cationic liposomes (lipoplex, 20 microgram shRNA per mouse, intrapleural) and pemetrexed (25 mg/kg intraperitoneal; 0.001-1,000 ng/ml in vitro), alone or combined, with nonspecific shRNA as control
• Main results:
  • In MSTO-211H cells transfected with TS shRNA, TS mRNA was downregulated by more than 90% versus untransfected cells; nonspecific shRNA produced no significant change
  • In vitro, TS shRNA plus PMX was more cytotoxic than PMX alone (IC50 2.74 plus or minus 0.20 ng/ml versus 38.82 plus or minus 1.70 ng/ml)
  • In the orthotopic mouse model, combined TS shRNA plus PMX reduced thoracic tumour burden and photon intensity compared with the other treated groups
  • Survival times by group: control 22.5 days; NS shRNA lipoplex 24.0 days (ILS 6.6%); TS shRNA lipoplex 28.5 days (26.6%); PMX 27.0 days (20.0%); PMX plus NS shRNA lipoplex 27.5 days (22.2%); PMX plus TS shRNA lipoplex greater than 39 days (greater than 75.0%)
  • With the combined treatment, 3 of 6 mice survived beyond 45 days; no significant survival difference between control and nonspecific shRNA groups
  • In tumour tissue, TS mRNA was reduced by roughly 30 and 50% in treated mice compared with untreated or nonspecific shRNA-treated mice
  • DiR-labelled shRNA lipoplex stayed in the pleural cavity up to 120 h after intrapleural injection, with no marked accumulation in major organs
• The authors' conclusion: The authors concluded that TS gene knockdown by RNAi restored chemosensitivity to PMX in MSTO-211H cells and that combination therapy of TS shRNA and PMX shows therapeutic promise for MPM
• Limitations the authors state:
  • The authors could not measure TS mRNA in tumours from the combination-treated mice because too little total RNA was obtained

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: Pemetrexed (Alimta), Malignant Mesothelioma, Pleural Mesothelioma, Chemotherapy.

Related studies

• Downregulation of thymidylate synthase and E2F1 by arsenic trioxide in mesothelioma — S.K. Lam, Y.Y. Li, et al. (2015)
• Antitumor effect of novel anti-podoplanin antibody NZ-12 against malignant pleural mesothelioma in an orthotopic xenograft model — S. Abe, M.K. Kaneko, et al. (2016)
• Thymidylate synthase and folyl-polyglutamate synthase are not clinically useful markers of response to pemetrexed in patients with malignant pleural mesothelioma — D.E. Lustgarten, C. Deshpande, et al. (2013)
• New tricks for old biomarkers: thymidylate synthase expression as a predictor of pemetrexed activity in malignant mesothelioma — P.A. Zucali, E. Giovannetti, et al. (2010)
• Antitumor effects of TRAIL-expressing mesenchymal stromal cells in a mouse xenograft model of human mesothelioma — M.J. Lathrop, E.K. Sage, et al. (2015)
• Micro-RNA-215 and -375 regulate thymidylate synthase protein expression in pleural mesothelioma and mediate epithelial to mesenchymal transition — F. Napoli, I. Rapa, et al. (2022)

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