Efficacy of repeated adenoviral suicide gene therapy in a localized murine tumor model

Our plain-English summary of Efficacy of repeated adenoviral suicide gene therapy in a localized murine tumor model, by E.S. Lambright, S.D. Force, M.E. Lanuti, et al (The Annals of Thoracic Surgery, 2000).

The study

• Authors: E.S. Lambright, S.D. Force, M.E. Lanuti, D.S. Wasfi, K.M. Amin, S.M. Albelda, L.R. Kaiser
• Journal: The Annals of Thoracic Surgery
• Published: 2000;70(6):1865-70; discussion 1870-1
• Cited by: 19 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Gene therapy using adenovirus to deliver herpes simplex virus thymidine kinase (Ad.HSVtk) followed by the administration of the prodrug ganciclovir has been an effective anticancer therapy in models of localized tumor (including malignant mesothelioma) and is currently being evaluated in clinical trials. To optimize this approach, we studied the effects of repeated injections of Ad.HSVtk in an animal model of localized tumor in both naive and immunized mice.

Methods: Immunocompetent animals with established abdominal tumor were treated with either one or three (given weekly) intraperitoneal injections of Ad.HSVtk (10(9) plaque-forming units) followed by daily ganciclovir and monitored for survival. Survival studies were also performed in mice previously immunized with adenovirus.

Results: Animals treated with multiple courses of Ad.HSVtk showed significantly improved survival versus singly injected animals and control animals with some long-term survivors in the multiple injected group. Preexisting neutralizing immunity did not diminish this survival advantage.

Conclusions: Multiple treatments using an adenoviral vector to deliver HSVtk significantly improves survival in a murine intraperitoneal tumor model. The presence of preexisting neutralizing antibodies does not blunt this effect. Repeat Ad.HSVtk is a feasible approach and may be a useful strategy in human cancer gene therapy.

In plain English

This was a laboratory experiment in mice testing a gene therapy approach that the authors' group had earlier tried in patients with malignant mesothelioma. It did not study asbestos, and the mice did not have mesothelioma. The authors used a mouse fibroblast tumor line in female BALB/c mice because, in their experience, available mouse mesothelioma models were rather resistant to this treatment. Mice with established abdominal tumors received one or three weekly abdominal injections of an adenovirus carrying the herpes simplex thymidine kinase gene. Each injection was followed by 6 days of ganciclovir, with 10 mice per group. In mice never exposed to adenovirus, control groups had a median survival of about 25 days. A single course gave 35 days, and three courses gave 45 days with 40% long-term survival. In mice first immunized against adenovirus, three courses gave a median survival of more than 55 days and 30% long-term survival. The authors concluded that repeated treatment improved survival in this mouse model even with pre-existing neutralizing antibodies, and suggested it may be feasible in future human trials.

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: Animal experiment (randomized treatment groups of mice, Kaplan-Meier survival analysis), with supporting laboratory cell-culture tests
• Who was studied: Female BALB/c mice, 6 to 8 weeks old, with abdominal (intraperitoneal) tumors from EJ-6-2-Bam-6A cells, a mouse fibroblast cell line transformed with the H-Ras oncogene (not a mesothelioma line). There were 10 mice per treatment group, in mice never exposed to adenovirus (naive) and in mice previously immunized with adenovirus. The work was done at the University of Pennsylvania and the Wistar Institute, Philadelphia.
• Exposure: No asbestos exposure was studied. Treatment was one course, or three weekly courses, of an abdominal injection of an adenovirus carrying the herpes simplex virus thymidine kinase gene (10 to the 9th power plaque-forming units), each followed by 6 days of abdominal ganciclovir at 50 mg/kg/day. Control groups received media only, ganciclovir only, or three courses of an adenovirus carrying a marker gene (lacZ).
• Main results:
  • In naive mice, the three control groups (media alone, ganciclovir alone, three courses of the lacZ marker virus) all had a median survival of approximately 25 days, and all were dead by 32 days.
  • In naive mice, a single course of the thymidine kinase virus plus ganciclovir gave a small but statistically significant survival increase (p = 0.0009), with a median survival of 35 days and some animals living to 80 days, but no long-term survivors.
  • In naive mice, three courses increased median survival to 45 days with a 40% long-term survival rate, which the authors called cure. This was significantly better than controls (p = 0.0001) and than a single course (p = 0.0226). A repeat experiment gave virtually identical results.
  • Mice immunized with adenovirus (n = 4 tested) had an average neutralizing antibody titer of 1:600 plus or minus 115. Naive mice had levels below the assay's limit of 1:25.
  • In immunized mice, controls had a median survival of 20 to 25 days. A single course raised median survival to 35 to 40 days (p less than 0.0001 versus control). Three courses gave a median survival of more than 55 days and 30% long-term survival (p = 0.0198); the figure legend describes this as a further improvement from multiple injections.
  • In cell culture, the thymidine kinase virus plus ganciclovir killed EJ-6-2-Bam-6A cells in a dose-related way. At the highest virus dose tested (MOI of 100), 80% of cells were killed.
• The authors' conclusion: The authors concluded that this therapy gave a survival advantage in a mouse intraperitoneal tumor model and that repeat treatment improved efficacy in both naive and immunized mice. They suggested that repeat treatments are a feasible strategy for future clinical trials in diseases such as malignant mesothelioma, brain tumor and ovarian carcinoma.
• Limitations the authors state:
  • The authors used a mouse fibroblast tumor line rather than a mouse mesothelioma model. They said that, in their experience, the available mouse mesothelioma models were rather resistant to this treatment, unlike most human mesothelioma lines.
  • The possible role of an immune response against the tumor was not specifically examined in this study.
  • Much higher antibody titers (up to 1:4,000) have been induced in patients after this therapy, and such levels may be more inhibitory than those modeled in the mice.
  • In the published discussion, the presenting author said that gene expression in immunized versus naive mice had not yet been evaluated with definitive conclusions, and that cellular infiltrates had not been quantified.

Topics

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

Medical terms in this study, explained in our Lexicon: Malignant Mesothelioma, Clinical Trial.

Related studies

• Gene therapy using adenovirus carrying the herpes simplex-thymidine kinase gene to treat in vivo models of human malignant mesothelioma and lung cancer — H.C. Hwang, W.R. Smythe, et al. (1995)
• Imaging in vivo herpes simplex virus thymidine kinase gene transfer to tumour-bearing rodents using positron emission tomography and — R. Hustinx, C.Y. Shiue, et al. (2001)
• Use of protamine to augment adenovirus-mediated cancer gene therapy — M. Lanuti, C.E. Kouri, et al. (1999)
• Differential sensitivity of thoracic malignant tumors to adenovirus-mediated drug sensitization gene therapy — W.R. Smythe, H.C. Hwang, et al. (1995)
• Gene-modified PA1-STK cells home to tumor sites in patients with malignant pleural mesothelioma — L.H. Harrison, P.O. Schwarzenberger, et al. (2000)
• Chemotherapy delivered after viral immunogene therapy augments antitumor efficacy via multiple immune-mediated mechanisms — Z.G. Fridlender, J. Sun, et al. (2010)

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