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Updated: Aug 18, 2026
Dissecting Host-virus Interaction in Lytic Replication of a Model Herpesvirus
Published on: October 7, 2011
Double suicide gene therapy using a replication defective herpes simplex virus vector reveals reciprocal interference
S Moriuchi1, D Wolfe, M Tamura
1Department of Molecular Genetics and Biochemistry, University of Pittsburgh Medical School, Pittsburgh, Pittsburgh, PA 15261, USA.
Abstract:
Herpes simplex virus thymidine kinase (HSV-TK) and Escherichia coli cytosine deaminase (CD) are non-mammalian enzymes capable of converting innocuous prodrugs into cytotoxic metabolites. Both enzymes have been utilized independently, as well as together in 'suicide' gene therapy protocols to eliminate tumor cells in vitro and in vivo. We have used a set of replication defective HSV vectors expressing either or both enzymes to compare the efficacies of single and double suicide gene therapies in the 9L gliosarcoma model in vitro and in vivo. In cell culture experiments at high and low multiplicities of infection, combined expression of the two genes by vector TOCD/TK along with exposure to the matching prodrugs (ganciclovir and 5-fluorocytosine) showed increased cytotoxicity compared with exposure to either prodrug alone. However, the two gene combination was inferior to single gene treatments, suggesting that HSVtk and CD are mutually counteractive in the prodrug-dependent killing of glioma cells. In animal experiments, survival was not significantly prolonged by administration of both prodrugs to TOCD/TK-treated animals, while each single gene/prodrug pair resulted in increased survival. These results indicate that single suicide gene systems employing HSVtk or CD may be preferable over combinations of the two.
Insights
Single suicide gene therapy using Herpes simplex virus thymidine kinase (HSV-TK) or Escherichia coli cytosine deaminase (CD) is more effective than combined therapy for glioma cells. Combining HSV-TK and CD enzymes with prodrugs did not improve tumor cell killing or survival in gliosarcoma models.
Area of Science:
- Oncolytic viruses
- Gene therapy
- Cancer research
Background:
- Herpes simplex virus thymidine kinase (HSV-TK) and Escherichia coli cytosine deaminase (CD) are non-mammalian enzymes used in suicide gene therapy.
- These enzymes convert prodrugs into cytotoxic agents to eliminate tumor cells.
- Previous studies utilized HSV-TK and CD independently or in combination for cancer treatment.
Purpose of the Study:
- To compare the efficacy of single and double suicide gene therapies using HSV-TK and CD in the 9L gliosarcoma model.
- To evaluate the combined effects of HSV-TK and CD gene expression with corresponding prodrugs (ganciclovir and 5-fluorocytosine).
- To determine if combined suicide gene therapy is superior to single gene therapy for glioma treatment.
Main Methods:
- Utilized replication-defective HSV vectors expressing either HSV-TK, CD, or both (TOCD/TK).
- Conducted in vitro cell culture experiments with varying multiplicities of infection.
- Performed in vivo animal experiments using the 9L gliosarcoma model in rats.
Main Results:
- In vitro, combined HSV-TK and CD expression with both prodrugs showed increased cytotoxicity compared to single prodrugs alone.
- However, the combined gene therapy was less effective than single gene treatments in cell culture.
- In vivo, TOCD/TK-treated animals receiving both prodrugs did not show significantly prolonged survival compared to single gene/prodrug treatments.
Conclusions:
- Single suicide gene systems utilizing either HSV-TK or CD may be preferable to combined systems for glioma treatment.
- HSV-TK and CD enzymes appear to be mutually counteractive in prodrug-dependent killing of glioma cells.
- Combined suicide gene therapy with HSV-TK and CD is not superior to single gene therapy and may be less effective.
