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Thymidine kinase-mediated killing of rat brain tumors
1Department of Surgery, School of Medicine, University of California, San Diego.
Abstract:
Gene therapy has many potential applications in central nervous system (CNS) disorders, including the selective killing of tumor cells in the brain. A rat brain tumor model was used to test the herpes simplex virus (HSV)-thymidine kinase (TK) gene for its ability to selectively kill C6 and 9L tumor cells in the brain following systemic administration of the nucleoside analog ganciclovir. The HSV-TK gene was introduced in vitro into tumor cells (C6-TK and 9L-TK), then these modified tumor cells were evaluated for their sensitivity to cell killing by ganciclovir. In a dose-response assay, both C6-TK and 9L-TK cells were 100 times more sensitive to killing by ganciclovir (median lethal dose: C6-TK, 0.1 microgram ganciclovir/ml; C6, 5.0 micrograms ganciclovir/ml) than unmodified wild-type tumor cells or cultured fibroblasts. In vivo studies confirmed the ability of intraperitoneal ganciclovir administration to kill established brain tumors in rats as quantified by both stereological assessment of brain tumor volumes and studies of animal survival over 90 days. Rats with brain tumors established by intracerebral injection of wild-type or HSV-TK modified tumor cells or by a combination of wild-type and HSV-TK-modified cells were studied with and without ganciclovir treatments. Stereological methods determined that ganciclovir treatment eliminated tumors composed of HSV-TK-modified cells while control tumors grew as expected (p < 0.001). In survival studies, all 10 rats with 9L-TK tumors treated with ganciclovir survived 90 days while all untreated rats died within 25 days. Curiously, tumors composed of combinations of 9L and 9L-TK cells could be eliminated by ganciclovir treatments even when only one-half of the tumor cells carried the HSV-TK gene. While not completely understood, this additional tumor cell killing appears to be both tumor selective and local in nature. It is concluded that HSV-TK gene therapy with ganciclovir treatment does selectively kill tumor cells in the brain and has many potential applications in CNS disorders, including the treatment of cancer.
Insights
Gene therapy using the herpes simplex virus-thymidine kinase (HSV-TK) gene effectively kills brain tumor cells in rats when combined with ganciclovir treatment. This approach shows promise for treating central nervous system cancers.
Area of Science:
- Neuro-oncology
- Molecular Biology
- Gene Therapy
Background:
- Central nervous system (CNS) disorders present significant therapeutic challenges.
- Gene therapy offers a potential strategy for targeted cancer treatment within the brain.
Purpose of the Study:
- To evaluate the efficacy of herpes simplex virus-thymidine kinase (HSV-TK) gene therapy in selectively eliminating rat brain tumors.
- To assess the impact of ganciclovir administration on tumor cell killing and animal survival.
Main Methods:
- In vitro modification of C6 and 9L tumor cells with the HSV-TK gene.
- Dose-response assays to determine ganciclovir sensitivity of modified vs. wild-type cells.
- In vivo studies using a rat brain tumor model with stereological volume assessment and survival analysis.
Main Results:
- HSV-TK modified cells exhibited 100-fold increased sensitivity to ganciclovir compared to wild-type cells.
- Systemic ganciclovir administration eradicated established brain tumors in rats.
- Ganciclovir treatment led to 100% survival at 90 days for rats with HSV-TK modified tumors, versus 25 days for untreated controls.
- Tumors with even 50% HSV-TK modified cells were eliminated by ganciclovir, suggesting a bystander effect.
Conclusions:
- HSV-TK gene therapy combined with ganciclovir effectively and selectively kills brain tumor cells.
- This gene therapy approach demonstrates significant potential for treating CNS cancers.
- The observed bystander effect warrants further investigation for optimizing therapeutic strategies.