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Retrovirus-mediated gene therapy of experimental brain neoplasms using the herpes simplex virus-thymidine
N G Rainov1, C M Kramm, K Aboody-Guterman
1Molecular Neurogenetics Unit, Massachusetts General Hospital, Boston, USA.
Abstract:
Recent results in experimental brain tumors indicate that transfer of sensitizing genes to tumor cells in vivo with subsequent drug treatment can reduce tumor masses and prolong the survival of rodents. In the present study, the 9L rat gliosarcoma model was used to evaluate the therapeutic effectiveness of the herpes simplex virus-thymidine kinase (HSV-tk) gene, delivered by a retrovirus vector, against tumor cells in the rat brain after systemic application of the nucleoside analogue ganciclovir (GCV). The HSV-tk gene was inserted into a retroviral vector (pMFG), which was produced using the amphotropic packaging cell line CRIP-MFG-S-HSV-TK. Packaging cells were implanted into established 9L tumors in the brains of syngeneic rats to effect gene delivery to tumor cells, followed by intraperitoneal GCV injections. Treated animals survived significantly longer (more than twice as long) than did the control groups. Brains from GCV-treated and nontreated animals were examined immunohistochemically at different time intervals after grafting of CRIP-MFG-S-HSV-TK cells and GCV treatment. Tumors in GCV-treated animals were significantly smaller as compared with nontreated animals at all time points. Sections stained immunohistochemically for HSV-TK confirmed gene transfer to tumor cells, which could be distinguished from packaging cells by different morphology and immunohistochemical staining for the retroviral envelope protein gp70. Approximately 45% of the cells in tumors implanted with CRIP-MFG-S-HSV-TK cells, but not treated with GCV, showed immunocytochemical staining for HSV-TK, demonstrating a high-efficiency of retrovirus-mediated gene transfer. Tumors in rats treated with packaging cells and GCV showed only 9% HSV-TK-positive cells after treatment, indicating that most cells expressing the HSV-tk gene were killed. The success of this therapeutic modality in experimental animals depends in large parts on the high efficiency of gene delivery and on the immune response against tumor cells.
Insights
Gene therapy using the herpes simplex virus-thymidine kinase (HSV-tk) gene and ganciclovir (GCV) significantly reduced brain tumor size and doubled survival time in a rat gliosarcoma model.
Area of Science:
- Neuro-oncology
- Gene Therapy
- Retroviral Vectors
Background:
- Experimental brain tumor treatments show promise with gene sensitization and drug therapy.
- The 9L rat gliosarcoma model is utilized for in vivo therapeutic evaluations.
Purpose of the Study:
- To assess the therapeutic efficacy of the herpes simplex virus-thymidine kinase (HSV-tk) gene delivered via retroviral vector.
- To evaluate the impact of ganciclovir (GCV) treatment on brain tumors following gene transfer.
Main Methods:
- HSV-tk gene inserted into a retroviral vector (pMFG) and produced using CRIP-MFG-S-HSV-TK packaging cells.
- Packaging cells implanted into established 9L tumors in rat brains, followed by systemic GCV administration.
- Immunohistochemical analysis performed to confirm gene transfer and assess tumor response.
Main Results:
- Animals treated with HSV-tk gene therapy and GCV survived significantly longer (more than double the control group).
- GCV-treated tumors were significantly smaller than those in control groups at all time points.
- High-efficiency retrovirus-mediated gene transfer (approximately 45% HSV-TK-positive cells) was observed, with significant cell killing (9% HSV-TK-positive cells post-treatment).
Conclusions:
- Retrovirus-mediated HSV-tk gene therapy combined with GCV is a viable therapeutic strategy for experimental brain tumors.
- Therapeutic success is attributed to efficient gene delivery and the resulting immune response against tumor cells.
- This approach demonstrates significant tumor reduction and prolonged survival in a preclinical brain tumor model.