An experimental model of retrovirus gene therapy for malignant brain tumors

Abstract

Recent research using rodent models of central nervous system gliomas indicates that a combination of gene transfer and drug treatment may be successful in killing tumor cells. In the present study, a mouse fibroblast-derived packaging cell line, psi 2, which releases a replication-defective retrovirus vector bearing the herpes simplex virus type 1 (HSV)-thymidine kinase (TK) gene, was grown with rat C6 tumor cells in the presence and absence of wild type Moloney murine leukemia virus (MoMLV). Consequently, tumor cells became sensitive to ganciclovir, which is selectively converted to a toxic nucleotide analog by HSV-TK. This killing effect was more effective in the presence than in the absence of wild type retrovirus both in culture and in subcutaneous tumors in nude mice. Tumors regressed in vivo and failed to regrow over a subsequent 10-day observation period after combined treatment with packaging cells, wild type MoMLV, and ganciclovir. This killing effect may be augmented by the ability of the helper retrovirus to package the vector in tumor cells and thus extend delivery of the HSV-TK gene to more tumor cells. This represents significant improvement in tumor therapy in this model system as compared with helper-free systems previously reported by the authors and others. Although additional improvements in the therapy can be envisioned, this approach may prove useful in combination with current modes of therapy for these insidious and lethal tumors.

Endothelial cell transfection with cationic liposomes and herpes simplex-thymidine kinase mediated killing

“…21 Mesothelial cells transduced with HSVtk showed a 3-4 log 10 reduction of IC 50 for GCV compared with nontransduced cells. 22 Similar positive results have also been demonstrated in vitro and in vivo for several other cell types including glioma 23,24 and ovarian carcinoma. 9 Several clinical trials are now in progress using the HSVtk drug sensitivity gene paradigm, and tumour responses have been observed.…”

Enhancement of tumor ablation by a selected HSV-1 thymidine kinase mutant

“…Clearly, mutant 30 is able to provide tumor ablation at a dose which only marginally slows tumors expressing wild-type TK. Given the short duration of the prodrug treatment (5 days) compared with that in other reports (14 to 21 days) [9][10][11]13,14,[21][22][23] these results are very compelling.…”

“…Rat C6 glioma cells have served as a model system to evaluate the efficacy of the TK/GCV paradigm in brain and subcutaneously. 2,10,[13][14][15] A new expression vector, pREP8⌬7:TK-GFP, was constructed to provide expression of green fluorescent protein (GFP) for detection purposes and thymidine kinase (wild-type or mutant 30; pREP8⌬7:30-GFP) ( Figure 1). These vectors were used to transfect stably rat C6 glioma cells that were subsequently selected for histidinol resistance and sorted for GFP expression as described in Materials and methods.…”

Herpes Simplex Virus Type 1/Adeno-Associated Virus Hybrid Vectors

“…Due to the low efficiency of gene transfer, MoMLV –based vectors have been mostly used for ex vivo gene therapy protocols [238, 239]. Although this strategy has shown some therapeutic success in experimental brain tumors [240, 241] it is not effective when used in human trials [242-245]. HSV/RV hybrid amplicon vectors containing genetic elements from MoMLV have been developed in order to transduce genes required for the de novo synthesis of small defective retrovirus vectors.…”