Gene Therapy for Osteosarcoma : "In Vitro" Characterization of Five Tumor Cell Lines and Development of Treatment Models "In Vivo"

Abstract

Four human osteosarcoma cell lines (MNNG, TE85, MG63, and G292) and a human-derived osteosarcoma metastatic to murine lung (MLM) were transduced "in vitro" using retroviral vectors containing the Herpes simplex thymidine kinase (HS-tk), human interleukin 2 (IL2). and B-galactosidase (BAG) genes. Each osteosarcoma cell line was stably transduced, and the HS-tk gene effectively conferred ganciclovir (GCV) susceptibility to transduced cells. Each cell line showed a bystander effect (whereby wild type tumor cells are killed by co-incubation with HS-tk positive tumor cells and GCV). MNNG cells were used to develop a series of experiments in athymic nude mice to investigate the utility of gene therapy for the treatment of experimental osteosarcomas. Subcutaneous implants of mixtures of tumor cells and HS-tk vector producer cells (vpc) resulted in the development of tumors which were completely cured upon administration of GCV. Subcutaneous implant of mixtures of transduced and wild-type cells resulted in a potent bystander effect upon administration of GCV, with complete tumor ablation when as little as ten percent of the cells were HS-tk positive. A significant anti-tumor response was seen against primary tumors comprised of unmodified cells when a secondary tumor of transduced cells was induced at a distance of one centimeter, which supports a soluble bystander factor model. The presence of IL2-transduced cells significantly improved the efficacy of treatment, suggesting a synergy between the HS-tk and IL2 gene products. A significant anti-tumor response was seen in the treatment of established osteosarcomas by the injection of HS-tk vpc.