Thymidine kinase-mediated killing of rat brain tumors

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.

Imaging progress of herpes simplex virus type 1 thymidine kinase suicide gene therapy in living subjects with positron emission tomography

“…Effectiveness of GCV in killing HSV1-tk and various mutant HSV1-tk expressing C6-glioma tumors have been previously reported. 31,41 As shown in Figures 1 and 3 were mainly due to exposure to GCV, mice carrying s.c. C6sr39 tumor xenografts were monitored for 2 weeks without GCV treatment (Fig 4a and b . There was also a 377% increase in the volume of C6sr39 tumors that had not been exposed to GCV in the 2-week period.…”

Selection of HSV-1 TK gene-transfected murine mammary carcinoma cells resistant to (E)-5-(2-bromovinyl)-2′-deoxyuridine (BVDU) and ganciclovir (GCV)

“…16,25 In tumor cells with an efficient bystander effect, the small percentage of GCV-resistant cells apparently were killed by the neighboring GCV-sensitive (functional TK-expressing) tumor cells. Also, Barba et al 26 found resistant colonies in vitro after GCV-treatment of HSV-1 TK gene-transfected tumor cell cultures, whereas in vivo, all tumor-bearing animals remained tumor-free after GCV treatment. Thus, the efficiency of the bystander cell killing in a particular cell line seems to affect the development of GCV-resistant tumor cell colonies.…”

Connexin 26 enhances the bystander effect in HSVtk/GCV gene therapy for human bladder cancer by adenovirus/PLL/DNA gene delivery

“…[11][12][13][14] Herpes simplex thymidine kinase/ganciclovir (HSVtk/ GCV) gene therapy has been demonstrated to treat effectively various types of cancers in vitro and in vivo. [15][16][17][18][19] In HSVtk/GCV gene therapy, the toxicity of GCV is extended from HSVtk-transduced cells to adjacent HSVtknegative cells through the so-called bystander effect. Some studies have shown that the bystander effect in HSVtk/GCV gene therapy is mediated by Cx expression and that the exogenous introduction of Cx 26 or Cx 43 enhances the bystander effect.…”