Dexamethasone inhibits the HSV-tk/ ganciclovir bystander effect in malignant glioma cells

BACKGROUND: HSV-tk/ ganciclovir (GCV) gene therapy has been extensively studied in the setting of brain tumors and largely relies on the bystander effect. Large studies have however failed to demonstrate any significant benefit of this strategy in the treatment of human brain tumors. Since dexamethasone is a frequently used symptomatic treatment for malignant gliomas, its interaction with the bystander effect and the overall efficacy of HSV-TK gene therapy ought to be assessed. METHODS: Stable clones of TK-expressing U87, C6 and LN18 cells were generated and their bystander effect on wild type cells was assessed. The effects of dexamethasone on cell proliferation and sensitivity to ganciclovir were assessed with a thymidine incorporation assay and a MTT test. Gap junction mediated intercellular communication was assessed with microinjections and FACS analysis of calcein transfer. The effect of dexamethasone treatment on the sensitivity of TK-expressing to FAS-dependent apoptosis in the presence or absence of ganciclovir was assessed with an MTT test. Western blot was used to evidence the effect of dexamethasone on the expression of Cx43, CD95, CIAP2 and Bcl(XL). RESULTS: Dexamethasone significantly reduced the bystander effect in TK-expressing C6, LN18 and U87 cells. This inhibition results from a reduction of the gap junction mediated intercellular communication of these cells (GJIC), from an inhibition of their growth and thymidine incorporation and from a modulation of the apoptotic cascade. CONCLUSION: The overall efficacy of HSV-TK gene therapy is adversely affected by dexamethasone co-treatment in vitro. Future HSV-tk/ GCV gene therapy clinical protocols for gliomas should address this interference of corticosteroid treatment

Therapeutic effect of suicide gene-transferred mesenchymal stem cells in a rat model of glioma

We evaluated a new therapeutic strategy for malignant glioma, which combines intratumoral inoculation of mesenchymal stem cells (MSCs) expressing cytosine deaminase gene with 5-fluorocytosine (5-FC) administration. For in vitro and in vivo experiments, MSCs were transfected with adenovirus carrying either enhanced green fluorescent protein gene (AdexCAEGFP) or cytosine deaminase gene (AdexCACD), to establish MSC-expressing EGFP (MSC-EGFP) or CD (MSC-CD). Co-culture of 9L glioma cells with MSC-CD in a medium containing 5-FC resulted in a remarkable reduction in 9L cell viability. The migratory ability of MSC-EGFP toward 9L cells was demonstrated by double-chamber assay. For the in vivo study, rats harboring 9L brain tumors were inoculated with MSC-EGFP or MSC-CD. Immunohistochemistry of rat brain tumors inoculated with MSC-EGFP showed intratumoral distribution of MSC-EGFP. Survival analysis of rats bearing 9L gliomas treated with intratumoral MSC-CD and intraperitoneal 5-FC resulted in significant prolongation of survival compared with control animals. In conclusion, molecular therapy combining suicide gene therapy and MSCs as a targeting vehicle represents a potential new therapeutic approach for malignant glioma, both with respect to the antitumor potential of this system and its neuroprotective effect on normal brain tissue