Lentiviral HSV-Tk. 007- mediated suicide gene therapy is not toxic for normal brain cells

Introduction Gene therapeutic strategies with suicide genes are currently investigated in clinical trials for brain tumors. Previously we have shown that lentiviral vectors delivering the suicide gene HSV-Tk to experimental brain tumors promote a highly significant treatment effect and are thus promising vectors for clinical translation. Aims Here, we tested lentiviral vectors delivering the suicide gene HSV-Tk.007, a highly active mutant of HSV-Tk, to rat brains as a preclinical toxicity study. We injected 106 VSV-G pseudotyped functional lentiviral particles harboring the suicide gene HSV-Tk.007 into the brain of healthy, immunocompetent rats. During prodrug treatment with Ganciclovir (GCV), we measured weight and assessed the behavior of the rats in an open field test. After 14 days of GCV treatment, we analyzed HSV-Tk.007 expression in different brain cell populations as well as inflammatory responses and apoptosis. Results During prodrug treatment with Ganciclovir, behavior experiments did not reveal differences between treated rats and the control groups. Analysis of HSV-Tk expression in different brain cell populations showed that transduced normal brain cells survived Ganciclovir treatment. There were no statistically significant differences in the number of transduced cells between treatment and control groups. Furthermore, inflammatory responses and apoptosis of brain cells were not observed. Conclusion Here we show that HSV-Tk.007 mediated suicide gene therapy is not toxic to normal brain cells. This observation is of high relevance for translation of lentivirus-mediated suicide gene therapies into the clinic to treat brain tumor patients.