gms | German Medical Science

Objective: Neural stem cells (NSC) have an inherent brain tumor tropism that can be exploited for targeted delivery of therapeutic genes to invasive gliomas. Here, we demonstrate that the non-invasive intranasal administration of tumor-targeting NSC is able to deliver a novel suicide gene (TK007) to intracerebrally growing human glioblastoma xenografts.

Method: Murine NSC were genetically modified to express the novel herpes simplex virus thymidine kinase variant (TK007). The biological activity of the NSC-mediated TK007/ganciclovir (GCV) system was assessed in cell survival and bystander assays using various human glioma cell lines. Therapeutic effects of intratumoral (3x10⁵ cells) and intranasal (1.5x10⁶) NSC-TK007 application alone and the sequential combination of both was tested using an intracranial U87 human glioblastoma model in nude mice. All animals received 50 mg/kg GCV i.p. for five consecutive days. Two control groups received either NaCl instead of GCV or NSC containing the empty vector (NSC-control) instead of NSC-TK007. The therapeutic effect was determined by assessment of tumor size by 7T MR-imaging on day 20 and by establishment of Kaplan-Meier survival curves. Each treatment or control group contained at least 11 animals.

Results: Cell survival and bystander assays confirmed the GCV catalytic activity of NSC expressed TK007 in a GCV dose-dependent manner and a significant bystander effect in 12.5% of cells. Intratumoral application of NSC-TK007 followed by systemic prodrug application of GCV led to a significant tumor growth inhibition of 72% versus the control groups (p<0.01, ANOVA) which translated into a prolonged survival time. Those receiving additional intranasal administration of NSC-TK007 displayed a significant tumor growth inhibition of 81% versus control groups (p<0.01) and a significantly longer survival time and long-term survival in 27%.

Conclusions: Our data demonstrate that the NSC-mediated TK007/GCV therapy, which is based on the clinically most widely used suicide system to date, is safe, nontoxic and effective in glioblastoma-bearing mice. Most importantly, our findings establish the intranasal application of therapeutically-modified NSC as a safe and non-invasive application method. This offers the possibility of multiple treatments using tumor targeting NSC with different therapeutic payloads during the disease course.