Engineering Suicide Gene Approaches to Improve Chemotherapeutic Response in Glioblastoma

Glioblastoma is the most common brain cancer in adults and is uniformly lethal. Existing therapies, namely surgery followed by temozolomide chemotherapy and radiation, fail to prevent disease recurrence and new treatment approaches are urgently needed. Suicide genes are a potentially promising approach for glioblastoma wherein viruses are used to transduce tumor cells to express a foreign protein that converts a prodrug into a toxic product, resulting in cell death. Utilizing the herpes simplex virus thymidine kinase (HSVtk) suicide gene, we designed novel fusion proteins we hypothesized to be post-translationally stabilized following temozolomide treatment. HSVtk was fused to PEST sequences (domains rich in proline, glutamate, serine, and threonine that control protein turnover) predicted to be stabilized via phosphorylation by p38, a kinase activated by the stress of temozolomide-mediated DNA damage. Suicide gene constructs were retrovirally transduced into human glioblastoma cell lines and analyzed for their stability and specificity to p38 by immunoblotting and flow cytometry. The results of this work demonstrate the potential utility of combining a suicide gene with traditional chemotherapy.