Treatment of glioblastoma multiforme using combined gene therapy in a murine model. Implications for the treatment of human patients?

PUNTEL; LOWENSTEIN; CASTRO

Rio de Janeiro

Encuentro; 1st Meeting of the Institute of Glia: a South American Alliance; 2011

Instituto of Glia

Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults, affecting ~18,000 new patients every year; its prognosis remains poor despite standard treatment with surgery, radiotherapy and chemotherapy (temozolomide)  [1-6]. Complete resection is mostly impossible due to the highly infiltrative nature of this disease. Residual GBM cells remaining within the non-neoplastic brain parenchyma eventually lead to tumor recurrence that is resistant to conventional chemotherapy and radiotherapy, ultimately leading to the patient?s death [2]. We have developed a novel immunotherapeutic approach for GBM using first generation adenoviral vectors (Ads) to deliver a combination of therapeutic transgenes into the tumor mass [7-13], which is slated to begin Phase I clinical testing this year. In our strategy we aim to reconstruct an immune circuit that is absent from the normal brain. Our gene therapy strategy consists of the conditionally cytotoxic Herpes Simplex type-1 thymidine kinase (TK) [8, 10], which kills proliferating tumor cells in the presence of the pro-drug gancyclovir (GCV), used in combination with human soluble fms-like tyrosine kinase 3 ligand (Flt3L), which recruits bone marrow-derived dendritic cells (DCs) to the normal brain or brain tumor microenvironment in mice [8, 14] and rats [15, 16]. In addition, Ad-Flt3L + Ad-TK induces GBM-specific immunological memory that improves survival in intracranial multifocal and recurrent models of GBM in both rats and mice [8, 9, 13, 17-19].             To reduce vector dose and facilitate GMP manufacturing of the clinical product, we engineered a novel, bi-cistronic HC-Ad vector that encodes for the first time, both constitutively expressed HSV1-TK and inducible Flt3L from a single HC-Ad vector genome. This project had two principal aims: First, to demonstrate therapeutic efficacy of the bi-cistronic HC-Ad in naïve rats bearing intracranial tumors, and also in tumor bearing rats which had been previously exposed to adenoviruses and therefore exhibited anti-Ad immunity. And second, to assess the safety profile of this approach by evaluating the biodistribution of HC-Ad vector genomes, systemic and neurological toxicity, and behavioral abnormalities over the course of one year post treatment. These data represent the first report of a bi-cistronic vector platform driving the expression of two therapeutic transgenes, i.e., constitutive HSV1-TK and inducible Flt3L. Further, our data demonstrate no promoter interference and optimum gene delivery and expression from within this single vector platform. Analysis of the efficacy, safety, and toxicity of this bicistronic HC-Ad vector in an animal model of GBM strongly support further pre-clinical testing and downstream process development of HC-Ad-TK/TetOn-Flt3L for a future Phase I clinical trial for GBM.