Study of the efficacy, biodistribution, and safety profile of therapeutic gutless adenovirus vectors as a prelude to a phase I clinical trial for glioblastoma.

Glioblastoma multiforme (GBM) is the most common and most aggressive primary brain tumor in humans. Systemic immunity against gene therapy vectors has been shown to hamper therapeutic efficacy; however, helper-dependent high-capacity adenovirus (HC-Ad) vectors elicit sustained transgene expression, even in the presence of systemic anti-adenoviral immunity. We engineered HC-Ads encoding the conditional cytotoxic herpes simplex type 1 thymidine kinase (TK) and the immunostimulatory cytokine fms-like tyrosine kinase ligand 3 (Flt3L). Flt3L expression is under the control of the regulatable Tet-ON system. In anticipation of a phase I clinical trial for GBM, we assessed the therapeutic efficacy, biodistribution, and clinical and neurotoxicity with escalating doses of HC-Ad-TetOn-Flt3L + HC-Ad-TK in rats. Intratumoral administration of these therapeutic HC-Ads in rats bearing large intracranial GBMs led to long-term survival in approximately 70% of the animals and development of antiglioma immunological memory without signs of neuropathology or systemic toxicity. Systemic anti-adenoviral immunity did not affect therapeutic efficacy. These data support the idea that it would be useful to develop HC-Ad vectors further as a therapeutic gene-delivery platform to implement GBM phase I clinical trials.

Herpes simplex virus type 1 thymidine kinase sequence fused to the lacz gene increases levels of {beta}-galactosidase activity per genome of high-capacity but not first-generation adenoviral vectors in vitro and in vivo.

Increased transgene expression per vector genome is an important goal in the optimization of viral vectors for gene therapy. Herein we demonstrate that herpes simplex virus type 1 (HSV1) thymidine kinase (TK) gene sequences (1,131 bp) fused to the 3' end of lacZ increase transgene expression from high-capacity adenoviral vectors (HCAd), but not from first-generation (Ad) vectors. The woodchuck hepatitis virus posttranscriptional regulatory element (WPRE), in contrast, increased transgene expression levels from Ad but not HCAd vectors. The differential activity of the HSV1 TK gene and WPRE sequences was detected both in vitro and in vivo and suggests potentially different mechanisms of action or the interaction of these elements with vector genomic sequences.