A Model for Optimizing Adenoviral Delivery in Human Cancer Gene Therapy Trials

Optimization of adenoviral delivery to the target volume is required for adenovirus-mediated cancer gene therapy to reach its maximal potential. The purpose of these studies was to develop a model of gene expression to improve adenovirus-mediated cancer gene therapy in the clinic. We measured the distribution of gene expression after a single deposit of a replication-competent adenovirus carrying the human sodium iodide symporter (hNIS) reporter gene was delivered to naive canine prostate and to human tumor xenografts. We generated hypothetical treatment plans for two prospective prostate cancer patients, using standard brachytherapy algorithms. In both models, the gene expression distribution from a single adenoviral deposit could be accurately described by a Gaussian function. In the naive canine prostate, a 0.1-ml deposit of 3 × 10¹¹ viral particles (VP) resulted in a gene expression volume of 1.14 ± 0.70 cm³, indicating that a minimum of 40 adenoviral deposits would be required to cover a 40-cm³ prostate with therapeutic gene expression. On a viral particle basis, the gene expression volume obtained in human tumor xenografts (7 × 10⁻¹² cm³/VP) was twice that (3.5 × 10⁻¹² cm³/VP) measured in the naive canine prostate. Hypothetical treatment plans for two prostates indicated that 26 and 57 0.1-ml adenoviral deposits would be required to cover, respectively, 24- and 49-cm³ prostates with gene expression. Although our studies focused on prostate, we believe the methodology to model gene expression presented here has much broader application to optimize treatment plans in other solid tumor sites; this assertion should be confirmed experimentally.