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This study describes a quantitative method to measure the magnitude and distribution of gene expression following local delivery of an adenoviral vector containing the human sodium iodide symporter (hNIS) reporter gene into the canine prostate. Following systemic administration of Na 99m TcO 4 , autoradiographs of prostate sections depicting hNIS-dependent 99m TcO 4 − uptake were digitized and stacked to produce a three-dimensional reconstruction of gene expression. Frequency histograms reflecting hNIS gene expression magnitude and volume were used to quantify hNIS function. The method demonstrated submillimeter resolution allowing for precise measurements of gene expression magnitude and volume in vivo . The method developed here could be applied to other reporter gene systems in which the readout can be digitized from thin tissue sections.

With the goal of optimizing adenovirus-mediated suicide gene therapy for prostate cancer, we have developed a method based on the human sodium iodide symporter (hNIS) that allows for noninvasive monitoring of adenoviral vectors and quantification of gene expression magnitude and volume within the prostate. A replication-competent adenovirus (Ad5-yCD/ mut TK SR39 rep -hNIS) coexpressing a therapeutic yeast cytosine deaminase (yCD)/mutant herpes simplex virus thymidine kinase ( mut TK SR39 ) fusion gene and the hNIS gene was developed. Ad5-yCD/ mut TK SR39 rep -hNIS and a replication-defective hNIS adenovirus (rAd-CMV-FLhNIS) were injected into contralateral lobes of the dog prostate and hNIS activity was monitored in live animals following administration of Na 99m TcO 4 using gamma camera scintigraphy. Despite the close proximity of the urinary bladder, 99m TcO 4 − uptake was readily detected in the prostate using viral dose levels (10 10 to 10 12 viral particles) that have been safely administered to humans. Due to its rapid clearance and short physical half-life (6 h), it was possible to obtain daily measurements of 99m TcO 4 − uptake in vivo, allowing for dynamic monitoring of reporter gene expression within the prostate as well as biodistribution throughout the body. High-resolution autoradiography of prostate sections coupled with 3D reconstruction of gene expression demonstrated that the magnitude and volume of gene expression could be quantified with submillimeter resolution. Implementation of the GENIS (gene expression of Na/I symporter) technology in the clinic will facilitate optimization of future human gene therapy trials.