Prostate cancer has become the most frequently occurring cancer and the second leading cause of cancer deaths in men. One novel approach to combat prostate cancer is gene therapy. A replication-deficient recombinant adenoviral vector (AdRSVlacZ) expressing bacterial ␤-galactosidase (␤-gal) (lacZ ) under the control of the Rous sarcoma virus promoter was used to determine which delivery route was best for the transduction of adenoviral vectors to the prostate. Using a canine model, adenoviral vectors were administered by intravenous, intra-arterial, and intraprostatic (i.p.) injections. After injections, the expression of the lacZ gene was measured in canine prostates as well as in various other organs to determine the distribution of the disseminated adenoviral vector by (a) the percentage of cells expressing lacZ in situ (5-bromo-4-chloro-3-indolyl ␤-D-galactoside staining), (b) ␤-gal enzymatic activity (colorimetric ␤-gal assay), and (c) polymerase chain reaction of genomic DNA using primers specific for the adenoviral genome. An i.p. injection of the adenoviral vector resulted in a greater transduction rate and expression level of lacZ in the prostate than either intravenous or intra-arterial (inferior vesical/prostatic artery) injections. Thus, an i.p. (or intratumoral) injection seems to be the best route to treat local regional prostate cancer by viral-based gene therapy.

The activity and expression of transgene ␤-galactosidase (lacZ) by replication-deficient adenoviral vectors (Ad-lacZ) containing prostate-specific promoters were compared using an in vivo canine model. The prostate tissue-specific promoters were prostate-specific antigen, probasin, and mouse mammary tumor virus long-terminal repeat, which were fused separately to an Escherichia coli lacZ gene. Dogs underwent laparotomy, and adenoviral vectors were delivered by direct intraprostatic injection. At 72 hours postinjection, the prostate and various other organs were harvested to evaluate the degree of prostate expression and dissemination of adenoviral vectors. Expression of lacZ in tissues was determined by 5-bromo-4-chloro-3-indolyl ␤-D-galactoside staining, ␤-galactosidase assay, and E. coli lacZ reverse transcriptase-polymerase chain reaction (PCR). The presence of adenoviral DNA sequences in canine tissues was determined by PCR using primers specific for the type 5 adenoviral genome. All three of the prostate-specific adenoviruses tested effectively expressed the lacZ gene in the canine prostate, but expression levels were lower than that of the control viral vector AdRSVlacZ following intraprostatic injection. By PCR, adenoviral vector DNA was detected in other organs and tissues, including the bladder and vas deferens. However, reverse transcriptase-PCR analysis revealed that prostate-specific Ad-lacZ vectors only transcribed lacZ mRNA in the prostate and not in nonprostatic tissues. Thus, these novel prostate-specific adenoviral vectors each have equal in vivo expression exclusively in the prostate and may potentially be used for prostate cancer gene therapy.