Viral Dose, Radioiodine Uptake, and Delayed Efflux in Adenovirus Mediated NIS Radiovirotherapy Correlates with Treatment Efficacy

We have constructed a prostate tumor specific conditionally replicating adenovirus (CRAd), named Ad5PB_RSV-NIS that expresses the human sodium iodine symporter gene (hNIS). LNCaP tumors were established in nude mice and infected with this CRAd to study tumor viral spread, NIS expression, and efficacy. Using quantitative polymerase chain reaction (QPCR) we found a linear correlation between the viral dose and viral genome copy numbers recovered after tumor infection. Confocal microscopy showed a linear correlation between adenovirus density and NIS expression. Radioiodine uptake vs. virus dose-response curves revealed that the dose response curve was not linear and displayed a lower threshold of detection at 10(7) vp and an upper plateau of uptake at 10(11) vp. The outcome of radiovirotherapy was highly dependent upon viral dose. At 10(10) vp no significant differences were observed between virotherapy alone or radiovirotherapy. However, when radioiodine therapy was combined with virotherapy at a dose of 10(11) vp, significant improvement in survival was observed, indicating a relationship between viral dose-response uptake and the efficacy of radiovirotherapy. The reasons behind the differences in radioiodine therapy efficacy can be ascribed to more efficient viral tumor spread and a decrease in the rate of radioisotope efflux. Our results have important implications regarding the desirables and undesirable characteristics of vectors for clinical translation of virus-mediated NIS transfer therapy