153. Adenoviral Gene Therapy Vectors Expressing the Adenovirus Death Protein Demonstrate Increased Transgene Expression In Vivo as Demonstrated by Dose-Volume Histogram Analysis of Reporter Gene Activity

Abstract

A current limitation of cancer gene therapy is the lack of significant efficacy in the clinic. To improve the effectiveness of adenovirus-delivered gene therapy for the treatment of cancer, we have evaluated various methods to increase transgene expression in vivo. One such method was to co-express the adenoviral death protein (ADP) in a replication-competent adenovirus (Ad5-hNISrep-ADP) also expressing the human sodium iodide symporter (hNIS) as a reporter gene. The ADP gene product has been shown by others to increase cell lysis and adenovirus spread in vitro. The hNIS gene product enables adenovirus-infected cells to uptake the radioactive tracer, 99mpertechnetate (99mTcO4-), which can be imaged non-invasively using gamma camera scintigraphy, and the volume of transgene expression can be quantified in thin tissue sections using dose-volume histogram (DVH) analysis. To study the possible effect of ADP on transgene expression in vivo, the volume of transgene expression was compared following direct injection of replication-competent adenoviruses lacking (Ad5-hNISrep) or containing (Ad5-hNISrep-ADP) ADP into contralateral lobes of the na|[iuml]|ve canine prostate and into human tumor xenografts implanted bilaterally in the hind legs of Balb/c mice. Following injection of 1|[times]|1011 vp (0.1 ml) in the canine prostate, the volume of hNIS-dependent uptake of 99mTcO4- with Ad5-hNISrep-ADP was on average 3-fold greater than with Ad5-hNISrep (5.0%|[plusmn]|1.3% vs. 1.5%|[plusmn]|0.5% of the prostate volume, respectively; n=3). Similarly, following injection of 1|[times]|1010 vp (0.05 ml) in human tumor xenografts (150 mm3), the extent of hNIS activity as a percentage of the tumor volume was 16.2%|[plusmn]|9.5% for Ad5-hNISrep-ADP versus 5.8%|[plusmn]|2.5% for Ad5-hNISrep (n=6), representing a 2.3-fold increase in transgene expression when ADP was present. These results indicate that inclusion of ADP in adenoviral gene therapy vectors can significantly improve the volume of transgene expression in vivo, which may translate into improved therapeutic efficacy when used in a clinical setting.