Promoter fragments from either the RNA (hTR) or the catalytic components (hTERT) of the telomerase genes can be potentially used to drive the cancer-selective expression of therapeutic genes in cancer gene therapy. To assess their selectivity in vivo, the authors have generated replication-incompetent adenoviruses in which either of these promoters drives the expression of the Na/I symporter (NIS). Transgene expression was monitored using positron emission tomography (PET) upon injection of ¹²⁴ I as tracer. The cover figure shows PET images reflecting NIS expression upon intratumoral administration of Ad-Luciferase (top panel), Ad-CMV-hNIS (second panel from the top), Ad-hTERT-NIS (third panel from the top) and Ad-hTR-NIS (bottom panel). The data demonstrate that both promoter fragments provide cancer-selective expression that can be visualized and quantitated by PET. Given that this methodology is directly scalable to humans and that the NIS gene has therapeutic potential, imaging gene expression using the NIS PET reporter gene could be applied to measure telomerase promoter-driven transgene expression in clinical trials. For details, see the article by Groot-Wassink et al. on page 4906 of this issue.

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