Adenoviral-mediated gene therapy for thyroid carcinoma using thymidine kinase controlled by thyroglobulin promoter demonstrates high specificity and low toxicity

A replication defective adenovirus transducing thymidine kinase (TK) gene u nder the control of the rat thyroglobulin (rTg) promoter (AdrTgtk) was deve loped to evaluate its cell-specific killing activity in gene therapy. We al so developed adenoviruses containing the TK gene driven by the cytomegalovi rus (CMV) promoter (Ad-CMVtk), and luciferase (Luc) gene driven by the rTg or CMV promoter (AdrTgLuc or AdCMVLuc). Luc activity in FRTL-5, HepG2 COS1, rMTC, hMTC, Hela, GH3, T98G, and CA77 cells was measured after infection w ith AdrTgLuc or AdCMVLuc. FRTL-5 cells produce thyroglobulin (Tg), whereas all other cells are non-Tg-producing cell lines. Transduction by AdCMVLuc c aused high Luc activity in all cell lines. However, infection with AdrTgLuc induced Luc activity only in FRTL-5 cells. AdCMVtk or AdrTgtk was used to transduce various cell lines to evaluate the different killing effect. Afte r infection with AdCMVtk vector followed by ganciclovir (GCV) treatment, ce ll growth was strongly suppressed in all cell lines compared both to noninf ected cells and to cells infected by AdCMVLuc in the presence of GCV. When FRTL-5 cells were infected with AdrTgtk followed by GCV treatment, more tha n 90% were killed, but only a minimal effect was observed in other cell lin es, indicating that the Tg promoter transduced TK expression only in Tg-pro ducing cells. When adenovirus is given intravenously, liver and spleen are the major organs infected. A high Luc activity was found in liver and splee n of AdCMVLuc treated animals. No Luc activity was found in liver and splee n of AdrTgLuc-treated animals, indicating that rTg does not transduce Luc e xpression in non-Tg-producing tissues in. vivo. No significant changes of t he serum transaminase levels and histologic abnormalities were found in ani mals treated with AdrTgtk/GCV compared with control animals. High levels of serum transaminases, lymphocyte infiltration, some Kupffer's cell prominen ce, and extensive single cell hypatocyte death were found in AdCMVtk/GCV-tr eated animals, indicating severe liver damage induced, as expected, by a no ncell-specific promoter. These results indicate that transfer of TK gene dr iven by the rTg promoter has thyroid cell-specific killing ability in the p resence of GCV, little in vivo toxicity, and should be useful in the future for treating thyroid Tg-producing cancers.