In vivo Adenovirus‐mediated Prodrug Gene Therapy for Carcinoembryonic Antigen‐producing Pancreatic Cancer

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Abstract
In gene therapy for malignancy, the herpes simplex virus thymidine kinase (HSVtk)‐ganciclovir (GCV) system has been widely used. For pancreatic cancer targeting, we estimated the therapeutic efficacy of gene transduction by an adenovirus‐carrying HSVtk gene under the control of a carci‐noembryonic antigen (CEA) promoter (AdCEAtk) followed by systemic administration of GCV. Four cell lines, CEA‐producing Su.86.86, BxPC‐3 (pancreatic cancer cells), MKN45 (gastric cancer cells) and CEA‐nonproducing HeLa, were used for analysis of GCV sensitivity induced by adeno‐viral gene transduction. To evaluate the therapeutic efficacy of AdCEAtk and GCV administration in human CEA‐positive pancreatic cancer in vivo, a subcutaneously implanted tumor‐bearing nude mouse model was used. When the HSVtk gene was transduced with a ubiquitous promoter into these cells, increase of the GCV sensitivity was independent of CEA‐production. In contrast, when the cells were transduced with a CEA promoter, the cell‐killing effect of GCV was increased in only CEA‐producing cells. For in vivo analysis, AdCEAtk was delivered into subcutaneously established tumors of Su.86.86 cells. Immunohistochemical staining of the tumor showed that HSVtk protein was expressed only in tumor cells, and tumor growth was markedly suppressed by administration of GCV. These results suggest that the adenovirus‐mediated transfer of HSVtk gene with CEA promoter specifically increases the GCV sensitivity of CEA‐producing pancreatic cancer cells in vitro and in vivo. This strategy may provide a useful tool for treating pancreatic cancer, especially CEA‐producing tumor cells.