Since RGD fiber-mutant adenovirus vector (AdRGD), which contains an
alphav-integrin tropism, is highly efficient in gene transduction to
melanoma, the AdRGD-mediated herpes simplex virus
thymidine kinase (HSVtk)/
ganciclovir (GCV) system is an attractive approach for
melanoma treatment. However, the intratumoral injection of AdRGD causes limited transgene expression in healthy normal tissue, due to unwanted vector spread. Herein, we describe our attempt to overcome this limitation related to the safety of HSVtk/GCV treatment by using AdRGD carrying either
melanoma-specific
tyrosinase (Tyr) promoter or
tumor-specific
telomerase reverse transcriptase (TERT) promoter instead of universal cytomegalovirus promoter. Our in vitro study revealed that Tyr promoter-regulated AdRGD exhibited high transgene expression specificity for
melanoma cells, and that TERT promoter-regulated AdRGD could induce efficient gene expression in
tumor cells, but was relatively quiescent in normal cells. Anti-B16BL6
melanoma effects in mice injected intratumorally with AdRGD-Tyr/HSVtk or AdRGD-TERT/HSVtk, after which GCV was injected intraperitoneally for 10 days, were comparable to those in mice injected with AdRGD-CMV/HSVtk
at 10 times less vector dosage. On the other hand, AdRGD-Tyr/HSVtk and AdRGD-TERT/HSVtk did not induce severe adverse effects even when they were intravenously injected into mice
at 10(9) plaque-forming units (PFU), whereas mice injected with AdRGD-CMV/HSVtk
at 10(8) PFU exhibited
body weight reduction and serum level increase of biochemical
enzymes for hepatotoxicity. These results indicate that AdRGD combined with transcriptional regulation using Tyr or TERT promoter is a potentially useful and safe vector system for suicide gene therapy for
melanoma.