Melanoma-specific expression in first-generation adenoviral vectors in vitro and in vivo -- use of the human tyrosinase promoter with human enhancers.

Current treatment regimens for patients with metastatic melanoma are not curative, and new treatment strategies are needed. One possible approach is targeted treatment using the tyrosinase promoter for melanoma-specific expression of genes delivered by adenoviral (Ad) vectors. In this study, a vector with the human minimal tyrosinase promoter and two human enhancer elements (2hE-hTyrP) was compared with different hybrid promoter constructs, containing tyrosinase regulatory sequences and the viral simian virus 40 (SV40) promoter. The tissue specificity of the first-generation vectors was measured by enhanced green fluorescence protein (EGFP) reporter flow cytometry in 12 human melanoma and nonmelanoma cell lines. In the melanotic melanoma cells, the activity of the 2hE-hTyrP promoter was comparable with the activity of the cytomegalovirus promoter, and the background expression levels obtained in the nonmelanoma cell lines confirmed the strict tissue-specific property of this promoter. The hybrid SV40-based promoters were effective, but no tissue specificity was observed even after the inclusion of tyrosinase enhancer elements identical to the elements used in the 2hE-hTyrP promoter. The in vivo tissue specificity of the 2hE-hTyrP vector was demonstrated in subcutaneous xenografted tumors by ex vivo detection of EGFP fluorescence with the IVIS Imaging equipment and fluorescence microscopy visualizing the in situ EGFP expression in tumor sections. The tyrosinase mRNA level in the 12 cell lines was measured by quantitative real-time RT-PCR, and the expression levels reliably reflected to what extent the 2hE-hTyrP promoter could drive the gene expression in the individual cell lines. In conclusion, the human tyrosinase promoter fused to two human tyrosinase enhancers (2hE-hTyrP) can be used for efficient tissue-specific expression from first-generation Ad vectors in melanoma cell lines both in vitro and in vivo, as predicted by the quantitative tyrosinase mRNA levels in the melanoma and nonmelanoma cell lines tested.