MIA (melanoma inhibitory activity) promoter mediated tissue-specific suicide gene therapy of malignant melanoma

Suicide gene therapy of malignant melanoma essentially requires efficient gene transfer and highly selective therapeutic gene expression. To achieve this, recombinant adeno-associated virus (rAAV) particles were constructed containing the tissue-specific promoter of the human melanoma inhibitory activity (hMIA) gene combined with four copies of the enhancer element of the murine tyrosinase gene. Three melanoma and one cervix carcinoma cell line were infected with rAAV particles carrying a reporter gene under control of the enhancer/hMIA promoter in order to determine transcriptional activity and specificity of this system. Viral particles containing the enhancer/hMIA promoter mediated reporter gene activity only in melanoma cells, whereas infection with a cytomegalovirus (CMV)-based promoter construct induced unspecific gene expression. Correspondingly, transient transduction with viral particles bearing the HSVtk gene under the control of the enhancer/MIA promoter elements followed by treatment with ganciclovir (GCV) resulted in growth inhibition only in melanoma cells, whereas the CMV promoter-based construct induced unspecific cytotoxicity. In vivo experiments in nude mice demonstrated that tumors originating from human melanoma cells disappeared after stable, but not transient transduction with vectors bearing the HSVtk gene under the control of the enhancer/hMIA promoter in response to GCV application. In face of higher transduction efficiency, these rAAV particles might therefore be a useful tool for suicide gene therapy of malignant melanoma.