A potentially tumour specific targeted radiotherapy/gene therapy strategy for treatment of malignant disease

Aims: We have developed a novel targeted radiotherapy/gene therapy strategy for treatment of malignant disease utilising introduction of the Noradrenaline transporter gene (NAT) into malignant cells. We introduced NAT into non-NAT expressing UVW glioma cells and endowed the cells with the ability to achieved high levels of [131I]MIBG and [211At]MABG uptake and dose-dependent cell kill. A requirement for cancer gene therapy, is tumour specific expression of therapeutic transgenes. We investigated potentially tumour specific promoters, (the human telomerase promoters hTERC and hTERT), for their capacity to express NAT in UVW glioma cells at levels sufficient for therapeutic effect following radionuclide administration. Methods: UVW cells were stably transfected with the NAT gene under the control of the RSV, hTERT or hTERC promoter elements. Gene expression levels were determined by MIBG uptake. Cytotoxicity was assessed in multicellular tumour spheroids via clonogenic survival and regrowth delay after administration of [211At]-astatinated benzylguanidine ([211At]MABG) and [131I]MIBG. Results and Conclusions: UVW cells transfected with RSV/NAT, hTERC/NAT and hTERT/NAT were endowed with the capacity for active uptake of [131I]MIBG and [211At]MABG. NAT gene expression via the hTERC and hTERT promoters resulted in uptake levels 70% and 60% of that achieved by the RSV promoter control. We observed dose dependant cell kill of clonogens derived from [131I]MIBG-treated spheroids. Reduction in surviving fraction was related to promoter activity. Administration of [211At]MABG resulted in spheroid sterilisation at doses 1000 times lower than those required using [131I]MIBG. All NAT transfected cells, regardless of the promoter employed, were sterilised by the same dosage of [211At]MABG. These results indicate that the human telomerase promoters are excellent candidates for tumour-specific transgene expression and that NAT gene transfer in combination [211At]MABG treatment is a potent anticancer strategy.