Robust cancer-specific gene expression by a novel cassette with hTERT and CMV promoter elements.

We developed and validated a novel hTERT/CMV promoter element-driven gene expression cassette that can robustly enhance cancer-specific gene expression. The following gene expressional elements were located in tandem within the plasmid construct: [hTERT core promoter, cytomegalovirus (CMV) minimized promoter, RU5' sequence, an inserted gene, BGH polyA, hTERT enhancer]; this is hereafter referred to as the hT/Cm-R-hT construct. Using various human cancer cell lines and normal cells, the cancer-specific transcription of the green fluorescent protein (GFP) gene was examined by western blotting and fluorescence microscopy. Cancer-specific gene expression was robustly achieved in the hT/Cm-R-hT plasmid in comparison to the other control hT/Cm-driven construct. Notably, the expression level of GFP observed in the hT/Cm-R-hT-driven construct was superior to that of the control plasmid with the conventional CMV promoter in HEK293 cells, which are known to possess higher hTERT activity than normal cells. We next examined the availability of hT/Cm-R-hT in detecting the target GFP expressing cancer cells from human peripheral blood mononuclear cells (PBMCs). The hT/Cm-R-hT plasmid successfully induced cancer-specific gene expression; the robust expression of GFP was observed in target HeLa cancer cells, whereas GFP was not visibly expressed in normal PBMCs. The plasmid allowed for the selective visualization of viable HeLa cancer cells in mixed cell cultures containing up to 10000-fold more PBMCs. These findings indicate that the hT/Cm-R-hT expressional system is a valuable tool for detecting viable cancer cells mixed with normal cells. The current system can therefore be applied to the in vitro detection of cancer cells that are disseminated in the blood and other types of body fluid in vivo. Since the current system can also be applied to other types of vectors, including virus vectors, this approach using the hTERT promoter-based construct is expected to become a valuable tool for enhancing cancer-specific gene expression.