CanScript, an 18-Base pair DNA sequence, boosts tumor cell-specific promoter activity: Implications for targeted gene therapy

Gene therapy protocols for the treatment of cancer often employ gene promoter sequences that are known to be overexpressed in specific tumor cell types relative to normal cells. These promoters, while specific, are often weakly active. It would be desirable to increase the activity of such promoters, while at the same time retain specificity, so that the therapeutic gene is more robustly expressed. Using a luciferase reporter DNA construct in both in vitro cell transfection assays and in vivo mouse tumor models, we have determined that in the absence of any other DNA sequence, a previously identified 18-base pair enhancer sequence called CanScript, lying upstream of the MSLN gene, has ∼25% of the promoter activity of CAG, a very strong non-specific promoter/enhancer, in tumor cells in which MSLN is highly expressed. Furthermore, tandem repeat copies of CanScript enhance transcription in a dose-dependent manner and, when coupled with promoter sequences that are active in tumor cells, increase promoter activity. These findings suggest that the incorporation of CanScript into gene constructs may have application in enhancing activity of promoters used in cancer-targeting gene therapy strategies, thereby improving therapeutic efficacy.