Non-Invasive Monitoring of Hsp70 Promoter Activity Using Firefly Luciferase and Cell Viability of Three Tumor Cell Lines Exposed to Different Levels of Heat

To better understand the temporal pattern of hsp70 transcription, three tumor cell lines (M21, SCCVII, NIH3T3) were transfected with a Hsp70A.1 promoter to express luciferase (luc). The cells were exposed to a range of temperatures (38-52°C) for 20 minutes and luciferase activity was measured using a CCD camera. Luciferase activity was assessed every 2 h for 12 h, then every 6 h for another 12 h, and finally every 12 h for an additional 84 h post stress. Each cell line had its own distinct temporal pattern of luciferase activity. The NIH3T3 cells had the highest luciferase activity at 46°C 12 h post-stress. The SCCVII line was the least heat resistant cell line. The human M21 line was the most heat resistant cell line, maximum luciferase activity occurred at 48°C and 48 h post-stress. At the highest level of luciferase activity, the SCCVII and the NIH3T3 line had 54% and 58% viable cells whereas the M21 line had 94%. The combination of assessing the luciferase activity and the viability of cells may be useful for gene therapy applications and for evaluating collateral thermal damage generated during treatment of biological tissue with heat.