Arrhenius analysis of the relationship between hyperthermia and Hsp70 promoter activation: a comparison between ex vivo and in vivo data.

PURPOSE

Tight regulation of gene expression in the region where therapy is necessary and for the duration required to achieve a therapeutic effect and to minimise systemic toxicity is very important for clinical applications of gene therapy. Hyperthermia in combination with a temperature sensitive heat shock protein (Hsp70) promoter presents a unique approach allowing non-invasive spatio-temporal control of transgene expression. In this study we investigated the in vivo and ex vivo relationship between temperature and duration of thermal stress with respect to the resulting gene expression using an Arrhenius analysis.

MATERIALS AND METHODS

A transgenic mouse expressing the luciferase reporter gene under the transcriptional control of a thermosensitive promoter was used to assure identical genotype for in vivo (mouse leg) and ex vivo (bone marrow mononuclear and embryonic fibroblast cells) studies. The mouse leg and cells were heated at different temperatures and different exposure times. Bioluminescence imaging and in vitro enzymatic assay were used to measure the resulting transgene expression.

RESULTS

We showed that temperature-induced Hsp70 promoter activation was modulated by both temperature as well as duration of hyperthermia. The relationship between temperature and duration of hyperthermia and the resulting reporter gene expression can be modelled by an Arrhenius analysis for both in vivo as well as ex vivo.

CONCLUSIONS

However, the increase in reporter gene expression after elevating the temperature of the thermal stress with 1°C is not comparable for in vivo and ex vivo situations. This information may be valuable for optimising clinical gene therapy protocols.