Feasibility of a predictive model of Hsp70b-activated gene therapy protein expression during ultrasound hyperthermia

Abstract

Gene therapy has been heralded as a possible approach to a variety of diseases and conditions, ranging from cancer and heart disease to blindness and neurodegenerative diseases. However, progress in gene therapy requires a delivery system that can control when and where the therapeutic proteins will be generated. Our study was performed to determine the feasibility of attaching heat-inducible promoters to genes of interest in order to control activation of the gene in vivo via ultrasound-induced hyperthermia monitored by MRI thermometry. We first demonstrated that gene therapy-mediated gene expression could be spatially and temporally controlled with this method. Further studies were subsequently performed to determine if the activation of a particular heat-inducible gene, Hsp70b, could be quantified and predicted a priori during hyperthermia, thus allowing advance knowledge of the protein levels over time. Experiments indicated that as the temperature and duration of a hyperthermic shock increased, peak expression levels of Hsp70b mRNA also increased until a saturation level was reached. In addition, as the duration of a hyperthermic shock increased, the time during which Hsp70b mRNA remained elevated also increased. Most significantly, a correlation was found between total Hsp70b mRNA production generated by thermal shock and thermal dose, a predictor of dose often used in hyperthermia therapies. The relationship found between total Hsp70b mRNA production and thermal dose suggests that a real-time predictive model of therapeutic protein dose kinetics after ultrasound-induced hyperthermia for gene therapy is feasible. However, the creation of such a model would require further precision experimentation for which ultrasonically-induced hyperthermia is not suited. A final study was performed and found that Hsp70b was not activated by the mechanical stress caused by ultrasound. These results confirm that a predictive model applicable to ultrasonically-induced hyperthermia could be developed using waterbath techniques that will allow tighter control of temperature.