MRI-monitored ultrasonic heating allows for the spatially controlled in vivo expression of the transgene luciferase in canine prostate

Efficient and controlled delivery is one of the largest obstacles towards effective clinical use of gene therapy. In this study, we investigate the use of MRI-monitored ultrasound to induce enhanced expression of luciferase after local injection of the gene construct Ad-HSP-Luc, an adenoviral vector containing a human hsp70B promoter and a transgene for the firefly luciferase gene. Using a construct that includes an hsp promoter allows us to activate the associated transgene only in areas that are subsequently heated after injection. Using ultrasound imaging, 1mL of purified virus was injected into both lobes of the prostates of three beagles. 48 hours later, under MRI guidance, we heated the left lobe of the prostate using a 1.5MHz ultrasound transducer driven by a multi-channel, RF driving system. Left lobe prostate temperature was maintained at or above 42/spl deg/C for periods of 25 minutes as measured by thermocouples placed in the prostate. After 12 hours, the dogs were sacrificed and the lobes were analyzed for luciferase activity. Increased luciferase expression was observed in areas that were exposed to ultrasonic heating. This study demonstrates the feasibility of using ultrasonic heating to spatially control transgene expression using a minimally invasive approach.