Focused ultrasound for targeted delivery of siRNA and efficient knockdown of Htt expression

RNA interference is a promising strategy for the treatment of Huntington's disease (HD) as it can specifically decrease the expression of the mutant Huntingtin protein (Htt). However, siRNA does not cross the blood-brain barrier and therefore delivery to the brain is limited to direct CNS delivery. Non-invasive delivery of siRNA through the blood-brain barrier (BBB) would be a significant advantage for translating this therapy to HD patients. Focused ultrasound (FUS), combined with intravascular delivery of microbubble contrast agent, was used to locally and transiently disrupt the BBB in the right striatum of adult rats. 48h following treatment with siRNA, the right (treated) and the left (control) striatum were dissected and analyzed for Htt mRNA levels. We demonstrate that FUS can non-invasively deliver siRNA-Htt directly to the striatum leading to a significant reduction of Htt expression in a dose dependent manner. Furthermore, we show that reduction of Htt with siRNA-Htt was greater when the extent of BBB disruption was increased. This study demonstrates that siRNA treatment for knockdown of mutant Htt is feasible without the surgical intervention previously required for direct delivery to the brain.