Noninvasive and Targeted Gene Delivery into the Brain Using Microbubble-Facilitated Focused Ultrasound

Abstract

Recombinant adeno-associated viral (rAAV) vectors are potentially powerful tools for gene therapy of CNS diseases, but their penetration into brain parenchyma is severely limited by the blood-brain barrier (BBB) and current delivery relies on invasive stereotactic injection. Here we evaluate the local, targeted delivery of rAAV vectors into the brains of mice by noninvasive, reversible, microbubble-facilitated focused ultrasound (FUS), resulting in BBB opening that can be monitored and controlled by magnetic resonance imaging (MRI). Using this method, we found that IV-administered AAV2-GFP (green fluorescence protein) with a low viral vector titer (1×109 vg/g) can successfully penetrate the BBB-opened brain regions to express GFP. We show that MRI monitoring of BBB-opening could serve as an indicator of the scale and distribution of AAV transduction. Transduction peaked at 3 weeks and neurons and astrocytes were affected. This novel, noninvasive delivery approach could significantly broaden the application of AAV-viral-vector-based genes for treatment of CNS diseases.

Focused ultrasound-induced blood-brain barrier opening for non-viral, non-invasive, and targeted gene delivery

“…We demonstrated that the transduction observed 2 days after BBB opening had a relative intensity that was 5-fold greater than that of the LpDNA only. The in vivo enhancement of transgene expression in the BBB-opened brain was consistent with our previous results that showed drugs and genes can be deposited at higher concentrations into targets by FUS-induced BBB opening [12,15], demonstrating the stability and repeatability of this FUS-BBB opening technique. We have proven that LpDNA with FUS sonication produces sufficient plasmid deposition to express both luciferase and GDNF production (Fig.…”

“…Most strategies have utilized viral vectors to deliver therapeutic genes through BBB opening [11,12]. However, there is little information available on delivery to the brain using non-viral vectors, the relevance of plasmid sequestration in liposomes on the localized transgene expression, or the effect of this treatment on transduction of genes.…”

“…It has also become one of the most promising strategies to achieve non-invasive and targeted CNS gene delivery [6,7,[11][12][13]. Ultrasound-mediated MB destruction has the potential to open the BBB tight junctions and trigger therapeutic agent deposition at specific sites with non-invasive sonication [14,15].…”

The Size of Blood–Brain Barrier Opening Induced by Focused Ultrasound is Dictated by the Acoustic Pressure

“…[17][18][19][20] For the relatively larger-size dextrans (500 and 2,000 kDa), IC was found to be the main mechanism for their successful trans-BBB delivery. Cavitation detection has not been reported in previous studies of FUS-enhanced delivery of larger agents, such as antibodies 4,[32][33][34] and gene vectors, 5,35,36 whose MWs are on the same scale as the 500 and 2,000 kDa dextran, respectively. The MI of the FUS used in those studies varied within the range of 0.63 to 1.56, and the MI corresponding to 0.84 MPa (1.5 MHz) in our study was 0.69, which was in the lower end of the aforementioned range.…”

Nanoscale drug delivery systems and the blood–brain barrier

“…74 Overall, the evidence supports the use of microbubble-enhanced focused ultrasound to locally and temporally disrupt the BBB to deliver viral vectors. 75 A second, less popular, but very interesting, way to physically open TJs is using electromagnetic waves. 76 A recent in vitro study 77 demonstrated that exposure to electromagnetic pulses can affect key TJ-related proteins, including ZO-1, occludin, and claudin-5.…”