Focused Ultrasound for Improved Delivery of AAV Vectors to the brain for the Treatment of Huntington's Disease

Huntington’s disease (HD) is a fatal, autosomal dominant, neurodegenerative disorder caused by a cytosine-adenine-guanine (CAG) trinucleotide repeat expansion in exon 1 of the HTT gene that encodes the huntingtin (HTT) protein. There are currently no cures for HD and lowering HTT mRNA via RNA interference (RNAi) gene therapy, appears to be a promising strategy. Gene delivery to the central nervous system (CNS) is challenging due to the presence of the blood brain barrier (BBB). Focused Ultrasound (FUS) with microbubbles (MB) can be used to temporarily disrupt the BBB in a less-invasive manner to deliver therapeutic genes to the CNS. Safe and reversible BBB opening has been reported from phase one clinical trials in patients with Alzheimer’s disease, Parkinson’s disease and Amyotrophic Lateral Sclerosis. However, no studies have been conducted to investigate the safety of FUS-mediated BBB opening in HD patients and there have been no preclinical studies testing the delivery of adeno-associated viral vectors (AAVs) in mouse models of HD. Here, we tested the delivery of ssAAV9 containing a miRNA (miR1050) targeting HTT mRNA using FUS in combination with MB to the right striatum of Q175 HD mice. Our results demonstrate that ss-AAV9-CBA-GFP infected astrocytes and neurons in the cortex and striatum of WT 2-month, zQ175 2- and 6-month-old mice following FUS treatment and tail vein injection of ss-AAV9-CBA-GFP at a dose of 2.2 × 1010 vg/g. The permeability of the BBB was assessed using gadolinium-enhanced T1-weighted images and our results show increased BBB permeability in the sonicated hemisphere of WT and HD mice. FUS-mediated AAV delivery also led to strong GFP expression in the FUS-treated hemisphere compared to the untreated hemisphere. These findings show that FUS+MB can be used to deliver an AAV-miRNA based gene therapy to specific brain regions in the zQ175 HD mouse model.

References
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Spronck, E.A., Brouwers, C.C., Vallès, A., de Haan, M., Petry, H., van Deventer, S.J., Konstantinova, P. and Evers, M.M., 2019. AAV5-miHTT gene therapy demonstrates sustained huntingtin lowering and functional improvement in Huntington disease mouse models. Molecular Therapy-Methods & Clinical Development, 13, pp.334-343.

Kofoed, R.H., Dibia, C.L., Noseworthy, K., Xhima, K., Vacaresse, N., Hynynen, K. and Aubert, I., 2022. Efficacy of gene delivery to the brain using AAV and ultrasound depends on serotypes and brain areas. Journal of Controlled Release, 351, pp.667-680.