Ultrasound-mediated blood–spinal cord barrier opening prolongs survival in an ALS mouse model

Background: Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by a progressive loss of motor neurons. The limited efficacy of recent therapies in clinical development may be linked to lack of drug penetration to the affected motor neurons due to the blood-brain barrier (BBB) and blood-spinal cord barrier (BSCB). Methods: In this work, the safety and efficacy of repeated short transient opening of the BSCB by low intensity pulsed ultrasound (US, sonication) was studied in females of an ALS mouse model (B6.Cg-Tg(SOD1*G93A)1Gur/J). The BSCB was disrupted using a 1 MHz ultrasound transducer coupled to the spinal cord, with and without injection of insulin-like growth factor 1 (IGF1), a neurotrophic factor that has previously shown efficacy in ALS models. Findings: Results in healthy mouse models demonstrated that the BSCB can be safely disrupted and IGF1 concentrations significantly enhanced after a single session of transient BSCB disruption (176 ±32 µg/g vs. 0.16 ±0.008 µg/g, p<0.0001). Five repeated weekly US performed in female ALS mice demonstrated a survival advantage in mice treated with IGF1 and ultrasound (US+IGF1) compared to treatment with IGF1 alone (176 vs. 166 days, p=0.0038). Surprisingly, this survival advantage was also present in mice treated with ultrasound (US) alone vs untreated mice (178.5 vs. 166.5 days, p=0.0061). Analysis of glial cell immunoreactivity and microglial transcriptome showing reduced cell proliferation pathways, in addition to lymphocyte infiltration, suggested that the beneficial effect of US or US+IGF1 could act through immune cell modulation. Interpretation: These results show the first step towards a possible beneficial impact of transient BSCB opening for ALS therapy and suggest implication of immune cells.