Focused ultrasound-microbubble treatment arrests the growth and formation of cerebral cavernous malformations.

Cerebral cavernous malformations (CCMs) are vascular lesions within the central nervous system that cause debilitating neurological symptoms. Currently, surgical excision and stereotactic radiosurgery, the primary treatment options, pose risks to some patients. Here we tested whether pulsed, low intensity, focused ultrasound-microbubble (FUS-MB) treatments control CCM growth and formation in a clinically representative Krit1 null murine model. FUS-MB under magnetic resonance imaging (MRI) guidance opened the blood-brain barrier, with gadolinium contrast agent deposition most evident at perilesional boundaries. Longitudinal MRI revealed that, at 1 month after treatment, FUS-MB halted the growth of 94% of treated CCMs. In contrast, untreated CCMs grew ~7-fold in volume. FUS-MB-treated CCMs exhibited a marked reduction in Krit1 null endothelial cells. In mice receiving multiple FUS-MB treatments with fixed peak-negative pressures, de novo CCM formation was reduced by 81%, indicating a prophylactic effect. Our findings support FUS-MB as a minimally invasive treatment modality that can safely arrest murine CCM growth and prevent de novo CCM formation in mice. If proven safe and effective in clinical trials, FUS-MB treatment may enhance therapeutic options for CCM patients.

Introduction

Purpose BBB opening without drug delivery

Study Objective To determine whether MRI-guided pulsed low-intensity focused ultrasound with microbubbles (FUS-MB) can halt growth and prevent de novo formation of cerebral cavernous malformations in a Krit1-null mouse model.

Animal model / Human subject Mouse (Mus musculus); experimental strains: Pdgfb-CreERT2;Krit1 fl/null or Cdh5-CreERT2;Krit1 fl/null (with PC::G5-tdT reporter); non-transgenic controls: C57BL/6; age: 9–13 weeks; sex: None

Disease model Cerebral cavernous malformations (CCM)

MRI or image guidance method MRI guidance using high-resolution T2-weighted and T1-RARE images (baseline MR imaging used to select and guide targeting of pre-selected CCMs)

Targeted brain region(s) Cerebral cortex

Cargo name and characteristics Gadobenate dimeglumine (Multihance) — gadolinium-based MRI contrast agent (small-molecule chelate) administered IV to visualize BBB opening; Tamoxifen — small-molecule selective estrogen receptor modulator given subcutaneously to induce Cre-mediated Krit1 gene ablation

Route of administration Subcutaneous (tamoxifen); Intravenous (gadolinium contrast agent)

Outcomes and Safety

Summary of Outcomes Focused ultrasound with microbubbles (FUS‑MB) in Krit1‑null mice safely opened the BBB, arrested growth of ~94% of treated cerebral cavernous malformations, reduced Krit1‑null endothelial cells and altered immune infiltration, and was effective using fixed peak‑negative pressures of 0.4–0.6 MPa (single and repeat regimens) as well as a PCD‑modulated PNP protocol (time‑averaged ~0.23–0.30 MPa), with repeat fixed‑PNP sonications producing an 81% reduction in de novo lesion formation.

Duration of biological effect 1 month

Safety-related matter FUS-MB (particularly with real-time PCD-modulated PNP) was well tolerated in Krit1 null mice: BBB opening was transient (largely closed by 24 h), MRI showed no acute or chronic increases in lesion bleeding or volume, no obvious histopathological differences between treated and contralateral hemispheres, and treatment did not increase de novo lesion formation. However, higher fixed PNPs (>0.4 MPa) produced oedema and haemosiderin deposits in lesion-free brain tissue, harmonic emissions increased at 0.6 MPa, and the authors note they did not perform a Perls stain to directly assess bleeding as a limitation.

Brain Region

Ultrasound Parameters

Ultrasound instrument RK-300 small bore FUS device (FUS Instruments); 1.13 MHz single-element transducer. Centre-mounted fibre-optic hydrophone: 10 mm diameter, 15 mm aperture.

FUS Frequency 1.13 MHz (primary transducer); acoustic-emission monitoring at subharmonic/ultraharmonics: 0.5f = 0.565 MHz, 1.5f = 1.695 MHz, 2.5f = 2.825 MHz

FUS Pressure 0.2 MPa, 0.05 MPa, 0.4 MPa

FUS Mode pulsed

Pulse duration 10 ms

Duration of a single FUS session 2 minutes

Focal Characteristics Focal depth: None; Focal length: None; Aperture size: 15 mm

Treatment frequency Multiple sessions

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