Current and Emerging Systems for Focused Ultrasound-Mediated Blood-Brain Barrier Opening

Delivering Gd-Labeled IgG Antibodies Into the Mouse Brain Following Focused Ultrasound Treatment

OBJECTIVE

Antibody-based therapy has emerged as a powerful tool for targeted treatment of neurological diseases, such as brain cancer and neurodegenerative disorders. However, direct, scalable, and safe confirmation of antibody delivery into the brain remains challenging. Antibodies can be effectively tracked when tagged with molecules that are detectable by medical imaging modalities, such as MRI, PET, or SPECT. In this study, we aimed to confirm gadolinium (Gd)-labeled IgG antibody delivery into the mouse brain using MRI, following exposure to focused ultrasound (FUS) and circulating microbubbles.

METHODS

We acquired MR images of the mouse brain to evaluate antibody delivery into the targeted brain region. First, we quantified the MR signal of Gd-labeled IgG antibodies in phantoms using preclinical 9.4 T and clinical 3 T MRI scanners. Then, we determined optimal ultrasound and MR imaging parameters to non-invasively and safely disrupt the blood-brain barrier in a localized and reversible manner and effectively monitor antibody delivery into the murine brain, respectively.

RESULTS

We confirmed that IgG antibodies can be reliably delivered into the murine brain using FUS and microbubble treatment and that we can track their biodistribution within the brain parenchyma using clinically relevant MR image sequences. The maximum detected volume of Gd-IgG antibody delivery (n = 4) was determined to be 0.12 ± 0.02 mm3 at t = 75.3 ± 17.3 minutes following treatment.

CONCLUSION

This work paves the way for a scalable and non-ionizing method for performing and evaluating antibody delivery into the brain.

Identifying new therapeutics for focused ultrasound-enhanced drug delivery in the management of glioblastoma

Glioblastoma, a grade IV astrocytoma, typically has a poor prognosis, with most patients succumbing within eighteen months of diagnosis and few experiencing long-term survival. Focused ultrasound, an emerging localized therapy, has shown promising results in early-phase studies for glioblastoma by improving the uptake of temozolomide and carboplatin. The blood-brain barrier is critical to homeostasis by regulating the movement of substances between the bloodstream and the central nervous system. While this barrier helps prevent infections from bloodborne pathogens, it also hinders the delivery of cancer therapies to gliomas. Combining focused ultrasound with circulating microbubbles enhances local blood-brain barrier permeability, facilitating the intratumoral uptake of systemic cancer therapies. The purpose of this study was to identify promising new therapeutics in the treatment of glioblastoma for localized drug delivery via focused ultrasound. This review provides an overview of the current standard of care for newly diagnosed and recurrent glioblastoma, identifies current therapies indicated for the treatment, discusses key aspects of microbubble resonators, describes focused ultrasound devices under evaluation in human trials, and concludes with a perspective of emerging therapeutics for future studies.

Overview of Therapeutic Ultrasound Applications and Safety Considerations: 2024 Update

A 2012 review of therapeutic ultrasound was published to educate researchers and physicians on potential applications and concerns for unintended bioeffects (doi: 10.7863/jum.2012.31.4.623). This review serves as an update to the parent article, highlighting advances in therapeutic ultrasound over the past 12 years. In addition to general mechanisms for bioeffects produced by therapeutic ultrasound, current applications, and the pre-clinical and clinical stages are outlined. An overview is provided for image guidance methods to monitor and assess treatment progress. Finally, other topics relevant for the translation of therapeutic ultrasound are discussed, including computational modeling, tissue-mimicking phantoms, and quality assurance protocols.

An update on the role of focused ultrasound in neuro-oncology

PURPOSE OF REVIEW

Brain tumor treatment presents challenges for patients and clinicians, with prognosis for many of the most common brain tumors being poor. Focused ultrasound (FUS) can be deployed in several ways to circumvent these challenges, including the need to penetrate the blood-brain barrier and spare healthy brain tissue. This article reviews current FUS applications within neuro-oncology, emphasizing ongoing or recently completed clinical trials.

RECENT FINDINGS

Most clinical interest in FUS for neuro-oncology remains focused on exploring BBB disruption to enhance the delivery of standard-of-care therapeutics. More recently, the application of FUS for radiosensitization, liquid biopsy, and sonodynamic therapy is garnering increased clinical attention to assist in tumor ablation, early detection, and phenotypic diagnosis. Preclinical studies show encouraging data for the immunomodulatory effects of FUS, but these findings have yet to be tested clinically.

SUMMARY

FUS is a burgeoning area of neuro-oncology research. Data from several forthcoming large clinical trials should help clarify its role in neuro-oncology care.

Metabolomic profile of cerebral tissue after acoustically-mediated blood-brain barrier opening in a healthy rat model: a focus on the contralateral side

Microbubble (MB)-assisted ultrasound (US) is an innovative modality for the non-invasive, targeted, and efficient delivery of therapeutic molecules into the brain. Previously, we reported the first metabolomic signature of blood-brain barrier opening (BBBO) induced by MB-assisted US. In the present study, the neurometabolic consequences of acoustically-mediated BBBO on cerebral tissue were investigated using multimodal metabolomics approaches. Sinusoid US waves (1 MHz, peak negative pressure 0.6 MPa, burst length 10 ms, total treatment time 30 s, MB bolus dose 0.7 × 105 MBs/g) were applied on the rats' right striatum (ipsilateral side). Brain was collected and both striata were then dissected 3 h, 2 days, and 1 week after BBBO. After tissue preparation, the samples were analyzed using nuclear magnetic resonance spectrometry (NMRS) and high-performance liquid chromatography coupled to mass spectrometry (HPLC-MS). Our findings showed a slight disruption of metabolic pathways in contralateral striata of animals. Analyses of metabolic pathways indicated changes in amino acid metabolisms. In addition, tryptophan derivate dosages revealed the perturbation of a central metabolite of the kynurenine pathway (i.e., 3-hydroxy-kynurenine). In conclusion, the acoustically-mediated BBBO of the ipsilateral cerebral hemisphere induced significant change in metabolism of contralateral one.

Focused ultrasound blood-brain barrier disruption in high-grade gliomas: Scoping review of clinical studies

BACKGROUND

This scoping review aims to comprehensively review the available literature on the safety and efficacy of focused ultrasound (FUS) for blood-brain barrier disruption (BBBD) in patients with high-grade gliomas, including glioblastoma (GBM). High-grade gliomas pose significant challenges in neuro-oncology due to their aggressiveness and intricate location, often limiting the efficacy of traditional treatments. FUS offers a promising approach by transiently disrupting the blood-brain barrier, thereby facilitating enhanced drug delivery to tumor cells while minimizing systemic side effects.

METHODS

A scoping review adhering to PRISMA guidelines was conducted to explore the literature on FUS-induced BBBD in glioma patients. PubMed and Embase databases were searched from inception to April 2024 using defined keywords. Original clinical studies focusing on FUS for BBBD in gliomas were included. Two reviewers independently screened records, with conflicts resolved by a third reviewer. Data extraction and quality assessment were performed accordingly.

RESULTS

A total of 1,310 studies were initially identified, resulting in nine eligible studies after screening and selection. These studies, published between 2016 and 2024, included 106 patients (39.6 % female) with ages ranging from 29 to 80 years. Recurrent GBM was the most common diagnosis (100 patients), with other diagnoses including anaplastic astrocytoma, diffuse infiltrating glioma, and oligodendroglioma. Various FUS devices and microbubble contrast agents were employed across the studies. Safety and efficacy were assessed in both experimental and clinical settings, with no significant adverse events reported during BBBD procedures. Notably, BBBD facilitated enhanced drug delivery to tumor tissue, demonstrating potential therapeutic benefits.

CONCLUSION

Studies investigating BBBD using FUS demonstrate promising outcomes in experimental and clinical settings. BBBD procedures in patients with malignant gliomas and recurrent GBM show safety and successful enhancement of drug delivery potential. Overall, FUS-mediated BBBD emerges as a safe and feasible approach for improving therapeutic outcomes in brain tumor patients, warranting further clinical exploration and optimization.

Cardiac gene delivery using ultrasound: State of the field

Over the past two decades, there has been tremendous and exciting progress toward extending the use of medical ultrasound beyond a traditional imaging tool. Ultrasound contrast agents, typically used for improved visualization of blood flow, have been explored as novel non-viral gene delivery vectors for cardiovascular therapy. Given this adaptation to ultrasound contrast-enhancing agents, this presents as an image-guided and site-specific gene delivery technique with potential for multi-gene and repeatable delivery protocols-overcoming some of the limitations of alternative gene therapy approaches. In this review, we provide an overview of the studies to date that employ this technique toward cardiac gene therapy using cardiovascular disease animal models and summarize their key findings.

Current clinical investigations of focused ultrasound blood-brain barrier disruption: A review

The blood-brain barrier (BBB) presents a formidable challenge in delivering therapeutic agents to the central nervous system. Ultrasound-mediated BBB disruption has emerged as a promising non-invasive technique to enhance drug delivery to the brain. This manuscript reviews fundamental principles of ultrasound-based techniques and their mechanisms of action in temporarily permeabilizing the BBB. Clinical trials employing ultrasound for BBB disruption are discussed, summarizing diverse applications ranging from the treatment of neurodegenerative diseases to targeted drug delivery for brain tumors. The review also addresses safety considerations, outlining the current understanding of potential risks and mitigation strategies associated with ultrasound exposure, including real-time monitoring and assessment of treatment efficacy. Among the large number of studies, significant successes are highlighted thus providing perspective on the future direction of the field.

Focused ultrasound-assisted delivery of immunomodulating agents in brain cancer

Focused ultrasound (FUS) combined with intravascularly circulating microbubbles can transiently increase the permeability of the blood-brain barrier (BBB) to enable targeted therapeutic delivery to the brain, the clinical testing of which is currently underway in both adult and pediatric patients. Aside from traditional cancer drugs, this technique is being extended to promote the delivery of immunomodulating therapeutics to the brain, including antibodies, immune cells, and cytokines. In this manner, FUS approaches are being explored as a tool to improve and amplify the effectiveness of immunotherapy for both primary and metastatic brain cancer, a particularly challenging solid tumor to treat. Here, we present an overview of the latest groundbreaking research in FUS-assisted delivery of immunomodulating agents to the brain in pre-clinical models of brain cancer, and place it within the context of the current immunotherapy approaches. We follow this up with a discussion on new developments and emerging strategies for this rapidly evolving approach.