Past, present and future of Focused Ultrasound as an adjunct or complement to DIPG/DMG therapy: A consensus of the 2021 FUSF DIPG meeting

The role of focused ultrasound for pediatric brain tumors: current insights and future implications on treatment strategies

INTRODUCTION

Focused ultrasound (FUS) is an innovative and emerging technology for the treatment of adult and pediatric brain tumors and illustrates the intersection of various specialized fields, including neurosurgery, neuro-oncology, radiation oncology, and biomedical engineering.

OBJECTIVE

The authors provide a comprehensive overview of the application and implications of FUS in treating pediatric brain tumors, with a special focus on pediatric low-grade gliomas (pLGGs) and the evolving landscape of this technology and its clinical utility.

METHODS

The fundamental principles of FUS include its ability to induce thermal ablation or enhance drug delivery through transient blood-brain barrier (BBB) disruption, emphasizing the adaptability of high-intensity focused ultrasound (HIFU) and low-intensity focused ultrasound (LIFU) applications.

RESULTS

Several ongoing clinical trials explore the potential of FUS in offering alternative therapeutic strategies for pathologies where conventional treatments fall short, specifically centrally-located benign CNS tumors and diffuse intrinsic pontine glioma (DIPG). A case illustration involving the use of HIFU for pilocytic astrocytoma is presented.

CONCLUSION

Discussions regarding future applications of FUS for the treatment of gliomas include improved drug delivery, immunomodulation, radiosensitization, and other technological advancements.

Current status and advances to improving drug delivery in diffuse intrinsic pontine glioma

Diffuse midline glioma (DMG), including tumors diagnosed in the brainstem (diffuse intrinsic pontine glioma - DIPG), is the primary cause of brain tumor-related death in pediatric patients. DIPG is characterized by a median survival of <12 months from diagnosis, harboring the worst 5-year survival rate of any cancer. Corticosteroids and radiation are the mainstay of therapy; however, they only provide transient relief from the devastating neurological symptoms. Numerous therapies have been investigated for DIPG, but the majority have been unsuccessful in demonstrating a survival benefit beyond radiation alone. Although many barriers hinder brain drug delivery in DIPG, one of the most significant challenges is the blood-brain barrier (BBB). Therapeutic compounds must possess specific properties to enable efficient passage across the BBB. In brain cancer, the BBB is referred to as the blood-brain tumor barrier (BBTB), where tumors disrupt the structure and function of the BBB, which may provide opportunities for drug delivery. However, the biological characteristics of the brainstem's BBB/BBTB, both under normal physiological conditions and in response to DIPG, are poorly understood, which further complicates treatment. Better characterization of the changes that occur in the BBB/BBTB of DIPG patients is essential, as this informs future treatment strategies. Many novel drug delivery technologies have been investigated to bypass or disrupt the BBB/BBTB, including convection enhanced delivery, focused ultrasound, nanoparticle-mediated delivery, and intranasal delivery, all of which are yet to be clinically established for the treatment of DIPG. Herein, we review what is known about the BBB/BBTB and discuss the current status, limitations, and advances of conventional and novel treatments to improving brain drug delivery in DIPG.

H3 K27M-altered glioma and diffuse intrinsic pontine glioma: Semi-systematic review of treatment landscape and future directions

H3 K27M-mutant diffuse glioma is a recently identified brain tumor associated with poor prognosis. As of 2016, it is classified by the World Health Organization as a distinct form of grade IV glioma. Despite recognition as an important prognostic and diagnostic feature in diffuse glioma, radiation remains the sole standard of care and no effective systemic therapies are available for H3K27M mutant tumors. This review will detail treatment interventions applied to diffuse midline glioma and diffuse intrinsic pontine glioma (DIPG) prior to the identification of the H3 K27M mutation, the current standard-of-care for H3 K27M-mutant diffuse glioma treatment, and ongoing clinical trials listed on www.clinicaltrials.gov evaluating novel therapeutics in this population. Current clinical trials were identified using clinicaltrials.gov, and studies qualifying for this analysis were active or ongoing interventional trials that evaluated a therapy in at least 1 treatment arm or cohort comprised exclusively of patients with DIPG and H3 K27M-mutant glioma. Forty-one studies met these criteria, including trials evaluating H3 K27M vaccination, chimeric antigen receptor T-cell therapy, and small molecule inhibitors. Ongoing evaluation of novel therapeutics is necessary to identify safe and effective interventions in this underserved patient population.

Insights into Targeted and Stimulus-Responsive Nanocarriers for Brain Cancer Treatment

Brain cancers, especially glioblastoma multiforme, are associated with poor prognosis due to the limited efficacy of current therapies. Nanomedicine has emerged as a versatile technology to treat various diseases, including cancers, and has played an indispensable role in combatting the COVID-19 pandemic as evidenced by the role that lipid nanocarrier-based vaccines have played. The tunability of nanocarrier physicochemical properties -including size, shape, surface chemistry, and drug release kinetics- has resulted in the development of a wide range of nanocarriers for brain cancer treatment. These nanocarriers can improve the pharmacokinetics of drugs, increase blood-brain barrier transfer efficiency, and specifically target brain cancer cells. These unique features would potentially allow for more efficient treatment of brain cancer with fewer side effects and better therapeutic outcomes. This review provides an overview of brain cancers, current therapeutic options, and challenges to efficient brain cancer treatment. The latest advances in nanomedicine strategies are investigated with an emphasis on targeted and stimulus-responsive nanocarriers and their potential for clinical translation.

Translating ultrasound-mediated drug delivery technologies for CNS applications

Ultrasound enhances drug delivery into the central nervous system (CNS) by opening barriers between the blood and CNS and by triggering release of drugs from carriers. A key challenge in translating setups from in vitro to in vivo settings is achieving equivalent acoustic energy delivery. Multiple devices have now been demonstrated to focus ultrasound to the brain, with concepts emerging to also target the spinal cord. Clinical trials to date have used ultrasound to facilitate the opening of the blood-brain barrier. While most have focused on feasibility and safety considerations, therapeutic benefits are beginning to emerge. To advance translation of these technologies for CNS applications, researchers should standardise exposure protocol and fine-tune ultrasound parameters. Computational modelling should be increasingly used as a core component to develop both in vitro and in vivo setups for delivering accurate and reproducible ultrasound to the CNS. This field holds promise for transformative advancements in the management and pharmacological treatment of complex and challenging CNS disorders.

Focused ultrasound-mediated blood-brain barrier opening is safe and feasible with moderately hypofractionated radiotherapy for brainstem diffuse midline glioma

BACKGROUND

Diffuse midline glioma (DMG) is a pediatric tumor with dismal prognosis. Systemic strategies have been unsuccessful and radiotherapy (RT) remains the standard-of-care. A central impediment to treatment is the blood-brain barrier (BBB), which precludes drug delivery to the central nervous system (CNS). Focused ultrasound (FUS) with microbubbles can transiently and non-invasively disrupt the BBB to enhance drug delivery. This study aimed to determine the feasibility of brainstem FUS in combination with clinical doses of RT. We hypothesized that FUS-mediated BBB-opening (BBBO) is safe and feasible with 39 Gy RT.

METHODS

To establish a safety timeline, we administered FUS to the brainstem of non-tumor bearing mice concurrent with or adjuvant to RT; our findings were validated in a syngeneic brainstem murine model of DMG receiving repeated sonication concurrent with RT. The brainstems of male B6 (Cg)-Tyrc-2J/J albino mice were intracranially injected with mouse DMG cells (PDGFB+, H3.3K27M, p53-/-). A clinical RT dose of 39 Gy in 13 fractions (39 Gy/13fx) was delivered using the Small Animal Radiation Research Platform (SARRP) or XRAD-320 irradiator. FUS was administered via a 0.5 MHz transducer, with BBBO and tumor volume monitored by magnetic resonance imaging (MRI).

RESULTS

FUS-mediated BBBO did not affect cardiorespiratory rate, motor function, or tissue integrity in non-tumor bearing mice receiving RT. Tumor-bearing mice tolerated repeated brainstem BBBO concurrent with RT. 39 Gy/13fx offered local control, though disease progression occurred 3-4 weeks post-RT.

CONCLUSION

Repeated FUS-mediated BBBO is safe and feasible concurrent with RT. In our syngeneic DMG murine model, progression occurs, serving as an ideal model for future combination testing with RT and FUS-mediated drug delivery.

Focused ultrasound gene delivery for the treatment of neurological disorders

The transformative potential of gene therapy has been demonstrated in humans. However, there is an unmet need for non-invasive targeted gene delivery and regulation in the treatment of brain disorders. Transcranial focused ultrasound (FUS) has gained tremendous momentum to address these challenges. FUS non-invasively modulates brain cells and their environment, and is a powerful tool to facilitate gene delivery across the blood-brain barrier (BBB) with millimeter precision and promptly regulate transgene expression. This review highlights technical aspects of FUS-mediated gene therapies for the central nervous system (CNS) and lessons learned from discoveries in other organs. Understanding the possibilities and remaining obstacles of FUS-mediated gene therapy will be necessary to harness remarkable technologies and create life-changing treatments for neurological disorders.

Translational strategies and systems biology insights for blood-brain barrier opening and delivery in brain tumors and Alzheimer's disease

The blood-brain barrier (BBB) plays a critical role in determining the effectiveness of systemic treatments for brain diseases. Over the years, several innovative approaches in BBB opening and drug delivery have been developed and progressed into clinical testing phases, including focused ultrasound (FUS) with circulating microbubbles, mannitol-facilitated delivery of anti-neoplastic drugs, receptor-mediated transcytosis (RMT) by antibody-drug conjugates (ADCs), and viral vectors for gene therapy. We provided a comprehensive review of the most recent clinical applications of these approaches in managing brain tumors and Alzheimer's disease (AD), two major devastating brain diseases. Moreover, the spatial-temporal molecular heterogeneity of the BBB under disease states emphasized the importance of utilizing emerging spatial systems biology approaches to unravel novel targets for intervention within BBB and tailor strategies for enhancing drug delivery to the brain. SEARCH STRATEGY AND SELECTION CRITERIA: Data for this Review were identified by searches of clinicaltrials.gov, MEDLINE, Current Contents, PubMed, and references from relevant articles using the search terms "blood-brain barrier", "CNS drug delivery", "BBB modulation", "clinical trials", "systems biology", "primary or metastatic brain tumors", "Alzheimer's disease". Abstracts and reports from meetings were included only when they related directly to previously published work. Only articles published in English between 1980 and 2023 were included.

Acoustomechanically activatable liposomes for ultrasonic drug uncaging

Ultrasound-activatable drug-loaded nanocarriers enable noninvasive and spatiotemporally-precise on-demand drug delivery throughout the body. However, most systems for ultrasonic drug uncaging utilize cavitation or heating as the drug release mechanism and often incorporate relatively exotic excipients into the formulation that together limit the drug-loading potential, stability, and clinical translatability and applicability of these systems. Here we describe an alternate strategy for the design of such systems in which the acoustic impedance and osmolarity of the internal liquid phase of a drug-loaded particle is tuned to maximize ultrasound-induced drug release. No gas phase, cavitation, or medium heating is necessary for the drug release mechanism. Instead, a non-cavitation-based mechanical response to ultrasound mediates the drug release. Importantly, this strategy can be implemented with relatively common pharmaceutical excipients, as we demonstrate here by implementing this mechanism with the inclusion of a few percent sucrose into the internal buffer of a liposome. Further, the ultrasound protocols sufficient for in vivo drug uncaging with this system are achievable with current clinical therapeutic ultrasound systems and with intensities that are within FDA and society guidelines for safe transcranial ultrasound application. Finally, this current implementation of this mechanism should be versatile and effective for the loading and uncaging of any therapeutic that may be loaded into a liposome, as we demonstrate for four different drugs in vitro, and two in vivo. These acoustomechanically activatable liposomes formulated with common pharmaceutical excipients promise a system with high clinical translational potential for ultrasonic drug uncaging of myriad drugs of clinical interest.

Focused ultrasound for brain metastases: an update on global clinical trials

BACKGROUND

Despite advances in immunotherapy and targeted treatments for malignancies of the central nervous system (CNS), the treatment of brain metastases (BMs) remains a formidable challenge, due largely to difficulties in crossing the blood-brain barrier (BBB), drug resistance, and molecular discrepancies. Focused ultrasound (FUS) is a non-invasive tool for BBB breaching, tumor ablation, enhancing drug delivery, promoting the release of tumor biomarkers for liquid biopsy, or the tumor microenvironment disruption. This paper presents a comprehensive review of the current literature related to FUS and its application in the treatment of brain metastasis.

METHODS

This review of the current literature via PubMed, Google Scholar, and Clincaltrials.gov focused on clinical trials in which FUS is used in the intracranial treatment of metastatic tumor, glioma, or GBM.

RESULTS

FUS is safe and effective for treatment of primary or metastatic brain tumors. FUS-augmented drug delivery can open BBB to facilitate the transport of chemotherapeutic agents, immunotherapies, and targeted treatments. The integration of FUS with liquid biopsy has considerable potential for early tumor detection, precise gene profiling, and personalized therapy. Sonodynamic therapy can induce tumor cell apoptosis and could potentially be used to enhance the outcomes of other tumor treatments, such as surgery and chemotherapy.

CONCLUSION

Further work is required to establish FUS as a standard therapy for BMs. FUS has the potential to transform brain tumor treatment, particularly when combined with immunotherapy and targeted therapy as a non-invasive alternative to surgery and radiation therapy.

Boosting the therapy of glutamine-addiction glioblastoma by combining glutamine metabolism therapy with photo-enhanced chemodynamic therapy

The complete treatment of high grade invasive glioblastoma (GBM) remains to be a great challenge, and it is of great importance to develop innovative therapeutic approaches. Herein, we found that GBM derived from U87 MG cells is a glutamine-addiction tumor, and jointly using glutamine-starvation therapy and photo-enhanced chemodynamic therapy (CDT) can significantly boost its therapy. We rationally fabricated tumor cell membrane coated Cu2-xSe nanoparticles (CS NPs) and an inhibitor of glutamine metabolism (Purpurin) for combined therapy, because glutamine rather than glucose plays a crucial role in the proliferation and growth of GBM cells, and serves as a precursor for the synthesis of glutathione (GSH). The resultant CS-P@CM NPs can be specifically delivered to the tumor site to inhibit glutamine metabolism in tumor cells, suppress tumor intracellular GSH, and increase H2O2 content, which benefit the CDT catalyzed by CS NPs. The cascade reaction can be further enhanced by irradiation with the second near-infrared (NIR-II) light at the maximum concentration of H2O2, which can be monitored by photoacoustic imaging. The NIR-II light irradiation can generate a large amount of reactive oxygen species (ROS) within a short time to kill tumor cells and enhance the CDT efficacy. This is the first work on the treatment of orthotopic malignant GBM through combined glutamine metabolism therapy and photo-enhanced CDT, and provides insights into the treatment of other solid tumors by modulating the metabolism of tumor cells.