The roles of thermal and mechanical stress in focused ultrasound-mediated immunomodulation and immunotherapy for central nervous system tumors

Ultrasound-responsive nanoparticles for imaging and therapy of brain tumors

Central nervous system (CNS) cancers, particularly glioblastoma (GBM), are associated with high mortality and disability rates. Despite aggressive surgical resection, radiotherapy, and chemotherapy, patient survival remains poor. The blood-brain barrier (BBB) significantly impedes therapeutic efficacy, making BBB penetration a critical focus of research. Focused ultrasound (FUS) combined with microbubbles (MBs) can transiently open the BBB through mechanisms such as cavitation, modulation of tight junction protein expression, and enhanced vesicular transport in endothelial cells. This review highlights precision delivery and personalized treatment strategies under ultrasound visualization, including precise control of ultrasound parameters and modulation of the immune microenvironment. We discuss the applications of ultrasound-responsive nanoparticles in brain tumor therapy, including enhanced radiotherapy, gene delivery, immunotherapy, and sonodynamic therapy (SDT), with a particular emphasis on piezoelectric catalytic immunotherapy. Finally, we provide insights into the clinical translation potential of ultrasound-responsive nanoparticles for personalized and precision treatment of brain tumors.

Ultrasound-assisted immunotherapy for malignant tumour

Malignant tumour represents a significant global public health concern. The advent of immunotherapy has brought about a revolutionary shift in the landscape of tumour treatment, offering a ray of hope to patients across the globe. Immunotherapy strategies have demonstrated considerable promise in clinical trials. However, the immunosuppressive environment within the tumour microenvironment has constituted a significant obstacle to the advancement of immunotherapies. It is therefore imperative to develop more efficacious and personalised approaches. The utilisation of non-invasive ultrasound-assisted immunotherapy represents a promising strategy. Ultrasound has the capacity to induce an immune response and stimulate other drugs to achieve a specific response, thereby reducing the toxic side effects of treatment and enhancing the outcome of immunotherapy. This paper presents a systematic introduction to the various mechanisms related to ultrasound and reviews the recent advancements of ultrasound-assisted tumour immunotherapy, including ultrasonic ablation, combined application with contrast agents, and sonodynamic therapy.

ATP released by ultrasound targeted microbubble cavitation induces vascular inflammation and improves immune checkpoint blockade efficacy

Rationale: Extracellular ATP (eATP) is a potent immune stimulant that functions as a damage-associated molecular pattern. The regulation of eATP is primarily mediated by cell surface ecto-nucleotidases (CD39 and CD73) which hydrolyze ATP into adenosine, a potent immune suppressor. CD39 and CD73 are upregulated in most cancers. Therapeutic strategies aimed at increasing ATP release in the tumor microenvironment or inhibiting adenosine activity are active areas of research in immuno-oncology. Ultrasound-Targeted Microbubble Cavitation (UTMC) is an externally applied, spatially targeted approach that has demonstrated synergy with immune checkpoint blockade (ICB) in solid tumors. However, the underlying mechanisms and optimal therapeutic combinations remain under investigation. We hypothesized that modulating purinergic signaling by UTMC could further leverage ICB efficacy. Methodologies: Here, we investigated non-ablative and flow-preserving UTMC to enhance ATP release and induce inflammatory responses in a murine syngeneic colorectal tumor model (MC38) with and without CD39 inhibition. We compared two UTMC pressures (400 and 850 kPa), evaluating their impact on tumor blood flow by contrast perfusion imaging, their ability to release ATP using bioluminescence, their effect on vascular inflammation and cancer cell death through histological analysis, their synergy with aPDL1 to improve ICB efficacy, immune cell infiltration to the tumor, and immune cell drainage to the tumor-draining lymph nodes (TDLN). Results: UTMC at 850 kPa and in CD39 knockout model released higher eATP concentrations, which correlated with increased vascular inflammation, enhanced cancer cell death, and reduced cancer cell proliferation. The combination of aPDL1 with UTMC and CD39 blockade significantly reduced tumor growth. This treatment also increased cytotoxic T cells (CTL), the CTL/Treg ratio, dendritic cells, and M1-prototype tumor-associated macrophages, while reducing M2-prototype macrophages within the tumor. In the TDLNs, the fully combined treatment elevated CTLs, dendritic cells, and M1-prototype macrophages, with a concurrent reduction in M2-prototype macrophages. Conclusion: Our findings support that purinergic signaling can be leveraged in combination with UTMC to improve ICB therapy.

Cryo-Shocked Tumor-Reprogrammed Sonosensitive Antigen-Presenting Cells Improving Sonoimmunotherapy via T Cells and NK Cells Immunity

Ultrasound therapy has turned up as a noninvasive multifunctional tool for cancer immunotherapy. However, the insufficient co-stimulating molecules and loss of peptide-major histocompatibility complex I (MHC-I) expression on tumor cells lead to poor therapy of sonoimmunotherapies. Herein, this work develops a sonosensitive system to augment MHC-I unrestricted natural killer (NK) cell-mediated innate immunity and T cell-mediated adaptive immunity by leveraging antigen presentation cell (APC)-like tumor cells. Genetically engineered tumor cells featuring sufficient co-stimulating molecules are cryo-shocked and conjugated with a sonosensitizer, hematoporphyrin monomethyl ether, using click chemistry. These cells (DPNLs) exhibit characteristics of tumor and draining lymph node homing. Under ultrasound, NK cell-mediated innate immunity within the tumor microenvironment could be activated, and T cells in the tumor-draining lymph nodes (TDLNs) are stimulated through co-stimulatory molecules. In combination with programmed cell death ligand 1 (PD-L1) antibody, DPNLs extend the survival time and inhibited lung metastasis in triple-negative breast cancer (TNBC) models. This study provides an alternative approach for sonoimmunotherapy with precise sonosensitizer delivery and enhanced NK cell and T cell activation.

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.

Abscopal effect of focused ultrasound combined immunotherapy in animal solid tumor model: a systematic reviews and meta-analysis

Introduction

The abscopal effect, a systemic anti-tumor response triggered by localized treatment, has gained attention but remains poorly understood. This study evaluates the efficacy and consistency of focused ultrasound (FUS) combined with immunotherapy in inducing the abscopal effect.

Methods

A systematic review and meta-analysis were conducted on preclinical studies using solid tumor models. Data on tumor response, immune modulation, and survival outcomes were analyzed to assess the combination therapy's effectiveness.

Results

FUS combined with immunotherapy enhanced anti-tumor responses at local and distant sites, with evidence of immune activation and increased abscopal effect rates. However, heterogeneity across tumor models and protocols was observed.

Discussion

The findings provide a theoretical basis for FUS-immunotherapy combinations in cancer treatment, while emphasizing the need for standardized protocols and further research to elucidate underlying mechanisms.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, identifier CRD42023460710.

MR Imaging-Guided Focused Ultrasound-Clinical Applications in Managing Malignant Gliomas

Malignant gliomas (MGs) are the most common primary brain tumors in adults. Despite recent advances in understanding the biology and potential therapeutic vulnerabilities of MGs, treatment options remain limited as the delivery of drugs is often impeded by the blood-brain barrier (BBB), and safe, complete surgical resection may not always be possible, especially for deep-seated tumors. In this review, the authors highlight emerging applications for MR imaging-guided focused ultrasound (MRgFUS) as a noninvasive treatment modality for MGs. Specifically, the authors discuss MRgFUS's potential role in direct tumor cell killing, opening the BBB, and modulating antitumor immunity.

Ultrasound frequency-controlled microbubble dynamics in brain vessels regulate the enrichment of inflammatory pathways in the blood-brain barrier

Microbubble-enhanced ultrasound provides a noninvasive physical method to locally overcome major obstacles to the accumulation of blood-borne therapeutics in the brain, posed by the blood-brain barrier (BBB). However, due to the highly nonlinear and coupled behavior of microbubble dynamics in brain vessels, the impact of microbubble resonant effects on BBB signaling and function remains undefined. Here, combined theoretical and prospective experimental investigations reveal that microbubble resonant effects in brain capillaries can control the enrichment of inflammatory pathways that are sensitive to wall shear stress and promote differential expression of a range of transcripts in the BBB, supporting the notion that microbubble dynamics exerted mechanical stress can be used to establish molecular, in addition to spatial, therapeutic windows to target brain diseases. Consistent with these findings, a robust increase in cytotoxic T-cell accumulation in brain tumors was observed, demonstrating the functional relevance and potential clinical significance of the observed immuno-mechano-biological responses.

Glioma stem cells remodel immunotolerant microenvironment in GBM and are associated with therapeutic advancements

Glioma is the most common primary tumor of the central nervous system (CNS). Glioblastoma (GBM) is incurable with current treatment strategies. Additionally, the treatment of recurrent GBM (rGBM) is often referred to as terminal treatment, necessitating hospice-level care and management. The presence of the blood-brain barrier (BBB) gives GBM a more challenging or "cold" tumor microenvironment (TME) than that of other cancers and gloma stem cells (GSCs) play an important role in the TME remodeling, occurrence, development and recurrence of giloma. In this review, our primary focus will be on discussing the following topics: niche-associated GSCs and macrophages, new theories regarding GSC and TME involving pyroptosis and ferroptosis in GBM, metabolic adaptations of GSCs, the influence of the cold environment in GBM on immunotherapy, potential strategies to transform the cold GBM TME into a hot one, and the advancement of GBM immunotherapy and GBM models.

Novel approaches to targeting gliomas at the leading/cutting edge

Despite decades of clinical trials and surgical advances, the most common high-grade glioma, glioblastoma (GBM), remains an incurable disease with a dismal prognosis. Because of its infiltrative nature, GBM almost always recurs at the margin, or leading edge, where tumor cells invade the surrounding brain parenchyma. This region of GBMs is unique, or heterogeneous, with its own microenvironment that is different from the tumor bulk or core. The GBM microenvironment at the margin contains immunosuppressive constituents as well as invasive and therapy-resistant tumor cells that are difficult to treat. In addition, the blood-brain barrier remains essentially intact at the infiltrative margin of tumors; further limiting the effectiveness of therapies. The invasive margin creates the greatest challenge for neurosurgeons when managing these tumors. The current paradigm of resection of GBM tumors mainly focuses on resection of the contrast-enhancing component of tumors, while GBMs extend well beyond the contrast enhancement. The infiltrative margin represents a unique challenge and opportunity for solutions that may overcome current limitations in tumor treatments. In this review of the current literature, the authors discuss the current and developing advances focused on the detection and treatment of GBM at the infiltrative margin and how this could impact patient outcomes.

Focused Ultrasound and Ultrasound Stimulated Microbubbles in Radiotherapy Enhancement for Cancer Treatment

Radiation therapy (RT) has been the standard of care for treating a multitude of cancer types. However, ionizing radiation has adverse short and long-term side effects which have resulted in treatment complications for decades. Thus, advances in enhancing the effects of RT have been the primary focus of research in radiation oncology. To avoid the usage of high radiation doses, treatment modalities such as high-intensity focused ultrasound can be implemented to reduce the radiation doses required to destroy cancer cells. In the past few years, the use of focused ultrasound (FUS) has demonstrated immense success in a number of applications as it capitalizes on spatial specificity. It allows ultrasound energy to be delivered to a targeted focal area without harming the surrounding tissue. FUS combined with RT has specifically demonstrated experimental evidence in its application resulting in enhanced cell death and tumor cure. Ultrasound-stimulated microbubbles have recently proved to be a novel way of enhancing RT as a radioenhancing agent on its own, or as a delivery vector for radiosensitizing agents such as oxygen. In this mini-review article, we discuss the bio-effects of FUS and RT in various preclinical models and highlight the applicability of this combined therapy in clinical settings.

Spatially targeted brain cancer immunotherapy with closed-loop controlled focused ultrasound and immune checkpoint blockade

Despite the challenges in treating glioblastomas (GBMs) with immune adjuvants, increasing evidence suggests that targeting the immune cells within the tumor microenvironment (TME) can lead to improved responses. Here, we present a closed-loop controlled, microbubble-enhanced focused ultrasound (MB-FUS) system and test its abilities to safely and effectively treat GBMs using immune checkpoint blockade. The proposed system can fine-tune the exposure settings to promote MB acoustic emission-dependent expression of the proinflammatory marker ICAM-1 and delivery of anti-PD1 in a mouse model of GBM. In addition to enhanced interaction of proinflammatory macrophages within the PD1-expressing TME and significant improvement in survival (P < 0.05), the combined treatment induced long-lived memory T cell formation within the brain that supported tumor rejection in rechallenge experiments. Collectively, our findings demonstrate the ability of MB-FUS to augment the therapeutic impact of immune checkpoint blockade in GBMs and reinforce the notion of spatially tumor-targeted (loco-regional) brain cancer immunotherapy.