Low-frequency ultrasound-mediated cytokine transfection enhances T cell recruitment at local and distant tumor sites

Low-Intensity Pulsed Ultrasound Dynamically Modulates the Migration of BV2 Microglia

OBJECTIVE

Low-intensity pulsed ultrasound (LIPUS) is a promising modality for neuromodulation. Microglia are the resident immune cells in the brain and their mobility is critical for maintaining brain homeostasis and alleviating neuroimmune pathologies. However, it is unclear whether and how LIPUS modulates microglial migration in physiological conditions.

METHODS

Here we examined the in vitro effects of LIPUS on the mobility of BV2 microglia by live cell imaging. Single-cell tracing of BV2 microglia migration was analyzed using ImageJ and Chemotaxis and Migration Tool software. Pharmacological manipulation was performed to determine the key molecular players involved in regulating ultrasound-dependent microglia migration.

RESULTS

We found that the distance of microglial migration was enhanced by LIPUS with increasing acoustic pressure. Removing the extracellular Ca2+ influx or depletion of intracellular Ca2+ stores suppressed ultrasound-enhanced BV2 migration. Furthermore, we found that blocking the reorganization of actin, or suppressing purinergic signaling by application of apyrase or hemi-channel inhibitors, both diminished ultrasound-induced BV2 migration. LIPUS stimulation also enhanced microglial migration in a lipopolysaccharide (LPS)-induced inflammatory environment.

CONCLUSION

LIPUS promoted microglia migration in both physiological and inflammatory environments. Calcium, cytoskeleton, and purinergic signaling were involved in regulating ultrasound-dependent microglial mobility. Our study reveals the biomechanical impact of ultrasound on microglial migration and highlights the potential of using ultrasound-based tools for modulation of microglial function.

Volumetric Passive Acoustic Mapping and Cavitation Detection of Nanobubbles under Low-Frequency Insonation

Gas bubbles, commonly used in medical ultrasound (US), witness advancements with nanobubbles (NB), providing improved capabilities over microbubbles (MB). NBs offer enhanced penetration into capillaries and the ability to extravasate into tumors following systemic injection, alongside prolonged circulation and persistent acoustic contrast. Low-frequency insonation (<1 MHz) with NBs holds great potential in inducing significant bioeffects, making the monitoring of their acoustic response critical to achieving therapeutic goals. We introduce a US-guided focused US system comprising a one-dimensional (1D) motorized rotating imaging transducer positioned within a low-frequency therapeutic transducer (center frequencies of 105 and 200 kHz), facilitating precise monitoring of NB cavitation activity in three-dimensional (3D) and comparison with MBs. Passive cavitation detection (PCD) revealed frequency-dependent responses, with NBs exhibiting significantly higher stable and inertial cavitation doses compared to MBs of the same gas volume when excited at a center frequency of 105 kHz and peak negative pressures ranging from 100 to 350 kPa. At 200 kHz, MBs showed higher cavitation doses than NBs. PCD showed that 105 kHz enhanced both NBs' and MBs' oscillations compared to 200 kHz. The system was further used for 3D passive acoustic mapping (PAM) to provide spatial resolution alongside PCD monitoring. Two-dimensional PAM was captured for each rotation angle and used to generate a complete 3D PAM reconstruction. Experimental results obtained from a tube phantom demonstrated consistent contrast PAM full-width half-maximum (FWHM) as a function of rotation angle, with similar FWHM between MBs and NBs. Frequency-selective PAM maps distinguished between stable and inertial cavitation via the harmonic, ultraharmonic and broadband content, offering insights into cavitation dynamics. These findings highlight NBs' superior performance at lower frequencies. The developed 3D-PAM technique with a 1D transducer presents a promising technology for real-time, noninvasive monitoring of cavitation-based US therapies.

Influence of cell shape on sonoporation efficiency in microbubble-facilitated delivery using micropatterned cell arrays

Microbubble-facilitated sonoporation is a rapid, versatile, and non-viral intracellular delivery technique with potential for clinical and ex vivo cell engineering applications. We developed a micropatterning-based approach to investigate the impact of cell shape on sonoporation efficacy. Cationic microbubbles were employed to enhance sonoporation by binding to the cell membrane electrostatically. NIH/3T3 fibroblasts were micropatterned into circle, square, triangle, and rectangle. A two-plate system ensured high-throughput and efficient sonoporation by controlling cationic microbubble-cell attachment. High-speed video microscopy captured the acoustic dynamics of microbubbles under short ultrasound pulses. Our findings reveal that for NIH/3T3 fibroblasts, rectangular cells achieved the highest sonoporation and survival rate, while square-shaped cells demonstrated the greatest propidium iodide uptake. Triangle-shaped NIH/3T3 fibroblasts displayed an initial rise then a plateau in the sonoporation and survival rate as the ultrasound pulse duration increased from 10 cycles to 100 cycles, and then to 200 cycles. Conversely, rectangle-shaped cells showed a decrease followed by a stabilization. Circle-shaped and rectangle-shaped HeLa cells exhibited similar sonoporation outcomes, which were not as effective as NIH/3T3 fibroblasts. This study underscores the significance of cell shape in optimizing sonoporation efficiency and highlights the potential of combining micropatterning with controlled targeting sonoporation to advance intracellular delivery technologies.

Recent Advancements in High-Frequency Ultrasound Applications from Imaging to Microbeam Stimulation

Ultrasound is a versatile and well-established technique using sound waves with frequencies higher than the upper limit of human hearing. Typically, therapeutic and diagnosis ultrasound operate in the frequency range of 500 kHz to 15 MHz with greater depth of penetration into the body. However, to achieve improved spatial resolution, high-frequency ultrasound (>15 MHz) was recently introduced and has shown promise in various fields such as high-resolution imaging for the morphological features of the eye and skin as well as small animal imaging for drug and gene therapy. In addition, high-frequency ultrasound microbeam stimulation has been demonstrated to manipulate single cells or microparticles for the elucidation of physical and functional characteristics of cells with minimal effect on normal cell physiology and activity. Furthermore, integrating machine learning with high-frequency ultrasound enhances diagnostics, including cell classification, cell deformability estimation, and the diagnosis of diabetes and dysnatremia using convolutional neural networks (CNNs). In this paper, current efforts in the use of high-frequency ultrasound from imaging to stimulation as well as the integration of deep learning are reviewed, and potential biomedical and cellular applications are discussed.

Advances in and prospects of immunotherapy for prostate cancer

Immunotherapy has shown promising therapeutic effects in hematological malignancies and certain solid tumors and has emerged as a critical and highly potential treatment modality for cancer. However, prostate cancer falls under the category of immune-resistant cold tumors, for which immunotherapy exhibits limited efficacy in patients with solid tumors. Thus, it is important to gain a deeper understanding of the tumor microenvironment in prostate cancer to facilitate immune system activation and overcome immune suppression to advance immunotherapy for prostate cancer. In this review, we discuss the immunosuppressive microenvironment of prostate cancer, which is characterized by the presence of few tumor-infiltrating lymphocytes, abundant immunosuppressive cells, low immunogenicity, and a noninflammatory phenotype, which significantly influences the efficacy of immunotherapy for prostate cancer. Immunotherapy is mainly achieved by activating the host immune system and overcoming immunosuppression. In this regard, we summarize the therapeutic advances in immune checkpoint blockade, immunogenic cell death, reversal of the immunosuppressive tumor microenvironment, tumor vaccines, immune adjuvants, chimeric antigen receptor T-cell therapy, and overcoming penetration barriers in prostate cancer, with the aim of providing novel research insights and approaches to enhance the effectiveness of immunotherapy for prostate cancer.

Ultrasound-Based Micro-/Nanosystems for Biomedical Applications

Due to the intrinsic non-invasive nature, cost-effectiveness, high safety, and real-time capabilities, besides diagnostic imaging, ultrasound as a typical mechanical wave has been extensively developed as a physical tool for versatile biomedical applications. Especially, the prosperity of nanotechnology and nanomedicine invigorates the landscape of ultrasound-based medicine. The unprecedented surge in research enthusiasm and dedicated efforts have led to a mass of multifunctional micro-/nanosystems being applied in ultrasound biomedicine, facilitating precise diagnosis, effective treatment, and personalized theranostics. The effective deployment of versatile ultrasound-based micro-/nanosystems in biomedical applications is rooted in a profound understanding of the relationship among composition, structure, property, bioactivity, application, and performance. In this comprehensive review, we elaborate on the general principles regarding the design, synthesis, functionalization, and optimization of ultrasound-based micro-/nanosystems for abundant biomedical applications. In particular, recent advancements in ultrasound-based micro-/nanosystems for diagnostic imaging are meticulously summarized. Furthermore, we systematically elucidate state-of-the-art studies concerning recent progress in ultrasound-based micro-/nanosystems for therapeutic applications targeting various pathological abnormalities including cancer, bacterial infection, brain diseases, cardiovascular diseases, and metabolic diseases. Finally, we conclude and provide an outlook on this research field with an in-depth discussion of the challenges faced and future developments for further extensive clinical translation and application.

Ultrasound-induced immune responses in tumors: A systematic review and meta-analysis

Ultrasound is widely used in the diagnosis and therapy of cancer. Tumors can be treated by thermal or mechanical tissue ablation. Furthermore, tumors can be manipulated by hyperthermia, sonodynamic therapy and sonoporation, e.g., by increasing tumor perfusion or the permeability of biological barriers to enhance drug delivery. These treatments induce various immune responses in tumors. However, conflicting data and high heterogeneity between experimental settings make it difficult to generalize the effects of ultrasound on tumor immunity. Therefore, we performed a systematic review to answer the question: "Does ultrasound alter the immune reaction of peripheral solid tumors in humans and animals compared to control conditions without ultrasound?" A systematic literature search was performed in PubMed, EMBASE, and Web of Science and 24,401 potentially relevant publications were identified. Of these, 96 publications were eligible for inclusion in the systematic review. Experiments were performed in humans, rats, and mice and focused on different tumor types, primarily breast and melanoma. We collected data on thermal and non-thermal ultrasound settings, the use of sono-sensitizers or sono-enhancers, and anti-tumor therapies. Six meta-analyses were performed to quantify the effect of ultrasound on tumor infiltration by T cells (cytotoxic, helper, and regulatory T cells) and on blood cytokines (interleukin-6, interferon-γ, tumor necrosis factor-α). We provide robust scientific evidence that ultrasound alters T cell infiltration into tumors and increases blood cytokine concentrations. Furthermore, we identified significant differences in immune cell infiltration based on tumor type, ultrasound settings, and mouse age. Stronger effects were observed using hyperthermia in combination with sono-sensitizers and in young mice. The latter may impair the translational impact of study results as most cancer patients are older. Thus, our results may help refining ultrasound parameters to enhance anti-tumor immune responses for therapeutic use and to minimize immune effects in diagnostic applications.

50-nm Gas-Filled Protein Nanostructures to Enable the Access of Lymphatic Cells by Ultrasound Technologies

Ultrasound imaging and ultrasound-mediated gene and drug delivery are rapidly advancing diagnostic and therapeutic methods; however, their use is often limited by the need for microbubbles, which cannot transverse many biological barriers due to their large size. Here, the authors introduce 50-nm gas-filled protein nanostructures derived from genetically engineered gas vesicles(GVs) that are referred to as 50 nmGVs. These diamond-shaped nanostructures have hydrodynamic diameters smaller than commercially available 50-nm gold nanoparticles and are, to the authors' knowledge, the smallest stable, free-floating bubbles made to date. 50 nmGVs can be produced in bacteria, purified through centrifugation, and remain stable for months. Interstitially injected 50 nmGVs can extravasate into lymphatic tissues and gain access to critical immune cell populations, and electron microscopy images of lymph node tissues reveal their subcellular location in antigen-presenting cells adjacent to lymphocytes. The authors anticipate that 50 nmGVs can substantially broaden the range of cells accessible to current ultrasound technologies and may generate applications beyond biomedicine as ultrasmall stable gas-filled nanomaterials.

The paths toward non-viral CAR-T cell manufacturing: A comprehensive review of state-of-the-art methods

Although CAR-T cell therapy has emerged as a game-changer in cancer immunotherapy several bottlenecks limit its widespread use as a front-line therapy. Current protocols for the production of CAR-T cells rely mainly on the use of lentiviral/retroviral vectors. Nevertheless, according to the safety concerns around the use of viral vectors, there are several regulatory hurdles to their clinical use. Large-scale production of viral vectors under "Current Good Manufacturing Practice" (cGMP) involves rigorous quality control assessments and regulatory requirements that impose exorbitant costs on suppliers and as a result, lead to a significant increase in the cost of treatment. Pursuing an efficient non-viral method for genetic modification of immune cells is a hot topic in cell-based gene therapy. This study aims to investigate the current state-of-the-art in non-viral methods of CAR-T cell manufacturing. In the first part of this study, after reviewing the advantages and disadvantages of the clinical use of viral vectors, different non-viral vectors and the path of their clinical translation are discussed. These vectors include transposons (sleeping beauty, piggyBac, Tol2, and Tc Buster), programmable nucleases (ZFNs, TALENs, and CRISPR/Cas9), mRNA, plasmids, minicircles, and nanoplasmids. Afterward, various methods for efficient delivery of non-viral vectors into the cells are reviewed.

Cell Membrane Perforation: Patterns, Mechanisms and Functions

Cell membrane is crucial for the cellular activities, and any disruption to it may affect the cells. It is demonstrated that cell membrane perforation is associated with some biological processes like programmed cell death (PCD) and infection of pathogens. Specific developments make it a promising technique to perforate the cell membrane controllably and precisely. The pores on the cell membrane provide direct pathways for the entry and exit of substances, and can also cause cell death, which means reasonable utilization of cell membrane perforation is able to assist intracellular delivery, eliminate diseased or cancerous cells, and bring about other benefits. This review classifies the patterns of cell membrane perforation based on the mechanisms into 1) physical patterns, 2) biological patterns, and 3) chemical patterns, introduces the characterization methods and then summarizes the functions according to the characteristics of reversible and irreversible pores, with the aim of providing a comprehensive summary of the knowledge related to cell membrane perforation and enlightening broad applications in biomedical science.

A T-Cell Inspired Sonoporation System Enhances Low-Dose X-Ray-Mediated Pyroptosis and Radioimmunotherapy Efficacy by Restoring Gasdermin-E Expression

Genome editing has the potential to improve the unsatisfactory therapeutic effect of antitumor immunotherapy. However, the cell plasma membrane prevents the entry of almost all free genome-manipulation agents. Therefore, a system can be spatiotemporally controlled and can instantly open the cellular membrane to allow the entry of genome-editing agents into target cells is needed. Here, inspired by the ability of T cells to deliver cytotoxins to cancer cells by perforation, an ultrasound (US)-controlled perforation system (UPS) is established to enhance the delivery of free genome-manipulating agents. The UPS can perforate the tumor cell membrane while maintaining cell viability via a controllable lipid peroxidation reaction. In vitro, transmembrane-incapable plasmids can enter cells and perform genome editing with the assistance of UPS, achieving an efficiency of up to 90%. In vivo, the UPS is biodegradable, nonimmunogenic, and tumor-targeting, enabling the puncturing of tumor cells under US. With the application of UPS-assisted genome editing, gasdermin-E expression in 4T1 tumor-bearing mice is successfully restored, which leads to pyroptosis-mediated antitumor immunotherapy via low-dose X-ray irradiation. This study provides new insights for designing a sonoporation system for genome editing. Moreover, the results demonstrate that restoring gasdermin expression by genome editing significantly improves the efficacy of radioimmunotherapy.

Enhanced capillary delivery with nanobubble-mediated blood-brain barrier opening and advanced high resolution vascular segmentation

Overcoming the blood-brain barrier (BBB) is essential to enhance brain therapy. Here, we utilized nanobubbles with focused ultrasound for targeted and improved BBB opening in mice. A microscopy technique method assessed BBB opening at a single blood vessel resolution employing a dual-dye labeling technique using green fluorescent molecules to label blood vessels and Evans blue brain-impermeable dye for quantifying BBB extravasation. A deep learning architecture enabled blood vessels segmentation, delivering comparable accuracy to manual segmentation with a significant time reduction. Segmentation outcomes were applied to the Evans blue channel to quantify extravasation of each blood vessel. Results were compared to microbubble-mediated BBB opening, where reduced extravasation was observed in capillaries with a diameter of 2-6 μm. In comparison, nanobubbles yield an improved opening in these capillaries, and equivalent efficacy to that of microbubbles in larger vessels. These results indicate the potential of nanobubbles to serve as enhanced agents for BBB opening, amplifying bioeffects in capillaries while preserving comparable opening in larger vessels.

Passive Acoustic Mapping for Convex Arrays With the Helical Wave Spectrum Method

Passive acoustic mapping (PAM) has emerged as a valuable imaging modality for monitoring the cavitation activity in focused ultrasound therapies. When it comes to imaging in the human abdomen, convex arrays are preferred due to their large acoustic window. However, existing PAM methods for convex arrays rely on the computationally expensive delay-and-sum (DAS) operation limiting the image reconstruction speed when the field-of-view (FOV) is large. In this work, we propose an efficient and frequency-selective PAM method for convex arrays. This method is based on projecting the helical wave spectrum (HWS) between cylindrical surfaces in the imaging field. Both the in silico and in vitro experiments showed that the HWS method has comparable image quality and similar acoustic cavitation source localization accuracy as the DAS-based methods. Compared to the frequency-domain and time-domain DAS methods, the time-complexity of the HWS method is reduced by one order and two orders of magnitude, respectively. A parallel implementation of the HWS method realized millisecond-level image reconstruction speed. We also show that the HWS method is inherently capable of mapping microbubble (MB) cavitation activity of different status, i.e., no cavitation, stable cavitation, or inertial cavitation. After compensating for the lens effects of the convex array, we further combined PAM formed by the HWS method and B-mode imaging as a real-time dual-mode imaging approach to map the anatomical location where MBs cavitate in a liver phantom experiment. This method may find use in applications where convex arrays are required for cavitation activity monitoring in real time.

Ultrasound-Sensitive Intelligent Nanosystems: A Promising Strategy for the Treatment of Neurological Diseases

Neurological diseases are a major global health challenge, affecting hundreds of millions of people worldwide. Ultrasound therapy plays an irreplaceable role in the treatment of neurological diseases due to its noninvasive, highly focused, and strong tissue penetration capabilities. However, the complexity of brain and nervous system and the safety risks associated with prolonged exposure to ultrasound therapy severely limit the applicability of ultrasound therapy. Ultrasound-sensitive intelligent nanosystems (USINs) are a novel therapeutic strategy for neurological diseases that bring greater spatiotemporal controllability and improve safety to overcome these challenges. This review provides a detailed overview of therapeutic strategies and clinical advances of ultrasound in neurological diseases, focusing on the potential of USINs-based ultrasound in the treatment of neurological diseases. Based on the physical and chemical effects induced by ultrasound, rational design of USINs is a prerequisite for improving the efficacy of ultrasound therapy. Recent developments of ultrasound-sensitive nanocarriers and nanoagents are systemically reviewed. Finally, the challenges and developing prospects of USINs are discussed in depth, with a view to providing useful insights and guidance for efficient ultrasound treatment of neurological diseases.

Protocol to assess extravasation of fluorescent molecules in mice after ultrasound-mediated blood-brain barrier opening

Blood-brain barrier disruption (BBBD) using focused ultrasound (FUS) and microbubbles (MBs) is an effective tool for therapeutic delivery to the brain. Here, we present an optimized protocol for quantifying fluorescent molecules extravasation in mice. We describe steps for ultrasound treatment, injection of MBs and fluorescent dyes, brain harvesting, microscopy imaging, and image postprocessing algorithm. Our protocol has proven to successfully conduct a diameter-dependent analysis that measures vascular leakage following FUS-mediated BBBD at a single blood vessel resolution. For complete details on the use and execution of this protocol, please refer to Katz et al.1.

Radiation Synergizes with IL2/IL15 Stimulation to Enhance Innate Immune Activation and Antitumor Immunity

Ionizing radiation is known to possess immune modulatory properties. However, how radiotherapy (RT) may complement with different types of immunotherapies to boost antitumor responses is unclear. In mice implanted with EO771 syngeneic tumors, NL-201 a stable, highly potent CD25-independent agonist to IL2 and IL15 receptors with enhanced affinity for IL2Rβγ was given with or without RT. Flow analysis and Western blot analysis was performed to determine the mechanisms involved. STING (-/-) and CD11c+ knockout mice were implanted with EO771 tumors to confirm the essential signaling and cell types required to mediate the effects seen. Combination of RT and NL-201 to enhance systemic immunotherapy with an anti-PD-1 checkpoint inhibitor was utilized to determine tumor growth inhibition and survival, along characterization of tumor microenvironment as compared with all other treatment groups. Here, we showed that RT, synergizing with NL-201 produced enhanced antitumor immune responses in murine breast cancer models. When given together, RT and NL-201 enhanced activation of the cytosolic DNA sensor cyclic GMP-AMP synthase-stimulator of IFN genes (cGAS-STING) pathway, resulting in increased type I IFN production in dendritic cells (DC), and consequently greater tumor infiltration and more efficient priming of antigen-specific T cells. The immune stimulatory mechanisms triggered by NL-201 and RT resulted in superior tumor growth inhibition and survival benefit in both localized and metastatic cancers. Our results support further preclinical and clinical investigation of this novel synergism regimen in locally advanced and metastatic settings.

Nonlinear Frequency Mixing Ultrasound Imaging of Nanoscale Contrast Agents

OBJECTIVE

Nanoscale ultrasound contrast agents show promise as alternatives for diagnostics and therapies due to their enhanced stability and ability to traverse blood vessels. Nonetheless, their reduced size limits echogenicity. This study introduces an enhanced nanobubble frequency mixing ultrasound imaging method, by capitalizing on their nonlinear acoustic response to dual-frequency excitation.

METHODS

A single broadband transducer (L12-3v) controlled by a programmable ultrasound system was used to transmit a dual-frequency single-cycle wavefront. The frequency mixing effect enabled simultaneous transducer capture of nanobubble-generated sum and difference frequencies in real time without the need for additional hardware or post-processing, by substituting the single-frequency wavefront in a standard contrast harmonic pulse inversion imaging protocol, with the dual-frequency wavefront.

RESULTS

Optimization experiments were conducted in tissue mimicking phantoms. Among the dual-frequency combinations that were tested, the highest contrast was obtained using 4&8 MHz. The nanobubble contrast improved with increased mechanical index, and achieved a maximal contrast improvement of 8.4 ± 0.5 dB compared to 4 MHz pulse inversion imaging. In imaging of a breast cancer tumor mouse model, after a systemic nanobubble injection, the contrast was improved by 3.4 ± 1.7, 4.8 ± 1.8, and 6.3 ± 1.6 dB for mechanical indices of 0.04, 0.08, and 0.1, respectively.

CONCLUSION

Nonlinear frequency mixing significantly improved the nanobubble contrast, which facilitated their imaging in-vivo.

SIGNIFICANCE

This study offers a new avenue to enhance ultrasound imaging utilizing nanobubbles, potentially leading to advancements in other diagnostic applications.

Dissemination of antibiotic resistance genes is regulated by iron oxides: Insight into the influence on bacterial transformation

The transportation of antibiotic resistance genes (ARGs) in manure-soil-plant continuums poses risks to human health. Horizontal gene transfer, particularly for bacterial transformation, is an important way for ARG dissemination. As crucial components in soils, iron oxides impacted the fates of various abiotic and biotic contaminants due to their active properties. However, whether they can influence the transformation of ARGs is unknown, which waits to be figured out to boost the assessment and control of ARG spread risks. In this study, we have investigated the effects of goethite, hematite, and magnetite (0-250 mg/L, with sizes < 100 nm and > 100 nm) on the transfer of ampicillin resistance genes to Escherichia coli cells. At lower iron oxide concentrations, the transformation of ARGs was first facilitated (transformation frequency reached up to 3.38-fold higher), but the facilitating effects gradually weakened and eventually disappeared as concentrations further increased. Particle size and iron oxide type were not the universal determinants controlling the transformation. At lower concentrations, iron oxides interacted with proteins and phospholipids in E. coli envelope structures, and induced the overgeneration of intracellular reactive oxygen species. Consequently, they led to pore formation and permeability enhancement on the cell membrane, thus promoting the transformation. The facilitation was also associated with the carrier-like effect of iron oxides for antibiotic resistance plasmids. At higher concentrations, the weakened facilitations were attributed to the aggregation of iron oxides. In this study, we highlight the crucial roles of the concentrations (contents) of iron oxides on the dissemination of ARGs in soils; this study may serve as a reference for ARG pollution control in future agricultural production.

Ultrasound combined with microbubble mediated immunotherapy for tumor microenvironment

The tumor microenvironment (TME) plays an important role in dynamically regulating the progress of cancer and influencing the therapeutic results. Targeting the tumor microenvironment is a promising cancer treatment method in recent years. The importance of tumor immune microenvironment regulation by ultrasound combined with microbubbles is now widely recognized. Ultrasound and microbubbles work together to induce antigen release of tumor cell through mechanical or thermal effects, promoting antigen presentation and T cells' recognition and killing of tumor cells, and improve tumor immunosuppression microenvironment, which will be a breakthrough in improving traditional treatment problems such as immune checkpoint blocking (ICB) and himeric antigen receptor (CAR)-T cell therapy. In order to improve the therapeutic effect and immune regulation of TME targeted tumor therapy, it is necessary to develop and optimize the application system of microbubble ultrasound for organs or diseases. Therefore, the combination of ultrasound and microbubbles in the field of TME will continue to focus on developing more effective strategies to regulate the immunosuppression mechanisms, so as to activate anti-tumor immunity and/or improve the efficacy of immune-targeted drugs, At present, the potential value of ultrasound combined with microbubbles in TME targeted therapy tumor microenvironment targeted therapy has great potential, which has been confirmed in the experimental research and application of breast cancer, colon cancer, pancreatic cancer and prostate cancer, which provides a new alternative idea for clinical tumor treatment. This article reviews the research progress of ultrasound combined with microbubbles in the treatment of tumors and their application in the tumor microenvironment.

Ultrasound-targeted microbubble technology facilitates SAHH gene delivery to treat diabetic cardiomyopathy by activating AMPK pathway

Diabetic cardiomyopathy (DCM) is a cardiovascular complication with no known cure. In this study, we evaluated the combination of ultrasound-targeted microbubble destruction (UTMD) and cationic microbubbles (CMBs) for cardiac S-adenosyl homocysteine hydrolase (SAHH) gene transfection as potential DCM therapy. Models of high glucose/fat (HG/HF)-induced H9C2 cells and streptozotocin-induced DCM rats were established. Ultrasound-mediated SAHH delivery using CMBs was a safe and noninvasive approach for spatially localized drug administration both in vitro and in vivo. Notably, SAHH overexpression increased cell viability and antioxidative stress and inhibited apoptosis of HG/HF-induced H9C2 cells. Likewise, UTMD-mediated SAHH delivery attenuated apoptosis, oxidative stress, cardiac fibrosis, and myocardial dysfunction in DCM rats. Activation of the AMPK/FOXO3/SIRT3 signaling pathway may be a key mechanism mediating the role of SAHH in regulating myocardial injury. Thus, UTMD-mediated SAHH transfection may be an important advancement in cardiac gene therapy for restoring ventricular function after DCM.

Nanomaterials augmented bioeffects of ultrasound in cancer immunotherapy

Immunotherapy as a milestone in cancer treatment has made great strides in the past decade, but it is still limited by low immune response rates and immune-related adverse events. Utilizing bioeffects of ultrasound to enhance tumor immunotherapy has attracted more and more attention, including sonothermal, sonomechanical, sonodynamic and sonopiezoelectric immunotherapy. Moreover, the emergence of nanomaterials has further improved the efficacy of ultrasound mediated immunotherapy. However, most of the summaries in this field are about a single aspect of the biological effects of ultrasound, which is not comprehensive and complete currently. This review proposes the recent progress of nanomaterials augmented bioeffects of ultrasound in cancer immunotherapy. The concept of immunotherapy and the application of bioeffects of ultrasound in cancer immunotherapy are initially introduced. Then, according to different bioeffects of ultrasound, the representative paradigms of nanomaterial augmented sono-immunotherapy are described, and their mechanisms are discussed. Finally, the challenges and application prospects of nanomaterial augmented ultrasound mediated cancer immunotherapy are discussed in depth, hoping to pave the way for cancer immunotherapy and promote the clinical translation of ultrasound mediated cancer immunotherapy through the reasonable combination of nanomaterials augmented ultrasonic bioeffects.

A Review of Ultrasound-Mediated Checkpoint Inhibitor Immunotherapy

Over the past decade, immunotherapy has emerged as a major modality in cancer medicine. However, despite its unprecedented success, immunotherapy currently benefits only a subgroup of patients, may induce responses of limited duration and is associated with potentially treatment-limiting side effects. In addition, responses to immunotherapeutics are sometimes diminished by the emergence of a complex array of resistance mechanisms. The efficacy of immunotherapy depends on dynamic interactions between tumour cells and the immune landscape in the tumour microenvironment. Ultrasound, especially in conjunction with cavitation-promoting agents such as microbubbles, can assist in the uptake and/or local release of immunotherapeutic agents at specific target sites, thereby increasing treatment efficacy and reducing systemic toxicity. There is also increasing evidence that ultrasound and/or cavitation may themselves directly stimulate a beneficial immune response. In this review, we summarize the latest developments in the use of ultrasound and cavitation agents to promote checkpoint inhibitor immunotherapy.

Protocol for in vitro sonoporation validation using non-targeted microbubbles for human studies of ultrasound-mediated gene delivery

Microbubbles are currently approved for diagnostic ultrasound imaging and are under evaluation in therapeutic protocols. Here, we present a protocol for in vitro sonoporation validation using non-targeted microbubbles for gene delivery. We describe steps for computational simulation, experimental calibration, reagent preparation, ultrasound treatment, validation, and gene expression analysis. This protocol uses approved diagnostic microbubbles and parameters that are applicable for human use. For complete details on the use and execution of this protocol, please refer to Bez et al. (2017).1.

Improving DNA vaccination performance through a new microbubble design and an optimized sonoporation protocol

As a non-viral transfection method, ultrasound and microbubble-induced sonoporation can achieve spatially targeted gene delivery with synergistic immunostimulatory effects. Here, we report for the first time the application of sonoporation for improving DNA vaccination performance. This study developed a new microbubble design with nanoscale DNA/PEI complexes loaded onto cationic microbubbles to attain significant increases in DNA-loading capacity (0.25 pg per microbubble) and in vitro transfection efficiency. Using live-cell imaging, we revealed the membrane perforation and cellular delivery characteristics of sonoporation. Using luciferase reporter gene for in vivo transfection, we showed that sonoporation increased the transfection efficiency by 40.9-fold when compared with intramuscular injection. Moreover, we comprehensively optimized the sonoporation protocol and further increased the transfection efficiency by 43.6-fold. Immunofluorescent staining results showed that sonoporation effectively activated the MHC-II+ immune cells. Using a hepatitis B DNA vaccine, sonoporation induced significantly higher serum antibody levels when compared with intramuscular injection, and the antibodies sustained for 56 weeks. In addition, we recorded the longest reported expression period (400 days) of the sonoporation-delivered gene. Whole genome resequencing confirmed that the gene with stable expression existed in an extrachromosomal state without integration. Our results demonstrated the potential of sonoporation for efficient and safe DNA vaccination.

Nanobubble-mediated cancer cell sonoporation using low-frequency ultrasound

Ultrasound insonation of microbubbles can form transient pores in cell membranes that enable the delivery of non-permeable extracellular molecules to the cells. Reducing the size of microbubble contrast agents to the nanometer range could facilitate cancer sonoporation. This size reduction can enhance the extravasation of nanobubbles into tumors after an intravenous injection, thus providing a noninvasive sonoporation platform. However, drug delivery efficacy depends on the oscillations of the bubbles, the ultrasound parameters and the size of the target compared to the membrane pores. The formation of large pores is advantageous for the delivery of large molecules, however the small size of the nanobubbles limit the bioeffects when operating near the nanobubble resonance frequency at the MHz range. Here, we show that by coupling nanobubbles with 250 kHz low frequency ultrasound, high amplitude oscillations can be achieved, which facilitate low energy sonoporation of cancer cells. This is beneficial both for increasing the uptake of a specific molecule and to improve large molecule delivery. The method was optimized for the delivery of four fluorescent molecules ranging in size from 1.2 to 70 kDa to breast cancer cells, while comparing the results to targeted microbubbles. Depending on the fluorescent molecule size, the optimal ultrasound peak negative pressure was found to range between 300 and 500 kPa. Increasing the pressure to 800 kPa reduced the fraction of fluorescent cells for all molecules sizes. The optimal uptake for the smaller molecule size of 4 kDa resulted in a fraction of 19.9 ± 1.8% of fluorescent cells, whereas delivery of 20 kDa and 70 kDa molecules yielded 14 ± 0.8% and 4.1 ± 1.1%, respectively. These values were similar to targeted microbubble-mediated sonoporation, suggesting that nanobubbles can serve as noninvasive sonoporation agents with a similar potency, and at a reduced bubble size. The nanobubbles effectively reduced cell viability and may thus potentially reduce the tumor burden, which is crucial for the success of cancer treatment. This method provides a non-invasive and low-energy tumor sonoporation theranostic platform, which can be combined with other therapies to maximize the therapeutic benefits of cancer treatment or be harnessed in gene therapy applications.

Sonodynamic amplification of cGAS-STING activation by cobalt-based nanoagonist against bone and metastatic tumor

The therapeutic effect of cancer immunotherapy is restrained by limited patient response rate caused by 'cold' tumors with an intrinsically immunosuppressive tumor microenvironment (TME). Activating stimulator of interferon genes (STING) confers promising antitumor immunity even in 'cold' tumors, but the further promotion of STING agonists is hindered by undesirable toxicity, low specificity and lack of controllability. Herein, an ultrasound-controllable cGAS-STING amplifying nanoagonist was constructed by coordinating mitochondria-targeting ligand triphenylphosphonium (TPP) to sonodynamic cobalt organic framework nanosheets (TPP@CoTCPP). The Co ions specifically amplify STING activation only when cytosolic mitochondrial DNA leakage is caused by sonocatalysis-induced ROS production and sensed by cGAS. A series of downstream innate immune proinflammatory responses induced by local cGAS-STING pathway activation under spatiotemporal ultrasound stimulation efficiently prime the antitumor T-cell response against bone metastatic tumor, a typical immunosuppressive tumor. We also found that the coordination of TPP augments the sonodynamic effect of CoTCPP nanosheets by reducing the band gap, improving O2 adsorption and enhancing electron transfer. Overall, our study demonstrates that the targeted and amplified cGAS-STING activation in cancer cell controlled by spatiotemporal ultrasound irradiation boosts high-efficiency sonodynamic-ionicimmunotherapy against immunosuppressive tumor.

50-nm gas-filled protein nanostructures to enable the access of lymphatic cells by ultrasound technologies

Ultrasound imaging and ultrasound-mediated gene and drug delivery are rapidly advancing diagnostic and therapeutic methods; however, their use is often limited by the need of microbubbles, which cannot transverse many biological barriers due to their large size. Here we introduce 50-nm gas-filled protein nanostructures derived from genetically engineered gas vesicles that we referred to as 50nm GVs. These diamond-shaped nanostructures have hydrodynamic diameters smaller than commercially available 50-nm gold nanoparticles and are, to our knowledge, the smallest stable, free-floating bubbles made to date. 50nm GVs can be produced in bacteria, purified through centrifugation, and remain stable for months. Interstitially injected 50nm GVs can extravasate into lymphatic tissues and gain access to critical immune cell populations, and electron microscopy images of lymph node tissues reveal their subcellular location in antigen-presenting cells adjacent to lymphocytes. We anticipate that 50nm GVs can substantially broaden the range of cells accessible to current ultrasound technologies and may generate applications beyond biomedicine as ultrasmall stable gas-filled nanomaterials.

Diameter-dependent assessment of microvascular leakage following ultrasound-mediated blood-brain barrier opening

Blood brain barrier disruption (BBBD) using focused ultrasound (FUS) and microbubbles (MB) is an effective tool for therapeutic delivery to the brain. BBBD depends to a great extent on MB oscillations. Because the brain vasculature is heterogenic in diameter, reduced MB oscillations in smaller blood vessels, together with a lower number of MBs in capillaries, can lead to variations in BBBD. Therefore, evaluating the impact of microvasculature diameter on BBBD is of great importance. We present a method to characterize molecules extravasation following FUS-mediated BBBD, at a single blood vessel resolution. Evans blue (EB) leakage was used as marker for BBBD, whereas blood vessels localization was done using FITC labeled Dextran. Automated image processing pipeline was developed to quantify the extent of extravasation as function of microvasculature diameter, including a wide range of vascular morphological parameters. Variations in MB vibrational response were observed in blood vessel mimicking fibers with varied diameters. Higher peak negative pressures (PNP) were required to initiate stable cavitation in fibers with smaller diameters. In vivo in the treated brains, EB extravasation increased as a function of blood vessel diameter. The percentage of strong BBBD blood vessels increased from 9.75% for 2-3 μm blood vessels to 91.67% for 9-10 μm. Using this method, it is possible to conduct a diameter-dependent analysis that measures vascular leakage resulting from FUS-mediated BBBD at a single blood vessel resolution.

Barrier-breaking effects of ultrasonic cavitation for drug delivery and biomarker release

Recently, emerging evidence has demonstrated that cavitation actually creates important bidirectional channels on biological barriers for both intratumoral drug delivery and extratumoral biomarker release. To promote the barrier-breaking effects of cavitation for both therapy and diagnosis, we first reviewed recent technical advances of ultrasound and its contrast agents (microbubbles, nanodroplets, and gas-stabilizing nanoparticles) and then reported the newly-revealed cavitation physical details. In particular, we summarized five types of cellular responses of cavitation in breaking the plasma membrane (membrane retraction, sonoporation, endocytosis/exocytosis, blebbing and apoptosis) and compared the vascular cavitation effects of three different types of ultrasound contrast agents in breaking the blood-tumor barrier and tumor microenvironment. Moreover, we highlighted the current achievements of the barrier-breaking effects of cavitation in mediating drug delivery and biomarker release. We emphasized that the precise induction of a specific cavitation effect for barrier-breaking was still challenged by the complex combination of multiple acoustic and non-acoustic cavitation parameters. Therefore, we provided the cutting-edge in-situ cavitation imaging and feedback control methods and suggested the development of an international cavitation quantification standard for the clinical guidance of cavitation-mediated barrier-breaking effects.

Ultrasound-targeted microbubble destruction remodels tumour microenvironment to improve immunotherapeutic effect

Cancer immunotherapy (CIT) has gained increasing attention and made promising progress in recent years, especially immune checkpoint inhibitors such as antibodies blocking programmed cell death 1/programmed cell death ligand 1 (PD-1/PD-L1) and cytotoxic T lymphocyte-associated protein 4 (CTLA-4). However, its therapeutic efficacy is only 10-30% in solid tumours and treatment sensitivity needs to be improved. The complex tissue environment in which cancers originate is known as the tumour microenvironment (TME) and the complicated and dynamic TME is correlated with the efficacy of immunotherapy. Ultrasound-targeted microbubble destruction (UTMD) is an emerging technology that integrates diagnosis and therapy, which has garnered much traction due to non-invasive, targeted drug delivery and gene transfection characteristics. UTMD has also been studied to remodel TME and improve the efficacy of CIT. In this review, we analyse the effects of UTMD on various components of TME, including CD8⁺ T cells, tumour-infiltrating myeloid cells, regulatory T cells, natural killer cells and tumour vasculature. Moreover, UTMD enhances the permeability of the blood-brain barrier to facilitate drug delivery, thus improving CIT efficacy in vivo animal experiments. Based on this, we highlight the potential of immunotherapy against various cancer species and the clinical application prospects of UTMD.

Focused ultrasound-mediated small-molecule delivery to potentiate immune checkpoint blockade in solid tumors

In the last decade, immune checkpoint blockade (ICB) has revolutionized the standard of treatment for solid tumors. Despite success in several immunogenic tumor types evidenced by improved survival, ICB remains largely unresponsive, especially in "cold tumors" with poor lymphocyte infiltration. In addition, side effects such as immune-related adverse events (irAEs) are also obstacles for the clinical translation of ICB. Recent studies have shown that focused ultrasound (FUS), a non-invasive technology proven to be effective and safe for tumor treatment in clinical settings, could boost the therapeutic effect of ICB while alleviating the potential side effects. Most importantly, the application of FUS to ultrasound-sensitive small particles, such as microbubbles (MBs) or nanoparticles (NPs), allows for precise delivery and release of genetic materials, catalysts and chemotherapeutic agents to tumor sites, thus enhancing the anti-tumor effects of ICB while minimizing toxicity. In this review, we provide an updated overview of the progress made in recent years concerning ICB therapy assisted by FUS-controlled small-molecule delivery systems. We highlight the value of different FUS-augmented small-molecules delivery systems to ICB and describe the synergetic effects and underlying mechanisms of these combination strategies. Furthermore, we discuss the limitations of the current strategies and the possible ways that FUS-mediated small-molecule delivery systems could boost novel personalized ICB treatments for solid tumors.

AMPK is required for recovery from metabolic stress induced by ultrasound microbubble treatment

Ultrasound-stimulated microbubble (USMB) treatment is a promising strategy for cancer therapy. USMB promotes drug delivery by sonoporation and enhanced endocytosis, and also impairs cell viability. However, USMB elicits heterogeneous effects on cell viability, with apparently minimal effects on a subset of cells. This suggests that mechanisms of adaptation following USMB allow some cells to survive and/or proliferate. Herein, we used several triple negative breast cancer cells to identify the molecular mechanisms of adaptation to USMB-induced stress. We found that USMB alters steady-state levels of amino acids, glycolytic intermediates, and citric acid cycle intermediates, suggesting that USMB imposes metabolic stress on cells. USMB treatment acutely reduces ATP levels and stimulates the phosphorylation and activation of AMP-activated protein kinase (AMPK). AMPK is required to restore ATP levels and support cell proliferation post-USMB treatment. These results suggest that AMPK and metabolic perturbations are likely determinants of the antineoplastic efficacy of USMB treatment.

Insights and Strategies of Melanoma Immunotherapy: Predictive Biomarkers of Response and Resistance and Strategies to Improve Response Rates

Despite the recent successes and durable responses with immune checkpoint inhibitors (ICI), many cancer patients, including those with melanoma, do not derive long-term benefits from ICI therapies. The lack of predictive biomarkers to stratify patients to targeted treatments has been the driver of primary treatment failure and represents an unmet medical need in melanoma and other cancers. Understanding genomic correlations with response and resistance to ICI will enhance cancer patients' benefits. Building on insights into interplay with the complex tumor microenvironment (TME), the ultimate goal should be assessing how the tumor 'instructs' the local immune system to create its privileged niche with a focus on genomic reprogramming within the TME. It is hypothesized that this genomic reprogramming determines the response to ICI. Furthermore, emerging genomic signatures of ICI response, including those related to neoantigens, antigen presentation, DNA repair, and oncogenic pathways, are gaining momentum. In addition, emerging data suggest a role for checkpoint regulators, T cell functionality, chromatin modifiers, and copy-number alterations in mediating the selective response to ICI. As such, efforts to contextualize genomic correlations with response into a more insightful understanding of tumor immune biology will help the development of novel biomarkers and therapeutic strategies to overcome ICI resistance.

Efficacy optimization of low frequency microbubble-mediated sonoporation as a drug delivery platform to cancer cells

Ultrasound insonation of microbubbles can be used to form pores in cell membranes and facilitate the local trans-membrane transport of drugs and genes. An important factor in efficient delivery is the size of the delivered target compared to the generated membrane pores. Large molecule delivery remains a challenge, and can affect the resulting therapeutic outcomes. To facilitate large molecule delivery, large pores need to be formed. While ultrasound typically uses megahertz frequencies, it was recently shown that when microbubbles are excited at a frequency of 250 kHz (an order of magnitude below the resonance frequency of these agents), their oscillations are significantly enhanced as compared to the megahertz range. Here, to promote the delivery of large molecules, we suggest using this low frequency and inducing large pore formation through the high-amplitude oscillations of microbubbles. We assessed the impact of low frequency microbubble-mediated sonoporation on breast cancer cell uptake by optimizing the delivery of 4 fluorescent molecules ranging from 1.2 to 70 kDa in size. The optimal ultrasound peak negative pressure was found to be 500 kPa. Increasing the pressure did not enhance the fraction of fluorescent cells, and in fact reduced cell viability. For the smaller molecule sizes, 1.2 kDa and 4 kDa, the groups treated with an ultrasound pressure of 500 kPa and MB resulted in a fraction of 58% and 29% of fluorescent cells respectively, whereas delivery of 20 kDa and 70 kDa molecules yielded 10% and 5%, respectively. These findings suggest that low-frequency (e.g., 250 kHz) insonation of microbubbles results in high amplitude oscillation in vitro that increase the uptake of large molecules. Successful ultrasound-mediated molecule delivery requires the careful selection of insonation parameters to maximize the therapeutic effect by increasing cell uptake.

Development of an ultrasound guided focused ultrasound system for 3D volumetric low energy nanodroplet-mediated histotripsy

Low pressure histotripsy is likely to facilitate current treatments that require extremely high pressures. An ultrasound guided focused ultrasound system was designed to accommodate a rotating imaging transducer within a low frequency therapeutic transducer that operates at a center frequency of 105 kHz. The implementation of this integrated system provides real-time therapeutic and volumetric imaging functions, that are used here for low-cost, low-energy 3D volumetric ultrasound histotripsy using nanodroplets. A two-step approach for low pressure histotripsy is implemented with this dual-array. Vaporization of nanodroplets into gaseous microbubbles was performed via the 1D rotating imaging probe. The therapeutic transducer is then used to detonate the vaporized nanodroplets and trigger potent mechanical effects in the surrounding tissue. Rotating the imaging transducer creates a circular vaporized nanodroplet shape which generates a round lesion upon detonation. This contrasts with the elongated lesion formed when using a standard 1D imaging transducer for nanodroplet activation. Optimization experiments show that maximal nanodroplet activation can be achieved with a 2-cycle excitation pulse at a center frequency of 3.5 MHz, and a peak negative pressure of 3.4 MPa (a mechanical index of 1.84). Vaporized nanodroplet detonation was achieved by applying a low frequency treatment at a center frequency of 105 kHz and mechanical index of 0.9. In ex-vivo samples, the rotated nanodroplet activation method yielded the largest lesion area, with a mean of 4.7 ± 0.5 mm², and a rounded shape. In comparison, standard fixed transducer nanodroplet activation resulted in an average lesion area of 2.6 ± 0.4 mm², and an elongated shape. This hybrid system enables to achieve volumetric low energy histotripsy, and thus facilitates the creation of precise, large-volume mechanical lesions in tissues, while reducing the pressure threshold required for standard histotripsy by over an order of magnitude.

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.

Low frequency nanobubble-enhanced ultrasound mechanotherapy for noninvasive cancer surgery

Scaling down the size of microbubble contrast agents to the nanometer level holds the promise for noninvasive cancer therapy. However, the small size of nanobubbles limits the obtained bioeffects as a result of ultrasound cavitation, when operating near the nanobubble resonance frequency. Here we show that coupled with low energy insonation at a frequency of 80 kHz, well below the resonance frequency of these agents, nanobubbles serve as noninvasive therapeutic warheads that trigger potent mechanical effects in tumors following a systemic injection. We demonstrate these capabilities in tissue mimicking phantoms, where a comparison of the acoustic response of micro- and nano-bubbles after insonation at a frequency of 250 or 80 kHz revealed that higher pressures were needed to implode the nanobubbles compared to microbubbles. Complete nanobubble destruction was achieved at a mechanical index of 2.6 for the 250 kHz insonation vs. 1.2 for the 80 kHz frequency. Thus, the 80 kHz insonation complies with safety regulations that recommend operation below a mechanical index of 1.9. In vitro in breast cancer tumor cells, the cell viability was reduced to 17.3 ± 1.7% of live cells. In vivo, in a breast cancer tumor mouse model, nanobubble tumor distribution and accumulation were evaluated by high frequency ultrasound imaging. Finally, nanobubble-mediated low frequency insonation of breast cancer tumors resulted in effective mechanical tumor ablation and tumor tissue fractionation. This approach provides a unique theranostic platform for safe, noninvasive and low energy tumor mechanotherapy.

Paving the Way to Solid Tumors: Challenges and Strategies for Adoptively Transferred Transgenic T Cells in the Tumor Microenvironment

T cells are important players in the antitumor immune response. Over the past few years, the adoptive transfer of genetically modified, autologous T cells-specifically redirected toward the tumor by expressing either a T cell receptor (TCR) or a chimeric antigen receptor (CAR)-has been adopted for use in the clinic. At the moment, the therapeutic application of CD19- and, increasingly, BCMA-targeting-engineered CAR-T cells have been approved and have yielded partly impressive results in hematologic malignancies. However, employing transgenic T cells for the treatment of solid tumors remains more troublesome, and numerous hurdles within the highly immunosuppressive tumor microenvironment (TME) need to be overcome to achieve tumor control. In this review, we focused on the challenges that these therapies must face on three different levels: infiltrating the tumor, exerting efficient antitumor activity, and overcoming T cell exhaustion and dysfunction. We aimed to discuss different options to pave the way for potent transgenic T cell-mediated tumor rejection by engineering either the TME or the transgenic T cell itself, which responds to the environment.

Cancer immunotherapy based on image-guided STING activation by nucleotide nanocomplex-decorated ultrasound microbubbles

The cytosolic innate immune sensor cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway is crucial for priming adaptive antitumour immunity through antigen-presenting cells (APCs). Natural agonists, such as cyclic dinucleotides (CDNs), activate the cGAS-STING pathway, but their clinical translation is impeded by poor cytosolic entry and serum stability, low specificity and rapid tissue clearance. Here we developed an ultrasound (US)-guided cancer immunotherapy platform using nanocomplexes composed of 2'3'-cyclic guanosine monophosphate-adenosine monophosphate (cGAMP) electrostatically bound to biocompatible branched cationic biopolymers that are conjugated onto APC-targeting microbubbles (MBs). The nanocomplex-conjugated MBs engaged with APCs and efficiently delivered cGAMP into the cytosol via sonoporation, resulting in activation of cGAS-STING and downstream proinflammatory pathways that efficiently prime antigen-specific T cells. This bridging of innate and adaptive immunity inhibited tumour growth in both localized and metastatic murine cancer models. Our findings demonstrate that targeted local activation of STING in APCs under spatiotemporal US stimulation results in systemic antitumour immunity and improves the therapeutic efficacy of checkpoint blockade, thus paving the way towards novel image-guided strategies for targeted immunotherapy of cancer.

Enhanced thrombolysis by endovascular low-frequency ultrasound with bifunctional microbubbles in venous thrombosis: in vitro and in vivo study

There is a need to improve the efficacy and safety of endovascular techniques in venous thrombotic diseases, and microbubble enhanced sonothrombolysis is a promising approach. However, whether endovascular low-frequency ultrasound (LFUS) can be utilized in microbubble enhanced sonothrombolysis is unclear. Here, we present a catheter-based thrombolytic system that combines unfocused low-frequency low-intensity ultrasound with novel fibrin-targeted drug-loaded bifunctional microbubbles. We develop an in vitro flow model and an in vivo rabbit inferior vena cava (IVC) thrombosis model to evaluate the safety and efficacy of the thrombolytic system. The results indicate that microbubble enhanced sonothrombolysis with endovascular LFUS treatment for 30 min is equally effective compared to pure pharmacologic treatment. Furthermore, the thrombolytic efficacy of this system is safely and substantially improved by the introduction of a fibrin-targeted drug-loaded bifunctional microbubble with a reduction of the fibrinolytic agent dosage by 60%. The microbubble enhanced endovascular LFUS sonothrombolysis system with excellent thrombolytic efficacy may serve as a new therapeutic approach for venous thrombotic diseases.

Nanodroplet-Mediated Low-Energy Mechanical Ultrasound Surgery

Mechanical ultrasound surgery methods use short, high-intensity pulses to fractionate tissues. This study reports the development of a two-step technology for low-energy mechanical ultrasound surgery of tissues using nanodroplets to reduce the pressure threshold. Step 1 consists of vaporizing the nanodroplets into gaseous microbubbles via megahertz ultrasound excitation. Then, low-frequency ultrasound is applied to the microbubbles, which turns them into therapeutic warheads that trigger potent mechanical effects in the surrounding tissue. The use of nanoscale nanodroplets coupled with low-frequency ultrasound reduces the pressure threshold required for mechanical ultrasound surgery by an order of magnitude. In addition, their average diameter of 300 nm can overcome challenges associated with the size of microbubbles. Optimization experiments were performed to determine the ultrasound parameters for nanodroplet vaporization and the subsequent microbubble implosion processes. Optimal vaporization was obtained when transmitting a 2-cycle excitation pulse at a center frequency of 5 MHz and a peak negative pressure of 4.1 MPa (mechanical index = 1.8). Low-frequency insonation of the generated microbubbles at a center frequency of 850, 250 or 80 kHz caused enhanced contrast reduction at a center frequency of 80 kHz, compared with the other frequencies, while operating at the same mechanical index of 0.9. Nanodroplet-mediated insonation of ex vivo chicken liver samples generated mechanical damage. Low-frequency treatment at a mechanical index of 0.9 and a center frequency of 80 kHz induced the largest lesion area (average of 0.59 mm²) compared with 250- and 850-kHz treatments with the same mechanical index (average lesions areas of 0.29 and 0.19 mm², respectively, p < 0.001). The two-step approach makes it possible to conduct both the vaporization and implosion stages at mechanical indices below 1.9, thus avoiding undesired mechanical damage. The findings indicate that coupled with low-frequency ultrasound, nanodroplets can be used for low-energy mechanical ultrasound surgery.

Ultrasound-Targeted Microbubble Destruction: Modulation in the Tumor Microenvironment and Application in Tumor Immunotherapy

Tumor immunotherapy has shown strong therapeutic potential for stimulating or reconstructing the immune system to control and kill tumor cells. It is a promising and effective anti-cancer treatment besides surgery, radiotherapy and chemotherapy. Presently, some immunotherapy methods have been approved for clinical application, and numerous others have demonstrated promising in vitro results and have entered clinical trial stages. Although immunotherapy has exhibited encouraging results in various cancer types, however, a large proportion of patients are limited from these benefits due to specific characteristics of the tumor microenvironment such as hypoxia, tumor vascular malformation and immune escape, and current limitations of immunotherapy such as off-target toxicity, insufficient drug penetration and accumulation and immune cell dysfunction. Ultrasound-target microbubble destruction (UTMD) treatment can help reduce immunotherapy-related adverse events. Using the ultrasonic cavitation effect of microstreaming, microjets and free radicals, UTMD can cause a series of changes in vascular endothelial cells, such as enhancing endothelial cells' permeability, increasing intracellular calcium levels, regulating gene expression, and stimulating nitric oxide synthase activities. These effects have been shown to promote drug penetration, enhance blood perfusion, increase drug delivery and induce tumor cell death. UTMD, in combination with immunotherapy, has been used to treat melanoma, non-small cell lung cancer, bladder cancer, and ovarian cancer. In this review, we summarized the effects of UTMD on tumor angiogenesis and immune microenvironment, and discussed the application and progress of UTMD in tumor immunotherapy.

Bidirectional Regulation of Cell Mechanical Motion via a Gold Nanorods-Acoustic Streaming System

Cell mechanical motion is a key physiological process that relies on the dynamics of actin filaments. Herein, a localized shear-force system based on gigahertz acoustic streaming (AS) is proposed, which can simultaneously realize intracellular delivery and cellular mechanical regulation. The results demonstrate that gold nanorods (AuNRs) can be delivered into the cytoplasm and even the nuclei of cancer and normal cells within a few minutes by AS stimulation. The delivery efficiency of AS stimulation is four times higher than that of endocytosis. Moreover, AS can effectively promote cytoskeleton assembly, regulate cell stiffness and change cell morphology. Since the inhibitory effect of AuNRs on cytoskeleton assembly, this AuNRs-AS system is able to inhibit or promote cell mechanical motion in a controlled manner by regulating the mechanical properties of cells. The bidirectional regulation of cell motion is further verified via scratch experiments, in which AuNRs-treated cells recover their motion ability through AS stimulation. In particular, the results of AuNRs-AS mechanical regulation on cell are related to the intrinsic properties of cell lines, revealing to more obvious effects on the cells with higher motor capacities. In summary, this acoustic technology has shown superiorities in controllable cell-motion manipulation, indicating its potential in building a multifunctional, integrated cytomechanics regulation platform.

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

BACKGROUND

Focused ultrasound (FUS) is an emerging technology, offering the capability of tuning and prescribing thermal and mechanical treatments within the brain. While early works in utilizing this technology have mainly focused on maximizing the delivery of therapeutics across the blood-brain barrier (BBB), the potential therapeutic impact of FUS-induced controlled thermal and mechanical stress to modulate anti-tumor immunity is becoming increasingly recognized.

OBJECTIVE

To better understand the roles of FUS-mediated thermal and mechanical stress in promoting anti-tumor immunity in central nervous system tumors, we performed a comprehensive literature review on focused ultrasound-mediated immunomodulation and immunotherapy in brain tumors.

METHODS

First, we summarize the current clinical experience with immunotherapy. Then, we discuss the unique and distinct immunomodulatory effects of the FUS-mediated thermal and mechanical stress in the brain tumor-immune microenvironment. Finally, we highlight recent findings that indicate that its combination with immune adjuvants can promote robust responses in brain tumors.

RESULTS

Along with the rapid advancement of FUS technologies into recent clinical trials, this technology through mild-hyperthermia, thermal ablation, mechanical perturbation mediated by microbubbles, and histotripsy each inducing distinct vascular and immunological effects, is offering the unique opportunity to improve immunotherapeutic trafficking and convert immunologically "cold" tumors into immunologically "hot" ones that are prone to generate prolonged anti-tumor immune responses.

CONCLUSIONS

While FUS technology is clearly accelerating concepts for new immunotherapeutic combinations, additional parallel efforts to detail rational therapeutic strategies supported by rigorous preclinical studies are still in need to leverage potential synergies of this technology with immune adjuvants. This work will accelerate the discovery and clinical implementation of new effective FUS immunotherapeutic combinations for brain tumor patients.

Advances and prospects of ultrasound targeted drug delivery systems using biomaterial-modified micro/nanobubbles for tumor therapy

The incidence of malignant tumors is rising rapidly and tends to be in the younger, which has been one of the most important factors endangering the safety of human life. Ultrasound micro/nanobubbles, as a noninvasive and highly specific antitumor strategy, can reach and destroy tumor tissue through their effects of cavitation and acoustic perforation under the guidance of ultrasound. Meanwhile, micro/nanobubbles are now used as a novel drug carrier, releasing drugs at a target region, especially on the prospects of biomaterial-modified micro/nanobubbles as a dual modality for drug delivery and therapeutic monitoring. and successful evaluation of the sonoporation mechanism(s), ultrasound parameters, drug type and dose will need to be addressed before translating this technology for clinical use. Therefore, this paper collects the literature on the experimental and clinical studies of ultrasound biomaterial-modified micro/nanobubbles therapy in vitro and in vivo in recent years.

Theranostic Microbubbles with Homogeneous Ligand Distribution for Higher Binding Efficacy

Phospholipid-coated targeted microbubbles are used for ultrasound molecular imaging and locally enhanced drug delivery, with the binding efficacy being an important trait. The use of organic solvent in microbubble production makes the difference between a heterogeneous or homogeneous ligand distribution. This study demonstrates the effect of ligand distribution on the binding efficacy of phospholipid-coated ανβ3-targeted microbubbles in vitro using a monolayer of human umbilical-vein endothelial cells and in vivo using chicken embryos. Microbubbles with a homogeneous ligand distribution had a higher binding efficacy than those with a heterogeneous ligand distribution both in vitro and in vivo. In vitro, 1.55× more microbubbles with a homogeneous ligand distribution bound under static conditions, while this was 1.49× more under flow with 1.25 dyn/cm2, 1.56× more under flow with 2.22 dyn/cm2, and 1.25× more in vivo. The in vitro dissociation rate of bound microbubbles with homogeneous ligand distribution was lower at low shear stresses (1–5 dyn/cm2). The internalized depth of bound microbubbles was influenced by microbubble size, not by ligand distribution. In conclusion, for optimal binding the use of organic solvent in targeted microbubble production is preferable over directly dispersing phospholipids in aqueous medium.

Sonoporation: Past, Present, and Future

A surge of research in intracellular delivery technologies is underway with the increased innovations in cell-based therapies and cell reprogramming. Particularly, physical cell membrane permeabilization techniques are highlighted as the leading technologies because of their unique features, including versatility, independence of cargo properties, and high-throughput delivery that is critical for providing the desired cell quantity for cell-based therapies. Amongst the physical permeabilization methods, sonoporation holds great promise and has been demonstrated for delivering a variety of functional cargos, such as biomolecular drugs, proteins, and plasmids, to various cells including cancer, immune, and stem cells. However, traditional bubble-based sonoporation methods usually require special contrast agents. Bubble-based sonoporation methods also have high chances of inducing irreversible damage to critical cell components, lowering the cell viability, and reducing the effectiveness of delivered cargos. To overcome these limitations, several novel non-bubble-based sonoporation mechanisms are under development. This review will cover both the bubble-based and non-bubble-based sonoporation mechanisms being employed for intracellular delivery, the technologies being investigated to overcome the limitations of traditional platforms, as well as perspectives on the future sonoporation mechanisms, technologies, and applications.

Ultrasound-targeted nucleic acid delivery for solid tumor therapy

Depending upon multiple factors, malignant solid tumors are conventionally treated by some combination of surgical resection, radiation, chemotherapy, and immunotherapy. Despite decades of research, therapeutic responses remain poor for many cancer indications. Further, many current therapies in our armamentarium are either invasive or accompanied by toxic side effects. In lieu of traditional pharmaceutics and invasive therapeutic interventions, gene therapies offer more flexible and potentially more durable approaches for new anti-cancer therapies. Nonetheless, many current gene delivery approaches suffer from low transfection efficiency due to physiological barriers limiting extravasation and uptake of genetic material. Additionally, systemically administered gene therapies may lack target-specificity, which can lead to off-target effects. To overcome these challenges, many preclinical studies have shown the utility of focused ultrasound (FUS) to increase macromolecule uptake in cells and tissue under image guidance, demonstrating promise for improved delivery of therapeutics to solid tumors. As FUS-based drug delivery is now being tested in several clinical trials around the world, FUS-targeted gene therapy for solid tumor therapy may not be far behind. In this review, we comprehensively cover the literature pertaining to preclinical attempts to more efficiently deliver therapeutic genetic material with FUS and offer perspectives for future studies and clinical translation.

Synergies between therapeutic ultrasound, gene therapy and immunotherapy in cancer treatment

Due to the ease of use and excellent safety profile, ultrasound is a promising technique for both diagnosis and site-specific therapy. Ultrasound-based techniques have been developed to enhance the pharmacokinetics and efficacy of therapeutic agents in cancer treatment. In particular, transfection with exogenous nucleic acids has the potential to stimulate an immune response in the tumor microenvironment. Ultrasound-mediated gene transfection is a growing field, and recent work has incorporated this technique into cancer immunotherapy. Compared with other gene transfection methods, ultrasound-mediated gene transfection has a unique opportunity to augment the intracellular uptake of nucleic acids while safely and stably modulating the expression of immunostimulatory cytokines. The development and commercialization of therapeutic ultrasound systems further enhance the potential translation. In this Review, we introduce the underlying mechanisms and ongoing preclinical studies of ultrasound-based techniques in gene transfection for cancer immunotherapy. Furthermore, we expand on aspects of therapeutic ultrasound that impact gene therapy and immunotherapy, including tumor debulking, enhancing cytokines and chemokines and altering nanoparticle pharmacokinetics as these effects of ultrasound cannot be fully dissected from targeted gene therapy. We finally explore the outlook for this rapidly developing field.