Angiogenesis-targeting microbubbles combined with ultrasound-mediated gene therapy in brain tumors

Focused ultrasound gene delivery for the treatment of neurological disorders

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

The relationship between surface drug distribution of Dox-loaded microbubbles and drug release/cavitation behaviors with ultrasound

Ultrasound (US)-triggered microbubbles (MBs) drug delivery is a promising tool for noninvasive and localized therapy. Several studies have shown the potential of drug-loaded MBs to boost the delivery of therapeutic substances to target tissue effectively. Nevertheless, little is known about the surface payload distribution affecting the cavitation activity and drug release behavior of the drug-loaded MBs. In this study, we designed a common chemodrug (Doxorubicin, Dox)-loaded MB (Dox-MBs) and regulated the payload distribution as uniform or cluster onto the outer surface of MBs. The Dox distribution on the MB shells was assessed by confocal fluorescence microscopic imaging. The acoustic properties of the Dox-MBs with different Dox distributions were evaluated by their acoustic stability and cavitation activities. The payload release and the fragments from Dox-MBs in response to different US parameters were measured and visualized by column chromatography and cryo-electron microscopy, respectively. By amalgamating these methodologies, we found that stable cavitation was sufficient for triggering uniform-loaded MBs to release their payload, but stable cavitation and inertial cavitation were required for cluster-loaded MBs. The released substances included free Dox and Dox-containing micelle/liposome; their portions depended on the payload distribution, acoustic pressure, cycle number, and sonication duration. Furthermore, we also revealed that the Dox-containing micelle/liposome in cluster-loaded MBs had the potential for multiple drug releases upon US sonication. This study compared uniform-loaded MBs and cluster-loaded MBs to enhance our comprehension of drug-loaded MBs mediated drug delivery.

Using focused ultrasound to modulate microglial structure and function

Transcranial focused ultrasound (FUS) has the unique ability to target regions of the brain with high spatial precision, in a minimally invasive manner. Neuromodulation studies have shown that FUS can excite or inhibit neuronal activity, demonstrating its tremendous potential to improve the outcome of neurological diseases. Recent evidence has also shed light on the emerging promise that FUS has, with and without the use of intravenously injected microbubbles, in modulating the blood-brain barrier and the immune cells of the brain. As the resident immune cells of the central nervous system, microglia are at the forefront of the brain's maintenance and immune defense. Notably, microglia are highly dynamic and continuously survey the brain parenchyma by extending and retracting their processes. This surveillance activity aids microglia in performing key physiological functions required for brain activity and plasticity. In response to stressors, microglia rapidly alter their cellular and molecular profile to help facilitate a return to homeostasis. While the underlying mechanisms by which both FUS and FUS + microbubbles modify microglial structure and function remain largely unknown, several studies in adult mice have reported changes in the expression of the microglia/macrophage marker ionized calcium binding adaptor molecule 1, and in their phagocytosis, notably of protein aggregates, such as amyloid beta. In this review, we discuss the demonstrated and putative biological effects of FUS and FUS + microbubbles in modulating microglial activities, with an emphasis on the key cellular and molecular changes observed in vitro and in vivo across models of brain health and disease. Understanding how this innovative technology can modulate microglia paves the way for future therapeutic strategies aimed to promote beneficial physiological microglial roles, and prevent or treat maladaptive responses.

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.

Targeted Microbubbles for Drug, Gene, and Cell Delivery in Therapy and Immunotherapy

Microbubbles are 1-10 μm diameter gas-filled acoustically-active particles, typically stabilized by a phospholipid monolayer shell. Microbubbles can be engineered through bioconjugation of a ligand, drug and/or cell. Since their inception a few decades ago, several targeted microbubble (tMB) formulations have been developed as ultrasound imaging probes and ultrasound-responsive carriers to promote the local delivery and uptake of a wide variety of drugs, genes, and cells in different therapeutic applications. The aim of this review is to summarize the state-of-the-art of current tMB formulations and their ultrasound-targeted delivery applications. We provide an overview of different carriers used to increase drug loading capacity and different targeting strategies that can be used to enhance local delivery, potentiate therapeutic efficacy, and minimize side effects. Additionally, future directions are proposed to improve the tMB performance in diagnostic and therapeutic applications.

Gene Therapy for Regenerative Medicine

The development of biological methods over the past decade has stimulated great interest in the possibility to regenerate human tissues. Advances in stem cell research, gene therapy, and tissue engineering have accelerated the technology in tissue and organ regeneration. However, despite significant progress in this area, there are still several technical issues that must be addressed, especially in the clinical use of gene therapy. The aims of gene therapy include utilising cells to produce a suitable protein, silencing over-producing proteins, and genetically modifying and repairing cell functions that may affect disease conditions. While most current gene therapy clinical trials are based on cell- and viral-mediated approaches, non-viral gene transfection agents are emerging as potentially safe and effective in the treatment of a wide variety of genetic and acquired diseases. Gene therapy based on viral vectors may induce pathogenicity and immunogenicity. Therefore, significant efforts are being invested in non-viral vectors to enhance their efficiency to a level comparable to the viral vector. Non-viral technologies consist of plasmid-based expression systems containing a gene encoding, a therapeutic protein, and synthetic gene delivery systems. One possible approach to enhance non-viral vector ability or to be an alternative to viral vectors would be to use tissue engineering technology for regenerative medicine therapy. This review provides a critical view of gene therapy with a major focus on the development of regenerative medicine technologies to control the in vivo location and function of administered genes.

Microbubble Delivery Platform for Ultrasound-Mediated Therapy in Brain Cancers

The blood-brain barrier (BBB) is one of the most selective endothelial barriers that protect the brain and maintains homeostasis in neural microenvironments. This barrier restricts the passage of molecules into the brain, except for gaseous or extremely small hydrophobic molecules. Thus, the BBB hinders the delivery of drugs with large molecular weights for the treatment of brain cancers. Various methods have been used to deliver drugs to the brain by circumventing the BBB; however, they have limitations such as drug diversity and low delivery efficiency. To overcome this challenge, microbubbles (MBs)-based drug delivery systems have garnered a lot of interest in recent years. MBs are widely used as contrast agents and are recently being researched as a vehicle for delivering drugs, proteins, and gene complexes. The MBs are 1-10 μm in size and consist of a gas core and an organic shell, which cause physical changes, such as bubble expansion, contraction, vibration, and collapse, in response to ultrasound. The physical changes in the MBs and the resulting energy lead to biological changes in the BBB and cause the drug to penetrate it, thus enhancing the therapeutic effect. Particularly, this review describes a state-of-the-art strategy for fabricating MB-based delivery platforms and their use with ultrasound in brain cancer therapy.

Major Strategies for Spatial Control of Ultrasound-Driven Gene Expression to Enhance Therapeutic Specificity

A major challenge of gene therapy is to achieve highly specific transgene expression in tissues of interest with minimized off-target expression. Ultrasound in combination with microbubbles can transiently increase permeability of desired cells or tissues and thereby facilitate gene transfer. This kind of ultrasound-driven transgene expression has gained increasing attention due to its deep tissue penetration and high spatiotemporal resolution. However, successful genetic manipulation in vivo with ultrasound need to well optimize various aspects involved in this process. Ultrasound parameters, microbubble dose, and gene vectors need to be optimized for highly increased transgene expression in the cells of interest. Conversely, the potential off-target transgene expression and toxicities need to be reduced by modification of gene vectors and/or promoter sequence. This review will discuss some major strategies for enhanced specificity of the ultrasound-mediated gene transfer in vivo. Five major strategies will be discussed, including the integration of real-time imaging methods, local injection, targeted microbubbles loaded with nucleic acids, stealth nanocarriers, and cell-specific promoter. The advantages and limitations of each strategy were outlined, hoping to provide a guideline for researchers in achieving high specific ultrasound-driven gene expression.

Suicide Gene Delivery System Mediated by Ultrasound-Targeted Microbubble Destruction: A Promising Strategy for Cancer Therapy

The treatment of malignant tumors has always been one of the challenges that have plagued researchers and clinicians. The ideal status in cancer treatment is to eliminate tumor cells while avoiding damage to normal tissues. Different approaches have been investigated to achieve such a goal, and suicide gene therapy has emerged as a novel mode of cancer treatment. This approach involves the delivery of genes encoding enzymes that activate non-toxic prodrugs into cytotoxic metabolites that cause the death of transfected cancer cells. Despite promising results obtained both in vitro and in vivo, this innovative approach has long been stalled in the clinic due to the lack of a suitable delivery system to introduce the suicide gene into cancer cells. Ultrasound-targeted microbubble destruction (UTMD) represents a valuable non-viral vector system for site-specific and noninvasive gene therapy. Ultrasound promotes intracellular uptake of therapeutic agents by increasing vascular and cell membrane permeability, especially in the presence of microbubbles. In this scenario, the true potential of suicide genes can be translated into clinically valuable treatments for patients. This review provides background information on suicide gene therapy and UTMD technology, summarizes the current state of knowledge about UTMD-mediated suicide gene delivery in cancer treatment, and presents an outlook on its future development.

Low-Intensity Focused Ultrasound Technique in Glioblastoma Multiforme Treatment

Glioblastoma is one of the central nervous system most aggressive and lethal cancers with poor overall survival rate. Systemic treatment of glioblastoma remains the most challenging aspect due to the low permeability of the blood-brain barrier (BBB) and blood-tumor barrier (BTB), limiting therapeutics extravasation mainly in the core tumor as well as in its surrounding invading areas. It is now possible to overcome these barriers by using low-intensity focused ultrasound (LIFU) together with intravenously administered oscillating microbubbles (MBs). LIFU is a non-invasive technique using converging ultrasound waves which can alter the permeability of BBB/BTB to drug delivery in a specific brain/tumor region. This emerging technique has proven to be both safe and repeatable without causing injury to the brain parenchyma including neurons and other structures. Furthermore, LIFU is also approved by the FDA to treat essential tremors and Parkinson's disease. It is currently under clinical trial in patients suffering from glioblastoma as a drug delivery strategy and liquid biopsy for glioblastoma biomarkers. The use of LIFU+MBs is a step-up in the world of drug delivery, where onco-therapeutics of different molecular sizes and weights can be delivered directly into the brain/tumor parenchyma. Initially, several potent drugs targeting glioblastoma were limited to cross the BBB/BTB; however, using LIFU+MBs, diverse therapeutics showed significantly higher uptake, improved tumor control, and overall survival among different species. Here, we highlight the therapeutic approach of LIFU+MBs mediated drug-delivery in the treatment of glioblastoma.

Dye-Sensitized Rare Earth Nanoparticles with Up/Down Conversion Luminescence for On-Demand Gas Therapy of Glioblastoma Guided by NIR-II Fluorescence Imaging

As the primary malignant tumor in the brain, glioblastoma exhibits a high mortality due to the challenges for complete treatment by conventional therapeutic methods. It is of great importance to develop innovative therapeutic agents and methods for treatment of glioblastoma. In this work, the imaging and therapy of glioblastoma are reported by using dye sensitized core-shell NaYF₄ :Yb/Tm@NaYF₄ :Nd nanoparticles with strong up/down-conversion luminescence, of which the ultraviolet up-conversion emissions at 348 and 365 nm are significantly enhanced by nearly 28 times and used to control the release of SO₂ from 5-Amino-1,3-dihydrobenzo[c]thiophene 2,2-dioxide prodrug for gas therapy, and the second near-infrared (NIR-II) down conversion emission at 1340 nm is increased five times and applied for imaging. It is revealed that the released SO₂ molecules not only cause oxidative stress damage of tumor cells, but also induce their pro-death autophagy by down-regulating the expression of p62 and up-regulating the ratio of LC3-II/LC3-I, ultimately inhibiting tumor growth. The work demonstrates the great potential of rare earth nano-platform with functions of NIR-II imaging and photo-controlled gas therapy in the diagnosis and treatment of orthotopic glioblastoma.

Towards controlled drug delivery in brain tumors with microbubble-enhanced focused ultrasound

Brain tumors are particularly challenging malignancies, due to their location in a structurally and functionally distinct part of the human body - the central nervous system (CNS). The CNS is separated and protected by a unique system of brain and blood vessel cells which together prevent most bloodborne therapeutics from entering the brain tumor microenvironment (TME). Recently, great strides have been made through microbubble (MB) ultrasound contrast agents in conjunction with ultrasound energy to locally increase the permeability of brain vessels and modulate the brain TME. As we elaborate in this review, this physical method can effectively deliver a wide range of anticancer agents, including chemotherapeutics, antibodies, and nanoparticle drug conjugates across a range of preclinical brain tumors, including high grade glioma (glioblastoma), diffuse intrinsic pontine gliomas, and brain metastasis. Moreover, recent evidence suggests that this technology can promote the effective delivery of novel immunotherapeutic agents, including immune check-point inhibitors and chimeric antigen receptor T cells, among others. With early clinical studies demonstrating safety, and several Phase I/II trials testing the preclinical findings underway, this technology is making firm steps towards shaping the future treatments of primary and metastatic brain cancer. By elaborating on its key components, including ultrasound systems and MB technology, along with methods for closed-loop spatial and temporal control of MB activity, we highlight how this technology can be tuned to enable new, personalized treatment strategies for primary brain malignancies and brain metastases.

The Impact of Surface Drug Distribution on the Acoustic Behavior of DOX-Loaded Microbubbles

Previous studies have reported substantial improvement of microbubble (MB)-mediated drug delivery with ultrasound when drugs are loaded onto the MB shell compared with a physical mixture. However, drug loading may affect shell properties that determine the acoustic responsiveness of MBs, producing unpredictable outcomes. The aim of this study is to reveal how the surface loaded drug (doxorubicin, DOX) affects the acoustic properties of MBs. A suitable formulation of MBs for DOX loading was first identified by regulating the proportion of two lipid materials (1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and 1,2-distearoyl-sn-glycero-3-phospho-rac-glycerol sodium salt (DSPG)) with distinct electrostatic properties. We found that the DOX loading capacity of MBs was determined by the proportion of DSPG, since there was an electrostatic interaction with DOX. The DOX payload reduced the lipid fluidity of MBs, although this effect was dependent on the spatial uniformity of DOX on the MB shell surface. Loading DOX onto MBs enhanced acoustic stability 1.5-fold, decreased the resonance frequency from 12–14 MHz to 5–7 MHz, and reduced stable cavitation dose by 1.5-fold, but did not affect the stable cavitation threshold (300 kPa). Our study demonstrated that the DOX reduces lipid fluidity and decreases the elasticity of the MB shell, thereby influencing the acoustic properties of MBs.

3-D Ultrafast Ultrasound Imaging of Microbubbles Trapped Using an Acoustic Vortex

Increasing the local concentration of microbubbles (MBs) within the blood flow plays a crucial role in several medical applications, but there are few imaging modalities available for volumetric tracking of the aggregated MBs in real time. Here we describe a device integrating acoustic vortex tweezers (AVTs) and ultrasound plane-wave imaging (PWI) to achieve the goal of controlling the spatial distribution of MBs in blood vessels and simultaneously monitoring this process using the same probe. Experiments were conducted using a 5-MHz 2-D array ultrasound probe (with three cycles of excitation at an acoustic pressure of 2000 kPa) and 1.2- [Formula: see text]-diameter MBs at a flow rate of 20 mm/s. The AVT waveform was produced by modulating the repetition frequency of the transmitted pulse asymmetrically (4 and 8 kHz at the inflow and outflow ends, respectively). In order to simultaneously capture MBs and carry out imaging with the same probe, the asymmetric AVT pulse signal and the ultrasound-imaging pulse signal were arranged in a staggered series, and the imaging was carried out using plane-wave pulses at nine angles (-7° to 7°) in compounded PWI (volume rate: 200 Hz). Microscopy observations showed that freely suspended MBs could indeed be gathered by the asymmetric AVT in the flow field to form an MBs cluster with a spot size of about [Formula: see text], which could resist the flow to remain at a fixed location for about 22 s. After the asymmetric AVT signal and the ultrasound-imaging pulse signal were turned on for 1 s, the ultrasound 3-D image showed that the signal intensity of the MB clusters increased by 13.1 dB ± 2.9 dB in relation to the background area. These results show that the proposed strategy can be used to accumulate flowing MBs at a desired location and to simultaneously observe this phenomenon. This tool could be used in the future to improve the outcomes of MB-related treatments for various diseases.

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.

Nanobiotechnology-assisted therapies to manage brain cancer in personalized manner

There are numerous investigated factors that limit brain cancer treatment efficacy such as ability of prescribed therapy to cross the blood-brain barrier (BBB), tumor specific delivery of a therapeutics, transport within brain interstitium, and resistance of tumor cells against therapies. Recent breakthroughs in the field of nano-biotechnology associated with developing multifunctional nano-theranostic emerged as an effective way to manage brain cancer in terms of higher efficacy and least possible adverse effects. Keeping challenges and state-of-art accomplishments into consideration, this review proposes a comprehensive, careful, and critical discussion focused on efficient nano-enabled platforms including nanocarriers for drug delivery across the BBB and nano-assisted therapies (e.g., nano-immunotherapy, nano-stem cell therapy, and nano-gene therapy) investigated for brain cancer treatment. Besides therapeutic efficacy point-of-view, efforts are being made to explore ways projected to tune such developed nano-therapeutic for treating patients in personalized manner via controlling size, drug loading, delivery, and retention. Personalized brain tumor management based on advanced nano-therapies can potentially lead to excellent therapeutic benefits based on unique genetic signatures in patients and their individual disease profile. Moreover, applicability of nano-systems as stimulants to manage the brain cancer growth factors has also been discussed in photodynamic therapy and radiotherapy. Overall, this review offers a comprehensive information on emerging opportunities in nanotechnology for advancing the brain cancer treatment.

Development and application of ultrasound contrast agents in biomedicine

With the rapid development of molecular imaging, ultrasound (US) medicine has evolved from traditional imaging diagnosis to integrated diagnosis and treatment at the molecular level. Ultrasound contrast agents (UCAs) play a crucial role in the integration of US diagnosis and treatment. As the micro-bubbles (MBs) in UCAs can enhance the cavitation effect and promote the biological effect of US, UCAs have also been studied in the fields of US thrombolysis, mediated gene transfer, drug delivery, and high intensity focused US. The application range of UCAs is expanding, and the value of their applications is improving. This paper reviews the development and application of UCAs in biomedicine in recent years, and the existing problems and prospects are pointed out.

Multi-mechanical waves against Alzheimer's disease pathology: a systematic review

Alzheimer’s disease (AD) is the most common cause of dementia, affecting approximately 40 million people worldwide. The ineffectiveness of the available pharmacological treatments against AD has fostered researchers to focus on alternative strategies to overcome this challenge. Mechanical vibrations delivered in different stimulation modes have been associated with marked improvements in cognitive and physical performance in both demented and non-demented elderly. Some of the mechanical-based stimulation modalities in efforts are earlier whole-body vibration, transcranial ultrasound stimulation with microbubble injection, and more recently, auditory stimulation. However, there is a huge variety of treatment specifications, and in many cases, conflicting results are reported. In this review, a search on Scopus, PubMed, and Web of Science databases was performed, resulting in 37 papers . These studies suggest that mechanical vibrations delivered through different stimulation modes are effective in attenuating many parameters of AD pathology including functional connectivity and neuronal circuit integrity deficits in the brains of AD patients, as well as in subjects with cognitive decline and non-demented older adults. Despite the evolving preclinical and clinical evidence on these therapeutic modalities, their translation into clinical practice is not consolidated yet. Thus, this comprehensive and critical systematic review aims to address the most important gaps in the reviewed protocols and propose optimal regimens for future clinical application.

Focused ultrasound: growth potential and future directions in neurosurgery

Over the past two decades, vast improvements in focused ultrasound (FUS) technology have made the therapy an exciting addition to the neurosurgical armamentarium. In this time period, FUS has gained US Food and Drug Administration (FDA) approval for the treatment of two neurological disorders, and ongoing efforts seek to expand the lesion profile that is amenable to ultrasonic intervention. In the following review, we highlight future applications for FUS therapy and compare its potential role against established technologies, including deep brain stimulation and stereotactic radiosurgery. Particular attention is paid to tissue ablation, blood-brain-barrier opening, and gene therapy. We also address technical and infrastructural challenges involved with FUS use and summarize the hurdles that must be overcome before FUS becomes widely accepted in the neurosurgical community.

Combining gene therapy with other therapeutic strategies and imaging agents for cancer theranostics

Cancer is one of the most prevalent and deadly diseases in the world, to which conventional treatment options, such as chemotherapy and radiotherapy, have been applied to overcome the disease or used in a palliative manner to enhance the quality of life of the patient. However, there is an urgent need to develop new preventive and treatment strategies to overcome the limitations of the commonly used approaches. The field of cancer nanomedicine, and more recently the field of nanotheranostics, where imaging and therapeutic agents are combined in a single platform, provide new opportunities for the treatment and the diagnosis of cancer. This combination could bring us closer to a more personalized and cared-for therapy, in opposition to the conventional and standardized approaches. Gene therapy is a promising strategy for the treatment of cancer that requires a transport system to efficiently deliver the genetic material into the target cells. Hence, the main purpose of this work was to review recent findings and developments regarding theranostic nanosystems that incorporate both gene therapy and imaging agents for cancer treatment.

Recent Advances in Stimulus-Responsive Nanocarriers for Gene Therapy

Gene therapy provides a promising strategy for curing monogenetic disorders and complex diseases. However, there are challenges associated with the use of viral delivery vectors. The advent of nanomedicine represents a quantum leap in the application of gene therapy. Recent advances in stimulus-responsive nonviral nanocarriers indicate that they are efficient delivery systems for loading and unloading of therapeutic nucleic acids. Some nanocarriers are responsive to cues derived from the internal environment, such as changes in pH, redox potential, enzyme activity, reactive oxygen species, adenosine triphosphate, and hypoxia. Others are responsive to external stimulations, including temperature gradients, light irradiation, ultrasonic energy, and magnetic field. Multiple stimuli-responsive strategies have also been investigated recently for experimental gene therapy.

Oscillatory behavior of microbubbles impacts efficacy of cellular drug delivery

Drug-loaded microbubbles have been proven to be an effective strategy for non-invasive and local drug delivery when combined with ultrasound excitation for targeted drug release. Inertial cavitation is speculated to be a major mechanism for releasing drugs from drug-loaded microbubbles, but it results in lethal cellular pore damage that greatly limits its application. Thus, we investigated the cellular vesicle attachment and uptake to evaluate the efficiency of drug delivery by modulating the behaviors of targeted microbubble oscillation. The efficiency of vesicle attachment on the targeted cell membrane was 36.5 ± 15.9% and 3.8 ± 2.3% under stable and inertial cavitation, respectively. Further, stable cavitation enhanced cell permeability (26.8 ± 3.2%), maintained cell viability (90.8 ± 2.1%), and showed 7.9 ± 1.9-fold enhancement of in vivo vesicle release on tumor vessels. Therefore, our results reveal the ability to improve drug delivery via stable cavitation induced by targeted microbubbles. We propose that this strategy might be suitable for tissue repair or neuromodulation.

Current Approaches for Glioma Gene Therapy and Virotherapy

Glioblastoma (GBM) is the most common and aggressive primary brain tumor in the adult population and it carries a dismal prognosis. Inefficient drug delivery across the blood brain barrier (BBB), an immunosuppressive tumor microenvironment (TME) and development of drug resistance are key barriers to successful glioma treatment. Since gliomas occur through sequential acquisition of genetic alterations, gene therapy, which enables to modification of the genetic make-up of target cells, appears to be a promising approach to overcome the obstacles encountered by current therapeutic strategies. Gene therapy is a rapidly evolving field with the ultimate goal of achieving specific delivery of therapeutic molecules using either viral or non-viral delivery vehicles. Gene therapy can also be used to enhance immune responses to tumor antigens, reprogram the TME aiming at blocking glioma-mediated immunosuppression and normalize angiogenesis. Nano-particles-mediated gene therapy is currently being developed to overcome the BBB for glioma treatment. Another approach to enhance the anti-glioma efficacy is the implementation of viro-immunotherapy using oncolytic viruses, which are immunogenic. Oncolytic viruses kill tumor cells due to cancer cell-specific viral replication, and can also initiate an anti-tumor immunity. However, concerns still remain related to off target effects, and therapeutic and transduction efficiency. In this review, we describe the rationale and strategies as well as advantages and disadvantages of current gene therapy approaches against gliomas in clinical and preclinical studies. This includes different delivery systems comprising of viral, and non-viral delivery platforms along with suicide/prodrug, oncolytic, cytokine, and tumor suppressor-mediated gene therapy approaches. In addition, advances in glioma treatment through BBB-disruptive gene therapy and anti-EGFRvIII/VEGFR gene therapy are also discussed. Finally, we discuss the results of gene therapy-mediated human clinical trials for gliomas. In summary, we highlight the progress, prospects and remaining challenges of gene therapies aiming at broadening our understanding and highlighting the therapeutic arsenal for GBM.

Ultrasound Combined With Microbubbles Loading BDNF Retrovirus to Open BloodBrain Barrier for Treatment of Alzheimer's Disease

Background: Brain-derived nerve growth factor (BDNF) is a promising effective target for the treatment of Alzheimer's disease (AD). BDNF, which has a high molecular weight, has difficulty in crossing the blood-brain barrier (BBB). The study aimed to prepare microbubbles loading brain-derived nerve growth factor (BDNF) retrovirus (MpLXSN-BDNF), to verify the characteristics of the microbubbles, and to study the therapeutic effect of the microbubbles combined with ultrasound on the opening of the blood-brain barrier in an AD rat model. Methods: 32 adult male SD rats were randomly divided into four groups: control group, ultrasound + pLXSN-EGFP microbubble group (U + MpLXSN-BDNF), ultrasound + pLXSN-BDNF microbubble group, and ultrasound + microbubble + pLXSN-BDNF virus group (U + MpLXSN-BDNF), with eight rats in each group. At the same time, the left hippocampus of rats was irradiated with low-frequency focused ultrasound guided by MRI to open the blood-brain barrier (BBB). The effects of BDNF overexpression on AD rats were evaluated behaviorally before and 1 month after the treatment. The number of acetylcholinesterase (ChAT)-positive cells and the content of acetylcholine (ACh) in brain tissues were determined by immunohistochemistry and high-performance liquid chromatography (HPLC), respectively. IF staining of synaptic spines and Western blot of synaptophysin presented herein detected synaptic density recovery. Results: Signal intensity enhancement at the BBB disruption sites could be observed on the MR images. The behavioral evaluation showed that the times of crossing the original platform in the U + MpLXSN-BDNF group increased significantly after treatment. Immunohistochemistry and HPLC revealed that the number of ChAT-positive neurons and the contents of ACh in the brain were significantly decreased in the treated groups compared with the controls. IF staining of synaptic spines and Western blot data of synaptophysin showed that the U + MpLXSN-BDNF group can recover the synaptic loss better by BDNF supplementation than the other treatment groups. Conclusion: Ultrasound combined with viral microbubbles carrying BDNF can increase the transfection efficiency of brain neurons, promote the high expression of exogenous gene BDNF, and play a therapeutic role in the AD model rats.

Recent Strategies for Targeted Brain Drug Delivery

Because the brain is the most important human organ, many brain disorders can cause severe symptoms. For example, glioma, one type of brain tumor, is progressive and lethal, while neurodegenerative diseases cause severe disability. Nevertheless, medical treatment for brain diseases remains unsatisfactory, and therefore innovative therapies are desired. However, the development of therapies to treat some cerebral diseases is difficult because the blood-brain barrier (BBB) or blood-brain tumor barrier prevents drugs from entering the brain. Hence, drug delivery system (DDS) strategies are required to deliver therapeutic agents to the brain. Recently, brain-targeted DDS have been developed, which increases the quality of therapy for cerebral disorders. This review gives an overview of recent brain-targeting DDS strategies. First, it describes strategies to cross the BBB. This includes BBB-crossing ligand modification or temporal BBB permeabilization. Strategies to avoid the BBB using local administration are also summarized. Intrabrain drug distribution is a crucial factor that directly determines the therapeutic effect, and thus it is important to evaluate drug distribution using optimal methods. We introduce some methods for evaluating drug distribution in the brain. Finally, applications of brain-targeted DDS for the treatment of brain tumors, Alzheimer's disease, Parkinson's disease, and stroke are explained.

Tornado-inspired acoustic vortex tweezer for trapping and manipulating microbubbles

Spatially concentrating and manipulating biotherapeutic agents within the circulatory system is a longstanding challenge in medical applications due to the high velocity of blood flow, which greatly limits drug leakage and retention of the drug in the targeted region. To circumvent the disadvantages of current methods for systemic drug delivery, we propose tornado-inspired acoustic vortex tweezer (AVT) that generates net forces for noninvasive intravascular trapping of lipid-shelled gaseous microbubbles (MBs). MBs are used in a diverse range of medical applications, including as ultrasound contrast agents, for permeabilizing vessels, and as drug/gene carriers. We demonstrate that AVT can be used to successfully trap MBs and increase their local concentration in both static and flow conditions. Furthermore, MBs signals within mouse capillaries could be locally improved 1.7-fold and the location of trapped MBs could still be manipulated during the initiation of AVT. The proposed AVT technique is a compact, easy-to-use, and biocompatible method that enables systemic drug administration with extremely low doses.

Focused Ultrasound and Microbubbles-Mediated Drug Delivery to Brain Tumor

The presence of blood–brain barrier (BBB) and/or blood–brain–tumor barriers (BBTB) is one of the main obstacles to effectively deliver therapeutics to our central nervous system (CNS); hence, the outcomes following treatment of malignant brain tumors remain unsatisfactory. Although some approaches regarding BBB disruption or drug modifications have been explored, none of them reach the criteria of success. Convention-enhanced delivery (CED) directly infuses drugs to the brain tumor and surrounding tumor infiltrating area over a long period of time using special catheters. Focused ultrasound (FUS) now provides a non-invasive method to achieve this goal via combining with systemically circulating microbubbles to locally enhance the vascular permeability. In this review, different approaches of delivering therapeutic agents to the brain tumors will be discussed as well as the characterization of BBB and BBTB. We also highlight the mechanism of FUS-induced BBB modulation and the current progress of this technology in both pre-clinical and clinical studies.

Addressing BBB Heterogeneity: A New Paradigm for Drug Delivery to Brain Tumors

Effective treatments for brain tumors remain one of the most urgent and unmet needs in modern oncology. This is due not only to the presence of the neurovascular unit/blood-brain barrier (NVU/BBB) but also to the heterogeneity of barrier alteration in the case of brain tumors, which results in what is referred to as the blood-tumor barrier (BTB). Herein, we discuss this heterogeneity, how it contributes to the failure of novel pharmaceutical treatment strategies, and why a "whole brain" approach to the treatment of brain tumors might be beneficial. We discuss various methods by which these obstacles might be overcome and assess how these strategies are progressing in the clinic. We believe that by approaching brain tumor treatment from this perspective, a new paradigm for drug delivery to brain tumors might be established.

Recent Advances on Ultrasound Contrast Agents for Blood-Brain Barrier Opening with Focused Ultrasound

The blood-brain barrier is the primary obstacle to efficient intracerebral drug delivery. Focused ultrasound, in conjunction with microbubbles, is a targeted and non-invasive way to disrupt the blood-brain barrier. Many commercially available ultrasound contrast agents and agents specifically designed for therapeutic purposes have been investigated in ultrasound-mediated blood-brain barrier opening studies. The new generation of sono-sensitive agents, such as liquid-core droplets, can also potentially disrupt the blood-brain barrier after their ultrasound-induced vaporization. In this review, we describe the different compositions of agents used for ultrasound-mediated blood-brain barrier opening in recent studies, and we discuss the challenges of the past five years related to the optimal formulation of agents.

In Vivo Tracking of Fluorinated Polypeptide Gene Carriers by Positron Emission Tomography Imaging

Fluorinated polymers have attracted increasing attention in gene delivery and cytosolic protein delivery in recent years. In vivo tracking of fluorinated polymers will be of great importance to evaluate their biodistribution, clearance, and safety. However, tracking of polymeric carriers without changing their chemical structures remains a huge challenge. Herein, we reported a series of fluorinated poly-l-(lysine) (F-PLL) with high gene transfection efficiency and excellent biodegradation. Radionuclide ¹⁸F was radiolabeled on F-PLL by halogen replacement without chemical modification. The radiolabeling of F-PLL offers positron emission tomography (PET) imaging for in vivo tracking of the polymers. The biodistribution of F-PLL and the DNA complexes revealed by micro-PET imaging illustrated the rapid clearance of fluorinated polymers from liver and intestine after intravenous administration. The results demonstrated that the polymer F-PLL will not be accumulated in the liver and spleen when administrated as a gene carrier. This work presents a new strategy for in vivo tracking fluorinated polymers via PET imaging.

Plasmid-loadable magnetic/ultrasound-responsive nanodroplets with a SPIO-NP dispersed perfluoropentane core and lipid shell for tumor-targeted intracellular plasmid delivery

Using ultrasound activating contrast agents to induce sonoporation is a potential strategy for effective lesion-targeted gene delivery. Previous reports have proven that submicron nanodroplets have a better advantage than microbubbles in that they can pass through tumor vasculature endothelial gaps by passive targeting; however, they cannot achieve an adequate dose in tumors to facilitate ultrasound-enhanced gene delivery. Additionally, a few studies focused on delivering macromolecular genetic materials (i.e. overexpression plasmid and CRISPR plasmid) have presented more unique advantages than small-molecular genetic materials (i.e. miRNA mimics, siRNA and shRNA etc.), such as enhancing the expression of target genes with long-term effectiveness. Thereby, we constructed novel plasmid-loadable magnetic/ultrasound-responsive nanodroplets, where superparamagnetic iron oxide nanoparticle dispersed perfluoropentane was encapsulated with lipids to which plasmids could be adhered, and branched polyethylenimine was used to protect the plasmids from enzymolysis. Furthermore, in vitro and in vivo studies were performed to verify the magnetic tumor-targeting ability of the plasmid-loadable magnetic/ultrasound-responsive nanodroplets and focused ultrasound enhanced intracellular plasmid delivery. The plasmid-loadable magnetic/ultrasound-responsive nanodroplets, carrying 16-19 plasmids per droplet, had desirable diameters less than 300 nm, and integrated the merits of excellent magnetic targeting capabilities and phase transition sensitivity to focused ultrasound. Under programmable focused ultrasound exposure, the plasmid-loadable magnetic/ultrasound-responsive nanodroplets underwent a phase-transition into echogenic microbubbles and the subsequent inertial cavitation of the microbubbles achieved an ∼40% in vitro plasmid delivery efficiency. Following intravenous administration, T2-weighted magnet resonance imaging, scanning electron microscopy and inductively coupled plasma optical emission spectrometry of the tumors showed significantly enhanced intratumoral accumulation of the plasmid-loadable magnetic/ultrasound-responsive nanodroplets under an external magnetic field. And a GFP ELISA assay and immunofluorescence staining indicated that focused ultrasound-induced inertial cavitation of the plasmid-loadable magnetic/ultrasound-responsive nanodroplets significantly enhanced the intracellular delivery of plasmids within the tumor after magnet-assisted accumulation, while only lower GFP levels were observed in the tumors on applying focused ultrasound or an external magnet alone. Taken together, utilizing the excellent plasmid-loadable magnetic/ultrasound-responsive nanodroplets combined with magnetism and ultrasound could efficiently deliver plasmids to cancer cells, which could be a potential strategy for macromolecular genetic material delivery in the clinic to treat cancer.

Treatment of Parkinson’s disease using focused ultrasound with GDNF retrovirus-loaded microbubbles to open the blood–brain barrier

This study aims to prepare ultrasound-targeted glial cell-derived neurotrophic factor (GDNF) retrovirus-loaded microbubbles (M pLXSN-GDNF) to verify the properties of the microbubbles and to study the therapeutic effect of the GDNF retrovirus-loaded microbubbles combined with ultrasound (U) to open the blood–brain barrier (BBB) in a Parkinson’s disease (PD) model in rats, allowing the retrovirus to pass through the BBB and transfect neurons in the substantia nigra of the midbrain, thereby increasing the expression of GDNF. The results of western blot analysis revealed significant differences between U + MpLXSN-EGFP, U + M + pLXSN-GDNF, and M pLXSN-GDNF (P < 0.05) groups. After 8 weeks of treatment, the evaluation of the effect of increased GDNF expression on behavioral deficits in PD model rats was conducted. The rotation symptom was significantly improved in the U + MpLXSN-GDNF group, and the difference before and after treatment was significant (P < 0.05). Also, the content of dopamine and the number of tyrosine hydroxylase-positive (dopaminergic) neurons were found to be higher in the brain of PD rats in the U + M pLXSN-GDNF group than in the control groups. Ultrasound combined with GDNF retrovirus-loaded microbubbles can enhance the transfection efficiency of neurons in vivo and highly express the exogenous GDNF gene to play a therapeutic role in PD model rats.

Augmentation of brain tumor interstitial flow via focused ultrasound promotes brain-penetrating nanoparticle dispersion and transfection

The delivery of systemically administered gene therapies to brain tumors is exceptionally difficult because of the blood-brain barrier (BBB) and blood-tumor barrier (BTB). In addition, the adhesive and nanoporous tumor extracellular matrix hinders therapeutic dispersion. We first developed the use of magnetic resonance image (MRI)-guided focused ultrasound (FUS) and microbubbles as a platform approach for transfecting brain tumors by targeting the delivery of systemically administered "brain-penetrating" nanoparticle (BPN) gene vectors across the BTB/BBB. Next, using an MRI-based transport analysis, we determined that after FUS-mediated BTB/BBB opening, mean interstitial flow velocity magnitude doubled, with "per voxel" flow directions changing by an average of ~70° to 80°. Last, we observed that FUS-mediated BTB/BBB opening increased the dispersion of directly injected BPNs through tumor tissue by >100%. We conclude that FUS-mediated BTB/BBB opening yields markedly augmented interstitial tumor flow that, in turn, plays a critical role in enhancing BPN transport through tumor tissue.

Microbubbles in combination with focused ultrasound for the delivery of quercetin-modified sulfur nanoparticles through the blood brain barrier into the brain parenchyma and relief of endoplasmic reticulum stress to treat Alzheimer's disease

The delivery of drugs across the blood-brain barrier (BBB) effectively and safely is one of the major challenges in the treatment of neurodegenerative diseases. In this work, we constructed a nano-system using microbubbles to promote the crossing of drugs across the BBB, where microbubbles in combination with focused ultrasound were used to mediate the transient opening of the BBB and delivery of nanomedicines. This system (Qc@SNPs-MB) was formed by embedding quercetin-modified sulfur nanoparticles (Qc@SNPs) in microbubbles (MB). Qc@SNPs-MB was destroyed instantly when exposed to ultrasonic pulses, and it enhanced the permeability of the blood vessels, resulting in the brief opening of the BBB owing to the "sonoporation" effect. Also, Qc@SNPs were released from the outer shell of the microbubbles and entered the brain across the open BBB, accumulating in the brain parenchyma. Due to the rapid accumulation of Qc@SNPs in the brain, it effectively reduced neuronal apoptosis, inflammatory response, calcium homeostasis imbalance, and oxidative stress, which are all mediated by endoplasmic reticulum stress, and protected nerve cells, thus treating Alzheimer's disease (AD) effectively. The Morris water maze experiment showed that the learning ability and memory ability of the AD mice treated with Qc@SNPs were significantly improved, and no obvious side effects were found. Therefore, Qc@SNPs-MB combined with ultrasound can provide an effective and safe drug delivery method for the treatment of neurodegenerative diseases and a promising strategy for endoplasmic reticulum stress therapy.

Tumor Contrast Imaging with Gas Vesicles by Circumventing the Reticuloendothelial System

Gas vesicles (GVs) are nanosized structures (45-800 nm) and have been reported to produce non-linear contrast signals, making them an attractive agent for molecular targeting of tumors. One barrier to their use for pre-clinical oncology studies is rapid uptake into the reticuloendothelial system (RES) and consequent rapid decrease in contrast signal after infusion ends and low signal on reperfusion after a bubble burst sequence. The purpose of this study was to examine suppression of the RES and surface modification of GVs to prolong contrast circulation in tumors for ultrasound imaging. Ultrasound imaging to measure dynamics of contrast signal intensity in tumor models was carried out using a 21-MHz high-frequency array transducer with the Vevo 2100 ultrasound system. The non-linear contrast signal from intravenously injected GVs compared with peak enhancement was measured during contrast wash-out and on reperfusion after a contrast burst sequence. Disrupting the RES by saturating the macrophage population or chemically inhibiting the Kupffer cell population with gadolinium or Intralipid preserves 62%-88% of GVs' contrast enhancement relative to peak during the wash-out phase and 32%-56% on reperfusion compared with 38% and 14%, respectively, for no disruption of the RES, indicating longer circulation of GVs in the tumor. Additionally, coating the GVs with 2-, 5- or 10-kDa polyethylene glycol (PEG) chains resulted in >70% contrast signal retention in the tumors during wash-out and, for 5- or 10-kDa PEG chains, a return to >45% of peak contrast signal on reperfusion. These findings indicate that GVs can be used as a contrast agent for tumor imaging and that disruption of the RES improved recirculation and maintained contrast enhancement caused by GVs in the tumors.

Blood-Brain Barrier and Delivery of Protein and Gene Therapeutics to Brain

Alzheimer’s disease (AD) and treatment of the brain in aging require the development of new biologic drugs, such as recombinant proteins or gene therapies. Biologics are large molecule therapeutics that do not cross the blood-brain barrier (BBB). BBB drug delivery is the limiting factor in the future development of new therapeutics for the brain. The delivery of recombinant protein or gene medicines to the brain is a binary process: either the brain drug developer re-engineers the biologic with BBB drug delivery technology, or goes forward with brain drug development in the absence of a BBB delivery platform. The presence of BBB delivery technology allows for engineering the therapeutic to enable entry into the brain across the BBB from blood. Brain drug development may still take place in the absence of BBB delivery technology, but with a reliance on approaches that have rarely led to FDA approval, e.g., CSF injection, stem cells, small molecules, and others. CSF injection of drug is the most widely practiced approach to brain delivery that bypasses the BBB. However, drug injection into the CSF results in limited drug penetration to the brain parenchyma, owing to the rapid export of CSF from the brain to blood. A CSF injection of a drug is equivalent to a slow intravenous (IV) infusion of the pharmaceutical. Given the profound effect the existence of the BBB has on brain drug development, future drug or gene development for the brain will be accelerated by future advances in BBB delivery technology in parallel with new drug discovery.

Molecular Ultrasound Imaging

Contrast-enhanced ultrasound (CEUS) imaging is a valuable tool for preclinical and clinical diagnostics. The most frequently used ultrasound contrast agents are microbubbles. Besides them, novel nano-sized materials are under investigation, which are briefly discussed in this chapter. For molecular CEUS, the ultrasound contrast agents are modified to actively target disease-associated molecular markers with a site-specific ligand. The most common markers for tumor imaging are related to neoangiogenesis, like the vascular endothelial growth factor receptor-2 (VEGFR2) and α_vβ₃ integrin. In this chapter, applications of molecular ultrasound to longitudinally monitor receptor expression during tumor growth, to detect neovascularization, and to evaluate therapy responses are described. Furthermore, we report on first clinical trials of molecular CEUS with VEGFR2-targeted phospholipid microbubbles showing promising results regarding patient safety and its ability to detect tumors of prostate, breast, and ovary. The chapter closes with an outlook on ultrasound theranostics, where (targeted) ultrasound contrast agents are used to increase the permeability of tumor tissues and to support drug delivery.

Scoping Review of Targeted Ultrasound Contrast Agents in the Detection of Angiogenesis

A systematic search was conducted to categorize targeted ultrasound contrast agents (UCAs) used in cancer-related angiogenesis detection. We identified 15 unique contrast agents from 2008 to March 2018. Most primary research articles studied UCAs targeted to vascular endothelial growth factor receptor or α_v β₃ -integrin. Breast cancer and colon cancer are the most common neoplastic processes in which these agents were studied. BR55 (Bracco Research SA, Geneva, Switzerland), a vascular endothelial growth factor receptor-targeting UCA, is the first targeted UCA that has completed phase 0 trials. Our review identifies a gap in the literature regarding the application of targeted UCAs in cancer models beyond breast and colon cancers and identifies other promising UCAs.

Local Tumor Ischemia-Reperfusion Mediated By Ultrasound-Targeted Microbubble Destruction Enhances The Anti-Tumor Efficacy Of Doxorubicin Chemotherapy

Background

Ultrasound-targeted microbubble destruction (UTMD) has been shown to be a promising noninvasive technique to change the tumor circulation, thus providing a potential method to increase reactive oxygen species (ROS) levels in tumors by inducing tumor tissue ischemia-reperfusion (IR). In this study, we investigated the feasibility of local tumor IR through UTMD to enhance the anti-tumor efficacy of doxorubicin (DOX) chemotherapy.

Methods

UTMD was used to induce local tumor IR. After the major blood supply of the tumor was restored, DOX was intravenously injected into the tumor-bearing mice. The superoxide dismutase (SOD) and catalase (CAT) activity and ROS levels were examined, and the anti-tumor efficacy was evaluated.

Results

UTMD blocked the circulation to the tumor for 30 mins. Slow reperfusion began to occur after 30 mins, and major blood supply was restored after 1 hr. The blood perfusion of the tumor completely recovered at 2 hrs. The activity of SOD in the tumors was significantly decreased at 2 hrs and 1 day after IR treatment with or without DOX treatment. The CAT activity showed no obvious changes at 2 hrs after IR treatment, whereas a significant decrease was found after 1 day in both the IR and DOX/IR groups. Moreover, higher levels of ROS were produced in the IR group and IR/DOX group. In vivo anti-tumor study indicated that the local tumor IR strategy may significantly enhance the anti-tumor efficacy of DOX chemotherapy.

Conclusion

UTMD provides a novel, simple and non-invasive technique for tumor IR. In combination with chemotherapy, UTMD may have high great potential to improve the anti-tumor efficacy of chemotherapeutic drugs.

Safety and efficacy of focused ultrasound induced blood-brain barrier opening, an integrative review of animal and human studies

The blood-brain barrier, while fundamental in maintaining homeostasis in the central nervous system, is a bottleneck to achieving efficacy for numerous therapeutics. Improved brain penetration is also desirable for reduced dose, cost, and systemic side effects. Transient disruption of the blood-brain barrier with focused ultrasound (FUS) can facilitate drug delivery noninvasively with precise spatial and temporal specificity. FUS technology is transcranial and effective without further drug modifications, key advantages that will accelerate adoption and translation of existing therapeutic pipelines. In this review, we performed a comprehensive literature search to build a database and provide a synthesis of ultrasound parameters and drug characteristics that influence the safety and efficacy profile of FUS to enhance drug delivery.

Applications of Ultrasound to Stimulate Therapeutic Revascularization

Many pathological conditions are characterized or caused by the presence of an insufficient or aberrant local vasculature. Thus, therapeutic approaches aimed at modulating the caliber and/or density of the vasculature by controlling angiogenesis and arteriogenesis have been under development for many years. As our understanding of the underlying cellular and molecular mechanisms of these vascular growth processes continues to grow, so too do the available targets for therapeutic intervention. Nonetheless, the tools needed to implement such therapies have often had inherent weaknesses (i.e., invasiveness, expense, poor targeting, and control) that preclude successful outcomes. Approximately 20 years ago, the potential for using ultrasound as a new tool for therapeutically manipulating angiogenesis and arteriogenesis began to emerge. Indeed, the ability of ultrasound, especially when used in combination with contrast agent microbubbles, to mechanically manipulate the microvasculature has opened several doors for exploration. In turn, multiple studies on the influence of ultrasound-mediated bioeffects on vascular growth and the use of ultrasound for the targeted stimulation of blood vessel growth via drug and gene delivery have been performed and published over the years. In this review article, we first discuss the basic principles of therapeutic ultrasound for stimulating angiogenesis and arteriogenesis. We then follow this with a comprehensive cataloging of studies that have used ultrasound for stimulating revascularization to date. Finally, we offer a brief perspective on the future of such approaches, in the context of both further research development and possible clinical translation.