Experimental investigation of the penetration of ultrasound nanobubbles in a gastric cancer xenograft

Progress in the treatment of drug-loaded nanomaterials in renal cell carcinoma

Renal cell carcinoma (RCC) is a common urinary tract tumor that arises from the highly heterogeneous epithelium of the renal tubules. The incidence of kidney cancer is second only to the incidence of bladder cancer, and has shown an upward trend over time. Although surgery is the preferred treatment for localized RCC, treatment decisions should be customized to individual patients considering their overall health status and the risk of developing or worsening chronic kidney disease postoperatively. Anticancer drugs are preferred to prevent perioperative and long-term postoperative complications; however, resistance to chemotherapy remains a considerable problem during the treatment process. To overcome this challenge, nanocarriers have emerged as a promising strategy for targeted drug delivery for cancer treatment. Nanocarriers can transport anticancer agents, achieving several-fold higher cytotoxic concentrations in tumors and minimizing toxicity to the remaining parts of the body. This article reviews the use of nanomaterials, such as liposomes, polymeric nanoparticles, nanocomposites, carbon nanomaterials, nanobubbles, nanomicelles, and mesoporous silica nanoparticles, for RCC treatment, and discusses their advantages and disadvantages.

Application of Nanoparticles in the Diagnosis of Gastrointestinal Diseases: A Complete Future Perspective

The diagnosis of gastrointestinal (GI) diseases currently relies primarily on invasive procedures like digestive endoscopy. However, these procedures can cause discomfort, respiratory issues, and bacterial infections in patients, both during and after the examination. In recent years, nanomedicine has emerged as a promising field, providing significant advancements in diagnostic techniques. Nanoprobes, in particular, offer distinct advantages, such as high specificity and sensitivity in detecting GI diseases. Integration of nanoprobes with advanced imaging techniques, such as nuclear magnetic resonance, optical fluorescence imaging, tomography, and optical correlation tomography, has significantly enhanced the detection capabilities for GI tumors and inflammatory bowel disease (IBD). This synergy enables early diagnosis and precise staging of GI disorders. Among the nanoparticles investigated for clinical applications, superparamagnetic iron oxide, quantum dots, single carbon nanotubes, and nanocages have emerged as extensively studied and utilized agents. This review aimed to provide insights into the potential applications of nanoparticles in modern imaging techniques, with a specific focus on their role in facilitating early and specific diagnosis of a range of GI disorders, including IBD and colorectal cancer (CRC). Additionally, we discussed the challenges associated with the implementation of nanotechnology-based GI diagnostics and explored future prospects for translation in this promising field.

Nanobubble technologies: Applications in therapy from molecular to cellular level

Nanobubbles are gaseous entities suspended in bulk liquids that have widespread beneficial usage in many industries. Nanobubbles are already proving to be versatile in furthering the effectiveness of disease treatment on cellular and molecular levels. They are functionalized with biocompatible and stealth surfaces to aid in the delivery of drugs. At the same time, nanobubbles serve as imaging agents due to the echogenic properties of the gas core, which can also be utilized for controlled and targeted delivery. This review provides an overview of the biomedical applications of nanobubbles, covering their preparation and characterization methods, discussing where the research is currently focused, and how they will help shape the future of biomedicine.

Molecular Dynamics Study of Laser Interaction with Nanoparticles in Liquids and Its Potential Application

Laser interaction with nanoparticles in liquid is the fundamental theoretical basis for many applications but it is still challenging to observe this nanoscale phenomenon within a few nanoseconds in liquid by experiment. The successful implementation of the two-temperature method integrated with molecular dynamics (TTM-MD) in laser interaction with bulk material has shown great potential in providing a panoramic view of the laser interaction with the nanoparticles. However, the current TTM-MD model has to divide the system into cubic cells, which leads to mistakes near the nanoparticle’s surface. We introduce the latest model, which performs the TTM-MD on each individual cluster instead of the cubic cells, and its high-performance parallel cluster analysis algorithm to update the cluster size. The cluster-based TTM-MD revealed the nanoparticle formation mechanism of laser fragmentation in liquid (LFL) and facilitated the study of laser fluence’s effect on the size distribution. In addition to LFL, this model is promising to be implemented in the laser thermal therapy of tumors, laser melting in liquid (LML), etc. Although cluster-based TTM-MD has proven to be a powerful tool for studying laser interaction with nanoparticles, a few challenges and future developments for the cluster-based TTM-MD, especially the ionization induced by femtosecond, are also discussed.

Highlights in ultrasound-targeted microbubble destruction-mediated gene/drug delivery strategy for treatment of malignancies

Ultrasound is one of the safest and most advanced medical imaging technologies that is widely used in clinical practice. Ultrasound microbubbles, traditionally used for contrast-enhanced imaging, are increasingly applied in Ultrasound-targeted Microbubble Destruction (UTMD) technology which enhances tissue and cell membrane permeability through cavitation and sonoporation, to result in a promising therapeutic gene/drug delivery strategy. Here, we review recent developments in the application of UTMD-mediated gene and drug delivery in the diagnosis and treatment of tumors, including the concept, mechanism of action, clinical application status, and advantages of UTMD. Furthermore, the future perspectives that should be paid more attention to in this field are prospected.

Theranostic nanobubbles towards smart nanomedicines

Targeted therapy and early accurate detection of malignant lesions are essential for the effectiveness of treatment and prognosis in cancer patients. The development of gaseous system as a versatile platform for the fabricated nanobubbles, has attracted much interest in improving the efficacy of ultrasound therapeutic, diagnostic, and theranostic platforms. Nano-sized bubble, as an ultrasound contrast agent, with spherical gas-filled structures exhibited contrast enhancement capability due to their inherent EPR effect. Additionally, nanobubbles exhibited good stability with extended retention time in the blood stream. The current review summarized various nanobubbles and discussed about the crucial parameters affecting the stability of ultrafine bubbles. Furthermore, therapeutic and theranostic gaseous systems for fighting against cancer were described.

Stable Thermally-Modulated Nanodroplet Ultrasound Contrast Agents

Liquid perfluorocarbon-based nanodroplets are stable enough to be used in extravascular imaging, but provide limited contrast enhancement due to their small size, incompressible core, and small acoustic impedance mismatch with biological fluids. Here we show a novel approach to overcoming this limitation by using a heating-cooling cycle, which we will refer to as thermal modulation (TM), to induce echogenicity of otherwise stable but poorly echogenic nanodroplets without triggering a transient phase shift. We apply thermal modulation to high-boiling point tetradecafluorohexane (TDFH) nanodroplets stabilized with a bovine serum albumin (BSA) shell. BSA-TDFH nanodroplets with an average diameter under 300 nanometers showed an 11.9 ± 5.4 mean fold increase in echogenicity on the B-mode and a 13.9 ± 6.9 increase on the nonlinear contrast (NLC) mode after thermal modulation. Once activated, the particles maintained their enhanced echogenicity (p < 0.001) for at least 13 h while retaining their nanoscale size. Our data indicate that thermally modulated nanodroplets can potentially serve as theranostic agents or sensors for various applications of contrast-enhanced ultrasound.

Bursting Microbubbles: How Nanobubble Contrast Agents Can Enable the Future of Medical Ultrasound Molecular Imaging and Image-Guided Therapy

The field of medical ultrasound has undergone a significant evolution since the development of microbubbles as contrast agents. However, due to their size, microbubbles remain in the vasculature, and therefore have limited clinical applications. Building a better - and smaller - bubble can expand the applications of contrast-enhanced ultrasound by allowing bubbles to extravasate from blood vessels - creating new opportunities. In this review, we summarize recent research on the formulation and use of NBs as imaging agents and as therapeutic vehicles. We discuss the ongoing debates in the field and reluctance to accepting NBs as an acoustically active construct and a potentially impactful clinical tool that can help shape the future of medical ultrasound. We hope that the overview of key experimental and theoretical findings in the NB field presented in this paper provides a fundamental framework that will help clarify NB-ultrasound interactions and inspire engagement in the field.

Stimuli-responsive nanobubbles for biomedical applications

Stimuli-responsive nanobubbles have received increased attention for their application in spatial and temporal resolution of diagnostic techniques and therapies, particularly in multiple imaging methods, and they thus have significant potential for applications in the field of biomedicine. This review presents an overview of the recent advances in the development of stimuli-responsive nanobubbles and their novel applications. Properties of both internal- and external-stimuli responsive nanobubbles are highlighted and discussed considering the potential features required for biomedical applications. Furthermore, the methods used for synthesis and characterization of nanobubbles are outlined. Finally, novel biomedical applications are proposed alongside the advantages and shortcomings inherent to stimuli-responsive nanobubbles.

Perfluoropentane-filled chitosan poly-acrylic acid nanobubbles with high stability for long-term ultrasound imaging in vivo

Reducing the size of ultrasound contrast agents (UCAs) will decrease the intensity of the ultrasound echogenic signals and reduce the stability of the bubbles. Therefore, it is a challenge to design nanobubbles that are less than 200 nm in size and that have both good imaging abilities and high stability for long-term imaging in vivo. In this work, we successfully prepared perfluoropentane-filled chitosan poly-acrylic acid (PFP-CS-PAA) nanobubbles with a size of about 100 nm via a direct simple core-template-free strategy. In vitro tests demonstrated that the nanobubbles showed satisfactory imaging capabilities in non-linear harmonic imaging mode and had significantly better stability than commercial Sonovue® lipid microbubbles. It was valuable to discover that the prepared PFP-CS-PAA nanobubbles could exhibit good imaging quality in rat livers for 10 min after intravenous injection. Also, the PFP-CS-PAA nanobubbles could maintain imaging capabilities in nude mouse tumors for 7 days after intratumoral injection, which indicated that these nanobubbles could keep their stability for a long time in vivo. To the best of our knowledge, the ultrasound imaging persistence time in vivo was the longest of currently reported polymer nanobubbles that are smaller than 200 nm. This new nanosized UCA with high stability has great potential for long-term ultrasound imaging in vivo. Tumor cellular uptake and histological analysis revealed that PFP-CS-PAA nanobubbles could be taken up into tumor cells, but no intracellular uptake was observed in the case of Sonovue®. Animal fluorescence imaging in vivo demonstrated that PFP-CS-PAA nanobubbles could be effectively cleared after intravenous injection within 168 h. MTT assays indicated that PFP-CS-PAA nanobubbles had appropriate biocompatibility. Abnormal levels of blood urea nitrogen were detected after the intravenous administration of PFP-CS-PAA nanobubbles to rats, and body-weight gain was inhibited for up to 6 d, but, after that, body weights recovered their tendency to increase.

Lipid-based Nanoplatforms in Cancer Therapy: Recent Advances and Applications

Though modern available cancer therapies are effective, they possess major adverse effects, causing non-compliance to patients. Furthermore, the majority of the polymeric-based medication platforms are certainly not universally acceptable, due to their several restrictions. With this juxtaposition, lipid-based medication delivery systems have appeared as promising drug nanocarriers to replace the majority of the polymer-based products because they are in a position to reverse polymer as well as, drug-associated restrictions. Furthermore, the amalgamation of the basic principle of nanotechnology in designing lipid nanocarriers, which are the latest form of lipid carriers, has tremendous chemotherapeutic possibilities as tumor-targeted drug-delivery pertaining to tumor therapy. Apart from this, it is reported that nearly 40% of the modern medication entities are lipophilic. Moreover, research continues to be efficient in attaining a significant understanding of the absorption and bioavailability of the developed lipids systems.

Construction of Nucleolin-Targeted Lipid Nanobubbles and Contrast-Enhanced Ultrasound Molecular Imaging in Triple-Negative Breast Cancer

PURPOSE

To construct aptamer AS1411-functionalized targeted lipid nanobubbles that could simultaneously target abnormally highly expressed nucleolin (NCL) on tumor tissue and neovasculature. Additionally, the study of their contrast-enhanced ultrasound molecular imaging capabilities in vitro and in vivo to explore new methods and approaches for the early and accurate diagnosis of triple-negative breast cancer (TNBC).

METHODS

First, the targeted lipid-nucleic acid molecules were constructed by an amide reaction. Then, the targeted lipid nanobubbles (AS1411-NBs) and nontargeted lipid nanobubbles (NBs) were prepared by membrane hydration, mechanical vibration and centrifugal floatation. The physicochemical characteristics and contrast-enhanced ultrasound imaging capabilities of AS1411-NBs and NBs were compared and analyzed in vitro and in vivo.

RESULTS

There were no significant differences between the AS1411-NBs and NBs in their concentration, average particle size or ultrasound imaging capabilities in vitro (P > 0.05). However, AS1411-NBs could simultaneously target NCL in tumor tissue and neovasculature to effectively prolong the duration of contrast-enhanced ultrasound imaging compared to NBs in vivo. The area under the time-intensity curve was significantly different between AS1411-NBs and NBs (P < 0.001), and the drug loading capacity of the AS1411-NBs was also significantly higher than that of the NBs (P < 0.05).

CONCLUSIONS

Aptamer AS1411-functionalized targeted lipid nanobubbles could significantly prolong the duration of contrast-enhanced ultrasound imaging to achieve dual-targeted ultrasound molecular imaging of tumor tissue and neovasculature. AS1411-NBs also have higher drug loading and targeted drug delivery capabilities compared with NBs, which can provide new methods and approaches for the early accurate diagnosis and effective treatment of TNBC.

Anti-G250 nanobody-functionalized nanobubbles targeting renal cell carcinoma cells for ultrasound molecular imaging

Traditional imaging examinations have difficulty in identifying benign and malignant changes in renal masses. This difficulty may be solved by ultrasound molecular imaging based on targeted nanobubbles, which could specifically enhance the ultrasound imaging of renal cell carcinomas (RCC) so as to discriminate benign and malignant renal masses. In this study, we aimed to prepare anti-G250 nanobody-functionalized targeted nanobubbles (anti-G250 NTNs) by coupling anti-G250 nanobodies to lipid nanobubbles and to verify their target specificity and binding ability to RCC cells that express G250 antigen and their capacity to enhance ultrasound imaging of RCC xenografts. Anti-G250 nanobodies were coupled to the lipid nanobubbles using the biotin-streptavidin bridge method. The average particle diameter of the prepared anti-G250 NTNs was 446 nm. Immunofluorescence confirmed that anti-G250 nanobodies were uniformly distributed on the surfaces of nanobubbles. In vitro experiments showed that the anti-G250 NTNs specifically bound to G250-positive 786-O cells and HeLa cells with affinities of 88.13% ± 4.37% and 71.8% ± 5.7%, respectively, and that they did not bind to G250-negative ACHN cells. The anti-G250 NTNs could significantly enhance the ultrasound imaging of xenograft tumors arising from 786-O cells and HeLa cells compared with blank nanobubbles, while the enhancement was not significant for xenograft tumors arising from ACHN cells. Immunofluorescence of tumor tissue slices confirmed that the anti-G250 NTNs could enter the tissue space through tumor blood vessels and bind to tumor cells specifically. In conclusion, anti-G250 nanobody-functionalized targeted nanobubbles could specifically bind to G250-positive RCC cells and enhance the ultrasound imaging of G250-positive RCC xenografts. This study has high-potential clinical application value for the diagnosis and differential diagnosis of renal tumors.

Theranostic nanobubble encapsulating a plasmon-enhanced upconversion hybrid nanosystem for cancer therapy

Nanobubble (NB), which simultaneously enhances ultrasound (US) images and access therapeutic platforms, is required for future cancer treatment. Methods: We designed a theranostic agent for novel cancer treatment by using an NB-encapsulated hybrid nanosystem that can be monitored by US and fluorescent imaging and activated by near-infrared (NIR) light. The nanosystem was transported to the tumor through the enhanced permeability and retention effect. The hybrid nanosystem comprised upconversion nanoparticle (UCNP) and mesoporous silica-coated gold nanorod (AuNR@mS) with the photosensitizer merocyanine 540 to realize dual phototherapy. Results: With the NIR light-triggered, the luminous intensity of the UCNP was enhanced by doping holmium ion and emitted visible green and red lights at 540 and 660 nm. The high optical density state between the UCNP and AuNR@mS can induce plasmonic enhancement to improve the photothermal and photodynamic effects, resulting in cell death by apoptosis. The nanosystem showed excellent stability to avoid the aggregation of nanoparticles during the treatment. JC-1 dye was used as an indicator of mitochondrial membrane potential to identify the mechanism of cell death. The results of in vitro and in vivo analyses confirmed the curative effect of improved dual phototherapy. Conclusion: We developed and showed the therapeutic functions of a novel nanosystem with the combination of multiple theranostic nanoplatforms that can be triggered and activated by 808 nm NIR laser and US.

The Study of Enhanced High-Intensity Focused Ultrasound Therapy by Sonodynamic N2O Microbubbles

High-intensity focused ultrasound (HIFU) is a representative non-invasive method of cancer therapy, but its low therapeutic efficacy and risk of damage to surrounding normal tissue hinder its further clinical development and application. Sonodynamic therapy (SDT) kills tumor cells through reactive oxygen molecules produced by sonosensitizers during ultrasound treatment. SDT can enhance HIFU efficacy like microbubbles. In this work, we developed nanoscale N₂O microbubbles (N₂O-mbs) by an improved mechanical oscillation method. These microbubbles showed good biocompatibility and tumor cell binding. The sonosensitivity of the N₂O-mbs was detected both extracellularly and intracellularly through the detection of reactive oxygen species generation. The toxic effects of these sonodynamic microbubbles on tumor cells and the synergistic effect on HIFU treatment were evaluated. Significant apoptosis was caused by reactive oxygen species produced by N₂O-mbs under ultrasound irradiation. N₂O-mbs combined with HIFU increased tumor cell necrosis and apoptosis in vitro and the coagulative necrotic volume and echo intensity in the bovine liver target area ex vivo. These sonodynamic microbubbles have been also demonstrated to efficiently inhibit tumor growth in vivo. N₂O-mbs have a significant impact on the treatment and ablation effect of HIFU due to the advantages of microbubble and extraordinary sonosensitivity. This finding suggests that N₂O-mbs may be a novel auxiliary agent for ultrasound that can be used to promote HIFU tumor thermal ablation.

A Deep Learning Approach for Targeted Contrast-Enhanced Ultrasound Based Prostate Cancer Detection

The important role of angiogenesis in cancer development has driven many researchers to investigate the prospects of noninvasive cancer diagnosis based on the technology of contrast-enhanced ultrasound (CEUS) imaging. This paper presents a deep learning framework to detect prostate cancer in the sequential CEUS images. The proposed method uniformly extracts features from both the spatial and the temporal dimensions by performing three-dimensional convolution operations, which captures the dynamic information of the perfusion process encoded in multiple adjacent frames for prostate cancer detection. The deep learning models were trained and validated against expert delineations over the CEUS images recorded using two types of contrast agents, i.e., the anti-PSMA based agent targeted to prostate cancer cells and the non-targeted blank agent. Experiments showed that the deep learning method achieved over 91 percent specificity and 90 percent average accuracy over the targeted CEUS images for prostate cancer detection, which was superior ( ) than previously reported approaches and implementations.

Construction of ultrasonic nanobubbles carrying CAIX polypeptides to target carcinoma cells derived from various organs

Background

Ultrasound molecular imaging is a novel diagnostic approach for tumors, whose key link is the construction of targeted ultrasound contrast agents. However, available targeted ultrasound contrast agents for molecular imaging of tumors are only achieving imaging in blood pool or one type tumor. No targeted ultrasound contrast agents have realized targeted ultrasound molecular imaging of tumor parenchymal cells in a variety of solid tumors so far. Carbonic anhydrase IX (CAIX) is highly expressed on cell membranes of various malignant solid tumors, so it’s a good target for ultrasound molecular imaging. Here, targeted nanobubbles carrying CAIX polypeptides for targeted binding to a variety of malignant tumors were constructed, and targeted binding ability and ultrasound imaging effect in different types of tumors were evaluated.

Results

The mean diameter of lipid targeted nanobubbles was (503.7 ± 78.47) nm, and the polypeptides evenly distributed on the surfaces of targeted nanobubbles, which possessed the advantages of homogenous particle size, high stability, and good safety. Targeted nanobubbles could gather around CAIX-positive cells (786-O and Hela cells), while they cannot gather around CAIX-negative cells (BxPC-3 cells) in vitro, and the affinity of targeted nanobubbles to CAIX-positive cells were significantly higher than that to CAIX-negative cells (P < 0.05). Peak intensity and duration time of targeted nanobubbles and blank nanobubbles were different in CAIX-positive transplanted tumor tissues in vivo (P < 0.05). Moreover, targeted nanobubbles in CAIX-positive transplanted tumor tissues produced higher peak intensity and longer duration time than those in CAIX-negative transplanted tumor tissues (P < 0.05). Finally, immunofluorescence not only confirmed targeted nanobubbles could pass through blood vessels to enter in tumor tissue spaces, but also clarified imaging differences of targeted nanobubbles in different types of transplanted tumor tissues.

Conclusions

Targeted nanobubbles carrying CAIX polypeptides can specifically enhance ultrasound imaging in CAIX-positive transplanted tumor tissues and could potentially be used in early diagnosis of a variety of solid tumors derived from various organs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12951-017-0307-0) contains supplementary material, which is available to authorized users.

The application of nanoparticles in diagnosis and theranostics of gastric cancer

Gastric cancer is the fourth most common cancer and the second leading cause of cancer related death worldwide. For the diagnosis of gastric cancer, apart from regular systemic imaging, the locoregional imaging is also of great importance. Moreover, there are still other ways for the detecting of gastric cancer, including the early detection of gastric cancer by endoscopy, the detection of gastric-cancer related biomarkers and the detection of circulating tumor cells (CTCs) of gastric cancer. However, conventional diagnostic methods are usually lack of specificity and sensitivity. Nanoparticles provide many benefits in the diagnosis of gastric cancer. Besides, nanoparticles are capable of integrating the functions of diagnosis and treatment together (theranostics). In this paper, we reviewed the applications of nanoparticles in diagnosis and theranostics of gastric cancer in the above mentioned aspects.

Inhibition of prostate cancer growth using doxorubicin assisted by ultrasound-targeted nanobubble destruction

Ultrasound (US)-targeted microbubble destruction has been widely used as an effective drug-delivery system. However, nanobubbles (NBs) have better stability and stronger penetration than microbubbles, and drug delivery assisted by US-targeted NB destruction (UTND) still needs to be investigated. Our aim was to investigate the effect of doxorubicin (DOX) on the inhibition of prostate cancer growth under UTND. Contrast-enhanced US imaging of transplanted PC3 prostate cancer in mice showed that under a combination of 1 W/cm² US power and a 100 Hz intermittent pulse with a “5 seconds on, 5 seconds off” mode, NBs with an average size of (485.7±33) nm were effectively destroyed within 15 minutes in the tumor location. PC3 cells and 20 tumor-bearing mice were divided into four groups: a DOX group, a DOX + NB group, a DOX + US group, and a DOX + NB + US group. The cell growth-inhibition rate and DOX concentration of xenografts in the DOX + NB + US group were highest. Based on another control group and these four groups, another 25 tumor-bearing mice were used to observe the treatment effect of nine DOX injections under UTND. The xenografts in the DOX + NB + US group decreased more obviously and had more cellular apoptosis than other groups. Finally, electron microscopy was used to estimate the cavitation effect of NBs under US irradiation in the control group, NB group, US group, and NB + US group. The results of scanning electron microscopy showed that PC3 cells in the DOX + NB + US group had more holes and significantly increased cell-surface folds. Meanwhile, transmission electric microscopy confirmed that more lanthanum nitrate particles entered the parenchymal cells in xenografts in the NB + US group compared with the other groups. This study suggested that UTND technology could be an effective method to promote drugs to function in US-irradiated sites, and the underlying mechanism may be associated with a cavitation effect.

Stable Encapsulation of Air in Mesoporous Silica Nanoparticles: Fluorocarbon-Free Nanoscale Ultrasound Contrast Agents

While gas-filled micrometer-sized ultrasound contrast agents vastly improve signal-to-noise ratios, microbubbles have short circulation lifetimes and poor extravasation from the blood. Previously reported fluorocarbon-based nanoscale contrast agents are more stable but their contrast is generally lower owing to their size and dispersity. The contrast agents reported here are composed of silica nanoparticles of ≈100 nm diameter that are filled with ≈3 nm columnar mesopores. Functionalization of the silica surface with octyl groups and resuspension with Pluronic F127 create particles with pores that remain filled with air but are stable in buffer and serum. Administration of high intensity focused ultrasound (HIFU) allows sensitive imaging of the silica nanoparticles down to 10(10) particles mL(-1) , with continuous imaging for at least 20 min. Control experiments with different silica particles supported the hypothesis that entrapped air could be pulled into bubble nuclei, which can then in turn act as acoustic scatterers. This process results in very little hemolysis in whole blood, indicating potential for nontoxic blood pool imaging. Finally, the particles are lyophilized and reconstituted or stored in PBS (phosphate-buffered saline, at least for four months) with no loss in contrast, indicating stability to storage and reformulation.

Comparison of the synergistic effect of lipid nanobubbles and SonoVue microbubbles for high intensity focused ultrasound thermal ablation of tumors

Microbubbles (MBs) are considered as an important enhancer for high intensity focused ultrasound (HIFU) treatment of benign or malignant tumors. Recently, different sizes of gas-filled bubbles have been investigated to improve the therapeutic efficiency of HIFU thermal ablation and reduce side effects associated with ultrasound power and irradiation time. However, nanobubbles (NBs) as an ultrasound contrast agent for synergistic therapy of HIFU thermal ablation remain controversial due to their small nano-size in diameter. In this study, phospholipid-shell and gas-core NBs with a narrow size range of 500–600 nm were developed. The synergistic effect of NBs for HIFU thermal ablation was carefully studied both in excised bovine livers and in breast tumor models of rabbits, and made a critical comparison with that of commercial SonoVue microbubbles (SonoVue MBs). In addition, the pathological changes of the targeted area in tumor tissue after HIFU ablation were further investigated. Phosphate buffer saline (PBS) was used as the control. Under the same HIFU parameters, the quantitative echo intensity of B-mode ultrasound image and the volume of coagulative necrosis in lipid NBs groups were significantly higher and larger than that in PBS groups, but could not be demonstrated a difference to that in SonoVue MBs groups both ex vivo and in vivo. These results showed that the synergistic effect of lipid NBs for HIFU thermal ablation were similar with that of SonoVue MBs, and further indicate that lipid NBs could potentially become an enhancer for HIFU thermal ablation of tumors.

Ultrasonic Nanobubbles Carrying Anti-PSMA Nanobody: Construction and Application in Prostate Cancer-Targeted Imaging

To facilitate prostate cancer imaging using targeted molecules, we constructed ultrasonic nanobubbles coupled with specific anti-PSMA (prostate specific membrane antigen) nanobodies, and evaluated their in vitro binding capacity and in vivo imaging efficacy. The “targeted” nanobubbles, which were constructed via a biotin-streptavidin system, had an average diameter of 487.60 ± 33.55 nm and carried the anti-PSMA nanobody as demonstrated by immunofluorescence. Microscopy revealed targeted binding of nanobubbles in vitro to PSMA-positive cells. Additionally, ultrasonography indicators of nanobubble imaging (including arrival time, peak time, peak intensity and enhanced duration) were evaluated for the ultrasound imaging in three kinds of animal xenografts (LNCaP, C4-2 and MKN45), and showed that these four indicators of targeted nanobubbles exhibited significant differences from blank nanobubbles. Therefore, this study not only presents a novel approach to target prostate cancer ultrasonography, but also provides the basis and methods for constructing small-sized and high-efficient targeted ultrasound nanobubbles.

Ultrasound imaging beyond the vasculature with new generation contrast agents

Current commercially available ultrasound contrast agents are gas-filled, lipid- or protein-stabilized microbubbles larger than 1 µm in diameter. Because the signal generated by these agents is highly dependent on their size, small yet highly echogenic particles have been historically difficult to produce. This has limited the molecular imaging applications of ultrasound to the blood pool. In the area of cancer imaging, microbubble applications have been constrained to imaging molecular signatures of tumor vasculature and drug delivery enabled by ultrasound-modulated bubble destruction. Recently, with the rise of sophisticated advancements in nanomedicine, ultrasound contrast agents, which are an order of magnitude smaller (100-500 nm) than their currently utilized counterparts, have been undergoing rapid development. These agents are poised to greatly expand the capabilities of ultrasound in the field of targeted cancer detection and therapy by taking advantage of the enhanced permeability and retention phenomenon of many tumors and can extravasate beyond the leaky tumor vasculature. Agent extravasation facilitates highly sensitive detection of cell surface or microenvironment biomarkers, which could advance early cancer detection. Likewise, when combined with appropriate therapeutic agents and ultrasound-mediated deployment on demand, directly at the tumor site, these nanoparticles have been shown to contribute to improved therapeutic outcomes. Ultrasound's safety profile, broad accessibility and relatively low cost make it an ideal modality for the changing face of healthcare today. Aided by the multifaceted nano-sized contrast agents and targeted theranostic moieties described herein, ultrasound can considerably broaden its reach in future applications focused on the diagnosis and staging of cancer.