Targeted contrast-enhanced ultrasound imaging of angiogenesis in an orthotopic mouse tumor model of renal carcinoma

Local Renal Treatments for Acute Kidney Injury: A Review of Current Progress and Future Translational Opportunities

Acute kidney injury (AKI) constitutes a significant public health concern, with limited therapeutic options to mitigate injury or expedite recovery. A novel therapeutic approach, local renal treatment, encompassing pharmacotherapy and surgical interventions, has exhibited positive outcomes in AKI management. Peri-renal administration, employing various delivery routes, such as the renal artery, intrarenal, and subcapsular sites, has demonstrated superiority over peripheral intravenous infusion. This review evaluates different drug delivery methods, analyzing their benefits and limitations, and proposes potential improvements. Renal decapsulation, particularly with the availability of minimally invasive techniques, emerges as an effective procedure warranting renewed consideration for AKI treatment. The potential synergistic effects of combined drug delivery and renal decapsulation could further advance AKI therapies. Clinical studies have already begun to leverage the benefits of local renal treatments, and with ongoing technological advancements, these modalities are expected to increasingly outperform systemic intravenous therapy.

Novel anti-VEGFR2 antibody-conjugated nanobubbles for targeted ultrasound molecular imaging in a rabbit VX2 hepatic tumor model

Nanobubbles (NBs), as ultrasound contrast agents, possess the potential for clinical applications in targeted ultrasound molecular imaging due to their small diameters and the specific molecular markers attached. Previous research studies mainly focused on the tumor-specific recruitment capability or drug carriers based on subcutaneous tumor models. In clinical trials, orthotopic tumor models are considered more clinically relevant and better predictive models for assessing drug efficacy compared to standard subcutaneous models. Here, we first prepared uniform-sized NBs with a soft chitosan-lipid membrane containing perfluoropropane gas and then anti-VEGFR2 antibodies were incorporated into NB membranes in order to achieve targeting ability toward tumor angiogenesis. The results of physicochemical characterization (the average size of 260.9 ± 3.3 nm and a PDI of 0.168 ± 0.036, n = 3) indicated that the targeted nanobubbles (tNBsv) have a spherical morphology and a vacant core. In vitro experiments found that the contrast enhancement abilities of tNBsv are similar to those of commercial SonoVue. In in vivo experiments, the orthotopic model of the rabbit VX2 hepatic tumor was used to evaluate the targeted binding ability of tNBsv toward tumor angiogenesis. Ultrasound sonograms revealed that tNBsv achieved the peak intensity of ultrasound imaging enhancement in the region of peripheral vasculature of VX2 tumors over non-targeted NBs or SonoVue, and the imaging time was longer than that of the other two. Ex vivo fluorescence imaging and examination using a confocal laser scanning microscope further verified that tNBsv were capable of binding to tumor angiogenesis. These results from our studies suggested that tNBsv are useful to develop an ultrasound imaging probe to evaluate anti-angiogenic cancer therapy by monitoring tumor angiogenesis.

In Vivo Ultrasound Molecular Imaging in the Evaluation of Complex Ovarian Masses: A Practical Guide to Correlation with Ex Vivo Immunohistochemistry

Ovarian cancer is the fifth leading cause of cancer-related deaths in women and the most lethal gynecologic cancer. It is curable when discovered at an early stage, but usually remains asymptomatic until advanced stages. It is crucial to diagnose the disease before it metastasizes to distant organs for optimal patient management. Conventional transvaginal ultrasound imaging offers limited sensitivity and specificity in the ovarian cancer detection. With molecularly targeted ligands addressing targets, such as kinase insert domain receptor (KDR), attached to contrast microbubbles, ultrasound molecular imaging (USMI) can be used to detect, characterize and monitor ovarian cancer at a molecular level. In this article, the authors propose a standardized protocol is proposed for the accurate correlation between in- vivo transvaginal KDR-targeted USMI and ex vivo histology and immunohistochemistry in clinical translational studies. The detailed procedures of in vivo USMI and ex vivo immunohistochemistry are described for four molecular markers, CD31 and KDR with a focus on how to enable the accurate correlation between in vivo imaging findings and ex vivo expression of the molecular markers, even if not the entire tumor could can be imaged by USMI, which is not an uncommon scenario in clinical translational studies. This work aims to enhance the workflow and the accuracy of characterization of ovarian masses on transvaginal USMI using histology and immunohistochemistry as reference standards, which involves sonographers, radiologists, surgeons, and pathologists in a highly collaborative research effort of USMI in cancer.

Non-Invasive Imaging and Scoring of Peritoneal Metastases in Small Preclinical Animal Models Using Ultrasound: A Preliminary Trial

Background: The peritoneum is a common site for the formation of metastases originating from several gastrointestinal and gynecological malignancies. A representative preclinical model to thoroughly explore the pathophysiological mechanisms and to study new treatment strategies is important. A major challenge for such models is defining and quantifying the (total) tumor burden in the peritoneal cavity prior to treatment, since it is preferable to use non-invasive methods. We evaluated ultrasound as a simple and easy-to-handle imaging method for this purpose. Methods: Peritoneal metastases were established in six WAG/Rij rats through i.p. injections of the colon carcinoma cell line CC-531. Using ultrasound, the location, number and size of intraperitoneal tumor nodules were determined by two independent observers. Tumor outgrowth was followed using ultrasound until the peritoneal cancer index (PCI) was ≥8. Interobserver variability and ex vivo correlation were assessed. Results: Visible peritoneal tumor nodules were formed in six WAG/Rij rats within 2–4 weeks after cell injection. In most animals, tumor nodules reached a size of 4–6 mm within 3–4 weeks, with total PCI scores ranging from 10–20. The predicted PCI scores using ultrasound ranged from 11–19 and from 8–18, for observer 1 and 2, respectively, which was quite similar to the ex vivo scores. Conclusions: Ultrasound is a reliable non-invasive method to detect intraperitoneal tumor nodules and quantify tumor outgrowth in a rat model.

Non-invasive molecular imaging of kidney diseases

In nephrology, differential diagnosis or assessment of disease activity largely relies on the analysis of glomerular filtration rate, urinary sediment, proteinuria and tissue obtained through invasive kidney biopsies. However, currently available non-invasive functional parameters, and most serum and urine biomarkers, cannot capture intrarenal molecular disease processes specifically. Moreover, although histopathological analyses of kidney biopsy samples enable the visualization of pathological morphological and molecular alterations, they only provide information about a small part of the kidney and do not allow longitudinal monitoring. These limitations not only hinder understanding of the dynamics of specific disease processes in the kidney, but also limit the targeting of treatments to active phases of disease and the development of novel targeted therapies. Molecular imaging enables non-invasive and quantitative assessment of physiological or pathological processes by combining imaging technologies with specific molecular probes. Here, we discuss current preclinical and clinical molecular imaging approaches in nephrology. Non-invasive visualization of the kidneys through molecular imaging can be used to detect and longitudinally monitor disease activity and can therefore provide companion diagnostics to guide clinical trials, as well as the safe and effective use of drugs.

Applications of Nanobiomaterials in the Therapy and Imaging of Acute Liver Failure

This review focuses on the therapeutic mechanisms, targeting strategies of various nanomaterials in acute liver failure, and recent advances of diverse nanomaterials for acute liver failure therapy, diagnosis, and imaging. This review provides an outlook on the applications of nanomaterials, especially on the new horizons in acute liver failure therapy, and inspires broader interests across various disciplines. Acute liver failure (ALF), a fatal clinical disease featured with overwhelming hepatocyte necrosis, is a grand challenge in global health. However, a satisfactory therapeutic option for curing ALF is still absent, other than liver transplantation. Nanobiomaterials are currently being developed for the diagnosis and treatment of ALF. The liver can sequester most of nanoparticles from blood circulation, which becomes an intrinsic superiority for nanobiomaterials targeting hepatic diseases. Nanobiomaterials can enhance the bioavailability of free drugs, thereby significantly improving the therapeutic effects in ALF. Nanobiomaterials can also increase the liver accumulation of therapeutic agents and enable more effective targeting of the liver or specific liver cells. In addition, stimuli-responsive, optical, or magnetic nanomaterials exhibit great potential in the therapeutical, diagnostic, and imaging applications in ALF. Therefore, therapeutic agents in combination with nanobiomaterials increase the specificity of ALF therapy, diminish adverse systemic effects, and offer a multifunctional theranostic platform. Nanobiomaterial holds excellent significance and prospects in ALF theranostics. In this review, we summarize the therapeutic mechanisms and targeting strategies of various nanobiomaterials in ALF. We highlight recent developments of diverse nanomedicines for ALF therapy, diagnosis, and imaging. Furthermore, the challenges and future perspectives in the theranostics of ALF are also discussed.

Antitumor effect of VEGFR2-targeted microbubble destruction with gemcitabine using an endoscopic ultrasound probe: In vivo mouse pancreatic ductal adenocarcinoma model

BACKGROUND

Ultrasound-targeted microbubble destruction (UTMD) induces cellular inflow of drugs at low intensity, while high intensity eradicates tumor vessels. Since vascular endothelial growth factor receptor 2 (VEGFR2) is highly expressed in pancreatic ductal adenocarcinoma (PDAC), VEGFR2-targeted microbubble (MB) might additionally increase the tissue specificity of drugs and thus improve antitumor effects. In addition, fixing the dual pulse intensity could maximize MB properties. This study evaluated the one-off (experiment 1) and cumulative (experiment 2) treatment effect of UTMD by regulating the dual pulse output applied to PDAC using VEGFR2-targeted MB.

METHODS

C57BL/6 mice inoculated with Pan-02 cells were allocated to five groups: VEGFR2-targeted MB+ gemcitabine (GEM), VEGFR2-targeted MB, non-targeted MB+GEM, GEM, and control groups. After injection of GEM or GEM and either VEGFR2-targeted or non-targeted MB, UTMD was applied for several minutes at low intensity followed by high intensity application. In experiment 1, mice were treated by the protocol described above and then euthanized immediately or at the tumor diameter doubling time (TDT). In experiment 2, the same protocol was repeated weekly and mice were euthanized at TDT regardless of protocol completion. Histological analysis by CD31 and VEGFR2 staining provided microvascular density (MVD) and VEGFR2 expression along vessels (VEGFR2v) or intra/peripheral cells (VEGFR2c).

RESULTS

In experiment 1, TDT was significantly longer in the VEGFR2-targeted MB+GEM group compared to the non-targeted MB+GEM, GEM, and control groups, while the VEGFR2-targeted MB group showed no statistical significance. MVD and VEGFR2v in the immediate euthanasia was significantly lower in the VEGFR2-targeted MB+GEM and VEGFR2-targeted MB groups than other conditions. In experiment 2, the VEGFR2-targeted MB+GEM group produced significantly longer TDT than the GEM or control groups, whereas the VEGFR2-targeted MB group showed no significant difference. Histology revealed significantly reduced VEGFR2v and VEGFR2c in the VEGFR2-targeted and non-targeted MB+GEM groups, while only VEGFR2v was significantly less in the VEGFR2-targeted MB group.

CONCLUSIONS

UTMD-mediated GEM therapy with the dual pulse application using VEGFR2-targeted MB substantially suppresses PDCA growth.

Development of a Translatable Ultrasound Molecular Imaging Agent for Inflammation

This study details the development, characterization and non-clinical efficacy of an ultrasound molecular imaging agent intended for molecular imaging of P-selectin in humans. A targeting ligand based on a recently discovered human selectin ligand was manufactured as fusion protein, and activity for human and mouse P- and E-selectin was evaluated by functional immunoassay. The targeting ligand was covalently conjugated to a lipophilic anchor inserted into a phospholipid microbubble shell. Three lots of the targeted microbubble drug product, TS-07-009, were produced, and assays for size distribution, zeta potential and morphology were established. The suitability of TS-07-009 as a molecular imaging agent was evaluated in vitro in a flow-based adhesion assay and in vivo using a canine model of transient myocardial ischemia. Selectivity for P-selectin over E-selectin was observed in both the human and murine systems. Contrast agent adhesion increased with P-selectin concentration in a dynamic adhesion assay. Significant contrast enhancement was observed on ultrasound imaging with TS-07-009 in post-ischemic canine myocardium at 30 or 90 min of re-perfusion. Negligible enhancement was observed in resting (no prior ischemia) hearts or with a control microbubble 90 min after ischemia. The microbubble contrast agent described here exhibits physiochemical properties and in vivo behavior suitable for development as a clinical imaging agent.

Ultrasound-Targeted Microbubble Destruction Enhances the Antitumor Efficacy of Doxorubicin in a Mouse Hepatocellular Carcinoma Model

The aim of the study described here was to investigate whether ultrasound-mediated microbubble destruction (UTMD) of targeted microbubbles conjugated with an anti-vascular endothelial growth factor receptor 2 (anti-VEGFR2) antibody can enhance the therapeutic effect of doxorubicin (DOX) on a mouse hepatocellular carcinoma (HCC) model bearing HEP-G2-RFP tumors. The growth of liver tumors in mice was inhibited by using Visistar VEGFR2 plus ultrasound irradiation and by DOX alone. DOX plus UTMD had an inhibitory effect on tumor growth beginning on the seventh day of treatment, while Visistar VEGFR2 alone and DOX alone had inhibitory effects beginning on the 11th day. DOX + UTMD significantly decreased tumor volume and tumor weight compared with DOX alone (p < 0.05) and Visistar VEGFR2 alone (p < 0.05). Compared with DOX alone and Visistar VEGFR2 alone, DOX + UTMD had the highest inhibitory effect on tumor angiogenesis and the highest apoptosis index. UTMD-targeted microbubbles can significantly enhance the antitumor effect of DOX on a mouse HCC model, inhibit angiogenesis and induce apoptosis in tumor cells.

Choosing The Right Animal Model for Renal Cancer Research

The increase in the life expectancy of patients with renal cell carcinoma (RCC) in the last decade is due to changes that have occurred in the area of preclinical studies. Understanding cancer pathophysiology and the emergence of new therapeutic options, including immunotherapy, would not be possible without proper research. Before new approaches to disease treatment are developed and introduced into clinical practice they must be preceded by preclinical tests, in which animal studies play a significant role. This review describes the progress in animal model development in kidney cancer research starting from the oldest syngeneic or chemically-induced models, through genetically modified mice, finally to xenograft, especially patient-derived, avatar and humanized mouse models. As there are a number of subtypes of RCC, our aim is to help to choose the right animal model for a particular kidney cancer subtype. The data on genetic backgrounds, biochemical parameters, histology, different stages of carcinogenesis and metastasis in various animal models of RCC as well as their translational relevance are summarized. Moreover, we shed some light on imaging methods, which can help define tumor microstructure, assist in the analysis of its metabolic changes and track metastasis development.

Application of Ultrasound-Targeted Microbubble Destruction-Mediated Exogenous Gene Transfer in Treating Various Renal Diseases

Chronic renal disease or acute renal injury could result in end-stage renal disease or renal failure. Sonoporation, induced by ultrasound-targeted microbubble destruction (UTMD), has evolved as a new technology for gene delivery. It increases the transfection efficiency of the genes into target kidney tissues. Moreover, UTMD-mediated gene delivery can directly repair the damaged tissues or improve the recruitment and homing of stem cells in the recovery of injured tissues, which has the potential to act as a non-viral and effective method to current gene therapy. This article reviews the mechanisms and applications of UTMD in terms of renal disease, including diabetic nephropathy, renal carcinoma, acute kidney injury, renal interstitial fibrosis, nephrotoxic nephritis, urinary stones, and acute rejection.

Dual-Targeted Microbubbles Specific to Integrin αVβ3 and Vascular Endothelial Growth Factor Receptor 2 for Ultrasonography Evaluation of Tumor Angiogenesis

Aggressive tumors are characterized by angiogenesis that promotes the migration and dissemination of tumor cells. Our aim was to develop a dual-targeted microbubble system for non-invasive evaluation of tumor angiogenesis in ultrasound. Avidinylated microbubbles were conjugated with biotinylated arginylglycylaspartic acid and vascular endothelial growth factor receptor 2 (VEGFR2) antibodies. Subcutaneous MHCC-97H liver carcinoma models were established. Non-targeted, αvβ3-targeted, VEGFR2-targeted and dual-targeted microbubbles was intravenously injected in series while acquiring ultrasound images of the tumor. The microbubbles were destroyed by a high-mechanical-index pulse 4 min after the injection. Peak intensity (PI) before and after the destructive pulse was recorded to compare contrast enhancement by different microbubbles. The targeting rates of the integrin-targeted, VEGFR2-targeted and dual-targeted groups were 95.02%, 96.04% and 94.23%, respectively, with no significant differences. Tumors in all groups were significantly enhanced. The time-intensity curve indicated no significant differences in arrival time, PI, area under the curve, amplitude and mean transit time. The difference in ultrasound signal intensity before and after the destructive pulse (⊿PI) for all targeted microbubble groups was significantly greater than that for the non-targeted microbubble group (all p values < 0.05), and the difference for the dual-targeted microbubble group was significantly greater than those of both mono-targeted groups (p <0.05).

Targeting of microbubbles: contrast agents for ultrasound molecular imaging

For contrast ultrasound imaging, the most efficient contrast agents comprise highly compressible gas-filled microbubbles. These micrometer-sized particles are typically filled with low-solubility perfluorocarbon gases, and coated with a thin shell, often a lipid monolayer. These particles circulate in the bloodstream for several minutes; they demonstrate good safety and are already in widespread clinical use as blood pool agents with very low dosage necessary (sub-mg per injection). As ultrasound is an ubiquitous medical imaging modality, with tens of millions of exams conducted annually, its use for molecular/targeted imaging of biomarkers of disease may enable wider implementation of personalised medicine applications, precision medicine, non-invasive quantification of biomarkers, targeted guidance of biopsy and therapy in real time. To achieve this capability, microbubbles are decorated with targeting ligands, possessing specific affinity towards vascular biomarkers of disease, such as tumour neovasculature or areas of inflammation, ischaemia-reperfusion injury or ischaemic memory. Once bound to the target, microbubbles can be selectively visualised to delineate disease location by ultrasound imaging. This review discusses the general design trends and approaches for such molecular ultrasound imaging agents, which are currently at the advanced stages of development, and are evolving towards widespread clinical trials.

Ultrasound Molecular Imaging of VEGFR-2 in Clear-Cell Renal Cell Carcinoma Tracks Disease Response to Antiangiogenic and Notch-Inhibition Therapy

Metastatic clear-cell renal cell carcinoma (ccRCC) affects thousands of patients worldwide each year. Antiangiogenic therapy has been shown to have beneficial effects initially, but resistance is eventually developed. Therefore, it is important to accurately track the response of cancer to different therapeutics in order to appropriately adjust the therapy to maximize efficacy. Change in tumor volume is the current gold standard for determining efficacy of treatment. However, functional variations can occur much earlier than measurable volume changes. Contrast-enhanced ultrasound (CEUS) is an important tool for assessing tumor progression and response to therapy, since it can monitor functional changes in the physiology. In this study, we demonstrate how ultrasound molecular imaging (USMI) can accurately track the evolution of the disease and molecular response to treatment. Methods A cohort of NSG (NOD/scid/gamma) mice was injected with ccRCC cells and treated with either the VEGF inhibitor SU (Sunitinib malate, Selleckchem, TX, USA) or the Notch pathway inhibitor GSI (Gamma secretase inhibitor, PF-03084014, Pfizer, New York, NY, USA), or started on SU and later switched to GSI (Switch group). The therapies used in the study focus on disrupting angiogenesis and proper vessel development. SU inhibits signaling of vascular endothelial growth factor (VEGF), which is responsible for the sprouting of new vasculature, and GSI inhibits the Notch pathway, which is a key factor in the correct maturation of newly formed vasculature. Microbubble contrast agents targeted to VEGFR-2 (VEGF Receptor) were delivered as a bolus, and the bound agents were imaged in 3D after the free-flowing contrast was cleared from the body. Additionally, the tumors were harvested at the end of the study and stained for CD31. Results The results show that MI can detect changes in VEGFR-2 expression in the group treated with SU within a week of the start of treatment, while differences in volume only become apparent after the mice have been treated for three weeks. Furthermore, USMI can detect response to therapy in 92% of cases after 1 week of treatment, while the detection rate is only 40% for volume measurements. The amount of targeting for the GSI and Control groups was high throughout the duration of the study, while that of the SU and Switch groups remained low. However, the amount of targeting in the Switch group increased to levels similar to those of the Control group after the treatment was switched to GSI. CD31 staining indicates significantly lower levels of patent vasculature for the SU group compared to the Control and GSI groups. Therefore, the results parallel the expected physiological changes in the tumor, since GSI promotes angiogenesis through the VEGF pathway, while SU inhibits it. Conclusion This study demonstrates that MI can track disease progression and assess functional changes in tumors before changes in volume are apparent, and thus, CEUS can be a valuable tool for assessing response to therapy in disease. Future work is required to determine whether levels of VEGFR-2 targeting correlate with eventual survival outcomes.

Detection of Atherosclerotic Plaques in the Rabbit Aorta Using Ultrasound Microbubbles Conjugated to Interleukin-18 Antibodies

BACKGROUND The purpose of the study was to investigate the ability of microbubbles (MBs) targeting interleukin-18 (IL-18) to detect plaques in a rabbit atherosclerotic plaque model. MATERIAL AND METHODS A rabbit atherosclerotic plaque model was established. The locations of the atherosclerotic plaques were verified by two-dimensional scanning and color Doppler flow imaging. An IL-18 antibody was conjugated to naked MBs (MBc) using the biotin-streptavidin conjugation method, resulting in the formation of MBIL-18. MBc and MBIL-18 were then used for contrast-enhanced ultrasound (CEUS) studies. The locations of CD34 and IL-18 within the plaques were determined by immunohistochemistry, and IL-18 expression levels in the plaques were determined by Western blot analysis. The relationships between IL-18 expression and the contrast intensity of the 2 MBs were analyzed. RESULTS MBc and MBIL-18 were both uniformly dispersed. Fluorescence microscopy and flow cytometry revealed that IL-18 was successfully conjugated to MBs. CEUS images showed that the intensity of the MBIL-18 signal was substantially enhanced and prolonged compared with that of the MBc signal. Immunohistochemistry showed that CD34 expression was significantly increased in the plaques and that IL-18 was mainly located in the inner parts and base of the atherosclerotic plaques. Western blot analysis revealed that IL-18 expression was higher in the plaque regions. Correlation analysis showed that IL-18 expression was correlated with the contrast intensity of MBIL-18 (r=0.903, P<0.05) but not with MBc (r=0.540, P>0.05). CONCLUSIONS MBs targeting IL-18 may be a novel, noninvasive method of diagnosing atherosclerotic plaques.

Experimental imaging in orthotopic renal cell carcinoma xenograft models: comparative evaluation of high-resolution 3D ultrasonography, in-vivo micro-CT and 9.4T MRI

In this study, we aimed to comparatively evaluate high-resolution 3D ultrasonography (hrUS), in-vivo micro-CT (μCT) and 9.4T MRI for the monitoring of tumor growth in an orthotopic renal cell carcinoma (RCC) xenograft model since there is a lack of validated, non-invasive imaging tools for this purpose. 1 × 10⁶ Caki-2 RCC cells were implanted under the renal capsule of 16 immunodeficient mice. Local and systemic tumor growth were monitored by regular hrUS, μCT and MRI examinations. Cells engrafted in all mice and gave rise to exponentially growing, solid tumors. All imaging techniques allowed to detect orthotopic tumors and to precisely calculate their volumes. While tumors appeared homogenously radiolucent in μCT, hrUS and MRI allowed for a better visualization of intratumoral structures and surrounding soft tissue. Examination time was the shortest for hrUS, followed by μCT and MRI. Tumor volumes determined by hrUS, μCT and MRI showed a very good correlation with each other and with caliper measurements at autopsy. 10 animals developed pulmonary metastases being well detectable by μCT and MRI. In conclusion, each technique has specific strengths and weaknesses, so the one(s) best suitable for a specific experiment may be chosen individually.

Molecular Ultrasound Imaging for the Detection of Neural Inflammation: A Longitudinal Dosing Pilot Study

Molecular ultrasound imaging provides the ability to detect physiologic processes noninvasively by targeting a variety of biomarkers in vivo. The current study was performed by exploiting an inflammatory biomarker, P-selectin, known to be present following spinal cord injury. Using a murine model (n = 6), molecular ultrasound imaging was performed using contrast microbubbles modified to target and adhere to P-selectin, prior to spinal cord injury (0D), acute stage postinjury (7D), and chronic stage (42D). Additionally, two imaging sessions were performed on each subject at specific time points, using doses of 30 μL and 100 μL. Upon analysis, targeted contrast analysis parameters were appreciably increased during the 7D scan compared with the 42D scan, without statistical significance. When examining the dose levels, the 30-μL dose demonstrated greater values than the 100-μL dose but lacked statistical significance. These findings provide additional preclinical evidence for the use of molecular ultrasound imaging for the possible detection of inflammation.

Ultrasound Molecular Imaging With BR55 in Patients With Breast and Ovarian Lesions: First-in-Human Results

Purpose We performed a first-in-human clinical trial on ultrasound molecular imaging (USMI) in patients with breast and ovarian lesions using a clinical-grade contrast agent (kinase insert domain receptor [KDR] -targeted contrast microbubble [MB_KDR]) that is targeted at the KDR, one of the key regulators of neoangiogenesis in cancer. The aim of this study was to assess whether USMI using MB_KDR is safe and allows assessment of KDR expression using immunohistochemistry (IHC) as the gold standard. Methods Twenty-four women (age 48 to 79 years) with focal ovarian lesions and 21 women (age 34 to 66 years) with focal breast lesions were injected intravenously with MB_KDR (0.03 to 0.08 mL/kg of body weight), and USMI of the lesions was performed starting 5 minutes after injection up to 29 minutes. Blood pressure, ECG, oxygen levels, heart rate, CBC, and metabolic panel were obtained before and after MB_KDR administration. Persistent focal MB_KDR binding on USMI was assessed. Patients underwent surgical resection of the target lesions, and tissues were stained for CD31 and KDR by IHC. Results USMI with MB_KDR was well tolerated by all patients without safety concerns. Among the 40 patients included in the analysis, KDR expression on IHC matched well with imaging signal on USMI in 93% of breast and 85% of ovarian malignant lesions. Strong KDR-targeted USMI signal was present in 77% of malignant ovarian lesions, with no targeted signal seen in 78% of benign ovarian lesions. Similarly, strong targeted signal was seen in 93% of malignant breast lesions with no targeted signal present in 67% of benign breast lesions. Conclusion USMI with MB_KDR is clinically feasible and safe, and KDR-targeted USMI signal matches well with KDR expression on IHC. This study lays the foundation for a new field of clinical USMI in cancer.

In vitro characterization and in vivo ultrasound molecular imaging of nucleolin-targeted microbubbles

Nucleolin (NCL) plays an important role in tumor vascular development. An increased endothelial expression level of NCL has been related to cancer aggressiveness and prognosis and has been detected clinically in advanced tumors. Here, with a peptide targeted to NCL (F3 peptide), we created an NCL-targeted microbubble (MB) and compared the performance of F3-conjugated MBs with non-targeted (NT) MBs both in vitro and in vivo. In an in vitro study, F3-conjugated MBs bound 433 times more than NT MBs to an NCL-expressing cell line, while pretreating cells with 0.5 mM free F3 peptide reduced the binding of F3-conjugated MBs by 84%, n = 4, p < 0.001. We then set out to create a method to extract both the tumor wash-in and wash-out kinetics and tumor accumulation following a single injection of targeted MBs. In order to accomplish this, a series of ultrasound frames (a clip) was recorded at the time of injection and subsequent time points. Each pixel within this clip was analyzed for the minimum intensity projection (MinIP) and average intensity projection (AvgIP). We found that the MinIP robustly demonstrates enhanced accumulation of F3-conjugated MBs over the range of tumor diameters evaluated here (2-8 mm), and the difference between the AvgIP and the MinIP quantifies inflow and kinetics. The inflow and clearance were similar for unbound F3-conjugated MBs, control (non-targeted) and scrambled control agents. Targeted agent accumulation was confirmed by a high amplitude pulse and by a two-dimensional Fourier Transform technique. In summary, F3-conjugated MBs provide a new imaging agent for ultrasound molecular imaging of cancer vasculature, and we have validated metrics to assess performance using low mechanical index strategies that have potential for use in human molecular imaging studies.

Targeted Contrast-Enhanced Ultrasound for Inflammation Detection

Molecular imaging is a form of nanotechnology that enables the noninvasive examination of biological processes in vivo. Radiopharmaceutical agents are used to target biochemical markers, permitting their detection and evaluation. Early visualization of molecular variations indicative of pathophysiological processes can aid in patient diagnoses and management decisions. Molecular imaging is performed by introducing into the body molecular probes, which are often contrast agents that have been nanoengineered to target and tether to molecules, thus enabling their radiologic identification. Through a nanoengineering process, ultrasound contrast agents can be targeted to specific molecules, extending ultrasound’s capabilities from the tissue to molecular level. Molecular ultrasound, or targeted contrast-enhanced ultrasound (TCEUS), has recently emerged as a popular molecular imaging technique due to its ability to provide real-time anatomic and functional information without ionizing radiation. However, molecular ultrasound represents a novel form of molecular imaging and consequently remains largely preclinical. This review explores the commonalities of TCEUS across several molecular targets and points to the need for standardization of kinetic behavior analysis. The literature underscores evidence gaps and the need for additional research. The application of TCEUS is unlimited but needs further standardization to ensure that future research studies are comparable.

Exploring Targeted Contrast-Enhanced Ultrasound to Detect Neural Inflammation

Targeted contrast-enhanced ultrasound (TCEUS) is an innovative method of molecular imaging used for detection of inflammatory biomarkers in vivo. By targeting ultrasound contrast to cell adhesion molecules (CAMs), which are known inflammatory markers within neural tissue, a more direct evaluation of neural inflammation can be made. Due to the novel nature of TCEUS, standardized methods of image analysis do not yet exist. Time intensity curve (TIC) shape analysis is currently used in magnetic resonance contrast imaging to determine temporal behavior of perfusion. Therefore, the presented research attempts to determine TIC shape analysis utility in TCEUS imaging by applying it to TCEUS scans targeted to CAMs present in neural inflammation. This was done in an animal model that underwent a traumatic spinal cord injury to induce inflammation ( n = 31). Subjects were divided into four groups, each receiving a TCEUS targeted to a different CAM seven days after surgery (P-selectin, intracellular adhesion molecule 1 [ICAM-1], vascular cell adhesion molecule 1 [VCAM-1], and control). TICs were generated using average pixel intensity within the injured region of the spinal cord. TIC shape analysis found similar curves were produced while targeting P-selectin and VCAM-1, both demonstrating rapid and sustained enhancement. Control injections demonstrated no enhancement. ICAM-1 injections demonstrated limited enhancement and a shape similar to the control.

[Molecular ultrasound imaging: Clinical applications]

BACKGROUND

Contrast-enhanced ultrasound imaging is increasingly being used in clinical applications, particularly for cardiovascular and liver diagnostics. In this context the availability of new molecular contrast agents and the initiation of clinical translation promises new options for pathomechanistic diagnostics.

MATERIAL AND METHODS

Analysis of the current literature on the development of molecular ultrasound contrast agents, the detection methods as well as the applications in preclinical and clinical studies.

RESULTS

Molecular contrast agents have become established in preclinical research for the detection of inflammation and angiogenesis and have been continuously refined over recent years. They consist of gas filled microbubbles with a diameter of 1-5 µm and the gas core is stabilized by a shell made of lipids, proteins or polymers to which biomolecules are conjugated that determine the target specificity. The agent BR55 is the first clinically evaluated molecular ultrasound contrast agent. It binds to the angiogenesis marker vascular endothelial growth factor receptor 2 (VEGFR2) and has been studied in several preclinical and clinical phase I and II studies on tumor diagnostics and characterization.

CONCLUSION

Molecular ultrasound imaging is rapidly evolving in preclinical research for a broad field of applications. Translation to clinical practice is conceivable for many indications and is already ongoing for BR55.

Intra-Animal Comparison between Three-dimensional Molecularly Targeted US and Three-dimensional Dynamic Contrast-enhanced US for Early Antiangiogenic Treatment Assessment in Colon Cancer

Purpose To perform an intra-animal comparison between (a) three-dimensional (3D) molecularly targeted ultrasonography (US) by using clinical-grade vascular endothelial growth factor receptor 2 (VEGFR2)-targeted microbubbles and (b) 3D dynamic contrast material-enhanced (DCE) US by using nontargeted microbubbles for assessment of antiangiogenic treatment effects in a murine model of human colon cancer. Materials and Methods Twenty-three mice with human colon cancer xenografts were randomized to receive either single-dose antiangiogenic treatment (bevacizumab, n = 14) or control treatment (saline, n = 9). At baseline and 24 hours after treatment, animals were imaged with a clinical US system equipped with a clinical matrix array transducer by using the following techniques: (a) molecularly targeted US with VEGFR2-targeted microbubbles, (b) bolus DCE US with nontargeted microbubbles, and (c) destruction-replenishment DCE US with nontargeted microbubbles. VEGFR2-targeted US signal, peak enhancement, area under the time-intensity curve, time to peak, relative blood volume (rBV), relative blood flow, and blood flow velocity were quantified. VEGFR2 expression and percentage area of blood vessels were assessed ex vivo with quantitative immunofluorescence and correlated with corresponding in vivo US parameters. Statistical analysis was performed with Wilcoxon signed rank tests and rank sum tests, as well as Pearson correlation analysis. Results Molecularly targeted US signal with VEGFR2-targeted microbubbles, peak enhancement, and rBV significantly decreased (P ≤ .03) after a single antiangiogenic treatment compared with those in the control group; similarly, ex vivo VEGFR2 expression (P = .03) and percentage area of blood vessels (P = .03) significantly decreased after antiangiogenic treatment. Three-dimensional molecularly targeted US signal correlated well with VEGFR2 expression (r = 0.86, P = .001), and rBV (r = 0.71, P = .01) and relative blood flow (r = 0.78, P = .005) correlated well with percentage area of blood vessels, while other US perfusion parameters did not. Conclusion Three-dimensional molecularly targeted US and destruction-replenishment 3D DCE US provide complementary molecular and functional in vivo imaging information on antiangiogenic treatment effects in human colon cancer xenografts compared with ex vivo reference standards. ^© RSNA, 2016 Online supplemental material is available for this article.

RGD-Targeted Ultrasound Contrast Agent for Longitudinal Assessment of Hep-2 Tumor Angiogenesis In Vivo

OBJECTIVE

To prepare arginine-glycine-aspartate (RGD)-targeted ultrasound contrast microbubbles (MBs) and explore the feasibility of their use in assessing dynamic changes in αvβ3 integrin expression in a murine model of tumor angiogenesis.

METHODS

RGD peptides were conjugated to the surfaces of microbubbles via biotin-avidin linkage. Microbubbles bearing RADfK peptides were prepared as controls. The RGD-MBs were characterized using an Accusizer 780 and optical microscopy. The binding specificity of the RGD-MBs for ανβ3-expressing endothelial cells (bEnd.3) was demonstrated in vitro by a competitive inhibition experiment. In an in vivo study, mice bearing tumors of three different stages were intravenously injected with RGD-MBs and subjected to targeted, contrast-enhanced, high-frequency ultrasound. Subsequently, tumors were harvested and sectioned for immunofluorescence analysis of ανβ3 expression.

RESULTS

The mean size of the RGD-MBs was 2.36 ± 1.7 μm. The RGD-MBs showed significantly higher adhesion levels to bEnd.3 cells compared to control MBs (P < 0.01). There was rarely binding of RGD-MBs to αvβ3-negative MCF-7 cells. Adhesion of the RGD-MBs to the bEnd.3 cells was significantly inhibited following treatment with anti-alpha(v) antibodies. The quantitative acoustic video intensity for high-frequency, contrast-enhanced ultrasound imaging of subcutaneous human laryngeal carcinoma (Hep-2) tumor xenografts was significantly higher in small tumors (19.89 ± 2.49) than in medium tumors (11.25 ± 2.23) and large tumors (3.38 ± 0.67) (P < 0.01).

CONCLUSIONS

RGD-MBs enable noninvasive in vivo visualization of changes in tumor angiogenesis during tumor growth in subcutaneous cancer xenografts.

Three-dimensional ultrasound molecular imaging of angiogenesis in colon cancer using a clinical matrix array ultrasound transducer

OBJECTIVES

We sought to assess the feasibility and reproducibility of 3-dimensional ultrasound molecular imaging (USMI) of vascular endothelial growth factor receptor 2 (VEGFR2) expression in tumor angiogenesis using a clinical matrix array transducer and a clinical grade VEGFR2-targeted contrast agent in a murine model of human colon cancer.

MATERIALS AND METHODS

Animal studies were approved by the Institutional Administrative Panel on Laboratory Animal Care. Mice with human colon cancer xenografts (n = 33) were imaged with a clinical ultrasound system and transducer (Philips iU22; X6-1) after intravenous injection of either clinical grade VEGFR2-targeted microbubbles or nontargeted control microbubbles. Nineteen mice were scanned twice to assess imaging reproducibility. Fourteen mice were scanned both before and 24 hours after treatment with either bevacizumab (n = 7) or saline only (n = 7). Three-dimensional USMI data sets were retrospectively reconstructed into multiple consecutive 1-mm-thick USMI data sets to simulate 2-dimensional imaging. Vascular VEGFR2 expression was assessed ex vivo using immunofluorescence.

RESULTS

Three-dimensional USMI was highly reproducible using both VEGFR2-targeted microbubbles and nontargeted control microbubbles (intraclass correlation coefficient, 0.83). The VEGFR2-targeted USMI signal significantly (P = 0.02) decreased by 57% after antiangiogenic treatment compared with the control group, which correlated well with ex vivo VEGFR2 expression on immunofluorescence (ρ = 0.93, P = 0.003). If only central 1-mm tumor planes were analyzed to assess antiangiogenic treatment response, the USMI signal change was significantly (P = 0.006) overestimated by an average of 27% (range, 2%-73%) compared with 3-dimensional USMI.

CONCLUSIONS

Three-dimensional USMI is feasible and highly reproducible and allows accurate assessment and monitoring of VEGFR2 expression in tumor angiogenesis in a murine model of human colon cancer.

Quantitative ultrasound molecular imaging

Ultrasound molecular imaging using targeting microbubbles is predominantly a semi-quantitative tool, thus limiting its potential diagnostic power and clinical applications. In the work described here, we developed a novel method for acoustic quantification of molecular expression. E-Selectin expression in the mouse heart was induced by lipopolysaccharide. Real-time ultrasound imaging of E-selectin expression in the heart was performed using E-selectin-targeting microbubbles and a clinical ultrasound scanner in contrast pulse sequencing mode at 14 MHz, with a mechanical index of 0.22-0.26. The level of E-selectin expression was quantified using a novel time-signal intensity curve analytical method based on bubble elimination, which consisted of curve-fitting the bi-exponential equation [Formula: see text] to the elimination phase of the myocardial time-signal intensity curve. Ar and Af represent the maximum signal intensities of the retained and freely circulating bubbles in the myocardium, respectively; λr and λf represent the elimination rate constants of the retained and freely circulating bubbles in the myocardium, respectively. Ar correlated strongly with the level of E-selectin expression (|r|>0.8), determined using reverse transcriptase real-time quantitative polymerase chain reaction, and the duration of post-lipopolysaccharide treatment-both linearly related to cell surface E-selectin protein (actual bubble target) concentration in the expression range imaged. Compared with a conventional acoustic quantification method (which used retained bubble signal intensity at 20 min post-bubble injection), this new approach exhibited greater dynamic range and sensitivity and was able to simultaneously quantify other useful characteristics (e.g., the microbubble half-life). In conclusion, quantitative determination of the level of molecular expression is feasible acoustically using a time-signal intensity curve analytical method based on bubble elimination.

Development of fluorous lipid-based nanobubbles for efficiently containing perfluoropropane

Nano-/microbubbles are expected not only to function as ultrasound contrast agents but also as ultrasound-triggered enhancers in gene and drug delivery. Notably, nanobubbles have the ability to pass through tumor vasculature and achieve passive tumor targeting. Thus, nanobubbles would be an attractive tool for use as ultrasound-mediated cancer theranostics. However, the amounts of gas carried by nanobubbles are generally lower than those carried by microbubbles because nanobubbles have inherently smaller volumes. In order to reduce the injection volume and to increase echogenicity, it is important to develop nanobubbles with higher gas content. In this study, we prepared 5 kinds of fluoro-lipids and used these reagents as surfactants to generate "Bubble liposomes", that is, liposomes that encapsulate nanobubbles such that the lipids serve as stabilizers between the fluorous gas and water phases. Bubble liposome containing 1-stearoyl-2-(18,18-difluoro)stearoyl-sn-glycero-3-phosphocholine carried 2-fold higher amounts of C3F8 compared to unmodified Bubble liposome. The modified Bubble liposome also exhibited increased echogenicity by ultrasonography. These results demonstrated that the inclusion of fluoro-lipid is a promising tool for generating nanobubbles with increased efficiency of fluorous gas carrier.

Ultrasound molecular imaging: Moving toward clinical translation

Ultrasound is a widely available, cost-effective, real-time, non-invasive and safe imaging modality widely used in the clinic for anatomical and functional imaging. With the introduction of novel molecularly-targeted ultrasound contrast agents, another dimension of ultrasound has become a reality: diagnosing and monitoring pathological processes at the molecular level. Most commonly used ultrasound molecular imaging contrast agents are micron sized, gas-containing microbubbles functionalized to recognize and attach to molecules expressed on inflamed or angiogenic vascular endothelial cells. There are several potential clinical applications currently being explored including earlier detection, molecular profiling, and monitoring of cancer, as well as visualization of ischemic memory in transient myocardial ischemia, monitoring of disease activity in inflammatory bowel disease, and assessment of arteriosclerosis. Recently, a first clinical grade ultrasound contrast agent (BR55), targeted at a molecule expressed in neoangiogenesis (vascular endothelial growth factor receptor type 2; VEGFR2) has been introduced and safety and feasibility of VEGFR2-targeted ultrasound imaging is being explored in first inhuman clinical trials in various cancer types. This review describes the design of ultrasound molecular imaging contrast agents, imaging techniques, and potential future clinical applications of ultrasound molecular imaging.

Emerging Imaging Modalities in Regenerative Medicine

The field of regenerative medicine has experienced considerable growth in recent years as the translation of pre-clinical biomaterials and cell- and gene-based therapies begin to reach clinical application. Until recently, the ability to monitor the serial responses to therapeutic treatments has been limited to post-mortem tissue analyses. With improvements in existing imaging modalities and the emergence of hybrid imaging systems, it is now possible to combine information related to structural remodeling with associated molecular events using non-invasive imaging. This review summarizes the established and emerging imaging modalities that are available for in vivo monitoring of clinical regenerative medicine therapies and discusses the strengths and limitations of each imaging modality.

Targeted ultrasound microbubble contrast agents for enhanced tumor imaging

In the field of medical ultrasound, ultrasound microbubbles are a new class of ultrasound contrast agents. Ultrasound microbubbles can be divided into two types: ordinary and targeted microbubbles. Ordinary microbubbles have been widely used in clinical practice. Targeted microbubbles are a special class of contrast agents and can be divided into micron- and nano-scale targeted microbubbles according to particle size. The former cannot pass through the endothelial gap due to the larger particle size, while the latter can pass through the vascular endothelium and allows for imaging of the extravascular tissues. Ultrasound combined with targeted microbubbles in enhancing tumor imaging shows greater advantages and has become an important topic of research; however, its unknown toxicity limits its wider application. In addition, ultrasound parameters still need to be optimized.