Cyanine 5.5 conjugated nanobubbles as a tumor selective contrast agent for dual ultrasound-fluorescence imaging in a mouse model

Targeted chitosan nanobubbles as a strategy to down-regulate microRNA-17 into B-cell lymphoma models

Introduction

MicroRNAs represent interesting targets for new therapies because their altered expression influences tumor development and progression. miR-17 is a prototype of onco-miRNA, known to be overexpressed in B-cell non-Hodgkin lymphoma (B-NHL) with peculiar clinic-biological features. AntagomiR molecules have been largely studied to repress the regulatory functions of up-regulated onco-miRNAs, but their clinical use is mainly limited by their rapid degradation, kidney elimination and poor cellular uptake when injected as naked oligonucleotides.

Methods

To overcome these problems, we exploited CD20 targeted chitosan nanobubbles (NBs) for a preferential and safe delivery of antagomiR17 to B-NHL cells.

Results

Positively charged 400 nm-sized nanobubbles (NBs) represent a stable and effective nanoplatform for antagomiR encapsulation and specific release into B-NHL cells. NBs rapidly accumulated in tumor microenvironment, but only those conjugated with a targeting system (antiCD20 antibodies) were internalized into B-NHL cells, releasing antagomiR17 in the cytoplasm, both in vitro and in vivo. The result is the down-regulation of miR-17 level and the reduction in tumor burden in a human-mouse B-NHL model, without any documented side effects.

Discussion

Anti-CD20 targeted NBs investigated in this study showed physico-chemical and stability properties suitable for antagomiR17 delivery in vivo and represent a useful nanoplatform to address B-cell malignancies or other cancers through the modification of their surface with specific targeting antibodies.

Targeting Diagnosis of High-Risk Papillary Thyroid Carcinoma Using Ultrasound Contrast Agent With the BRAFV600E Mutation: An Experimental Study

OBJECTIVE

High-risk papillary thyroid carcinoma (PTC) patients with BRAF mutation have lymph node and distant metastases and poor prognosis. Therefore, this study aims to develop a targeted ultrasound contrast agent for the BRAF^V600E mutation to screen high-risk PTC at early stage.

METHODS

The targeted lipid nanobubbles carrying BRAF^V600E antibody were prepared using thin film hydration-sonication and avidin-biotin binding methods. The physicochemical properties and stability of the targeted nanobubbles were detected by transmission electron microscopy, atomic force microscopy, and confocal laser scanning microscopy. The target binding abilities of the targeted nanobubbles in the PTC cells (B-CPAP) overexpressed mutant BRAF^V600E were evaluated by immunofluorescence staining, quantitative real-time polymerase chain reaction, western blot, and fluorescence microscopy. After PTC tumor models overexpressed mutant BRAF^V600E were established, the enhanced images of targeted lipid nanobubbles and untargeted lipid nanobubbles on PTC tumors in nude mice were observed using contrast-enhanced ultrasound imaging.

RESULTS

The targeted lipid nanobubbles revealed uniform, round morphology, and good stability with a nanoscale size. Besides, BRAF^V600E monoclonal antibody was observed to be combined on the surface of lipid nanobubbles. Furthermore, the targeted nanobubbles had a good targeting diagnosis ability in PTC cells with BRAF^V600E overexpression. Moreover, the targeted nanobubbles had better ultrasound enhancement and peak intensity of the time-intensity curve (P < .001) in PTC tumors with BRAF^V600E overexpression as compared to the untargeted lipid nanobubbles.

CONCLUSION

The targeted lipid nanobubbles carrying BRAF^V600E antibody could be regarded as a potential targeted ultrasound contrast agent for the diagnosis of high-risk PTC.

The Influence of Air Nanobubbles on Controlling the Synthesis of Calcium Carbonate Crystals

Numerous approaches have been developed to control the crystalline and morphology of calcium carbonate. In this paper, nanobubbles were studied as a novel aid for the structure transition from vaterite to calcite. The vaterite particles turned into calcite (100%) in deionized water containing nanobubbles generated by high-speed shearing after 4 h, in comparison to a mixture of vaterite (33.6%) and calcite (66.3%) by the reaction in the deionized water in the absence of nanobubbles. The nanobubbles can coagulate with calcite based on the potential energy calculated and confirmed by the extended DLVO (Derjaguin-Landau-Verwey-Overbeek) theory. According to the nanobubble bridging capillary force, nanobubbles were identified as the binder in strengthening the coagulation between calcite and vaterite and accelerated the transformation from vaterite to calcite.

Update of ultrasound-assembling fabrication and biomedical applications for heterogeneous polymer composites

As a power-driving approach, ultrasound irradiation is very appealing to the preparation or modification of new materials. In the review, we overviewed the latest development of ultrasound-mediated effects or reactions in polymer composites, and demonstrated its unique and powerful aspects on the polymerization or aggregation. The review generalized the different categories of heterogeneous polymer composites by defining the constituents, and described the shapes, sizes and basic properties of various purpose-specific or site-specific products. Importantly, the review paid more attention to the main biomedicine applications of heterogeneous polymer composites, such as drug or bioactive substance entrapment, delivery, release, imaging, and therapy, and emphasized many advantages of ultrasound-assembling approaches and heterogeneous polymer composites in biology and medicine fields. In addition, the review also indicated the prospective challenges of heterogeneous polymer composites both in ultrasound-assembling designs and in biomedical applications.

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.

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.

Trials in developing a nanoscale material for extravascular contrast-enhanced ultrasound targeting hepatocellular carcinoma

Background

Medical imaging is an important approach for the diagnosis of hepatocellular carcinoma (HCC), a common life threaten disease, however, the diagnostic efficiency is still not optimal. Developing a novel method to improve diagnosis is necessary. The aim of this project was to formulate a material that can combine with GPC3 of HCC for targeted enhanced ultrasound.

Methods

A material of sulfur hexafluoride (SF₆) filled liposome microbubbles and conjugated with synthesized peptide (LSPMbs) was prepared and assessed in vitro and vivo. Liposome microbubbles were made of DPPC, DPPG, DSPE-PEG2000,and SF₆, using thin film method to form shell, followed filling SF₆, and conjugating peptide. A carbodiimide method was used for covalent conjugation of peptide to LSMbs.

Results

The prepared LSPMbs appeared round shaped, with size of 380.9 ±  176.5 nm, and Zeta potential of −51.4 ±  10.4mV. LSPMbs showed high affinity to Huh-7 cells in vitro, presented good enhanced ultrasound effects, did not show cytotoxicity, and did not exhibit targeted fluorescence and enhanced ultrasound in animal xenograft tumors.

Conclusion

Extravascular contrast-enhanced ultrasound targeted GPC3 on HCC may not be realized, and the reason may be that targeted contrast agents of microbubbles are hard to access and accumulate in the tumor stroma and matrix.

Bulk nanobubbles in the mineral and environmental areas: Updating research and applications

In the last decade, the research with bulk nanobubbles (ultrafine bubbles with a diameter <1 μm, according to ISO 20480-1:2017) has been rapidly increasing in the academic and industrial environments. Nowadays, there are many applications reported in the literature, with several patents, procedures, and techniques on nanobubbles generation and an evergrowing research and many applications. Yet, most of those publications reporting bulk nanobubbles generation devices, do not bring information on measurements of size distribution or bubbles concentration (if nanobubbles). Further, there is a problem of scale and many of these products are small bench discontinuous rigs difficult to scale up, which might serve small scale purposes, but are not able for treating high flow-rate wastewaters or minerals pulps at industrial scale. These nanometric bubbles present interesting and peculiar properties such as high surface area per volume unit, high stability and longevity, surface charge in water and the ability to aggregate hydrophobic particles. These findings demonstrate their high potential for applications in many technological areas, which occur not only as isolated bubbles but also jointly with micro (~ 1-100 μm diameter) and/or macrobubbles (~100 μm - 2 mm diameter). This paper reviews the evolution of basic research on nanobubbles, the challenges concerning generation and stability and their applications in the mineral (flotation) and environmental areas (treatment of water and wastewaters or remediation of contaminated environments). Herein, because the importance in engineering, as a whole, most of the studies are based on the nanobubbles generated by depressurisation/hydrodynamic cavitation of the air-saturated water in flow constrictors (venturi, needle valves). In the mineral area, they appear to be responsible for increasing the recovery and flotation kinetics of fine (<74 μm) and ultrafine (<13 μm) particles at lower frother and collector dosages. In the environmental area, nanobubbles have been reported to enhance the removal of a variety of pollutants (emulsified oil, colloidal solids, organic/inorganic precipitates, ions) by flotation associated with bigger bubbles. More, the application of isolated nanobubbles on the removal of residual pollutants, such as amine and oil (both as flocs) were reported. Also, the use of ozone and oxygen nanobubbles has been studied for the remediation/decontamination of soil and aquatic ecosystems and for the oxidation of emerging pollutants in water and wastewater treatment. The future of nanobubbles in flotation separation research is highly promising; operating costs of the different forms of nanobubbles generation and bench studies should be validated through pilot and real scale with the continuous injection of these bubbles.

Nano-lipospheres as acoustically active ultrasound contrast agents: evolving tumor imaging and therapy technique

Applying nanobubbles (NBs) for contrast-enhanced ultrasound imaging has received increased attention. NBs are biocompatible, multifunctional, theranostic agents. Their properties of high echogenicity and stability create an agent suitable for ultrasonography diagnosis. Their favorable properties of size, in vivo stability, and ease of modification are being exploited to implement a theranostic platform for cancer treatment. The considerable development offers the potential to overcome drug resistance and adverse side effects that are associated with traditional chemotherapy. This review outlines the principles of ultrasonography and angiogenesis. Microbubbles and micelles are also discussed to underline the superior capabilities of NBs for the application. NBs could passively accumulate to tumor tissue by enhanced permeability and retention effect. In addition, it can also achieve the active transportation by surface modification. Active targeting modalities and stimuli-responsive drug delivery modifications generate a therapeutic vehicle. The cytotoxicity of NBs formulations, multimodal imaging capability, active targeting mechanisms, and drug delivery methods are highlighted to confirm the NB as a vehicle for targeted treatment and enhanced ultrasound imaging.

Lipid nanobubbles as an ultrasound-triggered artesunate delivery system for imaging-guided, tumor-targeted chemotherapy

PURPOSE

Herein, this study is to prepare folic acid (FA)-conjugated lipid nanobubbles (NBs) that highly load artesunate (Arte; FA-ALNBs), as an ultrasound (US)-triggered Arte delivery system for imaging-guided, tumor-targeted chemotherapy.

MATERIALS AND METHODS

The morphology, size, zeta potential, and stability of the FA-ALNBs were detected by optical microscopy and dynamic light scattering analysis. The cellular uptake of the FA-ALNBs was evaluated by confocal laser scanning microscopy and flow cytometry.

RESULTS

The FA-ALNBs showed uniform spheroidal structure, with 781.2±5.3 nm in average diameter, great physiological stability, and ~91.9%±1.1% encapsulation efficiency of Arte. Using focused US, about 36.1%±2.5% of the entrapped Arte was trigger-released from the FA-ALNBs. Owing to the US contrast property, FA-ALNBs showed an enhanced US signal in vitro when using an ultrasonic diagnostic apparatus with a 1-MHz linear transducer. Due to the FA receptor-mediated endocytosis effect, FA-ALNBs can be efficiently internalized by cells, showing an uptake ratio of about 56.4%±3.1%. FA-ALNBs showed an enhanced, dose-dependent cell-killing ability, while FA-ALNBs plus US irradiation exhibited a stronger anticancer effect in vitro. Post intravenous injection into tumor-bearing mice, FA-ALNBs showed an enhanced US contrast effect with increase in time, indicating the increasing accumulation of FA-ALNBs in tumor tissue, which peaked at 4 hours post injection. Focused US irradiation was conducted on the tumor region at 4 hours post injection of FA-ALNBs, which showed a greater tumor suppression effect after 30 days of treatment compared with all other treatment groups. Moreover, FA-ALNBs showed negligible systemic toxicity in vivo.

CONCLUSION

This versatile US-triggered drug delivery system with great anticancer efficacy was assessed both in vitro and in vivo, revealing great potential as a cancer theranostic agent for future application.

Spatially Uniform Tumor Treatment and Drug Penetration by Regulating Ultrasound with Microbubbles

Tumor microenvironment has different morphologies of vessels in the core and rim regions, which influences the efficacy of tumor therapy. Our study proposed to improve the spatial uniformity of the antivascular effect and drug penetration within the tumor core and rim in combination therapies by regulating ultrasound-stimulated microbubble destruction (USMD). Focused ultrasound at 2 MHz and lipid-shell microbubbles (1.12 ± 0.08 μm, mean ± standard deviation) were used to perform USMD. The efficiency of the antivascular effect was evaluated by intravital imaging to determine the optimal USMD parameters. Tumor perfusion and histological alterations in the tumor core and rim were used to analyze the spatial uniformity of the antivascular effect and liposomal-doxorubicin (5 mg/kg) penetration in the combination therapy. Tumor vessels of specific sizes were disrupted by regulating USMD: vessels with sizes of 11 ± 3, 14 ± 5, 19 ± 7, and 23 ± 10 μm were disrupted by stimulation at acoustic pressures of 3, 5, 7, and 9 MPa, respectively (each p < 0.05). The effective treatment time of USMD (at 2 × 10⁷ microbubbles/mouse, 7 MPa, and three cycles) was 60-120 min, which resulted in the disruption of 21-44% of vessels smaller than 50 μm. The reductions in perfusion and vascular density after combination therapy did not differ significantly between the tumor core and rim. This study found that regulating USMD can result in homogeneous antivascular effects and drug penetration within tumors and thereby improve the efficacy of combination therapies.

Cavitation-threshold Determination and Rheological-parameters Estimation of Albumin-stabilized Nanobubbles

Nanobubbles (NBs) are of high interest for ultrasound (US) imaging as contrast agents and therapy as cavitation nuclei. Because of their instability (Laplace pressure bubble catastrophe) and low sensitivity to US, reducing the size of commonly used microbubbles to submicron-size is not trivial. We introduce stabilized NBs in the 100-250-nm size range, manufactured by agitating human serum albumin and perfluoro-propane. These NBs were exposed to 3.34- and 5.39-MHz US, and their sensitivity to US was proven by detecting inertial cavitation. The cavitation-threshold information was used to run a numerical parametric study based on a modified Rayleigh-Plesset equation (with a Newtonian rheology model). The determined values of surface tension ranged from 0 N/m to 0.06 N/m. The corresponding values of dilatational viscosity ranged from 5.10-10 Ns/m to 1.10-9 Ns/m. These parameters were reported to be 0.6 N/m and 1.10-8 Ns/m for the reference microbubble contrast agent. This result suggests the possibility of using albumin as a stabilizer for the nanobubbles that could be maintained in circulation and presenting satisfying US sensitivity, even in the 3-5-MHz range.

Indocyanine green conjugated lipid microbubbles as an ultrasound-responsive drug delivery system for dual-imaging guided tumor-targeted therapy

Herein, a multifunctional traceable and ultrasound-responsive drug targeted delivery system based on indocyanine green (ICG) and folic acid (FA) covalently conjugated lipid microbubbles (ILMBs–FA) is proposed. After encapsulation of the anticancer drug resveratrol (RV), the composite (RILMBs–FA) with fluorescence and ultrasound imaging capacity was studied for highly sensitive dual-imaging guided tumor targeted therapy. The resulting RILMBs–FA with an average particle size of 1.32 ± 0.14 μm exhibited good stability and biocompatibility characteristics. The RILMBs–FA featured a high RV loading ratio and the encapsulated RV has been demonstrated to be released from the microbubbles triggered by ultrasound (US) waves. In addition, it was found that the linked FA could facilitate a high cellular uptake of RILMBs–FA via the FA receptor-mediated endocytosis pathway. Compared to free RV and RILMBs, RILMBs–FA with US irradiation demonstrated a more significant tumor cell-killing efficacy mediated by apoptosis in vitro. Eight hours post intravenous injection of RILMBs–FA, the composites showed maximum accumulation in tumorous tissues according to in vivo fluorescence and US images. This ultimately led to the best tumor inhibition effect among all tested drugs under US irradiation. In vivo biosafety evaluations showed that RILMBs–FA featured high biocompatibility characteristics and no significant systemic toxicity over the course of one month. Taken in concert, these results demonstrate the versatility of this drug delivery system with dual-imaging and ultrasound-triggered drug release characteristics for potential future applications in cancer theranostics.

Schematic representation of the synthesis of RILMBs–FA and application in tumor therapy.

pH-responsive pHLIP (pH low insertion peptide) nanoclusters of superparamagnetic iron oxide nanoparticles as a tumor-selective MRI contrast agent

Superparamagnetic iron oxide nanoparticles (SPION) are contrast agents used for noninvasive tumor magnetic resonance imaging (MRI). SPION with active targeting by tumor-specific ligands can effectively enhance the MRI sensitivity and specificity of tumors. However, the challenge remains when the tumor specific markers are yet to be determined, especially in the case of early tumor detection. In this study, the effectiveness of pH-responsive SPION via a pH low insertion peptide (pHLIP) to target tumor acidic microenvironments was investigated. Polylysine polymers were first successfully modified with pHLIP to have the pH-responsive capability. SPION pHLIP nanoclusters of 64, 82, 103, and 121nm size were then assembled by the pH-responsive polymers in a size-controlled manner. The pH-responsive SPION nanoclusters of the 64nm size exhibited the most effective pH-responsive retention in cells and tumor selective imaging in MRI. More importantly, the unique contrast enhancement of tumor inner core by the pH-responsive SPION in three different tumor models demonstrated the clinical potential to target tumor acidic microenvironment through pHLIP for tumor early detection and diagnosis by MRI.

STATEMENT OF SIGNIFICANCE

Detection and diagnosis of tumors at early stage are critical for the improvement of the survival rate of cancer patients. However, the challenge remains when the tumor specific markers are yet to be determined, especially in early tumor detection. pH low insertion peptide (pHLIP) has been used as a specific ligand to target the tumor acidic microenvironment for tumors at early and metastatic stages. Superparamagnetic iron nanoparticles (SPION) are contrast enhancing agents used in the noninvasive magnetic resonance imaging for tumors. This research has demonstrated that pH-responsive pHLIP nanoclusters of SPION were able to target different tumors and facilitate the noninvasive diagnosis of tumors by MRI.

Optically and acoustically triggerable sub-micron phase-change contrast agents for enhanced photoacoustic and ultrasound imaging

We demonstrate a versatile phase-change sub-micron contrast agent providing three modes of contrast enhancement: 1) photoacoustic imaging contrast, 2) ultrasound contrast with optical activation, and 3) ultrasound contrast with acoustic activation. This agent, which we name 'Cy-droplet', has the following novel features. It comprises a highly volatile perfluorocarbon for easy versatile activation, and a near-infrared optically absorbing dye chosen to absorb light at a wavelength with good tissue penetration. It is manufactured via a 'microbubble condensation' method. The phase-transition of Cy-droplets can be optically triggered by pulsed-laser illumination, inducing photoacoustic signal and forming stable gas bubbles that are visible with echo-ultrasound in situ. Alternatively, Cy-droplets can be converted to microbubble contrast agents upon acoustic activation with clinical ultrasound. Potentially all modes offer extravascular contrast enhancement because of the sub-micron initial size. Such versatility of acoustic and optical 'triggerability' can potentially improve multi-modality imaging, molecularly targeted imaging and controlled drug release.

Recent advances in ultrasound-based diagnosis and therapy with micro- and nanometer-sized formulations

Ultrasound (US) is one of the most frequently used imaging methods in the clinic. The broad spectrum of its applications can be increased by the use of gas-filled microbubbles (MB) as ultrasound contrast agents (UCA). In recent years, also nanoscale UCA like nanobubbles (NB), echogenic liposomes (ELIP) and nanodroplets have been developed, which in contrast to MB, are able to extravasate from the vessels into the tissue. New disease-specific UCA have been designed for the assessment of tissue biomarkers and advanced US to a molecular imaging modality. For this purpose, specific binding moieties were coupled to the UCA surface. The vascular endothelial growth factor receptor-2 (VEGFR-2) and P-/E-selectin are prominent examples of molecular US targets to visualize tumor blood vessels and inflammatory diseases, respectively. Besides their application in contrast-enhanced imaging, MB can also be employed for drug delivery to tumors and across the blood-brain barrier (BBB). This review summarizes the development of micro- and nanoscaled UCA and highlights recent advances in diagnostic and therapeutic applications, which are ready for translation into the clinic.

Enhancing the anti-multiple myeloma efficiency in a cancer stem cell xenograft model by conjugating the ABCG2 antibody with microbubbles for a targeted delivery of ultrasound mediated epirubicin

BACKGROUND

Although multiple myeloma (MM) treatment has improved in the last decade, it remains largely incurable. One of main reasons is that there are cancer stem cells (CSCs) in MM, which are responsible for MM's drug resistance and relapse. In this study, we used the targeting microbubbles (MBs) conjugated with anti-ABCG2 monoclonal antibody (mAb) for ultrasound mediated epirubicin (EPI) delivery to evaluate the therapeutic effectiveness of the novel agent in MM CSC xenograft model.

METHODS

MM CSCs, marked by CD138^-CD34^- cell phenotypes were isolated from human MM RPMI8226 cell line using immune magnetic activated cell sorting system, and inoculated into nonobese diabetic/severe combined immunodeficient mice by subcutaneous or intravenous injection. After the mice developed MM, they were intravenous injection treated with EPI, EPI-MBs+mAb, and EPI-MBs+mAb with ultrasound exposure, respectively.

RESULTS

All treated mice showed inhibited tumor sizes or bone lesions, decreased renal damages and anemia, and increased MM bearing mice' survival. In particular, the EPI-MBs+mAb plus ultrasound exhibited significantly enhanced therapeutic MM effectiveness by inducing apoptosis compared with other biologic agents.

CONCLUSION

The data provide evidence that EPI-MBs+mAb with ultrasound exposure might be available for treatment MM patients in clinic.

Nanomedicine

Nanomedicine, an offshoot of nanotechnology, is considered as one of the most promising technologies of the 21st century. Due to their minute size, nanomedicines can easily target difficult-to-reach sites with improved solubility and bioavailability and reduced adverse effects. They also act as versatile delivery systems, carrying both chemotherapeutics and imaging agents to targeted sites. Hence, nanomedicine can be used to achieve the same therapeutic effect at smaller doses than their conventional counterparts and can offer impressive resolutions for various life-threatening diseases. Although certain issues have been raised about the potential toxicities of nanomaterials, it is anticipated that the advances in nanomedicine will furnish clarifications to many of modern medicine's unsolved problems. This chapter aims to provide a comprehensive and contemporary survey of various nanomedicine products along with the major risks and side effects associated with the nanoparticles.

Improving performance of nanoscale ultrasound contrast agents using N,N-diethylacrylamide stabilization

The design of nanoscale yet highly echogenic agents for imaging outside of the vasculature and for ultrasound-mediated drug delivery remains a formidable challenge. We have previously reported on formulation of echogenic perfluoropropane gas nanobubbles stabilized by a lipid-pluronic surfactant shell. In the current work we describe the development of a new generation of these nanoparticles which consist of perfluoropropane gas stabilized by a surfactant and lipid membrane and a crosslinked network of N,N-diethylacrylamide. The resulting crosslinked nanobubbles (CL-PEG-NB) were 95.2±25.2nm in diameter and showed significant improvement in stability and retention of echogenic signal over 24h. In vivo analysis via ultrasound and fluorescence mediated tomography showed greater tumor extravasation and accumulation with CL-PEG-NB compared to microbubbles. Together these results demonstrate the capabilities and advantages of a new, more stable, nanometer-scale ultrasound contrast agent that can be utilized in future work for diagnostic scans and molecular imaging.

Multimodal micro, nano, and size conversion ultrasound agents for imaging and therapy

Ultrasound (US) is one of the most commonly used clinical imaging techniques. However, the use of US and US-based intravenous agents extends far beyond imaging. In particular, there has been a surge in the fabrication of multimodality US contrast agents and theranostic US agents for cancer imaging and therapy. The unique interaction of US waves with microscale and nanoscale agents has attracted much attention in the development of contrast agents and drug-delivery vehicles. The dimensions of the agent not only dictate how it behaves in vivo, but also how it interacts with US for imaging and drug delivery. Furthermore, these agents are also unique due to their ability to convert from the nanoscale to the microscale and vice versa, having imaging and therapeutic utility in both dimensions. Here, we review multimodality and multifunctional US-based agents, according to their size, and also highlight recent developments in size conversion US agents. WIREs Nanomed Nanobiotechnol 2016, 8:796-813. doi: 10.1002/wnan.1398 For further resources related to this article, please visit the WIREs website.

Anticancer activity of a thymidine quinoxaline conjugate is modulated by cytosolic thymidine pathways

BACKGROUND

High levels of thymidine kinase 1 (TK1) and thymidine phosphorylase (TYMP) are key molecular targets by thymidine therapeutics in cancer treatment. The dual roles of TYMP as a tumor growth factor and a key activation enzyme of anticancer metabolites resulted in a mixed outcome in cancer patients. In this study, we investigated the roles of TK1 and TYMP on a thymidine quinoxaline conjugate to evaluate an alternative to circumvent the contradictive role of TYMP.

METHODS

TK1 and TYMP levels in multiple liver cell lines were assessed along with the cytotoxicity of the thymidine conjugate. Cellular accumulation of the thymidine conjugate was determined with organelle-specific dyes. The impacts of TK1 and TYMP were evaluated with siRNA/shRNA suppression and pseudoviral overexpression. Immunohistochemical analysis was performed on both normal and tumor tissues. In vivo study was carried out with a subcutaneous liver tumor model.

RESULTS

We found that the thymidine conjugate had varied activities in liver cancer cells with different levels of TK1 and TYMP. The conjugate mainly accumulated at endothelial reticulum and was consistent with cytosolic pathways. TK1 was responsible for the cytotoxicity yet high levels of TYMP counteracted such activities. Levels of TYMP and TK1 in the liver tumor tissues were significantly higher than those of normal liver tissues. Induced TK1 overexpression decreased the selectivity of dT-QX due to the concurring cytotoxicity in normal cells. In contrast, shRNA suppression of TYMP significantly enhanced the selective of the conjugate in vitro and reduced the tumor growth in vivo.

CONCLUSIONS

TK1 was responsible for anticancer activity of dT-QX while levels of TYMP counteracted such an activity. The counteraction by TYMP could be overcome with RNA silencing to significantly enhance the dT-QX selectivity in cancer cells.

Folate-bovine serum albumin functionalized polymeric micelles loaded with superparamagnetic iron oxide nanoparticles for tumor targeting and magnetic resonance imaging

Polymeric micelles functionalized with folate conjugated bovine serum albumin (FA-BSA) and loaded with superparamagnetic iron oxide nanoparticles (SPIONs) are investigated as a specific contrast agent for tumor targeting and magnetic resonance imaging (MRI) in vitro and in vivo. The SPIONs-loaded polymeric micelles are produced by self-assembly of amphiphilic poly(HFMA-co-MOTAC)-g-PEGMA copolymers and oleic acid modified Fe3O4 nanoparticles and functionalized with FA-BSA by electrostatic interaction. The FA-BSA modified magnetic micelles have a hydrodynamic diameter of 196.1 nm, saturation magnetization of 5.5 emu/g, and transverse relaxivity of 167.0 mM(-1) S(-1). In vitro MR imaging, Prussian blue staining, and intracellular iron determination studies demonstrate that the folate-functionalized magnetic micelles have larger cellular uptake against the folate-receptor positive hepatoma cells Bel-7402 than the unmodified magnetic micelles. In vivo MR imaging conducted on nude mice bearing the Bel-7402 xenografts after bolus intravenous administration reveals excellent tumor targeting and MR imaging capabilities, especially at 24h post-injection. These findings suggest the potential of FA-BSA modified magnetic micelles as targeting MRI probe in tumor detection.

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.

Ultrasound-triggered phase transition sensitive magnetic fluorescent nanodroplets as a multimodal imaging contrast agent in rat and mouse model

Ultrasound-triggered phase transition sensitive nanodroplets with multimodal imaging functionality were prepared via premix Shirasu porous glass (SPG) membrane emulsification method. The nanodroplets with fluorescence dye DiR and SPIO nanoparticles (DiR-SPIO-NDs) had a polymer shell and a liquid perfluoropentane (PFP) core. The as-formed DiR-SPIO-NDs have a uniform size of 385±5.0 nm with PDI of 0.169±0.011. The TEM and microscopy imaging showed that the DiR-SPIO-NDs existed as core-shell spheres, and DiR and SPIO nanoparticles dispersed in the shell or core. The MTT and hemolysis studies demonstrated that the nanodroplets were biocompatible and safe. Moreover, the proposed nanodroplets exhibited significant ultrasound-triggered phase transition property under clinical diagnostic ultrasound irradiation due to the vaporization of PFP inside. Meanwhile, the high stability and R₂ relaxivity of the DiR-SPIO-NDs suggested its applicability in MRI. The in vivo T₂-weighted images of MRI and fluorescence images both showed that the image contrast in liver and spleen of rats and mice model were enhanced after the intravenous injection of DiR-SPIO-NDs. Furthermore, the ultrasound imaging (US) in mice tumor as well as MRI and fluorescence imaging in liver of rats and mice showed that the DiR-SPIO-NDs had long-lasting contrast ability in vivo. These in vitro and in vivo findings suggested that DiR-SPIO-NDs could potentially be a great MRI/US/fluorescence multimodal imaging contrast agent in the diagnosis of liver tissue diseases.