RNA biomarker release with ultrasound and phase-change nanodroplets

Amplification of Plasma MicroRNAs for Non-invasive Early Detection of Acute Rejection after Heart Transplantation With Ultrasound-Targeted Microbubble Destruction

OBJECTIVE

Acute rejection (AR) screening has always been the focus of patient management in the first several years after heart transplantation (HT). As potential biomarkers for the non-invasive diagnosis of AR, microRNAs (miRNAs) are limited by their low abundance and complex origin. Ultrasound-targeted microbubble destruction (UTMD) technique could temporarily alter vascular permeability through cavitation. We hypothesized that increasing the permeability of myocardial vessels might enhance the abundance of circulating AR-related miRNAs, thus enabling the non-invasive monitoring of AR.

METHODS

The Evans blue assay was applied to determine efficient UTMD parameters. Blood biochemistry and echocardiographic indicators were used to ensure the safety of the UTMD. AR of the HT model was constructed using Brown-Norway and Lewis rats. Grafted hearts were sonicated with UTMD on postoperative day (POD) 3. The polymerase chain reaction was used to identify upregulated miRNA biomarkers in graft tissues and their relative amounts in the blood.

RESULTS

Amounts of six kinds of plasma miRNA, including miR-142-3p, miR-181a-5p, miR-326-3p, miR-182, miR-155-5p and miR-223-3p, were 10.89 ± 1.36, 13.54 ± 2.15, 9.84 ± 0.70, 8.55 ± 2.00, 12.50 ± 3.96 and 11.02 ± 3.47 times higher in the UTMD group than those in the control group on POD 3. Plasma miRNA abundance in the allograft group without UTMD did not differ from that in the isograft group on POD 3. After FK506 treatment, no miRNAs increased in the plasma after UTMD.

CONCLUSION

UTMD can promote the transfer of AR-related miRNAs from grafted heart tissue to the blood, allowing non-invasive early detection of AR.

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

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

Sonoporation of Human Renal Proximal Tubular Epithelial Cells In Vitro to Enhance the Liberation of Intracellular miRNA Biomarkers

Ultrasound has previously been demonstrated to non-invasively cause tissue disruption. Small animal studies have demonstrated that this effect can be enhanced by contrast microbubbles and has the potential to be clinically beneficial in techniques such as targeted drug delivery or enhancing liquid biopsies when a physical biopsy may be inappropriate. Cavitating microbubbles in close proximity to cells increases membrane permeability, allowing small intracellular molecules to leak into the extracellular space. This study sought to establish whether cavitating microbubbles could liberate cell-specific miRNAs, augmenting biomarker detection for non-invasive liquid biopsies. Insonating human polarized renal proximal tubular epithelial cells (RPTECs), in the presence of SonoVue microbubbles, revealed that cellular health could be maintained while achieving the release of miRNAs, miR-21, miR-30e, miR-192 and miR-194 (respectively, 10.9-fold, 7.17-fold, 5.95-fold and 5.36-fold). To examine the mechanism of release, RPTECs expressing enhanced green fluorescent protein were generated and the protein successfully liberated. Cell polarization, cellular phenotype and cell viability after sonoporation were measured by a number of techniques. Ultrastructural studies using electron microscopy showed gap-junction disruption and pore formation on cellular surfaces. These studies revealed that cell-specific miRNAs can be non-specifically liberated from RPTECs by sonoporation without a significant decrease in cell viability.

Functional ultrasound-triggered phase-shift perfluorocarbon nanodroplets for cancer therapy

In recent years, because of their unique properties, the use of perfluorocarbon nanodroplets (PFC NDs) in ultrasound-mediated tumor theranostics has attracted increasing interest. PFC is one of the most stable organic compounds with high hydrophobicity. Phase-shift PFC NDs can be transformed into highly echogenic microbubbles for ultrasound and photoacoustic imaging by ultrasound and laser light. In addition, in the process of acoustic droplet vaporization, PFC NDs with cavitation nuclei can be combined with a variety of ultrasound technologies to produce cavitation effects for tumor ablation, antivascular therapy and release of therapeutic agents loaded in nanodroplets. Moreover, they can also be used to overcome tumor hypoxia by virtue of high oxygen solubility. In this review, first the preparation and stabilization of PFC NDs are summarized and then the issues and outlook are discussed. More importantly, multifunctional platforms based on PFC NDs for cancer diagnostics, therapy and theranostics are reviewed in detail.

Folic acid-functionalized gadolinium-loaded phase transition nanodroplets for dual-modal ultrasound/magnetic resonance imaging of hepatocellular carcinoma

Dual-modal molecular imaging by combining two imaging techniques can provide complementary information for early cancer diagnosis and therapeutic monitoring. In the present manuscript, folic acid (FA)-functionalized gadolinium-loaded nanodroplets (NDs) are introduced as dual-modal ultrasound (US)/magnetic resonance (MR) imaging contrast agents. These phase-change contrast agents (PCCAs) with alginate (Alg) stabilizing shell and a liquid perfluorohexane (PFH) core were successfully synthesized via the nano-emulsion method and characterized. In this regard, mouse hepatocellular carcinoma (Hepa1-6) as target cancer cells and mouse fibroblast (L929) as control cells were used. The in vitro and in vivo cytotoxicity assessments indicated that Gd/PFH@Alg and Gd/PFH@Alg-FA nanodroplets are highly biocompatible. Gd-loaded NDs do not induce organ toxicity, and no significant hemolytic activity in human red blood cells is observed. Additionally, nanodroplets exhibited strong ultrasound signal intensities as well as T₁-weighted MRI signal enhancement with a high relaxivity value of 6.40 mM^-1 s^-1, which is significantly higher than that of the clinical Gadovist contrast agent (r₁ = 4.01 mM^-1 s^-1). Cellular uptake of Gd-NDs-FA by Hepa1-6 cancer cells was approximately 2.5-fold higher than that of Gd-NDs after 12 h incubation. Furthermore, in vivo results confirmed that the Gd-NDs-FA bound selectively to cancer cells and were accumulated in the tumor region. In conclusion, Gd/PFH@Alg-FA nanodroplets have great potential as US/MR dual-modal imaging nanoprobes for the early diagnosis of cancer.

Acoustically responsive polydopamine nanodroplets: A novel theranostic agent

Ultrasound-induced cavitation has been used as a tool of enhancing extravasation and tissue penetration of anticancer agents in tumours. Initiating cavitation in tissue however, requires high acoustic intensities that are neither safe nor easy to achieve with current clinical systems. The use of cavitation nuclei can however lower the acoustic intensities required to initiate cavitation and the resulting bio-effects in situ. Microbubbles, solid gas-trapping nanoparticles, and phase shift nanodroplets are some examples in a growing list of proposed cavitation nuclei. Besides the ability to lower the cavitation threshold, stability, long circulation times, biocompatibility and biodegradability, are some of the desirable characteristics that a clinically applicable cavitation agent should possess. In this study, we present a novel formulation of ultrasound-triggered phase transition sub-micrometer sized nanodroplets (~400 nm) stabilised with a biocompatible polymer, polydopamine (PDA). PDA offers some important benefits: (1) facile fabrication, as dopamine monomers are directly polymerised on the nanodroplets, (2) high polymer biocompatibility, and (3) ease of functionalisation with other molecules such as drugs or targeting species. We demonstrate that the acoustic intensities required to initiate inertial cavitation can all be achieved with existing clinical ultrasound systems. Cell viability and haemolysis studies show that nanodroplets are biocompatible. Our results demonstrate the great potential of PDA nanodroplets as an acoustically active nanodevice, which is highly valuable for biomedical applications including drug delivery and treatment monitoring.

Methods of Generating Submicrometer Phase-Shift Perfluorocarbon Droplets for Applications in Medical Ultrasonography

Continued advances in the field of ultrasound and ultrasound contrast agents have created new approaches to imaging and medical intervention. Phase-shift perfluorocarbon droplets, which can be vaporized by ultrasound energy to transition from the liquid to the vapor state, are one of the most highly researched alternatives to clinical ultrasound contrast agents (i.e., microbubbles). In this paper, part of a special issue on methods in biomedical ultrasonics, we survey current techniques to prepare ultrasound-activated nanoscale phase-shift perfluorocarbon droplets, including sonication, extrusion, homogenization, microfluidics, and microbubble condensation. We provide example protocols and discuss advantages and limitations of each approach. Finally, we discuss best practice in characterization of this class of contrast agents with respect to size distribution and ultrasound activation.

Enhanced Detection of Cancer Biomarkers in Blood-Borne Extracellular Vesicles Using Nanodroplets and Focused Ultrasound

The feasibility of personalized medicine approaches will be greatly improved by the development of noninvasive methods to interrogate tumor biology. Extracellular vesicles shed by solid tumors into the bloodstream have been under recent investigation as a source of tumor-derived biomarkers such as proteins and nucleic acids. We report here an approach using submicrometer perfluorobutane nanodroplets and focused ultrasound to enhance the release of extracellular vesicles from specific locations in tumors into the blood. The released extracellular vesicles were enumerated and characterized using micro flow cytometry. Only in the presence of nanodroplets could ultrasound release appreciable levels of tumor-derived vesicles into the blood. Sonication of HT1080-GFP tumors did not increase the number of circulating tumor cells or the metastatic burden in the tumor-bearing embryos. A variety of biological molecules were successfully detected in tumor-derived extracellular vesicles, including cancer-associated proteins, mRNAs, and miRNAs. Sonication of xenograft HT1080 fibrosarcoma tumors released extracellular vesicles that contained detectable RAC1 mRNA with the highly tumorigenic N92I mutation known to exist in HT1080 cells. Deep sequencing serum samples of embryos with sonicated tumors allowed the identification of an additional 13 known heterozygous mutations in HT1080 cells. Applying ultrasound to HT1080 tumors increased tumor-derived DNA in the serum by two orders of magnitude. This work is the first demonstration of enhanced extracellular vesicle release by ultrasound stimulation and suggests that nanodroplets/ultrasound offers promise for genetic profiling of tumor phenotype and aggressiveness by stimulating the release of extracellular vesicles. Cancer Res; 77(1); 3-13. ©2016 AACR.

Nanodroplet-Vaporization-Assisted Sonoporation for Highly Effective Delivery of Photothermal Treatment

Sonoporation refers to the use of ultrasound and acoustic cavitation to temporarily enhance the permeability of cellular membranes so as to enhance the delivery efficiency of therapeutic agents into cells. Microbubble-based ultrasound contrast agents are often used to facilitate these cavitation effects. This study used nanodroplets to significantly enhance the effectiveness of sonoporation relative to using conventional microbubbles. Significant enhancements were demonstrated both in vitro and in vivo by using gold nanorods encapsulated in nanodroplets for implementing plasmonic photothermal therapy. Combined excitation by ultrasound and laser radiation is used to trigger the gold nanodroplets to induce a liquid-to-gas phase change, which induces cavitation effects that are three-to-fivefold stronger than when using conventional microbubbles. Enhanced cavitation also leads to significant enhancement of the sonoporation effects. Our in vivo results show that nanodroplet-vaporization-assisted sonoporation can increase the treatment temperature by more than 10 °C above that achieved by microbubble-based sonoporation.