Therapeutic Arteriogenesis by Ultrasound-Mediated VEGF 165 Plasmid Gene Delivery to Chronically Ischemic Skeletal Muscle

Cardiac gene delivery using ultrasound: State of the field

Over the past two decades, there has been tremendous and exciting progress toward extending the use of medical ultrasound beyond a traditional imaging tool. Ultrasound contrast agents, typically used for improved visualization of blood flow, have been explored as novel non-viral gene delivery vectors for cardiovascular therapy. Given this adaptation to ultrasound contrast-enhancing agents, this presents as an image-guided and site-specific gene delivery technique with potential for multi-gene and repeatable delivery protocols-overcoming some of the limitations of alternative gene therapy approaches. In this review, we provide an overview of the studies to date that employ this technique toward cardiac gene therapy using cardiovascular disease animal models and summarize their key findings.

Effect of Intramyocardial Administration of Baculovirus Encoding the Transcription Factor Tbx20 in Sheep With Experimental Acute Myocardial Infarction

BACKGROUND

Gene therapy has been proposed as a strategy to induce cardiac regeneration following acute myocardial infarction (AMI). Given that Tbx20, a transcription factor of the T-box subfamily, stimulates cell proliferation and angiogenesis, we designed a baculovirus overexpressing Tbx20 (Bv-Tbx20) and evaluated its effects in cultured cardiomyocytes and in an ovine model of AMI.

METHODS AND RESULTS

Cell proliferation and angiogenesis were measured in cardiomyocytes transduced with Bv-Tbx20 or Bv-Null (control). Subsequently, in sheep with AMI, Bv-Tbx20 or Bv-Null was injected in the infarct border. Cardiomyocyte cell cycle activity, angioarteriogenesis, left ventricular function, and infarct size were assessed. Cardiomyocytes transduced with BvTbx20 increased cell proliferation, cell cycle regulatory and angiogenic gene expression, and tubulogenesis. At 7 days posttreatment, sheep treated with Bv-Tbx20 showed increased Tbx20, promitotic and angiogenic gene expression, decreased levels of P21, increased Ki67- (17.09±5.73 versus 7.77±7.24 cardiomyocytes/mm2, P<0.05) and PHH3 (phospho-histone H3)-labeled cardiomyocytes (10.10±3.51 versus 5.23±2.87 cardiomyocytes/mm2, P<0.05), and increased capillary (2302.68±353.58 versus 1694.52±211.36 capillaries/mm2, P<0.001) and arteriolar (146.95±53.14 versus 84.06±16.84 arterioles/mm2, P<0.05) densities. At 30 days, Bv-Tbx20 decreased infarct size (9.89±1.92% versus 12.62±1.33%, P<0.05) and slightly improved left ventricular function. Baculoviral gene transfer-mediated Tbx20 overexpression exerted angiogenic and cardiomyogenic effects in vitro.

CONCLUSIONS

In sheep with AMI, Bv-Tbx20 induced angioarteriogenesis, cardiomyocyte cell cycle activity, infarct size limitation, and a slight recovery of left ventricular function, suggesting that Bv-Tbx20 gene therapy may contribute to cardiac regeneration following AMI.

Poly(Lactic-Co-Glycolic Acid) Microparticles for the Delivery of Model Drug Compounds for Applications in Vascular Tissue Engineering

INTRODUCTION

Localized delivery of angiogenesis-promoting factors such as small molecules, nucleic acids, peptides, and proteins to promote the repair and regeneration of damaged tissues remains a challenge in vascular tissue engineering. Current delivery methods such as direct administration of therapeutics can fail to maintain the necessary sustained release profile and often rely on supraphysiologic doses to achieve the desired therapeutic effect. By implementing a microparticle delivery system, localized delivery can be coupled with sustained and controlled release to mitigate the risks involved with the high dosages currently required from direct therapeutic administration.

METHODS

For this purpose, poly(lactic-co-glycolic acid) (PLGA) microparticles were fabricated via anti-solvent microencapsulation and the loading, release, and delivery of model angiogenic molecules, specifically a small molecule, nucleic acid, and protein, were assessed in vitro using microvascular fragments (MVFs).

RESULTS

The microencapsulation approach utilized enabled rapid spherical particle formation and encapsulation of model drugs of different sizes, all in one method. The addition of a fibrin scaffold, required for the culture of the MVFs, reduced the initial burst of model drugs observed in release profiles from PLGA alone. Lastly, in vitro studies using MVFs demonstrated that higher concentrations of microparticles led to greater co-localization of the model therapeutic (miRNA) with MVFs, which is vital for targeted delivery methods. It was also found that the biodistribution of miRNA using the delivered microparticle system was enhanced compared to direct administration.

CONCLUSION

Overall, PLGA microparticles, formulated and loaded with model therapeutic compounds in one step, resulted in improved biodistribution in a model of the vasculature leading to a future in translational revascularization.

Focused ultrasound-assisted delivery of immunomodulating agents in brain cancer

Focused ultrasound (FUS) combined with intravascularly circulating microbubbles can transiently increase the permeability of the blood-brain barrier (BBB) to enable targeted therapeutic delivery to the brain, the clinical testing of which is currently underway in both adult and pediatric patients. Aside from traditional cancer drugs, this technique is being extended to promote the delivery of immunomodulating therapeutics to the brain, including antibodies, immune cells, and cytokines. In this manner, FUS approaches are being explored as a tool to improve and amplify the effectiveness of immunotherapy for both primary and metastatic brain cancer, a particularly challenging solid tumor to treat. Here, we present an overview of the latest groundbreaking research in FUS-assisted delivery of immunomodulating agents to the brain in pre-clinical models of brain cancer, and place it within the context of the current immunotherapy approaches. We follow this up with a discussion on new developments and emerging strategies for this rapidly evolving approach.

Quantitative estimation of phospholipid molecules desorbed from a microbubble surface under ultrasound irradiation

Microbubbles have potential applications as drug and gene carriers, and drug release can be triggered by externally applied ultrasound irradiation while inside blood vessels. Desorption of molecules forming the microbubble shell can be observed under ultrasound irradiation of a single isolated microbubble, and the volume of desorbed molecules can be quantitatively estimated from the contact angle between the bubble and a glass plate. Microbubbles composed of a 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) shell and a poorly-soluble gas are created. When the microbubbles are exposed to a pulsed ultrasound, the contact angles increase dramatically; the percentage of DMPC molecules desorbed from the bubble surface reaches 70%. Vibration of a single bubble in the radial direction is measured using a laser Doppler vibrometer. The relationship between the vibrational characteristics and the amount of molecular desorption reveals that a larger vibrational amplitude of the bubble around the resonance size induces a larger amount of molecular desorption. These results support the possibility of controlling molecular desorption with pulsed ultrasound.

Novel theranostic approaches to neovascularized atherosclerotic plaques

As the global burden of atherosclerotic cardiovascular disease continues to rise, there is an increased demand for improved imaging techniques for earlier detection of atherosclerotic plaques and new therapeutic targets. Plaque lesions, vulnerable to rupture and thrombosis, are thought to be responsible for the majority of cardiovascular events, and are characterized by a large lipid core, a thin fibrous cap, and neovascularization. In addition to supplying the plaque core with increased inflammatory factors, these pathological neovessels are tortuous and leaky, further increasing the risk of intraplaque hemorrhage. Clinically, plaque neovascularization has been shown to be a significant and independent predictor of adverse cardiovascular outcomes. Microvessels can be detected through contrast-enhanced ultrasound (CEUS) imaging, however, clinical assessment in vivo is generally limited to qualitative measures of plaque neovascularization. There is no validated standard for quantitative assessment of the microvessel networks found in plaques. Advances in our understanding of the pathological mechanisms underlying plaque neovascularization and its significant role in the morbidity and mortality associated with atherosclerosis have made it an attractive area of research in translational medicine. Current areas of research include the development of novel therapeutic and diagnostic agents to target plaque neovascularization stabilization. With recent progress in nanotechnology, nanoparticles have been investigated for their ability to specifically target neovascularization. Contrast microbubbles have been similarly engineered to carry loads of therapeutic agents and can be visualized using CEUS. This review summarizes the pathogenesis, diagnosis, clinical significance of neovascularization, and importantly the emerging areas of theranostic tool development.

Ischemia Impaired Wound Healing Model in the Rat—Demonstrating Its Ability to Test Proangiogenic Factors

Chronic wounds remain a serious clinical problem with insufficient therapeutic approaches. In this study we investigated the dose dependency of rhVEGF165 in fibrin sealant in both ischemic and non-ischemic excision wounds using our recently developed impaired-wound healing model. An abdominal flap was harvested from the rat with unilateral ligation of the epigastric bundle and consequent unilateral flap ischemia. Two excisional wounds were set in the ischemic and non-ischemic area. Wounds were treated with three different rhVEGF165 doses (10, 50 and 100 ng) mixed with fibrin or fibrin alone. Control animals received no therapy. Laser Doppler imaging (LDI) and immunohistochemistry were performed to verify ischemia and angiogenesis. Wound size was monitored with computed planimetric analysis. LDI revealed insufficient tissue perfusion in all groups. Planimetric analysis showed slower wound healing in the ischemic area in all groups. Wound healing was fastest with fibrin treatment—irrespective of tissue vitality. Lower dose VEGF (10 and 50 ng) led to faster wound healing compared to high-dose VEGF. Immunohistochemistry showed the highest vessel numbers in low-dose VEGF groups. In our previously established model, different rhVEGF165 treatments led to dose-dependent differences in angiogenesis and wound healing, but the fastest wound closure was achieved with fibrin matrix alone.

Applications of Ultrasound-Mediated Gene Delivery in Regenerative Medicine

Research on the capability of non-viral gene delivery systems to induce tissue regeneration is a continued effort as the current use of viral vectors can present with significant limitations. Despite initially showing lower gene transfection and gene expression efficiencies, non-viral delivery methods continue to be optimized to match that of their viral counterparts. Ultrasound-mediated gene transfer, referred to as sonoporation, occurs by the induction of transient membrane permeabilization and has been found to significantly increase the uptake and expression of DNA in cells across many organ systems. In addition, it offers a more favorable safety profile compared to other non-viral delivery methods. Studies have shown that microbubble-enhanced sonoporation can elicit significant tissue regeneration in both ectopic and disease models, including bone and vascular tissue regeneration. Despite this, no clinical trials on the use of sonoporation for tissue regeneration have been conducted, although current clinical trials using sonoporation for other indications suggest that the method is safe for use in the clinical setting. In this review, we describe the pre-clinical studies conducted thus far on the use of sonoporation for tissue regeneration. Further, the various techniques used to increase the effectiveness and duration of sonoporation-induced gene transfer, as well as the obstacles that may be currently hindering clinical translation, are explored.

Synergies between therapeutic ultrasound, gene therapy and immunotherapy in cancer treatment

Due to the ease of use and excellent safety profile, ultrasound is a promising technique for both diagnosis and site-specific therapy. Ultrasound-based techniques have been developed to enhance the pharmacokinetics and efficacy of therapeutic agents in cancer treatment. In particular, transfection with exogenous nucleic acids has the potential to stimulate an immune response in the tumor microenvironment. Ultrasound-mediated gene transfection is a growing field, and recent work has incorporated this technique into cancer immunotherapy. Compared with other gene transfection methods, ultrasound-mediated gene transfection has a unique opportunity to augment the intracellular uptake of nucleic acids while safely and stably modulating the expression of immunostimulatory cytokines. The development and commercialization of therapeutic ultrasound systems further enhance the potential translation. In this Review, we introduce the underlying mechanisms and ongoing preclinical studies of ultrasound-based techniques in gene transfection for cancer immunotherapy. Furthermore, we expand on aspects of therapeutic ultrasound that impact gene therapy and immunotherapy, including tumor debulking, enhancing cytokines and chemokines and altering nanoparticle pharmacokinetics as these effects of ultrasound cannot be fully dissected from targeted gene therapy. We finally explore the outlook for this rapidly developing field.

Novel Technologies for Target Delivery of Therapeutics to the Placenta during Pregnancy: A Review

Uterine spiral artery remodeling is essential for placental perfusion and fetal growth and, when impaired, results in placental ischemia and pregnancy complications, e.g., fetal growth restriction, preeclampsia, premature birth. Despite the high incidence of adverse pregnancies, current treatment options are limited. Accordingly, research has shifted to the development of gene therapy technologies that provide targeted delivery of "payloads" to the placenta while limiting maternal and fetal exposure. This review describes the current strategies, including placental targeting peptide-bound liposomes, nanoparticle or adenovirus constructs decorated with specific peptide sequences and placental gene promoters delivered via maternal IV injection, directly into the placenta or the uterine artery, as well as noninvasive site-selective targeting of regulating genes conjugated with microbubbles via contrast-enhanced ultrasound. The review also provides a perspective on the effectiveness of these technologies in various animal models and their practicability and potential use for targeted placental delivery of therapeutics and genes in adverse human pregnancies affected by placental dysfunction.

Ultrasound-targeted microbubble destruction enhances the anti-tumor action of miR-4284 inhibitor in non-small cell lung cancer cells

MicroRNAs (miRNAs/miRs) are known to be involved in various human cancer types. Ultrasound-targeted microbubble destruction (UTMD) may improve the transfection efficiency of exogenous genes into target tissues and organs, thereby improving cancer treatment. In the present study, the role of miR-4284 in non-small cell lung cancer (NSCLC) was investigated and the effect of UTMD-mediated inhibition of miR-4284 on tumor progression was further analyzed. The expression of miR-4284 in NSCLC cells and tissues was detected by reverse transcription-quantitative PCR. UTMD-mediated inhibition of miR-4284 was achieved by co-transfection of microvesicles and miR-4284 inhibitors into NSCLC cells. A Cell Counting Kit-8 assay was used to determine NSCLC cell proliferation, and the migration and invasion of NSCLC cells were examined by Transwell assays. Compared with that in the control group, the expression of miR-4284 was increased in NSCLC tissues and cells. Knockdown of miR-4284 in NSCLC cells inhibited cell proliferation, migration and invasion. UTMD improved the transfection efficiency of miR-4284 inhibitors in NSCLC cells, resulting in more significant inhibition of tumor cell proliferation, migration and invasion. In conclusion, the results indicated that the expression of miR-4284 was increased in clinical samples and cell lines of NSCLC and that knockdown of miR-4284 inhibited the proliferation, migration and invasion of tumor cells. UTMD-mediated miR-4284 inhibition further promoted this effect, indicating that this technique may represent a novel strategy for the treatment of NSCLC.

Functional micro/nanobubbles for ultrasound medicine and visualizable guidance

Chemically functionalized gas-filled bubbles with a versatile micro/nano-sized scale have witnessed a long history of developments and emerging applications in disease diagnosis and treatments. In combination with ultrasound and image-guidance, micro/nanobubbles have been endowed with the capabilities of biomedical imaging, drug delivery, gene transfection and disease-oriented therapy. As an external stimulus, ultrasound (US)-mediated targeting treatments have been achieving unprecedented efficiency. Nowadays, US is playing a crucial role in visualizing biological/pathological changes in lives as a reliable imaging technique and a powerful therapeutic tool. This review retrospects the history of ultrasound, the chemistry of functionalized agents and summarizes recent advancements of functional micro/nanobubbles as US contrast agents in preclinical and transclinical research. Latest ultrasound-based treatment modalities in association with functional micro/nanobubbles have been highlighted as their great potentials for disease precision therapy. It is believed that these state-of-the-art micro/nanobubbles will become a booster for ultrasound medicine and visualizable guidance to serve future human healthcare in a more comprehensive and practical manner.

Spatiotemporal delivery of bioactive molecules for wound healing using stimuli-responsive biomaterials

Wound repair is a fascinatingly complex process, with overlapping events in both space and time needed to pave a pathway to successful healing. This additional complexity presents challenges when developing methods for the controlled delivery of therapeutics for wound repair and tissue engineering. Unlike more traditional applications, where biomaterial-based depots increase drug solubility and stability in vivo, enhance circulation times, and improve retention in the target tissue, when aiming to modulate wound healing, there is a desire to enable localised, spatiotemporal control of multiple therapeutics. Furthermore, many therapeutics of interest in the context of wound repair are sensitive biologics (e.g. growth factors), which present unique challenges when designing biomaterial-based delivery systems. Here, we review the diverse approaches taken by the biomaterials community for creating stimuli-responsive materials that are beginning to enable spatiotemporal control over the delivery of therapeutics for applications in tissue engineering and regenerative medicine.

Antagomir-155 Attenuates Acute Cardiac Rejection Using Ultrasound Targeted Microbubbles Destruction

Antagomir-155 is an artificial inhibitor of miRNA-155, which is expected to be a promising therapeutic target to attenuate acute cardiac rejection (ACR). However, its vulnerability of being degraded by endogenous nuclease and potential off-target effect make the authors seek for a more suitable way to delivery it. In attribution of efficiency and safety, ultrasound targeted microbubbles destruction (UTMD) turns out to be an appropriate method to deliver gene to target tissues. Here, cationic microbubbles to deliver antagomir-155 downregulating miRNA-155 in murine allograft hearts triggered by UTMD are synthesized. The viability of this therapy is verified by fluorescent microscopy. The biodistribution of antagomir-155 is analyzed by optical imaging system. The results show antagomir-155 delivered by UTMD which significantly decreases the levels of miR-155. Also, this therapy downregulates the expression of cytokines and inflammation infiltration. And allograft survival time is significantly prolonged. Therefore, antagomir-loaded microbubbles trigged by UTMD may provide a novel platform for ACR target treatment.

Low-frequency ultrasound-mediated cytokine transfection enhances T cell recruitment at local and distant tumor sites

Robust cytotoxic T cell infiltration has proven to be difficult to achieve in solid tumors. We set out to develop a flexible protocol to efficiently transfect tumor and stromal cells to produce immune-activating cytokines, and thus enhance T cell infiltration while debulking tumor mass. By combining ultrasound with tumor-targeted microbubbles, membrane pores are created and facilitate a controllable and local transfection. Here, we applied a substantially lower transmission frequency (250 kHz) than applied previously. The resulting microbubble oscillation was significantly enhanced, reaching an effective expansion ratio of 35 for a peak negative pressure of 500 kPa in vitro. Combining low-frequency ultrasound with tumor-targeted microbubbles and a DNA plasmid construct, 20% of tumor cells remained viable, and ∼20% of these remaining cells were transfected with a reporter gene both in vitro and in vivo. The majority of cells transfected in vivo were mucin 1+/CD45- tumor cells. Tumor and stromal cells were then transfected with plasmid DNA encoding IFN-β, producing 150 pg/106 cells in vitro, a 150-fold increase compared to no-ultrasound or no-plasmid controls and a 50-fold increase compared to treatment with targeted microbubbles and ultrasound (without IFN-β). This enhancement in secretion exceeds previously reported fourfold to fivefold increases with other in vitro treatments. Combined with intraperitoneal administration of checkpoint inhibition, a single application of IFN-β plasmid transfection reduced tumor growth in vivo and recruited efficacious immune cells at both the local and distant tumor sites.

Ultrasound-targeted microbubble destruction-mediated miR-767 inhibition suppresses tumor progression of non-small cell lung cancer

MicroRNAs (miRNAs/miRs) have important roles in tumor progression in various human cancers. Ultrasound-targeted microbubble destruction (UTMD)-mediated gene transfection has been considered a useful tool for improving cancer treatment. The present study aimed to investigate the role of miR-767 in non-small cell lung cancer (NSCLC) and further analyze the effects of UTMD-mediated miR-767 inhibition on tumor progression. The expression of miR-767 was measured by reverse transcription-quantitative PCR. UTMD-mediated miR-767 inhibition was achieved by the co-transfection of microbubbles and miR-767 inhibitor in NSCLC cells. Cell proliferation was assessed by a CCK-8 assay and cell migration and invasion were examined by a Transwell assay. The expression of miR-767 was increased in NSCLC serum, tissues and cells compared with controls. The reduction of miR-767 in NSCLC cells led to the inhibition of cell proliferation, migration and invasion. UTMD increased the transfection efficiency of the miR-767 inhibitor in NSCLC cells, and UTMD-mediated miR-767 inhibition resulted in a more significant suppressive effect on tumor cell proliferation, migration and invasion. Taken together, the results indicated that miR-767 expression is upregulated in both NSCLC clinical samples and cells. The downregulation of miR-767 can inhibit tumor cell proliferation, migration and invasion, and these effects are further promoted by UTMD-mediated miR-767 inhibition, which indicated the potential of a UTMD-mediated miR-767 inhibition as a novel therapeutic strategy for NSCLC treatment.

Revascularization and limb salvage following critical limb ischemia by nanoceria-induced Ref-1/APE1-dependent angiogenesis

In critical limb ischemia (CLI), overproduction of reactive oxygen species (ROS) and impairment of neovascularization contribute to muscle damage and limb loss. Cerium oxide nanoparticles (CNP, or 'nanoceria') possess oxygen-modulating properties which have shown therapeutic utility in various disease models. Here we show that CNP exhibit pro-angiogenic activity in a mouse hindlimb ischemia model, and investigate the molecular mechanism underlying the pro-angiogenic effect. CNP were injected into a ligated region of a femoral artery, and tissue reperfusion and hindlimb salvage were monitored for 3 weeks. Tissue analysis revealed stimulation of pro-angiogenic markers, maturation of blood vessels, and remodeling of muscle tissue following CNP administration. At a dose of 0.6 mg CNP, mice showed reperfusion of blood vessels in the hindlimb and a high rate of limb salvage (71%, n = 7), while all untreated mice (n = 7) suffered foot necrosis or limb loss. In vitro, CNP promoted endothelial cell tubule formation via the Ref-1/APE1 signaling pathway, and the involvement of this pathway in the CNP response was confirmed in vivo using immunocompetent and immunodeficient mice and by siRNA knockdown of APE1. These results demonstrate that CNP provide an effective treatment of CLI with excessive ROS by scavenging ROS to improve endothelial survival and by inducing Ref-1/APE1-dependent angiogenesis to revascularize an ischemic limb.

Adsorption and Desorption of a Phospholipid from Single Microbubbles under Pulsed Ultrasound Irradiation for Ultrasound-Triggered Drug Delivery

Microbubbles have potential for applications as drug and gene delivery systems, in which the release of a substance is triggered by an ultrasonic pulse. In this paper, we discuss the adsorption and desorption of a film of phospholipid on the surface of a single microbubble under ultrasound irradiation. Our optical observation system consisted of a high-speed camera, a laser Doppler vibrometer, and an ultrasound cell; 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) was used as the surfactant. The adsorption of the DMPC molecules onto the surface of the bubble was evaluated by measuring the contact angle between the bubble and a glass plate. A decrease of the contact angle of the bubble indicates desorption of the DMPC molecules from the bubble surface into the surrounding aqueous solution. The amount of DMPC molecules adsorbed on the bubble's surface is shown to decrease over time after bubble generation. The type and intensity of the pulsed ultrasound waves were varied so as to mimic ultrasound-triggered drug release. Increasing the number of cycles and the amplitude of the sound pressure of the pulsed ultrasound yielded a greater increase of the contact angle. We also measured the radial vibrations of the microbubbles in the ultrasound field. The vibrational characteristics of the microbubbles and the desorption characteristics of the DMPC molecules showed the same variation; namely, a greater sound pressure amplitude induced greater vibrational displacement and a larger amount of molecular desorption under resonance conditions. These results support the possibility of controlling drug release with pulsed ultrasound in a microbubble-based drug delivery system.

Minireview: Biophysical Mechanisms of Cell Membrane Sonopermeabilization. Knowns and Unknowns

Microbubble-assisted ultrasound has emerged as a promising method for the delivery of low-molecular-weight chemotherapeutic molecules, nucleic acids, therapeutic peptides, and antibodies in vitro and in vivo. Its clinical applications are under investigation for local delivery drug in oncology and neurology. However, the biophysical mechanisms supporting the acoustically mediated membrane permeabilization are not fully established. This review describes the present state of the investigations concerning the acoustically mediated stimuli (i.e., mechanical, chemical, and thermal stimuli) as well as the molecular and cellular actors (i.e., membrane pores and endocytosis) involved in the reversible membrane permeabilization process. The different hypotheses, which were proposed to give a biophysical description of the membrane permeabilization, are critically discussed.

A novel conjunction of folate-targeted carbon nanotubes containing protohemin and oridonin-liposome loaded microbubbles for cancer chemo-sonodynamic therapy

To facilitate targeting drug delivery and combined therapy, we constructed a novel drug carrier, in which oridonin-liposome containing microbubbles (LUMO) are covalently adhered to folic acid-conjugated multiwalled carbon nanotubes loaded with protohemin (FMTP) to form a novel conjugate (FMTP-LUMO). Oridonin (ORI) is used as a chemotherapeutic drug for chemotherapy (CHT), whereas protohemin (Ph) is applied in the field of sonodynamic therapy (SDT) as a sonosensitizer. In vitro release properties, cellular uptake and cytotoxicity in HepG-2 cells as well as in vivo antitumour effects in HepG-2 cell tumour-bearing mice submitted to chemo-sonodynamic therapy, SDT alone and CHT alone were evaluated upon ultrasound exposure. The results showed that the growth inhibition rates on FMTP-LUMO, FMTP, and LUMO were 95.4 ± 5.9%, 63.9 ± 7.4%, and 42.3 ± 2.9% in vitro, respectively. FMTP-LUMO exhibited strong binding to HepG-2 cells than MTP-LUMO. The chemo-sonodynamic therapy demonstrated a cooperative effect, resulting in significantly higher therapeutic efficacy for liver cancer. After treatment for 10 d, the tumour inhibition ratio for FMTP-LUMO exceeded to 90%, clearly higher than that of FMTP (42.8%) and LUMO (32.5%). Thus, FMTP-LUMO could serve as a highly effective drug carrier for chemo-sonodynamic therapy.

Applications of Ultrasound to Stimulate Therapeutic Revascularization

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

Vascular Endothelial Growth Factor Delivery to Placental Basal Plate Promotes Uterine Artery Remodeling in the Primate

Extravillous trophoblast (EVT) uterine artery remodeling (UAR) promotes placental blood flow, but UAR regulation is unproven. Elevating estradiol (E2) in early baboon pregnancy suppressed UAR and EVT vascular endothelial growth factor (VEGF) expression, but this did not prove that VEGF mediated this process. Therefore, our primate model of prematurely elevating E2 and contrast-enhanced ultrasound cavitation of microbubble (MB) carriers was used to deliver VEGF DNA to the placental basal plate (PBP) to establish the role of VEGF in UAR. Baboons were treated on days 25 to 59 of gestation (term, 184 days) with E2 alone or with E2 plus VEGF DNA-conjugated MBs briefly infused via a maternal peripheral vein on days 25, 35, 45, and 55. At each of these times an ultrasound beam was directed to the PBP to collapse the MBs and release VEGF DNA. VEGF DNA-labeled MBs per contrast agent was localized in the PBP but not the fetus. Remodeling of uterine arteries >25 µm in diameter on day 60 was 75% lower (P < 0.001) in E2-treated (7% ± 2%) than in untreated baboons (30% ± 4%) and was restored to normal by E2/VEGF. VEGF protein levels (signals/nuclear area) within the PBP were twofold lower (P < 0.01) in E2-treated (4.2 ± 0.9) than in untreated (9.8 ± 2.8) baboons and restored to normal by E2/VEGF (11.9 ± 1.6), substantiating VEGF transfection. Thus, VEGF gene delivery selectively to the PBP prevented the decrease in UAR elicited by prematurely elevating E2 levels, establishing the role of VEGF in regulating UAR in vivo during primate pregnancy.

Cardiovascular Imaging and Theranostics in Cardiovascular Pharmacotherapy

Imaging plays a pivotal role in the diagnostic and prognostic assessment of cardiovascular diseases. During the past two decades, there has been an expansion of the available imaging techniques, some of which are now part of routine clinical practice. Cardiovascular imaging of atherosclerosis is a useful instrument, and it can corroborate and expand pathophysiological evidence on cardiovascular disease, providing proof of concept for medical therapy and can predict its responsiveness, and it may be able to be used as surrogate endpoints for clinical trials. Theranostics is an emerging therapy that combines imaging and therapeutic functions, using imaging-based therapeutic delivery systems. Theranostics could partially overcome current imaging limitations and translate experimental evidence and large-scale trials assessing clinical endpoints, rationalising cardiovascular drug development and paving the way to personalised medicine. The medical community cannot overlook the use of cardiovascular imaging as a complementary and supportive adjunct to trials investigating clinical endpoints, which remain the mainstay for investigating the efficacy and safety of cardiovascular pharmacotherapy.

Concurrent Osteosarcoma Theranostic Strategy Using Contrast-Enhanced Ultrasound and Drug-Loaded Bubbles

Osteosarcoma (OS) is the most common bone tumor in children and teenagers. The multidrug resistant property of OS produces a major obstacle to chemotherapy, since the effective drug dose cannot be achieved via conventional drug delivery routes without serious systemic cytotoxicity. Microbubbles in conjunction with ultrasound (US) has recently been shown to spatially and temporally permeabilize the cellular membrane, promoting drug penetration into tumors. Here, we investigated whether drug (doxorubicin, DOX)-loaded bubbles (DOX-bubbles) can serve as drug-loaded carriers in combination with US in order to facilitate tumor drug delivery. The proposed bubbles have a high payload capacity (efficiency of 69.4 ± 9.1%, payload of 1.4 mg/mL) for DOX. In vitro data revealed that when used in combination with US (1-MHz), these DOX-bubbles facilitate DOX entering into tumor cells. In tumor-bearing animals, DOX-bubbles + US could provide 3.7-fold suppression of tumor growth compared with the group without insonation (1.8 ± 0.9 cm³ vs. 8.5 ± 2.2 cm³) because of the acceleration of DOX-induced tumor necrosis. In the meantime, the tumor perfusion and volume can be monitored by DOX-bubbles with contrast-enhanced ultrasound imaging. Our data provide useful information in support of translating the use of theranostic US-responsive bubbles for regulated tumor drug delivery into clinical use.

Nonviral ultrasound-mediated gene delivery in small and large animal models

Ultrasound-mediated gene delivery (sonoporation) is a minimally invasive, nonviral and clinically translatable method of gene therapy. This method offers a favorable safety profile over that of viral vectors and is less invasive as compared with other physical gene delivery approaches (e.g., electroporation). We have previously used sonoporation to overexpress transgenes in different skeletal tissues in order to induce tissue regeneration. Here, we provide a protocol that could easily be adapted to address various other targets of tissue regeneration or additional applications, such as cancer and neurodegenerative diseases. This protocol describes how to prepare, conduct and optimize ultrasound-mediated gene delivery in both a murine and a porcine animal model. The protocol includes the preparation of a microbubble-DNA mix and in vivo sonoporation under ultrasound imaging. Ultrasound-mediated gene delivery can be accomplished within 10 min. After DNA delivery, animals can be followed to monitor gene expression, protein secretion and other transgene-specific outcomes, including tissue regeneration. This procedure can be accomplished by a competent graduate student or technician with prior experience in ultrasound imaging or in performing in vivo procedures.

Computed tomography angiography evaluation of acute limb ischemia

Acute limb ischemia (ALI), a subclass of critical limb ischemia, is a medical emergency. The cause of ALI is usually thrombotic or embolic in nature, and the specific etiology often dictates the appropriate therapy. While the diagnosis is a clinical with common presenting symptoms, advances in ultrasound, computed tomography, and magnetic resonance technology have impacted the diagnosis and subsequent therapy. In ALI, the time to revascularization is critical and computed tomography angiography (CTA) provides a highly sensitive and specific technique for rapidly identifying occlusions and precisely defining vascular anatomy prior to interventions. In patients with significant renal disease, magnetic resonance angiography with or without contrast provides effective alternatives at the expense of imaging time. Treatment can include a variety of endovascular or surgical interventions, including thromboembolectomy, angioplasty, or bypass. Proper evaluation of the etiology of the ischemia, affected vasculature, and medical history is critical to select appropriate treatment and improve patient outcomes. Here, we examine the presentation, evaluation, and treatment of ALI and the role of CTA in diagnosis and therapy.

Improving the Angiogenic Potential of EPCs via Engineering with Synthetic Modified mRNAs

The application of endothelial progenitor cells (EPCs) for the revascularization of ischemic tissues, such as after myocardial infarction, stroke, and acute limb ischemia, has a huge clinical potential. However, the low retention and engraftment of EPCs as well as the poor survival of migrated stem cells in ischemic tissues still hamper the successful clinical application. Thus, in this study, we engineered, for the first time, murine EPCs with synthetic mRNAs to transiently produce proangiogenic factors vascular endothelial growth factor-A (VEGF-A), stromal cell-derived factor-1α (SDF-1α), and angiopoietin-1 (ANG-1). After the transfection of cells with synthetic mRNAs, significantly increased VEGF-A, SDF-1α, and ANG-1 protein levels were detected compared to untreated EPCs. Thereby, mRNA-engineered EPCs showed significantly increased chemotactic activity versus untreated EPCs and resulted in significantly improved attraction of EPCs. Furthermore, ANG-1 mRNA-transfected EPCs displayed a strong wound-healing capacity. Already after 12 hr, 94% of the created wound area in the scratch assay was closed compared to approximately 45% by untreated EPCs. Moreover, the transfection of EPCs with ANG-1 or SDF-1α mRNA also significantly improved the in vitro tube formation capacity; however, the strongest effect could be detected with EPCs simultaneously transfected with VEGF-A, SDF-1α, and ANG-1 mRNA. In the in vivo chicken chorioallantoic membrane (CAM) assay, EPCs transfected with ANG-1 mRNA revealed the strongest angiogenetic potential with significantly elevated vessel density and total vessel network length. In conclusion, this study demonstrated that EPCs can be successfully engineered with synthetic mRNAs encoding proangiogenic factors to improve their therapeutic angiogenetic potential in patients experiencing chronic or acute ischemic disease.

Ultrasound‑targeted microbubble destruction‑mediated miR‑205 enhances cisplatin cytotoxicity in prostate cancer cells

MicroRNAs (miRNAs) are non-coding ~20 nucleotides long sequences that function in the initiation and development of a number of cancers. Ultrasound-targeted microbubble destruction (UTMD) is an effective method for microRNA delivery. The aim of the present study was to investigate the potential roles of UTMD-mediated miRNA (miR)-205 delivery in the development of prostate cancer (PCa). In the present study, miR-205 expression was examined by reverse transcription-quantitative polymerase chain reaction assay. miR-205 mimics were transfected into PC-3 cells using the UTMD method, and the PC-3 cells were also treated with cisplatin. Cell proliferation, apoptosis, migration and invasion abilities were detected using Cell Counting kit-8, flow cytometry, wound healing and Transwell assays, respectively. In addition, the protein expression levels of caspase-9, cleaved-caspase 9, cytochrome c (cytoc), epithelial (E)-cadherin, matrix metalloproteinase-9 (MMP-9), phosphorylated (p)-extracellular signal-regulated kinase (ERK) and ERK were measured by western blot analysis. The results of the present study demonstrated that miR-205 expression was low in human PCa cell lines compared with healthy cells and that UTMD-mediated miR-205 delivery inhibited PCa cell proliferation, migration and invasion, and promoted apoptosis modulated by cisplatin compared with UTMD-mediated miR-negative control group and miR-205-treated group. Furthermore, it was demonstrated that UTMD-mediated miR-205 transfection increased the expression of caspase-9, cleaved-caspase 9, cytochrome c and E-cadherin, and decreased the expression of MMP-9 and p-ERK. Therefore, UTMD-mediated miR-205 delivery may be a promising method for the treatment of PCa.

* A Rodent Excision Model for Ischemia-Impaired Wound Healing

Delayed wound healing and the potentially resulting chronic wounds are a challenging clinical problem. Available therapeutic strategies are limited in both number and efficacy. For developing and establishing novel treatment approaches appropriate clinically relevant animal models are essential. The aim of the study was to establish a reliable and reproducible delayed wound healing model, which simulates the clinical scenario of compromised vascular tissue perfusion (hypoxia/ischemia). Therefore a standard rodent ischemic flap model was modified by challenging the tissue with ascending degrees of ischemia using different surgical approaches (minimal, mild, moderate, and severe ischemic invasive approach). Then a full-thickness circular wound was excised in both the non-/hypoperfused flap area and in the normally perfused contralateral region serving as an internal control. Wound healing progress was compared. Superficial tissue perfusion was measured by Laser Doppler imaging technique, which showed persistent ischemia in the moderate and severe invasive surgical approaches 7 days after wounding. Wound closure assessed by planimetric analysis occurred significantly slower in the ischemic wounds compared to the contralateral nonischemic wounds in the moderate invasive approach. Histologic evaluations in this approach showed signs of tissue necrosis and impaired angiogenesis in the ischemic wounds. Therefore, it can be concluded that this clinically relevant animal model is suitable to study mechanism in ischemia-impaired wound healing. Furthermore, it allows evaluating the efficacy of therapeutic strategies for impaired wound healing and comparing the results with an internal control wound.

Generation of Hutat2:Fc Knockin Primary Human Monocytes Using CRISPR/Cas9

The ability of monocytes to travel through the bloodstream, traverse tissue barriers, and aggregate at disease sites endows these cells with the attractive potential to carry therapeutic genes into the nervous system. However, gene editing in primary human monocytes has long been a challenge. Here, we applied the CRISPR/Cas9 system to deliver the large functional Hutat2:Fc DNA fragment into the genome of primary monocytes to neutralize HIV-1 transactivator of transcription (Tat), an essential neurotoxic factor that causes HIV-associated neurocognitive disorder (HAND) in the nervous system. Following homology-directed repair (HDR), ∼10% of the primary human monocytes exhibited knockin of the Hutat2:Fc gene in the AAVS1 locus, the "safe harbor" locus of the human genome, without selection. Importantly, the release of Hutat2:Fc by these modified monocytes protected neurons from Tat-induced neurotoxicity, reduced HIV replication, and restored T cell homeostasis. Moreover, compared with lentiviral transfection, CRISPR-mediated knockin had the advantage of maintaining the migrating function of monocytes. These results establish CRISPR/Cas9-mediated Hutat2:Fc knockin monocytes and provide a potential method to cross the blood-brain barrier for HAND therapy.

Cationic gas-filled microbubbles for ultrasound-based nucleic acids delivery

The use of ultrasound has gained great interest for nucleic acids delivery. Ultrasound can reach deep tissues in non-invasive manner. The process of sonoporation is based on the use of low-frequency ultrasound combined with gas-filled microbubbles (MBs) allowing an improved delivery of molecules including nucleic acids in the insonified tissue. For in vivo gene transfer, the engineering of cationic MBs is essential for creating strong electrostatic interactions between MBs and nucleic acids leading to their protection against nucleases degradation and high concentration within the target tissue. Cationic MBs must be stable enough to withstand nucleic acids interaction, have a good size distribution for in vivo administration, and enough acoustic activity to be detected by echography. This review aims to summarize the basic principles of ultrasound-based delivery and new knowledge acquired in these recent years about this method. A focus is made on gene delivery by discussing reported studies made with cationic MBs including ours. They have the ability for efficient delivery of plasmid DNA (pDNA), mRNA or siRNA. Last, we discuss about the key challenges that have to be faced for a fine use of this delivery system.

Mechanistic Insight into Sonoporation with Ultrasound-Stimulated Polymer Microbubbles

Sonoporation is emerging as a feasible, non-viral gene delivery platform for the treatment of cardiovascular disease and cancer. Despite promising results, this approach remains less efficient than viral methods. The objective of this work is to help substantiate the merit of polymeric microbubble sonoporation as a non-viral, localized cell permeation and payload delivery strategy by taking a ground-up approach to elucidating the fundamental mechanisms at play. In this study, we apply simultaneous microscopy of polymeric microbubble sonoporation over its intrinsic biophysical timescales-with sub-microsecond resolution to examine microbubble cavitation and millisecond resolution over several minutes to examine local macromolecule uptake through enhanced endothelial cell membrane permeability-bridging over six orders of magnitude in time. We quantified microbubble behavior and resulting sonoporation thresholds at transmit frequencies of 0.5, 1 and 2 MHz, and determined that sonic cracking is a necessary but insufficient condition to induce sonoporation. Further, sonoporation propensity increases with the extent of sonic cracking, namely, from partial to complete gas escape from the polymeric encapsulation. For the subset that exhibited complete gas escape from sonic cracking, a proportional relationship between the maximum projected gas area and resulting macromolecule uptake was observed. These results have revealed one aspect of polymeric bubble activity on the microsecond time scale that is associated with eliciting sonoporation in adjacent endothelial cells, and contributes toward an understanding of the physical rationale for sonoporation with polymer-encapsulated microbubble contrast agents.

The development of mechanically formed stable nanobubbles intended for sonoporation-mediated gene transfection

In this study, stable nano-sized bubbles (nanobubbles [NBs]) were produced using the mechanical agitation method in the presence of perfluorocarbon gases. NBs made with perfluoropropane had a smaller size (around 400 nm) compared to that of those made with perfluorobutane or nitrogen gas. The lipid concentration in NBs affected both their initial size and post-formulation stability. NBs formed with a final lipid concentration of 0.5 mg/ml tended to be more stable, having a uniform size distribution for 24 h at room temperature and 50 h at 4 °C. In vitro gene expression revealed that NBs/pDNA in combination with ultrasound (US) irradiation had significantly higher transfection efficacy in colon C26 cells. Moreover, for in vivo gene transfection in mice left limb muscles, there was notable local transfection activity by NBs/pDNA when combined with US irradiation. In addition, the aged NBs kept at room temperature or 4 °C were still functional at enhancing gene transfection in mice. We succeeded in preparing stable NBs for efficient in vivo gene transfection, using the mechanical agitation method.

Ultrasound Molecular Imaging of Angiogenesis Using Vascular Endothelial Growth Factor-Conjugated Microbubbles

Imaging of angiogenesis receptors could provide a sensitive and clinically useful method for detecting neovascularization such as occurs in malignant tumors, and responses to antiangiogenic therapies for such tumors. We tested the hypothesis that microbubbles (MB) tagged with human VEGF₁₂₁ (MB_VEGF) bind to the kinase insert domain receptor (KDR) in vitro and angiogenic endothelium in vivo, and that this specific binding can be imaged on a clinical ultrasound system. In this work, targeted adhesion of MB_VEGF was evaluated in vitro using a parallel plate flow system containing adsorbed recombinant human KDR. There was more adhesion of MB_VEGF to KDR-coated plates when the amount of VEGF₁₂₁ on each MB or KDR density on the plate was increased. MB_VEGF adhesion to KDR-coated plates decreased with increasing wall shear rate. On intravital microscopic imaging of bFGF-stimulated rat cremaster muscle, there was greater microvascular adhesion of MB_VEGF compared to that of isotype IgG-conjugated control MB (MB_CTL). To determine if MB_VEGF could be used to ultrasonically image angiogenesis, ultrasound imaging was performed in mice bearing squamous cell carcinoma after intravenous injection of MB_VEGF. Ultrasound videointensity enhancement in tumor was significantly higher for MB_VEGF (17.3 ± 9.7 dB) compared to MB_CTL (3.8 ± 4.4 dB, n = 6, p < 0.05). This work demonstrates the feasibility of targeted ultrasound imaging of an angiogenic marker using MB_VEGF. This approach offers a noninvasive bedside method for detecting tumor angiogenesis and could be extended to other applications such as molecular monitoring of therapeutic angiogenesis or antiangiogenic therapies in cardiovascular disease or cancer.

Cardiac Overexpression of S100A6 Attenuates Cardiomyocyte Apoptosis and Reduces Infarct Size After Myocardial Ischemia-Reperfusion

Background

Cardiomyocyte‐specific transgenic mice overexpressing S100A6, a member of the family of EF‐hand calcium‐binding proteins, develop less cardiac hypertrophy, interstitial fibrosis, and myocyte apoptosis after permanent coronary ligation, findings that support S100A6 as a potential therapeutic target after acute myocardial infarction. Our purpose was to investigate S100A6 gene therapy for acute myocardial ischemia‐reperfusion.

Methods and Results

We first performed in vitro studies to examine the effects of S100A6 overexpression and knockdown in rat neonatal cardiomyocytes. S100A6 overexpression improved calcium transients and protected against apoptosis induced by hypoxia‐reoxygenation via enhanced calcineurin activity, whereas knockdown of S100A6 had detrimental effects. For in vivo studies, human S100A6 plasmid or empty plasmid was delivered to the left ventricular myocardium by ultrasound‐targeted microbubble destruction in Fischer‐344 rats 2 days prior to a 30‐minute ligation of the left anterior descending coronary artery followed by reperfusion. Control animals received no therapy. Pretreatment with S100A6 gene therapy yielded a survival advantage compared to empty‐plasmid and nontreated controls. S100A6‐pretreated animals had reduced infarct size and improved left ventricular systolic function, with less myocyte apoptosis, attenuated cardiac hypertrophy, and less cardiac fibrosis.

Conclusions

S100A6 overexpression by ultrasound‐targeted microbubble destruction helps ameliorate myocardial ischemia‐reperfusion, resulting in lower mortality and improved left ventricular systolic function post–ischemia‐reperfusion via attenuation of apoptosis, reduction in cardiac hypertrophy, and reduced infarct size. Our results indicate that S100A6 is a potential therapeutic target for acute myocardial infarction.

Ultrasound-targeted microbubble destruction of calcium channel subunit α 1D siRNA inhibits breast cancer via G protein-coupled receptor 30

Estrogen has been closely associated with breast cancer. Several studies reported that Ca²⁺ signal and Ca²⁺ channels act in estrogen-modulated non-genomic pathway of breast cancer, however little was revealed on the function of L-type Ca²⁺ channels. The L-type Ca²⁺ channel subunit α 1D, named Cav1.3 was found in breast cancer cells. We aimed to investigate the expression and activity of Cav1.3 in human breast cancer, and reveal the effect of estrogen in regulating the expression of Cav1.3. The qRT-PCR and western blotting were employed to show that Cav1.3 was highly expressed in breast cancer tissues. E2 exposure rapidly upregulated the expression of Cav1.3 in dosage- and time-dependent manner, and promoted Ca²⁺ influx. The silencing of G protein-coupled estrogen receptor 30 (GPER1/GPR30) using siRNA transfection inhibited the upregulation of Cav1.3 and Ca²⁺ influx induced by E2. Moreover, the inhibition of Cav1.3 by siRNA transfection suppressed E2-induced second peak of Ca²⁺ signal, the expression of p-ERK1/2, and the cell proliferation. Ultrasound-targeted microbubble destruction (UTMD) of Cav1.3 siRNA was used in MCF-7 cells in vitro and in the tumor xenografts mice in vivo. The application of UTMD significantly suppressed the tumor growth and promoted the survival rate. In conclusion, E2 upregulated the expression of Cav1.3 for Ca²⁺ influx to promote the expression of p-ERK1/2 for cell proliferation. The study confirmed that the mechanism of E2 inducing the expression of Cav1.3 through a non-genomic pathway, and highlighted that UTMD of Cav1.3 siRNA is a powerful promising technology for breast cancer gene therapy.

Biophysical insight into mechanisms of sonoporation

This study presents a unique approach to understanding the biophysical mechanisms of ultrasound-triggered cell membrane disruption (i.e., sonoporation). We report direct correlations between ultrasound-stimulated encapsulated microbubble oscillation physics and the resulting cellular membrane permeability by simultaneous microscopy of these two processes over their intrinsic physical timescales (microseconds for microbubble dynamics and seconds to minutes for local macromolecule uptake and cell membrane reorganization). We show that there exists a microbubble oscillation-induced shear-stress threshold, on the order of kilopascals, beyond which endothelial cellular membrane permeability increases. The shear-stress threshold exhibits an inverse square-root relation to the number of oscillation cycles and an approximately linear dependence on ultrasound frequency from 0.5 to 2 MHz. Further, via real-time 3D confocal microscopy measurements, our data provide evidence that a sonoporation event directly results in the immediate generation of membrane pores through both apical and basal cell membrane layers that reseal along their lateral area (resealing time of ∼<2 min). Finally, we demonstrate the potential for sonoporation to indirectly initiate prolonged, intercellular gaps between adjacent, confluent cells (∼>30-60 min). This real-time microscopic approach has provided insight into both the physical, cavitation-based mechanisms of sonoporation and the biophysical, cell-membrane-based mechanisms by which microbubble acoustic behaviors cause acute and sustained enhancement of cellular and vascular permeability.

Detecting Tumor Metastases: The Road to Therapy Starts Here

Metastasis is the complex process by which primary tumor cells migrate and establish secondary tumors in an adjacent or distant location in the body. Early detection of metastatic disease and effective therapeutic options for targeting these detected metastases remain impediments to effectively treating patients with advanced cancers. If metastatic lesions are identified early, patients might maximally benefit from effective early therapeutic interventions. Further, monitoring patients whose primary tumors are effectively treated for potential metastatic disease onset is also highly valuable. Finally, patients with metastatic disease can be monitored for efficacy of specific therapeutic interventions through effective metastatic detection techniques. Thus, being able to detect and visualize metastatic lesions is key and provides potential to greatly improve overall patient outcomes. In order to achieve these objectives, researchers have endeavored to mechanistically define the steps involved in the metastatic process as well as ways to effectively detect metastatic progression. We presently overview various preclinical and clinical in vitro and in vivo assays developed to more efficiently detect tumor metastases, which provides the foundation for developing more effective therapies for this invariably fatal component of the cancerous process.

Evaluation of in vivo antitumor effects of low-frequency ultrasound-mediated miRNA-133a microbubble delivery in breast cancer

MicroRNAs (miRNAs), as a novel class of small noncoding RNAs, have been identified as important transcriptional and posttranscriptional inhibitors of gene expression. Ultrasound‐targeted microbubble destruction (UTMD) is a noninvasive method for microRNA delivery. We aimed to investigate the effect of UTMD of miR‐133a on breast cancer treatment. It has been reported that miRNA‐133a is involved in various cancers. miR‐133a was lowly expressed in breast cancer tissues and breast cancer cell lines MCF‐7 and MDA‐MB‐231. The miR‐133a expression was significantly upregulated under exogenous miRNA‐133a treatment in MCF‐7 and MDA‐MB‐231 cells analyzed by qRT‐PCR. Exogenous miR‐133a promoted the cell proliferation as determined by diphenyl tetrazolium bromide (MTT) assay and 5‐ethynyl‐2′‐deoxyuridine (EdU) staining. Epidermal growth factor receptor (EGFR) expression and Akt phosphorylation were significantly suppressed after miR‐133a transfection by western blot detection. We prepared the miR‐133a‐microbubble and injected it into breast cancer xenografts. The miR‐133a‐microbubble injection prolonged miR‐133a circulatory time by detecting the amount of miRNA‐133a in the plasma. No significant toxicity was observed on alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels at liver and albumin, blood urea nitrogen, or creatine kinase levels at kidney after miR‐133a‐microbubble injection. The tumor size of miR‐133a‐microbubble‐injected mice was smaller than that of the control group. Furthermore, the delivery efficiency of miR‐133a with low frequency was higher than that with common frequency. miR‐133a suppressed cell proliferation by suppressing the expression of EGFR and the phosphorylation of Akt. UTMD of miR‐133a inhibited the tumor growth and improved the survival rate in breast cancer mice. Our study provides new evidence that UTMD of miRNA is a promising platform for breast cancer therapy.

Microbubbles and Ultrasound: Therapeutic Applications in Diabetic Nephropathy

Diabetic nephropathy (DN) remains one of the most common causes of end-stage renal disease. Current therapeutic strategies aiming at optimization of serum glucose and blood pressure are beneficial in early stage DN, but are unable to fully prevent disease progression. With the limitations of current medical therapies and the shortage of available donor organs for kidney transplantation, the need for novel therapies to address DN complications and prevent progression towards end-stage renal failure is crucial. The development of ultrasound technology for non-invasive and targeted in-vivo gene delivery using high power ultrasound and carrier microbubbles offers great therapeutic potential for the prevention and treatment of DN. The promising results from preclinical studies of ultrasound-mediated gene delivery (UMGD) in several DN animal models suggest that UMGD offers a unique, non-invasive platform for gene- and cell-based therapies targeted against DN with strong clinical translation potential.

Increased local delivery of antagomir therapeutics to the rodent myocardium using ultrasound and microbubbles

Recent developments in microRNA (miRNA) research have identified these as important mediators in the pathophysiological response upon myocardial infarction (MI). Specific miRNAs can inhibit the translation of entire groups of mRNAs, which are involved in specific processes in the pathophysiology after MI, e.g. the fibrotic, apoptotic or angiogenic response. By modulating miRNAs in the heart, these processes can be tuned to improve cardiac function. Antagomirs are effective miRNA-inhibitors, but have a low myocardial specificity and cardiac antagomir treatment therefore requires high doses, which causes side effects. In the present study, ultrasound-triggered microbubble destruction (UTMD) was studied to increase specific delivery of antagomir to the myocardium. Healthy control mice were treated with UTMD and sacrificed at 30min, 24h and 48h, after which antagomir delivery in the heart was analyzed, both qualitatively and quantitatively. Additionally, potential harmful effects of treatment were analyzed by monitoring ECG, analyzing neutrophil invasion and cell death in the heart, and measuring troponin I after treatment. Finally, UTMD was tested for delivery of antagomir in a model of ischemia-reperfusion (I/R) injury. We found that UTMD can significantly increase local antagomir delivery to the non-ischemic heart with modest side-effects like neutrophil invasion without causing apoptosis. Delivered antagomirs enter cardiomyocytes within 30min after treatment and remains there for at least 48h. Interestingly, after I/R injury antagomir already readily enters the infarcted zone and we observed no additional benefit of UTMD for antagomir delivery. This study is the first to explore cardiac antagomir delivery using UTMD. In addition, it is the first to study tissue distribution of short RNA based therapeutics (~22 base pairs) at both the cellular and organ levels after UTMD to the heart in general. In summary, UTMD provides a myocardial delivery strategy for non-vascular permeable cardiac conditions later in the I/R response or chronic conditions like cardiac hypertrophy.

Therapeutic Angiogenesis by Ultrasound-Mediated MicroRNA-126-3p Delivery

OBJECTIVE

MicroRNAs are involved in many critical functions, including angiogenesis. Ultrasound-targeted microbubble destruction (UTMD) is a noninvasive technique for targeted vascular transfection of plasmid DNA and may be well suited for proangiogenic microRNA delivery. We aimed to investigate UTMD of miR-126-3p for therapeutic angiogenesis in chronic ischemia.

APPROACH AND RESULTS

The angiogenic potential of miR-126-3p was tested in human umbilical vein endothelial cells in vitro. UTMD of miR-126-3p was tested in vivo in Fischer-344 rats before and after chronic left femoral artery ligation, evaluating target knockdown, miR-126-3p and miR-126-5p expression, phosphorylated Tie2 levels, microvascular perfusion, and vessel density. In vitro, miR-126-3p-transfected human umbilical vein endothelial cells showed repression of sprouty-related protein-1 and phosphatidylinositol-3-kinase regulatory subunit 2, negative regulators of vascular endothelial growth factor and angiopoietin-1 signaling, increased phosphorylated Tie2 mediated by knockdown of phosphatidylinositol-3-kinase regulatory subunit 2 and greater angiogenic potential mediated by both vascular endothelial growth factor/vascular endothelial growth factor R2 and angiopoietin-1 /Tie2 effects. UTMD of miR-126-3p resulted in targeted vascular transfection, peaking early after delivery and lasting for >3 days, and resulting in inhibition of sprouty-related protein-1 and phosphatidylinositol-3-kinase regulatory subunit 2, with minimal uptake in remote organs. Finally, UTMD of miR-126-3p to chronic ischemic hindlimb muscle resulted in improved perfusion, vessel density, enhanced arteriolar formation, pericyte coverage, and phosphorylated Tie2 levels, without affecting miR-126-5p or delta-like 1 homolog levels.

CONCLUSIONS

UTMD of miR-126 results in improved tissue perfusion and vascular density in the setting of chronic ischemia by repressing sprouty-related protein-1 and phosphatidylinositol-3-kinase regulatory subunit 2 and enhancing vascular endothelial growth factor and angiopoietin-1 signaling, with no effect on miR-126-5p. UTMD is a promising platform for microRNA delivery, with applications for therapeutic angiogenesis.