Ultrasound and microbubble-assisted gene delivery: recent advances and ongoing challenges

A Systematic Study on Long-acting Nanobubbles: Current Advancement and Prospects on Theranostic Properties

Delivery of diagnostic drugs via nanobubbles (NBs) has shown to be an emerging field of study. Due to their small size, NBs may more easily travel through constricted blood vessels and precisely target certain bodily parts. NB is considered the major treatment for cancer treatment and other diseases which are difficult to diagnose. The field of NBs is dynamic and continues to grow as researchers discover new properties and seek practical applications in various fields. The predominant usage of NBs in novel drug delivery is to enhance the bioavailability, and controlled drug release along with imaging properties NBs are important because they may change interfacial characteristics including surface force, lubrication, and absorption. The quick diffusion of gas into the water was caused by a hypothetical film that was stimulated and punctured by a strong acting force at the gas/water contact of the bubble. In this article, various prominent aspects of NBs have been discussed, along with the long-acting nature, and the theranostical aspect which elucidates the potential marketed drugs along with clinical trial products. The article also covers quality by design aspects, different production techniques that enable method-specific therapeutic applications, increasing the floating time of the bubble, and refining its properties to enhance the prepared NB's quality. NB containing both analysis and curing properties makes it special from other nano-carriers. This work includes all the possible methods of preparing NB, its application, all marketed drugs, and products in clinical trials.

Role of microRNA-505 during tumor progression and metastasis

Late diagnosis of cancer in advanced stages due to the lack of screening methods is considered as the main cause of poor prognosis and high mortality rate among these patients. Therefore, it is necessary to investigate the molecular tumor biology in order to introduce biomarkers that can be used in cancer screening programs and early diagnosis. MicroRNAs (miRNAs) have key roles in regulation of the cellular pathophysiological processes. Due to the high stability of miRNAs in body fluids, they are widely used as the non-invasive tumor markers. According to the numerous reports about miR-505 deregulation in a wide range of cancers, we investigated the role of miR-505 during tumor progression. It was shown that miR-505 mainly has the tumor suppressor functions through the regulation of signaling pathways, chromatin remodeling, and cellular metabolism. This review has an effective role in introducing miR-505 as a suitable marker for the early cancer diagnosis.

mRNA Sonotransfection of Tumors with Polymeric Microbubbles: Co-Formulation versus Co-Administration

Despite its high potential, non-viral gene therapy of cancer remains challenging due to inefficient nucleic acid delivery. Ultrasound (US) with microbubbles (MB) can open biological barriers and thus improve DNA and mRNA passage. Polymeric MB are an interesting alternative to clinically used lipid-coated MB because of their high stability, narrow size distribution, and easy functionalization. However, besides choosing the ideal MB, it remains unclear whether nanocarrier-encapsulated mRNA should be administered separately (co-administration) or conjugated to MB (co-formulation). Therefore, the impact of poly(n-butyl cyanoacrylate) MB co-administration with mRNA-DOTAP/DOPE lipoplexes or their co-formulation on the transfection of cancer cells in vitro and in vivo is analyzed. Sonotransfection improved mRNA delivery into 4T1 breast cancer cells in vitro with co-administration being more efficient than co-formulation. In vivo, the co-administration sonotransfection approach also resulted in higher transfection efficiency and reached deeper into the tumor tissue. On the contrary, co-formulation mainly promoted transfection of endothelial and perivascular cells. Furthermore, the co-formulation approach is much more dependent on the US trigger, resulting in significantly lower off-site transfection. Thus, the findings indicate that the choice of co-administration or co-formulation in sonotransfection should depend on the targeted cell population, tolerable off-site transfection, and the therapeutic purpose.

Current Landscape of Gene Therapy for the Treatment of Cardiovascular Disorders

Cardiovascular disorders (CVD) are the primary cause of death worldwide. Multiple factors have been accepted to cause cardiovascular diseases; among them, smoking, physical inactivity, unhealthy eating habits, age, and family history are flag-bearers. Individuals at risk of developing CVD are suggested to make drastic habitual changes as the primary intervention to prevent CVD; however, over time, the disease is bound to worsen. This is when secondary interventions come into play, including antihypertensive, anti-lipidemic, anti-anginal, and inotropic drugs. These drugs usually undergo surgical intervention in patients with a much higher risk of heart failure. These therapeutic agents increase the survival rate, decrease the severity of symptoms and the discomfort that comes with them, and increase the overall quality of life. However, most individuals succumb to this disease. None of these treatments address the molecular mechanism of the disease and hence are unable to halt the pathological worsening of the disease. Gene therapy offers a more efficient, potent, and important novel approach to counter the disease, as it has the potential to permanently eradicate the disease from the patients and even in the upcoming generations. However, this therapy is associated with significant risks and ethical considerations that pose noteworthy resistance. In this review, we discuss various methods of gene therapy for cardiovascular disorders and address the ethical conundrum surrounding it.

CFTR and dystrophin encoding plasmids carrying both luciferase reporter gene, nuclear import specific sequences and triple helix sites

Duchenne Muscular Dystrophy and Cystic Fibrosis are two major monogenetic diseases which could be treated by non-viral gene therapy. For this purpose, plasmid DNA (pDNA) coding for the functional genes requires its equipment with signal molecules favouring its intracellular trafficking and delivery in the nucleus of the target cells. Here, two novel constructions of large pDNAs encoding the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) and full-length dystrophin (DYS) genes are reported. The expression of CFTR and DYS genes are driven respectively by the hCEF1 airway epithelial cells and spc5-12 muscle cells specific promoter. Those pDNAs encode also the luciferase reporter gene driven by the CMV promoter to evaluate gene delivery in animals by bioluminescence. In addition, oligopurine • oligopyrimidine sequences are inserted to enable equipment of pDNAs with peptides conjugated with a triple helix forming oligonucleotide (TFO). Furthermore, specific κB sequences are also inserted to promote their NFκB-mediated nuclear import. pDNA constructions are reported; transfection efficiency, tissue specific expression of CFTR and dystrophin in target cells, and triple helix formation are demonstrated. These plasmids are tools of interest to develop non-viral gene therapy of Cystic Fibrosis and Duchenne Muscular Dystrophy.

Microbubbles: Revolutionizing Biomedical Applications with Tailored Therapeutic Precision

BACKGROUND

Over the past ten years, tremendous progress has been made in microbubble-based research for a variety of biological applications. Microbubbles emerged as a compelling and dynamic tool in modern drug delivery systems. They are employed to deliver drugs or genes to targeted regions of interest, and then ultrasound is used to burst the microbubbles, causing site-specific delivery of the bioactive materials.

OBJECTIVE

The objective of this article is to review the microbubble compositions and physiochemical characteristics in relation to the development of innovative biomedical applications, with a focus on molecular imaging and targeted drug/gene delivery.

METHODS

The microbubbles are prepared by using various methods, which include cross-linking polymerization, emulsion solvent evaporation, atomization, and reconstitution. In cross-linking polymerization, a fine foam of the polymer is formed, which serves as a bubble coating agent and colloidal stabilizer, resulting from the vigorous stirring of a polymeric solution. In the case of emulsion solvent evaporation, there are two solutions utilized in the production of microbubbles. In atomization and reconstitution, porous spheres are created by atomising a surfactant solution into a hot gas. They are encapsulated in primary modifier gas. After the addition of the second gas or gas osmotic agent, the package is placed into a vial and sealed after reconstituting with sterile saline solution.

RESULTS

Microbubble-based drug delivery is an innovative approach in the field of drug delivery that utilizes microbubbles, which are tiny gas-filled bubbles, act as carriers for therapeutic agents. These microbubbles can be loaded with drugs, imaging agents, or genes and then guided to specific target sites.

CONCLUSION

The potential utility of microbubbles in biomedical applications is continually growing as novel formulations and methods. The versatility of microbubbles allows for customization, tailoring the delivery system to various medical applications, including cancer therapy, cardiovascular treatments, and gene therapy.

Appraisal for the Potential of Viral and Nonviral Vectors in Gene Therapy: A Review

Over the past few decades, gene therapy has gained immense importance in medical research as a promising treatment strategy for diseases such as cancer, AIDS, Alzheimer's disease, and many genetic disorders. When a gene needs to be delivered to a target cell inside the human body, it has to pass a large number of barriers through the extracellular and intracellular environment. This is why the delivery of naked genes and nucleic acids is highly unfavorable, and gene delivery requires suitable vectors that can carry the gene cargo to the target site and protect it from biological degradation. To date, medical research has come up with two types of gene delivery vectors, which are viral and nonviral vectors. The ability of viruses to protect transgenes from biological degradation and their capability to efficiently cross cellular barriers have allowed gene therapy research to develop new approaches utilizing viruses and their different genomes as vectors for gene delivery. Although viral vectors are very efficient, science has also come up with numerous nonviral systems based on cationic lipids, cationic polymers, and inorganic particles that provide sustainable gene expression without triggering unwanted inflammatory and immune reactions, and that are considered nontoxic. In this review, we discuss in detail the latest data available on all viral and nonviral vectors used in gene delivery. The mechanisms of viral and nonviral vector-based gene delivery are presented, and the advantages and disadvantages of all types of vectors are also given.

Selective attachment of a microtubule interacting peptide to plasmid DNA via a triplex forming oligonucleotide for transfection improvement

In nonviral gene therapy approaches, the linkage of signal molecules to plasmid DNA (pDNA) is of interest for guiding its delivery to the nucleus. Here, we report its linkage to a peptide (P_79-98) mediating migration on microtubules by using a triplex-forming oligonucleotide (TFO). pDNA of 5 kbp and 21 kbp containing 6 and 36 oligopurine • oligopyrimidine sites (TH), respectively, inserted outside the luciferase gene sequence were used. TFO with a dibenzocyclooctyl (DBCO) group in 3' end comprising some Bridged Nucleic Acid bases was conjugated by click chemistry with the peptide carrying an azide function in the C-terminal end. We found the formation of 6 and 18 triplex with pDNA of 5 kbp and 21 kbp, respectively. A twofold increase of the transfection efficiency was observed in the hind-limbs upon Hydrodynamic Limb Vein (HLV) injection in mice of naked P_79-98 -pDNA of 21 kbp. This work paves the way for the selective equipping of pDNA with intracellular targeting molecules while preserving the full expression of the encoded gene.

Mechanistic Insights and Therapeutic Delivery through Micro/Nanobubble-Assisted Ultrasound

Ultrasound with low frequency (20–100 kHz) assisted drug delivery has been widely investigated as a non-invasive method to enhance the permeability and retention effect of drugs. The functional micro/nanobubble loaded with drugs could provide an unprecedented opportunity for targeted delivery. Then, ultrasound with higher intensity would locally burst bubbles and release agents, thus avoiding side effects associated with systemic administration. Furthermore, ultrasound-mediated destruction of micro/nanobubbles can effectively increase the permeability of vascular membranes and cell membranes, thereby not only increasing the distribution concentration of drugs in the interstitial space of target tissues but also promoting the penetration of drugs through cell membranes into the cytoplasm. These advancements have transformed ultrasound from a purely diagnostic utility into a promising theragnostic tool. In this review, we first discuss the structure and generation of micro/nanobubbles. Second, ultrasound parameters and mechanisms of therapeutic delivery are discussed. Third, potential biomedical applications of micro/nanobubble-assisted ultrasound are summarized. Finally, we discuss the challenges and future directions of ultrasound combined with micro/nanobubbles.

Ultrasound-Mediated Drug Delivery: Sonoporation Mechanisms, Biophysics, and Critical Factors

Sonoporation, or the use of ultrasound in the presence of cavitation nuclei to induce plasma membrane perforation, is well considered as an emerging physical approach to facilitate the delivery of drugs and genes to living cells. Nevertheless, this emerging drug delivery paradigm has not yet reached widespread clinical use, because the efficiency of sonoporation is often deemed to be mediocre due to the lack of detailed understanding of the pertinent scientific mechanisms. Here, we summarize the current observational evidence available on the notion of sonoporation, and we discuss the prevailing understanding of the physical and biological processes related to sonoporation. To facilitate systematic understanding, we also present how the extent of sonoporation is dependent on a multitude of factors related to acoustic excitation parameters (ultrasound frequency, pressure, cavitation dose, exposure time), microbubble parameters (size, concentration, bubble-to-cell distance, shell composition), and cellular properties (cell type, cell cycle, biochemical contents). By adopting a science-backed approach to the realization of sonoporation, ultrasound-mediated drug delivery can be more controllably achieved to viably enhance drug uptake into living cells with high sonoporation efficiency. This drug delivery approach, when coupled with concurrent advances in ultrasound imaging, has potential to become an effective therapeutic paradigm.

Probing the interactions between air bubbles and (bio)interfaces at the nanoscale using FluidFM technology

Understanding the molecular mechanisms underlying bubble-(bio)surfaces interactions is currently a challenge that if overcame, would allow to understand and control the various processes in which they are involved. Atomic force microscopy is a useful technique to measure such interactions, but it is limited by the large size and instability of the bubbles that it can use, attached either on cantilevers or on surfaces. We here present new developments where microsized and stable bubbles are produced using FluidFM technology, which combines AFM and microfluidics. The air bubbles produced were used to probe the interactions with hydrophobic samples, showing that bubbles in water behave like hydrophobic surfaces. They thus could be used to measure the hydrophobic properties of microorganisms' surfaces, but in this case the interactions are also influenced by electrostatic forces. Finally a strategy was developed to functionalize their surface, thereby modulating their interactions with microorganism interfaces. This new method provides a valuable tool to understand bubble-(bio)surfaces interactions but also to engineer them.

Silencing of let-7b-5p inhibits ovarian cancer cell proliferation and stemness characteristics by Asp-Glu-Ala-Asp-box helicase 19A

The emergence and recurrence of ovarian cancer are associated with ovarian cancer stem cells. For cancer treatment, gene delivery of microbubbles (MB)-mediated microRNA (miRNA) is considered as a promising approach. In this study, our aim is to investigate the effects of MB-mediated let-7b-5p inhibitor on the proliferation and stemness characteristics of ovarian cancer (OVCA) cells. Let-7b-5p inhibitor mediated by MB was prepared (termed MB-let-7b-5p inhibitor), and the effects of MB-let-7b-5p inhibitor and let-7b-5p inhibitor on OVCA cell viability, proliferation and stemness characteristics were investigated. We found that MB-let-7b-5p inhibitor presented a higher transfection efficiency than let-7b-5p inhibitor alone. The inhibitory effect of MB-let-7b-5p inhibitor on OVCA cells was more significant than let-7b-5p inhibitor. Let-7b-5p targeted DEAD (Asp-Glu-Ala-Asp)-box helicase 19A (DDX19A), which was downregulated in OVCA cells. The downregulation of DDX19A reversed the inhibitory effects of MB-let-7b-5p inhibitor on OVCA cells. To sum up, we found that MB-let-7b-5p suppressed OVCA cell malignant behaviors by targeting DDX19A.

Rapid Magneto-Sonoporation of Adipose-Derived Cells

By permeabilizing the cell membrane with ultrasound and facilitating the uptake of iron oxide nanoparticles, the magneto-sonoporation (MSP) technique can be used to instantaneously label transplantable cells (like stem cells) to be visualized via magnetic resonance imaging in vivo. However, the effects of MSP on cells are still largely unexplored. Here, we applied MSP to the widely applicable adipose-derived stem cells (ASCs) for the first time and investigated its effects on the biology of those cells. Upon optimization, MSP allowed us to achieve a consistent nanoparticle uptake (in the range of 10 pg/cell) and a complete membrane resealing in few minutes. Surprisingly, this treatment altered the metabolic activity of cells and induced their differentiation towards an osteoblastic profile, as demonstrated by an increased expression of osteogenic genes and morphological changes. Histological evidence of osteogenic tissue development was collected also in 3D hydrogel constructs. These results point to a novel role of MSP in remote biophysical stimulation of cells with focus application in bone tissue repair.

Artificial intelligence and guidance of medicine in the bubble

Microbubbles are nanosized gas-filled bubbles. They are used in clinical diagnostics, in medical imaging, as contrast agents in ultrasound imaging, and as transporters for targeted drug delivery. They can also be used to treat thrombosis, neoplastic diseases, open arteries and vascular plaques and for localized transport of chemotherapies in cancer patients. Microbubbles can be filled with any type of therapeutics, cure agents, growth factors, extracellular vesicles, exosomes, miRNAs, and drugs. Microbubbles protect their cargo from immune attack because of their specialized encapsulated shell composed of lipid and protein. Filled with curative medicine, they could effectively circulate through the whole body safely and efficiently to reach the target area. The advanced bubble-based drug-delivery system, integrated with artificial intelligence for guidance, holds great promise for the targeted delivery of drugs and medicines.

Ultrasound Microbubble-Mediated VHL Regulates the Biological Behavior of Ovarian Cancer Cells

According to the literature, the von Hippel-Lindau (VHL) gene has a certain correlation with ovarian cancer. In this study, we investigated the effect and mechanism of ultrasound microbubble-mediated VHL on the biological function of ovarian cancer cells. Non-targeting lipid microbubbles and targeted lipid microbubbles were prepared. OVCAR-3 cells were treated with VHL mediated by ultrasound and microbubbles alone or together. Expressions of VHL, Akt, epithelial-mesenchymal-transition-related proteins and apoptosis-related proteins were detected by Western blot and quantitative real-time polymerase chain reaction as needed. The effect of ultrasound microbubble-mediated VHL on the proliferation, apoptosis, cell cycle, migration and invasion of OVCAR-3 cells was examined by Cell Counting Kit-8, flow cytometry, wound-healing assay and Transwell. Compared with other treatment methods, ultrasound microbubble mediation enhanced VHL expression in OVCAR-3 cells. Overexpression of liposome-mediated VHL inhibited the proliferation and migration; caused cell-cycle arrest; promoted apoptosis: downregulated the expressions of MMP2, MMP9, E-cadherin, Akt and Bcl-2; and upregulated the expressions of VHL and BCL2-associated X protein (BAX) in OVCAR-3 cells. The effect of microbubble-treated VHL was similar to liposome-mediated regulation, while ultrasound treatment enhanced the effect of VHL on OVCAR-3 cells. More interestingly, ultrasound microbubble-mediated VHL had the most obvious regulatory effect on OVCAR-3 cells. Ultrasound microbubble technology increases the transfection efficiency of VHL into OVCAR-3 cells and enhances the effect of VHL gene on the biological function of OVCAR-3 cells.

Current advances in ultrasound-combined nanobubbles for cancer-targeted therapy: a review of the current status and future perspectives

The non-specific distribution, non-selectivity towards cancerous cells, and adverse off-target side effects of anticancer drugs and other therapeutic molecules lead to their inferior clinical efficacy. Accordingly, ultrasound-based targeted delivery of therapeutic molecules loaded in smart nanocarriers is currently gaining wider acceptance for the treatment and management of cancer. Nanobubbles (NBs) are nanosize carriers, which are currently used as effective drug/gene delivery systems because they can deliver drugs/genes selectively to target sites. Thus, combining the applications of ultrasound with NBs has recently demonstrated increased localization of anticancer molecules in tumor tissues with triggered release behavior. Consequently, an effective therapeutic concentration of drugs/genes is achieved in target tumor tissues with ultimately increased therapeutic efficacy and minimal side-effects on other non-cancerous tissues. This review illustrates present developments in the field of ultrasound-nanobubble combined strategies for targeted cancer treatment. The first part of this review discusses the composition and the formulation parameters of NBs. Next, we illustrate the interactions and biological effects of combining NBs and ultrasound. Subsequently, we explain the potential of NBs combined with US for targeted cancer therapeutics. Finally, the present and future directions for the improvement of current methods are proposed.

NBs combined with ultrasound demonstrated the ability to enhance the targeting of anticancer agents and improve the efficacy.

Ultrasound Microbubble-Mediated microRNA-505 Regulates Cervical Cancer Cell Growth via AKT2

The application of ultrasound and microbubbles (USMB-) mediated microRNA (miR) is a promising approach of gene delivery for cancer treatment. We aimed to discuss the effects of USMB-miR-505 on cervical cancer (CC) development. miR-505 mediated by USMB was prepared. The effect of miR-505 on its transfection efficiency and the effect of miR-505 on HeLa cell proliferation, cell cycle, apoptosis, migration, and invasion were studied. The target gene of miR-505 was predicted, and its expression in CC was detected. The effect of the target gene on HeLa cells was further verified. USMB-miR-505 showed a higher transfection efficiency than miR-505 alone. The inhibitory effect of miR-505 mediated by USMB on HeLa cells was better than miR-505. miR-505 targeted AKT2, which was upregulated in CC. Overexpression of AKT2 reversed the inhibitory effect of USMB-miR-505 on HeLa cell malignant behaviors. Overall, we highlighted that USMB-miR-505 inhibited HeLa cell malignant behaviors by targeting AKT2.

Mechanisms underlying sonoporation: Interaction between microbubbles and cells

The past several decades have witnessed great progress in "smart drug delivery", an advance technology that can deliver genes or drugs into specific locations of patients' body with enhanced delivery efficiency. Ultrasound-activated mechanical force induced by the interactions between microbubbles and cells, which can stimulate so-called "sonoporation" process, has been regarded as one of the most promising candidates to realize spatiotemporal-controllable drug delivery to selected regions. Both experimental and numerical studies were performed to get in-depth understanding on how the microbubbles interact with cells during sonoporation processes, under different impact parameters. The current work gives an overview of the general mechanism underlying microbubble-mediated sonoporation, and the possible impact factors (e.g., the properties of cavitation agents and cells, acoustical driving parameters and bubble/cell micro-environment) that could affect sonoporation outcomes. Finally, current progress and considerations of sonoporation in clinical applications are reviewed also.

Ultrasound-targeted microbubble destruction optimized HGF-overexpressing bone marrow stem cells to repair fibrotic liver in rats

BACKGROUND/AIMS

Bone marrow mesenchymal stem cells (BMSCs) have shown their therapeutic potential in cytotherapy for liver fibrosis. However, the insufficient homing of BMSCs and undefined proliferation of BMSCs represent a significant challenge and largely limit the effective implementation. The aims of the present study were to determine whether stable expression of hepatic growth factor (HGF) in BMSCs coupled with ultrasound-targeted microbubble destruction (UTMD) technique could effectively and definitely alleviating carbon tetrachloride (CCl4)-induced liver fibrosis in rats.

MATERIALS AND METHODS

A rat model of liver fibrosis was acquired by injection of carbon tetrachloride (CCl4). The experimental rats were randomly assigned to the four groups: normal, CCl4, BMSCs-HGF/US, and BMSCs-HGF/UTMD groups. The BMSCs, transfected by recombinant adeno-associated virus vector encoding human genome sequence of HGF (BMSCs-HGF), were transplanted in rat via the tail vein. The homing efficiency of BMSCs was observed by immunofluorescence staining. The liver function and its morphological changes were analyzed by biochemical tests and liver histology. The expression of liver fibrosis markers including α-smooth muscle actin (α-SMA), collagen I, and vimentin were examined by immunohistochemistry and quantitative real-time polymerase chain reaction.

RESULTS

The homing efficiency of BMSCs in the fibrotic liver was significantly greater with the application of UTMD. The biochemical markers of liver function and histopathological results showed significantly better improvement in BMSCs-HGF/UTMD group than the other groups, and the serum levels of biochemical markers returned to normal ranges in 12 weeks in this group. Furthermore, the expression levels of liver fibrosis markers (α-SMA, collagen I, and Vimentin) were all significantly lower in BMSCs-HGF/UTMD group in comparison with other groups.

CONCLUSIONS

Our findings have demonstrated that stable expression of HGF in BMSCs and application of the UTMD technique facilitate the homing of BMSCs, and more importantly, which could further improve their alleviation of liver fibrosis. Therefore, these findings have an important clinical implication that AAV-BMSCs-HGF and UTMD hold promise as a novel therapeutic approach for liver fibrosis.

A Combination of UTMD-Mediated HIF-1α shRNA Transfection and TAE in the Treatment of Hepatic Cancer

To explore the antitumor effect of hypoxia-inducible factor-1α short hairpin RNA (HIF-1α shRNA) delivered by ultrasound targeted microbubble destruction (UTMD) and transcatheter arterial embolization (TAE) on rats with hepatic cancer. After the models of transplantation hepatoma were established, Wistar rats were randomly divided into 4 groups: Control group, UTMD group, TAE group, and UTMD+TAE group. Contrast-enhanced ultrasound (CEUS) was used to monitor tumor size on day 14 after four different treatments. Western blotting and immunohistochemistry were applied to measure the protein level of HIF-1α and VEGF in the hepatic cancer tissue. In comparison with UTMD+TAE group (21.25±10.68 days), the mean survival time was noticeably shorter in the Control group and TAE group (13.02±4.30 days and 15.03±7.32 days) (p<0.05, respectively). There was no statistical difference between UTMD+TAE group and UTMD group of the mean survival time (p>0.05). In addition, our results proved that the tumor sizes in UTMD+TAE group were obviously smaller than those in other groups (p<0.05, respectively). By CEUS, we clearly found that the tumor size was the smallest on day 14 in the UTMD+TAE group. The western blotting and immunohistochemistry results proved that the protein levels of HIF-1α and VEGF in UTMD+TAE group were obviously lower than those in TAE group and Control group on days 7 and 14 (p<0.05, respectively). However, there was no statistical difference between UTMD+TAE group and UTMD group (p>0.05). In this study we tried to explore the antitumor effect through a combination of UTMD-mediated HIF-1α shRNA transfection and TAE on rats with hepatic cancer. Our results showed that UTMD-mediated HIF-1α shRNA transfection and TAE can obviously silence HIF-1α and VEGF expression, thereby successfully inhibiting the growth of the tumor.

Enabling technologies for the preparation of multifunctional “bullets” for nanomedicine

Recent advances in nanotechnology, including modern enabling techniques that can improve synthetic preparation and drug formulations, have opened up new frontiers in nanomedicine with the development of nanoscale carriers and assemblies. The use of delivery platforms has attracted attention over the past decade as researchers shift their focus away from the development of new drug candidates, and toward new means with which to deliver therapeutic and/or diagnostic agents. This work will explore a transdisciplinary approach for the production of a number of nanomaterials, nanocomplexes and nanobubbles and their application in a variety of potential biological and theranostic protocols. Particular attention will be paid to nanobubbles, stimuli responsive nanoparticles and cyclodextrin grafted nanosystems produced under non-conventional conditions, such as microwave and ultrasound irradiation. Besides nanoparticles preparation, ultrasound can also act as an enabling technology when activating sensitive nanobubbles and nanoparticles.

Microbubbles for Nucleic Acid Delivery in Liver Using Mild Sonoporation

Ultrasound-mediated gene delivery is an interesting approach, which could help in increasing gene transfer in deep tissues. Moreover, it allows for performing experiments guided by the image to determine which elements are required. Microbubbles complexed with a eukaryotic expression cassette are excellent agents as they are responsive to ultrasounds and, upon oscillation, can destabilize membranes to enhance gene transfer. Here, we describe the preparation of positively charged microbubbles, plasmid free of antibiotic resistance marker, their combination and the conditions of ultrasound-mediated liver transfection post-systemic administration in mice. This association allowed us to obtain a superior liver gene expression at least over 8 months after a single injection.

A combination of ultrasound-targeted microbubble destruction with transplantation of bone marrow mesenchymal stem cells promotes recovery of acute liver injury

Background

Bone marrow mesenchymal stem cells (BMSCs) can provide an additional source of therapeutic stem cells for regeneration of liver cells during acute liver injury (ALI). However, the insufficient hepatic homing by the transplanted BMSCs limits their applications. Ultrasound-targeted microbubble destruction (UTMD) has been reported to promote the homing of transplanted stem cells into the ischemic myocardium. In this study, we investigated whether UTMD promotes the hepatic homing of BMSCs in ALI rats and evaluated the therapeutic effect.

Methods

BMSCs were isolated from the femurs and tibias of Sprague-Dawley (SD) rats. The isolated BMSCs were stably transfected with a lentivirus expressing enhanced green fluorescent protein (EGFP) that can be visualized and quantified in vivo after transplantation. Both tumor necrosis factor α (TNF-α) and stromal cell-derived factor 1 (SDF-1) were used to verify the appropriate ultrasound parameters. The ALI rats were divided into four groups: control, BMSCs, UTMD, and UTMD + BMSCs. The protein and mRNA expression levels of SDF-1, intercellular cell adhesion molecule (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1), hepatocyte growth factor (HGF), and monocyte chemotactic protein 1 (MCP-1) in the exposed livers were analyzed at 48 h after treatment. ALI recovery was determined by serum biochemical parameters and histology.

Results

The isolated rat BMSCs demonstrated a good proliferation potential that was both osteogenic and adipogenic in differentiation and expressed cluster of differentiation (CD) 29 and CD90, but not CD45 or CD11b/c. After BMSC and/or UTMD treatment, the number of GFP-labeled BMSCs in the UTMD + BMSCs group was significantly higher than that of the BMSCs group (9.8 ± 2.3 vs. 5.2 ± 1.1/per high-power field). Furthermore, the expression of GFP mRNA was performed for evaluation of the homing rate of BMSCs in injury sites as well. In addition, the expression levels of SDF-1, ICAM-1, VCAM-1, HGF, and MCP-1 were higher (p < 0.01) in UTMD+BMSCs group. The serum levels of biomarkers were significantly lower in the UTMD + BMSCs group, and the apoptotic rate of hepatocytes in the UTMD + BMSCs group was markedly lower than that of the BMSCs group (all p < 0.05). The hepatic pathology was significantly alleviated in the UTMD + BMSCs group.

Conclusions

UTMD treatment efficiently induced a favorable microenvironment for cell engraftment, resulting in improvement of hepatic homing of BMSCs, which was probably mediated through upregulation of the expression of adhesion molecules and cytokines. UTMD treatment appeared to be an effective and noninvasive approach to achieve better efficacy of BMSC-based therapy for repairing a severely injured liver.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-1098-4) contains supplementary material, which is available to authorized users.

On the Behaviour of Living Cells under the Influence of Ultrasound

Medical ultrasound technology is available, affordable, and non-invasive. It is used to detect, quantify, and heat tissue structures. This review article gives a concise overview of the types of behaviour that biological cells experience under the influence of ultrasound only, i.e., without the presence of microbubbles. The phenomena are discussed from a physics and engineering perspective. They include proliferation, translation, apoptosis, lysis, transient membrane permeation, and oscillation. The ultimate goal of cellular acoustics is the detection, quantification, manipulation and eradication of individual cells.

Shape oscillation and stability of an encapsulated microbubble translating in an acoustic wave

Encapsulated microbubbles (EMBs) are associated with a wide variety of important medical applications, including sonography, drug delivery, and sonoporation. The nonspherical oscillations, or shape modes, of EMBs strongly affect their stability and acoustic signature, and thus are an important factor to consider in the design and utilization of EMBs. Under acoustic forcing, EMBs often translate with significant velocity, which can excite shape modes, yet few studies have addressed the effect of translation on the shape stability of EMBs. In this work, the shape stability of an EMB subject to translation is investigated through development of an axisymmetric model for the case of small deformations. The potential flow in the bulk volume of the external flow is modeled using an asymptotic analysis. Viscous effects within the thin boundary layer at the interface are included, owing to the no-slip boundary condition, using Prosperetti's theory [Q. Appl. Math. 34, 339 (1977)]. In-plane stress and bending moment due to the encapsulation are incorporated into the model through the dynamic boundary condition at the interface. The evolution equations for radial oscillation, translation, and shape oscillation of an EMB are derived, which can be reduced to model an uncoated gas bubble by neglecting the encapsulation properties. These equations are solved numerically to analyze the shape mode stability of an EMB and a gas bubble subject to an acoustic, traveling plane wave. The findings demonstrate the counterintuitive result that translation has a more destabilizing effect on an EMB than on a gas bubble. The no-slip condition at the encapsulating membrane is the main factor responsible for mediating this interfacial instability due to translation.

Non-viral Gene Delivery

Although viral vectors comprise the majority of gene delivery vectors, their various safety, production, and other practical concerns have left a research gap to be addressed. The non-viral vector space encompasses a growing variety of physical and chemical methods capable of gene delivery into the nuclei of target cells. Major physical methods described in this chapter are microinjection, electroporation, and ballistic injection, magnetofection, sonoporation, optical transfection, and localized hyperthermia. Major chemical methods described in this chapter are lipofection, polyfection, gold complexation, and carbon-based methods. Combination approaches to improve transfection efficiency or reduce immunological response have shown great promise in expanding the scope of non-viral gene delivery.

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.

Homing of endogenous bone marrow mesenchymal stem cells to rat infarcted myocardium via ultrasound-mediated recombinant SDF-1α adenovirus in microbubbles

Stem cells can promote myocardial regeneration and accelerate the formation of new blood vessels. As such, transplanted stem cells represent a promising treatment modality for acute myocardial infarction (AMI). Stem cells spontaneously home to the infarcted myocardium using chemotaxis, in which the stromal cell-derived factor (SDF-1α) has been shown to be one of the most important chemokines. However, spontaneously secreted SDF-1α is short-lived, and therefore does not meet the needs of tissue repair. In this study, adenoviruses carrying SDF-1α genes were loaded on microbubble carriers and the adenoviruses were released into AMI rats by ultrasound targeted microbubble destruction. The possibility of in vivo self-transplantation of bone marrow mesenchymal stem cells (BMSCs) induced by overexpression of SDF-1α in the infarcted myocardium was explored by detecting the number of BMSCs homing from the peripheral blood to the myocardial infarcts. The concentration of SDF-1α in peripheral blood was significantly higher after transfection, and the number of BMSCs was significantly higher in the peripheral blood and infarcted area. Further analyses indicated that the number of homing BMSCs increased with increased SDF-1α expression. In conclusion, our results suggest that ultrasound mediated transduction of exogenous SDF-1α genes into myocardial infarcted AMI rats can effectively promote the homing of endogenous BMSCs into the heart. Moreover, the number of homing stem cells was controlled by the level of SDF-1α expression.

Cationic microbubbles and antibiotic-free miniplasmid for sustained ultrasound-mediated transgene expression in liver

Despite the increasing number of clinical trials in gene therapy, no ideal methods still allow non-viral gene transfer in deep tissues such as the liver. We were interested in ultrasound (US)-mediated gene delivery to provide long term liver expression. For this purpose, new positively charged microbubbles were designed and complexed with pFAR4, a highly efficient small length miniplasmid DNA devoid of antibiotic resistance sequence. Sonoporation parameters, such as insonation time, acoustic pressure and duration of plasmid injection were controlled under ultrasound imaging guidance. The optimization of these various parameters was performed by bioluminescence optical imaging of luciferase reporter gene expression in the liver. Mice were injected with 50μg pFAR4-LUC either alone, or complexed with positively charged microbubbles, or co-injected with neutral MicroMarker™ microbubbles, followed by low ultrasound energy application to the liver. Injection of the pFAR4 encoding luciferase alone led to a transient transgene expression that lasted only for two days. The significant luciferase signal obtained with neutral microbubbles decreased over 2days and reached a plateau with a level around 1 log above the signal obtained with pFAR4 alone. With the newly designed positively charged microbubbles, we obtained a much stronger bioluminescence signal which increased over 2days. The 12-fold difference (p<0.05) between MicroMarker™ and our positively charged microbubbles was maintained over a period of 6months. Noteworthy, the positively charged microbubbles led to an improvement of 180-fold (p<0.001) as regard to free pDNA using unfocused ultrasound performed at clinically tolerated ultrasound amplitude. Transient liver damage was observed when using the cationic microbubble-pFAR4 complexes and the optimized sonoporation parameters. Immunohistochemistry analyses were performed to determine the nature of cells transfected. The pFAR4 miniplasmid complexed with cationic microbubbles allowed to transfect mostly hepatocytes compared to its co-injection with MicroMarker™ which transfected more preferentially endothelial cells.

The Nanomechanics of Lipid Multibilayer Stacks Exhibits Complex Dynamics

The nanomechanics of lipid membranes regulates a large number of cellular functions. However, the molecular mechanisms underlying the plastic rupture of individual bilayers remain elusive. This study uses force clamp spectroscopy to capture the force-dependent dynamics of membrane failure on a model diphytanoylphosphatidylcholine multilayer stack, which is devoid of surface effects. The obtained kinetic measurements demonstrate that the rupture of an individual lipid bilayer, occurring in the bilayer parallel plane, is a stochastic process that follows a log-normal distribution, compatible with a pore formation mechanism. Furthermore, the vertical individual force-clamp trajectories, occurring in the bilayer orthogonal bilayer plane, reveal that rupturing process occurs through distinct intermediate mechanical transition states that can be ascribed to the fine chemical composition of the hydrated phospholipid moiety. Altogether, these results provide a first description of unanticipated complexity in the energy landscape governing the mechanically induced bilayer rupture process.

Ultrasound combined with targeted cationic microbubble-mediated angiogenesis gene transfection improves ischemic heart function

The present study aimed to construct targeted cationic microbubbles (TCMBs) by synthesizing cationic microbubbles conjugated to an intercellular adhesion molecule-1 (ICAM-1) antibody, and then to use the TCMBs to deliver the angiopoietin-1 (Ang-1) gene into infarcted heart tissue using ultrasound-mediated microbubble destruction. It was hypothesized that the TCMBs would accumulate in higher numbers than non-targeted cationic microbubbles (CMBs) in the infarcted heart, and would therefore increase the efficiency of targeted Ang-1 gene transfection and promote angiogenesis. The results of the study demonstrated that the ability of TCMBs to target inflammatory endothelial cells was 18.4-fold higher than that of the CMBs in vitro. The accumulation of TCMBs was greater than that of CMBs in TNF-α-stimulated human umbilical cord veins, indicated by a 212% higher acoustic intensity. In vivo, the TCMBs specifically accumulated in the myocardial infarct area in a rabbit model. Three days after ultrasound microbubble-mediated gene transfection, Ang-1 protein expression in the TCMB group was 2.7-fold higher than that of the CMB group. Angiogenesis, the thickness of the infarct region and the heart function of the TCMB group were all significantly improved compared with those in the CMB and control groups at 4 weeks following gene transfection (all P<0.01). Therefore, the results of the current study demonstrate that ultrasound-mediated TCMB destruction effectively delivered the Ang-1 gene to the infarcted myocardium, resulting in improved cardiac morphology and function in the animal model. Ultrasound-mediated TCMB destruction is a promising strategy for improving gene therapy in the future.

Vancomycin-loaded nanobubbles: A new platform for controlled antibiotic delivery against methicillin-resistant Staphylococcus aureus infections

Vancomycin (Vm) currently represents the gold standard against methicillin-resistant Staphylococcus aureus (MRSA) infections. However, it is associated with low oral bioavailability, formulation stability issues, and severe side effects upon systemic administration. These drawbacks could be overcome by Vm topical administration if properly encapsulated in a nanocarrier. Intriguingly, nanobubbles (NBs) are responsive to physical external stimuli such as ultrasound (US), promoting drug delivery. In this work, perfluoropentane (PFP)-cored NBs were loaded with Vm by coupling to the outer dextran sulfate shell. Vm-loaded NBs (VmLNBs) displayed ∼300nm sizes, anionic surfaces and good drug encapsulation efficiency. In vitro, VmLNBs showed prolonged drug release kinetics, not accompanied by cytotoxicity on human keratinocytes. Interestingly, VmLNBs were generally more effective than Vm alone in MRSA killing, with VmLNB antibacterial activity being more sustained over time as a result of prolonged drug release profile. Besides, VmLNBs were not internalized by staphylococci, opposite to Vm solution. Further US association promoted drug delivery from VmLNBs through an in vitro model of porcine skin. Taken together, these results support the hypothesis that proper Vm encapsulation in US-responsive NBs might be a promising strategy for the topical treatment of MRSA wound infections.

Nanobubbles: a promising efficienft tool for therapeutic delivery

In recent decades ultrasound-guided delivery of drugs loaded on nanocarriers has been the focus of increasing attention to improve therapeutic treatments. Ultrasound has often been used in combination with microbubbles, micron-sized spherical gas-filled structures stabilized by a shell, to amplify the biophysical effects of the ultrasonic field. Nanometer size bubbles are defined nanobubbles. They were designed to obtain more efficient drug delivery systems. Indeed, their small sizes allow extravasation from blood vessels into surrounding tissues and ultrasound-targeted site-specific release with minimal invasiveness. Additionally, nanobubbles might be endowed with improved stability and longer residence time in systemic circulation. This review will describe the physico-chemical properties of nanobubbles, the formulation parameters and the drug loading approaches, besides potential applications as a therapeutic tool.

The effects of low-frequency ultrasound and microbubbles on rabbit hepatic tumors

High-intensity focused ultrasound in combination with microbubbles (MBs) is able to inhibit the growth of VX2 rabbit liver tumors in vivo and prolong the survival time of the animals. In this study, we attempt to investigate the feasibility of VX2 tumor growth inhibition using low-frequency ultrasound (US)-mediated MB disruption. Forty-eight New Zealand rabbits with hepatic VX2 tumors were divided into four groups: control, MBs group, low-frequency US group, and US + MB group. The parameters of the US were 20 kHz, 2 W/cm², 40% duty cycle, 5 min, and once every other day for 2 weeks. At the end of the therapy experiment, 24 rabbits were euthanized, and the cancers were collected and cut into five sections for histological examination, immunohistochemistry, laser confocal microscopy, western blotting assays, and transmission electron microscopy (TEM). Another 24 rabbits were saved, and overall survival time was recorded. The tumor volumes in control, MB, US, and US + MB groups were 6.36 ± 0.58, 5.68 ± 0.42, 5.29 ± 0.26, and 2.04 ± 0.14 cm³, respectively (US + MB versus the other three groups, P < 0.01). Tumor cells manifested coagulation necrosis with internal calcification. Hematoxylin and eosin (H–E) staining revealed interstitial hemorrhage and intravascular thrombosis. The intensity of cyclooxygenase-2 (COX-2), and vascular endothelial growth factor (VEGF) in the US + MB group in the immunohistochemical staining, laser confocal microscopy, and western blotting assays was lower than that of the other three groups (P < 0.05). TEM of the US + MB group revealed vascular endothelial cell wall rupture, widened endothelial cell gaps, interstitial erythrocyte leakage, and microvascular thrombosis, while intact vascular endothelial cells and normal erythrocytes in the tumor vessels were observed in control, MB, and US groups. Rabbits treated with US + MB had a significantly longer overall survival than those in the other three groups (χ2 = 9.328, P = 0.0242). VX2 tumor growth could be inhibited by cavitation induced using low-frequency US and MB.

Efficient Gene Delivery by Sonoporation Is Associated with Microbubble Entry into Cells and the Clathrin-Dependent Endocytosis Pathway

Microbubble oscillation at specific ultrasound settings leads to permeabilization of surrounding cells. This phenomenon, referred to as sonoporation, allows for the in vitro and in vivo delivery of extracellular molecules, including plasmid DNA. To date, the biological and physical mechanisms underlying this phenomenon are not fully understood. The aim of this study was to investigate the interactions between microbubbles and cells, as well as the intracellular routing of plasmid DNA and microbubbles, during and after sonoporation. High-speed imaging and fluorescence confocal microscopy of HeLa cells stably expressing enhanced green fluorescent protein fused with markers of cellular compartments were used for this investigation. Soft-shelled microbubbles were observed to enter cells during sonoporation using experimental parameters that led to optimal gene transfer. They interacted with the plasma membrane in a specific area stained with fluorescent cholera subunit B, a marker of lipid rafts. This process was not observed with hard-shelled microbubbles, which were not efficient in gene delivery under our conditions. The plasmid DNA was delivered to late endosomes after 3 h post-sonoporation, and a few were found in the nucleus after 6 h. Gene transfer efficacy was greatly inhibited when cells were treated with chlorpromazine, an inhibitor of the clathrin-dependent endocytosis pathway. In contrast, no significant alteration was observed when cells were treated with filipin III or genistein, both inhibitors of the caveolin-dependent pathway. This study emphasizes that microbubble-cell interactions do not occur randomly during sonoporation; microbubble penetration inside cells affects the efficacy of gene transfer at specific ultrasound settings; and plasmid DNA uptake is an active mechanism that involves the clathrin-dependent pathway.

Galactosylated poly-L-lysine targeted microbubbles for ultrasound mediated antisense c-myc gene transfection in hepatocellular carcinoma cells

INTRODUCTION

The aim of the study was to investigate the efficiency of delivery and targeted binding of c-myc antisense oligodeoxynucleotide (ASODN) and find a novel therapy for hepatic carcinoma.

MATERIAL AND METHODS

A targeted ultrasound microbubble compound was synthesized to deliver the c-myc ASODN by ultrasound-targeted microbubble destruction (UTMD) and applied in hepatocellular carcinoma cells (HCC) and cancer bearing mice. Lipid microbubbles were conjugated with biotinylated galactosylated poly-L-lysine (G-PLL) and SonoVue to target the hepatocellular carcinoma SMMC7721 cells with asialoglycoprotein receptors. There were four groups in both in vitro and in vivo studies: control group (group A); c-myc ASODN + G-PLL (CG group, group B); c-myc ASODN + SonoVue (CUS group, group C); c-myc ASODN + G-PLL + SonoVue (CGUS group, group D). The expression of c-myc mRNA was detected by reverse transcription-polymerase chain reaction (RT-PCR), and proliferation investigations of the SMMC7721 cells were also performed. In addition, the tumor volume was calculated and compared among different groups.

RESULTS

The level of c-myc mRNA in the three experimental groups was significantly lower than that in the control group in vitro (p < 0.05). Furthermore, c-myc gene expression was suppressed more strongly in the CGUS group compared with other groups in both in vitro and in vivo studies (p < 0.05). In addition, ultrasound mediation of targeted microbubbles yielded the highest inhibition of tumor growth and cell proliferation among the four groups.

CONCLUSIONS

The use of a G-PLL targeted microbubble contrast agent combined with ultrasound exposure could be a potential method for increasing gene delivery efficiency. This technique is a promising nonviral approach that can be used in liver cancer.

Targeted microbubbles: a novel application for the treatment of kidney stones

Kidney stone disease is endemic. Extracorporeal shockwave lithotripsy was the first major technological breakthrough where focused shockwaves were used to fragment stones in the kidney or ureter. The shockwaves induced the formation of cavitation bubbles, whose collapse released energy at the stone, and the energy fragmented the kidney stones into pieces small enough to be passed spontaneously. Can the concept of microbubbles be used without the bulky machine? The logical progression was to manufacture these powerful microbubbles ex vivo and inject these bubbles directly into the collecting system. An external source can be used to induce cavitation once the microbubbles are at their target; the key is targeting these microbubbles to specifically bind to kidney stones. Two important observations have been established: (i) bisphosphonates attach to hydroxyapatite crystals with high affinity; and (ii) there is substantial hydroxyapatite in most kidney stones. The microbubbles can be equipped with bisphosphonate tags to specifically target kidney stones. These bubbles will preferentially bind to the stone and not surrounding tissue, reducing collateral damage. Ultrasound or another suitable form of energy is then applied causing the microbubbles to induce cavitation and fragment the stones. This can be used as an adjunct to ureteroscopy or percutaneous lithotripsy to aid in fragmentation. Randall's plaques, which also contain hydroxyapatite crystals, can also be targeted to pre-emptively destroy these stone precursors. Additionally, targeted microbubbles can aid in kidney stone diagnostics by virtue of being used as an adjunct to traditional imaging methods, especially useful in high-risk patient populations. This novel application of targeted microbubble technology not only represents the next frontier in minimally invasive stone surgery, but a platform technology for other areas of medicine.

In vitro and in vivo evaluation of vancomycin-loaded PMMA cement in combination with ultrasound and microbubbles-mediated ultrasound

Ultrasound (US) has been used to increase elution of antibiotic from an antibiotic-loaded poly(methyl methacrylate) (PMMA) bone cement (ALBC). We aimed to further investigate whether microbubbles-mediated US (US + MB) facilitate elution of vancomycin (VAN) from cylindrical specimens and enhance the activity of the eluted antibiotic against Staphylococcus aureus (S. aureus) in vitro. The study groups comprised cylindrical bone cement fabricated with VAN (VAN), ALBC using US (VAN + US), and ALBC using MB-mediated US (VAN + US + MB). We also carried out an in vivo study involving the activity of VAN from cylindrical cement implanted in tibiae of New Zealand white rabbits inoculated with S. aureus. We found that (1) in vitro, elution from VAN + US + MB cylinders was significantly higher than from either the VAN or VAN + US specimens; (2) the activity of the eluted VAN from the VAN + US + MB cylinders against planktonic S. aureus was significantly higher than from either the control or VAN or VAN + US specimens; and (3) in the rabbits, the activity of the eluted VAN from the VAN + US + MB cylinders against S. aureus was significantly higher than from either the control or VAN or VAN + US specimens. The present results suggest that VAN-loaded PMMA cement irradiated with MB-mediated US may have a role in controlling prosthetic joint infection.

Comparing efficiency of micro-RNA and mRNA biomarker liberation with microbubble-enhanced ultrasound exposure

Blood biomarkers are potentially powerful diagnostic tools that are limited clinically by low concentrations, the inability to determine biomarker origin and unknown patient baseline. Recently, ultrasound has been shown to liberate proteins and large mRNA biomarkers, overcoming many of these limitations. We have since demonstrated that adding lipid-stabilized microbubbles elevates mRNA concentration an order of magnitude compared with ultrasound without microbubbles, in vitro. Unfortunately the large size of some mRNA molecules may limit efficiency of release and hinder efficacy as an ultrasound-liberated biomarker. We hypothesize that smaller molecules will be released more efficiently with ultrasound than larger molecules. Although investigation of large libraries of biomarkers should be performed to fully validate this hypothesis, we focus on a small subset of mRNA and micro-RNAs. Specifically, we focus on miR-21 (22 base pairs [bp]), which is upregulated in certain forms of cancer, compared with previously investigated mammaglobin mRNA (502 bp). We also report release of micro-RNA miR-155 (22 bp) and housekeeping rRNA S18 (1869 bp). More than 10 million additional miR-21 copies per 100,000 cells are released with ultrasound-microbubble exposure. The low- molecular-weight miR-21 proved to be liberated 50 times more efficiently than high-molecular-weight mammaglobin mRNA, releasing orders of magnitude more miR-21 than mammaglobin mRNA under comparable conditions.

Inhibitory effects of subcutaneous tumors in nude mice mediated by low-frequency ultrasound and microbubbles

The aim of the present study was to investigate the sonication effects of 21-kHz ultrasound (US) with microbubbles (MBs) on the subcutaneous prostate tumors of nude mice. In total, 15 tumor-bearing nude mice were divided into three groups: The control group, the low-frequency US group and the US+MB group. The MBs used were from US contrast agent SonoVue. The parameters of the US were as follows: 21 kHz, 26 mW/cm² and a 40% duty cycle (2 sec on, 3 sec off) for 3 min, once every other day for 2 weeks. Color Doppler flow imaging, hematoxylin and eosin (HE) staining, immunoblotting and transmission electron microscopy (TEM) were used to evaluate the results. Following 2 weeks of treatment, the blood flow signal disappeared in the US+MB group only, and the tumor size was smaller when compared with the control and US groups. For the immunoblotting, the intensity of cyclooxygenase-2 and vascular endothelial growth factor in the US+MB group was lower compared with the other two groups. Tumor necrosis was present and the nucleus disappeared upon HE staining in the US+MB group. Upon TEM analysis, increased cytoplasmic vacuolation and dilatation of the perinuclear cisternae of the tumor cells were found in the US+MB group. In the control and US groups, the tumors had intact vascular endothelia and vessel lumens. However, lumen occlusion of the vessels was observed in the US+MB group. In conclusion, 21-kHz low-intensity US with MBs may result in vessel occlusion and growth inhibitory effects in the subcutaneous tumors of nude mice.

Reversal of multidrug resistance by stimuli-responsive drug delivery systems for therapy of tumor

Multidrug resistance (MDR) is a major obstacle to successful cancer therapy, especially for chemotherapy. The new drug delivery system (DDS) provides promising approaches to reverse MDR, for which the poor cellular uptake and insufficient intracellular drug release remain rate-limiting steps for reaching the drug concentration level within the therapeutic window. Stimulus-coupled drug delivery can control the drug-releasing pattern temporally and spatially, and improve the accumulation of chemotherapeutic agents at targeting sites. In this review, the applications of DDS which is responsive to different types of stimuli in MDR cancer therapy is introduced, and the design, construction, stimuli-sensitivity and the effect to reverse MDR of the stimuli-responsive DDS are discussed.

Micro- and nanobubbles: a versatile non-viral platform for gene delivery

Micro- and nanobubbles provide a promising non-viral strategy for ultrasound mediated gene delivery. Microbubbles are spherical gas-filled structures with a mean diameter of 1-8 μm, characterised by their core-shell composition and their ability to circulate in the bloodstream following intravenous injection. They undergo volumetric oscillations or acoustic cavitation when insonified by ultrasound and, most importantly, they are able to resonate at diagnostic frequencies. It is due to this behaviour that microbubbles are currently being used as ultrasound contrast agents, but their use in therapeutics is still under investigation. For example, microbubbles could play a role in enhancing gene delivery to cells: when combined with clinical ultrasound exposure, microbubbles are able to favour gene entry into cells by cavitation. Two different delivery strategies have been used to date: DNA can be co-administered with the microbubbles (i.e. the contrast agent) or 'loaded' in purposed-built bubble systems - indeed a number of different technological approaches have been proposed to associate genes within microbubble structures. Nanobubbles, bubbles with sizes in the nanometre order of magnitude, have also been developed with the aim of obtaining more efficient gene delivery systems. Their small sizes allow the possibility of extravasation from blood vessels into the surrounding tissues and ultrasound-targeted site-specific release with minimal invasiveness. In contrast, microbubbles, due to their larger sizes, are unable to extravasate, thus and their targeting capacity is limited to specific antigens present within the vascular lumen. This review provides an overview of the use of microbubbles as gene delivery systems, with a specific focus on recent research into the development of nanosystems. In particular, ultrasound delivery mechanisms, formulation parameters, gene-loading approaches and the advantages of nanometric systems will be described.

Novel gene delivery systems

Gene therapy is an emerging field in medical and pharmaceutical sciences because of its potential in treating chronic diseases like cancer, viral infections, myocardial infarctions, and genetic disorders. Application of gene therapy is limited because of lack of suitable methods for proper introduction of genes into cells and therefore, this is an area of interest for most of the researchers. To achieve successful gene therapy, development of proper gene delivery systems could be one of the most important factors. Several nonviral and viral gene transfer methods have been developed. Even though the viral agents have a high transferring efficiency, they are difficult to handle due to their toxicity. To overcome the safety problems of the viral counterpart, several nonviral in vitro and in vivo gene delivery systems are developed. Out of these, the most promising and latest systems include polymer-based nonviral gene carriers, dendrimers, and physical means like electroporation, microinjection, etc., Shunning of possible immunogenicity and toxicity, and the feasibility of repeated administration are some of the merits of nonviral gene delivery systems over viral gene delivery. An ideal nonviral gene carrying system should possess all these merits without any compromise to its gene transferring efficiency. The viral gene delivery systems include lytic and nonlytic vectors for drug delivery. Inspite of its toxicity they are still preferred because of their long term expression, stability, and integrity. This review explores the recent developments and relevancy of the novel gene delivery systems in gene therapy.

Cytokines for the treatment of gastrointestinal cancers: clinical experience and new perspectives

INTRODUCTION

Cytokines are key mediators of the immune system and have been proposed as therapeutic agents against cancer, either as recombinant proteins, or as transgenes in gene therapy approaches. Stimulation of immune responses against cancer cells is an appealing method to treat tumors with high risk of relapse and systemic dissemination.

AREAS COVERED

We provide a critical overview of clinical trials involving the use of cytokines for the treatment of liver, colon and pancreatic cancers. Special attention has been paid to advances in the field of gene therapy and oncolytic viruses. The potential of new developments still in a pre-clinical stage is also discussed. We have revised public sources of information (PubMed, US National Institutes of Health clinical trials database) up to January 2013.

EXPERT OPINION

The complexity of the immune system and the unfavorable pharmacokinetic properties of cytokines limit the efficacy of these molecules as single agents for the treatment of cancer. Expression from gene therapy vectors, together with new methods of targeting and stabilization, may overcome these hurdles. We believe cytokines will play a crucial role as part of combined approaches, enhancing the action of adoptive cell immunotherapy, oncolytic viruses or biological therapies.

Sonoporation: mechanistic insights and ongoing challenges for gene transfer

Microbubbles first developed as ultrasound contrast agents have been used to assist ultrasound for cellular drug and gene delivery. Their oscillation behavior during ultrasound exposure leads to transient membrane permeability of surrounding cells, facilitating targeted local delivery. The increased cell uptake of extracellular compounds by ultrasound in the presence of microbubbles is attributed to a phenomenon called sonoporation. In this review, we summarize current state of the art concerning microbubble-cell interactions and cellular effects leading to sonoporation and its application for gene delivery. Optimization of sonoporation protocol and composition of microbubbles for gene delivery are discussed.