Changes in cell morphology due to plasma membrane wounding by acoustic cavitation

Ultrasound meets the cell membrane: for enhanced endocytosis and drug delivery

Endocytosis plays a crucial role in drug delivery for precision therapy. As a non-invasive and spatiotemporal-controllable stimulus, ultrasound (US) has been utilized for improving drug delivery efficiency due to its ability to enhance cell membrane permeability. When US meets the cell membrane, the well-known cavitation effect generated by US can cause various biophysical effects, facilitating the delivery of various cargoes, especially nanocarriers. The comprehension of recent progress in the biophysical mechanism governing the interaction between ultrasound and cell membranes holds significant implications for the broader scientific community, particularly in drug delivery and nanomedicine. This review will summarize the latest research results on the biological effects and mechanisms of US-enhanced cellular endocytosis. Moreover, the latest achievements in US-related biomedical applications will be discussed. Finally, challenges and opportunities of US-enhanced endocytosis for biomedical applications will be provided.

Landscape of Cellular Bioeffects Triggered by Ultrasound-Induced Sonoporation

Sonoporation is the process of transient pore formation in the cell membrane triggered by ultrasound (US). Numerous studies have provided us with firm evidence that sonoporation may assist cancer treatment through effective drug and gene delivery. However, there is a massive gap in the body of literature on the issue of understanding the complexity of biophysical and biochemical sonoporation-induced cellular effects. This study provides a detailed explanation of the US-triggered bioeffects, in particular, cell compartments and the internal environment of the cell, as well as the further consequences on cell reproduction and growth. Moreover, a detailed biophysical insight into US-provoked pore formation is presented. This study is expected to review the knowledge of cellular effects initiated by US-induced sonoporation and summarize the attempts at clinical implementation.

Vibropolyfection: coupling polymer-mediated gene delivery to mechanical stimulation to enhance transfection of adherent cells

Background

With the success of recent non-viral gene delivery-based COVID-19 vaccines, nanovectors have gained some public acceptance and come to the forefront of advanced therapies. Unfortunately, the relatively low ability of the vectors to overcome cellular barriers adversely affects their effectiveness. Scientists have thus been striving to develop ever more effective gene delivery vectors, but the results are still far from satisfactory. Therefore, developing novel strategies is probably the only way forward to bring about genuine change. Herein, we devise a brand-new gene delivery strategy to boost dramatically the transfection efficiency of two gold standard nucleic acid (NA)/polymer nanoparticles (polyplexes) in vitro.

Results

We conceived a device to generate milli-to-nanoscale vibrational cues as a function of the frequency set, and deliver vertical uniaxial displacements to adherent cells in culture. A short-lived high-frequency vibrational load (t = 5 min, f = 1,000 Hz) caused abrupt and extensive plasmalemma outgrowths but was safe for cells as neither cell proliferation rate nor viability was affected. Cells took about 1 hr to revert to quasi-naïve morphology through plasma membrane remodeling. In turn, this eventually triggered the mechano-activated clathrin-mediated endocytic pathway and made cells more apt to internalize polyplexes, resulting in transfection efficiencies increased from 10-to-100-fold. Noteworthy, these results were obtained transfecting three cell lines and hard-to-transfect primary cells.

Conclusions

In this work, we focus on a new technology to enhance the intracellular delivery of NAs and improve the transfection efficiency of non-viral vectors through priming adherent cells with a short vibrational stimulation. This study paves the way for capitalizing on physical cell stimulation(s) to significantly raise the effectiveness of gene delivery vectors in vitro and ex vivo.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01571-x.

Shock Waves Enhance Expression of Glycosphingolipid Tumor Antigen on Renal Cell Carcinoma: Dynamics of Physically Unmasking Hidden Intracellular Markers Independent of Gene-Signaling Pathways

Antigens associated with tumors have proven valuable in cancer immunotherapy. Their insufficient expression in the majority of tumors, however, limits their potential value as therapeutic markers. Aiming for a noninvasive approach applicable in clinical practice, we investigated the possibility of using focused shock waves to induce membrane expression of hidden intracellular tumor markers. Here, we studied the in vitro effect of a thousand focused shock waves at 16 MPa overpressure on the membrane expression of a cytosolic glycosphingolipid, monosialosyl-galactosyl-globoside (MSGG). Double-staining flow cytometry with propidium-iodide and monoclonal antibody RM1 revealed an immediate increase in MSGG expression on renal carcinoma cells (18% ± 0.5%) that reached its peak value (20.73% ± 0.4%) within one hour after the shock waves. The results of immunoelectron microscopy confirmed the incorporation of MSGG into newly formed cytosolic vesicles and their integration with the cell membrane. Based on the enzymatic nature of MSGG production that is not controlled directly by genes, the immediate upregulation of MSGG membrane expression implies that a chain of mechanochemical events affecting subcellular structures are responsible for the shock-wave-induced antigenic modification. Physically unmasking hidden tumor antigens and enhancing their expression by focused shock waves presents a potential noninvasive method of boosting tumor immunogenicity as a theranostic strategy in cancer immunotherapy.

Effect of 1-MHz ultrasound on the proinflammatory interleukin-6 secretion in human keratinocytes

Keratinocytes, the main cell type of the skin, are one of the most exposed cells to environmental factors, providing a first defence barrier for the host and actively participating in immune response. In fact, keratinocytes express pattern recognition receptors that interact with pathogen associated molecular patterns and damage associated molecular patterns, leading to the production of cytokines and chemokines, including interleukin (IL)-6. Herein, we investigated whether mechanical energy transported by low intensity ultrasound (US) could generate a mechanical stress able to induce the release of inflammatory cytokine such IL-6 in the human keratinocyte cell line, HaCaT. The extensive clinical application of US in both diagnosis and therapy suggests the need to better understand the related biological effects. Our results point out that US promotes the overexpression and secretion of IL-6, associated with the activation of nuclear factor-κB (NF-κB). Furthermore, we observed a reduced cell viability dependent on exposure parameters together with alterations in membrane permeability, paving the way for further investigating the molecular mechanisms related to US exposure.

Comprehensive review on ultrasound-responsive theranostic nanomaterials: mechanisms, structures and medical applications

The field of theranostics has been rapidly growing in recent years and nanotechnology has played a major role in this growth. Nanomaterials can be constructed to respond to a variety of different stimuli which can be internal (enzyme activity, redox potential, pH changes, temperature changes) or external (light, heat, magnetic fields, ultrasound). Theranostic nanomaterials can respond by producing an imaging signal and/or a therapeutic effect, which frequently involves cell death. Since ultrasound (US) is already well established as a clinical imaging modality, it is attractive to combine it with rationally designed nanoparticles for theranostics. The mechanisms of US interactions include cavitation microbubbles (MBs), acoustic droplet vaporization, acoustic radiation force, localized thermal effects, reactive oxygen species generation, sonoluminescence, and sonoporation. These effects can result in the release of encapsulated drugs or genes at the site of interest as well as cell death and considerable image enhancement. The present review discusses US-responsive theranostic nanomaterials under the following categories: MBs, micelles, liposomes (conventional and echogenic), niosomes, nanoemulsions, polymeric nanoparticles, chitosan nanocapsules, dendrimers, hydrogels, nanogels, gold nanoparticles, titania nanostructures, carbon nanostructures, mesoporous silica nanoparticles, fuel-free nano/micromotors.

Optimization of the delivery of molecules into lymph nodes using a lymphatic drug delivery system with ultrasound

Conventional treatment for lymph node (LN) metastasis such as systemic chemotherapy have notable disadvantages that lead to the development of unwanted effects. Previously, we have reported the lymphatic administration of drugs into metastatic LNs using a lymphatic drug delivery system (LDDS). However, prior studies of the LDDS have not attempted to optimize the conditions for efficient drug delivery. Here, we investigated the influence of several factors on the efficiency of drug delivery by a LDDS in conjunction with ultrasound (US). First, the effect of the injection rate on delivery efficiency was evaluated. Fluorescent molecules injected into an upstream LN were delivered more effectively into a downstream LN when a lower injection rate was used. Second, the influence of molecular weight on drug delivery efficiency was determined. We found that molecules with a molecular weight >10,000 were poorly delivered into the LN. Finally, we assessed whether the administration route affected the delivery efficiency. We found that the delivery efficiency was higher when molecules were administered into an upstream LN that was close to the target LN. These findings revealed the importance of a drug's physical properties if it is to be administered by LDDS to treat LN metastasis.

Non-localized Increase in Lipid Content and Striation Pattern Formation Characterize the Sonoporated Plasma Membrane

Eukaryotic cells can survive sonoporation and repair their plasma membrane wounds. However, it is not clear how the repaired plasma membranes will differ from the intact ones. To answer this question, we used high-resolution confocal microscopy and scanning electron microscopy to study plasma membrane lipid alterations induced by sonoporation. First, we found that the wound-induced increase in membrane lipid content was not limited to the sonoporation sites. The degree of lipid increase was dependent on pore distance, calcium influx and pore size. Second, we observed interesting lipid striation patterns on the sonoporated plasma membranes. This patterning effect was reversible in the cell subjected to small-scale sonoporation and could be recognized using digital image orientation analysis. Third, we showed that actin stress fibers underneath the plasma membrane hindered the addition and the protrusion of lipids to produce the patterning effect. Our findings demonstrated that the sonoporated and repaired plasma membranes have distinct lipid distribution characteristics.

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.

Intracellular Delivery by Membrane Disruption: Mechanisms, Strategies, and Concepts

Intracellular delivery is a key step in biological research and has enabled decades of biomedical discoveries. It is also becoming increasingly important in industrial and medical applications ranging from biomanufacture to cell-based therapies. Here, we review techniques for membrane disruption-based intracellular delivery from 1911 until the present. These methods achieve rapid, direct, and universal delivery of almost any cargo molecule or material that can be dispersed in solution. We start by covering the motivations for intracellular delivery and the challenges associated with the different cargo types-small molecules, proteins/peptides, nucleic acids, synthetic nanomaterials, and large cargo. The review then presents a broad comparison of delivery strategies followed by an analysis of membrane disruption mechanisms and the biology of the cell response. We cover mechanical, electrical, thermal, optical, and chemical strategies of membrane disruption with a particular emphasis on their applications and challenges to implementation. Throughout, we highlight specific mechanisms of membrane disruption and suggest areas in need of further experimentation. We hope the concepts discussed in our review inspire scientists and engineers with further ideas to improve intracellular delivery.

Effect of laser fluence, nanoparticle concentration and total energy input per cell on photoporation of cells

Intracellular delivery of molecules can be increased by laser-exposure of carbon black nanoparticles to cause photoporation of the cells. Here we sought to determine effects of multiple laser exposure parameters on intracellular uptake and cell viability with the goal of determining a single unifying parameter that predicts cellular bioeffects. DU145 human prostate cancer cells in suspension with nanoparticles were exposed to near-infrared nanosecond laser pulses over a range of experimental conditions. Increased bioeffects (i.e., uptake and viability loss determined by flow cytometry) were seen when increasing laser fluence, number of pulses and nanoparticle concentration, and decreasing cell concentration. Bioeffects caused by different combinations of these four parameters were generally predicted by their cumulative energy input per cell, which served as a unifying parameter. This indicates that photoporation depends on what appears to be the cumulative effect of multiple cell-nanoparticle interactions from neighboring nanoparticles during a series of laser pulses.

Prolonging pulse duration in ultrasound-mediated gene delivery lowers acoustic pressure threshold for efficient gene transfer to cells and small animals

While ultrasound-mediated gene delivery (UMGD) has been accomplished using high peak negative pressures (PNPs) of 2 MPa or above, emerging research showed that this may not be a requirement for microbubble (MB) cavitation. Thus, we investigated lower-pressure conditions close to the MB inertial cavitation threshold and focused towards further increasing gene transfer efficiency and reducing associated cell damage. We created a matrix of 21 conditions (n = 3/cond.) to test in HEK293T cells using pulse durations spanning 18 μs-36 ms and PNPs spanning 0.5-2.5 MPa. Longer pulse duration conditions yielded significant increase in transgene expression relative to sham with local maxima between 20 J and 100 J energy curves. A similar set of 17 conditions (n = 4/cond.) was tested in mice using pulse durations spanning 18 μs-22 ms and PNPs spanning 0.5-2.5 MPa. We observed local maxima located between 1 J and 10 J energy curves in treated mice. Of these, several low pressure conditions showed a decrease in ALT and AST levels while maintaining better or comparable expression to our positive control, indicating a clear benefit to allow for effective transfection with minimized tissue damage versus the high-intensity control. Our data indicates that it is possible to eliminate the requirement of high PNPs by prolonging pulse durations for effective UMGD in vitro and in vivo, circumventing the peak power density limitations imposed by piezo-materials used in US transducers. Overall, these results demonstrate the advancement of UMGD technology for achieving efficient gene transfer and potential scalability to larger animal models and human application.

Photoporation Using Carbon Nanotubes for Intracellular Delivery of Molecules and Its Relationship to Photoacoustic Pressure

Exposure of carbon-black (CB) nanoparticles to near-infrared nanosecond-pulsed laser energy can cause efficient intracellular delivery of molecules by photoporation. Here, cellular bioeffects of multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) are compared to those of CB nanoparticles. In DU145 prostate-cancer cells, photoporation using CB nanoparticles transitions from (i) cells with molecular uptake to (ii) nonviable cells to (iii) fragmented cells with increasing laser fluence, as seen previously. In contrast, photoporation with MWCNTs causes uptake and, at higher fluence, fragmentation, but does not generate nonviable cells, and SWCNTs show little evidence of bioeffects, except at extreme laser conditions, which generate nonviable cells and fragmentation, but no significant uptake. These different behaviors cannot be explained by photoacoustic pressure output from the particles. All particle types emit a single, ≈100 ns, mostly positive-pressure pulse that increases in amplitude with laser fluence. Different particle types emit different peak pressures, which are highest for SWCNTs, followed by CB nanoparticles and then MWCNTs, which does not correlate with cellular bioeffects between different particle types. This study concludes that cellular bioeffects depend strongly on the type of carbon nanoparticle used during photoporation and that photoacoustic pressure is unlikely to play a direct mechanistic role in the observed bioeffects.

Mechanistic understanding the bioeffects of ultrasound-driven microbubbles to enhance macromolecule delivery

Ultrasound-driven microbubbles can trigger reversible membrane perforation (sonoporation), open interendothelial junctions and stimulate endocytosis, thereby providing a temporary and reversible time-window for the delivery of macromolecules across biological membranes and endothelial barriers. This time-window is related not only to cavitation events, but also to biological regulatory mechanisms. Mechanistic understanding of the interaction between cavitation events and cells and tissues, as well as the subsequent cellular and molecular responses will lead to new design strategies with improved efficacy and minimized side effects. Recent important progress on the spatiotemporal characteristics of sonoporation, cavitation-induced interendothelial gap and endocytosis, and the spatiotemporal bioeffects and the preliminary biological mechanisms in cavitation-enhanced permeability, has been made. On the basis of the summary of this research progress, this Review outlines the underlying bioeffects and the related biological regulatory mechanisms involved in cavitation-enhanced permeability; provides a critical commentary on the future tasks and directions in this field, including developing a standardized methodology to reveal mechanism-based bioeffects in depth, and designing biology-based treatment strategies to improve efficacy and safety. Such mechanistic understanding the bioeffects that contribute to cavitation-enhanced delivery will accelerate the translation of this approach to the clinic.

Enhancement of Angiogenesis by Ultrasound-Targeted Microbubble Destruction Combined with Nuclear Localization Signaling Peptides in Canine Myocardial Infarction

Objective

This study aimed to develop a gene delivery system using ultrasound-targeted microbubbles destruction (UTMD) combined with nuclear localization signal (NLS) and investigate its efficacy and safety for therapeutic angiogenesis in canine myocardial infarction (MI) model.

Methods

Fifty MI dogs were randomly divided into 5 groups and transfected with Ang-1 gene plasmid: (i) group A: only injection of microbubbles and Ang-1 plasmid; (ii) group B: only UTMD mediated gene transfection; (iii) group C: UTMD combined with classical NLS mediated gene transfection; (iv) group D: UTMD combined with mutational NLS mediated transfection; and (v) group E: UTMD combined with classical NLS in the presence of a nucleus transport blocker. The mRNA and protein expression of Ang-1 gene, microvessel density (MVD) cardiac troponin I (cTnI), and cardiac function were determined after transfection.

Results

The expression of mRNA and protein of Ang-1 gene in group C was significantly higher than that of the other groups (all P < 0.01). The MVD of group C was 10.2-fold of group A and 8.1-fold of group E (P < 0.01). The cardiac function in group C was significant improvement without cTnI rising.

Conclusions

The gene delivery system composed of UTMD and NLS is efficient and safe.

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.

Efficient gene therapy with a combination of ultrasound‑targeted microbubble destruction and PEI/DNA/NLS complexes

Current strategies of gene transfection are not efficient at achieving a notable therapeutic effect. The aim of the present study was to combine ultrasound‑targeted microbubble destruction (UTMD) with a polyethylenimine/pEGFP‑N3 plasmid/nuclear localization sequence (PEI/DNA/NLS) complex gene delivery system, and evaluate the transfection efficiency of enhanced green fluorescent protein (EGFP) gene delivery to 293T cells using this system. The formation of PEI/DNA/NLS complexes and the protective effects of PEI/NLS were verified by gel electrophoresis. Solutions consisting of the plasmid alone, PEI/DNA complexes, PEI/DNA/NLS complexes, UTMD+DNA, UTMD+PEI/DNA complexes, and UTMD+PEI/DNA/NLS complexes were transduced into 293T cells via ultrasound irradiation. The expression of GFP was observed using an inverted microscope and transfection efficiency was detected by flow cytometry following 24 h incubation in vitro. Cell activity was detected using a Cell Counting kit (CCK)‑8 assay. Gel electrophoresis confirmed the formation of PEI/DNA/NLS complexes and demonstrated that PEI/NLS exhibited protective effects on plasmid integrity for a limited time. Inverted microscope observations revealed that a greater GFP signal was observed with the combined action of PEI/DNA/NLS complexes with UTMD, and flow cytometry analysis demonstrated the highest level of transfection efficiency in this group. In addition, the viability of the cells detected by CCK‑8 and treated with PEI/DNA/NLS complexes with UTMD was >80%. In conclusion, the combination of UTMD and PEI/DNA/NLS complexes was highly effective for the efficient transfection of 293T cells without causing excessive cell damage. This method may provide a novel and effective gene transduction system to be applied in clinical treatments.

Phospholipid Capped Mesoporous Nanoparticles for Targeted High Intensity Focused Ultrasound Ablation

The mechanical effects of cavitation can be effective for therapy but difficult to control, thus potentially leading to off-target side effects in patients. While administration of ultrasound active agents such as fluorocarbon microbubbles and nanodroplets can locally enhance the effects of high intensity focused ultrasound (HIFU), it has been challenging to prepare ultrasound active agents that are small and stable enough to accumulate in tumors and internalize into cancer cells. Here, this paper reports the synthesis of 100 nm nanoparticle ultrasound agents based on phospholipid-coated, mesoporous, hydrophobically functionalized silica nanoparticles that can internalize into cancer cells and remain acoustically active. The ultrasound agents produce bubbles when subjected to short HIFU pulses (≈6 µs) with peak negative pressure as low as ≈7 MPa and at particle concentrations down to 12.5 µg mL-1 (7 × 109 particles mL-1 ). Importantly, ultrasound agents are effectively uptaken by cancer cells without cytotoxic effects, but HIFU insonation causes destruction of the cells by the acoustically generated bubbles, as demonstrated by (2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) and lactate dehydrogenase assays and flow cytometry. Finally, it is showed that the HIFU dose required to effectively eliminate cancer cells in the presence of ultrasound agents causes only a small temperature increase of ≈3.5 °C.

Stably engineered nanobubbles and ultrasound - An effective platform for enhanced macromolecular delivery to representative cells of the retina

Herein we showcase the potential of ultrasound-responsive nanobubbles in enhancing macromolecular permeation through layers of the retina, ultimately leading to significant and direct intracellular delivery; this being effectively demonstrated across three relevant and distinct retinal cell lines. Stably engineered nanobubbles of a highly homogenous and echogenic nature were fully characterised using dynamic light scattering, B-scan ultrasound and transmission electron microscopy (TEM). The nanobubbles appeared as spherical liposome-like structures under TEM, accompanied by an opaque luminal core and darkened corona around their periphery, with both features indicative of efficient gas entrapment and adsorption, respectively. A nanobubble +/- ultrasound sweeping study was conducted next, which determined the maximum tolerated dose for each cell line. Detection of underlying cellular stress was verified using the biomarker heat shock protein 70, measured before and after treatment with optimised ultrasound. Next, with safety to nanobubbles and optimised ultrasound demonstrated, each human or mouse-derived cell population was incubated with biotinylated rabbit-IgG in the presence and absence of ultrasound +/- nanobubbles. Intracellular delivery of antibody in each cell type was then quantified using Cy3-streptavidin. Nanobubbles and optimised ultrasound were found to be negligibly toxic across all cell lines tested. Macromolecular internalisation was achieved to significant, yet varying degrees in all three cell lines. The results of this study pave the way towards better understanding mechanisms underlying cellular responsiveness to ultrasound-triggered drug delivery in future ex vivo and in vivo models of the posterior eye.

Investigation of Microbubble Cavitation-Induced Calcein Release from Cells In Vitro

In the present study, microbubble (MB) cavitation signal analysis was performed together with calcein release evaluation in both pressure and exposure duration domains of the acoustic field. A passive cavitation detection system was used to simultaneously measure MB scattering and attenuation signals for subsequent extraction efficiency relative to MB cavitation activity. The results indicate that the decrease in the efficiency of extraction of calcein molecules from Chinese hamster ovary cells, as well as cell viability, is associated with MB cavitation activity and can be accurately predicted using inertial cavitation doses up to 0.18 V × s (R² > 0.9, p < 0.0001). No decrease in additional calcein release or cell viability was observed after complete MB sonodestruction was achieved. This indicates that the optimal exposure duration within which maximal sono-extraction efficiency is obtained coincides with the time necessary to achieve complete MB destruction. These results illustrate the importance of MB inertial cavitation in the sono-extraction process. To our knowledge, this study is the first to (i) investigate small molecule extraction from cells via sonoporation and (ii) relate the extraction process to the quantitative characteristics of MB cavitation acoustic spectra.

Sonoporation: Concept and Mechanisms

Contrast agents for ultrasound are now routinely used for diagnosis and imaging. In recent years, new promising possibilities for targeted drug delivery have been proposed that can be realized by using the microbubble composing ultrasound contrast agents (UCAs). The microbubbles can carry drugs and selectively adhere to specific sites in the human body. This capability, in combination with the effect known as sonoporation, provides great possibilities for localized drug delivery. Sonoporation is a process in which ultrasonically activated UCAs, pulsating nearby biological barriers (cell membrane or endothelial layer), increase their permeability and thereby enhance the extravasation of external substances. In this way drugs and genes can be delivered inside individual cells without serious consequences for the cell viability. Sonoporation has been validated both in-vitro using cell cultures and in-vivo in preclinical studies. However, today, the mechanisms by which molecules cross the biological barriers remain unrevealed despite a number of proposed theories. This chapter will provide a survey of the current studies on various hypotheses regarding the routes by which drugs are incorporated into cells or across the endothelial layer and possible associated microbubble acoustic phenomena.

Membrane blebbing as a recovery manoeuvre in site-specific sonoporation mediated by targeted microbubbles

Site-specific perforation of the plasma membrane can be achieved through ultrasound-triggered cavitation of a single microbubble positioned adjacent to the cell. However, for this perforation approach (sonoporation), the recovery manoeuvres invoked by the cell are unknown. Here, we report new findings on how membrane blebbing can be a recovery manoeuvre that may take place in sonoporation episodes whose pores are of micrometres in diameter. Each sonoporation site was created using a protocol involving single-shot ultrasound exposure (frequency: 1 MHz; pulse length: 30 cycles; peak negative pressure: 0.45 MPa) which triggered inertial cavitation of a single targeted microbubble (diameter: 1-5 µm). Over this process, live confocal microscopy was conducted in situ to monitor membrane dynamics, model drug uptake kinetics and cytoplasmic calcium ion (Ca(2+)) distribution. Results show that blebbing would occur at a recovering sonoporation site after its resealing, and it may emerge elsewhere along the membrane periphery. The bleb size was correlated with the pre-exposure microbubble diameter, and 99% of blebbing cases at sonoporation sites were inflicted by microbubbles larger than 1.5 µm diameter (analysed over 124 sonoporation episodes). Blebs were not observed at irreversible sonoporation sites or when sonoporation site repair was inhibited via extracellular Ca(2+) chelation. Functionally, the bleb volume was found to serve as a buffer compartment to accommodate the cytoplasmic Ca(2+) excess brought about by Ca(2+) influx during sonoporation. These findings suggest that membrane blebbing would help sonoporated cells restore homeostasis.

Apoptosis Induced by Microbubble-Assisted Acoustic Cavitation in K562 Cells: The Predominant Role of the Cyclosporin A-Dependent Mitochondrial Permeability Transition Pore

Acoustic cavitation of microbubbles has been described as inducing tumor cell apoptosis that is partly associated with mitochondrial dysfunction; however, the exact mechanisms have not been fully characterized. Here, low-intensity pulsed ultrasound (1 MHz, 0.3-MPa peak negative pressure, 10% duty cycle and 1-kHz pulse repetition frequency) was applied to K562 chronic myelogenous leukemia cells for 1 min with 10% (v/v) SonoVue microbubbles. After ultrasound exposure, the apoptotic index was determined by flow cytometry with annexin V-fluorescein isothiocyanate/propidium iodide. In addition, mitochondrial membrane potential (ΔΨm) was determined with the JC-1 assay. Translocation of apoptosis-associated protein cytochrome c was evaluated by Western blotting. We found that microbubble-assisted acoustic cavitation can increase the cellular apoptotic index, mitochondrial depolarization and cytochrome c release in K562 cells, compared with ultrasound treatment alone. Furthermore, mitochondrial dysfunction and apoptosis were significantly inhibited by cyclosporin A, a classic inhibitor of the mitochondrial permeability transition pore; however, the inhibitor of Bax protein, Bax-inhibiting peptide, could not suppress these effects. Our results suggest that mitochondrial permeability transition pore opening is involved in mitochondrial dysfunction after exposure to microbubble-assisted acoustic cavitation. Moreover, the release of cytochrome c from the mitochondria is dependent on cyclosporin A-sensitive mitochondrial permeability transition pore opening, but not formation of the Bax-voltage dependent anion channel complex or Bax oligomeric pores. These data provide more insight into the mechanisms underlying mitochondrial dysfunction induced by acoustic cavitation and can be used as a basis for therapy.

Treatment of hepatic carcinoma by low-frequency ultrasound and microbubbles: A case report

In vitro and in vivo studies have identified that low-frequency ultrasound (US) and microbubbles (MBs) mediate tumor inhibitory effects. However, the application of US in the clinical setting remains unclear. The aim of the present study was to investigate the clinically therapeutic effect of 20 kHz US in combination with MBs for the treatment of hepatic carcinoma. A 71-year-old male with a hepatic malignant tumor was admitted to Nantong University Affiliated Nantong Tumor Hospital (Nantong, China). The patient was subsequently sonicated with 20 kHz US and MBs over a period of five days. The low-frequency US parameters were set at 20 kHz, 2 W/cm², duty cycle 40% (on 2 sec, off 3 sec) for a duration of 5 min each day for a total of five days. Computed tomography (CT), contrast-enhanced US (CEUS) and carbohydrate antigen 19-9 (CA19-9) tests were performed to evaluate the therapeutic effects. Although the tumor size increased marginally on CT from 5.4 to 5.6 cm after US treatment, the intensity and enhanced-areas on the CT scans and CEUS decreased. The abdominal lymph node decreased in size, from 2.2 to 1.9 cm, and CA19-9 levels decreased from the pretreatment value of 2,007 to 734 U/ml. Therapy with low-frequency US combined with MBs may exhibit an antivasculature effect and may be used as a palliative treatment for patients with unresectable hepatic malignant tumors.

Effects of therapeutic ultrasound on the nucleus and genomic DNA

In recent years, data have been accumulating on the ability of ultrasound to affect at a distance inside the cell. Previous conceptions about therapeutic ultrasound were mainly based on compromising membrane permeability and triggering some biochemical reactions. However, it was shown that ultrasound can access deep to the nuclear territory resulting in enhanced macromolecular localization as well as alterations in gene and protein expression. Recently, we have reported on the occurrence of DNA double-strand breaks in different human cell lines exposed to ultrasound in vitro with some insight into the subsequent DNA damage response and repair pathways. The impact of these observed effects again sways between extremes. It could be advantageous if employed in gene therapy, wound and bone fracture-accelerated healing to promote cellular proliferation, or in cancer eradication if the DNA lesions would culminate in cell death. However, it could be a worrying sign if they were penultimate to further cellular adaptations to stresses and thus shaking the safety of ultrasound application in diagnosis and therapy. In this review, an overview of the rationale of therapeutic ultrasound and the salient knowledge on ultrasound-induced effects on the nucleus and genomic DNA will be presented. The implications of the findings will be discussed hopefully to provide guidance to future ultrasound research.

Ultrasonically triggered drug delivery: breaking the barrier

The adverse side-effects of chemotherapy can be minimized by delivering the therapeutics in time and space to only the desired target site. Ultrasound offers one fairly non-invasive method of accomplishing such precise delivery because its energy can disrupt nanosized containers that are designed to sequester the drug until the ultrasonic event. Such containers include micelles, liposomes and solid nanoparticles. Conventional micelles and liposomes are less acoustically sensitive to ultrasound because the strongest forces associated with ultrasound are generated by gas-liquid interfaces, which both of these conventional constructs lack. Acoustically activated carriers often incorporate a gas phase, either actively as preformed bubbles, or passively such as taking advantage of dissolved gasses that form bubbles upon insonation. Newer concepts include using liquids that form gas when insonated. This review focuses on the ultrasonically activated delivery of therapeutics from micelles, liposomes and solid particles. In vitro and in vivo results are summarized and discussed. Novel structural concepts from micelles and liposomes are presented. Mechanisms of ultrasonically activated release are discussed. The future of ultrasound in drug delivery is envisioned.

The use of ultrasound to release chemotherapeutic drugs from micelles and liposomes

Several drug delivery systems have been investigated to reduce the side effects of chemotherapy by encapsulating the therapeutic agent in a nanosized carrier until it reaches the tumor site. Many of these particles are designed to be responsive to the mechanical and thermal perturbations delivered by ultrasound. Once the nanoparticle reaches the desired location, ultrasound is applied to release the chemotherapy drug only in the vicinity of the targeted (cancer) site, thus avoiding any detrimental interaction with healthy cells in the body. Studies using liposomes and micelles have shown promising results in this area, as these nanoparticles with simple, yet effective structures, showed high efficiency as drug delivery vehicles both in vitro and in vivo. This article reviews the design and application of two novel nanosized chemotherapeutic carriers (i.e. micelles and liposomes) intended to be actuated by ultrasound.

Understanding ultrasound induced sonoporation: definitions and underlying mechanisms

In the past two decades, research has underlined the potential of ultrasound and microbubbles to enhance drug delivery. However, there is less consensus on the biophysical and biological mechanisms leading to this enhanced delivery. Sonoporation, i.e. the formation of temporary pores in the cell membrane, as well as enhanced endocytosis is reported. Because of the variety of ultrasound settings used and corresponding microbubble behavior, a clear overview is missing. Therefore, in this review, the mechanisms contributing to sonoporation are categorized according to three ultrasound settings: i) low intensity ultrasound leading to stable cavitation of microbubbles, ii) high intensity ultrasound leading to inertial cavitation with microbubble collapse, and iii) ultrasound application in the absence of microbubbles. Using low intensity ultrasound, the endocytotic uptake of several drugs could be stimulated, while short but intense ultrasound pulses can be applied to induce pore formation and the direct cytoplasmic uptake of drugs. Ultrasound intensities may be adapted to create pore sizes correlating with drug size. Small molecules are able to diffuse passively through small pores created by low intensity ultrasound treatment. However, delivery of larger drugs such as nanoparticles and gene complexes, will require higher ultrasound intensities in order to allow direct cytoplasmic entry.

Single-site sonoporation disrupts actin cytoskeleton organization

Sonoporation is based upon an ultrasound-microbubble cavitation routine that physically punctures the plasma membrane on a transient basis. During such a process, the actin cytoskeleton may be disrupted in tandem because this network of subcellular filaments is physically interconnected with the plasma membrane. Here, by performing confocal fluorescence imaging of single-site sonoporation episodes induced by ultrasound-triggered collapse of a single targeted microbubble, we directly observed immediate rupturing of filamentary actin (F-actin) at the sonoporation site (cell type: ZR-75-30; ultrasound frequency: 1 MHz; peak negative pressure: 0.45 MPa; pulse duration: 30 cycles; bubble diameter: 2-4 µm). Also, through conducting a structure tensor analysis, we observed further disassembly of the F-actin network over the next 60 min after the onset of sonoporation. The extent of F-actin disruption was found to be more substantial in cells with higher uptake of sonoporation tracer. Commensurate with this process, cytoplasmic accumulation of globular actin (G-actin) was evident in sonoporated cells, and in turn the G-actin : F-actin ratio was increased in a trend similar to drug-induced (cytochalasin D) actin depolymerization. These results demonstrate that sonoporation is not solely a membrane-level phenomenon: organization of the actin cytoskeleton is concomitantly perturbed.

Unraveling the caspase-mediated mechanism for phloroglucinol-encapsulated starch biopolymer against the breast cancer cell line MDA-MB-231

The main objective of the study is to decipher the mechanism underlying the anticancer activity of phloroglucinol-encapsulated starch biopolymer against the breast cancer cell line MDA-MB-231.

Membrane perforation and recovery dynamics in microbubble-mediated sonoporation

Transient sonoporation can essentially be epitomized by two fundamental processes: acoustically induced membrane perforation and its subsequent resealing. To provide insight into these processes, this article presents a new series of direct evidence on the membrane-level dynamics during and after an episode of sonoporation. Our direct observations were obtained from anchored fetal fibroblasts whose membrane topography was imaged in situ using real-time confocal microscopy. To facilitate controlled sonoporation at the single-cell level, microbubbles that can passively adhere to the cell membrane were first introduced at a 1:1 cell-to-bubble ratio. Single-pulse ultrasound exposure (1-MHz frequency, 10-cycle pulse duration, 0.85-MPa peak negative pressure in situ) was then applied to trigger microbubble pulsation/collapse, which, in turn, instigated membrane perforation. With this protocol, five membrane-level phenomena were observed: (i) localized perforation of the cell membrane was synchronized with the instant of ultrasound pulsing; (ii) perforation sites with temporal peak area <30 μm(2) were resealed successfully; (iii) during recovery, a thickened pore rim emerged, and its temporal progression corresponded with the pore closure action; (iv) membrane resealing, if successful, would generally be completed within 1 min of the onset of sonoporation, and the resealing time constant was estimated to be below 20 s; (v) membrane resealing would fail for overly large pores (>100 μm(2)) or in the absence of extracellular calcium ions. These findings serve to underscore the spatiotemporal complexity of membrane-level dynamics in sonoporation.

Physical methods for intracellular delivery: practical aspects from laboratory use to industrial-scale processing

Effective intracellular delivery is a significant impediment to research and therapeutic applications at all processing scales. Physical delivery methods have long demonstrated the ability to deliver cargo molecules directly to the cytoplasm or nucleus, and the mechanisms underlying the most common approaches (microinjection, electroporation, and sonoporation) have been extensively investigated. In this review, we discuss established approaches, as well as emerging techniques (magnetofection, optoinjection, and combined modalities). In addition to operating principles and implementation strategies, we address applicability and limitations of various in vitro, ex vivo, and in vivo platforms. Importantly, we perform critical assessments regarding (1) treatment efficacy with diverse cell types and delivered cargo molecules, (2) suitability to different processing scales (from single cell to large populations), (3) suitability for automation/integration with existing workflows, and (4) multiplexing potential and flexibility/adaptability to enable rapid changeover between treatments of varied cell types. Existing techniques typically fall short in one or more of these criteria; however, introduction of micro-/nanotechnology concepts, as well as synergistic coupling of complementary method(s), can improve performance and applicability of a particular approach, overcoming barriers to practical implementation. For this reason, we emphasize these strategies in examining recent advances in development of delivery systems.

Sonoporation as a cellular stress: induction of morphological repression and developmental delays

For sonoporation to be established as a drug/gene delivery paradigm, it is essential to account for the biological impact of this membrane permeation strategy on living cells. Here we provide new insight into the cellular impact of sonoporation by demonstrating in vitro that this way of permeating the plasma membrane may inadvertently induce repressive cellular features even while enhancing exogenous molecule uptake. Both suspension-type (HL-60) and monolayer (ZR-75-30) cells were considered in this investigation, and they were routinely exposed to 1-MHz pulsed ultrasound (pulse length, 100 cycles; pulse repetition frequency, 1 kHz; exposure period, 60 s) with calibrated field profile (spatial-averaged peak negative pressure, 0.45 MPa) and in the presence of microbubbles (cell:bubble ratio, 10:1). The post-exposure morphology of sonoporated cells (identified as those with calcein internalization) was examined using confocal microscopy, and their cell cycle progression kinetics were analyzed using flow cytometry. Results show that for both cell types investigated, sonoporated cells exhibited membrane shrinkage and intra-cellular lipid accumulation over a 2-h period. Also, as compared with normal cells, the deoxyribonucleic acid synthesis duration of sonoporated cells was significantly lengthened, indicative of a delay in cell cycle progression. These features are known to be characteristics of a cellular stress response, suggesting that sonoporation indeed constitutes as a stress to living cells. This issue may need to be addressed in optimizing sonoporation for drug/gene delivery purposes. On the other hand, it raises opportunities for developing other therapeutic applications via sonoporation.

Crucial factors and emerging concepts in ultrasound-triggered drug delivery

Time and space controlled drug delivery still remains a huge challenge in medicine. A novel approach that could offer a solution is ultrasound guided drug delivery. “Ultrasonic drug delivery” is often based on the use of small gas bubbles (so-called microbubbles) that oscillate and cavitate upon exposure to ultrasound waves. Some microbubbles are FDA approved contrast agents for ultrasound imaging and are nowadays widely investigated as promising drug carriers. Indeed, it has been observed that upon exposure to ultrasound waves, microbubbles may (a) release the encapsulated drugs and (b) simultaneously change the structure of the cell membranes in contact with the microbubbles which may facilitate drug entrance into cells. This review aims to highlight (a) major factors known so far which affect ultrasonic drug delivery (like the structure of the microbubbles, acoustic settings, etc.) and (b) summarizes the recent preclinical progress in this field together with a number of promising new concepts and applications.

Potential and problems in ultrasound-responsive drug delivery systems

Ultrasound is an important local stimulus for triggering drug release at the target tissue. Ultrasound-responsive drug delivery systems (URDDS) have become an important research focus in targeted therapy. URDDS include many different formulations, such as microbubbles, nanobubbles, nanodroplets, liposomes, emulsions, and micelles. Drugs that can be loaded into URDDS include small molecules, biomacromolecules, and inorganic substances. Fields of clinical application include anticancer therapy, treatment of ischemic myocardium, induction of an immune response, cartilage tissue engineering, transdermal drug delivery, treatment of Huntington’s disease, thrombolysis, and disruption of the blood–brain barrier. This review focuses on recent advances in URDDS, and discusses their formulations, clinical application, and problems, as well as a perspective on their potential use in the future.

Ultrasound-triggered Release from Micelles

Ultrasound is an ideal trigger for site-actuated drug delivery because it can be focused through the skin to internal targets without surgery. Thermal or mechanical energy can be delivered via tissue heating or bubble cavitation, respectively. Bubble cavitation, which concentrates energy that can trigger drug release from carriers, occurs more readily at low frequencies and at bubble resonant frequencies. Other mechanical and physical consequences of cavitation are reviewed. Micelles are nanosized molecular assemblies of amphiphilic molecules that spontaneously form in aqueous solution and possess a hydrophobic core capable of sequestering hydrophobic drugs. Micelles have traditionally been used to increase the solubility of hydrophobic therapeutics for oral and intravenous administration. For ultrasonic drug delivery, polymeric micelles containing polyethylene oxide blocks are preferred because they have longer circulation time in vivo. Passive delivery occurs when micelles accumulate in tumor tissues that have malformed capillaries with porous walls. In active delivery targeting ligands are attached to the micelles, which directs their binding to specific cells. Actuated delivery occurs when ultrasound causes drug release from micelles and is attributed to bubble cavitation since the amount released correlates with acoustic signatures of cavitation. The mechanisms of ultrasonic drug release are discussed, including the prevalent theory that gas bubble cavitation events create high shear stress and shock waves that transiently perturb the structure of the micelles and allow drug to escape from the hydrophobic core. Ultrasound also perturbs cell membranes, rendering them more permeable to drug uptake. Tumors in rats and mice have been successfully treated using low-frequency ultrasound and chemotherapeutics in polymeric micelles. Ultrasonically activated drug delivery has great clinical potential.

Ultrasound-induced new cellular mechanism involved in drug resistance

The acoustic effects in a biological milieu offer several scenarios for the reversal of multidrug resistance. In this study, we have observed higher sensitivity of doxorubicin-resistant uterine sarcoma MES-SA/DX5 cells to ultrasound exposure compared to its parent counterpart MES-SA cells; however, the results showed that the acoustic irradiation was genotoxic and could promote neotic division in exposed cells that was more pronounced in the resistant variant. The neotic progeny, imaged microscopically 24 hr post sonication, could contribute in modulating the final cell survival when an apoptotic dose of doxorubicin was combined with ultrasound applied either simultaneously or sequentially in dual-treatment protocols. Depending on the time and order of application of ultrasound and doxorubicin in combination treatments, there was either desensitization of the parent cells or sensitization of the resistant cells to doxorubicin action.

Use of ultrasound in drug delivery systems: emphasis on experimental methodology and mechanisms

Recent studies have shown that ultrasound energy could be applied for targeting or controlling drug release. This new concept of therapeutic ultrasound combined with drugs has induced a great amount of interest in various medical fields. In this paper, several experimental systems are cited in which ultrasound is being utilized to evaluate new application of this modality. The mechanisms of ultrasound-mediated drug delivery are discussed in addition to the review of current advances in the use of ultrasound in systems involving research in cancer therapy, gene therapy, microbubbles and other drug delivery in vitro and in vivo experiments.

Encapsulating nanoemulsions inside eLiposomes for ultrasonic drug delivery

An eLiposome is a liposome encapsulating an emulsion nanodroplet and can be used for drug delivery. For example, therapeutic agents are encapsulated inside the eLiposomes, and the application of ultrasound can cause the emulsion droplet to change from liquid to gas, thus increasing the volume inside the vesicle and causing rupture and the release of the drug. In this research, two different methods were used to prepare eLiposomes. In the first method, emulsion droplets were made of perfluorohexane or perfluoropentane and stabilized with 1,2-dipalmitoyl-sn-glycero-3-phosphate. A layer of 1,2-dimyristoyl-sn-glycero-3-phosphocholine was dried in a round-bottomed flask. Then the emulsion suspension was added to the flask. As the suspension hydrated the phospholipids, they formed liposomes around the emulsions. In the second method, emulsions and liposomes were made separately, and then they were mixed using ultrasound. The advantage of this second method compared to the previous one is that eLiposomes can be made with fewer restrictions because of incompatible combinations of surfactants. Dynamic light scattering and transmission electron microscopy were used to measure the size of the emulsions, liposomes, and eLiposomes. The size of eLiposomes is appropriate for extravasation into tumors with malformed capillary beds. We hypothesize that ultrasound breaks open these eLiposomes. Both types of eLiposomes were constructed with folate attached via a poly(ethylene glycol) tether to induce endocytosis of the eLiposome. The latter eLiposomes were successfully used to deliver calcein as a model drug to HeLa cells.

HIFU for palliative treatment of pancreatic cancer

High intensity focused ultrasound (HIFU) is a novel non-invasive modality for ablation of various solid tumors including uterine fibroids, prostate cancer, hepatic, renal, breast and pancreatic tumors. HIFU therapy utilizes mechanical energy in the form of a powerful ultrasound wave that is focused inside the body to induce thermal and/or mechanical effects in tissue. Multiple preclinical and non-randomized clinical trials have been performed to evaluate the safety and efficacy of HIFU for palliative treatment of pancreatic tumors. Substantial tumor-related pain reduction was achieved in most cases after HIFU treatment, and no significant side-effects were observed. This review provides a description of different physical mechanisms underlying HIFU therapy, summarizes the clinical experience obtained to date in HIFU treatment of pancreatic tumors, and discusses the challenges, limitations and new approaches in this modality.

Different effects of sonoporation on cell morphology and viability

The objective of our study was to investigate changes in cell morphology and viability after sonoporation. Sonoportion was achieved by ultrasound (21 kHz) exposure on adherent human prostate cancer DU145 cells in the cell culture dishes with the presence of microbubble contrast agents and calcein (a cell impermeant dye). We investigated changes in cell morphology immediately after sonoporation under scanning electron microscope (SEM) and changes in cell viability immediately and 6 h after sonoporation under fluorescence microscope. It was shown that various levels of intracellular calcein uptake and changes in cell morphology can be caused immediately after sonoporation: smooth cell surface, pores in the membrane and irregular cell surface. Immediately after sonoporation, both groups of cells with high levels of calcein uptake and low levels of calcein uptake were viable; 6 h after sonoporation, group of cells with low levels of calcein uptake still remained viable, while group of cells with high levels of calcein uptake died. Sonoporation induces different effects on cell morphology, intracellular calcein uptake and cell viability.

Microbubble therapy enhances anti-tumor properties of cisplatin and cetuximab in vitro and in vivo

OBJECTIVE

To determine if microbubble-mediated ultrasound therapy (MB-UST) can improve cisplatin or cetuximab cytotoxicity of head and neck squamous cell carcinoma (HNSCC) in vitro and in vivo by increasing tumor-specific drug delivery by disruption of tumor cell membranes and enhancing vascular permeability.

STUDY DESIGN

In vitro and in vivo study.

SETTING

University medical center.

SUBJECTS

Immunodeficient mice (6 weeks old) and 4 HNSCC cell lines.

METHODS

Changes to cell permeability were assessed in vitro after MB-UST. Cellular apoptosis resulting from adjuvant MB-UST with subtherapeutic doses of cisplatin or cetuximab was assessed by cell survival assays in vitro. The in vivo effect of adjuvant MB-UST in flank tumors was assessed in vivo with histological analysis and diffusion-weighted magnetic resonance imaging (DW-MRI).

RESULTS

In vitro results revealed that MB-UST can increase cell permeability and enhance drug uptake and apoptosis in 4 HNSCC cell lines. In vivo adjuvant MB-UST with cetuximab or cisplatin showed a statistically significant reduction in tumor size when compared with untreated controls. TUNEL analysis yielded a larger number of cells undergoing apoptosis in tumors treated with cetuximab and adjuvant MB-UST than did cetuximab alone but was not significantly greater in tumors treated with cisplatin and adjuvant MB-UST compared with cisplatin alone. DW-MRI analysis showed more free water, which corresponds to increased cell membrane disruption, in tumors treated with MB-UST.

CONCLUSION

MB-UST promotes disruption of cell membranes in tumor cells in vitro, which may be leveraged to selectively improve the uptake of conventional and targeted therapeutics in vivo.