Influence of polymer adjuvants on the ultrasound-mediated transfection of cells in culture

Dependence of endothelial drug delivery on monodisperse microbubble dynamics

Ultrasound insonification of microbubbles has been shown to increase vascular permeability to locally enhance drug delivery. For more effective and controllable therapeutic outcomes, uniform acoustic responses from microbubbles and a deeper understanding of the biophysical mechanisms of drug delivery are critical. In this study, we investigated the impact of monodisperse microbubble size and their dynamics on cellular responses and drug delivery outcomes in endothelial cells. Monodisperse microbubbles with radii of 1.5, 2.2, 2.7, and 2.9 μm were produced using a microfluidic flow-focusing device. Upon insonification (2 MHz, 220 kPa peak negative pressure, 10 cycles), the microbubble oscillation was captured in real-time at 10 million frames per second using ultra-high-speed imaging, while confocal microscopy was employed to observe cellular responses in both 2D and 3D. For the 65 microbubbles studied, the 2.2 μm microbubbles, i.e., corresponding to the resonant radius at 2 MHz ultrasound, exhibited the highest sonoporation rate (75 %), induced the largest membrane perforations (a median value of 78 μm2) and highest intracellular drug uptake. The 1.5 μm microbubbles achieved a comparable sonoporation rate (73 %), yet with significantly smaller membrane perforations (a median value of 20 μm2), lower intracellular drug uptake, and highest occurrence of transendothelial drug delivery pathways (64 %). Mechanistically, microbubble-generated shear stress was identified as the significant factor driving sonoporation, while normal stress did not show significance. In conclusion, our study highlights the importance of carefully selecting the microbubbles size to maximize microbubble-mediated drug delivery outcomes and facilitate safe translation of monodisperse microbubbles into clinical practice.

An Overview of Cell Membrane Perforation and Resealing Mechanisms for Localized Drug Delivery

Localized and reversible plasma membrane disruption is a promising technique employed for the targeted deposition of exogenous therapeutic compounds for the treatment of disease. Indeed, the plasma membrane represents a significant barrier to successful delivery, and various physical methods using light, sound, and electrical energy have been developed to generate cell membrane perforations to circumvent this issue. To restore homeostasis and preserve viability, localized cellular repair mechanisms are subsequently triggered to initiate a rapid restoration of plasma membrane integrity. Here, we summarize the known emergency membrane repair responses, detailing the salient membrane sealing proteins as well as the underlying cytoskeletal remodeling that follows the physical induction of a localized plasma membrane pore, and we present an overview of potential modulation strategies that may improve targeted drug delivery approaches.

Sonoporation-induced depolarization of plasma membrane potential: analysis of heterogeneous impact

Disrupting plasma membrane integrity would inevitably promote anomalous ion fluxes across the membrane and thereby upset the trans-membranous potential. In this article, we report new findings on how sonoporation as a physical membrane perforation strategy would lead to different forms of plasma membrane potential disruption. Our investigation was conducted with a customized fluorescence imaging platform that enabled live monitoring of plasma membrane potential in relation to individual sonoporation events triggered on HeLa cervical cancer cells. Sonovue microbubbles were used as sonoporation agents (added at a 4:3 cell-to-bubble ratio), and they were activated by 1-MHz pulsed ultrasound with 0.35-MPa peak negative pressure, 20-cycle pulse duration, 20-Hz pulse repetition frequency and 1-s total exposure duration. Results indicate that the plasma membrane potential response was heterogeneous among sonoporated cells: (i) membrane potential of irreversibly sonoporated cells was permanently depolarized; (ii) reversibly sonoporated cells exhibited either transient or sustained membrane depolarization; (iii) intact cells adjacent to sonoporated ones underwent transitory membrane depolarization. These findings effectively serve to substantiate the causal relationship between sonoporation and plasma membrane potential.

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.

Polymeric theranostics: using polymer-based systems for simultaneous imaging and therapy

Polymer-based nanomedicine is a large and fast growing field. Polymer-based systems have been extensively used as therapeutic carriers as well as bioimaging agents for example in tumour diagnosis. However, fewer polymeric systems have been able to combine both therapy and imaging in a new field that is called theranostics (theragnostics). This review aims to summarise the recent developments and trends on polymeric theranostics. Four different types of therapies/treatments are examined namely drug delivery, gene delivery, photodynamic therapy and hyperthermia treatment combined with different imaging moieties like magnetic resonance imaging agents, fluorescent agents and microbubbles for ultrasound imaging.

In vivo gene transfer into the ocular ciliary muscle mediated by ultrasound and microbubbles

This study aimed to assess application of ultrasound (US) combined with microbubbles (MB) to transfect the ciliary muscle of rat eyes. Reporter DNA plasmids encoding for Gaussia luciferase, β-galactosidase or the green fluorescent protein (GFP), alone or mixed with 50% Artison MB, were injected into the ciliary muscle, with or without US exposure (US set at 1 MHz, 2 W/cm(2), 50% duty cycle for 2 min). Luciferase activity was measured in ocular fluids at 7 and 30 days after sonoporation. At 1 week, the US+MB treatment showed a significant increase in luminescence compared with control eyes, injected with plasmid only, with or without MB (×2.6), and, reporter proteins were localized in the ciliary muscle by histochemical analysis. At 1 month, a significant decrease in luciferase activity was observed in all groups. A rise in lens and ciliary muscle temperature was measured during the procedure but did not result in any observable or microscopic damages at 1 and 8 days. The feasibility to transfer gene into the ciliary muscle by US and MB suggests that sonoporation may allow intraocular production of proteins for the treatment of inflammatory, angiogenic and/or degenerative retinal diseases.

Molecular sonography with targeted microbubbles: current investigations and potential applications

Sonography using targeted microbubbles affords a variety of diagnostic and potentially therapeutic clinical applications. It provides a whole new world of functional information at the cellular and molecular level. This information can then be used to diagnose and possibly prevent diseases at early stages as well as devise therapeutic strategies at the molecular level. It is also useful in monitoring tumor response to therapy and devising treatment timing and plans based on the molecular state of an individual's health. Moreover, targeted microbubble-enhanced sonography has several advantages over other imaging modalities, including widespread availability, low cost, fast acquisition times, and lack of radiation risk. These traits are likely to advance it as one of the imaging methods of choice in future clinical trials examining the impact of molecular imaging on treatment outcome. This review describes the fundamental concepts of targeted microbubble-enhanced sonography as well as its potential clinical applications.