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Multi-timescale Microscopy Methods for the Characterization of Fluorescently-labeled Microbubbles for Ultrasound-Triggered Drug Release

Microbubble contrast agents hold great promise for drug delivery applications with ultrasound. Encapsulating drugs in nanoparticles reduces systemic ...

SINTEF Industry

St. Olav’s Hospital

Norwegian University of Science and Technology

Compared with conventional chemotherapy, encapsulation of drugs in nanoparticles can improve efficacy and reduce toxicity. However, delivery of nanoparticles is often insufficient and heterogeneous because of various biological barriers and uneven tumor perfusion. We investigated a unique multifunctional drug delivery system consisting of microbubbles stabilized by polymeric nanoparticles (NPMBs), enabling ultrasound-mediated drug delivery. The aim was to examine mechanisms of ultrasound-mediated delivery and to determine if increased tumor uptake had a therapeutic benefit. Cellular uptake and toxicity, circulation and biodistribution were characterized. After intravenous injection of NPMBs into mice, tumors were treated with ultrasound of various pressures and pulse lengths, and distribution of nanoparticles was imaged on tumor sections. No effects of low pressures were observed, whereas complete bubble destruction at higher pressures improved tumor uptake 2.3 times, without tissue damage. An enhanced therapeutic effect was illustrated in a promising proof-of-concept study, in which all tumors exhibited regression into complete remission.

Ultrasound Improves the Delivery and Therapeutic Effect of Nanoparticle-Stabilized Microbubbles in Breast Cancer Xenografts.

Ultrasound and microbubbles have been found to improve the delivery of drugs and nanoparticles to tumor tissue. To obtain new knowledge on the influence of vascular parameters on extravasation and to elucidate the effect of acoustic pressure on extravasation and penetration of nanoscale particles into the extracellular matrix, real-time intravital multiphoton microscopy was performed during sonication of tumors growing in dorsal window chambers. The impact of vessel diameter, vessel structure and blood flow was characterized. Fluorescein isothiocyanate-dextran (2 MDa) was injected to visualize blood vessels. Mechanical indexes (MI) of 0.2-0.8 and in-house-made, nanoparticle-stabilized microbubbles or Sonovue were applied. The rate and extent of penetration into the extracellular matrix increased with increasing MI. However, to achieve extravasation, smaller vessels required MIs (0.8) higher than those of blood vessels with larger diameters. Ultrasound changed the blood flow rate and direction. Interestingly, the majority of extravasations occurred at vessel branching points.

Effect of Ultrasound on the Vasculature and Extravasation of Nanoscale Particles Imaged in Real Time.

To improve therapeutic efficacy of nanocarrier drug delivery systems, it is essential to improve their uptake and penetration in tumour tissue, enhance cellular uptake and ensure efficient drug release at the tumour site. Here we introduce a tumour targeting drug delivery system based on the ultrasound-mediated delivery of enzyme sensitive liposomes. These enzyme sensitive liposomes are coated with cleavable poly(ethylene glycol) (PEG) which will be cleaved by two members of the enzyme matrix metalloproteinase family (MMP-2 and MMP-9). Cleavage of the PEG coat can increase cellular uptake and will destabilize the liposomal membrane which can result in accelerated drug release. The main aim of the work was to study the effect of focused ultrasound and microbubbles on the delivery and therapeutic efficacy of the MMP sensitive liposome. The performance of the MMP sensitive liposome was compared to a non-MMP sensitive version and Doxil-like liposomes. In vitro, the cellular uptake and cytotoxicity of the liposomes were studied, while in vivo the effect of ultrasound and microbubbles on the tumour accumulation, biodistribution, microdistribution, and therapeutic efficacy were investigated. For all tested liposomes, ultrasound and microbubble treatment resulted in an improved tumour accumulation, increased extravasation, and increased penetration of the liposomes from blood vessels into the extracellular matrix. Surprisingly, penetration depth was independent of the ultrasound intensity used. Ultrasound-mediated delivery of free doxorubicin and the Doxil-like and MMP sensitive liposome resulted in a significant reduction in tumour volume 28 days post the first treatment and increased median survival. The MMP sensitive liposome showed better therapeutic efficacy than the non-MMP sensitive version indicating that cleaving the PEG-layer is important. However, the Doxil-like liposome outcompeted the MMP and non-MMP sensitive liposome, both with and without the use of ultrasound and microbubbles.

Ultrasound-mediated delivery enhances therapeutic efficacy of MMP sensitive liposomes.

Ultrasound (US) in combination with microbubbles (MB) has had promising results in improving delivery of chemotherapeutic agents. However, most studies are done in immunodeficient mice with xenografted tumors. We used two phenotypes of the spontaneous transgenic adenocarcinoma of the mouse prostate (TRAMP) model to evaluate if US + MB could enhance the therapeutic efficacy of cabazitaxel (Cab). Cab was either injected intravenously as free drug or encapsulated into nanoparticles. In both cases, Cab transiently reduced tumor and prostate volume in the TRAMP model. No additional therapeutic efficacy was observed combining Cab with US + MB, except for one tumor. Additionally, histology grading and immunostaining of Ki67 did not reveal differences between treatment groups. Mass spectrometry revealed that nanoparticle encapsulation of Cab increased the circulation time and enhanced the accumulation in liver and spleen compared with free Cab. The therapeutic results in this spontaneous, clinically relevant tumor model differ from the improved therapeutic response observed in xenografts combining US + MB and chemotherapy.

Ultrasound-Mediated Delivery of Chemotherapy into the Transgenic Adenocarcinoma of the Mouse Prostate Model.

Delivery of drugs and nanomedicines to tumors is often heterogeneous and insufficient and, thus, of limited efficacy. Microbubbles in combination with ultrasound have been found to improve delivery to tumors, enhancing accumulation and penetration. We used a subcutaneous prostate cancer xenograft model in mice to investigate the effect of free and nanoparticle-encapsulated cabazitaxel in combination with ultrasound and microbubbles with a lipid shell or a shell of nanoparticles. Sonopermeation reduced tumor growth and prolonged survival (26%-100%), whether the free drug was co-injected with lipid-shelled microbubbles or the nanoformulation was co-injected with lipid-shelled or nanoparticle-shelled microbubbles. Coherently with the improved therapeutic response, we found enhanced uptake of nanoparticles directly after ultrasound treatment that lasted several weeks (2.3 × -15.8 × increase). Neither cavitation dose nor total accumulation of nanoparticles could explain the variation within treatment groups, emphasizing the need for a better understanding of the tumor biology and mechanisms involved in ultrasound-mediated treatment.

Sonopermeation Enhances Uptake and Therapeutic Effect of Free and Encapsulated Cabazitaxel.

Therapeutic agents can benefit from encapsulation in nanoparticles, due to improved pharmacokinetics and biodistribution, protection from degradation, increased cellular uptake and sustained release. Microbubbles in combination with ultrasound have been shown to improve the delivery of nanoparticles and drugs to tumors and across the blood-brain barrier. Here, we evaluate two different microbubbles for enhancing the delivery of polymeric nanoparticles to cells in vitro: a commercially available lipid microbubble (Sonazoid) and a microbubble with a shell composed of protein and nanoparticles. Various ultrasound parameters are applied and confocal microscopy is employed to image cellular uptake. Ultrasound enhanced cellular uptake depending on the pressure and duty cycle. The responsible mechanisms are probably sonoporation and sonoprinting, followed by uptake, and to a smaller degree enhanced endocytosis. The use of commercial Sonazoid microbubbles leads to significantly lower uptake than when using nanoparticle-loaded microbubbles, suggesting that proximity between cells, nanoparticles and microbubbles is important, and that mainly nanoparticles in the shell are taken up, rather than free nanoparticles in solution.

Sonoporation Using Nanoparticle-Loaded Microbubbles Increases Cellular Uptake of Nanoparticles Compared to Co-Incubation of Nanoparticles and Microbubbles.

Sofie Snipstad

Department of Biotechnology and Nanomedicine

SINTEF Industry

Multi-timescale Microscopy Methods for the Characterization of Fluorescently-labeled Microbubbles for Ultrasound-Triggered Drug Release

Sofie Snipstad

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Biotechnology and Nanomedicine

SINTEF Industry

Multi-timescale Microscopy Methods for the Characterization of Fluorescently-labeled Microbubbles for Ultrasound-Triggered Drug Release

Department of Biotechnology and Nanomedicine