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Abstract:
Background:
The primary aim of our study was to evaluate the safety and potential toxicity of gemcitabine combined with microbubbles under sonication in inoperable pancreatic cancer patients. The secondary aim was to evaluate a novel image-guided microbubble-based therapy, based on commercially available technology, towards improving chemotherapeutic efficacy, preserving patient performance status, and prolonging survival.

Methods:
Ten patients were enrolled and treated in this Phase I clinical trial. Gemcitabine was infused intravenously over 30 min. Subsequently, patients were treated using a commercial clinical ultrasound scanner for 31.5 min. SonoVue® was injected intravenously (0.5 ml followed by 5 ml saline every 3.5 min) during the ultrasound treatment with the aim of inducing sonoporation, thus enhancing therapeutic efficacy.

Results:
The combined therapeutic regimen did not induce any additional toxicity or increased frequency of side effects when compared to gemcitabine chemotherapy alone (historical controls). Combination treated patients (n = 10) tolerated an increased number of gemcitabine cycles compared with historical controls (n = 63 patients; average of 8.3 ± 6.0 cycles, versus 13.8 ± 5.6 cycles, p = 0.008, unpaired t-test). In five patients, the maximum tumour diameter was decreased from the first to last treatment. The median survival in our patients (n = 10) was also increased from 8.9 months to 17.6 months (p = 0.011).

Conclusions:
It is possible to combine ultrasound, microbubbles, and chemotherapy in a clinical setting using commercially available equipment with no additional toxicities. This combined treatment may improve the clinical efficacy of gemcitabine, prolong the quality of life, and extend survival in patients with pancreatic ductal adenocarcinoma.

Keywords:
Ultrasound, Microbubbles, Sonoporation, Pancreatic cancer, Image-guided therapy, Clinical trial

Abstract:
In research and industrial processes, it is increasingly common practice to combine multiple measurement modalities. Nevertheless, experimental tools that allow the co-linear combination of optical and ultrasonic transmission have rarely been reported. The aim of this study was to develop and characterise a water-matched ultrasound transducer architecture using standard components, with a central optical window larger than 10 mm in diameter allowing for optical transmission. The window can be used to place illumination or imaging apparatus such as light guides, miniature cameras, or microscope objectives, simplifying experimental setups.

Four design variations of a basic architecture were fabricated and characterised with the objective to assess whether the variations influence the acoustic output. The basic architecture consisted of a piezoelectric ring and a glass disc, with an aluminium casing. The designs differed in piezoelectric element dimensions: inner diameter, ID = 10 mm, outer diameter, OD = 25 mm, thickness, TH = 4 mm or ID = 20 mm, OD = 40 mm, TH = 5 mm; glass disc dimensions OD = 20–50 mm, TH = 2–4 mm; and details of assembly.

The transducers’ frequency responses were characterised using electrical impedance spectroscopy and pulse-echo measurements, the acoustic propagation pattern using acoustic pressure field scans, the acoustic power output using radiation force balance measurements, and the acoustic pressure using a needle hydrophone. Depending on the design and piezoelectric element dimensions, the resonance frequency was in the range 350–630 kHz, the −6 dB bandwidth was in the range 87–97%, acoustic output power exceeded 1 W, and acoustic pressure exceeded 1 MPa peak-to-peak.

3D stress simulations were performed to predict the isostatic pressure required to induce material failure and 4D acoustic simulations. The pressure simulations indicated that specific design variations could sustain isostatic pressures up to 4.8 MPa.The acoustic simulations were able to predict the behaviour of the fabricated devices. A total of 480 simulations, varying material dimensions (piezoelectric ring ID, glass disc diameter, glass thickness) and drive frequency indicated that the emitted acoustic profile varies nonlinearly with these parameters.

Keywords:
Ultrasound transducer, De-fouling, Optical window, Acoustic field simulation

Abstract:
Experimental research of ultrasound to induce or improve delivery has snowballed in the past decade. In our work, we investigate the use of low-intensity ultrasound in combination with clinically approved microbubbles to enhance the therapeutic efficacy of chemotherapy. Ten voluntary patients with locally advanced or metastatic pancreatic adenocarcinoma were consecutively recruited. Following standard chemotherapy protocol (intravenous infusion of gemcitabine over 30 min), a clinical ultrasoundscanner was targeted at the largest slice of the tumour using modified non-linear contrastimaging settings (1.9 MHz center frequency, 0.27 MPa peak-negative pressure), and SonoVue® was injected intravenously. Ultrasound and microbubble treatment duration was 31.5 min. The combined therapy did not induce any additional toxicity or increase side effect frequency when compared to chemotherapy alone. Combination treated patients were able to tolerate an increased amount treatment cycles when compare historical controls (n = 63); average of 8.3±6.0 cycles, versus 13.8±5.6 cycles. The median survival also increased from 7.0 months to 17.6 months (p = 0.0044). In addition, five patients showed a primary tumor diameter decrease. Combined treatment of ultrasound,microbubbles, and gemcitabine does not increase side effects and may have the potential to increase the therapeutic efficacy of chemotherapy in patients with pancreatic adenocarcinoma.

Abstract:
Studying the effects of ultrasound on biological cells requires extensive knowledge of both the physical ultrasound and cellular biology. Translating knowledge between these fields can be complicated and time consuming. With the vast range of ultrasonic equipment available, nearly every research group uses different or unique devices. Hence, recreating the experimental conditions and results may be expensive or difficult. For this reason, we have developed devices to combat the common problems seen in state-of-the-art biomedical ultrasound research. In this paper, we present the design, fabrication, and characterisation of an open-source device that is easy to manufacture, allows for parallel sample sonication, and is highly reproducible, with complete acoustic calibration. This device is designed to act as a template for sample sonication experiments. We demonstrate the fabrication technique for devices designed to sonicate 24-well plates and OptiCell™ using three-dimensional (3D) printing and low-cost consumables. We increased the pressure output by electrical impedance matching of the transducers using transmission line transformers, resulting in an increase by a factor of 3.15. The devices cost approximately €220 in consumables, with a major portion attributed to the 3D printing, and can be fabricated in approximately 8 working hours. Our results show that, if our protocol is followed, the mean acoustic output between devices has a variance of <1%. We openly provide the 3D files and operation software allowing any laboratory to fabricate and use these devices at minimal cost and without substantial prior know-how.

Keywords:
Sonoporation, experimentation devices, rapid prototyping, ultrasound transducers

Abstract:
In this study, we analyse the behaviour of antibubbles when subjected to an ultrasonic pulse. Speci cally, we derive oscillating behaviour of acoustic antibubbles with a negligible outer shell, resulting in a Rayleigh Plesset equation of antibubble dynamics. Furthermore, we compare theoretical behaviour of antibubbles to behaviour of regular gas bubbles. We conclude that antibubbles and regular bubbles respond to an acoustic wave in a very similar manner if the antibubble's liquid core radius is less than half the antibubble radius. For larger cores, antibubbles demonstrate highly harmonic behaviour, which would make them suitable vehicles in ultrasonic imaging and ultrasound-guided drug delivery.

Abstract:
Purpose
Adenocarcinoma of the pancreas remains one of the most lethal human cancers. The high mortality rates associated with this form of cancer are subsequent to late-stage clinical presentation and diagnosis, when surgery is rarely possible and of modest chemotherapeutic impact. Survival rates following diagnosis with advanced pancreatic cancer are very low; typical mortality rates of 50 % are expected within 3 months of diagnosis. However, adjuvant chemotherapy improves the prognosis of patients even after palliative surgery, and successful newer neoadjuvant chemotherapeutical modalities have recently been reported. For patients whose tumours appear unresectable, chemotherapy remains the only option. During the past two decades, the nucleoside analogue gemcitabine has become the first-line chemotherapy for pancreatic adenocarcinoma. In this study, we aim to increase the delivery of gemcitabine to pancreatic tumours by exploring the effect of sonoporation for localised drug delivery of gemcitabine in an orthotopic xenograft mouse model of pancreatic cancer.

Experimental Design
An orthotopic xenograft mouse model of luciferase expressing MIA PaCa-2 cells was developed, exhibiting disease development similar to human pancreatic adenocarcinoma. Subsequently, two groups of mice were treated with gemcitabine alone and gemcitabine combined with sonoporation; saline-treated mice were used as a control group. A custom-made focused ultrasound transducer using clinically safe acoustic conditions in combination with SonoVue® ultrasound contrast agent was used to induce sonoporation in the localised region of the primary tumour only. Whole-body disease development was measured using bioluminescence imaging, and primary tumour development was measured using 3D ultrasound.

Results
Following just two treatments combining sonoporation and gemcitabine, primary tumour volumes were significantly lower than control groups. Additional therapy dramatically inhibited primary tumour growth throughout the course of the disease, with median survival increases of up to 10 % demonstrated in comparison to the control groups.

Conclusion
Combined sonoporation and gemcitabine therapy significantly impedes primary tumour development in an orthotopic xenograft model of human pancreatic cancer, suggesting additional clinical benefits for patients treated with gemcitabine in combination with sonoporation.

Keywords:
Sonoporation, Pancreatic cancer, Ultrasound, Chemotherapy, 3D ultrasound, Bioluminescence

Abstract:
Purpose:
The purpose of this study was to investigate the ability and efficacy of inducing sonoporation in a clinical setting, using commercially available technology, to increase the patients’ quality of life and extend the low Eastern Cooperative Oncology Group performance grade; as a result increasing the overall survival in patients with pancreatic adenocarcinoma.

Methods:
Patients were treated using a customized configuration of a commercial clinical ultrasound scanner over a time period of 31.5 min following standard chemotherapy treatment with gemcitabine. SonoVue® ultrasound contrast agent was injected intravascularly during the treatment with the aim to induce sonoporation.

Results:
Using the authors’ custom acoustic settings, the authors’ patients were able to undergo an increased number of treatment cycles; from an average of 9 cycles, to an average of 16 cycles when comparing to a historical control group of 80 patients. In two out of five patients treated, the maximum tumor diameter was temporally decreased to 80 ± 5% and permanently to 70 ± 5% of their original size, while the other patients showed reduced growth. The authors also explain and characterize the settings and acoustic output obtained from a commercial clinical scanner used for combined ultrasound microbubble and chemotherapy treatment.

Conclusions:
It is possible to combine ultrasound, microbubbles, and chemotherapy in a clinical setting using commercially available clinical ultrasound scanners to increase the number of treatment cycles, prolonging the quality of life in patients with pancreatic adenocarcinoma compared to chemotherapy alone.

Keywords:
Ultrasound, Microbubbles, Sonoporation, Chemotherapy

Abstract:
Ultrasonic imaging is becoming the most popular medical imaging modality, owing to the low price per examination and its safety. However, blood is a poor scatterer of ultrasound waves at clinical diagnostic transmit frequencies. For perfusion imaging, markers have been designed to enhance the contrast in B-mode imaging. These so-called ultrasound contrast agents consist of microscopically small gas bubbles encapsulated in biodegradable shells. In this review, the physical principles of ultrasound contrast agent microbubble behavior and their adjustment for drug delivery including sonoporation are described. Furthermore, an outline of clinical imaging applications of contrast-enhanced ultrasound is given. It is a challenging task to quantify and predict which bubble phenomenon occurs under which acoustic condition, and how these phenomena may be utilised in ultrasonic imaging. Aided by high-speed photography, our improved understanding of encapsulated microbubble behavior will lead to more sophisticated detection and delivery techniques. More sophisticated methods use quantitative approaches to measure the amount and the time course of bolus or reperfusion curves, and have shown great promise in revealing effective tumor responses to anti-angiogenic drugs in humans before tumor shrinkage occurs. These are beginning to be accepted into clinical practice. In the long term, targeted microbubbles for molecular imaging and eventually for directed anti-tumor therapy are expected to be tested.

Keywords:
Ultrasound, Drug delivery systems, Drug targeting, Sonoporation, Contrast media, Liver, Pancreas, Gastrointestinal tract

Abstract:
Ultrasound contrast agents consist of encapsulated bubbles in the micrometer size range. At low acoustic amplitudes these microbubbles pulsate linearly, but at high amplitudes they demonstrate highly nonlinear, destructive behaviour. Cellular drug uptake and lysis are increased under sonication, and even more so when a contrast agent is present, owing to the formation of transient porosities in the cell membrane (sonoporation). An overview is given of the physical mechanisms of microbubble behaviour. There are two hypotheses for explaining the sonoporation phenomenon, the first being bubble oscillations near a cell membrane, the second being bubble jetting through the cell membrane. Based on modelling, photography, and cellular uptake measurements, it is concluded that bubble jetting behaviour is unlikely to be the dominant sonoporation mechanism.

Keywords:
Jetting, Sonoporation

Abstract:
It has been proven, that the cellular uptake of drugs and genes is increased, when the region of interest is under ultrasound insonification, and even more when a contrast agent is present. This increased uptake has been attributed to the formation of transient porosities in the cell membrane, which are big enough for the transport of drugs into the cell (sonoporation). Owing to this technique, new ultrasound contrast agents that incorporate a therapeutic compound have become of interest. Combining ultrasound contrast agents with therapeutic substances, such a chemotherapeutics and virus vectors, may lead to a simple and economic method to instantly cure upon diagnosis, using conventional ultrasound scanners. There are two hypotheses for explaining the sonoporation phenomenon, the first being microbubble oscillations near a cell membrane, the second being microbubble jetting through the cell membrane. Based on modeling, high-speed photography, and recent cellular uptake measurements, it is concluded that microbubble jetting behavior is less likely to be the dominant sonoporation mechanism. Ultrasound-directed drug delivery using microbubbles is a promising method that has great potential in the treatment of malignant disorders.

Keywords:
Microbubbles, Ultrasound, Ultrasound contrast agent, Drug delivery, Sonoporation, Therapeutic bubbles

Abstract:
Glass windowed ultrasound transducers have several potential uses ranging from multi-modal research (ultrasound and optics) to industrial application in oil and gas or chemistry. In our work here we compare four different designs for transparent glass windowed ultrasound transducers. Each design was characterised using field scanning, radiation force measurements, frequency sensitivity measurement and FEM simulations. Field scans showed that small variations in design can greatly affect the size and location of the acoustic focus. The results coincided with those seen in the simulations. Radiation force measurements showed that the devices were able to easily exceed acoustic powers of 10W, with efficiencies of up to 40%. Isostatic simulations shows that the design also affects the physical strength of the devices. Current designs were able to withstand between 300 and 700 psi on the front surface. The devices were cost effective due to the minimal amount of materials necessary and the simple fabrication process. More work needs to be done to improve the power output and stress handling capabilities.

Keywords:
Ultrasound transducer

Abstract:
Clinical diagnostic ultrasound has been known as one of the safest imaging modalities available, yet very little is known about the cellular response to such acoustic conditions. With the increased interest in therapeutic ultrasound it is becoming ever more important to understand the effects of ultrasound on cells.In our work here we investigate the effect of clinical diagnostic ultrasound on several cell signalling proteins (p38 p-Thr180/p-Tyr182, ERK 1/2 p-Thr202/p-Tyr204 and p53 ac-Lys382) on leukaemia cells (MOLM-13) and monocytes. Our results show that leukaemia cells and monocytes react differently to ultrasound and microbubbles. A relatively small increase in p38 signalling was seen in the leukemic cells, and only at higher intensities in combination with microbubbles. In contrast the monocytes showed an increase in p38 signalling at all acoustic intensities with microbubbles and at the high acoustic intensity without microbubbles. Furthermore, the leukemic cells showed an overall increase in ERK 1/2 signalling whereas the monocytes showed a decrease. These results indicate that the leukaemia cells are less sensitive to stress induced by ultrasound and microbubbles when compared to normal monocytes. In conclusion, our results show that clinical diagnostic ultrasound does have a measurable effect on intracellular signalling but may differ drastically between different cell types. This may affect the conditions necessary for therapeutic ultrasound.

Keywords:
Phospho-signaling pathways, Ultrasound contrast agent

Abstract:
Therapeutic ultrasound has been in use for over 70 years but has primarily been a thermal modality. Sonoporation, the use of ultrasound and stable gas microbubbles in the size range of 2-10 μm to form transient pores in cell membranes, has been of great interest in the past 15 years. This technique could be used to improve the delivery of current drugs in very localised regions. There are several phenomena behind sonoporation that all occur non-exclusively: push, pull, jetting, inertial cavitation, shear and, translation. Pre-clinical work has shown that sonoporation can be used to reduce primary tumour burden and inhibit metastatic development. Our clinical trial showed that ultrasound in combination with microbubbles and chemotherapy can effectively double the number of chemotherapy cycles patients can undergo, meaning that the patients were healthier for a longer period of time. Nevertheless, sonoporation is still in its infancy and there is vast room for improvement in both the areas of microbubbles and ultrasound.

Keywords:
Sonoporation

Abstract:
Background: Pancreatic Adenocarcinoma (PDAC) represents one of the most lethal human cancers. Surgery is often unfeasible, and the tumors respond poorly to radiation or chemotherapeutic drugs. Consequently, pancreatic cancer represents a huge burden to society and the need for new therapeutic options is evident. Experimental research using ultrasound to improve therapeutic delivery has soared in the past decade. We aimed toevaluate the safety and potential toxicity of gemcitabine combined with microbubbles under sonication in inoperable pancreatic cancer patients. The secondary goal was to develop a novel image-guided microbubble-based therapy, based on commercially available technology, towards improving chemotherapeutic efficacy, preserving patient performance grade, and prolongation of survival. Methods: Ten patients were enrolled and treated in this Phase I clinical trial. Gemcitabine was infused intravenously over 30 min. Subsequently patients were treated using a commercial clinical ultrasound scanner for 31.5 min. SonoVue was injected intravenously (0.5 ml followed by 5 ml saline every 3.5 min) during the ultrasound treatment with the aim of enhancing therapeutic efficacy. Results: The combined therapeutic regimen did not induce any additional toxicity or increase side effect frequency when compared to gemcitabine chemotherapy alone (historical controls). Combination treated patients (n = 10) tolerated an increased number of gemcitabine cycles compared with historical controls (n = 63 patients; average of 8.3±6.0 cycles, versus 13.8±5.6 cycles). In five patients, the maximum tumor diameter was decreased during treatment. The median survival in our patients was also increased from 7.0 months to 17.6 months (p = 0.0044). Conclusions: We perform the first-in-human study evaluating the toxicity and efficacy of ultrasound and microbubble enhanced chemotherapy. It is possible to combine ultrasound, microbubbles, and chemotherapy in a clinical setting with no additional toxicity. This combined treatment may improve the clinical efficacy of chemotherapeutic agents, prolong the quality of life, and extend survival in patients with PDAC. Clinical trial information: NCT01674556.