Vascular effects of microbubble-enhanced, pulsed, focused ultrasound on liver blood perfusion

Effect of ultrasonic burst microbubbles on microwave coagulation hemostasis in a pig model of hepatic hemorrhage

To investigate the hemostatic efficacy of ultrasound in flash mode and/or microbubbles-assisted microwave coagulation for active liver hemorrhage. Thirty miniature pigs were randomly divided into five groups. Active hepatic hemorrhage was induced under ultrasound guidance. Treatment groups included microwave ablation (MWA), microbubbles with microwave ablation (MBs + MWA), ultrasound in flash mode with microwave ablation (Flash + MWA), ultrasound in flash mode with microbubbles and microwave ablation (Flash + MBs + MWA), and ultrasound in flash mode with phosphate-buffered saline and microwave ablation (Flash + PBS + MWA). Hemostasis time, blood tests, ultrasound, pathological inspections, and analysis were conducted. The Flash + MBs + MWA group showed the shortest hemostasis time, with 2.25 ± 0.45, 2.42 ± 0.51, and 5.50 ± 0.52 min for diaphragm, gallbladder, and hepatic artery bleeding. Highest blood cell stability and a significantly larger hemostatic lesion range were observed in this group on ultrasound. Pathological analysis revealed varied extents of liver sinus congestion and dilation. The combination of ultrasound contrast microbubbles system and microwave thermal coagulation can effectively treat active hepatic hemorrhage, and microbubbles in ultrasound Flash mode have an enhancing effect on microwave coagulation hemostasis.

Promoting the effect of microbubble-enhanced ultrasound on hyperthermia in rabbit liver

PURPOSE

The heat-sink effect is one reason for the insufficient temperature increase in hyperthermia (HT) treatment for cancer. Microbubbles (MBs) nucleate inertial cavitation under therapeutic ultrasound (TUS) exposure, which form microbubble-enhanced ultrasound (MEUS), which results in blocking blood perfusion in the targeted liver tissues. This study aimed to determine if synergistic effects exist during HT in the liver when combined with MEUS.

METHODS

Forty rabbits with surgically exposed livers were randomly divided into TUS + MB + HT, MB + HT, normal saline + HT, and MB + sham groups (n = 10 in each group). Liver perfusion was evaluated using contrast-enhanced ultrasound. The temperatures of the liver tissues were monitored using thermocouples. Pathological changes were determined by hematoxylin and eosin (H&E) staining. Serum hepatic transaminases were evaluated.

RESULTS

MEUS pretreatment almost completely blocked the perfusion of targeted areas. The TUS + MB + HT and MB + HT groups showed significantly higher temperatures in treated areas than those in the other groups. However, the TUS + MB + HT group exhibited a more stable and regular increase in temperatures in the fitting curves compared with the MB + HT group. H&E staining revealed swelling hepatocytes, hemorrhage, and thrombosis in the portal area in the TUS + MB + HT group.

CONCLUSION

MEUS reduced the blood perfusion in the targeted liver tissues, and, therefore, overcame the heat-sink effect during the HT procedure in rabbits. MEUS pretreatment might have the potential to enhance the therapeutic effect of HT.

PD-L1 Targeting Immune-Microbubble Complex Enhances Therapeutic Index in Murine Colon Cancer Models

Cancer immunotherapy has revolutionized the way different neoplasms are treated. Among the different variations of cancer immunotherapy, the checkpoint inhibitors targeting the programmed cell death protein 1 (PD-1)/programmed death-ligand 1 (PD-L1) axis have been validated and are currently used in the clinics. Nevertheless, these therapeutic antibodies are associated with significant side effects and are known to induce immune-related toxicities. To address these issues, we have developed an immune-microbubble complex (IMC) which not only reduces the toxicities associated with the antibodies but also enhances the therapeutic efficacy when combined with focused ultrasound. The concept of IMCs could be applied to any type of antibody-based treatment regimens to maximize their therapeutic potential.

Endothelial Cells, First Target of Drug Delivery Using Microbubble-Assisted Ultrasound

Microbubble-assisted ultrasound has emerged as a promising method for local drug delivery. Microbubbles are intravenously injected and locally activated by ultrasound, thus increasing the permeability of vascular endothelium for facilitating extravasation and drug uptake into the treated tissue. Thereby, endothelial cells are the first target of the effects of ultrasound-driven microbubbles. In this review, the in vitro and in vivo bioeffects of this method on endothelial cells are described and discussed, including aspects on the permeabilization of biologic barriers (endothelial cell plasma membranes and endothelial barriers), the restoration of their integrity, the molecular and cellular mechanisms involved in both these processes, and the resulting intracellular and intercellular consequences. Finally, the influence of the acoustic settings, microbubble parameters, treatment schedules and flow parameters on these bioeffects are also reviewed.

Sonoporation for Augmenting Chemotherapy of Pancreatic Ductal Adenocarcinoma

Pancreatic cancer is the third most common cancer diagnosed in the United States, with more than 53,000 new cases in 2017. It is the fourth leading cause of cancer-related death in both men and women. Nonetheless, there has been no significant improvement in survival for pancreatic ductal adenocarcinoma (PDAC) patients over the past 30+ years. For this reason, there is a considerable and urgent clinical need to develop innovative strategies for effective drug delivery and treatment monitoring, resulting in improved outcomes for patients with PDAC.This chapter describes the development of contrast-enhanced ultrasound image-guided drug delivery (CEUS-IGDD or sonoporation) to be that method and to translate it from the lab to the clinic. The initial clinical focus has been on a Phase I clinical trial for enhancing the effectiveness of standard chemotherapeutics for treatment of inoperable PDAC, which demonstrated a median survival increase from 8.9 months to 17.6 months in ten subjects augmented with sonoporation compared to 63 historical controls (p = 0.011). Recent efforts to optimize this platform and move forward to a larger Phase II clinical trial will be described.

Local Tumor Ischemia-Reperfusion Mediated By Ultrasound-Targeted Microbubble Destruction Enhances The Anti-Tumor Efficacy Of Doxorubicin Chemotherapy

Background

Ultrasound-targeted microbubble destruction (UTMD) has been shown to be a promising noninvasive technique to change the tumor circulation, thus providing a potential method to increase reactive oxygen species (ROS) levels in tumors by inducing tumor tissue ischemia-reperfusion (IR). In this study, we investigated the feasibility of local tumor IR through UTMD to enhance the anti-tumor efficacy of doxorubicin (DOX) chemotherapy.

Methods

UTMD was used to induce local tumor IR. After the major blood supply of the tumor was restored, DOX was intravenously injected into the tumor-bearing mice. The superoxide dismutase (SOD) and catalase (CAT) activity and ROS levels were examined, and the anti-tumor efficacy was evaluated.

Results

UTMD blocked the circulation to the tumor for 30 mins. Slow reperfusion began to occur after 30 mins, and major blood supply was restored after 1 hr. The blood perfusion of the tumor completely recovered at 2 hrs. The activity of SOD in the tumors was significantly decreased at 2 hrs and 1 day after IR treatment with or without DOX treatment. The CAT activity showed no obvious changes at 2 hrs after IR treatment, whereas a significant decrease was found after 1 day in both the IR and DOX/IR groups. Moreover, higher levels of ROS were produced in the IR group and IR/DOX group. In vivo anti-tumor study indicated that the local tumor IR strategy may significantly enhance the anti-tumor efficacy of DOX chemotherapy.

Conclusion

UTMD provides a novel, simple and non-invasive technique for tumor IR. In combination with chemotherapy, UTMD may have high great potential to improve the anti-tumor efficacy of chemotherapeutic drugs.

Normalization of Tumor Vasculature by Oxygen Microbubbles with Ultrasound

Tumor microenvironment influences the efficacy of anti-cancer therapies. The dysfunctional tumor vasculature limits the efficiency of oxygenation and drug delivery to reduce treatment outcome. A concept of tumor vascular normalization (VN), which inhibits angiogenesis to improve vessel maturity, blood perfusion, and oxygenation, has been demonstrated under the anti-angiogenic therapy. The efficiency of drug delivery and penetration is increased by enhancing perfusion and reducing interstitial fluid pressure during the time window of VN. However, anti-angiogenic agents only induce transient VN and then prune vessels to aggravate tumor hypoxia. To repair tumor vessels without altering vessel density, we proposed to induce tumor VN by local oxygen release via oxygen microbubbles with ultrasound. With tumor perfusion enhancement under ultrasound contrast imaging tracing, the time window of VN was defined as 2-8 days after a single oxygen microbubble treatment. The enhanced tumor oxygenation after oxygen microbubble treatment inhibited hypoxia inducible factor-1 alpha (HIF-1α)/vascular endothelial growth factor (VEGF) pathway to improve the morphology and function of tumor vasculature. The pericyte coverage and Hoechst penetration of tumor vessels increased without any changes to the vessel density. Finally, the intratumoral accumulation of anti-cancer drug doxorubicin could be increased 3-4 folds during tumor VN. These findings demonstrate that regulating tumor oxygenation by oxygen microbubbles could normalize dysfunctional vessels to enhance vascular maturity, blood perfusion, and drug penetration. Furthermore, ultrasound perfusion imaging provides a simple and non-invasive way to detect the VN time window, which increases the feasibility of VN in clinical cancer applications.

Effect of Microbubble-Enhanced Ultrasound on Radiofrequency Ablation of Rabbit Liver

Microbubble-enhanced ultrasound (MEUS) can non-invasively disrupt and block liver blood perfusion. It may potentially overcome the heat sink effect during a thermal ablation and consequently enhance radiofrequency ablation (RFA) of the liver. We propose a new strategy combining RFA with MEUS. For ultrasound treatment, an 831-kHz air-backed focused transducer directed 400-cycle bursts at 4.3 MPa to the liver at a 9-Hz rate. The treatment was nucleated by a lipids microbubble forming MEUS. Eighteen surgically exposed rabbit livers were treated using MEUS combined with RFA; the other 32 livers were treated using MEUS (n = 14) or RFA (n = 18) alone and served as the controls. Contrast ultrasound imaging confirmed that MEUS treatment significantly reduced liver blood perfusion by cutting contrast peak intensities in half (44.7%-54.1%) without severe liver function damage. The ablated liver volume treated using MEUS combined with RFA was 2.8 times greater than that treated using RFA alone. In conclusion, RFA of the liver can be safely and greatly enhanced by combination with MEUS pre-treatment.

Hemocoagulase Combined with Microbubble-Enhanced Ultrasound Cavitation for Augmented Ablation of Microvasculature in Rabbit VX2 Liver Tumors

We investigated a new method for combining microbubble-enhanced ultrasound cavitation (MEUC) with hemocoagulase (HC) atrox. Our goal was to induce embolic effects in the vasculature and combine these with an anti-angiogenic treatment strategy. Fourteen days after being implanted with a single slice of the liver VX2 tumor, rabbits were randomly divided into five groups: (i) a control group injected intra-venously with saline using a micropump; (ii) a group given only an injection of HC; (iii) a group treated only with ultrasound cavitation; (iv) a group treated with MEUC; (v) a group treated with MEUC + HC. Contrast-enhanced ultrasound was performed before treatment and 1 h and 7 d post-treatment to measure tumor size, enhancement and necrosis range. QontraXt software was used to determine the time-intensity curve of tumor blood perfusion and microvascular changes. At 1 h and 7 d after treatment with MEUC + HC, the parameters of the time-intensity curve, which included peak value, regional blood volume, regional blood flow and area under the curve value and which were measured using contrast-enhanced ultrasound, were significantly lower than those of the other treatment groups. The MEUC + HC treatment group exhibited significant growth inhibition relative to the ultrasound cavitation only, HC and MEUC treatment groups. No damage was observed in the surrounding normal tissues. These results support the feasibility of reducing the blood perfusion of rabbit VX2 liver tumors using a new method that combines MEUC and HC.

Effects of Non-Focused Microbubble-Enhanced and High-Intensity Focused Ultrasound on Hemostasis in a Rabbit Model of Liver Trauma

Uncontrolled hemorrhage after trauma to the liver can lead to death. The present study compared the effects of non-focused microbubble-enhanced ultrasound and high-intensity focused ultrasound on hepatic hemostasis in the injured liver. Blood perfusion level, serum liver enzyme levels and the aspartate transaminase/alanine transaminase ratio differed between the two types of treatment (all p values < 0.05). Hepatic cells in the microbubble-enhanced ultrasound group exhibited edema and compressed the hepatic sinus and blood vessels in the portal area. Coagulation and necrosis, inflammatory cell infiltration, and fibrous tissue encapsulation were observed in the high-intensity focused ultrasound group at later stages. The groups also differed in degree of ultrastructural damage and recovery time. Thus, microbubble-enhanced ultrasound has less of an impact on blood reperfusion and surrounding normal tissue than high-intensity focused ultrasound and is a better choice for the treatment of liver trauma.

Hemostatic mechanism underlying microbubble-enhanced non-focused ultrasound in the treatment of a rabbit liver trauma model

The aim of our study was to investigate the hemostatic mechanism underlying microbubble-enhanced non-focused ultrasound treatment of liver trauma. Thirty rabbits with liver trauma were randomly divided into three groups-the microbubble-enhanced ultrasound (MEUS; further subdivided based on exposure intensity into MEUS1 [0.11 W/cm²], MEUS2 [0.55 W/cm²], and MEUS3 [1.1 W/cm²]), ultrasound without microbubbles (US), and microbubbles without ultrasound (MB) groups. The pre- and post-treatment bleeding weight and visual bleeding scores were evaluated. The serum liver enzyme concentrations as well as the blood perfusion level represented by mean peak contrast intensity (PI) ratio in the treatment area were analyzed. The hemostatic mechanism was evaluated by histological and transmission electron microscopic examination of liver tissue samples. The MEUS subgroups 1-3 (grade 0-1, grade 0-2, and grade 1-2, respectively) exhibited significantly lower post-treatment visual bleeding scores than the US and MB groups (both, grade 3-4; all, P < 0.05). Subgroups MEUS1 (0.346 ± 0.345 g) and MEUS2 (2.232 ± 2.256 g) exhibited significantly lower post-treatment bleeding weight than the US and MB groups (5.698 ± 1.938 and 5.688 ± 2.317 g, respectively; all, P < 0.05). Additionally, MEUS subgroups 1-3 exhibited significantly lower post-treatment blood perfusion levels (PI ratios, 0.64 ± 0.085, 0.73 ± 0.045, and 0.84 ± 0.034, respectively) than the US and MB groups (PI ratios, 1.00 ± 0.005 and 0.99 ± 0.005, respectively; all, P < 0.05). In the MEUS group, hepatic cells became edematous and compressed the hepatic sinus and associated blood vessels. However, the serum liver enzyme levels were not significantly altered. Microbubble-enhanced non-focused ultrasound does not significantly affect blood perfusion and liver function and can be used to induce rapid hemostasis in case of liver trauma.

Effect of microbubble-enhanced ultrasound on percutaneous ethanol ablation of rat walker-256 tumour

OBJECTIVES

Percutaneous ethanol ablation (PEA) is an effective method for treating small liver cancer. Microbubble-enhanced ultrasound (MEUS) can potentially promote PEA by disrupting the tumour's circulation. In this study, treatment combining MEUS and PEA was performed to find any synergistic effects in tumour ablation.

METHODS

Ten rats bearing subcutaneous Walker-256 tumours were treated by MEUS combined with PEA. The other 18 tumour-bearing rats that were treated by MEUS or PEA served as the controls. MEUS was conducted by therapeutic ultrasound (TUS) and microbubble injection. TUS was operated at a frequency of 831 KHz with a pressure amplitude of 4.3 MPa. Tumour blood perfusion was assessed by contrast-enhanced ultrasound (CEUS), and the tumour necrosis rate was determined by histological examination.

RESULTS

CEUS showed that the tumour blood perfusion almost vanished in all of the MEUS-treated tumours. The contrast peak intensity dropped 84.8 % in the MEUS + PEA-treated tumours when compared to 46.3 % (p < 0.05) in the PEA-treated tumours 24 h after treatment. The tumour necrosis rate of the combination therapy was 97.50 %, which is much higher than that of the MEUS- (66.2 %) and PEA-treated (81.0 %) tumours.

CONCLUSION

PEA combined with MEUS can induce a much more complete tumour necrosis.

KEY POINTS

• This experiment demonstrated a novel method for enhancing percutaneous ethanol ablation. • Microbubble-enhanced therapeutic ultrasound is capable of disrupting tumour circulation. • Combined therapy of MEUS and PEA can induce more complete necrosis of tumours.

Sonochemotherapy: from bench to bedside

The combination of microbubbles and ultrasound has emerged as a promising method for local drug delivery. Microbubbles can be locally activated by a targeted ultrasound beam, which can result in several bio-effects. For drug delivery, microbubble-assisted ultrasound is used to increase vascular- and plasma membrane permeability for facilitating drug extravasation and the cellular uptake of drugs in the treated region, respectively. In the case of drug-loaded microbubbles, these two mechanisms can be combined with local release of the drug following destruction of the microbubble. The use of microbubble-assisted ultrasound to deliver chemotherapeutic agents is also referred to as sonochemotherapy. In this review, the basic principles of sonochemotherapy are discussed, including aspects such as the type of (drug-loaded) microbubbles used, the routes of administration used in vivo, ultrasound devices and parameters, treatment schedules and safety issues. Finally, the clinical translation of sonochemotherapy is discussed, including the first clinical study using sonochemotherapy.

Hemostatic effects of microbubble-enhanced low-intensity ultrasound in a liver avulsion injury model

OBJECTIVES

Microbubble-enhanced therapeutic ultrasound (MEUS) can block the blood flow in the organs. The aim of this study was to evaluate the hemostatic effect of microbubble-enhanced pulsed, low-intensity ultrasound in a New Zealand White rabbit model of avulsion trauma of the liver. The therapeutic ultrasound (TUS) transducer was operated with the frequency of 1.2 MHz and an acoustic pressure of 3.4 MPa. Microbubble-(MB) enhanced ultrasound (MEUS) (n = 6) was delivered to the distal part of the liver where the avulsion was created. Livers were treated by TUS only (n = 4) or MB only (n = 4) which served as controls. Bleeding rates were measured and contrast enhanced ultrasound (CEUS) was performed to assess the hemostatic effect, and liver hemoperfusion before and after treatment. Generally, bleeding rates decreased more than 10-fold after the treatment with MEUS compared with those of the control group (P<0.05). CEUS showed significant declines in perfusion. The peak intensity value and the area under the curve also decreased after insonation compared with those of the control group (P<0.05). Histological examination showed cloudy and swollen hepatocytes, dilated hepatic sinusoids, perisinusoidal spaces with erythrocyte accumulation in small blood vessels, obvious hemorrhage around portal areas and scattered necrosis in liver tissues within the insonation area of MEUS Group. In addition, necrosis was found in liver tissue 48 h after insonation. We conclude that MEUS might provide an effective hemostatic therapy for serious organ trauma such as liver avulsion injury.

Inhibition of hepatic fibrosis with artificial microRNA using ultrasound and cationic liposome-bearing microbubbles

We sought to investigate the antifibrotic effects of an artificial microRNA (miRNA) targeting connective tissue growth factor (CTGF) using the ultrasound-targeted cationic liposome-bearing microbubble destruction gene delivery system. Cationic liposomes were conjugated with microbubbles using a biotin-avidin system. Plasmids carrying the most effective artificial miRNA sequences were delivered by ultrasound-targeted cationic liposome-bearing microbubble destruction gene delivery system to rats with hepatic fibrosis. The results show that this method of gene delivery effectively transported the plasmids to the rat liver. The artificial miRNA reduced hepatic fibrosis pathological alterations as well as the protein and mRNA expressions of CTGF and transforming growth factor β1. Furthermore, the CTGF gene silencing decreased the levels of type I collagen and α-smooth muscle actin (P<0.01). These data suggest that delivery of an artificial miRNA targeted against CTGF using ultrasound-targeted cationic liposome-bearing microbubble destruction may be an efficacious therapeutic method to ameliorate hepatic fibrosis.

Impact of microbubble-enhanced ultrasound on liver ethanol ablation

Ethanol ablation (EA) is a safe and effective method for treating small liver cancer. However, the ethanol is rapidly washed out by blood perfusion, preventing its accumulation within tumors. Microbubble-enhanced ultrasound (MEUS) is capable of disrupting tumor and liver circulation. We hypothesized that this disruption could be used to enhance EA of normal liver tissue. We treated surgically exposed rabbit liver with a combination of MEUS and EA. The controls were treated with only MEUS or 0.05 mL EA. MEUS treatment was administered with a high-pressure-amplitude, pulsed therapeutic ultrasound device and intra-venous injection of microbubbles. Therapeutic ultrasound was delivered at an acoustic pressure of 4.3 MPa and a duty cycle of 0.22%. Contrast-enhanced ultrasound was performed to estimate liver blood perfusion. Livers were harvested for necrotic volume measurements 48 h after treatment. Contrast-enhanced ultrasound demonstrated that liver perfusion was temporally arrested, with a significant peak intensity decline from -46.9 ± 3.8 to -64.0 ± 3.3 dB, after MEUS treatment. The mean volume ablated in MEUS + EA-treated livers (3.3 ± 2.3 cm(3)) was more than 10 times larger than that in livers treated only with EA (0.3 ± 0.2 cm(3)). The volume of liver ablated by MEUS treatment alone was minor, scattered and immeasurable. These results indicate that MEUS disruption of the liver circulation can greatly promote EA of liver.