Transmission electron microscopy of VX2 liver tumors after high-intensity focused ultrasound ablation enhanced with SonoVue

Development and application of ultrasound contrast agents in biomedicine

With the rapid development of molecular imaging, ultrasound (US) medicine has evolved from traditional imaging diagnosis to integrated diagnosis and treatment at the molecular level. Ultrasound contrast agents (UCAs) play a crucial role in the integration of US diagnosis and treatment. As the micro-bubbles (MBs) in UCAs can enhance the cavitation effect and promote the biological effect of US, UCAs have also been studied in the fields of US thrombolysis, mediated gene transfer, drug delivery, and high intensity focused US. The application range of UCAs is expanding, and the value of their applications is improving. This paper reviews the development and application of UCAs in biomedicine in recent years, and the existing problems and prospects are pointed out.

Bifidobacterium-mediated high-intensity focused ultrasound for solid tumor therapy: comparison of two nanoparticle delivery methods

PURPOSE

This study was conducted to prepare a novel tumor-biotargeting high-intensity focused ultrasound (HIFU) synergist for indirectly delivering lipid nanoparticles based on the targeting ability of Bifidobacterium longum to the hypoxic region of solid tumors. The effects of two different delivery methods on the imaging and treatment of solid tumors enhanced by lipid nanoparticles were compared.

METHODS

Biotinylated lipid nanoparticles coated with PFH were prepared, cross-linked with B. longum in vitro using a streptavidin-conjugated B. longum antibody (SBA), and observed and detected by laser confocal microscopy and flow cytometry. Solid tumors were treated with HIFU and PFH/BL-NPs. The effects of different delivery methods on the tumor targeting and efficiency of retention of PFH/BL-NPs were observed using Small animal live imaging and frozen sections from small animals.

RESULTS

The PFH/BL-NPs prepared in this study showed good biocompatibility and safety. PFH/BL-NPs and B. longum were cross-linked in a cluster-like manner (confocal laser scanning microscope) in vitro, with a cross-linking rate of 84 ± 6.23% (flow cytometry). The delivery of B. longum followed by that of PFH/BL-NPs not only enhanced the ability of PFH/BL-NPs to target solid tumors (small animal live imaging), but also increased the retention time of PFH/BL-NPs in the tumor (frozen slices), enhancing the effect of the HIFU synergist.

CONCLUSION

Delivery of B. longum followed by that of PFH/BL-NPs can enhance the imaging of solid tumors and effectively improve the efficiency of HIFU treatment of solid tumors, providing a basis for further clinical work.

The Study of Enhanced High-Intensity Focused Ultrasound Therapy by Sonodynamic N2O Microbubbles

High-intensity focused ultrasound (HIFU) is a representative non-invasive method of cancer therapy, but its low therapeutic efficacy and risk of damage to surrounding normal tissue hinder its further clinical development and application. Sonodynamic therapy (SDT) kills tumor cells through reactive oxygen molecules produced by sonosensitizers during ultrasound treatment. SDT can enhance HIFU efficacy like microbubbles. In this work, we developed nanoscale N₂O microbubbles (N₂O-mbs) by an improved mechanical oscillation method. These microbubbles showed good biocompatibility and tumor cell binding. The sonosensitivity of the N₂O-mbs was detected both extracellularly and intracellularly through the detection of reactive oxygen species generation. The toxic effects of these sonodynamic microbubbles on tumor cells and the synergistic effect on HIFU treatment were evaluated. Significant apoptosis was caused by reactive oxygen species produced by N₂O-mbs under ultrasound irradiation. N₂O-mbs combined with HIFU increased tumor cell necrosis and apoptosis in vitro and the coagulative necrotic volume and echo intensity in the bovine liver target area ex vivo. These sonodynamic microbubbles have been also demonstrated to efficiently inhibit tumor growth in vivo. N₂O-mbs have a significant impact on the treatment and ablation effect of HIFU due to the advantages of microbubble and extraordinary sonosensitivity. This finding suggests that N₂O-mbs may be a novel auxiliary agent for ultrasound that can be used to promote HIFU tumor thermal ablation.

Antitumor effect of curcumin liposome after transcatheter arterial embolization in VX2 rabbits

Background: Hypoxia may affect the therapeutic efficacy of transcatheter arterial embolization (TAE), which is widely used in nonsurgical hepatocellular carcinoma (HCC). Liposomal curcumin can exert anticancer effect. Our purpose is to explore the antitumor effect of liposomal curcumin on the HCC after TAE.

Methods: The HepG2 cells were cultured under hypoxic condition (1% O₂) and then treated with curcumin liposome. Cell viability, apoptosis and cell cycle were respectively measured by CCK-8 and a flow cytometry. The VX2 rabbits were randomly distributed into three groups: control group with saline embolization, TAE group with lipiodol embolization and curcumin liposome group with curcumin liposome and lipiodol embolization. MRI and CT perfusion scanning were performed after embolization. The hepatocyte apoptosis was measured by the terminal deoxyribonucleotidyl transferse-mediated dUTP nick-end labelling (TUNEL). The vascular endothelial growth factor (VEGF) and microvessel density (MVD) were measured by immunohistochemical. RT-PCR and Western blot were performed to examine mRNA and protein levels.

Results: By regulating the apoptosis-related molecules, curcumin liposome obviously inhibited the cell viability and promoted the apoptosis in G1 phase. Curcumin liposome reduced the tumor size and alleviated neoplasia in VX2 rabbits. Curcumin liposome decreased the expressions of MVD and VEGF and increased the apoptosis of liver tissues. The levels of hypoxia-inducible factor-1α (HIF-1α) and survivin were suppressed by curcumin liposome both in hypoxic cells and liver tissues in the VX2 rabbits.

Conclusion: Curcumin liposome exerted antitumor effect by regulating the proliferation- and apoptosis-related molecules. Curcumin liposome suppressed the HIF-1α and survivin levels and inhibited the angiogenesis in VX2 rabbits after TAE.

Treatment of hepatic tumors by thermal versus mechanical effects of pulsed high intensity focused ultrasound in vivo

The purpose of this study is to comparatively assess the thermal versus mechanical effects of pulsed high intensity focused ultrasound (HIFU) treatment on hepatic tumors in vivo. Forty-five rabbits with hepatic VX2 tumors were randomly separated into three groups (15 animals per group) before HIFU ablation. The total HIFU energy (in situ) of 1250 J was used for each tumor for three groups. In groups I and II, animals were treated with 1 MHz pulsed ultrasound at 1 Hz pulsed repetition frequency (PRF), 0.5 duty cycle (0.5 s on and 0.5 s off) and10 s duration for one spot sonication. For group II, in addition to HIFU treatment, microbubbles (SonoVue, Bracco, Milan, Italy) were injected via vein before sonication acting as a synergist. In group III, animals were treated with 1 MHz pulsed ultrasound at 10 Hz PRF, 0.1 duty cycle (0.1 s on and 0.9 s off) and 10 s duration for one sonication. The total treatment spots were calculated according to the tumor volume. Tumors were examined with contrast-enhanced computed tomography (CECT) immediately prior to and post HIFU treatment. Histopathologic assessment was performed 3 h after treatment. Our study showed that all animals tolerated the HIFU treatment well. Our data showed that mechanical HIFU could lead to controlled injury in rabbit hepatic tumors with different histological changes in comparison to thermal HIFU with or without microbubbles.

Selective depletion of tumor neovasculature by microbubble destruction with appropriate ultrasound pressure

Low‐intensity ultrasound‐microbubble (LIUS‐MB) treatment is a promising antivascular therapy for tumors. We sought to determine whether LIUS‐MB treatment with an appropriate ultrasound pressure could achieve substantial and persistent cessation of tumor perfusion without having significant effects on normal tissue. Further, we investigated the mechanisms underlying this treatment. Murine S‐180 sarcomas, thigh muscles, and skin tissue from 60 tumor‐bearing mice were subjected to sham therapy, an ultrasound application combined with microbubbles in four different ultrasound pressures (0.5, 1.5, 3.0, 5.0 MPa), or ultrasound at 5.0 MPa alone. Subsequently, contrast‐enhanced ultrasonic imaging and histological studies were performed. Tumor microvessels, tumor cell necrosis, apoptosis, tumor growth, and survival were evaluated in 85 mice after treatment with the selected ultrasound pressure. We found that twenty‐four hours after LIUS‐MB treatment at 3.0 MPa, blood perfusion and microvessel density of the tumor had substantially decreased by 84 ± 8% and 84%, respectively (p < 0.01). Similar reductions were not observed in the muscle or skin. Additionally, an extreme reduction in the number of immature vessels was observed in the tumor (reduced by 90%, p < 0.01), while the decrease in mature vessels was not significant. Further, LIUS‐MB treatment at 3.0 MPa promoted tumor cell necrosis and apoptosis, delayed tumor growth, and increased the survival rate of tumor‐bearing mice (p < 0.01). These findings indicate that LIUS‐MB treatment with an appropriate ultrasound pressure could selectively and persistently reduce tumor perfusion by depleting the neovasculature. Therefore, LIUS‐MB treatment offers great promise for clinical applications in antivascular therapy for solid tumors.

What's new?

Selectively disrupting the flow of blood to solid tumors can halt tumor growth. But doing so clinically with antiangiogenic drugs is complicated by side effects, and the benefits often are transitory, owing to tumor cell resistance. An alternative to antiangiogenic drugs may be low‐intensity ultrasound‐microbubble (LIUS‐MB) treatment. Here, in mice, LIUS‐MB treatment delivered at 3.0 MPa resulted in immediate cessation of tumor perfusion, with effects lasting 24 hours. The same treatment had only minor effects on perfusion in normal tissue. Though the mechanism remains unclear, at 3.0 MPa LIUS‐MB treatment selectively depletes the tumor vasculature of immature, defective microvessels.

Application status of high intensity focused ultrasound in treatment of colorectal cancer liver metastases

The liver is the most common and important site of metastases for colorectal cancer, and liver metastasis is one of the important factors leading to treatment failure in colorectal cancer. The traditional methods for treating liver metastases of colorectal cancer (CRLM) are not satisfactory and are often associated with a poor prognosis. High intensity focused ultrasound (HIFU) as a new technique for local ablation of solid tumors not only has advantages of less trauma, fewer complications, faster recovery and definite tumor necrosis, but also can preserve and enhance the host anti-tumor immunity. In recent years, HIFU ablation has been increasingly used for the therapy of tumors in clinical settings. This paper gives an overview of mechanisms of action and application status of HIFU in the treatment of colorectal cancer liver metastases, and explores current challenges and future perspectives.

Iodine quantification with dual-energy CT: phantom study and preliminary experience with VX2 residual tumour in rabbits after radiofrequency ablation

OBJECTIVE

The purpose of our study was to validate iodine quantification in a phantom study with dual-source dual-energy CT (DECT) and to apply this technique to differentiate benign periablational reactive tissue from residual tumour in VX2 carcinoma in rabbits after radiofrequency ablation (RFA).

METHODS

We applied iodine quantification with DECT in a phantom and in VX2 carcinoma in rabbits after incomplete RFA to differentiate benign periablational reactive tissue from residual tumour and evaluated its efficacy in demonstrating response to therapeutic RFA. A series of tubes containing solutions of varying iodine concentration were scanned with DECT. The iodine concentration was calculated and compared with known true iodine concentration. Triple-phase contrast-enhanced DECT data on 24 rabbits with VX2 carcinoma were then assessed at Day 3 (n=6), 1 week (n=6), 2 weeks (n=6) and 3 weeks (n=6) after incomplete RFA independently by 2 readers. Dual-energy postprocessing was used to produce iodine-only images. Regions of interest were positioned on the iodine image over the lesion and, as a reference, over the aorta, to record iodine concentration in the lesion and in the aorta. The pathological specimens were sectioned in the same plane as DECT imaging, and the lesion iodine concentration and lesion-to-aorta iodine ratio of residual tumour and benign periablational reactive tissue were assessed.

RESULTS

There was excellent correlation between calculated and true iodine concentration (r=0.999, p<0.0001) in the phantom study. The lesion iodine concentration and lesion-to-aorta iodine ratio in residual tumour were significantly higher than in benign periablational reactive tissue in the 2-week group during the arterial phase (AP) (p<0.01) and in the 3-week group during both the AP (p<0.05) and the portal venous phase (p<0.05). There was no significant difference between them with respect to the lesion iodine concentration or lesion-to-aorta iodine ratio in the 3-day and 1-week groups.

CONCLUSION

Iodine quantification with DECT is accurate in a phantom study and can be used to differentiate benign periablational reactive tissue from residual tumour in VX2 carcinoma in rabbits after RFA.

ADVANCES IN KNOWLEDGE

Iodine quantification with DECT may help in differentiating benign periablational reactive tissue from residual tumour in VX2 carcinoma in rabbits after RFA.

The damages of high intensity focused ultrasound to transplanted hydatid cysts in abdominal cavities of rabbits with aids of ultrasound contrast agent and superabsorbent polymer

The present study investigates the damages of high intensity focused ultrasound (HIFU) to transplanted hydatid cysts in abdominal cavities of rabbits with aids of ultrasound contrast agent (UCA) and superabsorbent polymer (SAP) alone or in combination. A rabbit model with transplanted hydatid cyst was established by implanting hydatid cyst isolated from infected sheep liver, and HIFU was used to ablate the transplanted cysts with the aid of UCA and SAP alone or in combination. The hydatid cyst with thin wall, good elasticity, approximately spherical, and a diameter of approximately 30 mm was selected for the following experiments. According to our previous studies, a mixture of 0.1 g SAP and 0.5 ml anhydrous ethanol, and the solution of 0.1 ml UCA SonoVue, or both materials were injected into different cyst before HIFU ablation, respectively. The cyst inoculated with the SAP and UCA alone or in combination was immediately implanted into the abdominal cavity of rabbit for HIFU ablation at a dosage of 100 W acoustic powers. The ablation mode was spot scanning at the speed of 3 mm/s. Every target point was scanned three times; every ablating time lasted 3 s. The distance of each ablated layer was 5 mm. The total ablation time depended on the volume of cyst. The comparison of ultrasound image for each layer of hydatid cyst was made before and after HIFU ablation. The protoscolices in ablated cysts were stained by trypan blue exclusion assay, and their structures were observed by light microscopy. To estimate ablation effects of HIFU to the walls of hydatid cysts, the ultrastructure changes of cyst walls were examined by electron microscopy. The pathological changes of rabbits' skins through which ultrasound penetrated were observed to investigate the side effects of HIFU ablation. The results demonstrated that HIFU had some lethal effects to hydatid cysts in vivo, namely, echo enhancements of ultrasound images of cysts, increases in mortality rate of protoscolices from 15.19 % (HIFU alone) to 48.66 % (HIFU + SAP), 38.67 % (HIFU + UCA), and 67.75 % (HIFU + SAP + UCA), respectively, serious structural damages of protoscolices, and destructions or even disappearance of laminated layers and germinal layers in the walls of hydatid cysts ablated by HIFU aided with UCA and SAP alone or in combination. This study demonstrated that destructive effects of HIFU to transplanted hydatid cyst could be enhanced by UCA and SAP alone, but the destruction of HIFU aided with a combination of UCA and SAP to hydatid cysts was more effective than those aided with UCA or SAP alone. The enhanced thermal and cavitation effects of HIFU induced by UCA and SAP might be involved in the enhanced destructive effects of HIFU on hydatid cysts. There were no evidences of pathological changes on rabbits' skins overlying the hydatid cysts after HIFU ablation. The results suggested that the rabbit model with transplanted hydatid cyst may serve as an optional animal model for the experiments of HIFU ablation to hydatid cyst in vivo, and the materials of UCA and SAP were proved as enhancing agents of HIFU ablation to hydatid cysts, and HIFU at a dosage of 100 W acoustic powers was a safe and feasible parameter to ablate the hydatid cysts in this special animal model. These results laid a theoretical foundation for improving HIFU therapy for cystic echinococcosis by inoculation of UCA and SAP into hydatid cysts.

The influence of blood supply on high intensity focused ultrasound a preliminary study on rabbit hepatic VX2 tumors of different ages

RATIONALE AND OBJECTIVES

The aim of this study was to explore the effects of blood supply on high-intensity focused ultrasound (HIFU) applied to rabbit hepatic VX2 tumors of different ages.

MATERIALS AND METHODS

Eighteen rabbits with VX2 hepatic tumors were randomly divided into three groups according to the time of sacrifice after tumor implantation: 10, 15, or 20 days. Contrast-enhanced ultrasound was performed immediately before HIFU ablation. The same settings for HIFU dose parameters were used to ablate the central tumor area in each group, and the real-time temperature of the targeted site of the tumor was measured. After HIFU, the coagulation necrosis volumes of tumor tissue and the microvascular density of residual tumor tissue were determined.

RESULTS

Histopathologic analysis showed that the extent of a tumor's blood supply followed the order 10-day group > 15-day group > 20-day group (P < .01). Contrast-enhanced ultrasound showed the same results. There was no statistically significant difference among the three groups in terms of temperature-increase parameters during HIFU treatment (P > .05). However, there were statistically significant differences between the groups in terms of temperature-decrease parameters during HIFU treatment and in terms of necrosis volumes after HIFU treatment (P < .05). Necrosis volume was inversely related to absolute enhanced intensity (r = -0.823, P < .001).

CONCLUSIONS

The extent of a tumor's blood supply had a significant effect on the temperature-decrease phase but not on the temperature-increase phase during HIFU treatment. The longer the temperature-decrease phase, the more slowly heat dissipated after HIFU, resulting in larger coagulation necrosis volumes.

Enhanced ablation of high intensity focused ultrasound with microbubbles: an experimental study on rabbit hepatic VX2 tumors

PURPOSE

This study was designed to assess the enhanced effect of high intensity focused ultrasound (HIFU) ablation with microbubbles on rabbit hepatic VX2 tumors and to compare the detection sensitivity of CEUS and CECT to determine the residual viable tissue after ablation of HIFU.

METHODS

Forty rabbits with hepatic VX2 tumors were randomly separated into two groups (20 animals per group) before HIFU ablation. A bolus of 0.2 mL of saline or a microbubble-based ultrasound (US) contrast agent was injected intravenously to group I rabbits and group II rabbits, respectively. The HIFU ablation procedure was started 15 s after the injection. Tumors were examined with grayscale contrast-enhanced ultrasound (CEUS) and contrast-enhanced computed tomography (CECT) immediately before and after HIFU ablation. Histopathologic assessment was performed immediately after treatment imaging.

RESULTS

Before ablation, intense contrast enhancement during arterial phase was observed at the whole tumors or the periphery of the tumors by CEUS and CECT. Lower HIFU energy was used in group II than in group I (P < 0.001). Histopathologic assessment revealed local residual viable tumor tissues due to incomplete ablation in 47.4% (9/19) of tumors in group I and 10% (2/20) of tumors in group II (P < 0.05). The concordance rate of CEUS (90.9%) with histopathology on residual tumor detection was higher than that of CECT (27.3%, P < 0.05).

CONCLUSIONS

Introduction of the microbubble agent enhances HIFU therapeutic efficacy. CEUS proves to have high sensitivity in assessment of residual viable rabbit VX2 tumor after HIFU.