Ultrasound Combined With Microbubbles Increase the Delivery of Doxorubicin by Reducing the Interstitial Fluid Pressure

In Vivo Sonoporation Effect Under the Presence of a Large Amount of Micro-Nano Bubbles in Swine Liver

OBJECTIVES

Sonoporation as a method of intracellular drug and gene delivery has not yet progressed to being used in vivo. The aim of this study was to prove the feasibility of sonoporation at a level practical for use in vivo by using a large amount of carbon dioxide micro-nano bubbles.

METHODS

The carbon dioxide micro-nano bubbles and 100 mg of cisplatin were intra-arterially injected to the swine livers, and ultrasound irradiation was performed from the surface of the liver under laparotomy during the intra-arterial injection. After the intra-arterial injection, ultrasound-irradiated and nonirradiated liver tissues were immediately excised. Tissue platinum concentration was measured using inductively coupled plasma mass spectrometry. Liver tissue platinum concentrations were compared between the irradiated tissue and nonirradiated tissue using the Wilcoxon signed rank test.

RESULTS

The mean (SD) liver tissue platinum concentration was 6.260*103 (2.070) ng/g in the irradiated liver tissue and 3.280*103 (0.430) ng/g in the nonirradiated liver tissue, showing significantly higher concentrations in the irradiated tissue ( P = 0.004).

CONCLUSIONS

In conclusion, increasing the tissue concentration of administered cisplatin in the livers of living swine through the effect of sonoporation was possible in the presence of a large amount of micro-nano bubbles.

Ultrasound-Induced Tumor Perfusion Changes and Doxorubicin Delivery: A Study on Pulse Length and Pulse Repetition Frequency

OBJECTIVES

To investigate the appropriate combination of pulse length (PL) and pulse repetition frequency (PRF) when performing ultrasound stimulated microbubble (USMB) to enhance doxorubicin (DOX) delivery to tumors.

METHODS

A total of 48 tumor-bearing mice were divided into four groups, namely groups A-D. The mice in groups B-D were treated with chemotherapy and USMB treatment with different combinations of PL and PRF, and group A was control. Contrast-enhanced ultrasound imaging was conducted to analyze tumor blood perfusion. Fluorescence microscopy and high-performance liquid chromatography were used to qualitatively and quantitatively analyse DOX release. The structural changes of tumors were observed under light microscope and transmission electron microscope. Furthermore, another 24 tumor-bearing mice were treated with sonochemotherapy and some related inflammatory factors were measured to explore the underlying mechanism.

RESULTS

With PL of three cycles and PRF of 2 kHz, the tumor perfusion area ratio increased by 26.67%, and the DOX concentration was 4.69 times higher than the control (P < .001). With PL of 34.5 cycles and PRF of 200 Hz, the tumor perfusion area ratio decreased by 12.7% and DOX did not exhibit increased extravasation compared with the control. Microvascular rupture and hemorrhage were observed after long PL and low PRF treatment. While vasodilation and higher levels of some vasodilator inflammatory factors were found after treatment with short PL and high PRF.

CONCLUSIONS

USMB treatment using short PL and high PRF could enhance tumor blood perfusion and increase DOX delivery, whereas long PL and low PRF could not serve the same purpose.

Improved Therapeutic Delivery Targeting Clinically Relevant Orthotopic Human Pancreatic Tumors Engrafted in Immunocompromised Pigs Using Ultrasound-Induced Cavitation: A Pilot Study

Pancreatic tumors can be resistant to drug penetration due to high interstitial fluid pressure, dense stroma, and disarrayed vasculature. Ultrasound-induced cavitation is an emerging technology that may overcome many of these limitations. Low-intensity ultrasound, coupled with co-administered cavitation nuclei consisting of gas-stabilizing sub-micron scale SonoTran Particles, is effective at increasing therapeutic antibody delivery to xenograft flank tumors in mouse models. Here, we sought to evaluate the effectiveness of this approach in situ using a large animal model that mimics human pancreatic cancer patients. Immunocompromised pigs were surgically engrafted with human Panc-1 pancreatic ductal adenocarcinoma (PDAC) tumors in targeted regions of the pancreas. These tumors were found to recapitulate many features of human PDAC tumors. Animals were intravenously injected with the common cancer therapeutics Cetuximab, gemcitabine, and paclitaxel, followed by infusion with SonoTran Particles. Select tumors in each animal were targeted with focused ultrasound to induce cavitation. Cavitation increased the intra-tumor concentrations of Cetuximab, gemcitabine, and paclitaxel by 477%, 148%, and 193%, respectively, compared to tumors that were not targeted with ultrasound in the same animals. Together, these data show that ultrasound-mediated cavitation, when delivered in combination with gas-entrapping particles, improves therapeutic delivery in pancreatic tumors under clinically relevant conditions.

Microbubbles for human diagnosis and therapy

Microbubbles (MBs) were observed for the first time in vivo as a curious consequence of quick saline injection during ultrasound (US) imaging of the aortic root, more than 50 years ago. From this serendipitous event, MBs are now widely used as contrast enhancers for US imaging. Their intrinsic properties described in this review, allow a multitude of designs, from shell to gas composition but also from grafting targeting agents to drug payload encapsulation. Indeed, the versatile MBs are deeply studied for their dual potential in imaging and therapy. As presented in this paper, new generations of MBs now opens perspectives for targeted molecular imaging along with the development of new US imaging systems. This review also presents an overview of the different therapeutic strategies with US and MBs for cancer, cardiovascular diseases, and inflammation. The overall aim is to overlap those fields in order to find similarities in the MBs application for treatment enhancement associated with US. To conclude, this review explores the new scales of MBs technologies with nanobubbles development, and along concurrent advances in the US imaging field. This review ends by discussing perspectives for the booming future uses of MBs.

Interstitial fluid pressure as an emerging biomarker in solid tumors

The physical microenvironment of cancer is characterized by elevated stiffness and tissue pressure, the main component of which is the interstitial fluid pressure (IFP). Elevated IFP is an established negative predictive and prognostic parameter, directly affecting malignant behavior and therapy response. As such, measurement of the IFP would allow to develop strategies aimed at engineering the physical microenvironment of cancer. Traditionally, IFP measurement required the use of invasive methods. Recent progress in dynamic and functional imaging methods such as dynamic contrast enhanced (DCE) magnetic resonance imaging and elastography, combined with numerical models and simulation, allows to comprehensively assess the biomechanical landscape of cancer, and may help to overcome physical barriers to drug delivery and immune cell infiltration. Here, we provide a comprehensive overview of the origin of elevated IFP, and its role in the malignant phenotype. Also, we review the methods used to measure IFP using invasive and imaging based methods, and highlight remaining obstacles and potential areas of progress in order to implement IFP measurement in clinical practice.

Application of Ultrasound Combined with Microbubbles for Cancer Therapy

At present, cancer is one of the leading causes of death worldwide. Treatment failure remains one of the prime hurdles in cancer treatment due to the metastatic nature of cancer. Techniques have been developed to hinder the growth of tumours or at least to stop the metastasis process. In recent years, ultrasound therapy combined with microbubbles has gained immense success in cancer treatment. Ultrasound-stimulated microbubbles (USMB) combined with other cancer treatments including radiation therapy, chemotherapy or immunotherapy has demonstrated potential improved outcomes in various in vitro and in vivo studies. Studies have shown that low dose radiation administered with USMB can have similar effects as high dose radiation therapy. In addition, the use of USMB in conjunction with radiotherapy or chemotherapy can minimize the toxicity of high dose radiation or chemotherapeutic drugs, respectively. In this review, we discuss the biophysical properties of USMB treatment and its applicability in cancer therapy. In particular, we highlight important preclinical and early clinical findings that demonstrate the antitumour effect combining USMB and other cancer treatment modalities (radiotherapy and chemotherapy). Our review mainly focuses on the tumour vascular effects mediated by USMB and these cancer therapies. We also discuss several current limitations, in addition to ongoing and future efforts for applying USMB in cancer treatment.

Chemotherapy Augmentation Using Low-Intensity Ultrasound Combined with Microbubbles with Different Mechanical Indexes in a Pancreatic Cancer Model

The aim of the study was to explore the optimal mechanical indexes (MIs) for low-intensity ultrasound (LIUS) combined with microbubbles to enhance tumor blood perfusion and improve drug concentration in pancreatic cancer-bearing nude mice. Fifty-four nude mice bearing bilateral pancreatic tumors on the hind legs were randomly divided into three groups (the MI was set at 0.3, 0.7 and 1.1 in groups A, B and C, respectively). Five nude mice in each group were intravenously injected with the fluorescent dye DiR iodide (DiIC18(7),1,1'-dioctadecyl-3,3,3',3'-tetramethylindotricarbocyanine iodide); for each mouse, one tumor was treated with LIUS combined with microbubbles, and the contralateral tumor was exposed to sham ultrasound. In vivo fluorescence imaging was performed to detect the enrichment of intratumoral DiR iodide. Twelve mice in each group were intravenously injected with doxorubicin (DOX) and underwent ultrasound therapy as described above. Tumor blood perfusion changes were quantitatively evaluated with pre- and post-treatment contrast-enhanced ultrasound (CEUS, MI = 0.08). One hour after the post-treatment CEUS, nude mice were sacrificed to determine the DOX concentration in tumor tissue; one mouse in each group was sacrificed after ultrasound treatment for tumor hematoxylin-eosin staining examination. CEUS quantitative analysis and in vivo fluorescence images confirmed that LIUS at MI = 0.3 combined with microbubbles was able to enhance tumor blood flow and increase regional fluorescence dye DiR iodide concentration. The DOX concentration on the therapeutic side was significantly higher than that on the control side after ultrasound-stimulated (MI = 0.3) microbubble cavitation (USMC) treatment (1.45 ± 0.53 μg/g vs. 1.07 ± 0.46 μg/g, t = -5.163, p = 0.001). However, in groups B and C, there were no significant differences in DOX concentration between the therapeutic and control sides (Z = -0.297, -0.357, p = 0.766, 0.721). No hemorrhage or other tissue damage was observed in hematoxylin-eosin-stained tumor specimens of both sides in all groups. LIUS at MI = 0.3 combined with microbubbles was able to enhance tumor blood perfusion and improve local drug concentration in nude mice bearing pancreatic cancer.

Ultrasound and microbubbles to beat barriers in tumors: Improving delivery of nanomedicine

Successful delivery of drugs and nanomedicine to tumors requires a functional vascular network, extravasation across the capillary wall, penetration through the extracellular matrix, and cellular uptake. Nanomedicine has many merits, but penetration deep into the tumor interstitium remains a challenge. Failure of cancer treatment can be caused by insufficient delivery of the therapeutic agents. After intravenous administration, nanomedicines are often found in off-target organs and the tumor extracellular matrix close to the capillary wall. With circulating microbubbles, ultrasound exposure focused toward the tumor shows great promise in improving the delivery of therapeutic agents. In this review, we address the impact of focused ultrasound and microbubbles to overcome barriers for drug delivery such as perfusion, extravasation, and transport through the extracellular matrix. Furthermore, we discuss the induction of an immune response with ultrasound and delivery of immunotherapeutics. The review discusses mainly preclinical results and ends with a summary of ongoing clinical trials.

The Role of Ultrasound in Modulating Interstitial Fluid Pressure in Solid Tumors for Improved Drug Delivery

The unique microenvironment of solid tumors, including desmoplasia within the extracellular matrix, enhanced vascular permeability, and poor lymphatic drainage, leads to an elevated interstitial fluid pressure which is a major barrier to drug delivery. Reducing tumor interstitial fluid pressure is one proposed method of increasing drug delivery to the tumor. The goal of this topical review is to describe recent work using focused ultrasound with or without microbubbles to modulate tumor interstitial fluid pressure, through either thermal or mechanical effects on the extracellular matrix and the vasculature. Furthermore, we provide a review on techniques in which ultrasound imaging may be used to diagnose elevated interstitial fluid pressure within solid tumors. Ultrasound-based techniques show high promise in diagnosing and treating elevated interstitial pressure to enhance drug delivery.

Ultrasound-Responsive Cavitation Nuclei for Therapy and Drug Delivery

Therapeutic ultrasound strategies that harness the mechanical activity of cavitation nuclei for beneficial tissue bio-effects are actively under development. The mechanical oscillations of circulating microbubbles, the most widely investigated cavitation nuclei, which may also encapsulate or shield a therapeutic agent in the bloodstream, trigger and promote localized uptake. Oscillating microbubbles can create stresses either on nearby tissue or in surrounding fluid to enhance drug penetration and efficacy in the brain, spinal cord, vasculature, immune system, biofilm or tumors. This review summarizes recent investigations that have elucidated interactions of ultrasound and cavitation nuclei with cells, the treatment of tumors, immunotherapy, the blood-brain and blood-spinal cord barriers, sonothrombolysis, cardiovascular drug delivery and sonobactericide. In particular, an overview of salient ultrasound features, drug delivery vehicles, therapeutic transport routes and pre-clinical and clinical studies is provided. Successful implementation of ultrasound and cavitation nuclei-mediated drug delivery has the potential to change the way drugs are administered systemically, resulting in more effective therapeutics and less-invasive treatments.

Advances in low-frequency ultrasound combined with microbubbles in targeted tumor therapy

The development of low-frequency ultrasound imaging technology and the improvement of ultrasound contrast agent production technology mean that they play an increasingly important role in tumor therapy. The interaction between ultrasound and microbubbles and their biological effects can transfer and release microbubbles carrying genes and drugs to target tissues, mediate the apoptosis of tumor cells, and block the embolization of tumor microvasculature. With the optimization of ultrasound parameters, the development of targeted microbubbles, and the emergence of various composite probes with both diagnostic and therapeutic functions, low-frequency ultrasound combined with microbubble contrast agents will bring new hope for clinical tumor treatment.