Fluorescein-mediated sonodynamic therapy in a rat glioma model.

INTRODUCTION: Malignant gliomas have a dismal prognosis and significant efforts are being made to develop more effective treatments. Sonodynamic therapy (SDT) is an emerging modality for cancer treatment which combines ultrasound with sonosensitizers to produce a localized cytotoxic effect. The aim of this study is to demonstrate the efficacy of SDT with fluorescein (FL) and low-intensity focused ultrasound in inhibiting the growth of ectopic gliomas implanted in the rat's subcutaneous tissue. METHODS: In vivo cytotoxicity of FL-SDT was evaluated in C6 rat glioma cells which were inoculated subcutaneously. Tumor specific extracellular FL extravasation and accumulation was assessed with IVIS imaging in rats receiving systemic FL. Effects of FL-SDT with focused low-intensity ultrasound on tumor growth, and histological features of the rat's tumors were investigated. Treatment related apoptosis and necrosis were analyzed using hematoxylin & eosin, and apoptosis-specific staining. RESULTS: IVIS imaging revealed a high degree of FL accumulation within the tumor, with a nearly threefold increase in tumoral epifluorescence signal over background. SDT significantly inhibited outgrowth of ectopic C6 gliomas across all three FUS exposure conditions. TUNEL and active caspase-3 staining did not reveal conclusive trends across control and SDT condition for apoptosis. CONCLUSION: Our results suggest that SDT with FL and low-intensity FUS is effective in inhibiting the growth of ectopic malignant gliomas in rats. The selective FL extravasation and accumulation in the tumor areas where the blood-brain barrier is damaged suggests the tumor-specificity of the treatment. The possibility to use this treatment in intracranial models and in human gliomas will have to be explored in further studies.

Ultrasound-activated agents comprised of 5FU-bearing nanoparticles bonded to microbubbles inhibit solid tumor growth and improve survival.

Nanoparticle (NP) drug delivery vehicles may eventually offer improved tumor treatments; however, NP delivery from the bloodstream to tumors can be hindered by poor convective and/or diffusive transport. We tested whether poly(lactic-co-glycolic acid) NP delivery can be improved by covalently linking them to ultrasound (US)-activated microbubbles in a "composite-agent" formulation and whether drug 5-fluorouracil (5FU)-loaded NPs delivered in this fashion inhibit the growth of tumors that are typically not responsive to intravenously administered 5FU. After intravenous composite-agent injection, C6 gliomas implanted on Rag-1(-/-) mice were exposed to pulsed 1 MHz US, resulting in the delivery of 16% of the initial NP dose per gram tissue. This represented a five- to 57-fold increase in NP delivery when compared to multiple control groups. 5FU-bearing NP delivery from the composite-agent formulation resulted in a 67% reduction in tumor volume at 7 days after treatment, and animal survival increased significantly when compared to intravenous soluble 5FU administration. We conclude that NP delivery from US-activated composite agents may improve tumor treatment by offering a combination of better targeting, enhanced payload delivery, and controlled local drug release.

Guidelines for immunological analyses following focused ultrasound treatment.

Focused ultrasound (FUS) is a powerful emerging tool for non-invasive, non-ionizing targeted destruction of tumors. The last two decades have seen a growing body of preclinical and clinical literature supporting the capacity of FUS to increase nascent immune responses to tumors and to potentiate cancer immunotherapies (e.g. checkpoint inhibitors) through a variety of means, including immune modulation and drug delivery. With the rapid acceleration of this field and a multitude of FUS immunotherapy clinical trials having now been deployed worldwide, there is a need to streamline and standardize the methodology for immunological analyses field-wide. Recently, the Focused Ultrasound Foundation and Cancer Research Institute partnered to convene a group of over 85 leaders to discuss the nexus of FUS and immuno-oncology. The guidelines documented herein were assembled in response to recommendations that emerged from this discussion, emphasizing the urgent need for heightened accessibility of immune analysis methods and standardized protocols unique to the field. These guidelines are designated for existing stakeholders in the FUS immuno-oncology domain or those newly entering the field, to provide guidance on collection, storage, and immunological profiling of tissue or blood specimens in the context of FUS immunotherapy studies, and additionally offer templates for standardized deployment of these methods based on collective experience gained within the field to date. These guidelines are tumor-agnostic and provide evidence-based, consensus-based recommendations for both preclinical and clinical immune analysis of tissue and blood specimens.

Intracranial Sonodynamic Therapy With 5-Aminolevulinic Acid and Sodium Fluorescein: Safety Study in a Porcine Model.

BACKGROUND: Sonodynamic therapy (SDT) is an emerging ultrasound-based treatment modality for malignant gliomas which combines ultrasound with sonosensitizers to produce a localized cytotoxic and modulatory effect. Tumor-specificity of the treatment is achieved by the selective extravasation and accumulation of sonosensitizers in the tumor-bearing regions. The aim of this study is to demonstrate the safety of low-intensity ultrasonic irradiation of healthy brain tissue after the administration of FDA-approved sonosensitizers used for SDT in experimental studies in an in vivo large animal model. METHODS: In vivo safety of fluorescein (Na-Fl)- and 5 aminolevulinic acid (5-ALA)-mediated low-intensity ultrasound irradiation of healthy brain parenchyma was assessed in two sets of four healthy swine brains, using the magnetic resonance imaging (MRI)-guided Insightec ExAblate 4000 220 kHz system. After administration of the sonosensitizers, a wide fronto-parietal craniotomy was performed in pig skulls to allow transmission of ultrasonic beams. Sonication was performed on different spots within the thalamus and periventricular white matter with continuous thermal monitoring. Sonication-related effects were investigated with MRI and histological analysis. RESULTS: Post-treatment MRI images acquired within one hour following the last sonication, on day one, and day seven did not visualize any sign of brain damage. On histopathology, no signs of necrosis or apoptosis attributable to the ultrasonic treatments were shown in target areas. CONCLUSIONS: The results of the present study suggest that either Na-FL or 5-ALA-mediated sonodynamic therapies under MRI-guidance with the current acoustic parameters are safe towards healthy brain tissue in a large in vivo model. These results further support growing interest in clinical translation of sonodynamic therapy for intracranial gliomas and other brain tumors.

Noninvasive neuromodulation and thalamic mapping with low-intensity focused ultrasound.

OBJECTIVE Ultrasound can be precisely focused through the intact human skull to target deep regions of the brain for stereotactic ablations. Acoustic energy at much lower intensities is capable of both exciting and inhibiting neural tissues without causing tissue heating or damage. The objective of this study was to demonstrate the effects of low-intensity focused ultrasound (LIFU) for neuromodulation and selective mapping in the thalamus of a large-brain animal. METHODS Ten Yorkshire swine ( Sus scrofa domesticus) were used in this study. In the first neuromodulation experiment, the lemniscal sensory thalamus was stereotactically targeted with LIFU, and somatosensory evoked potentials (SSEPs) were monitored. In a second mapping experiment, the ventromedial and ventroposterolateral sensory thalamic nuclei were alternately targeted with LIFU, while both trigeminal and tibial evoked SSEPs were recorded. Temperature at the acoustic focus was assessed using MR thermography. At the end of the experiments, all tissues were assessed histologically for damage. RESULTS LIFU targeted to the ventroposterolateral thalamic nucleus suppressed SSEP amplitude to 71.6% ± 11.4% (mean ± SD) compared with baseline recordings. Second, we found a similar degree of inhibition with a high spatial resolution (∼ 2 mm) since adjacent thalamic nuclei could be selectively inhibited. The ventromedial thalamic nucleus could be inhibited without affecting the ventrolateral nucleus. During MR thermography imaging, there was no observed tissue heating during LIFU sonications and no histological evidence of tissue damage. CONCLUSIONS These results suggest that LIFU can be safely used to modulate neuronal circuits in the central nervous system and that noninvasive brain mapping with focused ultrasound may be feasible in humans.

MR image-guided delivery of cisplatin-loaded brain-penetrating nanoparticles to invasive glioma with focused ultrasound.

Systemically administered chemotherapeutic drugs are often ineffective in the treatment of invasive brain tumors due to poor therapeutic index. Within gliomas, despite the presence of heterogeneously leaky microvessels, dense extracellular matrix and high interstitial pressure generate a "blood-tumor barrier" (BTB), which inhibits drug delivery and distribution. Meanwhile, beyond the contrast MRI-enhancing edge of the tumor, invasive cancer cells are protected by the intact blood-brain barrier (BBB). Here, we tested whether brain-penetrating nanoparticles (BPN) that possess dense surface coatings of polyethylene glycol (PEG) and are loaded with cisplatin (CDDP) could be delivered across both the blood-tumor and blood-brain barriers with MR image-guided focused ultrasound (MRgFUS), and whether this treatment could control glioma growth and invasiveness. To this end, we first established that MRgFUS is capable of significantly enhancing the delivery of ~60nm fluorescent tracer BPN across the blood-tumor barrier in both the 9L (6-fold improvement) gliosarcoma and invasive F98 (28-fold improvement) glioma models. Importantly, BPN delivery across the intact BBB, just beyond the tumor edge, was also markedly increased in both tumor models. We then showed that a CDDP loaded BPN formulation (CDDP-BPN), composed of a blend of polyaspartic acid (PAA) and heavily PEGylated polyaspartic acid (PAA-PEG), was highly stable, provided extended drug release, and was effective against F98 cells in vitro. These CDDP-BPN were delivered from the systemic circulation into orthotopic F98 gliomas using MRgFUS, where they elicited a significant reduction in tumor invasiveness and growth, as well as improved animal survival. We conclude that this therapy may offer a powerful new approach for the treatment invasive gliomas, particularly for preventing and controlling recurrence.

Drug and gene delivery across the blood-brain barrier with focused ultrasound.

The blood-brain barrier (BBB) remains one of the most significant limitations to treatments of central nervous system (CNS) disorders including brain tumors, neurodegenerative diseases and psychiatric disorders. It is now well-established that focused ultrasound (FUS) in conjunction with contrast agent microbubbles may be used to non-invasively and temporarily disrupt the BBB, allowing localized delivery of systemically administered therapeutic agents as large as 100nm in size to the CNS. Importantly, recent technological advances now permit FUS application through the intact human skull, obviating the need for invasive and risky surgical procedures. When used in combination with magnetic resonance imaging, FUS may be applied precisely to pre-selected CNS targets. Indeed, FUS devices capable of sub-millimeter precision are currently in several clinical trials. FUS mediated BBB disruption has the potential to fundamentally change how CNS diseases are treated, unlocking potential for combinatorial treatments with nanotechnology, markedly increasing the efficacy of existing therapeutics that otherwise do not cross the BBB effectively, and permitting safe repeated treatments. This article comprehensively reviews recent studies on the targeted delivery of therapeutics into the CNS with FUS and offers perspectives on the future of this technology.

High-intensity focused ultrasound ablation enhancement in vivo via phase-shift nanodroplets compared to microbubbles.

BACKGROUND: During high-intensity focused ultrasound (HIFU) surgical procedures, there is a need to rapidly ablate pathological tissue while minimizing damage to healthy tissue. Current techniques are limited by relatively long procedure times and risks of off-target heating of healthy tissue. One possible solution is the use of microbubbles, which can improve the efficiency of thermal energy delivery during HIFU procedures. However, microbubbles also suffer from limitations such as low spatial selectivity and short circulation time in vivo. In this study, the use of a dual-perfluorocarbon nanodroplet that can enhance thermal ablation, yet retains high spatial selectivity and circulation half-life, was evaluated in vivo and compared to traditional microbubble agents during HIFU ablations of rat liver. METHODS: High-intensity focused ultrasound (1.1 MHz, 4.1 MPa, 15-s continuous wave) was applied to rat liver in vivo, and heating was monitored during sonication by magnetic resonance thermometry. Thermometry data were analyzed to quantify temperature rise and ablated area, both at the target and prefocally, for HIFU applied 5, 15, or 95 min after intravenous injection of either nanodroplet or microbubble agents. Sham control experiments (no injected agents) were also performed. RESULTS: At all three time points, nanodroplets significantly enhanced thermal delivery to the target, achieving temperatures 130 % higher and ablated areas 30 times larger than no-agent control sonications. Nanodroplets did not significantly enhance off-target surface heating. Microbubbles also resulted in significantly greater thermal delivery, but heating was concentrated at the proximal surface of the animal, causing skin burns. Furthermore, microbubbles resulted in lower thermal delivery to the desired target than even the control case, with the notable exception of the 95-min time point. CONCLUSIONS: Results indicate that the nanodroplet formulation studied here can substantially increase thermal delivery at the acoustic focus while avoiding prefocal heating. In contrast, microbubbles resulted in greater prefocal heating and less heating at the target. Furthermore, nanodroplets are sufficiently stable to enhance HIFU ablation in vivo for at least 1.5 h after injection. The use of a dual-perfluorocarbon nanodroplet formulation as described herein could substantially reduce HIFU procedure times without increasing the risk of skin burns.

Non-invasive delivery of stealth, brain-penetrating nanoparticles across the blood-brain barrier using MRI-guided focused ultrasound.

The blood-brain barrier (BBB) presents a significant obstacle for the treatment of many central nervous system (CNS) disorders, including invasive brain tumors, Alzheimer's, Parkinson's and stroke. Therapeutics must be capable of bypassing the BBB and also penetrate the brain parenchyma to achieve a desired effect within the brain. In this study, we test the unique combination of a non-invasive approach to BBB permeabilization with a therapeutically relevant polymeric nanoparticle platform capable of rapidly penetrating within the brain microenvironment. MR-guided focused ultrasound (FUS) with intravascular microbubbles (MBs) is able to locally and reversibly disrupt the BBB with submillimeter spatial accuracy. Densely poly(ethylene-co-glycol) (PEG) coated, brain-penetrating nanoparticles (BPNs) are long-circulating and diffuse 10-fold slower in normal rat brain tissue compared to diffusion in water. Following intravenous administration of model and biodegradable BPNs in normal healthy rats, we demonstrate safe, pressure-dependent delivery of 60nm BPNs to the brain parenchyma in regions where the BBB is disrupted by FUS and MBs. Delivery of BPNs with MR-guided FUS has the potential to improve efficacy of treatments for many CNS diseases, while reducing systemic side effects by providing sustained, well-dispersed drug delivery into select regions of the brain.