Ultrasound-mediated delivery of doxorubicin to the brain results in immune modulation and improved responses to PD-1 blockade in gliomas.

Given the marginal penetration of most drugs across the blood-brain barrier, the efficacy of various agents remains limited for glioblastoma (GBM). Here we employ low-intensity pulsed ultrasound (LIPU) and intravenously administered microbubbles (MB) to open the blood-brain barrier and increase the concentration of liposomal doxorubicin and PD-1 blocking antibodies (aPD-1). We report results on a cohort of 4 GBM patients and preclinical models treated with this approach. LIPU/MB increases the concentration of doxorubicin by 2-fold and 3.9-fold in the human and murine brains two days after sonication, respectively. Similarly, LIPU/MB-mediated blood-brain barrier disruption leads to a 6-fold and a 2-fold increase in aPD-1 concentrations in murine brains and peritumoral brain regions from GBM patients treated with pembrolizumab, respectively. Doxorubicin and aPD-1 delivered with LIPU/MB upregulate major histocompatibility complex (MHC) class I and II in tumor cells. Increased brain concentrations of doxorubicin achieved by LIPU/MB elicit IFN-γ and MHC class I expression in microglia and macrophages. Doxorubicin and aPD-1 delivered with LIPU/MB results in the long-term survival of most glioma-bearing mice, which rely on myeloid cells and lymphocytes for their efficacy. Overall, this translational study supports the utility of LIPU/MB to potentiate the antitumoral activities of doxorubicin and aPD-1 for GBM.

Repeated blood-brain barrier opening with a nine-emitter implantable ultrasound device in combination with carboplatin in recurrent glioblastoma: a phase I/II clinical trial.

Here, the results of a phase 1/2 single-arm trial (NCT03744026) assessing the safety and efficacy of blood-brain barrier (BBB) disruption with an implantable ultrasound system in recurrent glioblastoma patients receiving carboplatin are reported. A nine-emitter ultrasound implant was placed at the end of tumor resection replacing the bone flap. After surgery, activation to disrupt the BBB was performed every four weeks either before or after carboplatin infusion. The primary objective of the Phase 1 was to evaluate the safety of escalating numbers of ultrasound emitters using a standard 3 + 3 dose escalation. The primary objective of the Phase 2 was to evaluate the efficacy of BBB opening using magnetic resonance imaging (MRI). The secondary objectives included safety and clinical efficacy. Thirty-three patients received a total of 90 monthly sonications with carboplatin administration and up to nine emitters activated without observed DLT. Grade 3 procedure-related adverse events consisted of pre syncope (n = 3), fatigue (n = 1), wound infection (n = 2), and pain at time of device connection (n = 7). BBB opening endpoint was met with 90% of emitters showing BBB disruption on MRI after sonication. In the 12 patients who received carboplatin just prior to sonication, the progression-free survival was 3.1 months, the 1-year overall survival rate was 58% and median overall survival was 14.0 months from surgery.

Paclitaxel and Carboplatin in Combination with Low-intensity Pulsed Ultrasound for Glioblastoma.

PURPOSE: We recently reported on clinical trials for patients with recurrent glioblastoma where low-intensity pulsed ultrasound and microbubbles (LIPU/MB) improved paclitaxel or carboplatin delivery into the brain. Here, we report variable local tumor control with paclitaxel at the maximal/target dose in our phase I trial (NCT04528680). To address this, we investigated the combination of paclitaxel with carboplatin in preclinical glioma models. EXPERIMENTAL DESIGN: We performed MRI-based analysis to evaluate disease control in patients from our trial. We studied the cytotoxicity of paclitaxel and carboplatin against 11 human glioma lines as monotherapy and in combination at concentrations derived from human intraoperative studies. Synergy was assessed with the Loewe model and the survival benefit evaluated in two xenografts. We examined the effects on cell cycle progression, DNA damage, and apoptosis. RESULTS: Patients treated with paclitaxel and LIPU/MB exhibited variable local tumor control, which correlated with overall survival. We observed limited cross-resistance to paclitaxel and carboplatin in glioma lines, with almost a third of them being exclusively susceptible to one drug. This combination led to susceptibility of 81% of lines and synergy in 55% of them. The combination proved more efficacious in two intracranial xenografts when administered with LIPU/MB, leading to complementary effects on cell cycle arrest. CONCLUSIONS: Combining paclitaxel and carboplatin in gliomas may be more efficacious than monotherapy, as in other cancers, due to synergy and independent susceptibility to each drug. These results form the basis for an ongoing phase II trial (NCT04528680) where we investigate this combination with LIPU/MB.

Repeated blood-brain barrier opening with an implantable ultrasound device for delivery of albumin-bound paclitaxel in patients with recurrent glioblastoma: a phase 1 trial.

BACKGROUND: Low-intensity pulsed ultrasound with concomitant administration of intravenous microbubbles (LIPU-MB) can be used to open the blood-brain barrier. We aimed to assess the safety and pharmacokinetics of LIPU-MB to enhance the delivery of albumin-bound paclitaxel to the peritumoural brain of patients with recurrent glioblastoma. METHODS: We conducted a dose-escalation phase 1 clinical trial in adults (aged ≥18 years) with recurrent glioblastoma, a tumour diameter of 70 mm or smaller, and a Karnofsky performance status of at least 70. A nine-emitter ultrasound device was implanted into a skull window after tumour resection. LIPU-MB with intravenous albumin-bound paclitaxel infusion was done every 3 weeks for up to six cycles. Six dose levels of albumin-bound paclitaxel (40 mg/m2, 80 mg/m2, 135 mg/m2, 175 mg/m2, 215 mg/m2, and 260 mg/m2) were evaluated. The primary endpoint was dose-limiting toxicity occurring during the first cycle of sonication and albumin-bound paclitaxel chemotherapy. Safety was assessed in all treated patients. Analyses were done in the per-protocol population. Blood-brain barrier opening was investigated by MRI before and after sonication. We also did pharmacokinetic analyses of LIPU-MB in a subgroup of patients from the current study and a subgroup of patients who received carboplatin as part of a similar trial (NCT03744026). This study is registered with ClinicalTrials.gov, NCT04528680, and a phase 2 trial is currently open for accrual. FINDINGS: 17 patients (nine men and eight women) were enrolled between Oct 29, 2020, and Feb 21, 2022. As of data cutoff on Sept 6, 2022, median follow-up was 11·89 months (IQR 11·12-12·78). One patient was treated per dose level of albumin-bound paclitaxel for levels 1 to 5 (40-215 mg/m2), and 12 patients were treated at dose level 6 (260 mg/m2). A total of 68 cycles of LIPU-MB-based blood-brain barrier opening were done (median 3 cycles per patient [range 2-6]). At a dose of 260 mg/m2, encephalopathy (grade 3) occurred in one (8%) of 12 patients during the first cycle (considered a dose-limiting toxicity), and in one other patient during the second cycle (grade 2). In both cases, the toxicity resolved and treatment continued at a lower dose of albumin-bound paclitaxel, with a dose of 175 mg/m2 in the case of the grade 3 encephalopathy, and to 215 mg/m2 in the case of the grade 2 encephalopathy. Grade 2 peripheral neuropathy was observed in one patient during the third cycle of 260 mg/m2 albumin-bound paclitaxel. No progressive neurological deficits attributed to LIPU-MB were observed. LIPU-MB-based blood-brain barrier opening was most commonly associated with immediate yet transient grade 1-2 headache (12 [71%] of 17 patients). The most common grade 3-4 treatment-emergent adverse events were neutropenia (eight [47%]), leukopenia (five [29%]), and hypertension (five [29%]). No treatment-related deaths occurred during the study. Imaging analysis showed blood-brain barrier opening in the brain regions targeted by LIPU-MB, which diminished over the first 1 h after sonication. Pharmacokinetic analyses showed that LIPU-MB led to increases in the mean brain parenchymal concentrations of albumin-bound paclitaxel (from 0·037 µM [95% CI 0·022-0·063] in non-sonicated brain to 0·139 µM [0·083-0·232] in sonicated brain [3·7-times increase], p<0·0001) and carboplatin (from 0·991 µM [0·562-1·747] in non-sonicated brain to 5·878 µM [3·462-9·980] µM in sonicated brain [5·9-times increase], p=0·0001). INTERPRETATION: LIPU-MB using a skull-implantable ultrasound device transiently opens the blood-brain barrier allowing for safe, repeated penetration of cytotoxic drugs into the brain. This study has prompted a subsequent phase 2 study combining LIPU-MB with albumin-bound paclitaxel plus carboplatin (NCT04528680), which is ongoing. FUNDING: National Institutes of Health and National Cancer Institute, Moceri Family Foundation, and the Panattoni family.

Low-Intensity Pulsed Ultrasound-Mediated Blood-Brain Barrier Opening Increases Anti-Programmed Death-Ligand 1 Delivery and Efficacy in Gl261 Mouse Model.

Therapeutic antibodies targeting immune checkpoints have shown limited efficacy in clinical trials in glioblastoma (GBM) patients. Ultrasound-mediated blood-brain barrier opening (UMBO) using low-intensity pulsed ultrasound improved drug delivery to the brain. We explored the safety and the efficacy of UMBO plus immune checkpoint inhibitors in preclinical models of GBM. A blood-brain barrier (BBB) opening was performed using a 1 MHz preclinical ultrasound system in combination with 10 µL/g microbubbles. Brain penetration of immune checkpoint inhibitors was determined, and immune cell populations were evaluated using flow cytometry. The impact of repeated treatments on survival was determined. In syngeneic GL261-bearing immunocompetent mice, we showed that UMBO safely and repeatedly opened the BBB. BBB opening was confirmed visually and microscopically using Evans blue dye and magnetic resonance imaging. UMBO plus anti-PDL-1 was associated with a significant improvement of overall survival compared to anti-PD-L1 alone. Using mass spectroscopy, we showed that the penetration of therapeutic antibodies can be increased when delivered intravenously compared to non-sonicated brains. Furthermore, we observed an enhancement of activated microglia percentage when combined with anti-PD-L1. Here, we report that the combination of UMBO and anti-PD-L1 dramatically increases GL261-bearing mice's survival compared to their counterparts treated with anti-PD-L1 alone. Our study highlights the BBB as a limitation to overcome in order to increase the efficacy of anti-PD-L1 in GBM and supports clinical trials combining UMBO and in GBM patients.

Pilot study of repeated blood-brain barrier disruption in patients with mild Alzheimer's disease with an implantable ultrasound device.

BACKGROUND: Temporary disruption of the blood-brain barrier (BBB) using pulsed ultrasound leads to the clearance of both amyloid and tau from the brain, increased neurogenesis, and mitigation of cognitive decline in pre-clinical models of Alzheimer's disease (AD) while also increasing BBB penetration of therapeutic antibodies. The goal of this pilot clinical trial was to investigate the safety and efficacy of this approach in patients with mild AD using an implantable ultrasound device. METHODS: An implantable, 1-MHz ultrasound device (SonoCloud-1) was implanted under local anesthesia in the skull (extradural) of 10 mild AD patients to target the left supra-marginal gyrus. Over 3.5 months, seven ultrasound sessions in combination with intravenous infusion of microbubbles were performed twice per month to temporarily disrupt the BBB. 18F-florbetapir and 18F-fluorodeoxyglucose positron emission tomography (PET) imaging were performed on a combined PET/MRI scanner at inclusion and at 4 and 8 months after the initiation of sonications to monitor the brain metabolism and amyloid levels along with cognitive evaluations. The evolution of cognitive and neuroimaging features was compared to that of a matched sample of control participants taken from the Alzheimer's Disease Neuroimaging Initiative (ADNI). RESULTS: A total of 63 BBB opening procedures were performed in nine subjects. The procedure was well-tolerated. A non-significant decrease in amyloid accumulation at 4 months of - 6.6% (SD = 7.2%) on 18F-florbetapir PET imaging in the sonicated gray matter targeted by the ultrasound transducer was observed compared to baseline in six subjects that completed treatments and who had evaluable imaging scans. No differences in the longitudinal change in the glucose metabolism were observed compared to the neighboring or contralateral regions or to the change observed in the same region in ADNI participants. No significant effect on cognition evolution was observed in comparison with the ADNI participants as expected due to the small sample size and duration of the trial. CONCLUSIONS: These results demonstrate the safety of ultrasound-based BBB disruption and the potential of this technology to be used as a therapy for AD patients. Research of this technique in a larger clinical trial with a device designed to sonicate larger volumes of tissue and in combination with disease-modifying drugs may further enhance the effects observed. TRIAL REGISTRATION: ClinicalTrials.gov, NCT03119961.

Opening of the Blood-Brain Barrier Using Low-Intensity Pulsed Ultrasound Enhances Responses to Immunotherapy in Preclinical Glioma Models.

PURPOSE: The blood-brain barrier (BBB) inhibits adequate dosing/penetration of therapeutic agents to malignancies in the brain. Low-intensity pulsed ultrasound (LIPU) is a safe therapeutic method of temporary BBB disruption (BBBD) to enhance chemotherapeutic delivery to the tumor and surrounding brain parenchyma for treatment of glioblastoma. EXPERIMENTAL DESIGN: We investigated if LIPU could enhance therapeutic efficacy of anti-PD-1 in C57BL/6 mice bearing intracranial GL261 gliomas, epidermal growth factor receptor variant III (EGFRvIII) chimeric antigen receptor (CAR) T cells in NSG mice with EGFRvIII-U87 gliomas, and a genetically engineered antigen-presenting cell (APC)-based therapy producing the T-cell attracting chemokine CXCL10 in the GL261-bearing mice. RESULTS: Mice treated with anti-PD-1 and LIPU-induced BBBD had a median survival duration of 58 days compared with 39 days for mice treated with anti-PD-1, and long-term survivors all remained alive after contralateral hemisphere rechallenge. CAR T-cell administration with LIPU-induced BBBD resulted in significant increases in CAR T-cell delivery to the CNS after 24 (P < 0.005) and 72 (P < 0.001) hours and increased median survival by greater than 129%, in comparison with CAR T cells alone. Local deposition of CXCL10-secreting APCs in the glioma microenvironment with LIPU enhanced T-cell glioma infiltration during the therapeutic window (P = 0.004) and markedly enhanced survival (P < 0.05). CONCLUSIONS: LIPU increases immune therapeutic delivery to the tumor microenvironment with an associated increase in survival and is an emerging technique for enhancing novel therapies in the brain.

Ultrasound-induced blood-brain barrier disruption for the treatment of gliomas and other primary CNS tumors.

The treatment of primary brain tumors, especially malignant gliomas, remains challenging. The failure of most treatments for this disease is partially explained by the blood-brain barrier (BBB), which prevents circulating molecules from entering the brain parenchyma. Ultrasound-induced BBB disruption (US-BBBD) has recently emerged as a promising strategy to improve the delivery of therapeutic agents to brain tumors. A large body of preclinical studies has demonstrated that the association of low-intensity pulsed ultrasound with intravenous microbubbles can transiently open the BBB in a localized manner. The safety of this technique has been assessed in numerous preclinical studies in both small and large animal models. A large panel of therapeutic agents have been delivered to the brain in preclinical models, demonstrating both tumor control and increased survival. This technique has recently entered clinical trials with encouraging preliminary data. In this review, we describe the mechanisms and histological effects of US-BBBD and summarize the preclinical studies published to date. We furthermore provide an overview of the current clinical development and future potential of this promising technology.

Blood-brain barrier disruption with low-intensity pulsed ultrasound for the treatment of pediatric brain tumors: a review and perspectives.

Pediatric brain tumors are the most common solid tumor and the first cause of cancer death in childhood, adolescence, and young adulthood. Current treatments are far from optimal in most of these tumors and the prognosis remains dismal for many of them. One of the main causes of the failure of current medical treatments is in part due to the existence of the blood-brain barrier (BBB), which limits drug delivery to tumors. Opening of the BBB with low-intensity pulsed ultrasound (LIPU) has emerged during the last 2 decades as a promising technique for enhancing drug delivery to the brain. In preclinical models, enhanced delivery of a wide range of therapeutic agents, from low-molecular-weight drugs, to antibodies and immune cells, has been observed as well as tumor control and increased survival. This technique has recently entered clinical trials with extracranial and intracranial devices. The safety and feasibility of this technique has furthermore been shown in patients treated monthly for recurrent glioblastoma receiving carboplatin chemotherapy. In this review, the characteristics of the BBB in the most common pediatric brain tumors are reviewed. Then, principles and mechanisms of BBB disruption with ultrasound (US) are summarized and described at the histological and biological levels. Lastly, preclinical studies that have used US-induced BBB opening in tumor models, recent clinical trials, and the potential use of this technology in pediatrics are provided.

Ultrasound-Induced Blood-Spinal Cord Barrier Opening in Rabbits.

The blood-spinal cord barrier (BSCB) considerably limits the delivery and efficacy of treatments for spinal cord diseases. The blood-brain barrier can be safely opened with low-intensity pulsed ultrasound when microbubbles are simultaneously administered intravenously. This technique was tested on the BSCB in a rabbit model in this work. Twenty-three segments of spinal cord were sonicated with a 1-MHz unfocused pulsed ultrasound device and compared with non-sonicated segments. BSCB disruption was assessed using Evan's blue dye (EBD) extravasation. Tolerance was assessed by histologic analysis. An increased EBD concentration indicating BSCB disruption was clearly observed in sonicated segments compared with controls (p = 0.004). On one animal, which received 10 sonications, repetitive BSCB disruptions revealed no evidence of cumulative toxicity. BSCB can be disrupted using an unfocused pulsed ultrasound device in combination with microbubbles without neurotoxicity even in case of repeated sonications.

Temporary blood-brain barrier disruption by low intensity pulsed ultrasound increases carboplatin delivery and efficacy in preclinical models of glioblastoma.

INTRODUCTION: Glioblastoma (GBM) is the most common and aggressive primary brain cancer in adults. Few cytotoxic chemotherapies have been shown to be effective against GBM, due in part to the presence of the blood-brain barrier (BBB), which reduces the penetration of chemotherapies from the blood to the brain. Ultrasound-induced BBB opening (US-BBB) has been shown to increase the penetration of multiple chemotherapeutic agents in the brain in animal models. In the current study, the anti-tumor activity of carboplatin chemotherapy with and without US-BBB was investigated in several GBM mouse models. METHODS: First, the IC50 of two commercial (U87 and U251) and six patient-derived GBM cell lines (PDCL) to carboplatin was measured. Next, U87 was subcutaneously grafted to a nude mouse model to test the in vivo response of the tumor to carboplatin in the absence of the BBB. Lastly, nude mice bearing orthotopically xenografted GBM cell lines (U87 or a PDCL) were randomized to four experimental groups: (i) untreated, (ii) US-BBB alone, (iii) carboplatin alone and, (iv) carboplatin + US-BBB. Mice were treated once weekly for 4 weeks and monitored for toxicity, tumor growth, and survival. RESULTS: Carboplatin plus US-BBB enhanced survival (p = 0.03) and delayed tumor growth (p < 0.05) of GBM-bearing mice compared to carboplatin alone, with a 4.2-fold increase of carboplatin penetration in the brain, without evidence of significant neurological or systemic toxicity. CONCLUSIONS: Carboplatin efficacy was enhanced in GBM mouse models with US-BBB and appears to be a promising chemotherapy for this approach.

Safety and Feasibility of Repeated and Transient Blood-Brain Barrier Disruption by Pulsed Ultrasound in Patients with Recurrent Glioblastoma.

PURPOSE: The blood-brain barrier (BBB) limits the efficacy of drug therapies for glioblastoma (GBM). Preclinical data indicate that low-intensity pulsed ultrasound (LIPU) can transiently disrupt the BBB and increase intracerebral drug concentrations. PATIENTS AND METHODS: A first-in-man, single-arm, single-center trial (NCT02253212) was initiated to investigate the transient disruption of the BBB in patients with recurrent GBM. Patients were implanted with a 1-MHz, 11.5-mm diameter cranial ultrasound device (SonoCloud-1, CarThera). The device was activated monthly to transiently disrupt the BBB before intravenous carboplatin chemotherapy. RESULTS: Between 2014 and 2016, 21 patients were registered for the study and implanted with the SonoCloud-1; 19 patients received at least one sonication. In 65 ultrasound sessions, BBB disruption was visible on T1w MRI for 52 sonications. Treatment-related adverse events observed were transient and manageable: a transient edema at H1 and at D15. No carboplatin-related neurotoxicity was observed. Patients with no or poor BBB disruption (n = 8) visible on MRI had a median progression-free survival (PFS) of 2.73 months, and a median overall survival (OS) of 8.64 months. Patients with clear BBB disruption (n = 11) had a median PFS of 4.11 months, and a median OS of 12.94 months. CONCLUSIONS: SonoCloud-1 treatments were well tolerated and may increase the effectiveness of systemic drug therapies, such as carboplatin, in the brain without inducing neurotoxicity.See related commentary by Sonabend and Stupp, p. 3750.

Blood-brain barrier disruption in humans using an implantable ultrasound device: quantification with MR images and correlation with local acoustic pressure.

OBJECTIVE: One of the goals in this study was to set up a semiautomatic method to estimate blood-brain barrier disruption obtained in patients with glioblastoma by using an implantable, unfocused, ultrasound device. Another goal was to correlate the probability of significant ultrasound-induced signal enhancement (SUISE) with local acoustic pressure in the brain. METHODS: Gd-enhanced MR images acquired before and after ultrasound treatments were analyzed prospectively. The image sets were segmented, normalized, and coregistered to evaluate contrast enhancement. The volume of SUISE was calculated with voxels labeled as gray or white matter, in a cylindrical region of interest, and with enhancement above a given threshold. To validate the method, the resulting volumes of SUISE were compared to qualitative grades previously assigned by 3 clinicians for 40 ultrasound treatments in 15 patients. A parametric study was performed to optimize the algorithm prediction of the qualitative grades. The 3D acoustic field in the brain was estimated from measurements in water combined with simulations accounting for ultrasound attenuation in brain and overlaid on each MR image to correlate local acoustic pressure with the probability of SUISE (defined as enhancement > 10%). RESULTS: The algorithm predicted grade 2 or 3 and grade 3 openings with areas under the receiver operating characteristic curve of 0.831 and 0.995, respectively. The probability of SUISE was correlated with local acoustic pressure (R2 = 0.98) and was 3.33 times higher for gray matter than for white matter. CONCLUSIONS: An algorithm for evaluating blood-brain barrier disruption was validated and can be used for future clinical trials to further understand and quantify this technique in humans.Clinical trial registration no.: NCT02253212 (clinicaltrials.gov).

Sonothrombolysis.

Thrombo-occlusive disease is a leading cause of morbidity and mortality. In this chapter, the use of ultrasound to accelerate clot breakdown alone or in combination with thrombolytic drugs will be reported. Primary thrombus formation during cardiovascular disease and standard treatment methods will be discussed. Mechanisms for ultrasound enhancement of thrombolysis, including thermal heating, radiation force, and cavitation, will be reviewed. Finally, in-vitro, in-vivo and clinical evidence of enhanced thrombolytic efficacy with ultrasound will be presented and discussed.

Thrombolytic efficacy and enzymatic activity of rt-PA-loaded echogenic liposomes.

Echogenic liposomes (ELIP), that can encapsulate both recombinant tissue-type plasminogen activator (rt-PA) and microbubbles, are under development to improve the treatment of thrombo-occlusive disease. However, the enzymatic activity, thrombolytic efficacy, and stable cavitation activity generated by this agent has yet to be evaluated and compared to another established ultrasound-enhanced thrombolytic scheme. A spectrophotometric method was used to compare the enzymatic activity of the rt-PA incorporated into ELIP (t-ELIP) to that of rt-PA. An in vitro flow model was employed to measure the thrombolytic efficacy and dose of ultraharmonic emissions from stable cavitation for 120-kHz ultrasound exposure of three treatment schemes: rt-PA, rt-PA and the perfluorocarbon-filled microbubble Definity(®), and t-ELIP. The enzymatic activity of rt-PA incorporated into t-ELIP was 28 % that of rt-PA. Thrombolytic efficacy of t-ELIP or rt-PA and Definity(®) was equivalent when the dose of t-ELIP was adjusted to produce comparable enzymatic activity. Sustained bubble activity was nucleated from Definity but not from t-ELIP exposed to 120-kHz ultrasound. These results emphasize the advantages of encapsulating a thrombolytic and the importance of incorporating an insoluble gas required to promote sustained, stable cavitation activity.

In silico study of low-frequency transcranial ultrasound fields in acute ischemic stroke patients.

Ultrasound in the sub-megahertz range enhances thrombolysis and may be applied transcranially to ischemic stroke patients. The consistency of transcranial insonification needs to be evaluated. Acoustic and thermal simulations based on computed-tomography (CT) scans of 20 patients were performed. An unfocused 120-kHz transducer allowed homogeneous insonification of the thrombus, and positioning based on external landmarks performed similarly to an optimized placement based on CT data. With a weakly focused 500-kHz transducer, the landmark-based positioning underperformed. The predicted inter-patient variation of in situ acoustic pressure was similar with both the 120 and 500-kHz transducers for the optimized placement (18.0-26.4% relative standard deviation). The simulated maximum acoustic pressure in intervening tissues was 2.6 ± 0.6 and 2.0 ± 0.7 times the pressure in the thrombus for the 120-kHz and 500-kHz transducers, respectively. A 1 W/cm(2) insonification of the thrombus caused a 3.8 ± 2.2 °C increase in the bone for the 120-kHz transducer, and a 13.4 ± 3.3 °C increase for the 500-kHz transducer. Contralateral local maxima up to 1.1 times the pressure amplitude in the targeted zone were predicted for the 120-kHz transducer. We established two transducer placement approaches, one based on analysis of a head CT and the other using simple external, visible landmarks. Both approaches allowed consistent insonification of the thrombus.

Experimental validation of a finite-difference model for the prediction of transcranial ultrasound fields based on CT images.

The prevalence of stroke worldwide and the paucity of effective therapies have triggered interest in the use of transcranial ultrasound as an adjuvant to thrombolytic therapy. Previous studies have shown that 120 kHz ultrasound enhanced thrombolysis and allowed efficient penetration through the temporal bone. The objective of our study was to develop an accurate finite-difference model of acoustic propagation through the skull based on computed tomography (CT) images. The computational approach, which neglected shear waves, was compared with a simple analytical model including shear waves. Acoustic pressure fields from a two-element annular array (120 and 60 kHz) were acquired in vitro in four human skulls. Simulations were performed using registered CT scans and a source term determined by acoustic holography. Mean errors below 14% were found between simulated pressure fields and corresponding measurements. Intracranial peak pressures were systematically underestimated and reflections from the contralateral bone were overestimated. Determination of the acoustic impedance of the bone from the CT images was the likely source of error. High correlation between predictions and measurements (R(2) = 0.93 and R(2) = 0.88 for transmitted and reflected waves amplitude, respectively) demonstrated that this model is suitable for a quantitative estimation of acoustic fields generated during 40-200 kHz ultrasound-enhanced ischemic stroke treatment.

Feasibility study of cavitation-induced liposomal doxorubicin release in an AT2 Dunning rat tumor model.

BACKGROUND: Targeted and triggered release of liposomal drug using heat or ultrasound represents a promising treatment modality able to increase the therapeutic-totoxicity ratio of encapsulated drugs. PURPOSE: To study the ability for high-intensity focused ultrasound to induce liposomal drug release mainly by focused inertial cavitation in vitro and in an animal model. METHODS: A 1 MHz ultrasound setup has been developed for in vitro and in vivo drug release from a specific liposomal doxorubicin formulation at a target cavitation dose. RESULTS: Controlled cavitation at 1 MHz was applied within the tumors 48 hours after liposome injection according to preliminary pharmacokinetic study. A small non-significant therapeutic effect of US-liposomal treatment was observed compared to liposomes alone suggesting no beneficial effect of ultrasound in the current setup. CONCLUSION: The in vitro study provided a suitable ultrasound setup for delivering a cavitation dose appropriate for safe liposomal drug release. However, when converting to an in vivo model, no therapeutic benefit was observed. This may be due to a number of reasons, one of which may be the difficulty in converting in vitro findings to an in vivo model. In light of these findings, we discuss important design features for future studies.

Validation of an acoustic cavitation dose with hydroxyl radical production generated by inertial cavitation in pulsed mode: application to in vitro drug release from liposomes.

The purpose of this study was to define and validate an inertial cavitation dose (CD) based on the detection of broadband noise, designed to monitor ultrasound-mediated drug release from liposomes. The validation consists of using the terephthalate dosimeter to quantify by fluorescence measurements the extent of hydroxyl radical (()OH) production during inertial cavitation. Sonication of samples was performed using tone bursts (pulse repetition frequency (PRF): 10 Hz(-1) kHz, duty cycle (dc): 5-25%, Isppa: 4100-12,200 W/cm(2)) generated by a 1 MHz focused transducer. Three sets of ultrasound parameters with different PRF and dc were selected to be more precisely compared. Results demonstrated an excellent correlation between *OH radical production and CD for each set of parameters, but significant differences in hydroxyl radical levels were observed among the sets of parameters. The results were compared with other studies, and the same tendency of variation with pulse duration was demonstrated. Results also showed that the CD was not distorted by peak intensity variations and was a much more reliable indicator than sonication time. Consequently, one validated parameter was selected to monitor drug release from two liposome formulations, and compare their ultrasound sensitivity.