Transcranial histotripsy parameter study in primary and metastatic murine brain tumor models

Investigation of Optimum Production Conditions and the Stability of β-Cyclodextrin-Perfluorocarbon Nanocone Clusters for Histotripsy Applications

Nanocone clusters (NCCs) have been developed as clusters with inclusion complexes of FDA-approved β-cyclodextrin (βCD) and perfluorocarbons (PFC) (i.e., perfluoropentane (PFP) and perfluorohexane (PFH)) and have shown promise in nanoparticle-mediated histotripsy (NMH) applications owing to their lowered cavitation threshold, ease of production, and fluorocarbon quantification. However, there is still a lack of information on the best conditions of the synthesis of NCCs as a product that can have a maximum determinable fluorocarbon content and maintain the stability of the NCC during synthesis and when used as histotripsy agents or exposed to physiological conditions. These concerns about the stability of the clusters and the best possible formulation are investigated in the current work. The cluster formation potential was tested taking into consideration the nature of both PFCs and βCD by employing different synthesis conditions in terms of solution and environmental parameters such as concentration of solvent, stoichiometry between βCD and PFCs, temperature, pH, solvent type, etc. The best route of synthesis was then translated into various batch sizes and investigated in terms of the PFC loading and yield. These studies revealed that preparing NCCs in double-distilled water in an ice bath at the optimized solution concentration gave the highest yields and optimal PFC loading, as determined from gas chromatography. Furthermore, the stability of the clusters with different stoichiometries was scrutinized in varying concentrations, mechanical disruption times, pH levels, and temperature conditions, showing effects on each cluster's particle size in dynamic light scattering, visualized in transmission electron microscopy, and cavitation behavior in agarose gel tissue phantoms. These studies revealed stable clusters for all formulations, with PFH-containing NCCs emerging to be the most stable in terms of their cluster size and bubble formation potential in histotripsy. Finally, the shelf life of these clusters was investigated using DLS, which revealed a stable cluster. In conclusion, NCCs have shown high stability in terms of both synthesis, which can be replicated in gram-level production, and the cluster itself, which can be exposed to harsher conditions and still form stable bubbles in histotripsy.

Characterization of Blood-Brain Barrier Opening Induced by Transcranial Histotripsy in Murine Brains

OBJECTIVE

Transcranial histotripsy has shown promise as a non-invasive neurosurgical tool, as it has the ability to treat a wide range of locations in the brain without overheating the skull. One important effect of histotripsy in the brain is the blood-brain barrier (BBB) opening (BBBO) at the ablation site, but there is a knowledge gap concerning the extent of histotripsy-induced BBBO. Here we describe induction of BBBO by transcranial histotripsy and use of magnetic resonance imaging (MRI) and histology to quantify changes in BBBO at the periphery of the histotripsy ablation zone over time in the healthy mouse brain.

METHODS

An eight-element, 1 MHz histotripsy transducer with a focal distance of 32.5 mm was used to treat the brains of 23 healthy female BL6 mice. T1-gadolinium (T1-Gd) MR images were acquired immediately following histotripsy treatment and during each of the subsequent 4 wk to quantify the size and intensity of BBB leakage.

RESULTS

The T1-Gd MRI results revealed that the hyperintense BBBO volume increased over the first week and subsided gradually over the following 3 wk. Histology revealed complete loss of tight junction proteins and blood vessels in the center of the ablation region immediately after histotripsy, partial recovery in the periphery of the ablation zone 1 wk following histotripsy and near-complete recovery of tight junction complex after 4 wk.

CONCLUSION

These results provide the first evidence of transcranial histotripsy-induced BBBO and repair at the periphery of the ablation zone.

Advances in Tumor Management: Harnessing the Potential of Histotripsy

Tissue ablation techniques have long been used in clinical settings to treat various oncologic diseases. However, many of these techniques are invasive and can cause substantial adverse effects. Histotripsy is a noninvasive, nonionizing, nonthermal tissue ablation technique that has the potential to replace surgical interventions in various clinical settings. Histotripsy works by delivering high-intensity focused ultrasound waves to target tissue. These waves create cavitation bubbles within tissues that rapidly expand and collapse, thereby mechanically fractionating the tissue into acellular debris that is subsequently absorbed by the body's immune system. Preclinical and clinical studies have demonstrated the efficacy of histotripsy in treating a range of diseases, including liver, pancreatic, renal, and prostate tumors. Safety outcomes of histotripsy have been generally favorable, with minimal adverse effects reported. However, further studies are needed to optimize the technique and understand its long-term effects. This review aims to discuss the importance of histotripsy as a noninvasive tissue ablation technique, the preclinical and clinical literature on histotripsy and its safety, and the potential applications of histotripsy in clinical practice. Keywords: Tumor Microenvironment, Ultrasound-High-Intensity Focused (HIFU), Ablation Techniques, Abdomen/GI, Genital/Reproductive, Nonthermal Tissue Ablation, Histotripsy, Clinical Trials, Preclinical Applications, Focused Ultrasound © RSNA, 2024.

Revolutionizing brain interventions: the multifaceted potential of histotripsy

Histotripsy, a non-thermal ultrasound technique, holds significant promise in various applications within the realm of brain interventions. While its use for treating brain tumors is somewhat limited, focused ultrasound technology has been extensively investigated for a wide range of purposes within the brain, including disrupting the blood-brain barrier, supporting immunotherapy, addressing conditions like essential tremor, Parkinson's disease, Alzheimer's disease, epilepsy, and neuropathic pain. Research findings indicate that histotripsy can reduce tumor cells with fewer pulses, minimizing the risk of bleeding and cellular injury. The use of MRI sequences such as T2 and T2* enhances the evaluation of the effects of histotripsy treatment, facilitating non-invasive assessment of treated areas. Furthermore, histotripsy displays promise in creating precise brain lesions with minimal edema and inflammation, particularly in porcine models, suggesting considerable progress in the treatment of brain lesions. Moreover, studies confirm its feasibility, safety, and effectiveness in treating intracerebral hemorrhage by safely liquefying clots without causing significant harm to surrounding brain tissue., opening exciting possibilities for clinical applications. The development of transcranial MR-guided focused ultrasound systems based on histotripsy represents a significant breakthrough in overcoming the limitations associated with thermal ablation techniques. Histotripsy's ability to efficiently liquefy clots, minimize skull heating, and target shallow lesions near the skull establishes it as a promising alternative for various brain treatments. In conclusion, histotripsy offers diverse potential in the field of brain interventions, encompassing applications ranging from tumor treatment to the management of intracerebral hemorrhage. While challenges such as accurate monitoring and differentiation of treatment effects persist, ongoing research efforts and technological advancements continue to expand the role of histotripsy in both neurology and neurosurgery.

Insights from in vivo preclinical cancer studies with histotripsy

Histotripsy is the first noninvasive, non-ionizing, and non-thermal ablation technique that mechanically fractionates target tissue into acellular homogenate via controlled acoustic cavitation. Histotripsy has been evaluated for various preclinical applications requiring noninvasive tissue removal including cancer, brain surgery, blood clot and hematoma liquefaction, and correction of neonatal congenital heart defects. Promising preclinical results including local tumor suppression, improved survival outcomes, local and systemic anti-tumor immune responses, and histotripsy-induced abscopal effects have been reported in various animal tumor models. Histotripsy is also being investigated in veterinary patients with spontaneously arising tumors. Research is underway to combine histotripsy with immunotherapy and chemotherapy to improve therapeutic outcomes. In addition to preclinical cancer research, human clinical trials are ongoing for the treatment of liver tumors and renal tumors. Histotripsy has been recently approved by the FDA for noninvasive treatment of liver tumors. This review highlights key learnings from in vivo shock-scattering histotripsy, intrinsic threshold histotripsy, and boiling histotripsy cancer studies treating cancers of different anatomic locations and discusses the major considerations in planning in vivo histotripsy studies regarding instrumentation, tumor model, study design, treatment dose, and post-treatment tumor monitoring.