Kelsie Timbie

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, Alzheimers, Parkinsons 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.

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.

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

ABSTRACT 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 ˜ 60 nm fluorescent tracer BPN across the blood‐tumor barrier in both the 9 L (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. Graphical abstract Figure. No Caption available.

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.

Dual perfluorocarbon nanodroplets enhance high intensity focused ultrasound heating and extend therapeutic window in vivo

Perfluorocarbon microbubbles are known to enhance high intensity focused ultrasound (HIFU) ablation by cavitation. However, they can result in superficial skin heating, minimizing their clinical translation. Perfluorocarbon nanodroplets activate only at the higher pressures present at the acoustic focus. We hypothesized that a mixed perfluorocarbon nanodroplet formulation would minimize surface heating while still enhancing ablation. Tissue-mimicking phantoms containing microbubbles or nanodroplets were sonicated (1 MHz, 15 W, 60 s) to assess heating and lesion formation in vitro. Microbubbles or nanodroplets were injected into rats (n = 3) and HIFU (1 MHz, 15 W, 15 s) was focused into each liver while under MRI guidance. Temperature throughout the liver was tracked by MR thermometry. In vitro, microbubbles caused excess surface heating during HIFU, whereas nanodroplets did not. In vivo, microbubbles typically circulate for less than 15 min. In comparison, the nanodroplets remained viable in circulation f...

Ultrasound-targeted delivery of systemically administered therapeutic nanoparticles

The ultrasound (US)-targeted delivery of systemically administered drug and gene-bearing nanoparticles has emerged to become a robust area of investigation with clear clinical potential. Such approaches typically entail the concurrent injection of contrast agent microbubbles (MBs) and nanoparticles, followed by the application of US to the region of interest. US-activated MBs disrupt the surrounding microvessel, permitting nanoparticle delivery with precise spatial localization. Our group has previously shown that US-targeted nanoparticle delivery can amplify collateral artery growth, that the binding of nanoparticles to MBs enhances nanoparticle delivery, that non-viral gene nanocarrier transfection is dependent on both MB diameter and US pressure, and that solid tumor growth can be controlled by the US-targeted delivery of 5 FU nanoparticles. More recent studies center on developing MRI-guided focused ultrasound (FUS) for nanoparticle delivery across the blood brain-barrier (BBB), which is the foremost ...

Ultrasound-mediated delivery of brain-penetrating nanoparticles across the blood-tumor barrier

The intact blood-brain barrier (BBB) presents a major obstacle for drug delivery to the brain. In addition, both high interstitial pressure and a nanoporous electrostatically charged tissue composition, produce a “blood-tumor barrier” (BTB), further complicating the treatment of diseases like glioblastoma. Focused ultrasound (FUS) in conjunction with microbubbles (MB) has been shown to cause reversible, localized disruption of the BBB. Incorporating MR guidance with FUS offers the ability to exquisitely target the BBB disruption to specific regions of the brain, thereby permitting drug delivery in a highly localized manner. This work examines the ability of MR guided FUS to deliver highly specialized brain-penetrating nanoparticles (NP) across both the BBB and the BTB in tumor-bearing rats. NPs were 60 nm in diameter and covered with an exceptionally dense brush layer of PEG to permit excellent diffusion through brain tissue. Initial studies utilized fluorescent polystyrene tracer particles to measure NP delivery and inform dosing of cisplatin-loaded biodegradable NPs.

Inhibition of melanoma growth in a subcutaneous model using ultrasound with low duty cycle

Melanoma has a 5-year survival rate of <10%, primarily due to therapeutic resistance and immune tolerance. Durable responses to therapy of metastatic melanoma are enhanced when the anti tumor immune response is activated. FUS is an emerging non-invasive treatment modality for localized treatment of cancers. Traditionally FUS has been used exclusively for thermal ablation of the target sites; biological responses associated with both thermal and mechanical damage have not been investigated. Damaged tumor cells have release endogenous danger signals, which stimulate an immune response, suggesting that the patient’s dying cancer cells may serve as a therapeutic vaccine which stimulates an antitumor immune response. Specifically, we hypothesize that FUS will augment tumor antigen release and danger signals to mediate rejection of both FUS treated and untreated tumors.

Direct nanodroplet and microbubble comparison for high intensity focused ultrasound ablation enhancement and safety

High intensity focused ultrasound (HIFU) surgery often requires hours of ablation in order to treat an entire tumor. Both perfluorocarbon gaseous microbubbles and vaporized liquid droplets are known enhancers of HIFU thermal ablation. Microbubbles, however, often lead to surface or skin lesions. Furthermore, they have a relatively short half-life in vivo (minutes) rendering them insufficiently stable for an entire HIFU surgery, which can last several hours. Many droplet formulations require very high pressures to activate. Our aim was to design an agent that could shorten ablation procedures without sacrificing safety. We designed and investigated a perfluorocarbon nanodroplet composed of a 1:1 ratio of dodecafluoropentane and decafluorobutane. These are tuned to change phase and activate at only 2 MPa peak negative pressure with common HIFU pulse lengths, enabling focused and targeted activation. Additionally, they are stable at body temperature.

Enhanced in vivo and in vitro high intensity focused ultrasound ablation via phase-shift nanodroplets compared to microbubbles

Both pefluorocarbon microbubbles and nanodroplets have been investigated as enhancers of high intensity focused ultrasound (HIFU) thermal ablation, however microbubbles often lead to surface or skin lesions. We have designed and investigated a dual-perfluorocarbon (PFC) nanodroplet which has the benefits of sufficiently small size to extravasate from tumors, enhanced stability at body temperature, and sufficiently low acoustic threshold for vaporization. In vitro, microbubbles enhanced thermal depostion at the target site by 21%, but were found to cause surface heating up to 60.2±2.2°C. Nanodroplets caused no more surface heating (10.1±1.1°C) than the temperature rise observed in agent-free controls (9.8±0.8°C), and enhanced heating at the target by 51%. Circulation time of the nanodroplets was investigated in vivo. HIFU (1 MHz, 4.06 MPa, CW, 15 seconds) was applied to rat livers (n=3) up to 95 minutes after nanodroplet injection, and any thermal enhancement was detected simultaneously by MR thermometry. Temperature rises of up to 55 degrees above body temperature were observed out to 95 minutes. HIFU applied to control livers without nanodroplets induced only a 22°C maximal temperature rise. These results suggest that the nanodroplets are sufficiently stable to enhance HIFU ablation in vivo for at least 1.5 hours and could reduce focused ultrasound surgical procedure times by as much as 5 fold by more quickly ablating a larger region of tissue, without compromising safety.