MR-guided focused ultrasound: enhancement of intratumoral uptake of [3H]-docetaxelin vivo

An in-vivo study of the combined therapeutic effects of pulsed non-thermal focused ultrasound and radiation for prostate cancer

PURPOSE

The purpose of this study was to investigate the in vivo combined effects of pulsed focused ultrasound (pFUS) and radiation (RT) for prostate cancer treatment.

MATERIALS AND METHODS

An animal prostate tumor model was developed by implanting human LNCaP tumor cells in the prostates of nude mice. Tumor-bearing mice were treated with pFUS, RT or both (pFUS + RT) and compared with a control group. Non-thermal pFUS treatment was delivered by keeping the body temperature below 42 °C as measured real-time by MR thermometry and using a pFUS protocol (1 MHz, 25 W focused ultrasound; 1 Hz pulse rate with a 10% duty cycle for 60 sec for each sonication). Each tumor was covered entirely using 4-8 sonication spots. RT treatment with a dose of 2 Gy was delivered using an external beam (6 MV photon energy with dose rate 300MU/min). Following the treatment, mice were scanned weekly with MRI for tumor volume measurement.

RESULTS

The results showed that the tumor volume in the control group increased exponentially to 142 ± 6%, 205 ± 12%, 286 ± 22% and 410 ± 33% at 1, 2, 3 and 4 weeks after treatment, respectively. In contrast, the pFUS group was 29% (p < 0.05), 24% (p < 0.05), 8% and 9% smaller, the RT group was 7%, 10%, 12% and 18% smaller, and the pFUS + RT group was 32%, 39%, 41% and 44% (all with p < 0.05) smaller than the control group at 1, 2, 3, and 4 weeks post treatment, respectively. Tumors treated by pFUS showed an early response (i.e. the first 2 weeks), while the RT group showed a late response. The combined pFUS + RT treatment showed consistent response throughout the post-treatment weeks.

CONCLUSIONS

These results suggest that RT combined with non-thermal pFUS can significantly delay the tumor growth. The mechanism of tumor cell killing between pFUS and RT may be different. Pulsed FUS shows early tumor growth delay, while RT contributes to the late effect on tumor growth delay. The addition of pFUS to RT significantly enhanced the therapeutic effect for prostate cancer treatment.

Microbubbles Containing Lysolipid Enhance Ultrasound-Mediated Blood-Brain Barrier Breakdown In Vivo

Ultrasound and microbubbles (MBs) offer a noninvasive method of temporarily enhancing blood-brain barrier (BBB) permeability to therapeutics. To reduce off-target effects, it is desirable to minimize the ultrasound pressures required. It has been shown that a new formulation of MBs containing lysolipids (Lyso-MBs) can increase the cellular uptake of a model drug in vitro. The aim of this study is to investigate whether Lyso-MBs can also enhance BBB permeability in vivo. Female BALB/c mice are injected with either Lyso-MBs or control MBs and gadolinium-DTPA (Gd-DTPA) and exposed to ultrasound (500 kHz, 1 Hz pulse repetition frequency, 1 ms pulse length, peak-negative pressures 160-480 kPa) for 2 min. BBB permeabilization is measured via magnetic resonance imaging (7.0 T) of Gd-DTPA extravasation and subsequent histological examination of brain tissue to assess serum immunoglobulin G (IgG) extravasation (n = 8 per group). An approximately twofold enhancement in BBB permeability is produced by the Lyso-MBs at the highest ultrasound pressure compared with the control. These findings indicate that modifying the composition of phospholipid-shelled MBs has the potential to improve the efficiency of BBB opening, without increasing the ultrasound pressure amplitude required. This is particularly relevant for delivery of therapeutics deep within the brain.

Pilot performance of a dedicated prostate PET suitable for diagnosis and biopsy guidance

Background

Prostate cancer (PCa) represents one of the most common types of cancers facing the male population. Nowadays, to confirm PCa, systematic or multiparametric MRI-targeted transrectal or transperineal biopsies of the prostate are required. However, due to the lack of an accurate imaging technique capable to precisely locate cancerous cells in the prostate, ultrasound biopsies sample random parts of the prostate and, therefore, it is possible to miss regions where those cancerous cells are present. In spite of the improvement with multiparametric MRI, the low reproducibility of its reading undermines the specificity of the method. Recent development of prostate-specific radiotracers has grown the interest on using positron emission tomography (PET) scanners for this purpose, but technological improvements are still required (current scanners have resolutions in the range of 4–5 mm).

Results

The main goal of this work is to improve state-of-the-art PCa imaging and diagnosis. We have focused our efforts on the design of a novel prostate-dedicated PET scanner, named ProsPET. This system has small scanner dimensions defined by a ring of just 41 cm inner diameter. In this work, we report the design, implementation, and evaluation (both through simulations and real data) of the ProsPET scanner. We have been able to achieve < 2 mm resolution in reconstructed images and high sensitivity. In addition, we have included a comparison with the Philips Gemini-TF scanner, which is used for routine imaging of PCa patients. The ProsPET exhibits better contrast, especially for rod sizes as small as 4.5 mm in diameter. Finally, we also show the first reconstructed image of a PCa patient acquired with the ProsPET.

Conclusions

We have designed and built a prostate specific PET system, with a small footprint and improved spatial resolution when compared to conventional whole-body PET scanners. The gamma ray impact within each detector block includes accurate DOI determination, correcting for the parallax error. The potential role of combined organ-dedicated prostate-specific membrane antigen (PSMA) PET and ultrasound devices, as a prebiopsy diagnostic tool, could be used to guide sampling of the most aggressive sites in the prostate.

Microbubble-Mediated Delivery for Cancer Therapy

Despite an overall improvement in survival rates for cancer, certain resistant forms of the disease still impose a significant burden on patients and healthcare systems. Standard chemotherapy in these cases is often ineffective and/or gives rise to severe side effects. Targeted delivery of chemotherapeutics could improve both tumour response and patient experience. Hence, there is an urgent need to develop effective methods for this. Ultrasound is an established technique in both diagnosis and therapy. Its use in conjunction with microbubbles is being actively researched for the targeted delivery of small-molecule drugs. In this review, we cover the methods by which ultrasound and microbubbles can be used to overcome tumour barriers to cancer therapy.

Drug Delivery Strategies for Platinum-Based Chemotherapy

Few chemotherapeutics have had such an impact on cancer management as cis-diamminedichloridoplatinum(II) (CDDP), also known as cisplatin. The first member of the platinum-based drug family, CDDP's potent toxicity in disrupting DNA replication has led to its widespread use in multidrug therapies, with particular benefit in patients with testicular cancers. However, CDDP also produces significant side effects that limit the maximum systemic dose. Various strategies have been developed to address this challenge including encapsulation within micro- or nanocarriers and the use of external stimuli such as ultrasound to promote uptake and release. The aim of this review is to look at these strategies and recent scientific and clinical developments.

In Vitro Investigation of the Individual Contributions of Ultrasound-Induced Stable and Inertial Cavitation in Targeted Drug Delivery

Ultrasound-mediated targeted drug delivery is a therapeutic modality under development with the potential to treat cancer. Its ability to produce local hyperthermia and cell poration through cavitation non-invasively makes it a candidate to trigger drug delivery. Hyperthermia offers greater potential for control, particularly with magnetic resonance imaging temperature measurement. However, cavitation may offer reduced treatment times, with real-time measurement of ultrasonic spectra indicating drug dose and treatment success. Here, a clinical magnetic resonance imaging-guided focused ultrasound surgery system was used to study ultrasound-mediated targeted drug delivery in vitro. Drug uptake into breast cancer cells in the vicinity of ultrasound contrast agent was correlated with occurrence and quantity of stable and inertial cavitation, classified according to subharmonic spectra. During stable cavitation, intracellular drug uptake increased by a factor up to 3.2 compared with the control. Reported here are the value of cavitation monitoring with a clinical system and its subsequent employment for dose optimization.

Gene delivery to the spinal cord using MRI-guided focused ultrasound

Non-invasive gene delivery across the blood-spinal cord barrier (BSCB) remains a challenge for treatment of spinal cord injury and disease. Here, we demonstrate the use of magnetic resonance image-guided focused ultrasound (MRIgFUS) to mediate non-surgical gene delivery to the spinal cord using self-complementary adeno-associated virus serotype 9 (scAAV9). scAAV9 encoding green fluorescent protein (GFP) was injected intravenously in rats at three dosages: 4 × 10(8), 2 × 10(9) and 7 × 10(9) vector genomes per gram (VG g(-1)). MRIgFUS allowed for transient, targeted permeabilization of the BSCB through the interaction of focused ultrasound (FUS) with systemically injected Definity lipid-shelled microbubbles. Viral delivery at 2 × 10(9) and 7 × 10(9) VG g(-1) leads to robust GFP expression in FUS-targeted regions of the spinal cord. At a dose of 2 × 10(9) VG g(-1), GFP expression was found in 36% of oligodendrocytes, and in 87% of neurons in FUS-treated areas. FUS applications to the spinal cord could address a long-term goal of gene therapy: delivering vectors from the circulation to diseased areas in a non-invasive manner.

An in-vivo investigation of the therapeutic effect of pulsed focused ultrasound on tumor growth

PURPOSE

High-intensity focused ultrasound (HIFU) has been investigated for ablative therapy and drug enhancement for gene therapy and chemotherapy. The aim of this work is to explore the feasibility of pulsed focused ultrasound (pFUS) for cancer therapy using an in vivo animal model.

METHODS

A clinical HIFU system (InSightec ExAblate 2000) integrated with a 1.5 T GE MR scanner was used in this study. Suitable ultrasound parameters were investigated to perform nonthermal sonications, keeping the temperature elevation below 4 °C as measured in real time by MR thermometry. LNCaP cells (10(6)) were injected into the prostates of male mice (n = 20). When tumors reached a diameter of about 5 mm in 3D as measured on magnetic resonance imaging (MRI), the tumor-bearing mice (n = 8) were treated with pFUS (1 MHz frequency; 25 W acoustic power; 0.1 duty cycle; 60 s duration). A total of 4-6 sonications were used to cover the entire tumor volume under MR image guidance. The animals were allowed to survive for 4 weeks after the treatment. The tumor growth was monitored on high-resolution (0.2 mm) MRI weekly post treatment and was compared with that of the control group (n = 12).

RESULTS

Significant tumor growth delay was observed in the tumor-bearing mice treated with pFUS. The mean tumor volume for the pFUS treated mice remained the same 1 week after the treatment while the mean tumor volume of the control mice grew 42% over the same time. Two weeks after the pFUS treatment, the control group had a mean tumor volume 40% greater than that of the treated group. There was a greater variation in tumor volume at 4 weeks post treatment for both treated and control mice and a slightly faster tumor growth for the pFUS treated mice.

CONCLUSIONS

The authors' results demonstrated that pFUS may have a great potential for cancer therapy. Further experiments are warranted to understand the predominantly nonthermal cell killing mechanisms of pFUS and to derive optimal ultrasound parameters and fractionation schemes to maximize the therapeutic effect of pFUS.

Model-based feasibility assessment and evaluation of prostate hyperthermia with a commercial MR-guided endorectal HIFU ablation array

PURPOSE

Feasibility of targeted and volumetric hyperthermia (40-45 °C) delivery to the prostate with a commercial MR-guided endorectal ultrasound phased array system, designed specifically for thermal ablation and approved for ablation trials (ExAblate 2100, Insightec Ltd.), was assessed through computer simulations and tissue-equivalent phantom experiments with the intention of fast clinical translation for targeted hyperthermia in conjunction with radiotherapy and chemotherapy.

METHODS

The simulations included a 3D finite element method based biothermal model, and acoustic field calculations for the ExAblate ERUS phased array (2.3 MHz, 2.3 × 4.0 cm(2), ∼1000 channels) using the rectangular radiator method. Array beamforming strategies were investigated to deliver protracted, continuous-wave hyperthermia to focal prostate cancer targets identified from representative patient cases. Constraints on power densities, sonication durations and switching speeds imposed by ExAblate hardware and software were incorporated in the models. Preliminary experiments included beamformed sonications in tissue mimicking phantoms under MR temperature monitoring at 3 T (GE Discovery MR750W).

RESULTS

Acoustic intensities considered during simulation were limited to ensure mild hyperthermia (Tmax < 45 °C) and fail-safe operation of the ExAblate array (spatial and time averaged acoustic intensity ISATA < 3.4 W/cm(2)). Tissue volumes with therapeutic temperature levels (T > 41 °C) were estimated. Numerical simulations indicated that T > 41 °C was calculated in 13-23 cm(3) volumes for sonications with planar or diverging beam patterns at 0.9-1.2 W/cm(2), in 4.5-5.8 cm(3) volumes for simultaneous multipoint focus beam patterns at ∼0.7 W/cm(2), and in ∼6.0 cm(3) for curvilinear (cylindrical) beam patterns at 0.75 W/cm(2). Focused heating patterns may be practical for treating focal disease in a single posterior quadrant of the prostate and diffused heating patterns may be useful for heating quadrants, hemigland volumes or even bilateral targets. Treatable volumes may be limited by pubic bone heating. Therapeutic temperatures were estimated for a range of physiological parameters, sonication duty cycles and rectal cooling. Hyperthermia specific phasing patterns were implemented on the ExAblate prostate array and continuous-wave sonications (∼0.88 W/cm(2), 15 min) were performed in tissue-mimicking material with real-time MR-based temperature imaging (PRFS imaging at 3.0 T). Shapes of heating patterns observed during experiments were consistent with simulations.

CONCLUSIONS

The ExAblate 2100, designed specifically for thermal ablation, can be controlled for delivering continuous hyperthermia in prostate while working within operational constraints.

Prospects for enhancement of targeted radionuclide therapy of cancer using ultrasound

Ultrasound-mediated drug delivery is a promising means of enhancing delivery, distribution and effectiveness of drugs within tumours. In this review, prospects for exploiting ultrasound to improve the tumour delivery and distribution of radiolabelled antibodies for radioimmunotherapy and to overcome barriers imposed by tumour microenvironment are discussed.

Ultrasound-mediated targeted drug delivery generated by multifocal beam patterns: an in vitro study

Ultrasound-mediated targeted drug delivery has been a subject for a dedicated research activity for several decades. Nevertheless, in vitro studies in this field of research are characterized by their inconsistencies. To improve the repeatability of such experiments, a novel approach of multifocal spot generation was investigated. A multifocal pattern of 16 spots was utilized using an iterative Gerchberg-Saxton algorithm. The pattern was applied to insonate a 96-well Petri dish plate using a clinically available planar-phased array transducer with approximately 1000 elements with a central frequency of 0.55 MHz. The pattern was acoustically characterized and applied to a monolayer of human breast cancer cell line in the 96-well plate. With the help of ultrasonic contrast agents, the intracellular drug uptake was increased by an average factor of 3.5 compared with the control group.

Emerging technologies for image guidance and device navigation in interventional radiology

Recent developments in image-guidance and device navigation, along with emerging robotic technologies, are rapidly transforming the landscape of interventional radiology (IR). Future state-of-the-art IR procedures may include real-time three-dimensional imaging that is capable of visualizing the target organ, interventional tools, and surrounding anatomy with high spatial and temporal resolution. Remote device actuation is becoming a reality with the introduction of novel magnetic-field enabled instruments and remote robotic steering systems. Robots offer several degrees of freedom and unprecedented accuracy, stability, and dexterity during device navigation, propulsion, and actuation. Optimization of tracking and navigation of interventional tools inside the human body will be critical in converting IR suites into the minimally invasive operating theaters of the future with increased safety and unsurpassed therapeutic efficacy. In the not too distant future, individual image guidance modalities and device tracking methods could merge into autonomous, multimodality, multiparametric platforms that offer real-time data of anatomy, morphology, function, and metabolism along with on-the-fly computational modeling and remote robotic actuation. The authors provide a concise overview of the latest developments in image guidance and device navigation, while critically envisioning what the future might hold for 2020 IR procedures.

Quantitative study of focused ultrasound enhanced doxorubicin delivery to prostate tumor in vivo with MRI guidance

PURPOSE

The purpose of this study was to investigate the potential of MR-guided pulsed focused ultrasound (pFUS) for the enhancement of drug uptake in prostate tumors in vivo using doxorubicin (Dox).

METHODS

An antitumor drug Dox, an orthotopic animal prostate tumor model using human prostate cancer, LNCaP cell line, and a clinical FUS treatment system (InSightec ExAblate 2000) with a 1.5T GE MR scanner were used in this study. First, experiments on a tissue mimic phantom to determine the optimal acoustic power and exposure durations with a 10% duty cycle and a 1 Hz pulse rate were performed. The temperature variation was monitored using real-time MR thermometry. Second, tumor-bearing animals were treated with pFUS. There were three groups (n = 8/group): group 1 received pFUS + Dox (10 mg/kg i.v. injection immediately after pFUS exposure), group 2 received Dox only (10 mg/kg i.v. injection), and group 3 was a control. Animals were euthanized 2 h after the pFUS treatment. The Dox concentration in the treated tumors was measured by quantifying fluorescent tracers using a fluorometer. Third, the histological changes of tumors with and without pFUS treatments were evaluated. Finally, experiments were performed to study the spatial drug distribution in tumors after the pFUS treatment, in which two animals received pFUS + Dox, two animals received Dox only, and one animal was used as control. Two hours following the treatment, animals were euthanized and processed. The Dox distribution was determined using a fluorescence microscope.

RESULTS

Parametric measurements using a tissue phantom showed that the temperature increased with an increasing acoustic power (from 10 to 50 W) or sonication duration (from 10 to 60 s) with a given acoustic frequency of 1 MHz, duty cycle 10%, and pulse rate 1 Hz. A set of ultrasound parameters was identified with which the temperature elevation was less than 5 °C, which was used for nonthermal pFUS sonication. Increased Dox concentration (14.9 ± 2.5 μg/g) was measured in the pFUS-treated group compared to the Dox-only group (9.5 ± 1.6 μg/g), indicating an approximate 60% increase with p = 0.05. The results were consistent with the increased spatial drug distributions by fluorescence imaging. Histological analysis showed increased extravasation in pFUS-treated prostate tumors suggesting increased drug delivery with pFUS.

CONCLUSIONS

The results showed that pFUS-enhanced drug uptake in prostate tumors was significant. This increased uptake may be due to increased extravasation by pFUS. Optimal pFUS parameters may exist to maximize the drug uptake, and this study using Dox demonstrated a quantitative method for such systematic parametric studies. In addition, this study may provide useful data for the potential application of pFUS-mediated Dox delivery for prostate tumor therapy.

MR-guided pulsed high intensity focused ultrasound enhancement of docetaxel combined with radiotherapy for prostate cancer treatment

The purpose of this study is to evaluate the efficacy of the enhancement of docetaxel by pulsed focused ultrasound (pFUS) in combination with radiotherapy (RT) for treatment of prostate cancer in vivo. LNCaP cells were grown in the prostates of male nude mice. When the tumors reached a designated volume by MRI, tumor bearing mice were randomly divided into seven groups (n = 5): (1) pFUS alone; (2) RT alone; (3) docetaxel alone; (4) docetaxel + pFUS; (5) docetaxel + RT; (6) docetaxel + pFUS + RT, and (7) control. MR-guided pFUS treatment was performed using a focused ultrasound treatment system (InSightec ExAblate 2000) with a 1.5T GE MR scanner. Animals were treated once with pFUS, docetaxel, RT or their combinations. Docetaxel was given by i.v. injection at 5 mg kg(-1) before pFUS. RT was given 2 Gy after pFUS. Animals were euthanized 4 weeks after treatment. Tumor volumes were measured on MRI at 1 and 4 weeks post-treatment. Results showed that triple combination therapies of docetaxel, pFUS and RT provided the most significant tumor growth inhibition among all groups, which may have potential for the treatment of prostate cancer due to an improved therapeutic ratio.