Pilot Study on Combined Cancer Therapy by Thermo-sensitive Liposomes and Ultrasound Phased Arrays Induced Heating

Novel Thermosensitive Polymer-Modified Liposomes as Nano-Carrier of Hydrophobic Antitumor Drugs

Liposomes are potent nanocarriers to deliver chemotherapeutic drugs to tumors. However, the inefficient drug release hinders their application. Liposomes around 100 nm can extravasate through leaky microvasculature and accumulate in tumor tissue. Local hyperthermia (HT) augments the permeability of tumor microvasculature, resulting in enhanced intratumoral liposomal drug accumulation. Subsequently, thermosensitive liposomes (TSL) release their contents at elevated temperature. The combination of stealth TSL with phase transition temperature at 41 – 43 °C and mild local HT offers a promising clinical advance. This study identified thermal dose for liposome extravasation through tumor vessels and the optimum DSPE-PEG2000 concentration for triggered drug release from TSL. TSL were prepared with DSPE-PEG2000 concentration from 1 to 10 mol% and size of around 80 nm. Quenched carboxyfluorescein (CF) in the aqueous phase represented encapsulated drugs. In vitro temperature/time-dependent CF release and TSL stability in serum were quantified by fluorometry. In vivo CF release was observed by confocal microscopy in dorsal skin flap window chamber models implanted with human BLM melanoma. A circular resistive electric heating coil provided local HT. In vivo liposome extravasation was also studied in window chamber models of syngeneic B16 melanoma in mice with constitutive vascular endothelial cell expression of an eNOS-Tag-GFP fusion protein. The study of liposome extravasation through tumor microvasculature illustrated a thermal dose of 41 °C for 30 min tuned up the leakiness of tumor vessels towards liposomes of around 80 nm. A significant amount of liposomes escaped from circulation and intratumorally accumulated in the interstitial space. The in vitro temperature-dependent CF release indicated in vitro CF release increased with increasing DSPE-PEG2000 density. Six mol% and higher DSPE-PEG2000 caused content leakage at physiological temperature. Thus the optimum DSPE-PEG2000 concentration was 5 mol% (p < 0.05). These TSL released over 60 % of CF in one minute, and released almost 100 % of CF in one hour at 42 °C with encapsulation efficiency of 0.08 (mole/mole of CF/lipid). Content retention in 90 % serum at 37 °C for one hour was 96.6 %. In vivo optical intravital imaging showed immediate massive CF release above 41 °C. Incorporation of 5 mol% of DSPE-PEG2000 in the liposomal bilayer optimized stealth TSL content release triggered by HT (> 41 °C). In vivo tumor models confirmed in vitro TSL release characteristics. The superior application of TSL and mild HT will achieve both maximal intratumoral liposomal drug accumulation and rapid triggered drug release to aid in liposomal chemotherapy in clinical practice. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2650.

Focused ultrasound phased array systems have attracted increased attention for brain therapy applications. However, such systems currently lack a direct and real-time method to intraoperatively monitor ultrasound pressure distribution for securing treatment. This study proposes a dual-mode ultrasound phased array system design to support transmit/receive operations for concurrent ultrasound exposure and backscattered focal beam reconstruction through a spherically focused ultrasound array. A 256-channel ultrasound transmission system was used to transmit focused ultrasonic energy (full 256 channels), with an extended implementation of multiple-channel receiving function (up to 64 channels) using the same 256-channel ultrasound array. A coherent backscatter-received beam formation algorithm was implemented to map the point spread function (PSF) and focal beam distribution under a free-field/transcranial environment setup, with the backscattering generated from a strong scatterer (a point reflector or a microbubble-perfused tube) or a weakly scattered tissue-mimicking graphite phantom. Our results showed that PSF and focal beam can be successfully reconstructed and visualized in free-field conditions and can also be transcranially reconstructed following skull-induced aberration correction. In vivo experiments were conducted to demonstrate its capability to preoperatively and semiquantitatively map a focal beam to guide blood-brain barrier opening. The proposed system may have potential for real-time guidance of ultrasound brain intervention, and may facilitate the design of a dual-mode ultrasound phased array for brain therapeutic applications.

As a new type of interaction way, haptic feedback has attracted a lot of attention. Among different kinds of haptic feedback methods, contactless haptic feedback based on ultrasound array has become one of the most promising methods because of its simple structure, low cost, diverse feedback forms and flexible adjustment. This paper firstly discusses the mechanism of human body's tactile sensation in detail, and then analyzes the mechanism of the realization of haptic feedback by ultrasound phased array. Then the mathematical model of ultrasound phased array’s acoustic field is established, and the methods for solving single point and multi-point haptic feedback are presented. The energy efficiency is further optimized for the solution of multi-point haptic feedback.

Making the Most of Focused Ultrasound: Tissue Heating to Improve Chemotherapy Release.

Low-intensity transcranial focused ultrasound stimulation (tFUS), as a noninvasive neuromodulation modality, has shown to be effective in animals and even humans with improved millimeter-scale spatial resolution compared to its noninvasive counterparts. But conventional tFUS systems are built with bulky single-element ultrasound (US) transducers that must be mechanically moved to change the stimulation target. To achieve large-scale ultrasound neuromodulation (USN) within a given tissue volume, a US transducer array should electronically be driven in a beamforming fashion (known as US phased array) to steer focused ultrasound beams towards different neural targets. This paper presents the theory and design methodology of US phased arrays for USN at a large scale. For a given tissue volume and sonication frequency (f), the optimal geometry of a US phased array is found with an iterative design procedure that maximizes a figure of merit (FoM) and minimizes side/grating lobes (avoiding off-target stimulation). The proposed FoM provides a balance between the power efficiency and spatial resolution of a US array in USN. A design example of a US phased array has been presented for USN in a rat's brain with an optimized linear US array. In measurements, the fabricated US phased array with 16 elements (16.7×7.7×2 mm3), driven by 150 V (peak-peak) pulses at f = 833.3 kHz, could generate a focused US beam with a lateral resolution of 1.6 mm and pressure output of 1.15 MPa at a focal distance of 12 mm. The capability of the US phased array in beam steering and focusing from -60o to 60o angles was also verified in measurements.

Composite materials and structures are increasingly being applied in aerospace, marine, and wind power industries, as well as in commercial products. One main reason for the scientific interest in composite materials is their tailorable mechanical properties. However, because of the fiber-direction-dependent nature of its physical and mechanical properties, composite material’s property and failure behaviors are usually complex, typically involving various mechanisms depending on applications. Nondestructive testing plays a key role during composite fabrication and maintenance in service. Among the variety of nondestructive techniques available, ultrasound phased array technique has emerged as a promising new approach. Unlike a conventional ultrasound single element transducer, an ultrasound phased array sensor can control and focus acoustic energy to the desired directions and locations. This heightened flexibility and sensitivity is essential given complex shape of modern composite structures. Despite such promise, understanding and application of ultrasound phased array technique is limited due to the anisotropic nature of composite materials, as well as its high acoustic attenuation. Attenuation and velocity dispersion are the two major challenges to the ultrasound evaluation of composite structures; these two factors complicate the control of phased array ultrasound propagation both theoretically and experimentally. This is especially true for thick high attenuation carbon fiber or glass fiber composite materials that have been widely applied in aerospace and wind turbine industries. In our study, ultrasound phased array technique was applied to increase the acoustic penetration power in high acoustic attenuation composite materials. First, ultrasound phased array signal in isotropic materials was studied to calibrate the probe parameters. Then for composite materials, the dependence of ultrasound field on the number of active elements, steering angles, beam focusing laws and on the characteristics of materials was analyzed and optimized through theoretical simulations and experimental evaluations. Results showed that the steering angles and the parameters of beam focusing laws might change the ultrasound beam intensity and uniformity, which had a significant influence on the sensitivity and resolution of the technique; the anisotropic properties of composite materials could distort the ultrasound beam, which made the calibration a necessary and important procedure during practical inspections. The influence of ultrasound frequency and beam angle were also quantitatively evaluated. The proposed research has the potential to apply ultrasound phased array technique to the detection of defects in composite materials and the evaluation of composite structural health. The study of the interaction between ultrasound and composite structures will open the window for the successful application of ultrasound phased array technique.

Focused ultrasound has been pointed out the theoretical and technical feasibility to reconstruct image for monitoring ultrasound CNS therapeutic efficacy via the transcranial way. However, practically the transcranial ultrasound still encounters severe challenges including severe phase aberration and attenuation due to the skull to abrupt the backscattered beamforming. This study proposes a correlation average correction algorithm with the intention to reconstruct the focal beam even encounter skull-insert severe phase aberration. The algorithm is implemented in a dual-mode ultrasound 256-channel phased array system operated at full-channel emission and sparse-channel receiving (32 channels). The concept is based on the use of averaged phase-aberration correlation to reduce phase aberration as well as to gain the image contrast-to-noise ratio. In-vitro transcranial experiments were conducted to evaluate the performance of the beam corrected reconstruction algorithm. Results showed that transcranial focal beam distribution can be successfully reconstructed in a weakly scattered tissue-mimicking skull-inserted phantom, and the image intensity was evaluated to highly correlated with the in-situ deposited pressure level. The results of this study may provide implication directing the potential to use ultrasound phased array to simultaneously perform transcranial focal beam guidance for ultrasound brain therapy application such as BBB opening.

Long circulating liposomes are potent nanocarriers for the delivery of chemotherapeutic drugs to tumors. These liposomes can extravasate through leaky tumor microvasculature, and accumulate in the intratumoral space. However, inefficient drug release impairs efficacy, and hinders a successful application. Local hyperthermia (HT) can augment drug bioavailability and treatment efficacy by enhancing tumor vessel leakage for intratumoral liposomal drug accumulation, and triggering drug release from thermosensitive liposomes (TSL). Our study explored the thermal dose to maximize the permeability of tumor microvasculature for liposome extravasation and sequentially trigger drug release from the TSL in a two-step approach. We have optimized long-circulating TSL to improve content release efficiency under mild HT (Li et al. J Control Release 143(2):274-9, 2010). Doxorubicin (Dox) at a quenching concentration was encapsulated in TSL. In vitro temperature/time-dependent content release and TSL stability in serum were quantified by fluorometry. In vivo liposome extravasation was studied in dorsal skin flap window chamber models implanted with murine B16 melanoma, LLC carcinoma, BFS-1 sarcoma, and human BLM melanoma tumors in mice with constitutive vascular endothelial cell expression of an eNOS-Tag-GFP fusion protein using confocal microscopy. In vivo Dox release was observed in the same window chamber models. Mild HT induced a significant amount of liposome extravasation through tumor microvasculature, and intratumoral accumulation in the interstitial space in all tumor models. Minimum thermal dose of 41 °C for 30 min is required to open up tumor vessels. The permeability of tumor vessels increased over time with increasing thermal dose to 41 °C for 1 hr, and vasculature remained leaky for up to 8 hr post-HT. Increased permeability was not observed in heated normal vasculature or in non-heated tumor vasculature. Optimized Dox-TSL were stable at 37 °C and demonstrated efficient in vitro and in vivo drug release at 42 °C. Rapid intratumoral distribution of released Dox and delivery into tumor cells was observed, demonstrating strongly improved drug bioavailability. The superior application of TSL and mild HT will achieve both maximal intratumoral liposomal drug accumulation and rapid triggered drug release to aid liposomal chemotherapy in clinical practice. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2317. doi:10.1158/1538-7445.AM2011-2317

Focused ultrasound phased array systems have attracted increased attention for brain therapy applications. However, such systems currently lack a direct and real-time method to intraoperatively monitor ultrasound pressure distribution for securing treatment. This study proposes a dual-mode 256-channel ultrasound phased array system design to support transmit/receive operations for concurrent ultrasound exposure and backscattered focal-beam reconstruction through a spherically focused ultrasound array. A total 256-channel ultrasound transmission system was used to transmit focused ultrasonic energy, with an extended implementation of multiple-channel receiving function (up to 64 channels) using the same 256-channel ultrasound array. Our results showed that PSF and focal beam can be successfully reconstructed and visualized in free-field conditions, and can also be transcranially reconstructed following skull-induced aberration correction. In-vivo experiments were conducted to demonstrate its capability to pre-operatively and semi-quantitatively map a focal beam to guide blood-brain barrier (BBB)-opening. The proposed system may have potential for real-time guidance of ultrasound brain intervention, and may facilitate the design of a dual-mode ultrasound phased array for brain therapeutic applications.

Hyperthermia-induced doxorubicin delivery from thermosensitive liposomes via MR-HIFU in a pig model

Simple SummaryVarious nanoparticles have been developed over the last few decades for targeted drug delivery to cancerous tumors while reducing toxicities. Thermosensitive liposomes (TSL) belong to the category of triggered nanoparticle delivery systems, where drug release occurs in response to hyperthermic temperatures (typically, >40 ºC). After administration, the TSL-encapsulated drug circulates for extended duration (hours) in the blood stream. Localized hyperthermia of the targeted tissue results in localized drug release, enabling up to 25x tumor drug uptake compared to administration of unencapsulated drug. Here, we review the delivery kinetics of TSL and discuss how the interaction between drug, TSL and hyperthermia device affects drug delivery. Thus, this review provides guidelines on how to improve drug delivery by optimizing the combination of TSL, drug, and hyperthermia method. Many of the concepts discussed are applicable to a variety of other triggered nanoparticle delivery systems.Thermosensitive liposomes (TSL) are triggered nanoparticles that release the encapsulated drug in response to hyperthermia. Combined with localized hyperthermia, TSL enabled loco-regional drug delivery to tumors with reduced systemic toxicities. More recent TSL formulations are based on intravascular triggered release, where drug release occurs within the microvasculature. Thus, this delivery strategy does not require enhanced permeability and retention (EPR). Compared to traditional nanoparticle drug delivery systems based on EPR with passive or active tumor targeting (typically <5%ID/g tumor), TSL can achieve superior tumor drug uptake (>10%ID/g tumor). Numerous TSL formulations have been combined with various drugs and hyperthermia devices in preclinical and clinical studies over the last four decades. Here, we review how the properties of TSL dictate delivery and discuss the advantages of rapid drug release from TSL. We show the benefits of selecting a drug with rapid extraction by tissue, and with quick cellular uptake. Furthermore, the optimal characteristics of hyperthermia devices are reviewed, and impact of tumor biology and cancer cell characteristics are discussed. Thus, this review provides guidelines on how to improve drug delivery with TSL by optimizing the combination of TSL, drug, and hyperthermia method. Many of the concepts discussed are applicable to a variety of other triggered drug delivery systems.

Hyperthermia-mediated drug delivery induces biological effects at the tumor and molecular levels that improve cisplatin efficacy in triple negative breast cancer

Advanced strategies in liposomal cancer therapy: Problems and prospects of active and tumor specific drug release

The purpose of this study is to investigate the feasibility of using a 1 MHz cylindrical ultrasound phased array with multifocus pattern scanning to produce uniform heating for breast tumor thermal therapy. The breast was submerged in water and surrounded by the cylindrical ultrasound phased array. A multifocus pattern was generated and electrically scanned by the phased array to enlarge the treatment lesion in single heating. To prevent overheating normal tissues, a large planning target volume (PTV) would be divided into several planes with several subunits on each plane and sequentially treated with a cooling phase between two successive heatings of the subunit. Heating results for different target temperatures (Ttgt), blood perfusion rates and sizes of the PTV have been studied. Furthermore, a superficial breast tumor with different water temperatures was also studied. Results indicated that a higher target temperature would produce a slightly larger thermal lesion, and a higher blood perfusion rate would not affect the heating lesion size but increase the heating time significantly. The acoustic power deposition and temperature elevations in ribs can be minimized by orienting the acoustic beam from the ultrasound phased array approximately parallel to the ribs. In addition, a large acoustic window on the convex-shaped breast surface for the proposed ultrasound phased array and the cooling effect of water would prevent the skin overheating for the production of a lesion at any desired location. This study demonstrated that the proposed cylindrical ultrasound phased array can provide effective heating for breast tumor thermal therapy without overheating the skin and ribs within a reasonable treatment time.