Therapeutic Ultrasound for Enhanced Corneal Permeability to Macromolecules.

OBJECTIVES: Topically applied macromolecules have the potential to provide vision-saving treatments for many of the leading causes of blindness in the United States. The aim of this study was to determine if ultrasound can be applied to increase transcorneal drug delivery of macromolecules without dangerously overheating surrounding ocular tissues. METHODS: Dissected corneas of adult rabbits were placed in a diffusion cell between a donor compartment filled with a solution of macromolecules (40, 70 kDa, or 150 kDa) and a receiver compartment. Each cornea was exposed to the drug solution for 60 minutes, with the experimental group receiving 5 minutes of continuous ultrasound or 10 minutes of pulsed ultrasound at a 50% duty cycle (pulse repetition frequency of 500 ms on, 500 ms off) at the beginning of treatment. Unfocused circular ultrasound transducers were operated at 0.5 to 1 W/cm2 intensity and at 600 kHz frequency. RESULTS: The greatest increase in transcorneal drug delivery seen was 1.2 times (P < .05) with the application of pulsed ultrasound at 0.5 W/cm2 and 600 kHz for 10 minutes with 40 kDa macromolecules. Histological analysis revealed structural damage mostly in the corneal epithelium, with most damage occurring at the epithelial surface. CONCLUSIONS: This study suggests that ultrasound may be used for enhancing transcorneal delivery of macromolecules of lower molecular weights. Further research is needed on the long-term effects of ultrasound parameters used in this study on human ocular tissues.

Review of the Delivery Kinetics of Thermosensitive Liposomes.

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.

Selecting ideal drugs for encapsulation in thermosensitive liposomes and other triggered nanoparticles.

OBJECTIVE: Thermosensitive liposomes (TSL) and other triggered drug delivery systems (DDS) are promising therapeutic strategies for targeted drug delivery. However, successful designs with candidate drugs depend on many variables, including nanoparticle formulation, drug properties, and cancer cell properties. We developed a computational model based on experimental data to predict the potential efficacies of drugs when used with triggered DDS, such as TSL. METHODS: A computer model based on the Krogh cylinder was developed to predict uptake and cell survival with four anthracyclines when delivered by intravascular triggered DDS (e.g., TSL): doxorubicin (DOX), idarubicin (IDA), pirarubicin (PIR), and aclarubicin (ACLA). We simulated three tumor types derived from SVR angiosarcoma, LLC lung cancer, or SCC-1 oral carcinoma cells. In vitro cellular drug uptake and cytotoxicity data were obtained experimentally and incorporated into the model. RESULTS: For all three cell lines, ACLA and IDA had the fastest cell uptake, with slower uptake for DOX and PIR. Cytotoxicity was highest for IDA and lowest for ACLA. The computer model predicted the highest tumor drug uptake for ACLA and IDA, resulting from their rapid cell uptake. Overall, IDA was most effective and produced the lowest tumor survival fraction, with DOX being the second best. Perivascular drug penetration was reduced for drugs with rapid cell uptake, potentially limiting delivery to cancer cells distant from the vasculature. CONCLUSION: Combining simple in vitro experiments with a computer model could provide a powerful screening tool to evaluate the potential efficacy of candidate investigative drugs preceding TSL encapsulation and in vivo studies.

Extracorporeal Removal of Thermosensitive Liposomal Doxorubicin from Systemic Circulation after Tumor Delivery to Reduce Toxicities.

Thermosensitive liposomal doxorubicin (TSL-Dox) combined with localized hyperthermia enables targeted drug delivery. Tumor drug uptake occurs only during hyperthermia. We developed a novel method for removal of systemic TSL-Dox remaining after hyperthermia-triggered delivery to reduce toxicities. The carotid artery and jugular vein of Norway brown rats carrying two subcutaneous BN-175 tumors were catheterized. After allowing the animals to recover, TSL-Dox was infused at 7 mg/kg dose. Drug delivery to one of the tumors was performed by inducing 15 min microwave hyperthermia (43 °C). At the end of hyperthermia, an extracorporeal circuit (ECC) comprising a heating module to release drug from TSL-Dox followed by an activated carbon filter to remove free drug was established for 1 h (n = 3). A computational model simulated TSL-Dox pharmacokinetics, including ECC filtration, and predicted cardiac Dox uptake. In animals receiving ECC, we were able to remove 576 ± 65 mg of Dox (29.7 ± 3.7% of the infused dose) within 1 h, with a 2.9-fold reduction of plasma AUC. Fluorescent monitoring enabled real-time quantification of blood concentration and removed drug. Computational modeling predicted that up to 59% of drug could be removed with an ideal filter, and that cardiac uptake can be reduced up to 7×. We demonstrated removal of drug remaining after tumor delivery, reduced plasma AUC, and reduced cardiac uptake, suggesting reduced toxicity.

Untargeted Large Volume Hyperthermia Reduces Tumor Drug Uptake From Thermosensitive Liposomes.

GOAL: The impact of hyperthermia (HT) method on tumor drug uptake with thermosensitive liposomes (TSL) is not well understood. METHODS: We created realistic three-dimensional (3-D) computer models that simulate TSL-encapsulated doxorubicin (TSL-DOX) delivery in mouse tumors with three HT methods (thermistor probe (T), laser (L) and water bath (WB), at 15 min and 60 min HT duration), with corroborating in vivo studies. RESULTS: Average computer model-predicted tumor drug concentrations (µg/g) were 8.8(T, 15 min), 21.0(T, 60 min), 14.1(L, 15 min), 25.2(L, 60 min), 9.4(WB, 15 min), and 8.7(WB, 60 min). Tumor fluorescence was increased by 2.6 × (T) and 1.6 × (L) when HT duration was extended from 15 to 60 min (p < 0.05), with no increase for WB HT. Pharmacokinetic analysis confirmed that water bath HT causes rapid depletion of encapsulated TSL-DOX in systemic circulation due to the large heated tissue volume. CONCLUSIONS: Untargeted large volume HT causes poor tumor drug uptake from TSL.

Computer simulations of an irrigated radiofrequency cardiac ablation catheter and experimental validation by infrared imaging.

PURPOSE: To develop and validate a three-dimensional (3-D) computer model based on accurate geometry of an irrigated cardiac radiofrequency (RF) ablation catheter with microwave radiometry capability, and to test catheter performance. METHODS: A computer model was developed based on CAD geometry of a RF cardiac ablation catheter prototype to simulate electromagnetic heating, heat transfer, and computational fluid dynamics (blood flow, open irrigation, and natural convection). Parametric studies were performed; blood flow velocity (0-25 cm/s) and irrigation flow (0-40 ml/min) varied, both with perpendicular (PE) and parallel (PA) catheter orientations relative to tissue. Tissue Agar phantom studies were performed under similar conditions, and temperature maps were recorded via infrared camera. Computer model simulations were performed with constant voltage and with voltage adjusted to achieve maximum tissue temperatures of 95-105 °C. RESULTS: Model predicted thermal lesion width at 5 W power was 5.8-6.4 mm (PE)/6.5-6.6 mm (PA), and lesion depth was 4.0-4.3 mm (PE)/4.0-4.1 mm (PA). Compared to phantom studies, the mean errors of the computer model were as follows: 6.2 °C(PE)/4.3 °C (PA) for maximum gel temperature, 0.7 mm (10.9%) (PE)/0.1 mm (0.8%) (PA) for lesion width, and 0.3 mm (7.7%)(PE)/0.7 mm (19.1%) (PA) for lesion depth. For temperature-controlled ablation, model predicted thermal lesion width was 7-9.2 mm (PE)/8.6-9.2 mm (PA), and lesion depth was 4.3-5.5 mm (PE)/3.4-5.4 mm (PA). CONCLUSIONS: Computer models were able to reproduce device performance and to enable device evaluation under varying conditions. Temperature controlled ablation of irrigated catheters enables optimal tissue temperatures independent of patient-specific conditions such as blood flow.

Drug transport kinetics of intravascular triggered drug delivery systems.

Intravascular triggered drug delivery systems (IV-DDS) for local drug delivery include various stimuli-responsive nanoparticles that release the associated agent in response to internal (e.g., pH, enzymes) or external stimuli (e.g., temperature, light, ultrasound, electromagnetic fields, X-rays). We developed a computational model to simulate IV-DDS drug delivery, for which we quantified all model parameters in vivo in rodent tumors. The model was validated via quantitative intravital microscopy studies with unencapsulated fluorescent dye, and with two formulations of temperature-sensitive liposomes (slow, and fast release) encapsulating a fluorescent dye as example IV-DDS. Tumor intra- and extravascular dye concentration dynamics were extracted from the intravital microscopy data by quantitative image processing, and were compared to computer model results. Via this computer model we explain IV-DDS delivery kinetics and identify parameters of IV-DDS, of drug, and of target tissue for optimal delivery. Two parameter ratios were identified that exclusively dictate how much drug can be delivered with IV-DDS, indicating the importance of IV-DDS with fast drug release (~sec) and choice of a drug with rapid tissue uptake (i.e., high first-pass extraction fraction). The computational model thus enables engineering of improved future IV-DDS based on tissue parameters that can be quantified by imaging.

Closed-loop trans-skull ultrasound hyperthermia leads to improved drug delivery from thermosensitive drugs and promotes changes in vascular transport dynamics in brain tumors.

Effective drug delivery in brain tumors remains a major challenge in oncology. Although local hyperthermia and stimuli-responsive delivery systems, such as thermosensitive liposomes, represent promising strategies to locally enhance drug delivery in solid tumors and improve outcomes, their application in intracranial malignancies remains unexplored. We hypothesized that the combined abilities of closed-loop trans-skull Magnetic Resonance Imaging guided Focused Ultrasound (MRgFUS) hyperthermia with those of thermosensitive drugs can alleviate challenges in drug delivery and improve survival in gliomas. Methods: To conduct our investigations, we first designed a closed loop MR-guided Focused Ultrasound (MRgFUS) system for localized trans-skull hyperthermia (ΔT < 0.5 °C) in rodents and established safety thresholds in healthy mice. To assess the abilities of the developed system and proposed therapeutic strategy for FUS-triggered chemotherapy release we employed thermosensitive liposomal Dox (TSL-Dox) and tested it in two different glioma tumor models (F98 in rats and GL261 in mice). To quantify Dox delivery and changes in the transvascular transport dynamics in the tumor microenvironment we combined fluorescent microscopy, dynamic contrast enhanced MRI (DCE-MRI), and physiologically based pharmacokinetic (PBPK) modeling. Lastly, to assess the therapeutic efficacy of the system and of the proposed therapeutic strategy we performed a survival study in the GL261 glioma bearing mice. Results: The developed closed-loop trans-skull MRgFUS-hyperthermia system that operated at 1.7 MHz, a frequency that maximized the brain (FUS-focus) to skull temperature ratio in mice, was able to attain and maintain the desired focal temperature within a narrow range. Histological evidence (H&E and Nissl) suggests that focal temperature at 41.5 ± 0.5 °C for 10 min is below the threshold for tissue damage. Quantitative analysis of doxorubicin delivery from TSLs with MRgFUS-hyperthermia demonstrated 3.5-fold improvement in cellular uptake in GL261 glioma mouse tumors (p < 0.001) and 5-fold increase in delivery in F98 glioma rat tumors (p < 0.05), as compared to controls (TSL-Dox-only). Moreover, PBPK modeling of drug transport that was calibrated using the experimental data indicated that thermal stress could lead to significant improvement in the transvascular transport (2.3-fold increase in the vessel diffusion coefficient; P < 0.001), in addition to promoting targeted Dox release. Prospective experimental investigations with DCE-MRI during FUS-hyperthermia, supported these findings and provided evidence that moderate thermal stress (≈41 °C for up to 10 min) can promote acute changes in the vascular transport dynamics in the brain tumor microenvironment (Ktrans value for control vs. FUS was 0.0097 and 0.0148 min-1, respectively; p = 0.026). Crucially, survival analysis demonstrated significant improvement in the survival in the TSL-Dox-FUS group as compared to TSL-Dox-only group (p < 0.05), providing supporting evidence on the therapeutic potential of the proposed strategy. Conclusions: Our investigations demonstrated that spatially controlled thermal stress can be attained and sustained in the mouse brain, using a trans-skull closed-loop MRgFUS system, and used to promote the effective delivery of chemotherapy in gliomas from thermosensitive drugs. This system also allowed us to conduct mechanistic investigations that resulted in the refinement of our understanding on the role of thermal stress in augmenting mass and drug transport in brain tumors. Overall, our study established a new paradigm for effective drug delivery in brain tumors based on closed-loop ultrasound-mediated thermal stress and thermosensitive drugs.

Externally triggered smart drug delivery system encapsulating idarubicin shows superior kinetics and enhances tumoral drug uptake and response.

Rationale: Increasing the bioavailable drug level in a tumor is the key to enhance efficacy of chemotherapy. Thermosensitive smart drug delivery systems (SDDS) in combination with local hyperthermia facilitate high local drug levels, thus improving uptake in the tumor. However, inability to rapidly and efficiently absorb the locally released drug results in reduced efficacy, as well as undesired redistribution of the drug away from the tumor to the system. Methods: Based on this paradigm we propose a novel approach in which we replaced doxorubicin (DXR), one of the classic drugs for nanocarrier-based delivery, with idarubicin (IDA), a hydrophobic anthracycline used solely in the free form for treatment hematologic cancers. We established a series of in vitro and in vivo experiments to in depth study the kinetics of SDDS-based delivery, drug release, intratumor biodistribution and subsequent cell uptake. Results: We demonstrate that IDA is taken up over 10 times more rapidly by cancer cells than DXR in vitro. Similar trend is observed in in vivo online imaging and less drug redistribution is shown for IDA, together resulting in 4-times higher whole tumor drug uptake for IDA vs. DXR. Together his yielded an improved intratumoral drug distribution for IDA-SDDS, translating into superior tumor response compared to DXR-SDDS treatment at the same dose. Thus, IDA - a drug that is not used for treatment of solid cancers - shows superior therapeutic index and better outcome when administered in externally triggered SDDS. Conclusions: We show that a shift in selection of chemotherapeutics is urgently needed, away from the classic drugs towards selection based on properties of a chemotherapeutic in context of the nanoparticle and delivery mode, to maximize the therapeutic efficacy.

Computer Modeling of Drug Delivery with Thermosensitive Liposomes in a Realistic Three-Dimensional Geometry.

Thermosensitive liposomes (TSL) are nanoparticles that can encapsulate therapeutic drugs, and release those drugs when exposed to hyperthermic temperatures (>40 °C). Combined with localized hyperthermia, TSL enable focused drug delivery. In this study, we created a three-dimensional (3D) computer model for simulating delivery with TSL-encapsulated doxorubicin (TSL-Dox) to mouse tumors. A mouse hind limb was scanned by a 3D scanner and the resulting geometry was imported into finite element modeling software, with a virtual tumor added. Then, heating by a surface probe was simulated. Further, a drug delivery model was coupled to the heat transfer model to simulate drug delivery kinetics. For comparison, experimental studies in gel phantoms and in vivo fluorescence imaging studies in mice carrying lung tumor xenografts were performed. We report the tissue temperature profile, drug concentration profile and compare the experimental studies with the computer model. The thermistor produced very localized heating that resulted in highest drug delivery to regions near the probe. The average tumor temperature was 38.2˚C (range 34.4-43.4˚C), and produced an average tumor drug concentration of 11.8 µg/g (0.3-28.1 µg/g) after 15 min heating, and 25.6 µg/g (0.3-52 µg/g), after 60 min heating. The computer model reproduced the temperature profile compared to phantom experiments (mean error 0.71 °C, range 0.59-1.25 °C), as well as drug delivery profile as compared to in vivo studies. Our results suggest feasibility of using this approach to model drug delivery in preclinical studies with accurate model geometry.

Therapeutic Systems and Technologies: State-of-the-Art Applications, Opportunities, and Challenges.

In this review, we present current state-of-the-art developments and challenges in the areas of thermal therapy, ultrasound tomography, image-guided therapies, ocular drug delivery, and robotic devices in neurorehabilitation. Additionally, intellectual property and regulatory aspects pertaining to therapeutic systems and technologies are addressed.

Real-time fluorescence imaging for visualization and drug uptake prediction during drug delivery by thermosensitive liposomes.

Objective: Thermosensitive liposomal doxorubicin (TSL-Dox) is a promising stimuli-responsive nanoparticle drug delivery system that rapidly releases the contained drug in response to hyperthermia (HT) (>40 °C). Combined with localized heating, TSL-Dox allows highly localized delivery. The goals of this study were to demonstrate that real-time fluorescence imaging can visualize drug uptake during delivery, and can predict tumor drug uptake. Methods: Nude mice carrying subcutaneous tumors (Lewis lung carcinoma) were anesthetized and injected with TSL-Dox (5 mg/kg dose). Localized HT was induced by heating tumors for 15, 30 or 60 min via a custom-designed HT probe placed superficially at the tumor location. In vivo fluorescence imaging (excitation 523 nm, emission 610 nm) was performed before, during, and for 5 min following HT. After imaging, tumors were extracted, drug uptake was quantified by high-performance liquid chromatography, and correlated with in vivo fluorescence. Plasma samples were obtained before and after HT to measure TSL-Dox pharmacokinetics. Results: Local drug uptake could be visualized in real-time during HT. Compared to unheated control tumors, fluorescence of heated tumors increased by 4.6-fold (15 min HT), 9.3-fold (30 min HT), and 13.2-fold (60 min HT). HT duration predicted tumor drug uptake (p = .02), with tumor drug concentrations of 4.2 ± 1.3 µg/g (no HT), 7.1 ± 5.9 µg/g (15 min HT), 14.1 ± 6.7 µg/g (30 min HT) and 21.4 ± 12.6 µg/g (60 min HT). There was good correlation (R2 = 0.67) between fluorescence of the tumor region and tumor drug uptake. Conclusions: Real-time in vivo fluorescence imaging can visualize drug uptake during delivery, and can predict tumor drug uptake.

In vitro Measurement of Release Kinetics of Temperature Sensitive Liposomes with a Fluorescence Imaging System.

Temperature sensitive liposomes (TSL) are a promising type of nanoparticles for localized drug delivery. TSL typically release the contained drug at mild hyperthermic temperatures (40-42 °C). Combined with localized hyperthermia, this allows for local drug delivery. In vitro characterization of TSL involves measurements of drug release at varying temperatures, but current methods are inadequate due to low temporal resolution of ~8 - 10 seconds. We present a novel method for measuring the drug release with sub-second temporal resolution. In the proposed system, the TSL entrapping the fluorescent drug (Doxorubicin) are pumped through a capillary tube. The tube is rapidly heated to a desired temperature via Peltier element. Since fluorescence increases as drug is released from TSL, drug release kinetics can be measured via fluorescent imaging. By fitting exponential models, we calculated the time constants of drug release at temperatures of 39.5, 40.5 and 41.5.C were about 6.09, 2.06 and 1.03 seconds, respectively. Our initial tests show that the developed system can measure TSL release at subsecond resolution, and thus allow adequate in vitro evaluation of TSL formulations.

Permanent and Transient Electrophysiological Effects During Cardiac Cryoablation Documented by Optical Activation Mapping and Thermal Imaging.

OBJECTIVE: Cardiac catheter cryoablation is a safer alternative to radiofrequency ablation for arrhythmia treatment, but electrophysiological (EP) effects during and after freezing are not adequately characterized. The goal of this study was to determine transient and permanent temperature induced EP effects, during and after localized tissue freezing. METHODS: Conduction in right (RV) and left ventricles (LV) was studied by optical activation mapping during and after cryoablation in paced, isolated Langendorff-perfused porcine hearts. Cryoablation was performed endocardially (n=4) or epicardially (n=4) by a cryoprobe cooled to -120 °C for 8 minutes. Epicardial surface temperature was imaged with an infrared camera. Viability staining was performed after ablation. Motion compensation and co-registration was performed between optical mapping data, temperature image data, and lesion images. RESULTS: Cryoablation produced lesions 14.9 +/- 3.1 mm in diameter and 5.8 +/- 1.7 mm deep. A permanent lesion was formed in tissue cooled below -5 +/- 4 °C. Transient EP changes observed at temperatures between 17 and 37 °C during cryoablation surrounding the frozen tissue region directly correlated with local temperature, and include action potential (AP) duration prolongation, decrease in AP magnitude, and slowing in conduction velocity (Q10=2.0). Transient conduction block was observed when epicardial temperature reached <17 °C, but completely resolved upon tissue rewarming, within 5 minutes. CONCLUSION: Transient EP changes were observed surrounding the permanent cryo lesion (<-5 °C), including conduction block (-5 to 17 °C), and reduced conduction velocity (>17 °C). SIGNIFICANCE: The observed changes explain effects observed during clinical cryoablation, including transient increases in effective refractory period, transient conduction block, and transient slowing of conduction. The presented quantitative data on temperature dependence of EP effects may enable the prediction of the effects of clinical cryoablation devices.

Thermosensitive Liposomes for Image-Guided Drug Delivery.

Liposomes have been employed as cancer therapy clinically since the 1990s, with the primary benefit of reduced toxicity but no appreciable efficacy improvement. Thermosensitive liposomes (TSLs) are specifically formulated such that they release the encapsulated drug when exposed to hyperthermic temperatures in the fever range (~40-42°C) and have been investigated as cancer therapy for several decades, with first clinical trials initiated in the last decade. Combined with localized hyperthermia, TSLs allow precise drug delivery to a targeted region. Typically, the targeted tissue is exposed to localized hyperthermia facilitated by an image-guided hyperthermia device. Thus, TSLs enable image-guided drug delivery where drug is delivered to a tissue region identified by medical imaging. Recent TSL formulations are based on the more recent paradigm of intravascular triggered release, where drug is released rapidly (within seconds) while TSLs pass through the vasculature of the heated tissue region. The drug released within the blood then extravasates and is taken up by cancer cells. These TSLs enable up to 20-30 times higher tumor drug uptake compared to infusion of unencapsulated drug, and the dose locally delivered to the heated region can be modulated based on heating duration. This chapter reviews various TSL formulations, the different anticancer agents that have been encapsulated, as well as targeted cancer types. Further, the various hyperthermia devices that have been used for image-guided hyperthermia are reviewed, focusing on those that have been employed in human patients.

Localized delivery of therapeutic doxorubicin dose across the canine blood-brain barrier with hyperthermia and temperature sensitive liposomes.

Most drugs cannot penetrate the blood-brain barrier (BBB), greatly limiting the use of anti-cancer agents for brain cancer therapy. Temperature sensitive liposomes (TSL) are nanoparticles that rapidly release the contained drug in response to hyperthermia (>40 °C). Since hyperthermia also transiently opens the BBB, we hypothesized that localized hyperthermia can achieve drug delivery across the BBB when combined with TSL. TSL-encapsulated doxorubicin (TSL-Dox) was infused intravenously over 30 min at a dose of 0.94 mg/kg in anesthetized beagles (age ∼17 months). Following, a hyperthermia probe was placed 5-10 mm deep through one of four 3-mm skull burr holes. Hyperthermia was performed randomized for 15 or 30 min, at either 45 or 50 °C. Blood was drawn every 30 min to measure TSL-Dox pharmacokinetics. Nonsurvival studies were performed in four dogs, where brain tissue at the hyperthermia location was extracted following treatment to quantify doxorubicin uptake via high-performance liquid chromatography (HPLC) and to visualize cellular uptake via fluorescence microscopy. Survival studies for 6 weeks were performed in five dogs treated by a single hyperthermia application. Local doxorubicin delivery correlated with hyperthermia duration and ranged from 0.11 to 0.74 µg/g of brain tissue at the hyperthermia locations, with undetectable drug uptake in unheated tissue. Fluorescence microscopy demonstrated doxorubicin delivery across the BBB. Histopathology in Haematoxylin & Eosin (H&E) stained samples demonstrated localized damage near the probe. No animals in the survival group demonstrated significant neurological deficits. This study demonstrates that localized doxorubicin delivery to the brain can be facilitated by TSL-Dox with localized hyperthermia with no significant neurological deficits.

Lesion modeling, characterization, and visualization for image-guided cardiac ablation therapy monitoring.

In spite of significant efforts to improve image-guided ablation therapy, a large number of patients undergoing ablation therapy to treat cardiac arrhythmic conditions require repeat procedures. The delivery of insufficient thermal dose is a significant contributor to incomplete tissue ablation, in turn leading to the arrhythmia recurrence. Ongoing research efforts aim to better characterize and visualize RF delivery to monitor the induced tissue damage during therapy. Here, we propose a method that entails modeling and visualization of the lesions in real-time. The described image-based ablation model relies on classical heat transfer principles to estimate tissue temperature in response to the ablation parameters, tissue properties, and duration. The ablation lesion quality, geometry, and overall progression are quantified on a voxel-by-voxel basis according to each voxel's cumulative temperature and time exposure. The model was evaluated both numerically under different parameter conditions, as well as experimentally, using ex vivo bovine tissue samples undergoing ex vivo clinically relevant ablation protocols. The studies demonstrated less than 5°C difference between the model-predicted and experimentally measured end-ablation temperatures. The model predicted lesion patterns were within 0.5 to 1 mm from the observed lesion patterns, suggesting sufficiently accurate modeling of the ablation lesions. Lastly, our proposed method enables therapy delivery feedback with no significant workflow latency. This study suggests that the proposed technique provides reasonably accurate and sufficiently fast visualizations of the delivered ablation lesions.

A Unified Mathematical Model for Nano-Liposomal Drug Delivery to Solid Tumors.

Nanoparticles, such as liposomes, allow more targeted drug delivery for improved efficacy and/or reduced toxicity in both passive (e.g., Doxil) or active [e.g., thermo-sensitive liposomes (TSL)] release forms compared with unencapsulated drugs (i.e., conventional chemotherapy). Optimization and evaluation of these different drug delivery systems are experimentally challenging because of varying tissue parameters as well as limited avaiability of experimental data. Here, we present a novel unified mathematical model that can simulate various liposomal drug delivery systems and unencapsulated drugs with a single set of equations. We use this model to evaluate the chemotherapy performance of free Doxorubicin (as drug), as well as various liposomal drug delivery systems: 1) passive liposomes (Doxil) and 2) active-triggered TSL with either intravascular (TSLi) or extravascular (TSLe)-triggered release. Furthermore, we implemented a more accurate expression to consider incomplete liposomal drug release. The proposed model matches experimental in vivo results in terms of maximum drug concentration in tumor. The simulations predict better overall performance for all liposomal delivery systems than free Dox. TSLe is shown to be more efficient for less permeable and perfused tumors than other systems. The optimal release rate is lower for TSLe and Doxil than TSLi. The performance of free DOX changes a little for varying tumor characteristics such as perfusion and permeability.

Drug release kinetics of temperature sensitive liposomes measured at high-temporal resolution with a millifluidic device.

PURPOSE: Current release assays have inadequate temporal resolution ( ∼ 10 s) to characterise temperature sensitive liposomes (TSL) designed for intravascular triggered drug release, where release within the first few seconds is relevant for drug delivery. MATERIALS AND METHODS: We developed a novel release assay based on a millifluidic device. A 500 µm capillary tube was heated by a temperature-controlled Peltier element. A TSL solution encapsulating a fluorescent compound was pumped through the tube, producing a fluorescence gradient along the tube due to TSL release. Release kinetics were measured by analysing fluorescence images of the tube. We measured three TSL formulations: traditional TSL (DPPC:DSPC:DSPE-PEF2000,80:15:5), MSPC-LTSL (DPPC:MSPC:DSPE-PEG2000,85:10:5) and MPPC-LTSL (DPPC:MMPC:PEF2000,86:10:4). TSL were loaded with either carboxyfluorescein (CF), Calcein, tetramethylrhodamine (TMR) or doxorubicin (Dox). TSL were diluted in one of the four buffers: phosphate buffered saline (PBS), 10% bovine serum albumin (BSA) solution, foetal bovine serum (FBS) or human plasma. Release was measured between 37-45 °C. RESULTS: The millifluidic device allowed measurement of release kinetics within the first few seconds at ∼5 ms temporal resolution. Dox had the fastest release and highest release %, followed by CF, Calcein and TMR. Of the four buffers, release was fastest in human plasma, followed by FBS, BSA and PBS. CONCLUSIONS: The millifluidic device allows measurement of TSL release at unprecedented temporal resolution, thus allowing adequate characterisation of TSL release at time scales relevant for intravascular triggered drug release. The type of buffer and encapsulated compound significantly affect release kinetics and need to be considered when designing and evaluating novel TSL-drug combinations.