Ultrasonic enhancement of drug penetration in solid tumors

Using imaging modalities to predict nanoparticle distribution and treatment efficacy in solid tumors: The growing role of ultrasound

Nanomedicine in oncology has not had the success in clinical impact that was anticipated in the early stages of the field's development. Ideally, nanomedicines selectively accumulate in tumor tissue and reduce systemic side effects compared to traditional chemotherapeutics. However, this has been more successful in preclinical animal models than in humans. The causes of this failure to translate may be related to the intra- and inter-patient heterogeneity of the tumor microenvironment. Predicting whether a patient will respond positively to treatment prior to its initiation, through evaluation of characteristics like nanoparticle extravasation and retention potential in the tumor, may be a way to improve nanomedicine success rate. While there are many potential strategies to accomplish this, prediction and patient stratification via noninvasive medical imaging may be the most efficient and specific strategy. There have been some preclinical and clinical advances in this area using MRI, CT, PET, and other modalities. An alternative approach that has not been studied as extensively is biomedical ultrasound, including techniques such as multiparametric contrast-enhanced ultrasound (mpCEUS), doppler, elastography, and super-resolution processing. Ultrasound is safe, inexpensive, noninvasive, and capable of imaging the entire tumor with high temporal and spatial resolution. In this work, we summarize the in vivo imaging tools that have been used to predict nanoparticle distribution and treatment efficacy in oncology. We emphasize ultrasound imaging and the recent developments in the field concerning CEUS. The successful implementation of an imaging strategy for prediction of nanoparticle accumulation in tumors could lead to increased clinical translation of nanomedicines, and subsequently, improved patient outcomes. This article is categorized under: Diagnostic Tools In Vivo Nanodiagnostics and Imaging Therapeutic Approaches and Drug Discovery Nanomedicine for Oncologic Disease Therapeutic Approaches and Drug Discovery Emerging Technologies.

Polymer-drug conjugates: Design principles, emerging synthetic strategies and clinical overview

Adagen, an enzyme replacement treatment for adenosine deaminase deficiency, was the first protein-polymer conjugate to be approved in early 1990s. Post this regulatory approval, numerous polymeric drugs and polymeric nanoparticles have entered the market as advanced or next-generation polymer-based therapeutics, while many others have currently been tested clinically. The polymer conjugation to therapeutic moiety offers several advantages, like enhanced solubilization of drug, controlled release, reduced immunogenicity, and prolonged circulation. The present review intends to highlight considerations in the design of therapeutically effective polymer-drug conjugates (PDCs), including the choice of linker chemistry. The potential synthetic strategies to formulate PDCs have been discussed along with recent advancements in the different types of PDCs, i.e., polymer-small molecular weight drug conjugates, polymer-protein conjugates, and stimuli-responsive PDCs, which are under clinical/preclinical investigation. Current impediments and regulatory hurdles hindering the clinical translation of PDC into effective therapeutic regimens for the amelioration of disease conditions have been addressed.

Breaking through the barrier: Modelling and exploiting the physical microenvironment to enhance drug transport and efficacy

Pharmaceutical compounds are the main pillar in the treatment of various illnesses. To administer these drugs in the therapeutic setting, multiple routes of administration have been defined, including ingestion, inhalation, and injection. After administration, drugs need to find their way to the intended target for high effectiveness, and this penetration is greatly dependent on obstacles the drugs encounter along their path. Key hurdles include the physical barriers that are present within the body and knowledge of those is indispensable for progress in the development of drugs with increased therapeutic efficacy. In this review, we examine several important physical barriers, such as the blood-brain barrier, the gut-mucosal barrier, and the extracellular matrix barrier, and evaluate their influence on drug transport and efficacy. We explore various in vitro model systems that aid in understanding how parameters within the barrier model affect drug transfer and therapeutic effect. We conclude that physical barriers in the body restrict the quantity of drugs that can pass through, mainly as a consequence of the barrier architecture. In addition, the specific physical properties of the tissue can trigger intracellular changes, altering cell behavior in response to drugs. Though the barriers negatively influence drug distribution, physical stimulation of the surrounding environment may also be exploited as a mechanism to control drug release. This drug delivery approach is explored in this review as a potential alternative to the conventional ways of delivering therapeutics.

The Role of Ultrasound in Modulating Interstitial Fluid Pressure in Solid Tumors for Improved Drug Delivery

The unique microenvironment of solid tumors, including desmoplasia within the extracellular matrix, enhanced vascular permeability, and poor lymphatic drainage, leads to an elevated interstitial fluid pressure which is a major barrier to drug delivery. Reducing tumor interstitial fluid pressure is one proposed method of increasing drug delivery to the tumor. The goal of this topical review is to describe recent work using focused ultrasound with or without microbubbles to modulate tumor interstitial fluid pressure, through either thermal or mechanical effects on the extracellular matrix and the vasculature. Furthermore, we provide a review on techniques in which ultrasound imaging may be used to diagnose elevated interstitial fluid pressure within solid tumors. Ultrasound-based techniques show high promise in diagnosing and treating elevated interstitial pressure to enhance drug delivery.

Therapeutic Ultrasound Parameter Optimization for Drug Delivery Applied to a Murine Model of Hepatocellular Carcinoma

Ultrasound and microbubble (USMB)-mediated drug delivery is a valuable tool for increasing the efficiency of the delivery of therapeutic agents to cancer while maintaining low systemic toxicity. Typically, selection of USMB drug delivery parameters used in current research settings are either based on previous studies described in the literature or optimized using tissue-mimicking phantoms. However, phantoms rarely mimic in vivo tumor environments, and the selection of parameters should be based on the application or experiment. In the following study, we optimized the therapeutic parameters of the ultrasound drug delivery system to achieve the most efficient in vivo drug delivery using fluorescent semiconducting polymer nanoparticles as a model nanocarrier. We illustrate that voltage, pulse repetition frequency and treatment time (i.e., number of ultrasound pulses per therapy area) delivered to the tumor can successfully be optimized in vivo to ensure effective delivery of the semiconducting polymer nanoparticles to models of hepatocellular carcinoma. The optimal in vivo parameters for USMB drug delivery in this study were 70 V (peak negative pressure = 3.4 MPa, mechanical index = 1.22), 1-Hz pulse repetition frequency and 100-s therapy time. USMB-mediated drug delivery using in vivo optimized ultrasound parameters caused an up to 2.2-fold (p < 0.01) increase in drug delivery to solid tumors compared with that using phantom-optimized ultrasound parameters.

Evaluation of low-intensity pulsed ultrasound on doxorubicin delivery in 2D and 3D cancer cell cultures

The aim of our study was to evaluate the influence of low-intensity pulsed US on the delivery of doxorubicin (DOX) into MDA-MB-231 triple-negative breast cancer and A549 non-small cell lung cancer cell 2D and 3D cultures. US with pulse repetition frequency of 10 Hz and 1 MHz center frequency was generated with peak negative pressure of 0.5 MPa and 50% duty cycle. SonoVue microbubbles were used. Spheroids were formed using 3D Bioprinting method. DOX delivery in 2D and 3D cultures was assessed using fluorescence microscopy. US without the addition of microbubbles did not enhance the penetration of DOX into monolayer-cultured cells and tumor spheroids. In the presence of microbubbles US improved the delivery of DOX into the edge end middle zones of A549 and MDA-MB-231 spheroids. Application of low-intensity pulsed US in combination with microbubbles may be a promising approach to enhance the delivery of DOX into tumor spheroids.

In situ forming implants exposed to ultrasound enhance therapeutic efficacy in subcutaneous murine tumors

In situ forming implants (ISFIs) allow for a high initial intratumoral concentration and sustained release of the chemotherapeutic. However, clinical translation is impeded primarily due to limited drug penetration from the tumor/boundary interface and poor intratumoral drug retention. Therapeutic ultrasound (TUS) has become a popular approach for improving drug penetration of transdermal devices and increasing cellular uptake of nanoparticles. These effects are driven by the mechanical and thermal bioeffects associated with TUS. In this study, we characterize the released drug penetration, retention, and overall therapeutic response when exposing ISFI to the combination of the mechanical and thermal effects of TUS (C-TUS). ISFIs were intratumorally injected into subcutaneous murine tumors then exposed to C-TUS (exposure: 5 min, duty factor: 0.33, frequency: 3 MHz, intensity: 2.2 W/cm2, pulse duration: 2 ms, pulse repetition frequency: 165 Hz, effective radiating area: 5 cm2, energy delivered: 896 J, time average intensity: 0.88 W/cm2). Tumors treated with the combination of ISFI + C-TUS demonstrated a 2.5-fold increase in maximum drug penetration and a 3-fold increase in drug retention at 5- and 8-days post-injection, respectively, compared to ISFIs without TUS exposure. These improvements in drug penetration and retention translated into an enhanced therapeutic response. Mice treated with ISFI + C-TUS showed a 62.6% reduction in tumor progression, a 50.0% increase in median survival time, and a 26.6% increase in necrotic percentage compared to ISFIs without TUS exposure. Combining intratumoral ISFIs with TUS may be beneficial for addressing some long-standing challenges with local drug delivery in cancer treatment and may serve as a viable noninvasive method to improve the poor clinical success of local drug delivery systems.

The use of ultrasound to increase the uptake and cytotoxicity of dual taxane and P-glycoprotein inhibitor loaded, solid core nanoparticles in drug resistant cells

The objective of this study was to use ultrasound in combination with nanoparticulate formulations of taxane drugs for an additive approach to overcome multidrug resistance (MDR). Polymeric nanoparticulate formulations containing both chemotherapeutic taxane drugs and a polymeric inhibitor (MePEG₁₇-b-PCL₅) of drug resistant proteins have been previously developed in an attempt to overcome MDR in cells. High frequency (>1 MHz) ultrasound has been shown to increase the uptake of cytotoxic drugs in MDR proliferating cells and has been suggested as a different way to overcome MDR, resensitize drug resistant cancer cells and allow for chemotherapeutic efficacy. MDCK-MDR cells were incubated with docetaxel (DTX) or paclitaxel (PTX) loaded, solid core, nanoparticles made from a 50:50 ratio of two diblock copolymers, MePEG₁₁₄-b-PCL₂₀₀ and MePEG₁₇-b-PCL₅ (PCL₂₀₀/PCL₅). The accumulation of drug in MDCK-MDR cells was measured using radiolabeled drug and the viability of cells was determined using an MTS cell proliferation assay. The effect of ultrasound (4 MHz, 32 W/cm², 10 s, 25% duty cycle) on drug uptake and cell viability was studied. Using free DTX or PTX, MDCK-MDR cells were killed at sublethal doses of drug with the P-gp inhibitor (MePEG₁₇-b-PCL₅) present at a concentration of just 0.006% (m/v) and cell death began after just 3 h of incubation. Using sublethal incubation doses of PTX or DTX in PCL₂₀₀/PCL₅ nanoparticles for 90 min, followed by a second exposure to blank PCL₂₀₀/PCL₅ nanoparticles, cell viability dropped by approximately 60% at 24 h. Drug accumulation increased by 1.43-1.9 fold following five bursts of ultrasound applied at 90 min. Both, increased ultrasound exposure and increased concentrations of blank nanoparticles during the second incubation allowed for increased levels of cell death. The combined use of ultrasound with taxane and P-gp inhibitor loaded polymeric nanoparticles may allow for increased accumulation of drug and inhibitor which may then release both agents inside cells in a controlled manner to overcome drug resistance in MDR cells.

Observing Bubble Cavitation by Back-Propagation of Acoustic Emission Signals

Temporal- and spatial-resolved observations of microbubble cavitation generated through high-intensity ultrasound irradiation are key in improving both the efficiency and efficacy of ultrasound-assisted drug delivery systems. A method of measuring bubble cavitation applying an image-reconstruction technique of back-propagation of an acoustic cavitation emission (ACE) signal is proposed. A high-intensity focused ultrasound wave (pump wave) irradiates the bubble synchronously using ultrasound recording equipment to acquire the timing of the RF signal, which is produced when the bubble radiates a secondary wave during bubble cavitation. The ACE signal source is reconstructed through ultrasound-wave back-propagation followed by amplitude deconvolution. The proposed method was applied to microbubbles of an ultrasound contrast agent by changing the sound pressure of the pump wave. The method reliability of the temporal resolution was verified by simulating the amplitude-modulated signal of the virtual sound source. The temporal transition of the ACE signal exhibited sub-microsecond-order fluctuations in the signal intensity. From the amplitude signal image and the instantaneous frequency image reconstruction of the proposed method, two different ACE phenomena were visualized. One is the periodic pattern by the beat signals from the harmonic and ultraharmonic component of nonlinear oscillation under low-intensity ultrasound conditions. The other is the nonperiodic temporal and spatial distributions of this irradiation under high-intensity ultrasound conditions.

Enhanced microbubble contrast agent oscillation following 250 kHz insonation

Microbubble contrast agents are widely used in ultrasound imaging and therapy, typically with transmission center frequencies in the MHz range. Currently, an ultrasound center frequency near 250 kHz is proposed for clinical trials in which ultrasound combined with microbubble contrast agents is applied to open the blood brain barrier, since at this low frequency focusing through the human skull to a predetermined location can be performed with reduced distortion and attenuation compared to higher frequencies. However, the microbubble vibrational response has not yet been carefully evaluated at this low frequency (an order of magnitude below the resonance frequency of these contrast agents). In the past, it was assumed that encapsulated microbubble expansion is maximized near the resonance frequency and monotonically decreases with decreasing frequency. Our results indicated that microbubble expansion was enhanced for 250 kHz transmission as compared with the 1 MHz center frequency. Following 250 kHz insonation, microbubble expansion increased nonlinearly with increasing ultrasonic pressure, and was accurately predicted by either the modified Rayleigh-Plesset equation for a clean bubble or the Marmottant model of a lipid-shelled microbubble. The expansion ratio reached 30-fold with 250 kHz at a peak negative pressure of 400 kPa, as compared to a measured expansion ratio of 1.6 fold for 1 MHz transmission at a similar peak negative pressure. Further, the range of peak negative pressure yielding stable cavitation in vitro was narrow (~100 kPa) for the 250 kHz transmission frequency. Blood brain barrier opening using in vivo transcranial ultrasound in mice followed the same trend as the in vitro experiments, and the pressure range for safe and effective treatment was 75-150 kPa. For pressures above 150 kPa, inertial cavitation and hemorrhage occurred. Therefore, we conclude that (1) at this low frequency, and for the large oscillations, lipid-shelled microbubbles can be approximately modeled as clean gas microbubbles and (2) the development of safe and successful protocols for therapeutic delivery to the brain utilizing 250 kHz or a similar center frequency requires consideration of the narrow pressure window between stable and inertial cavitation.

Combination of chemotherapy and photodynamic therapy for cancer treatment with sonoporation effects

To overcome the limitations of single therapy, chemotherapy has been studied to be combined with photodynamic therapy. However, nanomedicine combining anticancer drug and photosensitizer still cannot address the insufficiency of drug delivery and the off-targeting effect. To address drug delivery issue, we have developed a doxorubicin encapsulating human serum albumin nanoparticles/chlorin e6 encapsulating microbubbles (DOX-NPs/Ce6-MBs) complex system. Microbubbles enable ultrasound-triggered local delivery via sonoporation for maximizing the drug delivery to a target site. In both in vitro and in vivo experiments, the developed DOX-NPs/Ce6-MBs drug delivery complex could be confirmed to transfer drugs deeply and effectively into cancerous tumors through the following three steps; (1) the local release of nanoparticles due to the cavitation of DOX-NPs/Ce6-MBs; (2) the enhanced extravasation of DOX-NPs and Ce6-liposome/micelle due to the sonoporation phenomenon; (3) the improved penetration of extravasated nanomedicines into the deep tumor region due to the mechanical energy of ultrasound. As a result, the developed DOX-NPs/Ce6-MBs complex with ultrasound irradiation showed increased therapeutic effects compared to the case where no ultrasound irradiation was applied. The DOX-NPs/Ce6-MBs was concluded from this study to be the optimal drug delivery system for external-stimuli local combination (chemotherapy + PDT) therapy.

Dual-drug nanomedicine with hydrophilic F127-modified magnetic nanocarriers assembled in amphiphilic gelatin for enhanced penetration and drug delivery in deep tumor tissue

Introduction

Deep penetration of large-sized drug nanocarriers into tumors is important to improve the efficacy of tumor therapy.

Methods

In this study, we developed a size-changeable “Trojan Horse” nanocarrier (THNC) composed of paclitaxel (PTX)-loaded Greek soldiers (GSs; ~20 nm) assembled in an amphiphilic gelatin matrix with hydrophilic losartan (LST) added.

Results

With amphiphilic gelatin matrix cleavage by matrix metalloproteinase-2, LST showed fast release of up to 60% accumulated drug at 6 h, but a slow release kinetic (~20%) was detected in the PTX from the GSs, indicating that THNCs enable controllable release of LST and PTX drugs for penetration into the tumor tissue. The in vitro cell viability in a 3D tumor spheroid model indicated that the PTX-loaded GSs liberated from THNCs showed deeper penetration as well as higher cytotoxicity, reducing a tumor spheroid to half its original size and collapsing the structure of the tumor microenvironment.

Conclusion

The results demonstrate that the THNCs with controlled drug release and deep penetration of magnetic GSs show great potential for cancer therapy.

Main-chain polyacetal conjugates with HIF-1 inhibitors: temperature-responsive, pH-degradable drug delivery vehicles

Main-chain polymer-drug conjugates are prepared from polyacetals (PA) and three hydrophobic diol-based HIF-1 inhibitors. The new conjugates are temperature-responsive with lower critical solution temperature (LCST) behavior and are intrinsically pH-degradable. While soluble in plasma at room temperature, they lose solubility above a target temperature that can be adjusted to virtually any temperature of physicological interest, providing mechanisms for site-specific delivery by active thermal targeting or temperature-induced gelation. The reverse phase transition temperature can be precisely tuned by proper choice of four structural variables that characterize the amphiphilic diol and divinyl ether monomers used in the synthesis, or by adjusting the content of drug incorporated within the polymer. These main-chain PA-drug conjugates also allow for site-specific controlled release as they degrade in acidic microenvironments such as tumors. The degradation rates increase with decreasing pH, degradation products are neutral, and pristine drug is released, without any remnants of the conjugation chemistry.

Nonviral cancer gene therapy: Delivery cascade and vector nanoproperty integration

Gene therapy represents a promising cancer treatment featuring high efficacy and limited side effects, but it is stymied by a lack of safe and efficient gene-delivery vectors. Cationic polymers and lipid-based nonviral gene vectors have many advantages and have been extensively explored for cancer gene delivery, but their low gene-expression efficiencies relative to viral vectors limit their clinical translations. Great efforts have thus been devoted to developing new carrier materials and fabricating functional vectors aimed at improving gene expression, but the overall efficiencies are still more or less at the same level. This review analyzes the cancer gene-delivery cascade and the barriers, the needed nanoproperties and the current strategies for overcoming these barriers, and outlines PEGylation, surface-charge, size, and stability dilemmas in vector nanoproperties to efficiently accomplish the cancer gene-delivery cascade. Stability, surface, and size transitions (3S Transitions) are proposed to resolve those dilemmas and strategies to realize these transitions are comprehensively summarized. The review concludes with a discussion of the future research directions to design high-performance nonviral gene vectors.

Synergistic Effects of Nanodrug, Ultrasound Hyperthermia, and Thermal Ablation on Solid Tumors-An Animal Study

OBJECTIVE

Delivery barriers of nanodrug in large tumors due to heterogeneous blood supply, elevated interstitial pressure, and long transport distances can degrade the efficacy of cancer treatment. In this study, we proposed a therapeutic strategy to improve the tumor growth inhibition by injecting pegylated liposomal doxorubicin (PLD), and then applying a short time of ultrasound hyperthermia (HT) on the entire solid tumor, and inflicting ultrasound thermal ablation (Ab) in the low-perfused tumor region.

METHODS

BALB/c female mice with an average weight of 20 g were adopted and murine breast cancer cells 4T1 were subcutaneously implanted into the flank. A 1.0-MHz planar and a 0.47-MHz focused ultrasound transducers were used, respectively, for the HT and Ab treatment.

RESULTS

For a PLD dose of 5 mg/kg, the PLD + HT(42 °C, 10 min) group caused a significant decrease in the tumor size as compared with the control and the PLD group, but there were no significant differences between the PLD + HT group and the PLD + Ab(56 °C, 49 s) + HT group. For a PLD dose of 3 mg/kg, the tumor sizes among the four groups were mutually significant. The level of reduction in tumor was PLD + Ab + HT > PLD + HT > PLD > control.

CONCLUSION

The combination of anticancer nanodrug and ultrasound thermal treatment could remarkably suppress cancer tumor growth with a minimum compromise of side effects.

SIGNIFICANCE

The strategy of using thermal Ab in locations that are not reached by nanodrug with mild HT shows a promising potential for the entire tumor treatment.

A Review of Thermo- and Ultrasound-Responsive Polymeric Systems for Delivery of Chemotherapeutic Agents

There has been an exponential increase in research into the development of thermal- and ultrasound-activated delivery systems for cancer therapy. The majority of researchers employ polymer technology that responds to environmental stimuli some of which are physiologically induced such as temperature, pH, as well as electrical impulses, which are considered as internal stimuli. External stimuli include ultrasound, light, laser, and magnetic induction. Biodegradable polymers may possess thermoresponsive and/or ultrasound-responsive properties that can complement cancer therapy through sonoporation and hyperthermia by means of High Intensity Focused Ultrasound (HIFU). Thermoresponsive and other stimuli-responsive polymers employed in drug delivery systems can be activated via ultrasound stimulation. Polyethylene oxide/polypropylene oxide co-block or triblock polymers and polymethacrylates are thermal- and pH-responsive polymer groups, respectively but both have proven to have successful activity and contribution in chemotherapy when exposed to ultrasound stimulation. This review focused on collating thermal- and ultrasound-responsive delivery systems, and combined thermo-ultrasonic responsive systems; and elaborating on the advantages, as well as shortcomings, of these systems in cancer chemotherapy. The mechanisms of these systems are explicated through their physical alteration when exposed to the corresponding stimuli. The properties they possess and the modifications that enhance the mechanism of chemotherapeutic drug delivery from systems are discussed, and the concept of pseudo-ultrasound responsive systems is introduced.

Stereotactic modulation of blood-brain barrier permeability to enhance drug delivery

Drug delivery in the CNS is limited by endothelial tight junctions forming the impermeable blood-brain barrier. The development of new treatment paradigms has previously been hampered by the restrictiveness of the blood-brain barrier to systemically administered therapeutics. With recent advances in stereotactic localization and noninvasive imaging, we have honed the ability to modulate, ablate, and rewire millimetric brain structures to precisely permeate the impregnable barrier. The wide range of focused radiations offers endless possibilities to disrupt endothelial permeability with different patterns and intensity following 3-dimensional coordinates offering a new world of possibilities to access the CNS, as well as to target therapies. We propose a review of the current state of knowledge in targeted drug delivery using noninvasive image-guided approaches. To this end, we focus on strategies currently used in clinics or in clinical trials such as targeted radiotherapy and magnetic resonance guided focused ultrasound, but also on more experimental approaches such as magnetically heated nanoparticles, electric fields, and lasers, techniques which demonstrated remarkable results both in vitro and in vivo. We envision that biodistribution and efficacy of systemically administered drugs will be enhanced with further developments of these promising strategies. Besides therapeutic applications, stereotactic platforms can be highly valuable in clinical applications for interventional strategies that can improve the targetability and efficacy of drugs and macromolecules. It is our hope that by showcasing and reviewing the current state of this field, we can lay the groundwork to guide future research in this realm.

Low-Frequency Ultrasound Enhances Paclitaxel Efficacy in EMT6 Subcutaneous Tumors in Balb/c Mice

BACKGROUND

The objective of this study was to explore the effects of 30 kHz ultrasound on the efficacy of paclitaxel in subcutaneous breast tumors in Balb/c mice in vivo.

MATERIALS AND METHODS

40 Balb/c female mice were divided into 5 groups: model control group, paclitaxel intraperitoneal (ip) group (20 mg/kg, ip, at 3 day intervals for a total of 3 doses (q3d×3)), paclitaxel intratumoral (it) group (20 mg/kg, it, q3d×3), paclitaxel intraperitoneal (20 mg/kg, ip, q3d×3) combined with low-frequency ultrasound (LFU) group, and paclitaxel intratumoral (20 mg/kg, it, q3d×3) combined with LFU group. Ultrasound parameters were 30 kHz, 200 MW intensity, 15 min, q3d×3. The antitumoral effect was determined by examining the tumor weight in subcutaneously inoculated EMT6 breast carcinoma models in Balb/c mice. All subcutaneous tumors were examined using high performance liquid chromatography (HPLC) upon completion of the experiments. Drug concentrations in the subcutaneous tumors were also analyzed using HPLC. Finally, paraffin sections of the subcutaneous tumors were made, and after hematoxylin and eosin staining, the tumor morphology was examined under a light microscope.

RESULTS

LFU combined with paclitaxel significantly restrained tumor growth in transplanted subcutaneous EMT6 tumors in Balb/c mice, and this effect correlated with increased local concentrations of paclitaxel in the tumors. Body weight measurement did not reveal significant adverse effects on the Balb/c mice during the study.

CONCLUSION

LFU combined with paclitaxel has a significant synergistic effect in the treatment of breast cancer.

Strategies for improving the intratumoral distribution of liposomal drugs in cancer therapy

INTRODUCTION

A major limitation of current liposomal cancer therapies is the inability of liposome therapeutics to penetrate throughout the entire tumor mass. This inhomogeneous distribution of liposome therapeutics within the tumor has been linked to treatment failure and drug resistance. Both liposome particle transport properties and tumor microenvironment characteristics contribute to this challenge in cancer therapy. This limitation is relevant to both intravenously and intratumorally administered liposome therapeutics.

AREAS COVERED

Strategies to improve the intratumoral distribution of liposome therapeutics are described. Combination therapies of intravenous liposome therapeutics with pharmacologic agents modulating abnormal tumor vasculature, interstitial fluid pressure, extracellular matrix components, and tumor associated macrophages are discussed. Combination therapies using external stimuli (hyperthermia, radiofrequency ablation, magnetic field, radiation, and ultrasound) with intravenous liposome therapeutics are discussed. Intratumoral convection-enhanced delivery (CED) of liposomal therapeutics is reviewed.

EXPERT OPINION

Optimization of the combination therapies and drug delivery protocols are necessary. Further research should be conducted in appropriate cancer types with consideration of physiochemical features of liposomes and their timing sequence. More investigation of the role of tumor associated macrophages in intratumoral distribution is warranted. Intratumoral infusion of liposomes using CED is a promising approach to improve their distribution within the tumor mass.

Targeted Mesoporous Iron Oxide Nanoparticles-Encapsulated Perfluorohexane and a Hydrophobic Drug for Deep Tumor Penetration and Therapy

A magneto-responsive energy/drug carrier that enhances deep tumor penetration with a porous nano-composite is constructed by using a tumor-targeted lactoferrin (Lf) bio-gate as a cap on mesoporous iron oxide nanoparticles (MIONs). With a large payload of a gas-generated molecule, perfluorohexane (PFH), and a hydrophobic anti-cancer drug, paclitaxel (PTX), Lf-MIONs can simultaneously perform bursting gas generation and on-demand drug release upon high-frequency magnetic field (MF) exposure. Biocompatible PFH was chosen and encapsulated in MIONs due to its favorable phase transition temperature (56 °C) and its hydrophobicity. After a short-duration MF treatment induces heat generation, the local pressure increase via the gasifying of the PFH embedded in MION can substantially rupture the three-dimensional tumor spheroids in vitro as well as enhance drug and carrier penetration. As the MF treatment duration increases, Lf-MIONs entering the tumor spheroids provide an intense heat and burst-like drug release, leading to superior drug delivery and deep tumor thermo-chemo-therapy. With their high efficiency for targeting tumors, Lf-MIONs/PTX-PFH suppressed subcutaneous tumors in 16 days after a single MF exposure. This work presents the first study of using MF-induced PFH gasification as a deep tumor-penetrating agent for drug delivery.

Magnetic Resonance-Guided Drug Delivery

The use of clinical imaging modalities for the guidance of targeted drug delivery systems, known as image-guided drug delivery (IGDD), has emerged as a promising strategy for enhancing antitumor efficacy. MR imaging is particularly well suited for IGDD applications because of its ability to acquire images and quantitative measurements with high spatiotemporal resolution. The goal of IGDD strategies is to improve treatment outcomes by facilitating planning, real-time guidance, and personalization of pharmacologic interventions. This article reviews basic principles of targeted drug delivery and highlights the current status, emerging applications, and future paradigms of MR-guided drug delivery.

DDMC-p53 gene therapy with or without cisplatin and microwave ablation

Lung cancer remains the leading cause of death in cancer patients. Severe treatment side effects and late stage of disease at diagnosis continue to be an issue. We investigated whether local treatment using 2-diethylaminoethyl-dextran methyl methacrylate copolymer with p53 (DDMC-p53) with or without cisplatin and/or microwave ablation enhances disease control in BALBC mice. We used a Lewis lung carcinoma cell line to inoculate 140 BALBC mice, which were divided into the following seven groups; control, cisplatin, microwave ablation, DDMC-p53, DDMC-p53 plus cisplatin, DDMC-p53 plus microwave, and DDMC-p53 plus cisplatin plus microwave. Microwave ablation energy was administered at 20 W for 10 minutes. Cisplatin was administered as 1 mL/mg and the DDMC-p53 complex delivered was 0.5 mL. Increased toxicity was observed in the group receiving DDMC-p53 plus cisplatin plus microwave followed by the group receiving DDMC-p53 plus cisplatin. Infection after repeated treatment administration was a major issue. We conclude that a combination of gene therapy using DDMC-p53 with or without cisplatin and microwave is an alternative method for local disease control. However, more experiments are required in a larger model to identify the appropriate dosage profile.

Cavitation-enhanced delivery of insulin in agar and porcine models of human skin

Ultrasound-assisted transdermal insulin delivery offers a less painful and less invasive alternative to subcutaneous insulin injections. However, ultrasound-based drug delivery, otherwise known as sonophoresis, is a highly variable phenomenon, in part dependent on cavitation. The aim of the current work is to investigate the role of cavitation in transdermal insulin delivery. Fluorescently stained, soluble Actrapid insulin was placed on the surface of human skin-mimicking materials subjected to 265 kHz, 10% duty cycle focused ultrasound. A confocally and coaxially aligned 5 MHz broadband ultrasound transducer was used to detect cavitation. Two different skin models were used. The first model, 3% agar hydrogel, was insonated with a range of pressures (0.25-1.40 MPa peak rarefactional focal pressure-PRFP), with and without cavitation nuclei embedded within the agar at a concentration of 0.05% w/v. The second, porcine skin was insonated at 1.00 and 1.40 MPa PRFP. In both models, fluorescence measurements were used to determine penetration depth and concentration of delivered insulin. Results show that in agar gel, both insulin penetration depth and concentration only increased significantly in the presence of inertial cavitation, with up to a 40% enhancement. In porcine skin the amount of fluorescent insulin was higher in the epidermis of those samples that were exposed to ultrasound compared to the control samples, but there was no significant increase in penetration distance. The results underline the importance of instigating and monitoring inertial cavitation during transdermal insulin delivery.

Internal polymer scaffolding in lipid-coated microbubbles for control of inertial cavitation in ultrasound theranostics

A lipid–polymer composite structure was developed for tuning of inertial cavitation activity of microbubbles under ultrasound exposure. This strategy has the potential to increase the safety of ultrasound theranostic applications assisted by microbubble cavitation.

A new brain drug delivery strategy: focused ultrasound-enhanced intranasal drug delivery

Central nervous system (CNS) diseases are difficult to treat because of the blood-brain barrier (BBB), which prevents most drugs from entering into the brain. Intranasal (i.n.) administration is a promising approach for drug delivery to the brain, bypassing the BBB; however, its application has been restricted to particularly potent substances and it does not offer localized delivery to specific brain sites. Focused ultrasound (FUS) in combination with microbubbles can deliver drugs to the brain at targeted locations. The present study proposed to combine these two different platform techniques (FUS+i.n.) for enhancing the delivery efficiency of intranasally administered drugs at a targeted location. After i.n. administration of 40 kDa fluorescently-labeled dextran as the model drug, FUS targeted at one region within the caudate putamen of mouse brains was applied in the presence of systemically administered microbubbles. To compare with the conventional FUS technique, in which intravenous (i.v.) drug injection is employed, FUS was also applied after i.v. injection of the same amount of dextran in another group of mice. Dextran delivery outcomes were evaluated using fluorescence imaging of brain slices. The results showed that FUS+i.n. enhanced drug delivery within the targeted region compared with that achieved by i.n. only. Despite the fact that the i.n. route has limited drug absorption across the nasal mucosa, the delivery efficiency of FUS+i.n. was not significantly different from that of FUS+i.v.. As a new drug delivery platform, the FUS+i.n. technique is potentially useful for treating CNS diseases.

Image-guided interventional therapy for cancer with radiotherapeutic nanoparticles

One of the major limitations of current cancer therapy is the inability to deliver tumoricidal agents throughout the entire tumor mass using traditional intravenous administration. Nanoparticles carrying beta-emitting therapeutic radionuclides that are delivered using advanced image-guidance have significant potential to improve solid tumor therapy. The use of image-guidance in combination with nanoparticle carriers can improve the delivery of localized radiation to tumors. Nanoparticles labeled with certain beta-emitting radionuclides are intrinsically theranostic agents that can provide information regarding distribution and regional dosimetry within the tumor and the body. Image-guided thermal therapy results in increased uptake of intravenous nanoparticles within tumors, improving therapy. In addition, nanoparticles are ideal carriers for direct intratumoral infusion of beta-emitting radionuclides by convection enhanced delivery, permitting the delivery of localized therapeutic radiation without the requirement of the radionuclide exiting from the nanoparticle. With this approach, very high doses of radiation can be delivered to solid tumors while sparing normal organs. Recent technological developments in image-guidance, convection enhanced delivery and newly developed nanoparticles carrying beta-emitting radionuclides will be reviewed. Examples will be shown describing how this new approach has promise for the treatment of brain, head and neck, and other types of solid tumors.

Optical clearing in photoacoustic flow cytometry

Clinical applications of photoacoustic (PA) flow cytometry (PAFC) for detection of circulating tumor cells in deep blood vessels are hindered by laser beam scattering, that result in loss of PAFC sensitivity and resolution. We demonstrate biocompatible and rapid optical clearing (OC) of skin to minimize light scattering and thus, increase optical resolution and sensitivity of PAFC. OC effect was achieved in 20 min by sequent skin cleaning, microdermabrasion, and glycerol application enhanced by massage and sonophoresis. Using 0.8 mm mouse skin layer over a blood vessel in vitro phantom we demonstrated 1.6-fold decrease in laser spot blurring accompanied by 1.6-fold increase in PA signal amplitude from blood background. As a result, peak rate for B16F10 melanoma cells in blood flow increased 1.7-fold. By using OC we also demonstrated the feasibility of PA contrast improvement for human hand veins.