Drug delivery to the brain using thermosensitive liposome and local hyperthermia

Emerging Nano-Carrier Strategies for Brain Tumor Drug Delivery and Considerations for Clinical Translation

Treatment of brain tumors is challenging since the blood–brain tumor barrier prevents chemotherapy drugs from reaching the tumor site in sufficient concentrations. Nanomedicines have great potential for therapy of brain disorders but are still uncommon in clinical use despite decades of research and development. Here, we provide an update on nano-carrier strategies for improving brain drug delivery for treatment of brain tumors, focusing on liposomes, extracellular vesicles and biomimetic strategies as the most clinically feasible strategies. Finally, we describe the obstacles in translation of these technologies including pre-clinical models, analytical methods and regulatory issues.

In situ vaccination with laser interstitial thermal therapy augments immunotherapy in malignant gliomas

INTRODUCTION

Laser interstitial thermal therapy (LITT) remains a promising advance in the treatment of primary central nervous system malignancies. As indications for its use continue to expand, there has been growing interest in its ability to induce prolonged blood brain barrier (BBB) permeability through hyperthermia, potentially increasing the effectiveness of current therapeutics including BBB-impermeant agents and immunotherapy platforms.

METHODS

In this review, we highlight the mechanism of hyperthermic BBB disruption and LITT-induced immunogenic cell death in preclinical models and humans. Additionally, we summarize ongoing clinical trials evaluating a combination approach of LITT and immunotherapy, which will likely serve as the basis for future neuro-oncologic treatment paradigms.

RESULTS

There is evidence to suggest a highly immunogenic response to laser interstitial thermal therapy through activation of both the innate and adaptive immune response. These mechanisms have been shown to potentiate standard methods of oncologic care. There are only a limited number of clinical trials are ongoing to evaluate the utility of LITT in combination with immunotherapy.

CONCLUSION

LITT continues to be studied as a possible technique to bridge the gap between exciting preclinical results and the limited successes seen in the field of neuro-oncology. Preliminary data suggests a substantial benefit for use of LITT as a combination therapy in several clinical trials. Further investigation is required to determine whether or not this treatment paradigm can translate into long-term durable results for primary intracranial malignancies.

Preparation, Optimization, and Evaluation of Methoxy Poly(ethylene glycol)-co-Poly(ε-caprolactone) Nanoparticles Loaded by Rivastigmine for Brain Delivery

The objective of this study was to formulate and investigate the neuropharmacokinetics and pharmacodynamics of rivastigmine (Riv) loaded methoxy poly(ethylene glycol)-co-poly(ε-caprolactone) (MPEG-PCL) nanoparticles (Riv-NPs) in rats after IV administration. The MPEG-PCL was synthesized via ring-opening polymerization of ε-caprolactone by MPEG and used to prepare Riv-NPs by the nanoprecipitation method. Response surface D-optimal design was applied to optimize Riv-NPs drug delivery system. The optimized formulation showed a particle size (PS) of 98.5 ± 2.1 nm, drug loading (DL) of 19.2 ± 1.1%, and sustained release behavior of the drug. Moreover, the optimized Riv-NPs were characterized by AFM and DSC analyses. A simple and sensitive HPLC-DAD method for bioanalysis was developed and successfully applied to the pharmacokinetic study. The neuropharmacokinetic study in rats indicated that the integration plot was linear, and the brain uptake clearance of the drug-loaded in MPEG-PCL NPs was significantly higher than the free drug. Furthermore, results of pharmacodynamic studies using the Morris water maze test demonstrated faster regain of memory loss with Riv-NPs when compared to the free drug solution. The results revealed that the mentioned biodegradable nanoparticle holds promise as a suitable drug carrier for brain drug delivery.

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.

Transport of drugs from blood vessels to tumour tissue

The effectiveness of anticancer drugs in treating a solid tumour is dependent on delivery of the drug to virtually all cancer cells in the tumour. The distribution of drug in tumour tissue depends on the plasma pharmacokinetics, the structure and function of the tumour vasculature and the transport properties of the drug as it moves through microvessel walls and in the extravascular tissue. The aim of this Review is to provide a broad, balanced perspective on the current understanding of drug transport to tumour cells and on the progress in developing methods to enhance drug delivery. First, the fundamental processes of solute transport in blood and tissue by convection and diffusion are reviewed, including the dependence of penetration distance from vessels into tissue on solute binding or uptake in tissue. The effects of the abnormal characteristics of tumour vasculature and extravascular tissue on these transport properties are then discussed. Finally, methods for overcoming limitations in drug transport and thereby achieving improved therapeutic results are surveyed.

Thermal Therapy Approaches for Treatment of Brain Tumors in Animals and Humans

Primary brain tumors are often aggressive, with short survival from time of diagnosis even with standard of care therapies such as surgery, chemotherapy, and radiation therapy. Thermal therapies have been extensively investigated as both primary and adjuvant therapy. Although thermal therapies are not yet widely used clinically, there have been several promising approaches demonstrated in both animals and humans. This review presents thermal therapy approaches in animal and human studies, including both hyperthermia (temperatures ~42°C-45°C) and thermal ablation (temperatures > 50°C). Hyperthermia is primarily used as adjuvant to chemotherapy and radiotherapy, and is the most widely studied radiation sensitizer where enhanced efficacy has been shown in human patients with brain cancer. Hyperthermia has additional beneficial effects such as immunogenic effects, and opening of the bloodbrain barrier to potentially enhance drug delivery, for example in combination with nanoparticle drug delivery systems. Thermal ablation uses high temperatures for direct local tumor destruction, and it found its way into clinical use as laser interstitial thermal therapy (LITT). This review presents various hyperthermia and ablation approaches, including a review of different devices and methods that have been used for thermal therapies, such as radiofrequency/microwaves, laser, high-intensity focused ultrasound, and magnetic nanoparticles. Current research efforts include the combination of advanced thermal therapy devices, such as focused ultrasound with radiation, as well as the use of thermal therapies to enhance chemotherapy delivery across the blood-brain barrier.

In vivo evaluation of small-molecule thermoresponsive anticancer drugs potentiated by hyperthermia

Hyperthermia used as an adjuvant with chemotherapy is highly promising in the treatment of certain cancers. Currently, the small molecule drugs used in combination with hyperthermia were not designed for this application. Herein, we report the evaluation of a chlorambucil and a ruthenium compound modified with a long fluorous chain, which exhibit thermoresponsive activity in colorectal adenocarcinoma xenografts in athymic mice in combination with mild hyperthermia (42 °C). Intraperitoneal injection of the derivatives followed by local hyperthermia showed a synergistic tumor growth reduction by 79% and 90% for the chlorambucil and ruthenium-based derivatives, respectively, with the latter exhibiting a higher synergy in combination with hyperthermia compared to the monotherapies. Histological analysis shows that both derivatives in combination with hyperthermia significantly decrease the number of proliferating tumor cells.

Lactoferrin- and antitransferrin-modified liposomes for brain targeting of the NK3 receptor agonist senktide: preparation and in vivo evaluation

The aim of this work was to evaluate the capability of lactoferrin- and antitransferrin-modified long circulating liposomes to deliver the hydrophilic peptide senktide, a selective NK3 receptor agonist unable to cross the blood brain barrier, to central nervous system by using an indirect method based on in vivo microdialysis studies to estimate the responsiveness of nucleus accumbens shell dopamine to senktide. To this purpose, senktide was encapsulated in different targeted and not-targeted stealth liposomes prepared using film hydration method. Formulations were characterized in terms of morphology, size distribution, zeta potential, encapsulation efficiency, and antibody presence on the liposome surface. In vivo microdialysis studies were performed injecting intravenously the senktide-loaded liposomes and comparing obtained dopamine levels with those found with the free senktide given intracerebroventricularly. Results showed that all vesicles were spherical, small in size (around 120 nm), homogeneously dispersed, and slightly negatively charged. TEM analysis, using an anti IgG secondary antibody with 10nm gold nanoparticles at its distal end, demonstrated the successful linkage of the antibody on the liposomal surface. Intravenously administered in rats, senktide-loaded targeted stealth liposomes elicited a significant increase of dialysate dopamine in the nucleus accumbens shell, which was comparable to that of the free senktide given intracerebroventricularly when antitransferrin-targeted liposomes were tested. On the contrary, control stealth liposomes did not affect dopamine levels. Senktide brain levels were higher using the antitransferrin-targeted liposomes in comparison with the lactoferrin ones, while the opposite was obtained in the liver tissue where the highest senktide accumulation was always found.

Treatment of malignant glioma using hyperthermia

Thirty pathologically diagnosed patients with grade III–IV primary or recurrent malignant glioma (tumor diameter 3–7 cm) were randomly divided into two groups. The control group underwent conventional radiotherapy and chemotherapy. In the hyperthermia group, primary cases received hyperthermia treatment, and patients with recurrent tumors were treated with hyperthermia in com-bination with radiotherapy and chemotherapy. Hyperthermia treatment was administered using a 13.56-MHz radio frequency hyperthermia device. Electrodes were inserted into the tumor with the aid of a CT-guided stereotactic apparatus and heat was applied for 1 hour. During 3 months after hyperthermia, patients were evaluated with head CT or MRI every month. Gliomas in the hyper-thermia group exhibited growth retardation or growth termination. Necrosis was evident in 80% of the heated tumor tissue and there was a decrease in tumor diameter. Our findings indicate that ra-dio frequency hyperthermia has a beneficial effect in the treatment of malignant glioma.

Nanotechnological advances for the delivery of CNS therapeutics

Effective non-invasive treatment of neurological diseases is often limited by the poor access of therapeutic agents into the central nervous system (CNS). The majority of drugs and biotechnological agents do not readily permeate into brain parenchyma due to the presence of two anatomical and biochemical dynamic barriers: the blood-brain barrier (BBB) and blood-cerebrospinal fluid barrier (BCSFB). Therefore, one of the most significant challenges facing CNS drug development is the availability of effective brain targeting technology. Recent advances in nanotechnology have provided promising solutions to this challenge. Several nanocarriers ranging from the more established systems, e.g. polymeric nanoparticles, solid lipid nanoparticles, liposomes, micelles to the newer systems, e.g. dendrimers, nanogels, nanoemulsions and nanosuspensions have been studied for the delivery of CNS therapeutics. Many of these nanomedicines can be effectively transported across various in vitro and in vivo BBB models by endocytosis and/or transcytosis, and demonstrated early preclinical success for the management of CNS conditions such as brain tumors, HIV encephalopathy, Alzheimer's disease and acute ischemic stroke. Future development of CNS nanomedicines need to focus on increasing their drug-trafficking performance and specificity for brain tissue using novel targeting moieties, improving their BBB permeability and reducing their neurotoxicity.

Strategies for enhancing antibody delivery to the brain

Antibodies and antibody conjugates have emerged as important tools for cancer therapy. However, a major therapeutic challenge for the use of antibodies is their inability to cross the blood-brain barrier (BBB) to reach tumors localized in the central nervous system (CNS). Multiple methods have been developed to enhance antibody delivery to the CNS, including direct injection, mechanical or biochemical disruption of the BBB, conjugation to a 'molecular Trojan horse', cationization, encapsulation in nanoparticles and liposomes, and more recently, stem cell-mediated antibody delivery. In this review, we discuss each of these approaches, highlighting their successes and the obstacles that remain to be overcome.

Preparation and characterization of tegafur magnetic thermosensitive liposomes

The purpose was to study the preparation and properties of tegafur magnetic thermosensitive liposomes. The method was to employ an improved chemical coprecipitation method for preparing nano-magnetic particles and a reverse-phase evaporation and ultrasonic method for preparing tegafur magnetic thermosensitive liposomes. The results showed that tegafur magnetic thermosensitive liposomes were prepared successfully. They had comparatively strong magnetism and superparamagnetism, and their temperature showed a linear positive correlation with dosages and the field strength under a current value. The conclusion was that tegafur magnetic thermosensitive liposomes with comparatively small particle size, superparamagnetism and comparatively strong magnetism were prepared successfully.

Controlling the in vivo activity of Wnt liposomes

Liposomes offer a method of delivering small molecules, nucleic acids, and proteins to sites within the body. Typically, bioactive materials are encapsulated within the liposomal aqueous core and liposomal phase transition is elicited by pH or temperature changes. We developed a new class of liposomes for the in vivo delivery of lipid-modified proteins. First, we show that the inclusion of a chromophore into the liposomal or vesosomal membrane renders these lipid vesicles extremely sensitive to very small (muJ) changes in energy. Next, we demonstrate that the lipid-modified Wnt protein is not encapsulated within a liposome but rather is tethered to the exoliposomal surface in an active configuration. When applied to intact skin, chromophore-modified liposomes do not penetrate past the corneal layer of the epidermis, but remain localized to the site of application. Injury to the epidermis allows rapid penetration of liposomes into the dermis, which suggests that mild forms of dermabrasion will greatly enhance transdermal delivery of liposome-packaged molecules. Finally, we demonstrate that topical application of Wnt3a liposomes rapidly stimulates proliferation of cells in the corneal layer, resulting in a thicker, more fibrillous epidermis.

Targeted nanoparticle-based drug delivery and diagnosis

Nanotechnology, or systems/device manufacture at sizes generally ranging between 1 and 100 nm, is a multidisciplinary scientific field undergoing explosive development. The genesis of nanotechnology can be traced to advances in medicine, communications, genomics and robotics. One of the greatest values of nanotechnology will be in the development of new and effective medical treatments (i.e. nanomedicine). This review focuses on the potential of nanomedicine as it relates to the development of nanoparticles for enabling and improving the targeted delivery of therapeutic and diagnostic agents. We highlight the use of nanoparticles for specific intra-compartmental analysis using the examples of delivery to malignant cancers, to the central nervous system, and across the gastrointestinal barriers.

New Delivery Approaches for Pediatric Brain Tumors

For many types of childhood brain tumors, including malignant gliomas, disease progression at the primary site is the predominant mode of treatment failure. Accordingly, interest has been directed during the last decade on exploring strategies to enhance the delivery of therapeutically active agents into the tumor microenvironment. Two approaches that have been the focus of considerable attention in the treatment of adult malignant brain tumors include interstitial administration of chemotherapeutic agents using time-release polymers and convection-enhanced delivery of immunotoxin conjugates targeted to receptors overexpressed in brain tumors relative to normal brain cells. Although it remains to be determined whether these approaches will lead to meaningful improvements in disease control and long-term prognosis in children with brain tumors, the encouraging results from studies in adults support the rationale for further exploring these strategies in the pediatric setting.

Therapeutic efficacy of targeting chemotherapy using local hyperthermia and thermosensitive liposome: evaluation of drug distribution in a rat glioma model

A method was developed of targeting chemotherapy using thermosensitive liposomes to treat malignant gliomas. Using the brain heating system, when the tumour core is heated to >43 degrees C, the tumour infiltrating zone is exposed to mild hyperthermia (40-43 degrees C). Thermosensitive liposomes were designed to release their contents at 40 degrees C to target both the tumour core and tumour infiltrating zone. The present study investigated the anti-tumour effect on rat glioma models in tumour drug uptake and tumour growth delay studies. Elevated accumulation of ADR in the rat C6 glioma after treatment was obtained in the area heated to >40 degrees C. However, there was no significant difference between the areas heated to 40-42 degrees C and >43 degrees C. Furthermore, it was found that ADR concentrations in the mildly hyperthermic areas were significantly higher following treatment with liposomal ADR than with free ADR. The animals treated with the new combination therapy had significantly longer overall survival time in comparison to those receiving other treatments. Thus, thermosensitive liposomes release their contents in response to mild hyperthermia and this combination therapy has a greater therapeutic efficacy for malignant brain tumours. This method is a promising approach for the treatment of malignant glioma patients.

The role of liposomes in drug delivery and diagnostic imaging: a review

This manuscript is not intended as a comprehensive overview of the large filed of liposome technology and all its applications. However, our intent was to present current data, which are active, cutting-edge research. Because of their unique properties liposomes will continue to be investigated in drug delivery and imaging systems, and very likely will be incorporated into our discipline of veterinary medicine as the clinical applications of liposomes continue to expand.

Hyperthermia enhances thermal-neutron-induced cell death of human glioblastoma cell lines at low concentrations of 10B

PURPOSE

To examine the ability of pre- vs. post-irradiation hyperthermia to enhance the effectiveness of thermal neutrons to kill human glioblastoma cells.

METHODS AND MATERIALS

Human glioblastoma cell lines, T98G, A7, A172, and U 87MG, were exposed to thermal neutrons from the Kyoto University Research (KUR) reactor or to 60Co gamma-rays. Hyperthermia was tested before and after irradiation of T98G (44 degrees C, 15 min) and A7 cells (44 degrees C, 40 min), and with different concentrations (0-30 ppm) of 10B-boric acid. The biological end point of all experiments was cell survival measured by a colony formation assay.

RESULTS

The relative biological effectiveness (RBE) values of thermal neutrons for these cell lines compared with 60Co gamma-rays were 1.8-2.0 at their D(0) values. When T98G and A7 cells were heated after thermal neutron irradiation, there was a synergistic effect at low 10B concentrations (up to 5 ppm for T98G and up to 10 ppm for A7 cells). With high concentrations of boron (10-30 ppm for T98G and 20-30 ppm for A7 cells), hyperthermia and neutron irradiation interact additively rather than synergistically. There was no enhancement when cells were heated before thermal neutron irradiation. These results suggest that the radiosensitizing effect of hyperthermia may be attributed to partial inhibition of the repair of the potentially lethal damage caused by neutron irradiation.