Boron neutron capture therapy of primary and metastatic brain tumors

Dendritic Structures Functionalized with Boron Clusters, in Particular Carboranes, and Their Biological Properties

The presence of a large number of boron atoms in boron clusters make them attractive tools for the treatment of cancer using boron neutron capture therapy (BNCT). Since the quantity of boron atoms present in the target cell directly affects the effectiveness of BNCT, the idea of gathering a high number of boron atoms in a single entity has emerged many years ago. In this perspective, using hyper-branched macromolecules such as dendrimers appears as an interesting solution. In this review, we will first present the synthesis of diverse dendritic entities (dendrimers, dendrons, and Janus dendrimers) that incorporate boron clusters, in particular carboranes, anywhere in their structure. Four parts of this review present the synthesis of dendrimers having boron clusters on the surface, or inside their structure, of dendrons and of Janus dendrimers, bearing boron clusters. Practically all these boronated dendritic structures were synthesized with the objective to study their biological properties, but in fact only a few of them have been tested against cancerous cells, and even a smaller number was tested in BNCT experiments. The biological experiments are discussed in the fifth part of this review. A good efficiency is generally observed with the boronated dendrimers, even in animal models, with an increase in their mean survival time (MST).

Construction of targeted 10B delivery agents and their uptake in gastric and pancreatic cancer cells

Boron Neutron Capture Therapy (BNCT) is a new binary radiation therapy for tumor tissue, which kills tumor cells with neutron capture reaction. Boron neutron capture therapy has become a technical means for glioma, melanoma, and other diseases has been included in the clinical backup program. However, BNCT is faced with the key problem of developing and innovating more efficient boron delivery agents to solve the targeting and selectivity. We constructed a tyrosine kinase inhibitor-L-p-boronophenylalanine (TKI-BPA) molecule, aiming to improve the selectivity of boron delivery agents by conjugating targeted drugs while increasing the molecular solubility by adding hydrophilic groups. It shows excellent selectivity in differential uptake of cells, and its solubility is more than 6 times higher than BPA, leading to the saving of boron delivery agents. This modification method is effective for improving the efficiency of the boron delivery agent and is expected to become a potential alternative with high clinical application value.

Design of Beam Shaping Assemblies for Accelerator-Based BNCT With Multi-Terminals

To moderate fast neutrons produced by accelerator to appropriate therapeutic energies for boron neutron capture therapy (BNCT), beam shaping assembly (BSA) is required definitely. In this work, based on a model of 2.5 MeV/30 mA proton accelerator, the Monte Carlo simulation software MCNPX was employed to design multi-terminal BSAs. All parameters for both the thermal and epithermal neutron beams at the exit ports of the designed BSAs meet the treatment recommendation values proposed by the International Atomic Energy Agency (IAEA). The clinical parameters of the thermal and epithermal neutron beams were also calculated for clinical indication consideration.

Mapping the Relative Biological Effectiveness of Proton, Helium and Carbon Ions with High-Throughput Techniques

Large amounts of high quality biophysical data are needed to improve current biological effects models but such data are lacking and difficult to obtain. The present study aimed to more efficiently measure the spatial distribution of relative biological effectiveness (RBE) of charged particle beams using a novel high-accuracy and high-throughput experimental platform. Clonogenic survival was selected as the biological endpoint for two lung cancer cell lines, H460 and H1437, irradiated with protons, carbon, and helium ions. Ion-specific multi-step microplate holders were fabricated such that each column of a 96-well microplate is spatially situated at a different location along a particle beam path. Dose, dose-averaged linear energy transfer (LETd), and dose-mean lineal energy (yd) were calculated using an experimentally validated Geant4-based Monte Carlo system. Cells were irradiated at the Heidelberg Ion Beam Therapy Center (HIT). The experimental results showed that the clonogenic survival curves of all tested ions were yd-dependent. Both helium and carbon ions achieved maximum RBEs within specific yd ranges before biological efficacy declined, indicating an overkill effect. For protons, no overkill was observed, but RBE increased distal to the Bragg peak. Measured RBE profiles strongly depend on the physical characteristics such as yd and are ion specific.

Enhancement of Radiation Effectiveness in Proton Therapy: Comparison Between Fusion and Fission Methods and Further Approaches

Proton therapy as a promising candidate in cancer treatment has attracted much attentions and many studies have been performed to investigate the new methods to enhance its radiation effectiveness. In this regard, two research groups have suggested that using boron isotopes will lead to a radiation effectiveness enhancement, using boron-11 agent to initiate the proton fusion reaction (P-BFT) and using boron-10 agent to capture the low energy secondary neutrons (NCEPT). Since, these two innovative methods have not been approved clinically, they have been recalculated in this report, discussed and compared between them and also with the traditional proton therapy to evaluate their impacts before the experimental investigations. The calculations in the present study were performed by Geant4 and MCNPX Monte Carlo Simulation Codes were utilized for obtaining more precision in our evaluations of these methods impacts. Despite small deviations in the results from the two MC tools for the NCEPT method, a good agreement was observed regarding the delivered dose rate to the tumor site at different depths while, for P-BFT related calculations, the GEANT4 was in agreement with the analytical calculations by means of the detailed cross-sections of proton-¹¹B fusion. Accordingly, both the methods generate excess dose rate to the tumor several orders of magnitude lower than the proton dose rate. Also, it was found that, the P-BFT has more significant enhancement of effectiveness, when compared to the NCEPT, a method with impact strongly depended on the tumor's depth. On the other hand, the advantage of neutron risk reduction proposed by NCEPT was found to give no considerable changes in the neutron dose absorption by healthy tissues.

Perspectives on dendritic architectures and their biological applications: From core to cell

The challenges of medicine today include the increasing stipulation for sensitive and effective systems that can improve the pathological responses with a simultaneous reduction in accumulation and drug side effects. The demand can be fulfilled through the advancements in nanomedicine that includes nanostructures and nanodevices for diagnosing, treating, and prevention of various diseases. In this respect, the nanoscience provides various novel techniques with carriers such as micelles, dendrimers, particles and vesicles for the transportation of active moieties. Further, an efficient way to improve these systems is through stimuli a responsive system that utilizes supramolecular hyperbranched structures to meet the above criteria. The stimuli-responsive dendritic architectures exhibit spatial, temporal, convenient, effective, safety and controlled drug release in response to specific trigger through electrostatic interactions plus π stacking. The stimuli-responsive systems are capable of sequestering the drug molecules underneath a predefined set of conditions and discharge them in a different environment through either exogenous or endogenous stimulus. The incorporation of photoresponsive moieties at various components of dendrimer such as core, branches or at the peripheral end exaggerates its significance in various allied fields of nanotechnology which includes sensors, photoswitch, electronic widgets and in drug delivery systems. This is due to the light instigated geometrical modifications at the core or at the surface molecules which generates huge conformational changes throughout the hyperbranched structure. Further, numerous synthetic methodologies have been investigated for utilization of dendrimers in therapeutic drug delivery and its applicability towards stimuli responsive systems such as photo-instigated, thermal-instigated, and pH-instigated hyperbranched structures and their advancement in the field of nanomedicine. This paper highlights the fascinating theoretical advances and principal mechanisms of dendrimer synthesis and their ability to capture light that strengthens its applicability from radiant energy to medical photonics.

Europium-Doped Gd2O3 Nanotubes Increase Bone Mineral Density in Vivo and Promote Mineralization in Vitro

Europium-doped Gd₂O₃ nanotubes (Gd₂O₃:Eu³⁺ NTs) have been extensively applied in the field of bioscience for their photostability and magnetic properties. Nevertheless, the distribution and interaction between Gd₂O₃:Eu³⁺ NTs and metabolism of bone are not yet sufficiently understood. In this study, a systematic study of the toxicity and distribution of Gd₂O₃:Eu³⁺ NTs in mice after oral administration was carried out. The results showed that a small number of the Gd₂O₃:Eu³⁺ NTs could pass through biological barriers into the lung, liver, and spleen, but a high concentration was observed in bone. Furthermore, the effects of Gd₂O₃:Eu³⁺ NTs on bone metabolism were systematically studied in vitro and in vivo when accumulating in bone. After being administered to mice, the Gd₂O₃:Eu³⁺ NTs extremely enhanced the bone mineral density and bone biomechanics. In vitro the Gd₂O₃:Eu³⁺ NTs increased the alkaline phosphatase (ALP) activity and mineralization and promoted the expression of osteogenesis genes in preosteoblasts MC3T3-E1 through activation of the BMP signaling pathway. This study will be significant for appropriate application of Gd₂O₃:Eu³⁺ NTs in the biomedical field and expounding the molecular mechanism of bone metabolism.

Dendrimers as Innovative Radiopharmaceuticals in Cancer Radionanotherapy

Radiotherapy is one of the most commonly used cancer treatments, with an estimate of 40% success that could be improved further if more efficient targeting and retention of radiation at the tumor site were achieved. This review focuses on the use of dendrimers in radionanotherapy, an emerging technology aimed to improve the efficiency of radiotherapy by implementing nanovectorization, an already established praxis in drug delivery and diagnosis. The labeling of dendrimers with radionuclides also aims to reduce the dose of radiolabeled materials and, hence, their toxicity and tumor resistance. Examples of radiolabeled dendrimers with alpha, beta, and Auger electron emitters are commented, along with the use of dendrimers in boron neutron capture therapy (BNCT). The conjugation of radiolabeled dendrimers to monoclonal antibodies for a more efficient targeting and the application of dendrimers in gene delivery radiotherapy are also covered.

In vivo biodistribution and toxicity of Gd2O3:Eu3+ nanotubes in mice after intraperitoneal injection

To better understand the potential impact of Gd₂O₃:Eu³⁺ nanotubes on human health, we investigated their biodistribution, subacute toxicity, and hepatic injury in mice under different dosages (4.0, 40.0, and 400.0 mg kg⁻¹).

Extracellular biosynthesis of gadolinium oxide (Gd2O3) nanoparticles, their biodistribution and bioconjugation with the chemically modified anticancer drug taxol

As a part of our programme to develop nanobioconjugates for the treatment of cancer, we first synthesized extracellular, protein-capped, highly stable and well-dispersed gadolinium oxide (Gd2O3) nanoparticles by using thermophilic fungus Humicola sp. The biodistribution of the nanoparticles in rats was checked by radiolabelling with Tc-99m. Finally, these nanoparticles were bioconjugated with the chemically modified anticancer drug taxol with the aim of characterizing the role of this bioconjugate in the treatment of cancer. The biosynthesized Gd2O3 nanoparticles were characterized by UV-vis spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoemission spectroscopy (XPS). The Gd2O3-taxol bioconjugate was confirmed by UV-vis spectroscopy and fluorescence microscopy and was purified by using high performance liquid chromatography (HPLC).

Multi-functional polymeric nanoparticles for tumour-targeted drug delivery

The use of nanoparticles as drug delivery vehicles for anticancer therapeutics has great potential to revolutionise the future of cancer therapy. As tumour architecture causes nanoparticles to preferentially accumulate at the tumour site, their use as drug delivery vectors results in the localisation of a greater amount of the drug load at the tumour site; thus improving cancer therapy and reducing the harmful nonspecific side effects of chemotherapeutics. In addition, formulation of these nanoparticles with imaging contrast agents provides a very efficient system for cancer diagnostics. Given the exhaustive possibilities available to polymeric nanoparticle chemistry, research has quickly been directed at multi-functional nanoparticles, combining tumour targeting, tumour therapy and tumour imaging in an all-in-one system, providing a useful multi-modal approach in the battle against cancer. This review will discuss the properties of nanoparticles that allow for such multiple functionality, as well as recent scientific advances in the area of multi-functional nanoparticles for cancer therapeutics.

Peptide dendrimers

Dendrimers are branched structures and represent a fast growing field covering many areas of chemistry. Various types of dendrimers differing in composition and structure are mentioned, together with their practical use spanning from catalysis, transport vehicles to synthetic vaccines. The main stress is given to peptide dendrimers, namely, multiple antigenic peptides (MAPs). Their synthesis, physicochemical properties, biological activities, etc. have been described with many examples. MAPs can be used as diagnostics, mimetics, for complexation of different cations, as vaccines against parasites, bacteria, viruses, etc.

Comparison of cell uptake, biodistribution and tumor retention of folate-coated and PEG-coated gadolinium nanoparticles in tumor-bearing mice

The purpose of these studies was to compare the cell uptake, biodistribution and tumor retention of folate-coated and PEG-coated gadolinium (Gd) nanoparticles. Gd is a potential agent for neutron capture therapy (NCT) of tumors. Gd nanoparticles were engineered from oil-in-water microemulsion templates. To obtain folate-coated nanoparticles, a folate ligand [folic acid chemically linked to distearoylphosphatidylethanolamine (DSPE) via a PEG spacer MW 3350] was included in nanoparticle preparations. Similarly, control nanoparticles were coated with DSPE-PEG-MW 3350 (PEG-coated). Nanoparticles were characterized based on size, size distribution, morphology, biocompatibility and tumor cell uptake. In vivo studies were carried out in KB (human nasopharyngeal carcinoma) tumor-bearing athymic mice. Biodistribution and tumor retention studies were carried out at pre-determined time intervals after injection of nanoparticles (10 mg/kg). Gd nanoparticles did not aggregate platelets or activate neutrophils. The retention of nanoparticles in the blood 8, 16 and 24 h post-injection was 60%, 13% and 11% of the injected dose (ID), respectively. A maximum Gd tumor localization of 33+/-7 microg Gd/g was achieved. Both folate-coated and PEG-coated nanoparticles had comparable tumor accumulation. However, the cell uptake and tumor retention of folate-coated nanoparticles was significantly enhanced over PEG-coated nanoparticles. Thus, the benefits of folate ligand coating were to facilitate tumor cell internalization and retention of Gd-nanoparticles in the tumor tissue. The engineered nanoparticles may have potential in tumor-targeted delivery of Gd thereby enhancing the therapeutic success of NCT.

The use of positron emission tomography to develop boron neutron capture therapy treatment plans for metastatic malignant melanoma

Centers in Japan and the United States are extending boron neutron capture therapy (BNCT) to the treatment of malignant melanoma (MM). Positron emission tomography (PET) has been used to image glioblastoma multiforme with 18F-boronophenylalanine (18F-BPA) for the purpose of generating 10B distribution maps. These distribution maps can be used to improve the BNCT treatment planning. 18F-BPA was given to a patient with widely metastatic MM involving the thorax and brain. 18F-BPA PET scans of the chest and the head were obtained and compared to the computed tomograms (CT) and magnetic resonance (MR) images. The lung metastases seen on the chest CT images and intracranial metastases seen on CT and MR images were correlated with the PET images. The PET images clearly identified a brain lesion that was difficult to identify on MR and CT images. The 18F-BPA lung and peri-oral mucous gland activity was intense indicating a relatively high concentration of BPA. The intensity seen in the peri-oral mucous glands is consistent with the experiences in the BNCT clinical trials. These results have implications in the use of BNCT outside of the cranium. The PET images allow the generation of treatment plans that are consistent with the clinical findings. PET imaging with 18F-BPA can be used to identify potential tumors that may be amenable to BNCT and to improve treatment plans prior to BNCT.

Influence of formulation parameters on gadolinium entrapment and tumor cell uptake using folate-coated nanoparticles

Emulsifying wax and polyoxyl 2 stearyl ether (Brij 72) nanoparticles (2 mg/ml) containing high concentrations of gadolinium hexanedione (GdH) (0-3 mg) have been engineered from oil-in-water microemulsion templates. Solid nanoparticles were cured by cooling warm microemulsion templates (prepared at 55 degrees C) to room temperature in one vessel. Nanoparticles were characterized by transmission electron microscopy (TEM), photon correlation spectroscopy (PCS) and gel permeation chromatography (GPC). To obtain folate-coated nanoparticles, a folate ligand was added to either the microemulsion templates or nanoparticle suspensions at 25 degrees C. Since the concentration of Gd in the tumor is critical to the success of Gd-neutron capture therapy (NCT), the effects of various formulation factors on GdH entrapment in nanoparticles as well as tumor-targeting were studied. GdH entrapment in nanoparticles was affected mostly by the method of GdH incorporation and surfactant concentration used in preparing the microemulsion templates. Cell uptake studies were carried out in KB cells (human nasopharyngeal epidermal carcinoma cell line). The method of adding folate ligand to the formulations did not significantly affect nanoparticle cell uptake (P>0.11; t-test). However, the concentration of folate ligand added to nanoparticles had the greatest influence on nanoparticle uptake (P<0.01; t-test). The results showed that GdH entrapment and cell uptake were optimized and suggested that engineered folate-coated nanoparticles may serve as effective carrier systems for Gd-NCT of tumors.

Vascular targeted endoradiotherapy of tumors using alpha-particle-emitting compounds: theoretical analysis

PURPOSE

To establish the theoretical framework and study the feasibility of (211)At-labeled anti-tenascin chimeric 81C6 monoclonal antibody (mAb) as anti-vascular endoradiotherapy for the treatment of glioblastoma multiforme (GBM) tumors.

METHODS AND MATERIALS

The morphology of blood vessels from histologic images was analyzed and used along with reaction-diffusion equations to assess the activity concentration of (211)At-labeled chimeric 81C6 mAb in GBM tumor and normal-brain tissue. Alpha particle microdosimetry was then used to assess the survival probability and average absorbed dose for tumor and normal tissue endothelial cells (ECs) per unit vascular cumulated activity concentration q(source) (MBq-s g(-1)). In turn, these survival probabilities were used to assess the probability of failure Phi for a single vessel. Furthermore, using the vessel density, the specific tumor control probability per unit mass of tumor tissue (tcp) and the specific normal-tissue complication probability per unit mass of normal-brain tissue (ntcp) were estimated. The specific tumor control probability, tcp, was used to assess the overall tumor control probability (TCP) as a function of tumor mass.

RESULTS

The levels of (211)At-labeled ch81C6 mAb cumulated activity concentration in GBM tumor tissue were approximately five times higher than that in normal-brain tissue. Thus, the average absorbed dose to tumor ECs was higher than that of normal tissue ECs, and the survival probability for GBM ECs was lower than for normal-brain tissue ECs. Consequently, the resulting vessel-failure probability, Phi, for GBM tumor and for normal-brain tissue differ considerably, yielding a q(source) range between 10(3) and 10(4) MBq-s g(-1).

CONCLUSIONS

This theoretical analysis demonstrated that (211)At-labeled chimeric 81C6 is an effective anti-vascular therapy for the treatment of GBM tumors, yielding a tcp higher than 0.999 for vascular cumulated activity concentrations q(source) higher than 1 x 10(4) MBq-s g(-1), while yielding a low probability for normal-brain tissue damage.

Gadolinium-loaded nanoparticles engineered from microemulsion templates

Microemulsions (oil-in-water) have been used as templates to engineer stable emulsifying wax and Brij 72 (polyoxyl 2 stearyl ether) nanoparticles. The technique is simple, reproducible, and amenable to large-scale production of stable nanoparticles having diameters below 100 nm. Investigation of the process variables showed that the amount of surfactant used in the preparation of microemulsion templates had the greatest influence on the microemulsion window, as well as the properties and stability of the cured nanoparticles. Emulsifying wax and Brij 72 nanoparticles (2 mg/mL) made with 3 mM polyoxyl 20 stearyl ether and 2.3mM polysorbate 80, respectively, were the most stable based on retention of nanoparticle size over time. Gadolinium acetylacetonate (GdAcAc), a potential anticancer agent for neutron capture therapy (NCT), was entrapped in stable nanoparticles. The apparent water solubility of GdAcAc was increased more than 2000-fold by entrapment into nanoparticles. The entrapment efficiency of GdAcAc was about 100% for emulsifying wax nanoparticles and 86% for Brij 72 nanoparticles, as determined by gel permeation chromatography (GPC). Elution profiles were obtained with light scattering (counts per second) to detect nanoparticles and ultraviolet (UV) absorption of GdAcAc at 288 nm. Challenges of these cured nanoparticles in biologically relevant media such as 10% fetal bovine serum, 10 mM phosphate-buffered saline, 150 mM NaCl, and 10% lactose at 37 degrees C for 60 min demonstrated that these nanoparticles are stable. The ease of preparation of these very small and stable nanoparticles, and the ability to entrap lipophilic drugs such as GdAcAc with high efficiency, suggested that these systems may have potential in cell targeting, especially for specific delivery to tumor cells for NCT.

Gadolinium neutron-capture therapy using novel gadopentetic acid-chitosan complex nanoparticles: in vivo growth suppression of experimental melanoma solid tumor

The potential of gadolinium neutron-capture therapy (Gd-NCT) for cancer was evaluated using chitosan nanoparticles as a novel gadolinium device. The nanoparticles, incorporating 1200 microg of natural gadolinium, were administered intratumorally twice in mice bearing subcutaneous B16F10 melanoma. The thermal neutron irradiation was performed for the tumor site, with the fluence of 6. 32x10(12) neutrons/cm(2), 8 h after the second gadolinium administration. After the irradiation, the tumor growth in the nanoparticle-administered group was significantly suppressed compared to that in the gadopentetate solution-administered group, despite radioresistance of melanoma and the smaller Gd dose than that administered in past Gd-NCT trials. This study demonstrated the potential usefulness of Gd-NCT using gadolinium-loaded nanoparticles.

Chitosan-gadopentetic acid complex nanoparticles for gadolinium neutron-capture therapy of cancer: preparation by novel emulsion-droplet coalescence technique and characterization

PURPOSE

The gadopentetic acid (Gd-DTPA)-loaded chitosan nanoparticles (Gd-nanoCPs) were prepared for gadolinium neutron-capture therapy (Gd-NCT) and characterized and evaluated as a device for intratumoral (i.t.) injection.

METHODS

Gd-nanoCPs were prepared by a novel emulsion-droplet coalescence technique. The effects of the deacetylation degree of chitosan and Gd-DTPA concentration in chitosan medium on the particle size and the gadolinium content in Gd-nanoCPs were examined. In vitro Gd-DTPA release from Gd-nanoCPs was evaluated using an isotonic phosphate-buffered saline solution (PBS, pH 7.4) and human plasma. In vivo Gd-DTPA retention in the tumor after i.t. injection of Gd-nanoCPs was estimated on mice bearing s.c. B16F10 melanoma.

RESULTS

Gd-nanoCPs with the highest Gd content, which were obtained using 100% deacetylated chitosan in 15% Gd-DTPA aqueous solution, were 452 nm in diameter and 45% in Gd-DTPA content. A lower deacetylation degree of chitosan led to an increase in particle size and a decrease in Gd-DTPA content in Gd-nanoCPs. As Gd-DTPA concentration in the chitosan solution increased, Gd-DTPA content in Gd-nanoCPs increased but the particle size did not vary. Gd-DTPA loaded to Gd-nanoCPs was hardly released over 7 days in PBS (1.8%) despite the high water solubility of Gd-DTPA. In contrast, 91% of Gd-DTPA was released in plasma over 24 hours. When Gd-nanoCPs were i.t. injected, 92% of Gd-DTPA injected effectually without outflow was held in the tumor tissue for 24 hours, which was different from the case of gadopentetate solution injection (only 1.2%).

CONCLUSIONS

Gd-nanoCPs highly incorporating Gd-DTPA were successfully prepared by the emulsion-droplet coalescence technique. Their releasing properties and their ability for long-term retention of Gd-DTPA in the tumor indicated that Gd-nanoCPs might be useful as an i.t. injectable device for Gd-NCT.