The acceleration of boron neutron capture therapy using multi-linked mercaptoundecahydrododecaborate (BSH) fused cell-penetrating peptide

BNCT pancreatic cancer treatment strategy with glucose-conjugated boron drug

Multidisciplinary therapy centered on radical surgery for resectable pancreatic cancer is expected to prolong prognosis, but relies on CA19-9 biomarker levels to determine treatment strategy. Boron neutron capture therapy (BNCT) is a chemoradiotherapy using tumor hyperaccumulator boron drugs and neutron irradiation. The purpose of this study is to investigate novel boron drug agents for BNCT for pancreatic cancer. Bioinformatics was used to evaluate the uptake of current boron amino acid (BPA) drugs for BNCT into pancreatic cancer. The expression of the amino acid transporter LAT1, a BPA uptake transporter, was low in pancreatic cancer and even lower in high CA19-9 pancreatic cancer. In contrast, the glucose transporter was high in high CA19-9 pancreatic cancers and inversely correlated with LAT1 expression. Considering the low EPR effect in pancreatic cancer, we synthesized a small molecule Glucose-BSH, which is boron BSH bound to glucose, and confirmed its specific uptake in pancreatic cancer. uptake of Glucose-BSH was confirmed in an environment compatible with the tumor microenvironment. The therapeutic efficacy and safety of Glucose-BSH by therapeutic neutron irradiation were confirmed with BNCT. We report Glucose-BSH boron drug discovery study of a Precision Medicine BNCT with application to high CA19-9 pancreatic cancer.

Incorporating boron distribution variations in microdosimetric kinetic model-based relative biological effectiveness calculations for boron neutron capture therapy

This study introduces the MKM_B model, an approach derived from the MKM model, designed to evaluate the biological effectiveness of Boron Neutron Capture Therapy (BNCT) in the face of challenges from varying microscopic boron distributions. The model introduces a boron compensation factor, allowing for the assessment of compound Biological Effectiveness (CBE) values for different boron distributions. Utilizing the TOPAS simulation platform, the lineal energy spectrum of particles in BNCT was simulated, and the sensitivity of the MKM_B model to parameter variations and the influence of cell size on the model were thoroughly investigated. The CBE values for 10B-boronphenylalanine (BPA) and 10B-sodium (BSH) were determined to be 3.70 and 1.75, respectively. These calculations were based on using the nucleus radius of 2.5 μm and the cell radius of 5 μm while considering a 50% surviving fraction. It was observed that as cell size decreased, the CBE values for both BPA and BSH increased. Additionally, the model parameter rd was identified as having the most significant impact on CBE, with other parameters showing moderate effects. The development of the MKM_B model enables the accurate prediction of CBE under different boron distributions in BNCT. This model offers a promising approach to optimize treatment planning by providing increased accuracy in biological effectiveness.

Targeted strategies to deliver boron agents across the blood-brain barrier for neutron capture therapy of brain tumors

Boron neutron capture therapy (BNCT), as an innovative radiotherapy technology, has demonstrated remarkable outcomes when compared to conventional treatments in the management of recurrent and refractory brain tumors. However, in BNCT of brain tumors, the blood-brain barrier is a main stumbling block for restricting the transport of boron drugs to brain tumors, while the tumor targeting and retention of boron drugs also affect the BNCT effect. This review focuses on the recent development of strategies for delivering boron drugs crossing the blood-brain barrier and targeting brain tumors, providing new insights for the development of efficient boron drugs for the treatment of brain tumors.

HER-2-Targeted Boron Neutron Capture Therapy with Carborane-integrated Immunoliposomes Prepared via an Exchanging Reaction

Boron neutron capture therapy (BNCT) is a promising modality for cancer treatment because of its minimal invasiveness. To maximize the therapeutic benefits of BNCT, the development of efficient platforms for the delivery of boron agents is indispensable. Here, carborane-integrated immunoliposomes were prepared via an exchanging reaction to achieve HER-2-targeted BNCT. The conjugation of an anti-HER-2 antibody to carborane-integrated liposomes successfully endowed these liposomes with targeting properties toward HER-2-overexpressing human ovarian cancer cells (SK-OV3); the resulting BNCT activity toward SK-OV3 cells obtained using the current immunoliposomal system was 14-fold that of the l-BPA/fructose complex, which is a clinically available boron agent. Moreover, the growth of spheroids treated with this system followed by thermal neutron irradiation was significantly suppressed compared with treatment with the l-BPA/fructose complex.

In vivo investigation of boron-rich nanodrugs for treating triple-negative breast cancers via boron neutron capture therapy

Triple-negative breast cancer (TNBC) is characterized by highly proliferative cancer cells and is the only subtype of breast cancer that lacks a targeted therapy. Boron neutron capture therapy (BNCT) is an approach that combines chemotherapy with radiotherapy and can potentially offer beneficial targeted treatment for TNBC patients owing to its unique ability to eradicate cancer cells selectively while minimizing damage to the surrounding healthy cells. Since BNCT relies on specific delivery of a high loading of B10 to the tumor site, there is growing research interest to develop more potent boron-based drugs for BNCT that can overcome the limitations of small-molecule boron compounds. In this study, polyethylene-glycol-coated boron carbon oxynitride nanoparticles (PEG@BCNO) of size 134.2±23.6nm were prepared as a promising drug for BNCT owing to their high boron content and enhanced biocompatibility. The therapeutic efficiency of PEG@BCNO was compared with a state-of-the-art 10BPA boron drug in mice bearing MDA-MB-231 tumor. In the orthotopic mouse model, PEG@BCNO showed higher B10 accumulation in the tumor tissues (6 μg 10B/g tissue compared to 3 μg 10B/g tissue in mice administered B10-enriched 10BPA drug) despite using the naturally occurring 11B/10B boron precursor in the preparation of the BCNO nanoparticles. The in vivo biodistribution of PEG@BCNO in mice bearing MDA-MB-231 showed a tumor/blood ratio of ~3.5, which is comparable to that of the state-of-the-art 10BPA-fructose drug. We further demonstrated that upon neutron irradiation, the mice bearing MDA-MB-231 tumor cells treated with PEG@BCNO and 10BPA showed tumor growth delay times of 9 days and 1 day, respectively, compared to mice in the control group after BNCT. The doubling times (DTs) for mice treated with PEG@BCNO and 10BPA as well as mice in the control group were calculated to be 31.5, 19.8, and 17.7 days, respectively. Immunohistochemical staining for the p53 and caspase-3 antibodies revealed that mice treated with PEG@BCNO showed lower probability of cancer recurrence and greater level of cellular apoptosis than mice treated with 10BPA and mice in the control group. Our study thus demonstrates the potential of pegylated BCNO nanoparticles in effectively inhibiting the growth of TNBC tumors compared to the state-of-the-art boron drug 10BPA.

Proposal of recommended experimental protocols for in vitro and in vivo evaluation methods of boron agents for neutron capture therapy

Recently, boron neutron capture therapy (BNCT) has been attracting attention as a minimally invasive cancer treatment. In 2020, the accelerator-based BNCT with L-BPA (Borofalan) as its D-sorbitol complex (Steboronine®) for head and neck cancers was approved by Pharmaceutical and Medical Devices Agency for the first time in the world. As accelerator-based neutron generation techniques are being developed in various countries, the development of novel tumor-selective boron agents is becoming increasingly important and desired. The Japanese Society of Neutron Capture Therapy believes it is necessary to propose standard evaluation protocols at each stage in the development of boron agents for BNCT. This review summarizes recommended experimental protocols for in vitro and in vivo evaluation methods of boron agents for BNCT based on our experience with L-BPA approval.

In Vivo Application of Carboranes for Boron Neutron Capture Therapy (BNCT): Structure, Formulation and Analytical Methods for Detection

Carboranes have emerged as one of the most promising boron agents in boron neutron capture therapy (BNCT). In this context, in vivo studies are particularly relevant, since they provide qualitative and quantitative information about the biodistribution of these molecules, which is of the utmost importance to determine the efficacy of BNCT, defining their localization and (bio)accumulation, as well as their pharmacokinetics and pharmacodynamics. First, we gathered a detailed list of the carboranes used for in vivo studies, considering the synthesis of carborane derivatives or the use of delivery system such as liposomes, micelles and nanoparticles. Then, the formulation employed and the cancer model used in each of these studies were identified. Finally, we examined the analytical aspects concerning carborane detection, identifying the main methodologies applied in the literature for ex vivo and in vivo analysis. The present work aims to identify the current strengths and weakness of the use of carboranes in BNCT, establishing the bottlenecks and the best strategies for future applications.

The Dawn of a New Era: Tumor-Targeting Boron Agents for Neutron Capture Therapy

Cancer is widely recognized as one of the most devastating diseases, necessitating the development of intelligent diagnostic techniques, targeted treatments, and early prognosis evaluation to ensure effective and personalized therapy. Conventional treatments, unfortunately, suffer from limitations and an increased risk of severe complications. In light of these challenges, boron neutron capture therapy (BNCT) has emerged as a promising approach for cancer treatment with unprecedented precision to selectively eliminate tumor cells. The distinctive and promising characteristics of BNCT hold the potential to revolutionize the field of oncology. However, the clinical application and advancement of BNCT technology face significant hindrance due to the inherent flaws and limited availability of current clinical drugs, which pose substantial obstacles to the practical implementation and continued progress of BNCT. Consequently, there is an urgent need to develop efficient boron agents with higher boron content and specific tumor-targeting properties. Researchers aim to address this need by integrating tumor-targeting strategies with BNCT, with the ultimate goal of establishing BNCT as an effective, readily available, and cutting-edge treatment modality for cancer. This review delves into the recent advancements in integrating tumor-targeting strategies with BNCT, focusing on the progress made in developing boron agents specifically designed for BNCT. By exploring the current state of BNCT and emphasizing the prospects of tumor-targeting boron agents, this review provides a comprehensive overview of the advancements in BNCT and highlights its potential as a transformative treatment option for cancer.

Cell penetrating peptides: Highlighting points in cancer therapy

Cell-penetrating peptides (CPPs), first identified in HIV a few decades ago, deserved great attention in the last two decades; especially to support the penetration of anticancer drug means. In the drug delivery discipline, they have been involved in various approaches from mixing with hydrophobic drugs to the use of genetically conjugated proteins. The early classification as cationic and amphipathic CPPs has been extended to a few more classes such as hydrophobic and cyclic CPPs so far. Developing potential sequences utilized almost all methods of modern science: choosing high-efficiency peptides from natural protein sequences, sequence-based comparison, amino acid substitution, obtaining chemical and/or genetic conjugations, in silico approaches, in vitro analysis, animal experiments, etc. The bottleneck effect in this discipline reveals the complications that modern science faces in drug delivery research. Most CPP-based drug delivery systems (DDSs) efficiently inhibited tumor volume and weight in mice, but only in rare cases reduced their levels and continued further processes. The integration of chemical synthesis into the development of CPPs made a significant contribution and even reached the clinical stage as a diagnostic tool. But constrained efforts still face serious problems in overcoming biobarriers to reach further achievements. In this work, we reviewed the roles of CPPs in anticancer drug delivery, focusing on their amino acid composition and sequences. As the most suitable point, we relied on significant changes in tumor volume in mice resulting from CPPs. We provide a review of individual CPPs and/or their derivatives in a separate subsection.

Calculation of the DNA damage yield and relative biological effectiveness in boron neutron capture therapy via the Monte Carlo track structure simulation

Objective.Boron neutron capture therapy (BNCT) is an advanced cellular-level hadron therapy that has exhibited remarkable therapeutic efficacy in the treatment of locally invasive malignancies. Despite its clinical success, the intricate nature of relative biological effectiveness (RBE) and mechanisms responsible for DNA damage remains elusive. This work aims to quantify the RBE of compound particles (i.e. alpha and lithium) in BNCT based on the calculation of DNA damage yields via the Monte Carlo track structure (MCTS) simulation.Approach. The TOPAS-nBio toolkit was employed to conduct MCTS simulations. The calculations encompassed four steps: determination of the angle and energy spectra on the nuclear membrane, quantification of the database containing DNA damage yields for ions with specific angle and energy, accumulation of the database and spectra to obtain the DNA damage yields of compound particles, and calculation of the RBE by comparison yields of double-strand break (DSB) with the reference gamma-ray. Furthermore, the impact of cell size and microscopic boron distribution was thoroughly discussed.Main results. The DSB yields induced by compound particles in three types of spherical cells (radius equal to 10, 8, and 6μm) were found to be 13.28, 17.34, 22.15 Gy Gbp-1for boronophenylalanine (BPA), and 1.07, 3.45, 8.32 Gy Gbp-1for sodium borocaptate (BSH). The corresponding DSB-based RBE values were determined to be 1.90, 2.48, 3.16 for BPA and 0.15, 0.49, 1.19 for BSH. The calculated DSB-based RBE showed agreement with experimentally values of compound biological effectiveness for melanoma and gliosarcoma. Besides, the DNA damage yield and DSB-based RBE value exhibited an increasing trend as the cell radius decreased. The impact of the boron concentration ratio on RBE diminished once the drug enrichment surpasses a certain threshold.Significance. This work is potential to provide valuable guidance for accurate biological-weighted dose evaluation in BNCT.

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).

Multi-Functional Boron-Delivery Agents for Boron Neutron Capture Therapy of Cancers

Boron neutron capture therapy (BNCT) is a binary cancer treatment that involves the irradiation of ¹⁰B-containing tumors with low-energy neutrons (thermal or epithermal). The alpha particles and recoiling Li nuclei that are produced in the ¹⁰B-capture nuclear reaction are high-linear-energy transfer particles that destroy boron-loaded tumor cells; therefore, BNCT has the potential to be a localized therapeutic modality. Two boron-delivery agents have been used in clinical trials of BNCT in patients with malignant brain tumors, cutaneous melanoma, or recurrent tumors of the head and neck region, demonstrating the potential of BNCT in the treatment of difficult cancers. A variety of potentially highly effective boron-delivery agents have been synthesized in the past four decades and tested in cells and animal models. These include boron-containing nucleosides, peptides, proteins, polyamines, porphyrins, liposomes, monoclonal antibodies, and nanoparticles of various types. The most promising agents are multi-functional boronated molecules and nanoparticles functionalized with tumor cell-targeting moieties that increase their tumor selectivity and contain a radiolabel or fluorophore to allow quantification of ¹⁰B-biodistribution and treatment planning. This review discusses multi-functional boron agents reported in the last decade, but their full potential can only be ascertained after their evaluation in BNCT clinical trials.

Boron-peptide conjugates with angiopep-2 for boron neutron capture therapy

Boron neutron capture therapy (BNCT) induces intracellular nuclear reaction to destroy cancer cells during thermal neutron irradiation. To selectively eliminate cancer cells but avoid harmful effects on normal tissues, novel boron-peptide conjugates with angiopep-2, namely ANG-B, were constructed and evaluated in preclinical settings. Boron-peptide conjugates were synthesized using solid-phase peptide synthesis, and the molecular mass was validated by mass spectrometry afterwards. Boron concentrations in 6 cancer cell lines and an intracranial glioma mouse model after treatments were analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Phenylalanine (BPA) was tested in parallel for comparison. In vitro treatment with boron delivery peptides significantly increased boron uptake in cancer cells. BNCT with 5 mM ANG-B caused 86.5% ± 5.3% of clonogenic cell death, while BPA at the same concentration caused 73.3% ± 6.0% clonogenic cell death. The in vivo effect of ANG-B in an intracranial glioma mouse model was evaluated by PET/CT imaging at 31 days after BNCT. The mouse glioma tumours in the ANG-B-treated group were shrunk by 62.9% on average, while the BPA-treated tumours shrank by only 23.0%. Therefore, ANG-B is an efficient boron delivery agent, which has low cytotoxicity and high tumour-to-blood ratio. Based on these experimental results, we expected that ANG-B may leverage BNCT performance in clinical applications in future.

Next-Generation Boron Drugs and Rational Translational Studies Driving the Revival of BNCT

BNCT is a high-linear-energy transfer therapy that facilitates tumor-directed radiation delivery while largely sparing adjacent normal tissues through the biological targeting of boron compounds to tumor cells. Tumor-specific accumulation of boron with limited accretion in normal cells is the crux of successful BNCT delivery. Given this, developing novel boronated compounds with high selectivity, ease of delivery, and large boron payloads remains an area of active investigation. Furthermore, there is growing interest in exploring the immunogenic potential of BNCT. In this review, we discuss the basic radiobiological and physical aspects of BNCT, traditional and next-generation boron compounds, as well as translational studies exploring the clinical applicability of BNCT. Additionally, we delve into the immunomodulatory potential of BNCT in the era of novel boron agents and examine innovative avenues for exploiting the immunogenicity of BNCT to improve outcomes in difficult-to-treat malignancies.

Organosilica nanoparticles containing sodium borocaptate (BSH) provide new prospects for boron neutron capture therapy (BNCT): efficient cellular uptake and enhanced BNCT efficacy

Boron neutron capture therapy (BNCT), a method based on the fission of boron-10 upon neutron irradiation, has emerged as an attractive option for radiation therapy. To date, the main drugs used in BNCT are 4-boronophenylalanine (BPA) and sodium borocaptate (BSH). While BPA has been extensively tested in clinical trials, the use of BSH has been limited, mainly due to its poor cellular uptake. Here, we describe a novel type of mesoporous silica-based nanoparticle containing BSH covalently attached to a nanocarrier. Synthesis and characterization of these nanoparticles (BSH-BPMO) are presented. The synthetic strategy involves a click thiol-ene reaction with the boron cluster, providing hydrolytically stable linkage with the BSH in four steps. The BSH-BPMO nanoparticles were efficiently taken up into cancer cells and accumulated in the perinuclear region. Inductively coupled plasma (ICP) measurements of boron uptake in cells highlight the important role of the nanocarrier in the enhancement of boron internalization. BSH-BPMO nanoparticles were also taken up and distributed throughout tumour spheroids. BNCT efficacy was examined by the neutron exposure of the tumour spheroids. BSH-BPMO loaded spheroids were completely destroyed upon neutron irradiation. In contrast, neutron irradiation of tumour spheroids loaded with BSH or BPA resulted in significantly less spheroid shrinkage. The significant difference in BNCT efficacy of the BSH-BPMO was correlated with the improved boron uptake via the nanocarrier. Overall, these results demonstrate the critical role of the nanocarrier in BSH internalization and the enhanced BNCT efficacy of the BSH-BPMO compared with BSH and BPA, two drugs used in BNCT clinical trials.

New Boron Delivery Agents

This proceeding article compiles current research on the development of boron delivery drugs for boron neutron capture therapy that was presented and discussed at the National Cancer Institute (NCI) Workshop on Neutron Capture Therapy that took place on April 20-22, 2022. The most used boron sources are icosahedral boron clusters attached to peptides, proteins (such as albumin), porphyrin derivatives, dendrimers, polymers, and nanoparticles, or encapsulated into liposomes. These boron clusters and/or carriers can be labeled with contrast agents allowing for the use of imaging techniques, such as PET, SPECT, and fluorescence, that enable quantification of tumor-localized boron and their use as theranostic agents.

Development of a 2-(2-Hydroxyphenyl)-1H-benzimidazole-Based Fluorescence Sensor Targeting Boronic Acids for Versatile Application in Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) is an attractive approach to treating cancers. Currently, only one ¹⁰B-labeled boronoagent (Borofalan, BPA) has been approved for clinical BNCT in Japan, and methods for predicting and measuring BNCT efficacy must be established to support the development of next-generation ¹⁰B-boronoagents. Fluorescence sensors targeting boronic acids can achieve this because the amount and localization of ¹⁰B in tumor tissues directly determine BNCT efficacy; however, current sensors are nonoptimal given their slow reaction rate and weak fluorescence (quantum yield < 0.1). Herein, we designed and synthesized a novel small molecular-weight fluorescence sensor, BITQ, targeting boronic acids. In vitro qualitative and quantitative properties of BITQ were assessed using a fluorophotometer and a fluorescence microscope together with BPA quantification in blood samples. BITQ exhibited significant quantitative and selective fluorescence after reacting with BPA (post-to-pre-fluorescence ratio = 5.6; quantum yield = 0.53); the fluorescence plateaued within 1 min after BPA mixing, enabling the visualization of intracellular BPA distribution. Furthermore, BITQ quantified the BPA concentration in mouse blood with reliability comparable with that of current methods. This study identifies BITQ as a versatile fluorescence sensor for analyzing boronic acid agents. BITQ will contribute to ¹⁰B-boronoagent development and promote research in BNCT.

Carborane-Containing Folic Acid bis-Amides: Synthesis and In Vitro Evaluation of Novel Promising Agents for Boron Delivery to Tumour Cells

The design of highly selective low-toxic, low-molecular weight agents for boron delivery to tumour cells is of decisive importance for the development of boron neutron capture therapy (BNCT), a modern efficient combined method for cancer treatment. In this work, we developed a simple method for the preparation of new closo- and nido-carborane-containing folic acid bis-amides containing 18-20 boron atoms per molecule. Folic acid derivatives containing nido-carborane residues were characterised by high water solubility, low cytotoxicity, and demonstrated a good ability to deliver boron to tumour cells in in vitro experiments (up to 7.0 µg B/10⁶ cells in the case of U87 MG human glioblastoma cells). The results obtained demonstrate the high potential of folic acid-nido-carborane conjugates as boron delivery agents to tumour cells for application in BNCT.

Reaction of Chloroacetyl-Modified Peptides with Mercaptoundecahydrododecaborate (BSH) Is Accelerated by Basic Amino Acid Residues in the Peptide

We assessed a reactivity of chloroacetyl-modified tripeptides consisting of various amino acid residues (Cl-3X) and mercaptoundecahydrododecaborate (BSH) by converting Cl-3X to its reactant (BS-3X). We showed that the Cl-3X consisting of basic amino acid residues (e.g., Arg) reacted with BSH effectively and its conversion decreased as the number of Arg residues in the Cl-3X decreased. Furthermore, a reactivity of the peptides with introduction of an alkyl linker between the triarginine and the chloroacetyl group (Cl-Cn-3R) with BSH decreased with increasing alkyl linker length. These results indicate that an electrostatic attraction of positively charged amino acid residues in the tripeptides and negatively charged BSH causes BSH to gather in a vicinity of the chloroacetyl group, resulting in an accelerated reaction. This work should aid a development of new boron agents using BSH in boron neutron capture therapy.

Tailored hyaluronic acid-based nanogels as theranostic boron delivery systems for boron neutron cancer therapy

Boron-rich nanocarriers possess great potential for advanced boron neutron capture therapy (BNCT) as an effective radiation treatment for invasive malignant tumors. If additionally, they can be imaged in a non-invasive and real-time manner allowing the assessment of local boron concentration, they could serve for dose calculation and image-guided BNCT to enhance tumor treatment efficacy. To meet this challenge, this study describes the design of a theranostic nanogel, enriched in ¹⁰B and fluorescent dye, to achieve selective imaging, and sufficient accumulation of boron at the tumor site. The boron-rich and fluorescent nanogels can be easily obtained via temperature triggered-assembly of hyaluronic acid (HA) modified with a thermoresponsive terpolymer. The latter was specifically designed to enable the efficient encapsulation of the fluorescent dye – an aza‑boron-dipyrromethene (aza-BODIPY) – linked to ¹⁰B-enriched sodium borocaptate (BSH), in addition to induce nanogel formation below room temperature, and to enable their core-crosslinking by hydrazone bond formation. The HA nanogel considerably concentrates aza-BODIPY-BSH into the hydrophobic nanodomains made of the terpolymer chains. Here, we present the detailed synthesis of the HA-terpolymer conjugate, nanogel formation, and characterization in terms of size, morphology, and stability upon storage, as well as the biological behavior of the boron nanocarrier using real-time fluorescence imaging in cells and in vivo. This work suggested the potential of the theranostic HA nanogel as a boron delivery system for the implementation of BNCT in brain cancer and sarcoma.

Multimodal Applications of Zinc Gallate-Based Persistent Luminescent Nanoparticles in Cancer Treatment: Tumor Margining, Diagnosis, and Boron Neutron Capture Therapy

On the basis of the boron neutron capture therapy (BNCT) modality, we have designed and synthesized a zinc gallate (ZnGa₂O₄)-based nanoformulation for developing an innovative theranostic approach for cancer treatment. Initially, the (ZnGa_1.995Cr_0.005O₄ or ZnGa₂O₄:(0.5%)Cr persistent luminescence nanoparticles (PLNPs) embedded on silica matrix were synthesized. Their surface functionalization was performed using organic synthesis strategies to attach the amine functional moieties which were further coupled with poly(vicinal diol). These diols were helpful for conjugation with ¹⁰B(OH)₃, which subsequently served to couple with an in-house-synthesized variant of pH-(low)-insertion peptide (pHLIP) finally giving a tumor-targeting nanoformulation. Most importantly, the polymeric diols helped in conjugation of a substantial number of ¹⁰B to provide the therapeutic dose required for effective BNCT. This nanoformulation internalized substantially (∼80%) to WEHI-164 cancer cells within 6 h. Tumor homing studies indicated that the accumulation of this formulation at the acidic tumor site was within 2 h. The in vitro evaluation of the formulation against WEHI-164 cancer cells followed by neutron irradiation revealed its potent cytotoxicity with IC₅₀ ∼ 25 μM. In the case of studies on animal models, the melanoma-induced C57BL/6 and fibrosarcoma-induced BALB/c mice were treated with formulations through intratumoral and intravenous injections, respectively, followed by neutron irradiation, leading to a significant killing of the cancer cells, which was evidenced by a reduction in tumor volume (75-80%) as compared with a control tumor. Furthermore, the histopathological studies confirmed a damaging effect only on tumor cells, while there was no sign of damage to the vital organs in treated mice as well as in controls.

Radiotherapy for glioblastoma: clinical issues and nanotechnology strategies

Glioblastoma multiforme (GBM) is the most common primary brain cancer in adults with poor prognosis. Despite the current state of knowledge on its genetic characteristics, relatively little progress has been made in improving the treatment of patients with this fatal disease. Radiotherapy (RT) has been identified as a crucial treatment for GBM following surgical resection to improve both local control and survival. Unfortunately, radiotherapy resistance is frequently observed in GBM patients, which is the major reason for the high mortality rate of cancer patients. Radioresistance of GBM is often multifactorial and heterogeneous, and associated with the recurrence of GBM after surgery. Nanotechnology has gained increasing attention and has already been investigated for optimization of radiosensitization due to the unique properties of nanobiomaterials, such as photoelectric decay characteristics or potential as carriers for drug delivery to the central nervous system. A large body of preclinical data has accumulated over the past several years, in which nanotechnology-based strategies exhibit promising potential to enhance the radiosensitivity of GBM, both in cellular and animal models. In this review, we summarize the mechanisms of GBM radioresistance, including tumor cell-intrinsic factors as well as tumor microenvironment (TME). We further discuss current nano-biotechnology-based radiosensitizer in the treatment of GBM, summarize the latest findings, highlight challenges, and put forward prospects for the future of nano-radiosensitizers. These data suggest that nanotechnology has the potential to address many of the clinical challenges and nanobiomaterials would become promising next-generation radiotherapy sensitizers for GBM treatment.

Improving Membrane Activity and Cargo Delivery Efficacy of a Cell-Penetrating Peptide by Loading with Carboranes

Cell-penetrating peptides (CPPs) have emerged as versatile tools to increase the intracellular accumulation of different kinds of cargoes. For an efficient cellular uptake and drug delivery, their organization into a distinct and stable secondary structure at the outer surface of the plasma membrane is a hallmark and supports optimal lipid-peptide interactions. Incorporation of hydrophobic moieties, such as carboranes (CBs), has the potential to increase the lipophilicity of peptides, and thus, to facilitate the formation of secondary structures. Herein, we present synthesis and biophysical as well as biological characterization of carborane-CPP conjugates having incorporated one or more CB clusters. Our results highlight the possibility to modulate the secondary structure of CPPs by the addition of CB's leading to constructs with altered membrane activity and promising use in terms of nucleic acid delivery.

Combined BNCT and PET for theranostics

This short review summarizes the issue of boron distribution monitoring in boron neutron capture therapy (BNCT), which remains a serious drawback of this powerful oncological treatment. Here we present the monitoring methods that are presently used with particular emphasis on the positron emission tomography (PET) which has the highest potential to be used for the real-time monitoring of boron biodistribution. We discuss the possibility of using present PET scanners to determine the boron uptake in vivo before the BNCT treatment with the use of p-boronphenylalanine (BPA) labeled with 18F isotope. Several examples of preclinical studies and clinical trials performed with the use of [18F]FBPA are shown. We also discuss shortly the perspectives of using other radiotracers and boron carriers which may significantly improve the boron imaging with the use of the state-of-the-art Total-Body PET scanners providing a theranostic approach in the BNCT.

Molecular Mechanisms of Drug Resistance in Glioblastoma

Glioblastoma multiforme (GBM) is the most common and fatal primary brain tumor, is highly resistant to conventional radiation and chemotherapy, and is not amenable to effective surgical resection. The present review summarizes recent advances in our understanding of the molecular mechanisms of therapeutic resistance of GBM to already known drugs, the molecular characteristics of glioblastoma cells, and the barriers in the brain that underlie drug resistance. We also discuss the progress that has been made in the development of new targeted drugs for glioblastoma, as well as advances in drug delivery across the blood-brain barrier (BBB) and blood-brain tumor barrier (BBTB).

Hyaluronic acid-decorated carborane-TAT conjugation nanomicelles: A potential boron agent with enhanced selectivity of tumor cellular uptake

Boron neutron capture therapy (BNCT) has received widespread attention as a new type of radiation therapy. The main problem encountered in BNCT is insufficient tumor cellular uptake of boron agents. In this study, cell-penetrating peptide TAT-conjugated o-carborane was synthesized. The conjugation can self-assemble to form positively charged carborane-TAT micelles, and then adsorb negatively charged hyaluronic acid (HA) to give core-shell structured carborane-TAT@HA micelles. Carborane-TAT@HA micelles exhibits a large amount of boron uptake at the tumor tissue through the enhanced permeability and retention (EPR) effect and the ability of HA to bind to CD44 receptors. Carborane-TAT@HA was wrapped by the HA shell during systemic circulation to avoid non-specific uptake of TAT with normal cells, while tumor microenvironment-responsive shedding of HA shell could expose Carborane-TAT to penetrate the cell membrane into tumor cells. Experiments have proved the enhanced selectivity of tumor cellular uptake of the boron drug, displayed excellent drug delivery potential, and can meet the basic requirements of BNCT.

Theranostics in Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) has the potential to specifically destroy tumor cells without damaging the tissues infiltrated by the tumor. BNCT is a binary treatment method based on the combination of two agents that have no effect when applied individually: ¹⁰B and thermal neutrons. Exclusively, the combination of both produces an effect, whose extent depends on the amount of ¹⁰B in the tumor but also on the organs at risk. It is not yet possible to determine the ¹⁰B concentration in a specific tissue using non-invasive methods. At present, it is only possible to measure the ¹⁰B concentration in blood and to estimate the boron concentration in tissues based on the assumption that there is a fixed uptake of ¹⁰B from the blood into tissues. On this imprecise assumption, BNCT can hardly be developed further. A therapeutic approach, combining the boron carrier for therapeutic purposes with an imaging tool, might allow us to determine the ¹⁰B concentration in a specific tissue using a non-invasive method. This review provides an overview of the current clinical protocols and preclinical experiments and results on how innovative drug development for boron delivery systems can also incorporate concurrent imaging. The last section focuses on the importance of proteomics for further optimization of BNCT, a highly precise and personalized therapeutic approach.

Modular Synthetic Approach to Carboranyl‒Biomolecules Conjugates

The development of novel, tumor-selective and boron-rich compounds as potential agents for use in boron neutron capture therapy (BNCT) represents a very important field in cancer treatment by radiation therapy. Here, we report the design and synthesis of two promising compounds that combine meta-carborane, a water-soluble monosaccharide and a linking unit, namely glycine or ethylenediamine, for facile coupling with various tumor-selective biomolecules bearing a free amino or carboxylic acid group. In this work, coupling experiments with two selected biomolecules, a coumarin derivative and folic acid, were included. The task of every component in this approach was carefully chosen: the carborane moiety supplies ten boron atoms, which is a tenfold increase in boron content compared to the l-boronophenylalanine (l-BPA) presently used in BNCT; the sugar moiety compensates for the hydrophobic character of the carborane; the linking unit, depending on the chosen biomolecule, acts as the connection between the tumor-selective component and the boron-rich moiety; and the respective tumor-selective biomolecule provides the necessary selectivity. This approach makes it possible to develop a modular and feasible strategy for the synthesis of readily obtainable boron-rich agents with optimized properties for potential applications in BNCT.

Peptides-based therapy and diagnosis. Strategies for non-invasive therapies in cancer

In recent years, remarkable progress was registered in the field of cancer research. Though, cancer still represents a major cause of death and cancer metastasis a problem seeking for urgent solutions as it is the main reason for therapeutic failure. Unfortunately, the most common chemotherapeutic agents are non-selective and can damage healthy tissues and cause side effects that affect dramatically the quality of life of the patients. Targeted therapy with molecules that act specifically at the tumour sites interacting with overexpressed cancer receptors is a very promising strategy for achieving the specific delivery of anticancer drugs, radioisotopes or imaging agents. This review aims to give an overview on different strategies for targeting cancer cell receptors localised either at the extracellular matrix or at the cell membrane. Molecules like antibodies, aptamers and peptides targeting the cell surface are presented with advantages and disadvantages, with emphasis on peptides. The most representative peptides are described, including cell penetrating peptides, homing and anticancer peptides with particular consideration on recent discoveries.

Nanocząstki o wysokiej zawartości boru jako potencjalne nośniki w terapii borowo-neutronowej

Podstawą terapii borowo-neutronowej (boron neutron capture therapy, BNCT) jest selektywne dostarczenie boru do komórek nowotworowych, a następnie napromienienie zmienionego chorobowo miejsca wiązką neutronów. W wyniku tego procesu dochodzi do rozszczepienia jądra izotopu 10B, co powoduje uwolnienie energii niszczącej komórki nowotworowe. Mimo że badania związane z BNCT trwają od lat 50. XX wieku, pozostaje ona wciąż terapią eksperymentalną. Jest to związane m.in. z brakiem nośników umożliwiających szybkie i skuteczne wprowadzanie 10B do środowiska nowotworu. Tak więc często podnoszonym zagadnieniem i jednym z głównych wyzwań dla rozwoju BNCT, jest poszukiwanie selektywnych związków dostarczających wymaganą ilość tego pierwiastka. Istotnym aspektem są badania nad nanometrycznymi strukturami, takimi jak liposomy zawierające związki bogate w bor lub nieorganiczne nanocząstki – węglik boru czy azotek boru. Ze względu na dużą zawartość boru oraz możliwość modyfikacji powierzchni tych nanocząstek, mogą się one okazać wyjątkowo atrakcyjnym narzędziem w celowanej BNCT. Równie ważnym problemem tej terapii jest opracowanie precyzyjnych powiązań między źródłem neutronów, specyfiką wiązki a rodzajem zastosowanego nośnika. W artykule wskazujemy na wysoki potencjał związków bogatych w bor jako nośników w celowanej terapii borowo-neutronowej.

Improvement of Water Solubility of Mercaptoundecahydrododecaborate (BSH)-Peptides by Conjugating with Ethylene Glycol Linker and Interaction with Cyclodextrin

We previously developed a conjugate consisting of 10B cluster BSH and tri-arginine peptide (BSH-3R). This could potentially be used as a boron agent for boron neutron capture therapy; however, it possesses poor water solubility and thus needs to be improved for use as medicine. In this study, we devised several means of improving the water solubility of BSH-3R. As one of them, we used cyclodextrin (CD), which was expected to improve the water solubility resulting from interaction of the BSH-3R with CD. We evaluated the solubility of BSH-3R in aqueous CD solution by using reverse-phase high-performance liquid chromatography. As we expected, the solubility of BSH-3R was increased in a manner dependent on the addition of β-CD and γ-CD in aqueous solution. Furthermore, we synthesized BSH conjugated to oligoarginine having various chain lengths (BSH-nR) and BSH-3R with ethylene glycol linkers introduced between BSH and 3R (BSH-nEg-3R). The water solubility of these BSH peptides was also evaluated and the results showed that the introduction of nEg to BSH-3R markedly improved the water solubility. Furthermore, we found that the water solubility of these peptides can be further improved by also applying CD.

A periodic development of BPA and BSH based derivatives in boron neutron capture therapy (BNCT)

A schematic representation of various judicious approaches for the synthesis of BPA and BSH modified compounds for effective BNCT.

The Therapeutic Effects of Dodecaborate Containing Boronophenylalanine for Boron Neutron Capture Therapy in a Rat Brain Tumor Model

Simple Summary

We have developed a new boron compound for application in boron neutron capture therapy (BNCT) named boronophenylalanine–amide alkyl dodecaborate (BADB). It is characterized by a larger amount of ¹⁰B per molecule, linking boronphenylalanine (BPA) and dodecaborate, and we conducted various experiments on its efficacy. Its high accumulation at the cellular level made it a promising novel drug, but it did not sufficiently accumulate in brain tumor tissue when intravenously administered. However, in neutron irradiation experiments, the drug showed remarkably high compound biological effectiveness and significantly prolonged the survival time in rat brain tumor models. We confirmed the antitumor efficacy of BADB in BNCT and its additional efficacy when administered in combination with BPA. Though this drug showed poor results when administered as a single agent, it was superior to BPA alone when administered in combination with BPA, making it a drug that we have been waiting for in our clinical practice.

Abstract

Background: The development of effective boron compounds is a major area of research in the study of boron neutron capture therapy (BNCT). We created a novel boron compound, boronophenylalanine–amide alkyl dodecaborate (BADB), for application in BNCT and focused on elucidating how it affected a rat brain tumor model. Methods: The boron concentration of F98 rat glioma cells following exposure to boronophenylalanine (BPA) (which is currently being utilized clinically) and BADB was evaluated, and the biodistributions in F98 glioma-bearing rats were assessed. In neutron irradiation studies, the in vitro cytotoxicity of each boron compound and the in vivo corresponding therapeutic effect were evaluated in terms of survival time. Results: The survival fractions of the groups irradiated with BPA and BADB were not significantly different. BADB administered for 6 h after the termination of convection-enhanced delivery ensured the highest boron concentration in the tumor (45.8 μg B/g). The median survival time in the BADB in combination with BPA group showed a more significant prolongation of survival than that of the BPA group. Conclusion: BADB is a novel boron compound for BNCT that triggers a prolonged survival effect in patients receiving BNCT.

Optimization of preparation methods for high loading content and high encapsulation efficiency of BSH into liposomes

To optimize the preparation methods for liposomes encapsulating mercaptoundecahydrododecaborate (BSH), we examined BSH and lipid concentrations that increased the boron content in liposomes. We improved the BSH encapsulation efficiency and boron content of the liposomes from 4.2 to 45.9 % and 9.5-54.3 μg, respectively, by changing the lipid concentration from 10 to 150 mg/mL. Notably, the boron content increased significantly from 26.2 μg to 326.3 μg at a constant lipid concentration of 30 mg/mL with increased BSH concentrations.

In Vitro Studies to Define the Cell-Surface and Intracellular Targets of Polyarginine-Conjugated Sodium Borocaptate as a Potential Delivery Agent for Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) requires pharmaceutical innovations and molecular-based evidence of effectiveness to become a standard cancer therapeutic in the future. Recently, in Japan, 4-borono-L-phenylalanine (BPA) was approved as a boron agent for BNCT against head and neck (H&N) cancers. H&N cancer appears to be a suitable target for BPA-BNCT, because the expression levels of L-type amino acid transporter 1 (LAT1), one of the amino acid transporters responsible for BPA uptake, are elevated in most cases of H&N cancer. However, in other types of cancer including malignant brain tumors, LAT1 is not always highly expressed. To expand the possibility of BNCT for these cases, we previously developed poly-arginine peptide (polyR)-conjugated mercaptoundecahydrododecaborate (BSH). PolyR confers the cell membrane permeability and tumor selectivity of BSH. However, the molecular determinants for the properties are not fully understood. In this present study, we have identified the cluster of differentiation 44 (CD44) protein and translational machinery proteins as a major cell surface target and intracellular targets of BSH-polyR, respectively. CD44, also known as a stem cell-associated maker in various types of cancer, is required for the cellular uptake of polyR-conjugated molecules. We showed that BSH-polyR was predominantly delivered to a CD44^High cell population of cancer cells. Once delivered, BSH-polyR interacted with the translational machinery components, including the initiation factors, termination factors, and poly(A)-biding protein (PABP). As a proof of principle, we performed BSH-polyR-based BNCT against glioma stem-like cells and revealed that BSH-polyR successfully induced BNCT-dependent cell death specifically in CD44^High cells. Bioinformatics analysis indicated that BSH-polyR would be suitable for certain types of malignant tumors. Our results shed light on the biochemical properties of BSH-polyR, which may further contribute to the therapeutic optimization of BSH-BNCT in the future.

Peptide-Drug Conjugates and Their Targets in Advanced Cancer Therapies

Cancer became recently the leading cause of death in industrialized countries. Even though standard treatments achieve significant effects in growth inhibition and tumor elimination, they cause severe side effects as most of the applied drugs exhibit only minor selectivity for the malignant tissue. Hence, specific addressing of tumor cells without affecting healthy tissue is currently a major desire in cancer therapy. Cell surface receptors, which bind peptides are frequently overexpressed on cancer cells and can therefore be considered as promising targets for selective tumor therapy. In this review, the benefits of peptides as tumor homing agents are presented and an overview of the most commonly addressed peptide receptors is given. A special focus was set on the bombesin receptor family and the neuropeptide Y receptor family. In the second part, the specific requirements of peptide-drug conjugates (PDC) and intelligent linker structures as an essential component of PDC are outlined. Furthermore, different drug cargos are presented including classical and recent toxic agents as well as radionuclides for diagnostic and therapeutic approaches. In the last part, boron neutron capture therapy as advanced targeted cancer therapy is introduced and past and recent developments are reviewed.

Electrosprayed chitosan/alginate/polyvinyl alcohol nanoparticles as boric acid carriers for 10Boron neutron capture therapy

Aim: To improve the killing efficacy of head and neck squamous cells (SAS) by boric acid-mediated boron neutron capture therapy (BNCT). Materials & methods: Boric acid-containing chitosan/alginate/polyvinyl alcohol nanoparticles (B-capNPs) were manufactured using the nano-electrospray process. Results: Less than 10% of the boric acid leaked from the B-capNPs over 2 days. The B-capNPs killed up to 2.8-fold more SAS cells and reduced cytotoxicity tenfold when compared with pure boric acid alone. B-capNPs show selective uptake in tumor cells with tumor/normal ratios of SAS to normal (NIH 3T3) and macrophage (RAW 264.7) cells of 4.0 and 3.5, respectively, which are greater than the minimum acceptable tumor/normal ratio for BNCT of 2.5. Conclusion: These findings illustrate that B-capNPs may be more superior as BNCT drugs than pure boric acid.

TargetCPP: accurate prediction of cell-penetrating peptides from optimized multi-scale features using gradient boost decision tree

Cell-penetrating peptides (CPPs) are short length permeable proteins have emerged as drugs delivery tool of therapeutic agents including genetic materials and macromolecules into cells. Recently, CPP has become a hotspot avenue for life science research and paved a new way of disease treatment without harmful impact on cell viability due to nontoxic characteristic. Therefore, the correct identification of CPPs will provide hints for medical applications. Considering the shortcomings of traditional experimental CPPs identification, it is urgently needed to design intelligent predictor for accurate identification of CPPs for the large scale uncharacterized sequences. We develop a novel computational method, called TargetCPP, to discriminate CPPs from Non-CPPs with improved accuracy. In TargetCPP, first the peptide sequences are formulated with four distinct encoding methods i.e., composite protein sequence representation, composition transition and distribution, split amino acid composition, and information theory features. These dominant feature vectors were fused and applied intelligent minimum redundancy and maximum relevancy feature selection method to choose an optimal subset of features. Finally, the predictive model is learned through different classification algorithms on the optimized features. Among these classifiers, gradient boost decision tree algorithm achieved excellent performance throughout the experiments. Notably, the TargetCPP tool attained high prediction Accuracy of 93.54% and 88.28% using jackknife and independent test, respectively. Empirical outcomes prove the superiority and potency of proposed bioinformatics method over state-of-the-art methods. It is highly anticipated that the outcomes of this study will provide a strong background for large scale prediction of CPPs and instructive guidance in clinical therapy and medical applications.

A Selective Carborane-Functionalized Gastrin-Releasing Peptide Receptor Agonist as Boron Delivery Agent for Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) allows the selective elimination of malignant tumor cells without affecting healthy tissue. Although this binary radiotherapy approach has been known for decades, BNCT failed to reach the daily clinics to date. One of the reasons is the lack of selective boron delivery agents. Using boron loaded peptide conjugates, which address G protein-coupled receptors overexpressed on tumor cells allow the intracellular accumulation of boron. The gastrin-releasing peptide receptor (GRPR) is a well-known target in cancer diagnosis and can potentially be used for BNCT. Here, we present the successful introduction of multiple bis-deoxygalactosyl-carborane building blocks to the GRPR-selective ligand [d-Phe⁶, β-Ala¹¹, Ala¹³, Nle¹⁴]Bn(6-14) (sBB2L) generating peptide conjugates with up to 80 boron atoms per molecule. Receptor activation was retained, metabolic stability was increased, and uptake into PC3 cells was proven without showing any intrinsic cytotoxicity. Furthermore, undesired uptake into liver cells was suppressed by using l-deoxygalactosyl modified carborane building blocks. Due to its high boron loading and excellent GRPR selectivity, this conjugate can be considered as a promising boron delivery agent for BNCT.

Tuning a modular system - synthesis and characterisation of a boron-rich s-triazine-based carboxylic acid and amine bearing a galactopyranosyl moiety

Introduction of a bis(isopropylidene)-protected galactopyranosyl moiety in s-triazine-based boron-rich carboxylic acids and amines results in soluble and suitable coupling partners for tumour-selective biomolecules with applications as selective agents for boron neutron capture therapy (BNCT). Bearing either a carboxylic acid or primary amine as a functional group, these compounds are highly versatile and thus largely extend the possible coupling strategies with suitable biomolecules. Modification of the gastrin-releasing peptide receptor (GRPR) selective agonist [d-Phe⁶, β-Ala¹¹, Ala¹³, Nle¹⁴]Bn(6-14) with the carboxylic acid derivative yielded a bioconjugate with an optimal receptor activation and internalisation profile. This demonstrates the great potential of this approach for the development of novel boron delivery agents.

Application of Nitroimidazole-Carbobane-Modified Phenylalanine Derivatives as Dual-Target Boron Carriers in Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) has received extensive attention as noninvasive cell-level oncotherapy for treating solid cancer tumors. However, boron-containing drugs such as l-boronophenylalanine (BPA) and sodium borocaptate have low boron content and/or poor tumor-targeting ability, limiting their application. In this study, we designed and synthesized a series of nontoxic, dual-target boron carriers (B139, B142, and B151) with the ability to accumulate specifically in tumor cells. We found that the B139 uptake into hypoxic tumor regions was high, with a 70-fold boron content compared to BPA. In addition, in vivo observation showed that B139 can be trapped in tumor cells for a prolonged period and maintains an effective therapeutic concentration, with a peak boron concentration of 50.7 μg/g and a high tumor: blood boron ratio of >3, achieving ideal BNCT conditions. Cytotoxicity evaluation in mice further proved that B139 is safe and reliable. Therefore, B139 has great potential for BNCT application as a dual-target, safe, and efficient boron carrier.

Selective Neuropeptide Y Conjugates with Maximized Carborane Loading as Promising Boron Delivery Agents for Boron Neutron Capture Therapy

G-protein-coupled receptors like the human Y₁ receptor (hY₁R) are promising targets in cancer therapy due to their high overexpression on cancer cells and their ability to internalize together with the bound ligand. This mechanism was exploited to shuttle boron atoms into cancer cells for the application of boron neutron capture therapy (BNCT), a noninvasive approach to eliminate cancer cells. A maximized number of carboranes was introduced to the hY₁R-preferring ligand [F⁷,P³⁴]-NPY by solid phase peptide synthesis. Branched conjugates loaded with up to 80 boron atoms per peptide molecule exhibited a maintained receptor activation profile, and the selective uptake into hY₁R-expressing cells was demonstrated by internalization studies. In order to ensure appropriate solubility in aqueous solution, we proved the need for eight hydroxyl groups per carborane. Thus, we suggest the utilization of bis-deoxygalactosyl-carborane building blocks in solid phase peptide synthesis to produce selective boron delivery agents for BNCT.

Remarkable Boron Delivery Of iRGD-Modified Polymeric Nanoparticles For Boron Neutron Capture Therapy

Purpose

Boron neutron capture therapy (BNCT) is an emerging binary radiotherapy, which is limited for application due to the challenge of targeted delivery into tumor nowadays. Here, we propose the use of iRGD-modified polymeric nanoparticles for active targeted delivery of boron and doxorubicin (DOX) in BNCT.

Methods

¹⁰B-enriched BSH was covalently grafted to PEG-PCCL to prepare ¹⁰B-polymer, then surface-modified with iRGD. And, DOX was physically incorporated into polymers afterwards. Characterization of prepared polymers and in vitro release profile of DOX from polymers were determined by several methods. Cellular uptake of DOX was observed by confocal microscope. Accumulation of boron in cells and tissues was analyzed by ICP-MS. Biodistribution of DOX was studied by ex vivo fluorescence imaging and quantitative measurement. Tumor vascular normalization of Endostar for promoting delivery efficiency of boron on refractory B16F10 tumor was also studied.

Results

The polymers were monodisperse and spheroidal in water with an average diameter of 24.97 nm, which were relatively stable at physiological pH and showed a sustained release of DOX, especially at endolysosomal pH. Enhanced cellular delivery of DOX was found in iRGD-modified polymer group. Cellular boron uptake of iRGD-modified polymers in A549 cells was remarkably raised fivefold (209.83 ng ¹⁰B/10⁶ cells) compared with BSH. The polymers represented prolonged blood circulation, enhanced tumor accumulation of ¹⁰B against BSH, and favorable tumor:normal tissue boron concentration ratios (tumor:blood = 14.11, tumor:muscle = 19.49) in A549 tumor-bearing mice 24 hrs after injection. Both fluorescence imaging and quantitative measurement showed the highest tumor accumulation of DOX at 24 hrs after injecting of iRGD-modified polymers. Improvement of vascular integrity and reduction of vascular mimicries were found after Endostar injection, and raised tumor accumulation of boron as well.

Conclusion

The developed nanoparticle is an inspiring candidate for the safe clinical application for BNCT.

Enlargement of a Modular System-Synthesis and Characterization of an s-Triazine-Based Carboxylic Acid Ester Bearing a Galactopyranosyl Moiety and an Enormous Boron Load

The amount of boron accumulated in tumor tissue plays an important role regarding the success of the boron neutron capture therapy (BNCT). In this article, we report a modular system, combining readily available starting materials, like glycine, 1,3,5-triazine and the well-known 9-mercapto-1,7-dicarba-closo-dodecaborane(12), as well as α-d-galactopyranose for increased hydrophilicity, with a novel boron-rich tris-meta-carboranyl thiol.