Poly(vinyl alcohol) boosting therapeutic potential of p-boronophenylalanine in neutron capture therapy by modulating metabolism

A Critical Review of Radiation Therapy: From Particle Beam Therapy (Proton, Carbon, and BNCT) to Beyond

In this paper, we discuss the role of particle therapy—a novel radiation therapy (RT) that has shown rapid progress and widespread use in recent years—in multidisciplinary treatment. Three types of particle therapies are currently used for cancer treatment: proton beam therapy (PBT), carbon-ion beam therapy (CIBT), and boron neutron capture therapy (BNCT). PBT and CIBT have been reported to have excellent therapeutic results owing to the physical characteristics of their Bragg peaks. Variable drug therapies, such as chemotherapy, hormone therapy, and immunotherapy, are combined in various treatment strategies, and treatment effects have been improved. BNCT has a high dose concentration for cancer in terms of nuclear reactions with boron. BNCT is a next-generation RT that can achieve cancer cell-selective therapeutic effects, and its effectiveness strongly depends on the selective ¹⁰B accumulation in cancer cells by concomitant boron preparation. Therefore, drug delivery research, including nanoparticles, is highly desirable. In this review, we introduce both clinical and basic aspects of particle beam therapy from the perspective of multidisciplinary treatment, which is expected to expand further in the future.

Enzyme-instructed supramolecular assemblies promote intracellular boron accumulation for boron neutron capture therapy

Selective accumulation of boron agents in cancer cells is of critical importance for BNCT. Here we involve enzyme-instructed supramolecular assembly (EISA) to facilitate the accumulation of a typical boron agent borylphenylalanine (BPA) in cancer cells. By covalently conjugating BPA to the phosphorylated assembly precursor, the boron-bearing precursors undergo phosphatase-catalyzed dephosphorylation to yield assembly molecules, which then self-assemble to form nanomaterials. Due to the up-regulated phosphatase activity of cancer cells, kinetic preference allows the EISA to accumulate boron in HeLa cells selectively. Interestingly, by attaching BPA on the backbone or side-chain of precursor, the boron-bearing isomers show different assembly propensity with time-dependent morphology change, which leads to the differentiated accumulation of boron inside cells. Overall, the optimized boron-bearing assembly precursor could significantly improve the boron accumulation compared with BPA in cancer cells. In this study, we have demonstrated a convenient method to introduce boron agents to cancer cells. We envision that the EISA-mediated accumulation of boron will be helpful in the design of boron agents to facilitate BNCT treatment.

Fabrication of Cationic Poly(vinyl alcohol) Films Cross-Linked Using Copolymers Containing Quaternary Ammonium Cations, Benzoxaborole, and Carboxy Groups

Water-insoluble cationic poly(vinyl alcohol) (PVA) films were fabricated using a mixed aqueous solution of PVA and poly([2-(methacryloyloxy)ethyl]trimethylammonium chloride (METAC)-co-methacrylic acid (MAAc)-co-5-methacrylamido-1,2-benzoxaborole (MAAmBO)) copolymer (3D). The surface of the PVA film is typically negatively charged, and simple fabrication methods for water-insoluble PVA films with cationic surface charges are required to expand their application fields. METAC, which has a permanent positive charge owing to the presence of a quaternary ammonium cation, was selected as the cationic unit. The MAAc and MAAmBO units were used as two types of cross-linking structures for the thermal cross-linking of the hydroxy and carboxy groups of the MAAc unit (covalent bonding) as well as the diol and benzoxaborole groups of the MAAmBO unit (dynamic covalent bonding). The films were thermally cross-linked at 135 °C for 4 h without the addition of materials. After immersion in surplus water at 80 °C for 3 h, the cross-linked PVA/3D films retained almost 100% of their weights. The ζ-potential of the water-insoluble PVA/3D film was 9.4 ± 0.8 mV. The PVA/3D film was strongly dyed using anionic acid red 1 (AR1) because of its positively charged surface. Interestingly, it could also be slightly dyed using cationic methylene blue (MB) and became transparent (original state) after immersion in water for 2 days. These results suggested that positive and negative charges coexisted in the PVA/3D film, and the surface properties were positively inclined. Moreover, the degree of hemolysis of the PVA/3D films was similar to that of the negative control, which showed high blood compatibility. To our knowledge, this is the first report on the fabrication of water-insoluble cationic PVA films using two types of cross-linking structures containing carboxy and benzoxaborole groups. The cross-linked PVA films were analyzed using Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), and contact angle (CA) and ζ-potential measurement, as well as by determining the mechanical properties, adsorption of charged molecules, and biocompatibility. These readily fabricated water-insoluble PVA films with positive charges can show potential applications in sensors, adsorption systems, and antimicrobial materials.

[Drug Discovery Targeting an Amino Acid Transporter for Diagnosis and Therapy]

Nutrients are essential for all living organisms. Because growing cancer cells have strong metabolic demands, nutrient transporters are constitutively increased to facilitate the nutrient uptake. Among these nutrient transporters, L-type amino acid transporter 1 (LAT1), which transports large neutral amino acids including essential amino acids, is critical for cancer growth. Therefore, LAT1 has been considered as an attractive target for diagnosis and therapy of cancers. We have developed several lines of compounds for cancer diagnosis and therapy. To diagnose cancer by using positron emission tomography (PET) probes, we have created amino acid derivatives which are selectively transported by LAT1 and accumulated in cancer cells. In addition to amino acid derivatives as the LAT1 inhibitors, we also have made non-amino acid small compounds as anti-cancer drugs which inhibit LAT1 function and suppress tumor growth. The LAT1 targeting anti-cancer drug showed low toxicity but strong effects on various types of cancer cells in animal models. The novel PET probe is approved for clinical research and the new anti-cancer drug has been under clinical trial. Small compounds targeting the amino acid transporter bring us new tools for cancer diagnosis and therapy.

Composites of Nucleic Acids and Boron Clusters (C2B10H12) as Functional Nanoparticles for Downregulation of EGFR Oncogene in Cancer Cells

Epidermal growth factor receptor (EGFR) is one of the most promising molecular targets for anticancer therapy. We used boron clusters as a platform for generation of new materials. For this, functional DNA constructs conjugated with boron clusters (B-ASOs) were developed. These B-ASOs, built from 1,2-dicarba-closo-dodecaborane linked with two anti-EGFR antisense oligonucleotides (ASOs), form with their complementary congeners torus-like nanostructures, as previously shown by atomic force microscope (AFM) and transmission electron cryo-microscopy (cryo-TEM) imaging. In the present work, deepened studies were carried out on B-ASO's properties. In solution, B-ASOs formed four dominant complexes as confirmed by non-denaturing polyacrylamide gel electrophoresis (PAGE). These complexes exhibited increased stability in cell lysate comparing to the non-modified ASO. Fluorescently labeled B-ASOs localized mostly in the cytoplasm and decreased EGFR expression by activating RNase H. Moreover, the B-ASO complexes altered the cancer cell phenotype, decreased cell migration rate, and arrested the cells in the S phase of cell cycle. The 1,2-dicarba-closo-dodecaborane-containing nanostructures did not activate NLRP3 inflammasome in human macrophages. In addition, as shown by inductively coupled plasma mass spectrometry (ICP MS), these nanostructures effectively penetrated the human squamous carcinoma cells (A431), showing their potential applicability as anticancer agents.

Fructose-functionalized polymers to enhance therapeutic potential of p-boronophenylalanine for neutron capture therapy

In boron neutron capture therapy (BNCT), boron drugs should accumulate selectively within a tumor and be quickly cleared from blood and normal organs. However, it is usually challenging to achieve the efficient tumor accumulation and the quick clearance simultaneously. Here we report the complex composed of a fructose-modified poly(ethylene glycol)-poly(l-lysine) block copolymer and p-boronophenylalanine, termed PEG-P[Lys/Lys(fructose)]-BPA, as a boron delivery system permitting selective accumulation within the target tumor with quick clearance from normal organs as well as blood. Our PEG-P[Lys/Lys(fructose)]-BPA could be internalized into tumor cells through LAT1 amino acid transporter-mediated endocytosis and retain in the targeted cells, thereby accomplishing more efficient accumulation and retention in a subcutaneous tumor than clinically used fructose-BPA complexes. Importantly, the moderately cationic property of the polymer facilitated renal clearance and PEG-P[Lys/Lys(fructose)]-BPA exhibited high accumulation contrast between the target tumor and the blood/normal organ. Finally, upon thermal neutron irradiation, PEG-P[Lys/Lys(fructose)]-BPA significantly inhibited the tumor growth in mice. PEG-P[Lys/Lys(fructose)]-BPA may be a promising boron delivery system for BNCT.

Boron-enriched polyvinyl-alcohol/boric-acid nanoparticles for boron neutron capture therapy

Background: Due to the noninvasive nature of boron neutron capture therapy (BNCT), it is considered a promising cancer treatment method. Aim: To investigate whether polyvinyl alcohol/boric acid crosslinked nanoparticles (PVA/BA NPs) are an efficient delivery system for BNCT. Materials & methods: PVA/BA NPs were synthesized and cocultured with brain and oral cancers cells for BNCT. Results: PVA/BA NPs had a boron-loading capacity of 7.83 ± 1.75 w/w%. They accumulated in brain and oral cancers cells at least threefold more than in fibroblasts and macrophages. The IC50 values of the brain and oral cancers cells were at least ninefold and sixfold lower than those of fibroblasts and macrophages, respectively. Conclusion: Theoretically, PVA/BA NPs target brain and oral cancers cells and could offer improved therapeutic outcomes of BNCT.

Construction of Boronophenylalanine-Loaded Biodegradable Periodic Mesoporous Organosilica Nanoparticles for BNCT Cancer Therapy

Biodegradable periodic mesoporous organosilica (BPMO) has recently emerged as a promising type of mesoporous silica-based nanoparticle for biomedical applications. Like mesoporous silica nanoparticles (MSN), BPMO possesses a large surface area where various compounds can be attached. In this work, we attached boronophenylalanine (¹⁰BPA) to the surface and explored the potential of this nanomaterial for delivering boron-10 for use in boron neutron capture therapy (BNCT). This cancer therapy is based on the principle that the exposure of boron-10 to thermal neutron results in the release of α-particles that kill cancer cells. To attach ¹⁰BPA, the surface of BPMO was modified with diol groups which facilitated the efficient binding of ¹⁰BPA, yielding ¹⁰BPA-loaded BPMO (¹⁰BPA-BPMO). Surface modification with phosphonate was also carried out to increase the dispersibility of the nanoparticles. To investigate this nanomaterial’s potential for BNCT, we first used human cancer cells and found that ¹⁰BPA-BPMO nanoparticles were efficiently taken up into the cancer cells and were localized in perinuclear regions. We then used a chicken egg tumor model, a versatile and convenient tumor model used to characterize nanomaterials. After observing significant tumor accumulation, ¹⁰BPA-BPMO injected chicken eggs were evaluated by irradiating with neutron beams. Dramatic inhibition of the tumor growth was observed. These results suggest the potential of ¹⁰BPA-BPMO as a novel boron agent for BNCT.

Polyvinyl alcohol increased growth, migration, invasion, and sphere size in the PK-8 pancreatic ductal adenocarcinoma cell line

Polyvinyl alcohol (PVA) is a water-soluble synthetic polymer used in eye drops, embolization particles, and artificial cartilage. It has also been shown to cause expansion of functional multipotent self-renewing hematopoietic stem cells under serum-free conditions. In this study, we examined the effects of PVA on human pancreatic ductal adenocarcinoma (PDAC) cell lines using 2-dimensional (2D) and 3D-cultures with serum-free medium. In the 2D-culture, PVA-treatment induced an aggregated colony-like appearance in PDAC cells. It increased the growth of PK-8 cells in a dose-dependent manner as well as significantly increasing migration and invasion abilities. qRT-PCR showed an increase in α2 integrin and a decrease in matrix metalloprotease levels in PVA-treated PK-8 cells. Through qRT-PCR analysis, β1 integrin expression at the mRNA level was found to be decreased; however, it was unaltered at the protein level when assessed using FACS analysis. PVA further induced mesenchymal to epithelial transition-like alterations, including increased E-cadherin and decreased Vimentin and N-cadherin expression. Four cancer stem cell (CSC) markers were higher in PVA-treated PK-8 cells compared to controls. In 3D-culture, PVA-treated PK-8 cells showed a rod-like appearance with larger sphere size and higher growth ability. qRT-PCR showed that CSC markers did not increase and 2 of 4 drug transporters had decreased in PVA-treated PK-8 cells. These findings suggest that PVA increases the growth, migration, invasion, and sphere size of PK-8 cells, but does not increase the proportion of pancreatic CSCs under 3D-culture conditions with serum-free medium.

Tumor vasculature-targeted 10B delivery by an Annexin A1-binding peptide boosts effects of boron neutron capture therapy

Background

p-Boronophenylalanine (¹⁰BPA) is a powerful ¹⁰B drug used in current clinical trials of BNCT. For BNCT to be successful, a high (500 mg/kg) dose of ¹⁰BPA must be administered over a few hours. Here, we report BNCT efficacy after rapid, ultralow-dose administration of either tumor vasculature-specific annexin A1-targeting IFLLWQR (IF7)-conjugated ¹⁰BPA or borocaptate sodium (¹⁰BSH).

Methods

(1) IF7 conjugates of either ¹⁰B drugs intravenously injected into MBT2 bladder tumor-bearing mice and biodistribution of ¹⁰B in tumors and normal organs analyzed by prompt gamma-ray analysis. (2) Therapeutic effect of IF7-¹⁰B drug-mediated BNCT was assessed by either MBT2 bladder tumor bearing C3H/He mice and YTS-1 tumor bearing nude mice.

Results

Intravenous injection of IF7C conjugates of either ¹⁰B drugs into MBT2 bladder tumor-bearing mice promoted rapid ¹⁰B accumulation in tumor and suppressed tumor growth. Moreover, multiple treatments at ultralow (10–20 mg/kg) doses of IF7-¹⁰B drug-mediated BNCT significantly suppressed tumor growth in a mouse model of human YTS-1 bladder cancer, with increased Anxa1 expression in tumors and infiltration by CD8-positive lymphocytes.

Conclusions

We conclude that IF7 serves as an efficient ¹⁰B delivery vehicle by targeting tumor tissues via the tumor vasculature and could serve as a relevant vehicle for BNCT drugs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-020-07760-x.

Internalization into cancer cells of zwitterionic amino acid polymers via amino acid transporter recognition

Zwitterionic amino acid polymers are internalized into cancer cells via their recognition capability for amino acid transporters, which is overexpressed on cancer cells compared with normal cells.

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.

Polymer-conjugated glucosamine complexed with boric acid shows tumor-selective accumulation and simultaneous inhibition of glycolysis

We synthesized unique water-soluble synthetic-polymer, styrene-maleic acid copolymer (SMA) conjugated glucosamine (SG); which formed a stable complex with boric acid (BA). This complex had a mean particle size of 15 nm by light scattering, and single peak in gel permeation chromatography. The particles were taken up by tumor cells five times faster than free BA in vitro and liberated BA at acidic tumor pH (5-7). Liberated BA inhibited glycolysis and resulted in tumor suppression in vivo. Intravenously injected SGB-complex did bind with albumin, and plasma half-life was about 8 h in mice, and accumulated to tumor tissues about 10 times more than in normal organs. IC₅₀ of SGB-complex for HeLa cells under pO₂ of 6-9% was about 20 μg/ml (free BA equivalent), 150 times more potent than free BA. Neutron irradiation of human oral cancer cells with SGB-complex resulted in 16 times greater cell-killing than that without SGB-complex. In vivo antitumor effect was evaluated after neutron irradiation only once in SCC VII tumor bearing mice and significant tumor suppression was confirmed. These results indicate that SGB-complex is a unique multifunctional anticancer agent with much more potent activity under low pO₂ conditions as in large advanced cancers.

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.

Bimodal Therapeutic Agents Against Glioblastoma, One of the Most Lethal Forms of Cancer

About 95 % of people diagnosed with glioblastoma die within five years. Glioblastoma is the most aggressive central nervous system tumour. It is necessary to make progress in the glioblastoma treatment so that advanced chemotherapy drugs or radiation therapy or, ideally, two-in-one hybrid systems should be implemented. Tyrosine kinase receptors-inhibitors and boron neutron capture therapy (BNCT), together, could provide a therapeutic strategy. In this work, sunitinib decorated-carborane hybrids were prepared and biologically evaluated identifying excellent antitumoral- and BNCT-agents. One of the selected hybrids was studied against glioma-cells and found to be 4 times more cytotoxic than sunitinib and 1.7 times more effective than ¹⁰ B-boronophenylalanine fructose complex when the cells were irradiated with neutrons.

Closo-Carboranyl- and Metallacarboranyl [1,2,3]triazolyl-Decorated Lapatinib-Scaffold for Cancer Therapy Combining Tyrosine Kinase Inhibition and Boron Neutron Capture Therapy

One of the driving forces of carcinogenesis in humans is the aberrant activation of receptors; consequently, one of the most promising mechanisms for cancer treatment is receptor inhibition by chemotherapy. Although a variety of cancers are initially susceptible to chemotherapy, they eventually develop multi-drug resistance. Anti-tumor agents overcoming resistance and acting through two or more ways offer greater therapeutic benefits over single-mechanism entities. In this study, we report on a new family of bifunctional compounds that, offering the possibility of dual action (drug + radiotherapy combinations), may result in significant clinical benefits. This new family of compounds combines two fragments: the drug fragment is a lapatinib group, which inhibits the tyrosine kinase receptor activity, and an icosahedral boron cluster used as agents for neutron capture therapy (BNCT). The developed compounds were evaluated in vitro against different tyrosine kinase receptors (TKRs)-expressing tumoral cells, and in vitro–BNCT experiments were performed for two of the most promising hybrids, 19 and 22. We identified hybrid 19 with excellent selectivity to inhibit cell proliferation and ability to induce necrosis/apoptosis of glioblastoma U87 MG cell line. Furthermore, derivative 22, bearing a water-solubility-enhancing moiety, showed moderate inhibition of cell proliferation in both U87 MG and colorectal HT-29 cell lines. Additionally, the HT-29 cells accumulated adequate levels of boron after hybrids 19 and 22 incubations rendering, and after neutron irradiation, higher BNCT-effects than BPA. The attractive profile of developed hybrids makes them interesting agents for combined therapy.

Visible light mediated PVA-tyramine hydrogels for covalent incorporation and tailorable release of functional growth factors

PVA-Tyr hydrogel facilitated covalent incorporation can control release of pristine growth factors while retaining their native bioactivity.