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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.

Glioblastoma (GBM) is the most malignant brain tumor and is highly resistant to intensive combination therapies and anti-VEGF therapies. To assess the resistance mechanism to anti-VEGF therapy, we examined the vessels of GBMs in tumors that were induced by the transduction of p53⁺/⁻ heterozygous mice with lentiviral vectors containing oncogenes and the marker GFP in the hippocampus of GFAP-Cre recombinase (Cre) mice. We were surprised to observe GFP⁺ vascular endothelial cells (ECs). Transplantation of mouse GBM cells revealed that the tumor-derived endothelial cells (TDECs) originated from tumor-initiating cells and did not result from cell fusion of ECs and tumor cells. An in vitro differentiation assay suggested that hypoxia is an important factor in the differentiation of tumor cells to ECs and is independent of VEGF. TDEC formation was not only resistant to an anti-VEGF receptor inhibitor in mouse GBMs but it led to an increase in their frequency. A xenograft model of human GBM spheres from clinical specimens and direct clinical samples from patients with GBM also showed the presence of TDECs. We suggest that the TDEC is an important player in the resistance to anti-VEGF therapy, and hence a potential target for GBM therapy.

Background Colorectal cancer (CRC) is considered the third most common type of cancer worldwide. Tumor-associated macrophages (TAMs) have been shown to promote drug resistance. Adenosine-to-inosine RNA-editing, as regulated by adenosine deaminase acting on RNA (ADAR), is a process that induces the posttranscriptional modification of critical oncogenes. The aim of this study is to determine whether the signals from cancer cells would induce RNA-editing in macrophages. Methods The effects of RNA-editing on phenotypes in macrophages were analyzed using clinical samples and in vitro and in vivo models. Results The intensity of the RNA-editing enzyme ADAR1 (Adenosine deaminase acting on RNA 1) in cancer and mononuclear cells indicated a strong positive correlation between the nucleus and cytoplasm. The ADAR1-positive mononuclear cells were positive for CD68 and CD163, a marker for M2 macrophages. Cancer cells transport pro-inflammatory cytokines or ADAR1 protein directly to macrophages via the exosomes, promoting RNA-editing in AZIN1 (Antizyme Inhibitor 1) and GLI1 (Glioma-Associated Oncogene Homolog 1) and resulting in M2 macrophage polarization. GLI1 RNA-editing in the macrophages induced by cancer cells promotes the secretion of SPP1, which is supplied to the cancer cells. This activates the NFκB pathway in cancer cells, promoting oxaliplatin resistance. When the JAK inhibitors were administered, oncogenic RNA-editing in the macrophages was suppressed. This altered the macrophage polarization from M2 to M1 and decreased oxaliplatin resistance in cancer cells. Conclusions This study revealed that ADAR1-high TAMs are crucial in regulating drug resistance in CRC and that targeting ADAR1 in TAMs could be a promising treatment approach for overcoming drug resistance in CRC.

Immune checkpoint inhibitors (ICIs) are effective against many advanced malignancies. However, many patients are nonresponders to immunotherapy, and overcoming this resistance to treatment is important. Boron neutron capture therapy (BNCT) is a local chemoradiation therapy with the combination of boron drugs that accumulate selectively in cancer and the neutron irradiation of the cancer site. Here, we report the first boron neutron immunotherapy (B‐NIT), combining BNCT and ICI immunotherapy, which was performed on a radioresistant and immunotherapy‐resistant advanced‐stage B16F10 melanoma mouse model. The BNCT group showed localized tumor suppression, but the anti‐PD‐1 antibody immunotherapy group did not show tumor suppression. Only the B‐NIT group showed strong tumor growth inhibition at both BNCT‐treated and shielded distant sites. Intratumoral CD8+ T‐cell infiltration and serum high mobility group box 1 (HMGB1) levels were higher in the B‐NIT group. Analysis of CD8+ T cells in tumor‐infiltrating lymphocytes (TILs) showed that CD62L‐ CD44+ effector memory T cells and CD69+ early‐activated T cells were predominantly increased in the B‐NIT group. Administration of CD8‐depleting mAb to the B‐NIT group completely suppressed the augmented therapeutic effects. This indicated that B‐NIT has a potent immune‐induced abscopal effect, directly destroying tumors with BNCT, inducing antigen‐spreading effects, and protecting normal tissue. B‐NIT, immunotherapy combined with BNCT, is the first treatment to overcome immunotherapy resistance in malignant melanoma. In the future, as its therapeutic efficacy is demonstrated not only in melanoma but also in other immunotherapy‐resistant malignancies, B‐NIT can become a new treatment candidate for advanced‐stage cancers. Boron neutron capture therapy leads to new treatment option to overcome cancer immunotherapy resistance.

The worldwide prevalence of type 2 diabetes (T2D), which is caused by a combination of environmental and genetic factors, is increasing. With regard to genetic factors, variations in the gene encoding Cdk5 regulatory associated protein 1–like 1 (Cdkal1) have been associated with an impaired insulin response and increased risk of T2D across different ethnic populations, but the molecular function of this protein has not been characterized. Here, we show that Cdkal1 is a mammalian methylthiotransferase that biosynthesizes 2-methylthio-N6-threonylcarbamoyladenosine (ms2t6A) in tRNALys(UUU) and that it is required for the accurate translation of AAA and AAG codons. Mice with pancreatic β cell–specific KO of Cdkal1 (referred to herein as β cell KO mice) showed pancreatic islet hypertrophy, a decrease in insulin secretion, and impaired blood glucose control. In Cdkal1-deficient β cells, misreading of Lys codon in proinsulin occurred, resulting in a reduction of glucose-stimulated proinsulin synthesis. Moreover, expression of ER stress–related genes was upregulated in these cells, and abnormally structured ER was observed. Further, the β cell KO mice were hypersensitive to high fat diet–induced ER stress. These findings suggest that glucose-stimulated translation of proinsulin may require fully modified tRNALys(UUU), which could potentially explain the molecular pathogenesis of T2D in patients carrying cdkal1 risk alleles.

Adenosine-to-inosine RNA editing is a process mediated by adenosine deaminases that act on the RNA (ADAR) gene family. It has been discovered recently as an epigenetic modification dysregulated in human cancers. However, the clinical significance of RNA editing in patients with liver metastasis from colorectal cancer (CRC) remains unclear. The current study aimed to systematically and comprehensively investigate the significance of adenosine deaminase acting on RNA 1 (ADAR1) expression status in 83 liver metastatic tissue samples collected from 36 patients with CRC. The ADAR1 expression level was significantly elevated in liver metastatic tissue samples obtained from patients with right-sided, synchronous, or RAS mutant-type CRC. ADAR1-high liver metastasis was significantly correlated with remnant liver recurrence after hepatic metastasectomy. A high ADAR1 expression was a predictive factor of remnant liver recurrence (area under the curve = 0.72). Results showed that the ADAR1 expression level could be a clinically relevant predictive indicator of remnant liver recurrence. Patients with liver metastases who have a high ADAR1 expression requires adjuvant chemotherapy after hepatic metastasectomy.

Most cases of colorectal cancers (CRCs) are microsatellite stable (MSS), which frequently demonstrate lower response rates to immune checkpoint inhibitors (ICIs). RNA editing produces neoantigens by altering amino acid sequences. In this study, RNA editing was induced artificially by chemoradiation therapy (CRT) to generate neoantigens in MSS CRCs. Altogether, 543 CRC specimens were systematically analyzed, and the expression pattern of ADAR1 was investigated. In vitro and in vivo experiments were also performed. The RNA editing enzyme ADAR1 was upregulated in microsatellite instability–high CRCs, leading to their high affinity for ICIs. Although ADAR1 expression was low in MSS CRC, CRT including oxaliplatin (OX) treatment upregulated RNA editing levels by inducing ADAR1. Immunohistochemistry analyses showed the upregulation of ADAR1 in patients with CRC treated with CAPOX (capecitabine + OX) radiation therapy relative to ADAR1 expression in patients with CRC treated only by surgery (p < 0.001). Compared with other regimens, CRT with OX effectively induced RNA editing in MSS CRC cell lines (HT29 and Caco2, p < 0.001) via the induction of type 1 interferon-triggered ADAR1 expression. CRT with OX promoted the RNA editing of cyclin I, a neoantigen candidate. Neoantigens can be artificially induced by RNA editing via an OX–CRT regimen. CRT can promote proteomic diversity via RNA editing.

RNA editing by adenosine deaminase acting on RNA (ADAR) enzymes plays a role in cancer progression. However, its clinical significance in metastatic colorectal cancer (CRC) remains unclear. This study aimed to evaluate whether ADAR1 expression predicts prognosis and treatment response in colorectal cancer (CRC) with synchronous liver metastasis. This study included 40 patients with stage IV CRC and synchronous liver metastases. ADAR1 expression in tumor tissues was evaluated using immunohistochemistry. Expression levels were quantified using the immunoreactive score, and associations with clinicopathological features, overall survival (OS), and chemotherapy response were examined. High ADAR1 expression was significantly associated with multiple liver metastases ( P  = 0.0206), lymph node metastasis ( P = 0.0241), and reduced response to chemotherapy ( P  = 0.0224). Significantly shorter OS was observed in patients with high ADAR1 expression in the nucleus ( P  = 0.0458). ADAR1 expression was an independent prognostic factor comparable to the presence of extrahepatic metastases. Low ADAR1 expression was correlated with a higher likelihood of achieving a response to chemotherapy. ADAR1 expression can reflect tumor aggressiveness and chemotherapy resistance in patients with CRC and synchronous liver metastasis. ADAR1 has considerable potential as a dual-purpose biomarker for stratifying patients based on prognosis and optimizing treatment intensity.

Background Boron neutron capture therapy (BNCT) is a molecularly targeted chemoradiation modality that relies on boron delivery agents such as p-borophenylalanine (BPA), which require LAT1 (L-type amino acid transporter 1) for tumor uptake. However, the limited efficacy of BPA in LAT1-low tumors restricts its therapeutic scope. To address this limitation, we developed a tumor marker–guided BNCT strategy targeting cancers overexpressing the clinically validated glycan biomarker CA19-9. Methods We conducted transcriptomic analyses using The Cancer Genome Atlas (TCGA) datasets to identify LAT1-low cancers with high CA19-9 expression. These analyses revealed elevated expression of fucosyltransferase 3 (FUT3), which underlies CA19-9 biosynthesis, in pancreatic, biliary, and ovarian malignancies. Based on this, we synthesized a novel boron compound, fucose-BSH, designed to selectively accumulate in CA19-9–positive tumors. We evaluated its physicochemical properties, pharmacokinetics, biodistribution, and antitumor efficacy in cell lines and xenograft models, comparing its performance to that of BPA. Results Fucose-BSH demonstrated significantly greater boron uptake in CA19-9–positive cell lines (AsPC-1, Panc 04.03, HuCCT-1, HSKTC, OVISE) compared to CA19-9–negative PANC-1. In HuCCT-1 xenografts, boron accumulation reached 36.2 ppm with a tumor/normal tissue ratio of 2.1, outperforming BPA. Upon neutron irradiation, fucose-BSH–mediated BNCT achieved > 80% tumor growth inhibition. Notably, fucose-BSH retained therapeutic efficacy in LAT1-deficient models where BPA was ineffective, confirming LAT1-independent targeting. Conclusions This study establishes a novel precision BNCT approach by leveraging CA19-9 as a tumor-selective glycan marker for boron delivery. Fucose-BSH offers a promising platform for expanding BNCT to previously inaccessible LAT1-low malignancies, including pancreatic, biliary, and ovarian cancers. These findings provide a clinically actionable strategy for tumor marker–driven chemoradiation and lay the foundation for translational application in BNCT. This strategy has the potential to support companion diagnostic development and precision stratification in ongoing and future BNCT clinical trials. Translational Relevance Malignancies with elevated CA19-9 expression, such as pancreatic, biliary, and ovarian cancers, are associated with poor prognosis and limited response to current therapies. This study presents a tumor marker–guided strategy for boron neutron capture therapy (BNCT) by leveraging CA19-9 glycan biology to enable selective tumor targeting via fucose-BSH, a novel boron compound. Through transcriptomic data mining and preclinical validation, fucose-BSH demonstrated LAT1-independent boron delivery, potent BNCT-mediated cytotoxicity, and tumor-specific accumulation in CA19-9–positive models. These findings support a precision chemoradiation approach that addresses a critical gap in BNCT applicability, offering a clinically actionable pathway for patient stratification and therapeutic development in CA19-9–expressing cancers. Graphical Abstract

Reduced expression in immortalized cells/Dickkopf-3 (REIC/Dkk-3) is a tumor suppressor and its overexpression has been shown to exert anti-tumor effects as a therapeutic target gene in many human cancers. Recently, we demonstrated the anti-glioma effects of an adenoviral vector carrying REIC/Dkk-3 with the super gene expression system (Ad-SGE-REIC). Anti-vascular endothelial growth factor treatments such as bevacizumab have demonstrated convincing therapeutic advantage in patients with glioblastoma. However, bevacizumab did not improve overall survival in patients with newly diagnosed glioblastoma. In this study, we examined the effects of Ad-SGE-REIC on glioma treated with bevacizumab. Ad-SGE-REIC treatment resulted in a significant reduction in the number of invasion cells treated with bevacizumab. Western blot analyses revealed the increased expression of several endoplasmic reticulum stress markers in cells treated with both bevacizumab and Ad-SGE-REIC, as well as decreased β-catenin protein levels. In malignant glioma mouse models, overall survival was extended in the combination therapy group. These results suggest that the combination therapy of Ad-SGE-REIC and bevacizumab exerts anti-glioma effects by suppressing the angiogenesis and invasion of tumors. Combined Ad-SGE-REIC and bevacizumab might be a promising strategy for the treatment of malignant glioma.