Tumor-targeting hyaluronic acid/fluorescent carborane complex for boron neutron capture therapy.

In cancer therapeutics, boron neutron capture therapy (BNCT) requires a platform for selective and efficient 10B delivery into tumor tissues for a successful treatment. However, the use of carborane, a promising candidate with high boron content and biostability, has significant limitations in the biomedical field due to its poor water-solubility and tumor-selectivity. To overcome these hurdles, we present in this study a fluorescent nano complex, combining fluorescent carborane and sodium hyaluronate for high boron concentration and tumor-selectivity. Tumor cells actively internalized the complex through binding hyaluronan to CD44, overexpressed on the tumor cell surface. Furthermore, the subcellular distribution of this complex could also be detected due to its fluorescent properties. Moreover, after thermal neutron irradiations, the complex produced excellent cytotoxicity, equal to or greater than that of the clinically-used BPA-fructose. Therefore, this novel complex could be potentially more suitable for BNCT than the boron agent.

Folate receptor-targeted novel boron compound for boron neutron capture therapy on F98 glioma-bearing rats.

Folic acid (FA) has high affinity for the folate receptor (FR), which is limited expressed in normal human tissues, but over-expressed in several tumor cells, including glioblastoma cells. In the present work, a novel pteroyl-closo-dodecaborate conjugate (PBC) was developed, in which the pteroyl group interacts with FR, and the efficacy of boron neutron capture therapy (BNCT) using PBC was investigated. Thus, in vitro and in vivo studies were performed using F98 rat glioma cells and F98 glioma-bearing rats. For the in vivo study, boronophenylalanine (BPA) was intravenously administered, while PBC was administered by convection-enhanced delivery (CED)-a method for direct local drug infusion into the brain of rats. Furthermore, a combination of PBC administered by CED and BPA administered by intravenous (i.v.) injection was also investigated. In the biodistribution experiment, PBC administration at 6 h after CED termination showed the highest cellular boron concentrations (64.6 ± 29.6 µg B/g). Median survival time (MST) of untreated controls was 23.0 days (range 21-24 days). MST of rats administered PBC (CED) followed by neutron irradiation was 31 days (range 26-36 days), which was similar to that of rats administered i.v. BPA (30 days; range 25-37 days). Moreover, the combination group [PBC (CED) and i.v. BPA] showed the longest MST (38 days; range 28-40 days). It is concluded that a significant MST increase was noted in the survival time of the combination group of PBC (CED) and i.v. BPA compared to that in the single-boron agent groups. These findings suggest that the combination use of PBC (CED) has additional effects.

Cytotoxicity of Tirapazamine (3-Amino-1,2,4-benzotriazine-1,4-dioxide)-Induced DNA Damage in Chicken DT40 Cells.

Tirapazamine (TPZ) is an anticancer drug with highly selective cytotoxicity toward hypoxic cells. TPZ is converted to a radical intermediate under hypoxic conditions, and this intermediate interacts with intracellular macromolecules, including DNA. TPZ has been reported to indirectly induce DNA double-strand breaks (DSBs) through the formation of various intermediate DNA lesions under hypoxic conditions. Although the topoisomerase II-DNA complex has been identified as one of these intermediates, other lesions have not yet been defined. In order to obtain a deeper understanding of the mechanisms responsible for the selective cytotoxicity of TPZ toward hypoxic cells, its cellular sensitivity was systematically examined with genetically isogenic DNA-repair-deficient mutant DT40 cell lines. Our results showed that tdp1-/-, tdp2-/-, parp1-/-, and aptx1-/- cells displayed hypersensitivity to TPZ only under hypoxic conditions. These results strongly suggest that the accumulation of the topoisomerase I-trapped DNA complex, topoisomerase II-trapped DNA complex, and abortive ligation products with 5'-AMP are the potential causes of TPZ-induced hypoxic cell death. Furthermore, our genetic analysis revealed that under normoxic conditions (as well as hypoxic conditions), TPZ exhibited significant cytotoxicity toward cell lines deficient in homologous recombination, nonhomologous end joining, base excision repair, and translesion synthesis. Ascorbic acid, a radical scavenger, suppressed TPZ-induced cytotoxicity toward normoxic cells. These results suggest the involvement of oxidative DNA damage and DSBs produced by reactive oxygen species generated from superoxide, a byproduct of the oxidation of TPZ radical intermediates in normoxic cells. Collectively, our results demonstrate that TPZ induces oxidative DNA damage under normoxic and hypoxic conditions and selectively introduces abortive topoisomerase-DNA complexes and unligatable DNA ends under hypoxic conditions.

Comparison of the pharmacokinetics between L-BPA and L-FBPA using the same administration dose and protocol: a validation study for the theranostic approach using [18F]-L-FBPA positron emission tomography in boron neutron capture therapy.

BACKGROUND: Boron neutron capture therapy (BNCT) is a cellular-level particle radiation therapy that combines the selective delivery of boron compounds to tumour tissue with neutron irradiation. L-p-Boronophenylalanine (L-BPA) is a boron compound now widely used in clinical situations. Determination of the boron distribution is required for successful BNCT prior to neutron irradiation. Thus, positron emission tomography with [18F]-L-FBPA, an 18F-labelled radiopharmaceutical analogue of L-BPA, was developed. However, several differences between L-BPA and [18F]-L-FBPA have been highlighted, including the different injection doses and administration protocols. The purpose of this study was to clarify the equivalence between L-BPA and [19F]-L-FBPA as alternatives to [18F]-L-FBPA. METHODS: SCC-VII was subcutaneously inoculated into the legs of C3H/He mice. The same dose of L-BPA or [19F]-L-FBPA was subcutaneously injected. The time courses of the boron concentrations in blood, tumour tissue, and normal tissue were compared between the groups. Next, we administered the therapeutic dose of L-BPA or the same dose of [19F]-L-FBPA by continuous infusion and compared the effects of the administration protocol on boron accumulation in tissues. RESULTS: There were no differences between L-BPA and [19F]-L-FBPA in the transition of boron concentrations in blood, tumour tissue, and normal tissue using the same administration protocol. However, the normal tissue to blood ratio of the boron concentrations in the continuous-infusion group was lower than that in the subcutaneous injection group. CONCLUSIONS: No difference was noted in the time course of the boron concentrations in tumour tissue and normal tissues between L-BPA and [19F]-L-FBPA. However, the administration protocol had effects on the normal tissue to blood ratio of the boron concentration. In estimating the BNCT dose in normal tissue by positron emission tomography (PET), we should consider the possible overestimation of the normal tissue to blood ratio of the boron concentrations derived from the values measured by PET on dose calculation.

DNA damage induced by boron neutron capture therapy is partially repaired by DNA ligase IV.

Boron neutron capture therapy (BNCT) is a particle radiation therapy that involves the use of a thermal or epithermal neutron beam in combination with a boron ((10)B)-containing compound that specifically accumulates in tumor. (10)B captures neutrons and the resultant fission reaction produces an alpha ((4)He) particle and a recoiled lithium nucleus ((7)Li). These particles have the characteristics of high linear energy transfer (LET) radiation and therefore have marked biological effects. High-LET radiation is a potent inducer of DNA damage, specifically of DNA double-strand breaks (DSBs). The aim of the present study was to clarify the role of DNA ligase IV, a key player in the non-homologous end-joining repair pathway, in the repair of BNCT-induced DSBs. We analyzed the cellular sensitivity of the mouse embryonic fibroblast cell lines Lig4-/- p53-/- and Lig4+/+ p53-/- to irradiation using a thermal neutron beam in the presence or absence of (10)B-para-boronophenylalanine (BPA). The Lig4-/- p53-/- cell line had a higher sensitivity than the Lig4+/+ p53-/-cell line to irradiation with the beam alone or the beam in combination with BPA. In BNCT (with BPA), both cell lines exhibited a reduction of the 50 % survival dose (D 50) by a factor of 1.4 compared with gamma-ray and neutron mixed beam (without BPA). Although it was found that (10)B uptake was higher in the Lig4+/+ p53-/- than in the Lig4-/- p53-/- cell line, the latter showed higher sensitivity than the former, even when compared at an equivalent (10)B concentration. These results indicate that BNCT-induced DNA damage is partially repaired using DNA ligase IV.

Detection of γH2AX foci in mouse normal brain and brain tumor after boron neutron capture therapy.

AIM: In this study, we investigated γH2AX foci as markers of DSBs in normal brain and brain tumor tissue in mouse after BNCT. BACKGROUND: Boron neutron capture therapy (BNCT) is a particle radiation therapy in combination of thermal neutron irradiation and boron compound that specifically accumulates in the tumor. (10)B captures neutrons and produces an alpha ((4)He) particle and a recoiled lithium nucleus ((7)Li). These particles have the characteristics of extremely high linear energy transfer (LET) radiation and therefore have marked biological effects. High LET radiation causes severe DNA damage, DNA DSBs. As the high LET radiation induces complex DNA double strand breaks (DSBs), large proportions of DSBs are considered to remain unrepaired in comparison with exposure to sparsely ionizing radiation. MATERIALS AND METHODS: We analyzed the number of γH2AX foci by immunohistochemistry 30 min or 24 h after neutron irradiation. RESULTS: In both normal brain and brain tumor, γH2AX foci induced by (10)B(n,α)(7)Li reaction remained 24 h after neutron beam irradiation. In contrast, γH2AX foci produced by γ-ray irradiation at contaminated dose in BNCT disappeared 24 h after irradiation in these tissues. CONCLUSION: DSBs produced by (10)B(n,α)(7)Li reaction are supposed to be too complex to repair for cells in normal brain and brain tumor tissue within 24 h. These DSBs would be more difficult to repair than those by γ-ray. Excellent anti-tumor effect of BNCT may result from these unrepaired DSBs induced by (10)B(n,α)(7)Li reaction.

Synthesis and in vitro evaluation of thiododecaborated α, α- cycloalkylamino acids for the treatment of malignant brain tumors by boron neutron capture therapy.

Boron-neutron capture therapy (BNCT) is an attractive technique for cancer treatment. As such, α, α-cycloalkyl amino acids containing thiododecaborate ([B12H11](2-)-S-) units were designed and synthesized as novel boron delivery agents for BNCT. In the present study, new thiododecaborate α, α-cycloalkyl amino acids were synthesized, and biological evaluation of the boron compounds as boron carrier for BNCT was carried out.

Evaluation of SCCVII tumor cell survival in clamped and non-clamped solid tumors exposed to carbon-ion beams in comparison to X-rays.

The aim of this study was to measure the RBE (relative biological effectiveness) and OER (oxygen enhancement ratio) for survival of cells within implanted solid tumors following exposure to 290MeV/nucleon carbon-ion beams or X-rays. Squamous cell carcinoma cells (SCCVII) were transplanted into the right hind legs of syngeneic C3H male mice. Irradiation with either carbon-ion beams with a 6-cm spread-out Bragg peak (SOBP, at 46 and 80keV/µm) or X-rays was delivered to 5-mm or less diameter tumors. We defined three different oxygen statuses of the irradiated cells. Hypoxic and normoxic conditions in tumors were produced by clamping or not clamping the leg to avoid blood flow. Furthermore, single-cell suspensions were prepared from non-irradiated tumors and directly used to determine the radiation response of aerobic cells. Single-cell suspensions (aerobic condition) were fully air-saturated. Single-cell suspensions were prepared from excised and trypsinized tumors, and were used for in vivo-in vitro colony formation assays to obtain cell survival curves. The RBE values increased with increasing LET in SOBP beams. The maximum RBE values in three different oxygen conditions; hypoxic tumor, normoxic tumor and aerobic cells, were 2.16, 1.76 and 1.66 at an LET of 80keV/µm, respectively. After X-ray irradiation the OERh/n values (hypoxic tumor/normoxic tumor) were lower than the OERh/a (hypoxic tumor/aerobic cells), and were 1.87±0.13 and 2.52±0.11, respectively. The OER values of carbon-ion irradiated samples were small in comparison to those of X-ray irradiated samples. However, no significant changes of the OER at proximal and distal positions within the SOBP carbon-ion beams were observed. To conclude, we found that the RBE values for cell survival increased with increasing LET and that the OER values changed little with increasing LET within the SOBP carbon-ion beams.

The impact of TP53 status of tumor cells including the type and the concentration of administered 10B delivery agents on compound biological effectiveness in boron neutron capture therapy.

Human head and neck squamous cell carcinoma cells transfected with mutant TP53 (SAS/mp53) or neo vector (SAS/neo) were inoculated subcutaneously into left hind legs of nude mice. After the subcutaneous administration of a 10B-carrier, boronophenylalanine-10B (BPA) or sodium mercaptododecaborate-10B (BSH), at two separate concentrations, the 10B concentrations in tumors were measured using γ-ray spectrometry. The tumor-bearing mice received 5-bromo-2'-deoxyuridine (BrdU) continuously to label all intratumor proliferating (P) tumor cells, then were administered with BPA or BSH. Subsequently, the tumors were irradiated with reactor neutron beams during the time of which 10B concentrations were kept at levels similar to each other. Following irradiation, cells from some tumors were isolated and incubated with a cytokinesis blocker. The responses of BrdU-unlabeled quiescent (Q) and total (= P + Q) tumor cells were assessed based on the frequencies of micronucleation using immunofluorescence staining for BrdU. In both SAS/neo and SAS/mp53 tumors, the compound biological effectiveness (CBE) values were higher in Q cells and in the use of BPA than total cells and BSH, respectively. The higher the administered concentrations were, the smaller the CBE values became, with a clearer tendency in SAS/neo tumors and the use of BPA than in SAS/mp53 tumors and BSH, respectively. The values for BPA that delivers into solid tumors more dependently on uptake capacity of tumor cells than BSH became more alterable. Tumor micro-environmental heterogeneity might partially influence on the CBE value. The CBE value can be regarded as one of the indices showing the level of intratumor heterogeneity.

Experimentally determined relative biological effectiveness of cyclotron-based epithermal neutrons designed for clinical BNCT: in vitro study.

A neutron beam for boron neutron capture therapy (BNCT) of deep-seated tumours is designed to maintain a high flux of epithermal neutrons, while keeping the thermal and fast neutron component as low as possible. These neutrons (thermal and fast) have a high relative biological effectiveness in comparison with high energy photon beams used for conventional X-ray radiotherapy. In the past, neutrons for the purpose of BNCT were generated using nuclear reactors. However, there are various challenges that arise when installing a reactor in a hospital environment. From 2006, the Kyoto University Research Reactor Institute, in collaboration with Sumitomo Heavy Industries, began the development of an accelerator-based neutron source for clinical BNCT in a bid to overcome the shortcomings of a nuclear reactor-based neutron source. Following installation and beam performance testing, in vitro studies were performed to assess the biological effect of the neutron beam. Four different cell lines were prepared and irradiated using the accelerator-based neutron source. Following neutron and gamma ray irradiation, the survival curve for each cell line was calculated. The biological end point to determine the relative biological effectiveness (RBE) was set to 10% cell survival, and the D10 for each cell line was determined. The RBE of the accelerator-based neutron beam was evaluated to be 2.62.

Pharmacokinetic Study of 14C-Radiolabeled p-Boronophenylalanine (BPA) in Sorbitol Solution and the Treatment Outcome of BPA-Based Boron Neutron Capture Therapy on a Tumor-Bearing Mouse Model.

BACKGROUND AND OBJECTIVE: Boron neutron capture therapy (BNCT) is a binary cancer treatment that combines boron administration and neutron irradiation. The tumor cells take up the boron compound and the subsequent neutron irradiation results in a nuclear fission reaction caused by the neutron capture reaction of the boron nuclei. This produces highly cytocidal heavy particles, leading to the destruction of tumor cells. p-boronophenylalanine (BPA) is widely used in BNCT but is insoluble in water and requires reducing sugar or sugar alcohol as a dissolvent to create an aqueous solution for administration. The purpose of this study was to investigate the pharmacokinetics of 14C-radiolabeled BPA using sorbitol as a dissolvent, which has not been reported before, and confirm whether neutron irradiation with a sorbitol solution of BPA can produce an antitumor effect of BNCT. MATERIALS AND METHODS: In this study, we evaluated the sugar alcohol, sorbitol, as a novel dissolution aid and examined the consequent stability of the BPA for long-term storage. U-87 MG and SAS tumor cell lines were used for in vitro and in vivo experiments. We examined the pharmacokinetics of 14C-radiolabeled BPA in sorbitol solution, administered either intravenously or subcutaneously to a mouse tumor model. Neutron irradiation was performed in conjunction with the administration of BPA in sorbitol solution using the same tumor cell lines both in vitro and in vivo. RESULTS: We found that BPA in sorbitol solution maintains stability for longer than in fructose solution, and can therefore be stored for a longer period. Pharmacokinetic studies with 14C-radiolabeled BPA confirmed that the sorbitol solution of BPA distributed through tumors in much the same way as BPA in fructose. Neutron irradiation was found to produce dose-dependent antitumor effects, both in vitro and in vivo, after the administration of BPA in sorbitol solution. CONCLUSION: In this report, we demonstrate the efficacy of BPA in sorbitol solution as the boron source in BNCT.

Correction: Imamichi et al. Extracellular Release of HMGB1 as an Early Potential Biomarker for the Therapeutic Response in a Xenograft Model of Boron Neutron Capture Therapy. Biology 2022, 11, 420.

In the original publication [...].

Usefulness of combined treatment with continuous administration of tirapazamine and mild temperature hyperthermia in γ-ray irradiation in terms of local tumour response and lung metastatic potential.

PURPOSE: To evaluate the usefulness of combined treatment with continuous administration of a hypoxic cytotoxin, tirapazamine (TPZ), and mild temperature hyperthermia (MTH) in γ-ray irradiation in terms of local tumour response and lung metastatic potential, referring to the response of intratumour quiescent (Q) cells. MATERIALS AND METHODS: B16-BL6 melanoma tumour-bearing C57BL/6 mice were continuously given 5-bromo-2'-deoxyuridine (BrdU) to label all proliferating (P) cells. The tumour-bearing mice then received γ-ray irradiation after a single intraperitoneal injection or 24 h continuous subcutaneous infusion of TPZ, either with or without MTH. Immediately after the irradiation, cells from some tumours were isolated and incubated with a cytokinesis blocker. The responses of the Q and total (= P + Q) cell populations were assessed based on the frequency of micronuclei using immunofluorescence staining for BrdU. In other tumour-bearing mice, 17 days after irradiation, macroscopic lung metastases were enumerated. RESULTS: Continuous administration elevated the sensitivity of both the total and Q cells, especially the total cells. MTH raised the sensitivity of Q cells more remarkably in both single and continuous administrations, probably because of more exposure to TPZ in intermediately hypoxic areas derived mainly from chronic hypoxia through MTH. With or without irradiation, TPZ, especially administered continuously and combined with MTH, decreased the number of lung metastases. CONCLUSION: The combination of continuous long-term administration of TPZ and MTH in γ-ray irradiation was thought to be promising because of its potential to enhance local tumour response and repress lung metastatic potential.

Extracellular Release of HMGB1 as an Early Potential Biomarker for the Therapeutic Response in a Xenograft Model of Boron Neutron Capture Therapy.

Boron neutron capture therapy (BNCT) is a non-invasive therapeutic technique for treating malignant tumors, however, methods to evaluate its therapeutic efficacy and adverse reactions are lacking. High mobility group box 1 (HMGB1) is an inflammatory molecule released during cell death. Therefore, we aimed to investigate HMGB1 as a biomarker for BNCT response, by examining the early responses of tumor cells to 10B-boronophenylalanine (BPA)-based BNCT in the Kyoto University Nuclear Reactor. Extracellular HMGB1 release was significantly increased in human squamous carcinoma SAS and melanoma A375 cells 24 h after neutron irradiation but not after γ-irradiation. At 3 days post-BPA-based BNCT irradiation in a SAS xenograft mouse model, plasma HMGB1 levels were higher than those in the non-irradiation control, and HMGB1 was detected in both nuclei and cytoplasm in tumor cells. Additionally, increased plasma HMGB1 levels post-BNCT irradiation were detected even when tumors decreased in size. Collectively, these results indicate that the extracellular HMGB1 release occurs at an early stage and is persistent when tumors are reduced in size; therefore, it is a potential biomarker for evaluating the therapeutic response during BNCT.

Synthesis and evaluation of cyclic RGD-boron cluster conjugates to develop tumor-selective boron carriers for boron neutron capture therapy.

Boron-containing agents play a key role in successful boron neutron capture therapy (BNCT). Icosahedral boron cluster-Arg-Gly-Asp (RGD) peptide conjugates were designed, synthesized, and evaluated for the biodistribution to develop tumor-selective boron carriers. Integrin αvß3 is an attractive target for anti-tumor drug delivery because of its specific expression in proliferating endothelial and tumor cells of various origins. We, therefore, selected a c(RGDfK) moiety recognizing αvß3 as an active tumor-targeting device to conjugate with icosahedral boron-10 clusters, disodium mercaptododecaborate (BSH) or o-carborane as a thermal neutron-sensitizing unit. Preparation of o-carborane derivatives involved microwave irradiation, and resulted in high yields in a short time. An in vitro cell adhesion assay on αvß3-positive U87MG and SCCVII cells demonstrated the high binding affinity of conjugates to integrin αvß3 (IC(50)=0.19-2.66 µM). Biodistribution experiments using SCCVII-bearing mice indicated that GPU-201 showed comparable tumor uptake and a significantly longer retention in tumors compared with BSH. These results suggest that GPU-201 is a promising candidate for use in BNCT.

HIF-1α affects sensitivity of murine squamous cell carcinoma to boron neutron capture therapy with BPA.

Purpose To examine whether hypoxia and Hif-1α affect sensitivity of murine squamous cell carcinoma cells to boron neutron capture therapy (BNCT).Materials and methods SCC VII and SCC VII Hif-1α-deficient mouse tumor cells were incubated under normoxic or hypoxic conditions, and cell survival after BNCT was assessed. The intracellular concentration of the 10B-carrier, boronophenylalanine-10B (BPA), was estimated using an autoradiography technique. The expression profile of SLC7A5, which is involved in the uptake of BPA, and the amount of DNA damage caused by BNCT with BPA were examined. A cell survival assay was performed on cell suspensions prepared from tumor-bearing mice.Results Hypoxia ameliorated SCC VII cell survival after neutron irradiation with BPA, but not BSH. Hypoxia-treated SCC VII cells showed decreased intracellular concentrations of BPA and the down-regulated expression of the SLC7A5 protein. BPA uptake and the SLC7A5 protein were not decreased in hypoxia-treated Hif-1α-deficient cells, the survival of which was lower than that of SCC VII cells. More DNA damage was induced in SCC VII Hif-1α-deficient cells than in SCC VII cells. In experiments using tumor-bearing mice, the survival of SCC VII Hif-1α-deficient cells was lower than that of SCC VII cells.Conclusion. Hypoxia may decrease the effects of BNCT with BPA, whereas the disruption of Hif-1α enhanced sensitivity to BNCT with BPA.

Suppression of Tumor Growth in a Rabbit Hepatic Cancer Model by Boron Neutron Capture Therapy With Liposomal Boron Delivery Systems.

BACKGROUND/AIM: Tumor cell destruction by boron neutron capture therapy (BNCT) is attributed to the nuclear reaction between 10B and thermal neutrons. The accumulation of 10B atoms in tumor cells without affecting adjacent healthy cells is crucial for effective BNCT. We previously reported that several types of liposomal boron delivery systems (BDS) delivered effective numbers of boron atoms to cancer tissues, and showed tumor-growth suppression after thermal neutron irradiation. In the present study, we examined the effects of BNCT after intra-arterial infusion of 10B-borono-dodecaborate (10BSH) by liposomal BDS in rabbit hepatic cancer models. MATERIALS AND METHODS: We prepared 10BSH-entrapped transferrin-conjugated polyethylene glycol liposomes constructed with distearoyl-boron lipid (TF-PEG-DSBL), and performed thermal neutron irradiation at the Kyoto University Institute for Integrated Radiation and Nuclear Science after intra-arterial infusion into rabbit VX-2 hepatic tumors. RESULTS: Concentrations of 10B in VX-2 tumors on delivery with TF-PEG-DSBL liposomes reached 25 ppm on day 3 after the injection. Tumor growth was suppressed by thermal neutron irradiation after intra-arterial injection of this 10BSH-containing liposomal BDS, without damage to normal cells. CONCLUSION: The present results demonstrate the applicability of 10B-containing TF-PEG-DSBL liposomes as a novel intra-arterial boron carrier in BNCT for cancer.

BNCT for primary synovial sarcoma.

Synovial sarcoma is a rare tumor requiring new treatment methods. A 46-year-old woman with primary monophasic synovial sarcoma in the left thigh involving the sciatic nerve, declining surgery because of potential dysfunction of the affected limbs, received two courses of BNCT. The tumor thus reduced was completely resected with no subsequent recurrence. The patient is now able to walk unassisted, and no local recurrence has been observed, demonstrating the applicability of BNCT as adjuvant therapy for synovial sarcoma. Further study and analysis with more experience accumulation are needed to confirm the real impact of BNCT efficacy for its application to synovial sarcoma.

Ascorbic acid 2-glucocide reduces micronucleus induction in distant splenic T lymphocytes following head irradiation.

PURPOSE: Evidence from in vivo studies suggests there are enhanced radiation effects in abscopal regions after local head gamma ray irradiation. Splenocyte apoptosis and T lymphocyte micronuclei were induced at higher rates than what would be estimated given the dose at a shielded, distant position. In addition, we evaluated the radio-protective effects of ascorbic acid, acting as a radical scavenger on enhanced radiation effects in the shielded spleen following local head irradiation. METHODS AND MATERIALS: The heads of C3H mice were exposed to gamma-rays (10-20Gy), while the other parts of the body were shielded with a 5cm-thick lead block. The effective dose for the spleen was calculated at 1.0-2.0Gy. Splenocytes were isolated 24h after cranial irradiation and their apoptosis was measured with an Elisa kit (Roche). The induction of T lymphocyte micronuclei was studied using the cytokinesis-block micronucleus assay. The ascorbic acid glucoside, 2-O-alpha-d-glucopyranosyl-l-ascorbic acid (AA-2G), was orally administered to mice 1h before whole body irradiation. The radio protective effects of AA-2G were estimated by comparing the induction of splenocyte damage (by apoptosis) and micronucleus induction. RESULTS: The splenocyte damage, as measured by the above two methods, was more excessive than what would be expected given exposure to 1.0-2.0Gy of radiation. Our results suggest that the effects were enhanced in a distant, non-irradiated organ after localized irradiation. Plasma ascorbic acid concentrations were increased 8-10x over control. Treatment with ascorbic acid slightly protected mouse splenocytes from the induction of apoptosis by the enhanced effects of radiation in the abscopal region. However, ascorbic acid significantly inhibited micronucleus induction in splenic T lymphocytes following local head irradiation. CONCLUSIONS: Our results suggest that ascorbic acid effectively scavenged radiation-induced radicals and protected against the enhanced effects of radiation in an abscopal region after local head gamma ray irradiation.

Effect of Rapamycin on the Radio-Sensitivity of Cultured Tumor Cells Following Boron Neutron Capture Reaction.

BACKGROUND: Mammalian target of rapamycin (mTOR) signaling pathway has been implicated in multiple mechanisms of resistance to anticancer drugs and poor treatment outcomes in various human cancers. Meanwhile, clinical boron neutron capture therapy (BNCT) has been carried out for patients with malignant gliomas, melanomas, inoperable head and neck tumors and oral cancers. This study aimed to evaluate the effect of mTOR inhibition on radio-sensitivity of cultured tumor cells in BNCT, employing p-boronophenylalanine-10B (BPA) as a 10B-carrier. METHODS: Cultured SAS cells had been incubated for 48 h at RPMI medium with mTOR inhibitor, rapamycin at the dose of 1 µM, and then continuously incubated for 2 more hours at RPMI medium containing both BPA at the 10B concentration of 10 ppm and rapamycin (1 µM). Subsequently, the SAS cells received reactor neutron beams, and then surviving fraction and micronucleus frequency were determined. RESULTS: SAS cells incubated with rapamycin showed resistance to γ-rays compared with no treatment with rapamycin. The efficiency of delivery of 10B from BPA into cultured SAS cells was reduced through combining with rapamycin, leading to reduced sensitivity following boron neutron capture reaction. CONCLUSIONS: Since many tumors are characterized by deregulated PI3K/AKT/mTOR pathway, rapamycin is thought to inhibit the pathway and tumor growth. However, it was revealed that rapamycin can also inhibit the transport of 10B for BNCT into tumor cells. When BNCT is combined with mTOR inhibitor, the efficiency as cancer treatment can be reduced by repression of distributing 10B in tumor cells, warranting precaution when the two strategies are combined.