Neutron autoradiography to study boron compound microdistribution in an oral cancer model

Boric Acid Affects Cell Proliferation, Apoptosis, and Oxidative Stress in ALL Cells

T-cell acute lymphoblastic leukemia (T-ALL) is a type of acute lymphoblastic leukemia from early T-cell progenitors. Interest grows in creating less toxic agents and therapies for chemo-resistant T-ALL cancer. Recently, elemental boron has special properties useful in the creation of new drugs. Studies have revealed the cytotoxic properties of boric acid (BA) on cancer, but not fully understood. We aimed to investigate the effect of BA on cell proliferation, apoptosis, and oxidative stress in the Jurkat cells. The effects of BA on cell viability were determined by 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) assay for 24-48-72 h. The impact of BA on apoptosis was analyzed by acridine orange/ethidium bromide. Expression of apoptosis regulatory genes (Bcl-2, Bax, Caspase-3-8-9) and apoptotic miRNA (miR-21) was used by real-time quantitative polymerase chain reaction (RT-qPCR). The total oxidant status (TOS), total antioxidant status (TAS), and the oxidative stress index (OSI) value were calculated for oxidative stress. We determined the cytotoxic activity of BA on Jurkat cells by using XTT and defined the IC50 concentration (802.7 μg/mL) of BA. The findings clearly show that BA inhibited Jurkat cell proliferation dose-dependently. BA induced apoptosis through downregulated anti-apoptotic genes, and upregulated pro-apoptotic genes. Additionally, we found that BA significantly reduced the expression of miR-21 (p<0.001). Our findings demonstrated that different doses of BA increased TAS levels while decreasing TOS levels in Jurkat cells. Our study suggests that BA might be potential anti-cancer agent candidate in ALL via inhibition of cell proliferation, induced apoptosis, and reducing the amounts of anti-oxidants in cells.

Neutron spectroscopy with TENIS using an artificial neural network

In this research, a ThErmal Neutron Imaging System (TENIS) consisting of two perpendicular sets of plastic scintillator arrays for boron neutron capture therapy (BNCT) application has been investigated in a completely different approach for neutron energy spectrum unfolding. TENIS provides a thermal neutron map based on the detection of 2.22 MeV gamma-rays resulting from 1H(nth, γ)2D reactions, but in the present study, the 70-pixel thermal neutron images have been used as input data for unfolding the energy spectrum of incident neutrons. Having generated the thermal neutron images for 109 incident mono-energetic neutrons, a 70 × 109 response matrix has been generated using the MCNPX2.6 code for feeding into the artificial neural network tools of MATLAB. The errors of the final results for mono-energetic neutron sources are less than 10% and the root mean square error (RMSE) for the unfolded neutron spectrum of 252Cf is about 0.01. The agreement of the unfolding results for mono-energetic and 252Cf neutron sources confirms the performance of the TENIS system as a neutron spectrometer.

Optimizing Boron Neutron Capture Therapy (BNCT) to Treat Cancer: An Updated Review on the Latest Developments on Boron Compounds and Strategies

Boron neutron capture therapy (BNCT) is a tumor-selective particle radiotherapy. It combines preferential boron accumulation in tumors and neutron irradiation. The recent initiation of BNCT clinical trials employing hospital-based accelerators rather than nuclear reactors as the neutron source will conceivably pave the way for new and more numerous clinical trials, leading up to much-needed randomized trials. In this context, it would be interesting to consider the implementation of new boron compounds and strategies that will significantly optimize BNCT. With this aim in mind, we analyzed, in this review, those articles published between 2020 and 2023 reporting new boron compounds and strategies that were proved therapeutically useful in in vitro and/or in vivo radiobiological studies, a critical step for translation to a clinical setting. We also explored new pathologies that could potentially be treated with BNCT and newly developed theranostic boron agents. All these radiobiological advances intend to solve those limitations and questions that arise during patient treatment in the clinical field, with BNCT and other therapies. In this sense, active communication between clinicians, radiobiologists, and all disciplines will improve BNCT for cancer patients, in a cost- and time-effective way.

Enhanced Resolution of Neutron Autoradiography with UV-C Sensitization to Study Boron Microdistribution in Animal Models

The assessment of boron microdistribution is essential to evaluate the suitability of boron neutron capture therapy (BNCT) in different biological models. In our laboratory, we have reported a methodology to produce cell imprints on polycarbonate through UV-C sensitization. The aim of this work is to extend the technique to tissue samples in order to enhance spatial resolution. As tissue structure largely differs from cultured cells, several aspects must be considered. We studied the influence of the parameters involved in the imprint and nuclear track formation, such as neutron fluence, different NTDs, etching and UV-C exposure times, tissue absorbance, thickness, and staining, among others. Samples from different biological models of interest for BNCT were used, exhibiting homogeneous and heterogeneous histology and boron microdistribution. The optimal conditions will depend on the animal model under study and the resolution requirements. Both the imprint sharpness and the fading effect depend on tissue thickness. While 6 h of UV-C was necessary to yield an imprint in CR-39, only 5 min was enough to observe clear imprints on Lexan. The information related to microdistribution of boron obtained with neutron autoradiography is of great relevance when assessing new boron compounds and administration protocols and also contributes to the study of the radiobiology of BNCT.

Measurement of an evaporation coefficient in tissue sections as a correction factor for 10B determination

Boron neutron capture therapy (BNCT) is a cancer treatment option that combines preferential uptake of a boron compound in tumors and irradiation with thermal neutrons. For treatment planning, the boron concentration in different tissues must be considered. Neutron autoradiography using nuclear track detectors (NTD) can be applied to study both the concentration and microdistribution of boron in tissue samples. Histological sections are obtained from frozen tissue by cryosectioning. When the samples reach room temperature, they undergo an evaporation process, which leads to an increase in the boron concentration. To take this effect into account, certain correction factors (evaporation coefficients, CEv) must be applied. With this aim, a protocol was established to register and analyze mass variation of tissue sections, measured with a semimicro scale. Values of ambient temperature, pressure, and humidity were simultaneously recorded. Reproducible results of evaporation curves and CEv values were obtained for different tissue samples, which allowed the systematization of the procedure. This study could contribute to a more precise determination of boron concentration in tissue samples through the neutron autoradiography technique, which is of great relevance to make dosimetric calculations in BNCT.

Animal Tumor Models for Boron Neutron Capture Therapy Studies (Excluding Central Nervous System Solid Tumors)

Translational research in adequate experimental models is necessary to optimize boron neutron capture therapy (BNCT) for different pathologies. Multiple radiobiological in vivo studies have been performed in a wide variety of animal models, studying multiple boron compounds, routes of compound administration, and a range of administration strategies. Animal models are useful for the study of the stability and potential toxicity of new boron compounds or delivery systems, BNCT theranostic strategies, the evaluation of biomarkers to monitor BNCT therapeutic and adverse effects, and to study the BNCT immune response by the host against tumor cells. This article will mention examples of these studies, highlighting the importance of experimental animal models for the advancement of BNCT. Animal models are essential to design novel, safe, and effective clinical BNCT protocols for existing or new targets for BNCT.

Importance of radiobiological studies for the advancement of boron neutron capture therapy (BNCT)

Boron neutron capture therapy (BNCT) is a tumour selective particle radiotherapy, based on the administration of boron carriers incorporated preferentially by tumour cells, followed by irradiation with a thermal or epithermal neutron beam. BNCT clinical results to date show therapeutic efficacy, associated with an improvement in patient quality of life and prolonged survival. Translational research in adequate experimental models is necessary to optimise BNCT for different pathologies. This review recapitulates some examples of BNCT radiobiological studies for different pathologies and clinical scenarios, strategies to optimise boron targeting, enhance BNCT therapeutic effect and minimise radiotoxicity. It also describes the radiobiological mechanisms induced by BNCT, and the importance of the detection of biomarkers to monitor and predict the therapeutic efficacy and toxicity of BNCT alone or combined with other strategies. Besides, there is a brief comment on the introduction of accelerator-based neutron sources in BNCT. These sources would expand the clinical BNCT services to more patients, and would help to make BNCT a standard treatment modality for various types of cancer. Radiobiological BNCT studies have been of utmost importance to make progress in BNCT, being essential to design novel, safe and effective clinical BNCT protocols.

Anti-cancer effect of boron derivatives on small-cell lung cancer

BACKGROUND

Anti-cancer activity of boron has been reported. Although many boron derivatives such as boric acid (BA) have been discovered to have anticancer effects, there are many boron derivatives whose anticancer effects have not yet been discovered. Some of these include sodium pentaborate pentahydrate (NaB), which has had limited research on its anticancer effects, and sodium perborate tetrahydrate (SPT), whose anticancer effect has yet to be discovered. The aim of this study was to investigate the anti-cancer effects of boric acid (BA), sodium pentaborate pentahydrate (NaB), and sodium perborate tetrahydrate (SPT) against small-cell lung cancer (SCLC) cell line DMS-114 cells in vitro.

METHODS

EC50 concentrations and effects of BA, NaB, and SPT on cell survival were detected with an MTS assay. The colony-forming unit (CFU) assay was used to assess their effects on cell colony formation capability. Their effects on apoptosis were determined by an Annexin-V assay. A cell cycle analysis was performed to understand at what phase the cell cycle is arrested. Real-Time PCR (RT-PCR) was used to evaluate the mRNA levels of apoptotic, anti-apoptotic, and tumor suppressor genes. Western blotting was used to determine the protein levels of p53 and Caspase 3.

RESULTS

The survival rates of DMS-114 cells decreased with BA, NaB and SPT after 72 h of treatment and the EC50 concentrations ​​of DMS-114 and MRC-5 cells differed 5.5-fold in BA treatment, 5,2-fold in NaB treatment and 10-fold in SPT treatment. Colony unit numbers were decreased from 350 to 128, from 320 to 95, and from 430 to 96 in the BA, NaB, and SPT treatment groups, respectively. The apoptosis increased by 10, 19, and 42 percent after treatment with BA, NaB, and SPT for 72 h, respectively. Following 72 h of treatment with BA, NaB, and SPT, some pro-apoptotic and tumor suppressor genes were upregulated and some anti-apoptotic genes were downregulated. Cell cycle arrests were detected at the G2/M phase in the BA, and NaB treatment groups and at the Sub-G1 phase in the SPT treatment group. The protein levels of P53 and Caspase 3 increased with BA, NaB and SPT treatment for 72 h.

CONCLUSIONS

BA, NaB and SPT show anti-cancer activity in the DMS-114 cell line without damaging MRC-5 cells, and some of the molecular mechanisms are involved in apoptosis and cell cycle arrest.

Quantitative autoradiography in boron neutron capture therapy considering the particle ranges in the samples

PURPOSE

Boron neutron capture therapy is a cellular-scale particle therapy exploiting boron neutron capture reactions in boron compounds distributed in tumour cells. Its therapeutic effect depends on both the accumulation of boron in tumour cells and the neutron fluence. Autoradiography is used to visualise the micro-distribution of boron compounds.

METHODS

Here, we present an equation for the relationship between boron concentration and pit density on the solid-state nuclear track detector, taking into consideration the particle ranges in the samples. This equation is validated using liver-tissue sections and boron standard solutions. Moreover, we present a simple co-localisation system for pit and tissue-section images that requires no special equipment.

RESULTS

The equation reproduces the experimentally observed trends between boron concentration and pit density. This equation provides a theoretical explanation for the widely used calibration curve between pit density and boron concentration; it also provides a method to correct for differences of tissue-section thickness in quantitative autoradiography.

CONCLUSIONS

Using the equation together with this co-localisation system could improve micro-scale quantitative estimation in tissue sections.

Neutron autoradiography to study the microdistribution of boron in the lung

In Argentina, a multi-institutional project has been established to assess the feasibility of applying BNCT ex-situ to the treatment of patients with multiple metastases in both lungs. Within this context, this work aims at applying the neutron autoradiography technique to study boron microdistribution in the lung. A comprehensive analysis of the different aspects for the generation of autoradiographic images of both normal and metastatic BDIX rat lungs was achieved. Histology, boron uniformity, optimal tissue thickness and water content in tissue were explored for the two types of samples. A qualitative and a quantitative analysis were performed. No heterogeneities in uptake were observed in normal lung. Conversely, samples with metastasis showed preferential boron uptake in the tumour areas with respect to surrounding tissue. Surrounding tissue would present a slightly higher uptake of boron than the normal lung. Quantitative results of boron concentration values and ratios determined by neutron autoradiography were obtained. In order to contribute to BNCT dosimetry, further analysis increasing the number of samples is warranted.

Neutron Autoradiography Combined With UV-C Sensitization: Toward the Intracellular Localization of Boron

Our group has reported the imprint formation of biological material on polycarbonate nuclear track detectors by UV-C exposure, which is used as an approach to simultaneously visualize cell imprints and nuclear tracks coming from the boron neutron capture reaction. Considering that the cell nucleus has a higher UV-C absorption than the cytoplasm and that hematoxylin preferentially stains the nucleus, we proposed to enhance the contrast between these two main cell structures by hematoxylin staining before UV-C sensitization. In this study, several experiments were performed in order to optimize UV-C exposure parameters and chemical etching conditions for cell imprint formation using the SK-BR-3 breast cancer cell line. The proposed method improves significantly the resolution of the cell imprints. It allows clear differentiation of the nucleus from the rest of the cell, together with nuclear tracks pits. Moreover, it reduces considerably the UV-C exposure time, an important experimental issue. The proposed methodology can be applied to study the boron distribution independently from the chosen cell line and/or boron compounds.

Electroporation optimizes the uptake of boron-10 by tumor for boron neutron capture therapy (BNCT) mediated by GB-10: a boron biodistribution study in the hamster cheek pouch oral cancer model

Boron neutron capture therapy (BNCT) is a promising cancer binary therapy modality that utilizes the nuclear capture reaction of thermal neutrons by boron-10 resulting in a localized release of high- and low-linear energy transfer (LET) radiation. Electrochemotherapy (ECT) is based on electroporation (EP) that induces opening of pores in cell membranes, allowing the entry of compounds. Because EP is applied locally to a tumor, the compound is incorporated preferentially by tumor cells. Based on the knowledge that the therapeutic success of BNCT depends centrally on the boron content in tumor and normal tissues and that EP has proven to be an excellent facilitator of tumor biodistribution of an anti-tumor agent, the aim of this study was to evaluate if EP can optimize the delivery of boronated compounds. We performed biodistribution studies and qualitative microdistribution analyses of boron employing the boron compound sodium decahydrodecaborate (GB-10) + EP in the hamster cheek pouch oral cancer model. Syrian hamsters with chemically induced exophytic squamous cell carcinomas were used. A typical EP treatment was applied to each tumor, varying the moment of application with respect to the administration of GB-10 (early or late). The results of this study showed a significant increase in the absolute and relative tumor boron concentration and optimization of the qualitative microdistribution of boron by the use of early EP + GB-10 versus GB-10 without EP. This strategy could be a tool to improve the therapeutic efficacy of BNCT/GB-10 in vivo.

Extending neutron autoradiography technique for boron concentration measurements in hard tissues

The neutron autoradiography technique using polycarbonate nuclear track detectors (NTD) has been extended to quantify the boron concentration in hard tissues, an application of special interest in Boron Neutron Capture Therapy (BNCT). Chemical and mechanical processing methods to prepare thin tissue sections as required by this technique have been explored. Four different decalcification methods governed by slow and fast kinetics were tested in boron-loaded bones. Due to the significant loss of the boron content, this technique was discarded. On the contrary, mechanical manipulation to obtain bone powder and tissue sections of tens of microns thick proved reproducible and suitable, ensuring a proper conservation of the boron content in the samples. A calibration curve that relates the ¹⁰B concentration of a bone sample and the track density in a Lexan NTD is presented. Bone powder embedded in boric acid solution with known boron concentrations between 0 and 100 ppm was used as a standard material. The samples, contained in slim Lexan cases, were exposed to a neutron fluence of 10¹² cm^-2 at the thermal column central facility of the RA-3 reactor (Argentina). The revealed tracks in the NTD were counted with an image processing software. The effect of track overlapping was studied and corresponding corrections were implemented in the presented calibration curve. Stochastic simulations of the track densities produced by the products of the ¹⁰B thermal neutron capture reaction for different boron concentrations in bone were performed and compared with the experimental results. The remarkable agreement between the two curves suggested the suitability of the obtained experimental calibration curve. This neutron autoradiography technique was finally applied to determine the boron concentration in pulverized and compact bone samples coming from a sheep experimental model. The obtained results for both type of samples agreed with boron measurements carried out by ICP-OES within experimental uncertainties. The fact that the histological structure of bone sections remains preserved allows for future boron microdistribution analysis.