The Anti-Proliferative Effect of Boron Neutron Capture Therapy in a Prostate Cancer Xenograft Model

Novel Self-Forming Nanosized DDS Particles for BNCT: Utilizing A Hydrophobic Boron Cluster and Its Molecular Glue Effect

BNCT is a non-invasive cancer therapy that allows for cancer cell death without harming adjacent cells. However, the application is limited, owing to the challenges of working with clinically approved boron (B) compounds and drug delivery systems (DDS). To address the issues, we developed self-forming nanoparticles consisting of a biodegradable polymer, namely, “AB-type Lactosome (AB-Lac)” loaded with B compounds. Three carborane isomers (o-, m-, and p-carborane) and three related alkylated derivatives, i.e., 1,2-dimethy-o-carborane (diC1-Carb), 1,2-dihexyl-o-carborane (diC6-Carb), and 1,2-didodecyl-o-carborane (diC12-Carb), were separately loaded. diC6-Carb was highly loaded with AB-Lac particles, and their stability indicated the “molecular glue” effect. The efficiency of in vitro B uptake of diC6-Carb for BNCT was confirmed at non-cytotoxic concentration in several cancer cell lines. In vivo/ex vivo biodistribution studies indicated that the AB-Lac particles were remarkably accumulated within 72 h post-injection in the tumor lesions of mice bearing syngeneic breast cancer (4T1) cells, but the maximum accumulation was reached at 12 h. In ex vivo B biodistribution, the ratios of tumor/normal tissue (T/N) and tumor/blood (T/Bl) of the diC6-Carb-loaded particles remained stably high up to 72 h. Therefore, we propose the diC6-Carb-loaded AB-Lac particles as a promising candidate medicine for BNCT.

Anti-tumor effect of boron neutron capture therapy in pelvic human colorectal cancer in a mouse model

Local recurrence of colorectal cancer (CRC) can occur in patients after curative resection, and additional surgical resection may therefore be required; however, this is a significant burden for patients, because additional surgical resection may necessitate the resection of other organs such as the bladder, prostate, uterus, or sacral bone. Therefore, there is a need for alternative therapeutic strategies. We focused on boron neutron capture therapy (BNCT) as a treatment modality that can selectively target tumor cells without excessive damage to normal tissues. The usefulness of BNCT to pelvic CRC remains unknown. This study investigated the anti-cancer effect of boronophenylalanine (BPA)-mediated BNCT in a previously established mouse model of pelvic recurrence of CRC. Uptake of BPA in CRC was observed both in vitro and in vivo, and the concentrations were sufficient for BNCT. Our results are the first to show that BPA-mediated BNCT prolonged the survival of experimental mice with pelvic tumors; moreover, it did not cause any obvious severe side effects in the treated animals. In conclusion, BPA-mediated BNCT could contribute to treating local recurrence of pelvic CRC.

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.

Boron neutron capture therapy for urological cancers

Boron neutron capture therapy is based on a nuclear reaction between the nonradioactive isotope boron-10 and either low-energy thermal neutrons or high-energy epithermal neutrons, which generate high linear energy transfer α particles and a recoiled lithium nucleus (⁷ Li) that selectively destroys the DNA helix in tumor cells. Boron neutron capture therapy is an emerging procedure aimed at improving the therapeutic ratio for the traditional treatment of various malignancies, which has been studied clinically in a variety of diseases, including glioblastoma, head and neck cancer, cutaneous melanoma, hepatocellular carcinoma, lung cancer, and extramammary Paget's disease. However, boron neutron capture therapy has not been clinically performed for urological cancers, excluding genital extramammary Paget's disease that appeared at the scrotum to penis area. In this review, we aimed to provide an updated summary of the current clinical literature of patients treated with boron neutron capture therapy and to focus on the future prospects of boron neutron capture therapy for urological cancers.

Molecular characterization of canine SHP2 mutants and anti-tumour effect of SHP2 inhibitor, SHP099, in a xenograft mouse model of canine histiocytic sarcoma

Canine histiocytic sarcoma (HS) is an aggressive and highly metastatic neoplasm. Mutations in src homology 2 domain-containing phosphatase 2 (SHP2; encoded by PTPN11), which recently have been identified in canine HS tumour cells, could be attractive therapeutic targets for SHP099, an allosteric inhibitor of SHP2. Here, molecular characteristics of wild-type SHP2 and four SHP2 mutants (p.Ala72Gly, p.Glu76Gln, p.Glu76Ala and p.Gly503Val), including one that was newly identified in the present study, were investigated. Furthermore, in vivo effects of SHP099 on a HS cell line carrying SHP2 p.Glu76Ala were examined using a xenograft mouse model. While SHP2 Glu76 mutant cell lines and SHP2 wild-type/Gly503 mutant cell lines are highly susceptible and non-susceptible to SHP099, respectively, a cell line carrying the newly identified SHP2 p.Ala72Gly mutation exhibited moderate susceptibility to SHP099. Among recombinant wild-type protein and four mutant SHP2 proteins, three mutants (SHP2 p.Ala72Gly, p.Glu76Gln, p.Glu76Ala) were constitutively activated, while no activity was detected in wild-type SHP2 and SHP2 p.Gly503Val. Activities of these constitutively activated proteins were suppressed by SHP099; in particular, Glu76 mutants were highly sensitive. In the xenograft mouse model, SHP099 showed anti-tumour activity against a SHP2 p.Glu76Ala mutant cell line. Thus, there was heterogeneity in molecular characteristics among SHP2 mutants. SHP2 p.Glu76Ala and perhaps p.Glu76Gln, but not wild-type SHP2 or SHP2 p.Gly503Val, were considered to be oncogenic drivers targetable with SHP099 in canine HS. Further studies will be needed to elucidate the potential of SHP2 p.Ala72Gly as a therapeutic target of SHP099 in canine HS.

Evaluation of local, regional and abscopal effects of Boron Neutron Capture Therapy (BNCT) combined with immunotherapy in an ectopic colon cancer model

OBJECTIVE

The aim of the present study was to evaluate the local and regional therapeutic efficacy and abscopal effect of BNCT mediated by boronophenyl-alanine, combined with Bacillus Calmette-Guerin (BCG) as an immunotherapy agent in this model.

METHODS

The local effect of treatment was evaluated in terms of tumor response in the irradiated tumor-bearing right hind flank. Metastatic spread to tumor-draining lymph nodes was analyzed as an indicator of regional effect. The abscopal effect of treatment was assessed as tumor growth inhibition in the contralateral (non-irradiated) left hind flank inoculated with tumor cells 2 weeks post-irradiation. The experimental groups BNCT, BNCT + BCG, BCG, Beam only (BO), BO +BCG, SHAM (tumor-bearing, no treatment, same manipulation) were studied.

RESULTS

BNCT and BNCT + BCG induced a highly significant local anti-tumor response, whereas BCG alone induced a weak local effect. BCG and BNCT + BCG induced a significant abscopal effect in the contralateral non-irradiated leg. The BNCT + BCG group showed significantly less metastatic spread to tumor-draining lymph nodes vs SHAM and vs BO.

CONCLUSION

This study suggests that BNCT + BCG-immunotherapy would induce local, regional and abscopal effects in tumor-bearing animals. BNCT would be the main effector of the local anti-tumor effect whereas BCG would be the main effector of the abscopal effect.

ADVANCES IN KNOWLEDGE

Although the local effect of BNCT has been widely evidenced, this is the first study to show the local, regional and abscopal effects of BNCT combined with immunotherapy, contributing to comprehensive cancer treatment with combined therapies.

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.

An In Vivo Mouse Model of Pelvic Recurrence of Human Colorectal Cancer

Pelvic recurrence of colorectal cancer is a crucial problem because radical surgery can lead to excessive invasion. Novel therapeutic strategies are required instead of surgery. However, there are few suitable models because of the difficulty in transplanting and observing tumors in the pelvis. We have established an appropriate injection site suitable for the establishment of colorectal cancer pelvic recurrence that allows for the observation of tumor growth. DLD-1 cells stably expressing luciferase (DLD-1 clone#1-Luc) were inoculated into various points of female BALB/c nude mice and the engrafted cells were analyzed with an imaging system employing bioluminescent signals and computed tomography. Weekly analysis with the imaging system showed that a triangular area defined by the vagina, the anus, and the ischial spine was suitable for the engraftment of pelvic tumors. The imaging system was able to detect the engrafted tumor 7 days after the inoculation of cells. Weight loss was observed in our model, and overall survival was 21–42 days. Tumor involvement of adjacent organs was detected histopathologically, as is the case in the clinical situation. These findings suggest that this model is valid for evaluations of the therapeutic effects of novel treatments under development. It is hoped that this model will be used in preclinical research.

Preparation of pentagamaboronon-0 and its fructose and sorbitol complexes as boron carrier for boron neutron capture therapy (BNCT) application

Development of specific and selective boron carriers is indispensable for boron neutron capture therapy (BNCT) application. Pentagamaboronon-0 (PGB-0) is a promising candidate as boron carrier compound due to the low but selective cytotoxicity in breast cancer cells. Formerly we reported synthesis of PGB-0 which was ineffective due to its low aqueous solubility. In the present study, we, therefore, introduced the new PGB-0 preparation complexed with sugars to increase its solubility in water. By synthesizing at room temperature and using flash chromatography for the purification, we produced PGB-0 with a yield of 40%. PGB-0 fructose complex (PGB-0-F) and PGB-0 sorbitol complex (PGB-0-Sor) were obtained with smaller particle size compared to PGB-0 suspension in water. Based on the MTT assay, the cytotoxicity of PGB-0-F and PGB-0-Sor were higher than PGB-0 even though still categorized as low cytotoxic agents. In conclusion, we provided PGB-0 with a new method and improved its solubility in water. Further investigations are still needed to develop more efficient PGB-0 as boron carrier for BNCT in various cancers.

Biophysical characterization of a model antibody drug conjugate

Antibody drug conjugates (ADC) are important next-generation biopharmaceuticals and thus require stringent structure characterization as is the case for monoclonal antibodies. We have tested several biophysical techniques, i.e., circular dichroism, analytical ultracentrifugation, differential scanning calorimetry and fluorescence spectroscopy, to characterize a fluorescein-labeled monoclonal antibody as a model ADC. These techniques indicated possible small structure and stability changes by the conjugation, while largely retaining the tertiary structure of the antibody, consistent with unaltered biological activities. Thus, the above biophysical techniques are effective at detecting changes in the structural properties of ADC.