BNCT induced immunomodulatory effects contribute to mammary tumor inhibition

In vivo investigation of boron-rich nanodrugs for treating triple-negative breast cancers via boron neutron capture therapy

Triple-negative breast cancer (TNBC) is characterized by highly proliferative cancer cells and is the only subtype of breast cancer that lacks a targeted therapy. Boron neutron capture therapy (BNCT) is an approach that combines chemotherapy with radiotherapy and can potentially offer beneficial targeted treatment for TNBC patients owing to its unique ability to eradicate cancer cells selectively while minimizing damage to the surrounding healthy cells. Since BNCT relies on specific delivery of a high loading of B10 to the tumor site, there is growing research interest to develop more potent boron-based drugs for BNCT that can overcome the limitations of small-molecule boron compounds. In this study, polyethylene-glycol-coated boron carbon oxynitride nanoparticles (PEG@BCNO) of size 134.2±23.6nm were prepared as a promising drug for BNCT owing to their high boron content and enhanced biocompatibility. The therapeutic efficiency of PEG@BCNO was compared with a state-of-the-art 10BPA boron drug in mice bearing MDA-MB-231 tumor. In the orthotopic mouse model, PEG@BCNO showed higher B10 accumulation in the tumor tissues (6 μg 10B/g tissue compared to 3 μg 10B/g tissue in mice administered B10-enriched 10BPA drug) despite using the naturally occurring 11B/10B boron precursor in the preparation of the BCNO nanoparticles. The in vivo biodistribution of PEG@BCNO in mice bearing MDA-MB-231 showed a tumor/blood ratio of ~3.5, which is comparable to that of the state-of-the-art 10BPA-fructose drug. We further demonstrated that upon neutron irradiation, the mice bearing MDA-MB-231 tumor cells treated with PEG@BCNO and 10BPA showed tumor growth delay times of 9 days and 1 day, respectively, compared to mice in the control group after BNCT. The doubling times (DTs) for mice treated with PEG@BCNO and 10BPA as well as mice in the control group were calculated to be 31.5, 19.8, and 17.7 days, respectively. Immunohistochemical staining for the p53 and caspase-3 antibodies revealed that mice treated with PEG@BCNO showed lower probability of cancer recurrence and greater level of cellular apoptosis than mice treated with 10BPA and mice in the control group. Our study thus demonstrates the potential of pegylated BCNO nanoparticles in effectively inhibiting the growth of TNBC tumors compared to the state-of-the-art boron drug 10BPA.

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.

Macrophages as Promising Carriers for Nanoparticle Delivery in Anticancer Therapy

Macrophages play a critical role in the immune response due to their ability to recognize and remove pathogens, as well as present antigens, which are involved in inflammation, but they are also one of the most abundant immune cell populations present in the tumor microenvironment. In recent years, macrophages have become promising cellular carriers for drug and nanoparticle delivery to the tumor microenvironment, mainly due to their natural properties such as biocompatibility, degradability, lack of immunogenicity, long half-life in circulation, crossing biological barriers, and the possibility of migration and accumulation at a site of inflammation such as a tumor. For the effectiveness of this therapeutic strategy, known as "Trojan horse", it is important that the nanoparticles engulfed by macrophages do not affect their proper functioning. In our review, we discussed how the size, shape, chemical and mechanical properties of nanoparticles influence their internalization by macrophages. In addition, we described the promising research utilizing macrophages, their cell membranes and macrophage-derived exosomes as drug carriers in anticancer therapy. As a prospect of the wider use of this therapeutic strategy, we postulate its future application in boron delivery to the tumor environment in boron neutron capture therapy.

Therapeutic Efficacy, Radiotoxicity and Abscopal Effect of BNCT at the RA-3 Nuclear Reactor Employing Oligo-Fucoidan and Glutamine as Adjuvants in an Ectopic Colon Cancer Model in Rats

Boron neutron capture therapy (BNCT) is based on the preferential uptake of ¹⁰B compounds by tumors, followed by neutron irradiation. The aim of this study was to assess, in an ectopic colon cancer model, the therapeutic efficacy, radiotoxicity, abscopal effect and systemic immune response associated with (BPA/Borophenylalanine+GB-10/Decahydrodecaborate)-BNCT (Comb-BNCT) alone or in combination with Oligo-Fucoidan (O-Fuco) or Glutamine (GLN), compared to the "standard" BPA-BNCT protocol usually employed in clinical trials. All treatments were carried out at the RA-3 nuclear reactor. Boron biodistribution studies showed therapeutic values above 20 ppm ¹⁰B in tumors. At 7 weeks post-treatment, the ratio of tumor volume post-/pre-BNCT was significantly smaller for all BNCT groups vs. SHAM (p < 0.05). The parameter "incidence of tumors that underwent a reduction to ≤50% of initial tumor volume" exhibited values of 62% for Comb-BNCT alone, 82% for Comb-BNCT+GLN, 73% for Comb-BNCT+O-Fuco and only 30% for BPA-BNCT. For BPA-BNCT, the incidence of severe dermatitis was 100%, whereas it was significantly below 70% (p ≤ 0.05) for Comb-BNCT, Comb-BNCT+O-Fuco and Comb-BNCT+GLN. Considering tumors outside the treatment area, 77% of Comb-BNCT animals had a tumor volume lower than 50 mm³ vs. 30% for SHAM (p ≤ 0.005), suggesting an abscopal effect of Comb-BNCT. Inhibition of metastatic spread to lymph nodes was observed in all Comb-BNCT groups. Considering systemic aspects, CD8⁺ was elevated for Comb-BNCT+GLN vs. SHAM (p ≤ 0.01), and NK was elevated for Comb-BNCT vs. SHAM (p ≤ 0.05). Comb-BNCT improved therapeutic efficacy and reduced radiotoxicity compared to BPA-BNCT and induced an immune response and an abscopal effect.

Particle radiotherapy in the era of radioimmunotherapy

Radiotherapy (RT) is one of the key modalities for cancer treatment, and more than 70% of tumor patients will receive RT during the course of their disease. Particle radiotherapy, such as proton radiotherapy, carbon-ion radiotherapy (CIRT) and boron neutron capture therapy (BNCT), is currently available for the treatment of patients Immunotherapy combined with photon RT has been successfully used in the clinic. The effect of immunotherapy combined with particle RT is an area of interest. However, the molecular mechanisms underlying the effects of combined immunotherapy and particle RT remain largely unknown. In this review, we summarize the properties of different types of particle RT and the mechanisms underlying their radiobiological effects. Additionally, we compared the main molecular players in photon RT and particle RT and the mechanisms involved the RT-mediated immune response.

Next-Generation Boron Drugs and Rational Translational Studies Driving the Revival of BNCT

BNCT is a high-linear-energy transfer therapy that facilitates tumor-directed radiation delivery while largely sparing adjacent normal tissues through the biological targeting of boron compounds to tumor cells. Tumor-specific accumulation of boron with limited accretion in normal cells is the crux of successful BNCT delivery. Given this, developing novel boronated compounds with high selectivity, ease of delivery, and large boron payloads remains an area of active investigation. Furthermore, there is growing interest in exploring the immunogenic potential of BNCT. In this review, we discuss the basic radiobiological and physical aspects of BNCT, traditional and next-generation boron compounds, as well as translational studies exploring the clinical applicability of BNCT. Additionally, we delve into the immunomodulatory potential of BNCT in the era of novel boron agents and examine innovative avenues for exploiting the immunogenicity of BNCT to improve outcomes in difficult-to-treat malignancies.

Enhancement in the Therapeutic Efficacy of In Vivo BNCT Mediated by GB-10 with Electroporation in a Model of Oral Cancer

Boron neutron capture therapy (BNCT) combines preferential tumor uptake of ¹⁰B compounds and neutron irradiation. Electroporation induces an increase in the permeability of the cell membrane. We previously demonstrated the optimization of boron biodistribution and microdistribution employing electroporation (EP) and decahydrodecaborate (GB-10) as the boron carrier in a hamster cheek pouch oral cancer model. The aim of the present study was to evaluate if EP could improve tumor control without enhancing the radiotoxicity of BNCT in vivo mediated by GB-10 with EP 10 min after GB-10 administration. Following cancerization, tumor-bearing hamster cheek pouches were treated with GB-10/BNCT or GB-10/BNCT + EP. Irradiations were carried out at the RA-3 Reactor. The tumor response and degree of mucositis in precancerous tissue surrounding tumors were evaluated for one month post-BNCT. The overall tumor response (partial remission (PR) + complete remission (CR)) increased significantly for protocol GB-10/BNCT + EP (92%) vs. GB-10/BNCT (48%). A statistically significant increase in the CR was observed for protocol GB-10/BNCT + EP (46%) vs. GB-10/BNCT (6%). For both protocols, the radiotoxicity (mucositis) was reversible and slight/moderate. Based on these results, we concluded that electroporation improved the therapeutic efficacy of GB-10/BNCT in vivo in the hamster cheek pouch oral cancer model without increasing the radiotoxicity.

Boron Vehiculating Nanosystems for Neutron Capture Therapy in Cancer Treatment

Boron neutron capture therapy is a low-invasive cancer therapy based on the neutron fission process that occurs upon thermal neutron irradiation of ¹⁰B-containing compounds; this process causes the release of alpha particles that selectively damage cancer cells. Although several clinical studies involving mercaptoundecahydro-closo-dodecaborate and the boronophenylalanine-fructose complex are currently ongoing, the success of this promising anticancer therapy is hampered by the lack of appropriate drug delivery systems to selectively carry therapeutic concentrations of boron atoms to cancer tissues, allowing prolonged boron retention therein and avoiding the damage of healthy tissues. To achieve these goals, numerous research groups have explored the possibility to formulate nanoparticulate systems for boron delivery. In this review. we report the newest developments on boron vehiculating drug delivery systems based on nanoparticles, distinguished on the basis of the type of carrier used, with a specific focus on the formulation aspects.

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.

In vivo evaluation of the effects of combined boron and gadolinium neutron capture therapy in mouse models

While boron neutron capture therapy (BNCT) depends primarily on the short flight range of the alpha particles emitted by the boron neutron capture reaction, gadolinium neutron capture therapy (GdNCT) mainly relies on gamma rays and Auger electrons released by the gadolinium neutron capture reaction. BNCT and GdNCT can be complementary in tumor therapy. Here, we studied the combined effects of BNCT and GdNCT when boron and gadolinium compounds were co-injected, followed by thermal neutron irradiation, and compared these effects with those of the single therapies. In cytotoxicity studies, some additive effects (32‒43%) were observed when CT26 cells were treated with both boron- and gadolinium-encapsulated PEGylated liposomes (B- and Gd-liposomes) compared to the single treatments. The tumor-suppressive effect was greater when BNCT was followed by GdNCT at an interval of 10 days rather than vice versa. However, tumor suppression with co-injection of B- and Gd-liposomes into tumor-bearing mice followed by neutron beam irradiation was comparable to that observed with Gd-liposome-only treatment but lower than B-liposome-only injection. No additive effect was observed with the combination of BNCT and GdNCT, which could be due to the shielding effect of gadolinium against thermal neutrons because of its overwhelmingly large thermal neutron cross section.

Exploring the Biological and Physical Basis of Boron Neutron Capture Therapy (BNCT) as a Promising Treatment Frontier in Breast Cancer

Simple Summary

BNCT is a biologically targeted, densely ionizing form of radiation therapy that allows for increased tumor cell kill, while reducing toxicity to surrounding normal tissues. Although BNCT has been investigated in the treatment of head and neck cancers and recurrent brain tumors, its applicability to breast cancer has not been previoulsy investigated. In this review we discuss the physical and biological properties of various boronated compounds, and advantages and challenges associated with the potential use of BNCT in the treatment of breast cancer.

Abstract

BNCT is a high LET radiation therapy modality that allows for biologically targeted radiation delivery to tumors while reducing normal tissue impacts. Although the clinical use of BNCT has largely been limited to phase I/II trials and has primarily focused on difficult-to-treat malignancies such as recurrent head and neck cancer and recurrent gliomas, recently there has been a renewed interest in expanding the use of BNCT to other disease sites, including breast cancer. Given its high LET characteristics, its biologically targeted and tumor specific nature, as well as its potential for use in complex treatment settings including reirradiation and widespread metastatic disease, BNCT offers several unique advantages over traditional external beam radiation therapy. The two main boron compounds investigated to date in BNCT clinical trials are BSH and BPA. Of these, BPA in particular shows promise in breast cancer given that is taken up by the LAT-1 amino acid transporter that is highly overexpressed in breast cancer cells. As the efficacy of BNCT is directly dependent on the extent of boron accumulation in tumors, extensive preclinical efforts to develop novel boron delivery agents have been undertaken in recent years. Preclinical studies have shown promise in antibody linked boron compounds targeting ER/HER2 receptors, boron encapsulating liposomes, and nanoparticle-based boron delivery systems. This review aims to summarize the physical and biological basis of BNCT, the preclinical and limited clinical data available to date, and discuss its potential to be utilized for the successful treatment of various breast cancer disease states.

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.

Hadrontherapy techniques for breast cancer

Radiotherapy plays a key role in breast cancer treatment, and recent technical advances have been made to improve the therapeutic window by limiting the risk of radiation-induced toxicity or by increasing tumor control. Hadrontherapy is a form a radiotherapy relying on particle beams; compared with photon beams, particle beams have specific physical, radiobiological and immunological properties, which can be valuable in diverse clinical situations. To date, available hadrontherapy techniques for breast cancer irradiation include proton therapy, carbon ion radiation therapy, fast neutron therapy and boron neutron capture therapy. This review analyzes the current rationale and level of evidence for each hadrontherapy technique for breast cancer.

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.

Synthesis of maleimide-functionalized carboranes and their utility in Michael addition reactions

Carboranyl maleimides were obtained and their reactivity with S- and N-nucleophiles was demonstrated.