Gold Nanostars: A Novel Platform for Developing 211At-Labeled Agents for Targeted Alpha-Particle Therapy

Preclinical evaluation of [211At]At-AuNP-ABDMPL16 for targeted alpha therapy in Melanoma

PURPOSE

The aim of this study is to overcome the challenges of poor tumor penetration and systemic toxicity in targeted alpha therapy (TAT) while also evaluating its immunomodulatory effects to enhance antitumor immune responses in melanoma treatment.

METHODS

This study developed a 211At-labeled single-domain antibody agent ([211At]At-AuNP-ABDMPL16) targeting PD-L1, a protein overexpressed in melanoma cells. The binding affinity and internalization of [211At]At-AuNP-ABDMPL16 were evaluated in vitro using melanoma cell lines. In vivo studies in melanoma-bearing mice were conducted to assess biodistribution, pharmacokinetics, therapeutic efficacy, and the immune response induced by the treatment.

RESULTS

[211At]At-AuNP-ABDMPL16 demonstrated high binding affinity and efficient internalization in melanoma cells, resulting in significant tumor cell death through α-particle radiation. In vivo, [211At]At-AuNP-ABDMPL16 preferentially accumulated in tumors, inhibited tumor growth, and prolonged survival in melanoma-bearing mice. The treatment also triggered a robust anti-tumor immune response, marked by increased cytotoxic T lymphocytes and reduced regulatory T cells within the tumor microenvironment, with minimal systemic toxicity.

CONCLUSION

[211At]At-AuNP-ABDMPL16 shows promise as a novel therapeutic for melanoma, combining effective tumor targeting with potent cytotoxic and immune-activating effects. These findings support further investigation of this 211At-labeled single-domain antibodies in clinical applications.

Optimizing near-infrared-activated gold nanostructures for targeted combination cancer therapy

The application of near-infrared (NIR)-activated gold nanostructures, particularly gold nanostars (AuNSs) and gold nanorods (AuNRs), has emerged as a promising strategy in targeted combination cancer therapy (Figure 1). These nanostructures leverage their unique localized surface plasmon resonance (LSPR) properties, which enable effective absorption and conversion of NIR light into heat, facilitating photothermal therapy (PTT) to selectively destroy cancer cells. Recent advancements in the synthesis and functionalization of AuNSs and AuNRs have enhanced their biocompatibility, stability, and therapeutic efficacy. This review highlights the mechanisms by which these gold nanostructures can be optimized for synergistic effects when combined with other therapeutic modalities such as chemotherapy and photodynamic therapy (PDT). We discuss the importance of surface modifications that improve tumor targeting and retention, as well as the potential to overcome limitations associated with conventional therapies. The integration of AuNSs and AuNRs into multi-faceted treatment regimens represents a significant step forward in the development of effective cancer therapies, aiming to maximize therapeutic outcomes while minimizing side effects.

Current landscape and future directions of targeted-alpha-therapy for glioblastoma treatment

Glioblastoma (GB) is the most aggressive malignancy of the central nervous system. Despite two decades of intensive research since the establishment of the standard of care, emerging strategies have yet to produce consistent satisfactory outcomes. Because of its specific localisation and intricate characteristics, GB is a uniquely regulated solid tumour with a strong resistance to therapy. Advances in targeted radionuclide therapy (TRT), particularly with the introduction of a-emitting radionuclides, have unveiled potential avenues for the management of GB. Recent preclinical and clinical studies underscored promising advancements for targeted-α-therapy (TAT), but these therapeutic approaches exhibit a vast design heterogeneity, encompassing diverse radionuclides, vectors, target molecules, and administration modalities. This review seeks to critically assess the therapeutic landscape of GB through the perspective of TAT. Here, the focus is made on the advancements and limitations of in vivo explorations, pilot studies, and clinical trials, to determine the best directions for future investigations. In doing so, we hope to identify existing challenges and draw insights that might pave the way towards a more effective therapeutic approach.

Optimized chelator and nanoparticle strategies for high-activity 103Pd-loaded biodegradable brachytherapy seeds

BACKGROUND

Brachytherapy (BT) is routinely used in the treatment of various cancers. Current BT relies on the placement of large sources of radioactivity at the tumor site, requiring applicators that may cause local traumas and lesions. Further, they suffer from inflexibility in where they can be placed and some sources reside permanently in the body, causing potential long-term discomfort. These issues can be circumvented through injectable sources, prepared as biodegradable materials containing radionuclides that form solid seeds after administration. The level of radioactivity contained in such seeds must be sufficient to achieve substantial local irradiation. In this report, we investigate two different strategies for biodegradable BT seeds.

RESULTS

The first strategy entails injectable seeds based on 103Pd-labeled palladium-gold alloy nanoparticles ([103Pd]PdAuNPs). These were prepared by combining [103Pd]PdH2Cl4 and AuHCl4, followed by lipophilic surface coating and dispersed in lactose octaisobutyrate and ethanol (LOIB:EtOH), in overall radiochemical yield (RCY) of 83%. With the second strategy, [103Pd]Pd-SSIB was prepared by conjugating the [16]aneS4 chelator with lipophilic sucrose septaisobutyrate (SSIB) followed by complexation with [103Pd]PdH2Cl4 (RCY = 99%) and mixed with LOIB:EtOH. [103Pd]Pd-SSIB was likewise formulated as injectable liquid forming seeds by mixing with LOIB. Both formulations reached activities of 1.0-1.5 GBq/mL and negligible release of radioactivity after injection of 100 µL (100-150 MBq) into aqueous buffer or mouse serum of less than 1% over one month.

CONCLUSION

Both strategies for forming injectable BT seeds containing high 103Pd activity resulted in high radiolabeling yields, high activity per seed, and high activity retention. We consider both strategies suitable for BT, with the preferable strategy using a [16]aneS4 chelator due to its higher biodegradability.

Nanoradiopharmaceuticals: An Attractive Concept in Oncotherapy

Radiopharmaceuticals are of significant importance in the fields of tumor imaging and therapy. In recent decades, the increasing role of nanotechnology has led to the attractive concept of nanoradiopharmaceuticals. Consequently, it is imperative to provide a concise summary of the necessary guidelines to facilitate the translation of nanoradiopharmaceuticals. In this work, we have presented the contents of radiolabeling strategies and some applications of nanoradiopharmaceuticals. Such a framework can assist researchers in identifying more pertinent insights or making more informed decisions in the study of nanoradiopharmaceuticals.

Astatine-211 and actinium-225: two promising nuclides in targeted alpha therapy

Nuclear medicine therapy offers a promising approach for tumor treatment, as the energy emitted during radionuclide decay causes irreparable damage to tumor cells. Notably, α-decay exhibits an even more significant destructive potential. By conjugating α-nuclides with antibodies or small-molecule inhibitors, targeted alpha therapy (TAT) can enhance tumor destruction while minimizing toxic side effects, making TAT an increasingly attractive antineoplastic strategy. Astatine-211 ( 211At) and actinium-225 ( 225Ac) have emerged as highly effective agents in TAT due to their exceptional physicochemical properties and biological effects. In this review, we highlight the applications of 211At-/ 225Ac-radiopharmaceuticals, particularly in specific tumor targets, such as prostate-specific membrane antigen (PSMA) in prostate cancers, cluster of differentiation (CD) in hematological malignancies, human epidermal growth factor receptor-2 (HER2) in ovarian cancers, and somatostatin receptor (SSTR) in neuroendocrine tumors. We synthesize the progress from preclinical and clinical trials to provide insights into the promising potential of 211At-/ 225Ac-radiopharmaceuticals for future treatments.

Strong Affinity between Astatine and Silver: An Available Approach to Anchoring 211At in Nanocarrier for Locoregional Oncotherapy

Recently, 211At-related endoradiotherapy has emerged as an important oncotherapy strategy. Conjugating 211At with a nanocarrier provides a vital candidate for radionuclide therapy of various malignant tumors. In this study, we proposed utilizing the intrinsically high affinity of heavy halogens and sulfhydryl compounds for metallic silver to achieve highly efficient conjugation between 211At and Ag-based nanoparticles in a simple way. 211At@Ag-PEG-FA was obtained via a one-pot assembly of 211At, Ag, and SH-PEG-FA in extremely high radiolabeling yield (>95%) within 15 min and maintained excellent stability in simulated physiochemical media. Additionally, the prepared 211At@Ag-PEG-FA demonstrated specific binding to the breast cancer cell line (4T1), with a high endocytosis rate and low reflux, leading to significant cell growth inhibition. 211At@Ag-PEG-FA exhibits an excellent antitumor effect that completely suppressed tumor growth during the first week, effectively prolonging the median survival of mice to 44 days, relative to 18 days in the control group. All of the mice exhibited minimal side effects from 211At@Ag-PEG-FA in the experiment, indicating its acceptable biosafety. Our work shows that the strong affinity of Ag can be utilized to produce radioactivated nanomedicines with excellent stability and high efficiency, which also provides some valuable insights for the 211At radiolabeling of general compounds.

Production, purification and formulation of nanoradiopharmaceutical with 211At: An emerging candidate for targeted alpha therapy

INTRODUCTION

Astatine-211 has attained significant interest in the recent times as a promising radioisotope for targeted alpha therapy (TAT) of cancer. In this study, we report the production of 211At via 209Bi (α, 2n) 211At reaction in a cyclotron and development of a facile radiochemical separation procedure to isolate 211At for formulation of nanoradiopharmaceuticals.

METHODS

Natural bismuth oxide target in pelletized form wrapped in Al foil was irradiated with 30 MeV α-beam in an AVF cyclotron. The irradiated target was dissolved in 2 M HNO3 followed by selective precipitation of Bi as Bi(OH)3 under alkaline condition. The radiochemically separated 211At was used for labeling cyclic RGD peptide conjugated gold nanoparticles (Au-RGD NPs) by surface adsorption. The radiochemical stability of 211At-Au-RGD NPs was evaluated in phosphate buffered saline (PBS) and human serum media.

RESULTS

The batch yield of 211At at the end of irradiation was ∼6 MBq.μA-1.h-1. After radiochemical separation, ∼80 % of 211At could be retrieved with >99.9 % radionuclidic purity. Au-RGD NPs (particle size 8.4±0.8 nm) could be labeled with 211At with >99 % radiolabeling yield. The radiolabeled nanoparticles retained their integrity in PBS and human serum media over a period of 21 h.

CONCLUSIONS

The present strategy simplifies 211At production in terms of purification and would increase affordable access to this radioisotope for TAT of cancer.

Brain intratumoural astatine-211 radiotherapy targeting syndecan-1 leads to durable glioblastoma remission and immune memory in female mice

BACKGROUND

Glioblastoma (GB), the most aggressive brain cancer, remains a critical clinical challenge due to its resistance to conventional treatments. Here, we introduce a locoregional targeted-α-therapy (TAT) with the rat monoclonal antibody 9E7.4 targeting murine syndecan-1 (SDC1) coupled to the α-emitter radionuclide astatine-211 (211At-9E7.4).

METHODS

We orthotopically transplanted 50,000 GL261 cells of murine GB into the right striatum of syngeneic female C57BL/6JRj mice using stereotaxis. After MRI validation of tumour presence at day 11, TAT was injected at the same coordinates. Biodistribution, efficacy, toxicity, local and systemic responses were assessed following application of this protocol. The 9E7.4 monoclonal antibody was labelled with iodine-125 (125I) for biodistribution and with astatine-211 (211At) for the other experiments.

FINDINGS

The 211At-9E7.4 TAT demonstrated robust efficacy in reducing orthotopic tumours and achieved improved survival rates in the C57BL/6JRj model, reaching up to 70% with a minimal activity of 100 kBq. Targeting SDC1 ensured the cerebral retention of 211At over an optimal time window, enabling low-activity administration with a minimal toxicity profile. Moreover, TAT substantially reduced the occurrence of secondary tumours and provided resistance to new tumour development after contralateral rechallenge, mediated through the activation of central and effector memory T cells.

INTERPRETATION

The locoregional 211At-9E7.4 TAT stands as one of the most efficient TAT across all preclinical GB models. This study validates SDC1 as a pertinent therapeutic target for GB and underscores 211At-9E7.4 TAT as a promising advancement to improve the treatment and quality of life for patients with GB.

FUNDING

This work was funded by the French National Agency for Research (ANR) "France 2030 Investment Plan" Labex Iron [ANR-11-LABX-18-01], The SIRIC ILIAD [INCa-DGOS-INSERM-18011], the French program "Infrastructure d'Avenir en Biologie-Santé" (France Life Imaging) [ANR-11-INBS-0006], the PIA3 of the ANR, integrated to the "France 2030 Investment Plan" [ANR-21-RHUS-0012], and support from Inviscan SAS (Strasbourg, France). It was also related to: the ANR under the frame of EuroNanoMed III (project GLIOSILK) [ANR-19-ENM3-0003-01]; the "Région Pays-de-la-Loire" under the frame of the Target'In project; the "Ligue Nationale contre le Cancer" and the "Comité Départemental de Maine-et-Loire de la Ligue contre le Cancer" (CD49) under the frame of the FusTarG project and the "Tumour targeting, imaging and radio-therapies network" of the "Cancéropôle Grand-Ouest" (France). This work was also funded by the Institut National de la Santé et de la Recherche Médicale (INSERM), the University of Nantes, and the University of Angers.

Production of [211At]NaAt solution under GMP compliance for investigator-initiated clinical trial

BACKGROUND

The alpha emitter astatine-211 (211At) is garnering attention as a novel targeted alpha therapy for patients with refractory thyroid cancer resistant to conventional therapy using beta emitter radioiodine (131I). Herein, we aimed to establish a robust method for the manufacturing and quality control of [211At]NaAt solution for intravenous administration under the good manufacturing practice guidelines for investigational products to conduct an investigator-initiated clinical trial.

RESULTS

211At was separated and purified via dry distillation using irradiated Bi plates containing 211At obtained by the nuclear reaction of 209Bi(4He, 2n)211At. After purification, the 211At trapped in the cold trap was collected in a reaction vessel using 15 mL recovery solution (1% ascorbic acid and 2.3% sodium hydrogen carbonate). After stirring the 211At solution for 1 h inside a closed system, the reaction solution was passed through a sterile 0.22 μm filter placed in a Grade A controlled area and collected in a product vial to prepare the [211At]NaAt solution. According to the 3-lot tests, decay collected radioactivity and radiochemical yield of [211At]NaAt were 78.8 ± 6.0 MBq and 40 ± 3%, respectively. The radiochemical purity of [211At]At- obtained via ion-pair chromatography at the end of synthesis (EOS) was 97 ± 1%, and remained > 96% 6 h after EOS; it was detected at a retention time (RT) 3.2-3.3 min + RT of I-. LC-MS analysis indicated that this principal peak corresponded with an astatide ion (m/z = 210.988046). In gamma-ray spectrometry, the 211At-related peaks were identified (X-ray: 76.9, 79.3, 89.3, 89.8, and 92.3 keV; γ-ray: 569.7 and 687.0 keV), whereas the peak at 245.31 keV derived from 210At was not detected during the 22 h continuous measurement. The target material, Bi, was below the 9 ng/mL detection limit in all lots of the finished product. The pH of the [211At]NaAt solution was 7.9-8.6; the concentration of ascorbic acid was 9-10 mg/mL. Other quality control tests, including endotoxin and sterility tests, confirmed that the [211At]NaAt solution met all quality standards.

CONCLUSIONS

We successfully established a stable method of [211At]NaAt solution that can be administered to humans intravenously as an investigational product.

Methods for Radiolabeling Nanoparticles (Part 3): Therapeutic Use

Following previously published systematic reviews on the diagnostic use of nanoparticles (NPs), in this manuscript, we report published methods for radiolabeling nanoparticles with therapeutic alpha-emitting, beta-emitting, or Auger's electron-emitting isotopes. After analyzing 234 papers, we found that different methods were used with the same isotope and the same type of nanoparticle. The most common type of nanoparticles used are the PLGA and PAMAM nanoparticles, and the most commonly used therapeutic isotope is 177Lu. Regarding labeling methods, the direct encapsulation of the isotope resulted in the most reliable and reproducible technique. Radiolabeled nanoparticles show promising results in metastatic breast and lung cancer, although this field of research needs more clinical studies, mainly on the comparison of nanoparticles with chemotherapy.

Investigating the Heaviest Halogen: Lessons Learned from Modeling the Electronic Structure of Astatine's Small Molecules

We present a systematic study of electron-correlation and relativistic effects in diatomic molecular species of the heaviest halogen astatine (At) within relativistic single- and multireference coupled-cluster approaches and relativistic density functional theory. We establish revised reference ab initio data for the ground states of At₂, HAt, AtAu, and AtO⁺ using a highly accurate relativistic effective core potential model and in-house basis sets developed for accurate modeling of molecules with large spin-orbit effects. Spin-dependent relativistic effects on chemical bonding in the ground state are comparable to the binding energy or even exceed it in At₂. Electron-correlation effects near the equilibrium internuclear separation are mostly dynamical and can be adequately captured using single-reference CCSD(T). However, bond elongation in At₂ and, especially, AtO⁺ results in rapid manifestation of its multireference character. While useful for evaluating the spin-orbit effects on the ground-state bonding and properties, the two-component density functional theory lacks predictive power, especially in combination with popular empirically adjusted exchange-correlation functionals. This drawback supports the necessity to develop new functionals for reliable quantum-chemical models of heavy-element compounds with strong relativistic effects.

Astatine-211-Labeled Gold Nanoparticles for Targeted Alpha-Particle Therapy via Intravenous Injection

Alpha-particle radiotherapy has gained considerable attention owing to its potent anti-cancer effect. ²¹¹At, with a relatively short half-life of 7.2 h, emits an alpha particle within a few cell diameters with high kinetic energy, which damages cancer cells with high biological effectiveness. In this study, we investigated the intravenous injection of ²¹¹At-labeled gold nanoparticles (AuNPs) for targeted alpha-particle therapy (TAT). Different kinds of surface-modified gold nanoparticles can be labeled with ²¹¹At in high radiochemical yield in 5 min, and no purification is necessary. The in vivo biodistribution results showed the accumulation of 5 nm ²¹¹At-AuNPs@mPEG at 2.25% injection dose per gram (% ID/g) in tumors within 3 h via the enhanced permeability and retention (EPR) effect. Additionally, we observed a long retention time in tumor tissues within 24 h. This is the first study to demonstrate the anti-tumor efficacy of 5 nm ²¹¹At-AuNPs@mPEG that can significantly suppress tumor growth in a pancreatic cancer model via intravenous administration. AuNPs are satisfactory carriers for ²¹¹At delivery, due to simple and efficient synthesis processes and high stability. The intravenous administration of 5 nm ²¹¹At-AuNPs@mPEG has a significant anti-tumor effect. This study provides a new framework for designing nanoparticles suitable for targeted alpha-particle therapy via intravenous injection.