Targeted Alpha Therapy of Glioma Using 211At-Labeled Heterodimeric Peptide Targeting Both VEGFR and Integrins

Radiotheranostic landscape: A review of clinical and preclinical development

BACKGROUND

Radiotheranostics combines diagnostic imaging with targeted radionuclide therapy, representing a transformative approach in precision oncology. Landmark approvals of Lutathera® and Pluvicto® have catalyzed significant advancements in this field, driving research into novel radionuclides, targeting strategies, and clinical applications. This review evaluates the evolving clinical and preclinical landscape of radiotheranostics, highlighting advancements, emerging trends, and persistent challenges in radionuclide therapy.

METHODS

A comprehensive analysis was performed, encompassing active clinical trials as of December 2024, sourced from ClinicalTrials.gov and TheranosticTrials.org. Preclinical developments were evaluated through a review of recent literature, focusing on innovations in radionuclide production, targeting molecules, and radiochemistry.

RESULTS

In reviewing the clinical landscape, agents targeting somatostatin receptors (SSTR) and prostate-specific membrane antigen (PSMA) still dominate the field, but new targets such as fibroblast activation protein (FAP), integrins, and gastrin-releasing peptide receptors (GRPR) are gaining traction in both clinical and preclinical development. While small molecules and peptides remain the most common radionuclide carriers, antibody-based carriers including bispecific antibodies, immunoglobin-derived antigen-binding fragments, and antibody-mimetic proteins are on the rise due to their specificity and adaptability. Innovations in radioligand design are driving a shift from agonists to antagonists, accompanied by the development of modified peptides with enhanced pharmacokinetics and tumor-targeting properties. Next-generation therapeutic radionuclides, such as the beta-emitter terbium-161 and alpha-emitters actinium-225 and lead-212, are under investigation to complement or replace lutetium-177, addressing the need for improved efficacy and reduced toxicity. Paired isotopic radionuclides are gaining popularity for their ability to optimize imaging and therapeutic dosimetry as they offer near-identical specificity, biodistribution, and metabolism. Additionally, radiohybrid systems represent an innovative approach to chelating chemically distinct radionuclide pairs within a single molecule, further enhancing flexibility in radiotheranostic design.

CONCLUSION

Radiotheranostics has transformed cancer care through its precision and adaptability, but challenges in radionuclide production, regulatory frameworks, and workforce training hinder broader adoption. Advances in isotopic pairing, next-generation radionuclides, and radiohybrid systems in preclinical and clinical settings hold promise to overcome these barriers. Collaborative efforts among academia, industry, and regulatory bodies are critical to accelerating innovation and optimizing clinical outcomes.

Enhancing the Stability of 211At Radiopharmaceuticals: Insights from Ortho-Substituent Strategies

Astatine-211 (211At) is a promising alpha-emitting radionuclide for targeted alpha therapy (TAT), delivering high linear energy transfer (LET) and a short radiation range, making it ideal for cancer treatment while minimizing damage to surrounding healthy tissue. This viewpoint highlights recent advancements in the development of astatine-211 compounds for TAT, with a focus on the role of neighboring substituents in enhancing in vivo stability. By mitigating deastatination, these structural modifications improve radiopharmaceutical integrity, paving the way for more effective and clinically viable 211At-based radiopharmaceuticals.

Targeting tumor microenvironment with RGD-functionalized nanoparticles for precision cancer therapy

The need for precision therapies arises from the complexities associated with high-risk types of cancer, due to their aggressiveness and resistance to treatment. These diseases represent a global issue that requires transversal strategies involving cooperation among oncology specialists and experts from related fields, including nanomedicine. Nanoparticle-mediated active targeting of tumors has proven to be a revolutionary approach to address the most challenging neoplasms by overcoming the poor permeation at tumor site of untargeted, and nowadays questioned, strategies that rely solely on Enhanced Permeability and Retention (EPR) effects. The decoration of nanoparticles with Arg-Gly-Asp (RGD) peptides, which selectively target integrins on the cell membrane, marks a turning point in tumor microenvironment (TME) targeted strategies, enabling precision and efficiency in the delivery of chemotherapeutics. This review delves into the intricacies of the TME's features and targetable components (i.e. integrins), and the development of RGDs for nanoparticles' functionalization for active TME targeting. It provides a translational perspective on the integration of RGD-functionalized nanoparticles in oncology, highlighting their potential to overcome current therapeutic challenges, particularly in precision medicine. The current landscape of targeted nanomedicines in the clinic, and the development of RGD-nanomedicine for pediatric cancers are also discussed.

Alpha Atlas: Mapping global production of α-emitting radionuclides for targeted alpha therapy

Targeted Alpha Therapy has shown great promise in cancer treatment, sparking significant interest over recent decades. However, its broad adoption has been impeded by the scarcity of alpha-emitters and the complexities related to their use. The availability of these radionuclides is often constrained by the intricate production processes and purification, as well as regulatory and logistical challenges. Moreover, the high cost and technical difficulties associated with handling and applying alpha-emitting radionuclides pose additional barriers to their clinical implementation. This Alpha Atlas provides an in-depth overview of the leading alpha-particle emitting radionuclide candidates for clinical use, focusing on their production processes and supply chains. By mapping the current facilities that produce and supply these radionuclides, this atlas aims to assist researchers, clinicians, and industries in initiating or scaling up the applications of alpha-emitters. The Alpha Atlas aspires to act as a strategic guide, facilitating collaboration and driving forward the integration of these potent therapeutic agents into cancer treatment practices.

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.

Integrin Targeting and Beyond: Enhancing Cancer Treatment with Dual-Targeting RGD (Arginine-Glycine-Aspartate) Strategies

Integrins, an important superfamily of cell adhesion receptors, play an essential role in cancer progression, metastasis, and angiogenesis, establishing them as prime targets for both diagnostic and therapeutic applications. Despite their significant potential, integrin-targeted therapies have faced substantial challenges in clinical trials, including variable efficacy and unmet high expectations. Nevertheless, the consistent expression of integrins on tumor and stromal cells underscores their ongoing relevance and potential. Traditional RGD-based imaging and therapeutic agents have faced limitations, such as inconsistent target expression and rapid systemic clearance, which have reduced their effectiveness. To overcome these challenges, recent research has focused on advancing RGD-based strategies and exploring innovative solutions. This review offers a thorough analysis of the latest developments in the RGD-integrin field, with a particular focus on addressing previous limitations. It delves into new dual-targeting approaches and cutting-edge RGD-based agents designed to improve both tumor diagnosis and therapeutic outcomes. By examining these advancements, this review illuminates new pathways for enhancing the specificity and efficacy of integrin-targeted therapies, paving the way for more effective cancer diagnosis and treatment strategies.

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.

Peptides as Targeting Agents and Therapeutics: A Brief Overview

The controllability and specificity of peptides make them ideal for targeting therapeutic delivery systems and as therapeutic agents that interfere with the essential functions of pathogens and tumors. Peptides can also mimic natural protein structures or parts thereof, agonize receptors, and be conjugated to other molecules that will self-assemble. In this short Review, we discuss research from the last ten years into peptide use in three arenas: the treatment of cancer, the treatment of pathogens, and the targeting of specific organs and organelles. These studies demonstrate the successful application of targeting and therapeutic peptides in vitro and in vivo and show the promising range of applications peptides can have going forward.

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.

Targeted Alpha Therapy for Glioblastoma: Review on In Vitro, In Vivo and Clinical Trials

Glioblastoma (GB), a prevalent and highly malignant primary brain tumour with a very high mortality rate due to its resistance to conventional therapies and invasive nature, resulting in 5-year survival rates of only 4-17%. Despite recent advancements in cancer management, the survival rates for GB patients have not significantly improved over the last 10-20 years. Consequently, there exists a critical unmet need for innovative therapies. One promising approach for GB is Targeted Alpha Therapy (TAT), which aims to selectively deliver potentially therapeutic radiation doses to malignant cells and the tumour microenvironment while minimising radiation exposure to surrounding normal tissue with or without conventional external beam radiation. This approach has shown promise in both pre-clinical and clinical settings. A review was conducted following PRISMA 2020 guidelines across Medline, SCOPUS, and Embase, identifying 34 relevant studies out of 526 initially found. In pre-clinical studies, TAT demonstrated high binding specificity to targeted GB cells, with affinity rates between 60.0% and 84.2%, and minimal binding to non-targeted cells (4.0-5.6%). This specificity significantly enhanced cytotoxic effects and improved biodistribution when delivered intratumorally. Mice treated with TAT showed markedly higher median survival rates compared to control groups. In clinical trials, TAT applied to recurrent GB (rGB) displayed varying success rates in extending overall survival (OS) and progression-free survival. Particularly effective when integrated into treatment regimens for both newly diagnosed and recurrent cases, TAT increased the median OS by 16.1% in newly diagnosed GB and by 36.4% in rGB, compared to current standard therapies. Furthermore, it was generally well tolerated with minimal adverse effects. These findings underscore the potential of TAT as a viable therapeutic option in the management of GB.

A Proof-of-Concept Study on the Theranostic Potential of 177 Lu-labeled Biocompatible Covalent Polymer Nanoparticles for Cancer Targeted Radionuclide Therapy

Theranostic nanomedicine combined bioimaging and therapy probably rises more helpful and interesting opportunities for personalized medicine. In this work, 177 Lu radiolabeling and surface PEGylation of biocompatible covalent polymer nanoparticles (CPNs) have generated a new theranostic nanoformulation (177 Lu-DOTA-PEG-CPNs) for targeted diagnosis and treatment of breast cancer. The in vitro anticancer investigations demonstrate that 177 Lu-DOTA-PEG-CPNs possess excellent bonding capacity with breast cancer cells (4T1), inhibiting the cell viability, leading to cell apoptosis, arresting the cell cycle, and upregulating the reactive oxygen species (ROS), which can be attributed to the good targeting ability of the nanocarrier and the strong relative biological effect of the radionuclide labelled compound. Single photon emission computed tomography/ computed tomography (SPECT/CT) imaging and in vivo biodistribution based on 177 Lu-DOTA-PEG-CPNs reveal that notable radioactivity accumulation at tumor site in murine 4T1 models with both intravenous and intratumoral administration of the prepared radiotracer. Significant tumor inhibition has been observed in mice treated with 177 Lu-DOTA-PEG-CPNs, of which the median survival was highly extended. More strikingly, 50 % of mice intratumorally injected with 177 Lu-DOTA-PEG-CPNs was cured and showed no tumor recurrence within 90 days. The outcome of this work can provide new hints for traditional nanomedicines and promote clinical translation of 177 Lu radiolabeled compounds efficiently.

Carrier systems of radiopharmaceuticals and the application in cancer therapy

Radiopharmaceuticals play a vital role in cancer therapy. The carrier of radiopharmaceuticals can precisely locate and guide radionuclides to the target, where radionuclides kill surrounding tumor cells. Effective application of radiopharmaceuticals depends on the selection of an appropriate carrier. Herein, different types of carriers of radiopharmaceuticals and the characteristics are briefly described. Subsequently, we review radiolabeled monoclonal antibodies (mAbs) and their derivatives, and novel strategies of radiolabeled mAbs and their derivatives in the treatment of lymphoma and colorectal cancer. Furthermore, this review outlines radiolabeled peptides, and novel strategies of radiolabeled peptides in the treatment of neuroendocrine neoplasms, prostate cancer, and gliomas. The emphasis is given to heterodimers, bicyclic peptides, and peptide-modified nanoparticles. Last, the latest developments and applications of radiolabeled nucleic acids and small molecules in cancer therapy are discussed. Thus, this review will contribute to a better understanding of the carrier of radiopharmaceuticals and the application in cancer therapy.

Biocompatible conjugated polymer nanoparticles labeled with 225Ac for tumor endoradiotherapy

Recently, endoradiotherapy based on actinium-225 (225Ac) has attracted increasing attention, which is due to its α particles can generate maximal damage to cancer cells while minimizing unnecessary radiation effects on healthy tissues. Herein, 111In/225Ac-radiolabeled conjugated polymer nanoparticles (CPNs) coated with amphiphilic polymer DSPE-PEG-DOTA have been developed as a new injectable nano-radiopharmaceuticals for cancer endoradiotherapy under the guidance of nuclear imaging. Single photon emission computed tomography/computed tomography (SPECT/CT) using 111In-DOTA-PEG-CPNs as nano probe indicates a prolonged retention of radiolabeled nanocarriers, which was consistent with the in vivo biodistribution examined by direct radiometry analysis. Significant inhibition of tumor growth has been observed in murine 4T1 models treated with 225Ac-DOTA-PEG-CPNs when compared to mice treated with PBS or DOTA-PEG-CPNs. The 225Ac-DOTA-PEG-CPNs group experienced no single death within 24 days with the median survival considerably extended to 35 days, while all the mice treated with PBS or DOTA-PEG-CPNs died at 20 days post injection. Additionally, the histopathology studies demonstrated no obvious side effects on healthy tissues after treatment with 225Ac-DOTA-PEG-CPNs. All these results reveal that the new 225Ac-labeled DOTA-PEG-CPNs is promising as paradigm for endoradiotherapy.

Effective Treatment of SSTR2-Positive Small Cell Lung Cancer Using 211At-Containing Targeted α-Particle Therapy Agent Which Promotes Endogenous Antitumor Immune Response

Small cell lung cancer (SCLC) is a neuroendocrine tumor with a high degree of malignancy. Due to limited treatment options, patients with SCLC have a poor prognosis. We have found, however, that intravenously administered octreotide (Oct) armed with astatine-211 ([211At]SAB-Oct) is effective against a somatostatin receptor 2 (SSTR2)-positive SCLC tumor in SCLC tumor-bearing BALB/c nude mice. In biodistribution analysis, [211At]SAB-Oct achieved the highest concentration in the SCLC tumors up to 3 h after injection as time proceeded. A single intravenous injection of [211At]SAB-Oct (370 kBq) was sufficient to suppress SSTR2-positive SCLC tumor growth in treated mice by inducing DNA double-strand breaks. Additionally, a multitreatment course (370 kBq followed by twice doses of 370 kBq for a total of 1110 kBq) inhibited the growth of the tumor compared to the untreated control group without significant off-target toxicity. Surprisingly, we found that [211At]SAB-Oct could up-regulate the expressions of calreticulin and major histocompatibility complex I (MHC-I) on the tumor cell membrane surface, suggesting that α-particle internal irradiation may activate an endogenous antitumor immune response through the regulation of immune cells in the tumor microenvironment, which could synergically enhance the efficacy of immunotherapy. We conclude that [211At]SAB-Oct is a potential new therapeutic option for SSTR2-positive SCLC.

Astatine-211 based radionuclide therapy: Current clinical trial landscape

Astatine-211 (²¹¹At) has physical properties that make it one of the top candidates for use as a radiation source for alpha particle-based radionuclide therapy, also referred to as targeted alpha therapy (TAT). Here, we summarize the main results of the completed clinical trials, further describe ongoing trials, and discuss future prospects.