Synthesis and Characterization of (89)Zr-Labeled Ultrasmall Nanoparticles

AGuIX nanoparticle-nanobody bioconjugates to target immune checkpoint receptors

This article presents bioconjugates combining nanoparticles (AGuIX) with nanobodies (VHH) targeting Programmed Death-Ligand 1 (PD-L1, A12 VHH) and Cluster of Differentiation 47 (CD47, A4 VHH) for active tumor targeting. AGuIX nanoparticles offer theranostic capabilities and an efficient biodistribution/pharmacokinetic profile (BD/PK), while VHH's reduced size (15 kDa) allows efficient tumor penetration. Site-selective sortagging and click chemistry were compared for bioconjugation. While both methods yielded bioconjugates with similar functionality, click chemistry demonstrated higher yield and could be used for the conjugation of various VHH. The specific targeting of AGuIX@VHH has been demonstrated in both in vitro and ex vivo settings, paving the way for combined targeted immunotherapies, radiotherapy, and cancer imaging.

Perspectives for Improving the Tumor Targeting of Nanomedicine via the EPR Effect in Clinical Tumors

Over the past few decades, the enhanced permeability and retention (EPR) effect of nanomedicine has been a crucial phenomenon in targeted cancer therapy. Specifically, understanding the EPR effect has been a significant aspect of delivering anticancer agents efficiently to targeted tumors. Although the therapeutic effect has been demonstrated in experimental models using mouse xenografts, the clinical translation of the EPR effect of nanomedicine faces several challenges due to dense extracellular matrix (ECM), high interstitial fluid pressure (IFP) levels, and other factors that arise from tumor heterogeneity and complexity. Therefore, understanding the mechanism of the EPR effect of nanomedicine in clinics is essential to overcome the hurdles of the clinical translation of nanomedicine. This paper introduces the basic mechanism of the EPR effect of nanomedicine, the recently discussed challenges of the EPR effect of nanomedicine, and various strategies of recent nanomedicine to overcome the limitations expected from the patients' tumor microenvironments.

Nanoparticles for MRI-guided radiation therapy: a review

The development of nanoparticle agents for MRI-guided radiotherapy is growing at an increasing pace, with clinical trials now underway and many pre-clinical evaluation studies ongoing. Gadolinium and iron-oxide-based nanoparticles remain the most clinically advanced nanoparticles to date, although several promising candidates are currently under varying stages of development. Goals of current and future generation nanoparticle-based contrast agents for MRI-guided radiotherapy include achieving positive signal contrast on T1-weighted MRI scans, local radiation enhancement at clinically relevant concentrations and, where applicable, avoidance of uptake by the reticuloendothelial system. Exploiting the enhanced permeability and retention effect or the use of active targeting ligands on nanoparticle surfaces is utilised to promote tumour uptake. This review outlines the current status of promising nanoparticle agents for MRI-guided radiation therapy, including several platforms currently undergoing clinical evaluation or at various stages of the pre-clinical development process. Challenges facing nanoparticle agents and possible avenues for current and future development are discussed.

Current State of Targeted Radiometal-Based Constructs for the Detection and Treatment of Disease in the Brain

The continual development of radiopharmaceutical agents for the field of nuclear medicine is integral to promoting the necessity of personalized medicine. One way to greatly expand the selection of radiopharmaceuticals available is to broaden the range of radionuclides employed in such agents. Widening the scope of development to include radiometals with their variety of physical decay characteristics and chemical properties opens up a myriad of possibilities for new actively targeted molecules and bioconjugates. This is especially true to further advance the imaging and treatment of disease in the brain. Over the past few decades, imaging of disease in the brain has heavily relied on agents which exploit metabolic uptake. However, through utilizing the broad range of physical characteristics that radiometals offer, the ability to target other processes has become more available. The varied chemistries of radiometals also allows for them to incorporated into specifically designed diverse constructs. A major limitation to efficient treatment of disease in the brain is the ability for relevant agents to penetrate the blood-brain barrier. Thus, along with efficient disease targeting, there must be intentional thought put into overcoming this challenge. Here, we review the current field of radiometal-based agents aimed at either imaging or therapy of brain disease that have been evaluated through at least in vivo studies.

Roadmap for metal nanoparticles in radiation therapy: current status, translational challenges, and future directions

This roadmap outlines the potential roles of metallic nanoparticles (MNPs) in the field of radiation therapy. MNPs made up of a wide range of materials (from Titanium, Z = 22, to Bismuth, Z = 83) and a similarly wide spectrum of potential clinical applications, including diagnostic, therapeutic (radiation dose enhancers, hyperthermia inducers, drug delivery vehicles, vaccine adjuvants, photosensitizers, enhancers of immunotherapy) and theranostic (combining both diagnostic and therapeutic), are being fabricated and evaluated. This roadmap covers contributions from experts in these topics summarizing their view of the current status and challenges, as well as expected advancements in technology to address these challenges.

EPR-mediated tumor targeting using ultrasmall-hybrid nanoparticles: From animal to human with theranostic AGuIX nanoparticles

Interest of tumor targeting through EPR effect is still controversial due to intrinsic low targeting efficacy and rare translation to human cancers. Moreover, due to different reasons, it has generally been described for relatively large nanoparticles (NPs) (hydrodynamic diameter > 10 nm). In this review EPR effect will be discussed for ultrasmall NPs using the example of the AGuIX® NP (Activation and Guiding of Irradiation by X-ray) recently translated in clinic. AGuIX® NP is a 4 ± 2 nm hydrodynamic diameter polysiloxane based NP. Since AGuIX® NP biodistribution is monitored by magnetic resonance imaging (MRI) and its activation is triggered by irradiation upon X-rays, this NP is well adapted for a theranostic approach of radiotherapy cancer treatment. Here we show that AGuIX® NP is particularly well suited to benefit from EPR-mediated tumor targeting thanks to an ultrasmall size and efficacy under irradiation at small dose. Indeed, intravenously-injected AGuIX® NP into rodent cancer models passively reached the tumor and revealed no toxicity, favoured by renal clearance. Moreover, translation of AGuIX® NP accumulation and retention into humans carrying brain metastases was validated during a first-in-man phase Ib trial taking advantage of easy biodistribution monitoring by MRI.

Nuclear imaging approaches facilitating nanomedicine translation

Nanomedicine approaches can effectively modulate the biodistribution and bioavailability of therapeutic agents, improving their therapeutic index. However, despite the ever-increasing amount of literature reporting on preclinical nanomedicine, the number of nanotherapeutics receiving FDA approval remains relatively low. Several barriers exist that hamper the effective preclinical evaluation and clinical translation of nanotherapeutics. Key barriers include insufficient understanding of nanomedicines' in vivo behavior, inadequate translation from murine models to larger animals, and a lack of patient stratification strategies. Integrating quantitative non-invasive imaging techniques in nanomedicine development offers attractive possibilities to address these issues. Among the available imaging techniques, nuclear imaging by positron emission tomography (PET) and single-photon emission computed tomography (SPECT) are highly attractive in this context owing to their quantitative nature and uncontested sensitivity. In basic and translational research, nuclear imaging techniques can provide critical quantitative information about pharmacokinetic parameters, biodistribution profiles or target site accumulation of nanocarriers and their associated payload. During clinical evaluation, nuclear imaging can be used to select patients amenable to nanomedicine treatment. Here, we review how nuclear imaging-based approaches are increasingly being integrated into nanomedicine development and discuss future developments that will accelerate their clinical translation.

Biodegradable micro-sized discoidal polymeric particles for lung-targeted delivery system

Various types of particle-based drug delivery systems have been explored for the treatment of pulmonary diseases; however, bio-distribution and elimination of the particles should be monitored for better understanding of their therapeutic efficacy and safety. This study aimed to characterize the biological properties of micro-sized discoidal polymeric particles (DPPs) as lung-targeted drug delivery carriers. DPPs were prepared using a top-down fabrication approach and characterized by assessing size and zeta potential. They were labeled with zirconium-89 (⁸⁹Zr), and bio-distribution studies and PET imaging were performed for 7 days after intravenous administration. Their hydrodynamic size was 2.8 ± 6.1 μm and average zeta potential was -39.9 ± 5.39 mV. At doses of 5, 12.5, and 25 mg/kg, they showed no acute toxicity in nude mice. Desferrioxamine (DFO)-functionalized ⁸⁹Zr-labeled DPPs gave a decay-corrected radiochemical yield of 82.1 ± 0.2%. Furthermore, ⁸⁹Zr-DPPs, from chelate-free labeling methods, showed a yield of 48.5 ± 0.9%. Bio-distribution studies and PET imaging showed ⁸⁹Zr-DFO-DPPs to be mainly accumulated in the lungs and degraded within 3 d of injection. However, ⁸⁹Zr-DFO-DPPs showed significantly low uptake in the bone. Overall, our results suggested micro-sized DPPs as promising drug delivery carriers for the targeted treatment of various pulmonary diseases.

Functionalization of theranostic AGuIX® nanoparticles for PET/MRI/optical imaging

A novel trifunctional imaging probe containing a chelator of radiometal for PET, a NIR heptamethine cyanine dye, and a bioconjugatable handle, has been grafted onto AGuIX® nanoparticles via a Michael addition reaction. The resulting functionalized nanoparticles have been fully characterized, radiolabelled with ⁶⁴Cu, and evaluated in a mice TSA tumor model using multimodal (PET/MRI/optical) imaging.

The controlled dual functionalization of AGuIX® nanoparticles afforded trimodal imaging (PET/MRI/fluorescence) theranostic agents.

Functionalization of Gadolinium Chelates Silica Nanoparticle through Silane Chemistry for Simultaneous MRI/64Cu PET Imaging

Multimodal nanoprobes are highly demanded for biomedical imaging applications to enhance the reliability of the diagnostic results. Among different types of nano-objects, ultrasmall silica gadolinium nanoparticle (SiGdNP) appears as a safe, effective, and versatile platform for this purpose. In this study, a new method to functionalize SiGdNP based on silane chemistry has been reported. Two types of chelating silanes (APTES-DOTAGA and APTES-NODAGA) have been synthesized and grafted on SiGdNP by a simple one-step protocol. This functionalization strategy requires no other reactants or catalyzers and does not compromise the ultrasmall size of the particles. NODAGA-functionalized particle has been labeled with ⁶⁴Cu isotope and injected intravenously to mice bearing TS/A carcinoma tumor for biodistribution study to demonstrate its potential as a bimodal MRI/PET imaging agent. A fully integrated MRI/PET system was used to simultaneously monitor the distribution of the particle. The results showed that the functionalized particle maintained properties of a renal clearable NP which could rapidly escape through kidneys and had low retention in other organs, especially liver, even though its accumulation in the tumor was modest.

AGuIX® from bench to bedside-Transfer of an ultrasmall theranostic gadolinium-based nanoparticle to clinical medicine

AGuIX^® are sub-5 nm nanoparticles made of a polysiloxane matrix and gadolinium chelates. This nanoparticle has been recently accepted in clinical trials in association with radiotherapy. This review will summarize the principal preclinical results that have led to first in man administration. No evidence of toxicity has been observed during regulatory toxicity tests on two animal species (rodents and monkeys). Biodistributions on different animal models have shown passive uptake in tumours due to enhanced permeability and retention effect combined with renal elimination of the nanoparticles after intravenous administration. High radiosensitizing effect has been observed with different types of irradiations in vitro and in vivo on a large number of cancer types (brain, lung, melanoma, head and neck…). The review concludes with the second generation of AGuIX nanoparticles and the first preliminary results on human.

A tunable one-pot three-component synthesis of an125I and Gd-labelled star polymer nanoparticle for hybrid imaging with MRI and nuclear medicine

Bimodal radioiodine/Gd labelled polymeric nanoparticles prepared using a versatile one-step three-component click reaction.

One-pot direct synthesis for multifunctional ultrasmall hybrid silica nanoparticles

A novel and simple route to synthesize ultrasmall silica nanoparticles having hydrodynamic diameters under 10 nm for imaging and therapeutic applications.

Multimodal nanoparticle imaging agents: design and applications

Molecular imaging, where the location of molecules or nanoscale constructs can be tracked in the body to report on disease or biochemical processes, is rapidly expanding to include combined modality or multimodal imaging. No single imaging technique can offer the optimum combination of properties (e.g. resolution, sensitivity, cost, availability). The rapid technological advances in hardware to scan patients, and software to process and fuse images, are pushing the boundaries of novel medical imaging approaches, and hand-in-hand with this is the requirement for advanced and specific multimodal imaging agents. These agents can be detected using a selection from radioisotope, magnetic resonance and optical imaging, among others. Nanoparticles offer great scope in this area as they lend themselves, via facile modification procedures, to act as multifunctional constructs. They have relevance as therapeutics and drug delivery agents that can be tracked by molecular imaging techniques with the particular development of applications in optically guided surgery and as radiosensitizers. There has been a huge amount of research work to produce nanoconstructs for imaging, and the parameters for successful clinical translation and validation of therapeutic applications are now becoming much better understood. It is an exciting time of progress for these agents as their potential is closer to being realized with translation into the clinic. The coming 5-10 years will be critical, as we will see if the predicted improvement in clinical outcomes becomes a reality. Some of the latest advances in combination modality agents are selected and the progression pathway to clinical trials analysed.This article is part of the themed issue 'Challenges for chemistry in molecular imaging'.

Iron Oxide Nanoradiomaterials: Combining Nanoscale Properties with Radioisotopes for Enhanced Molecular Imaging

The combination of the size-dependent properties of nanomaterials with radioisotopes is emerging as a novel tool for molecular imaging. There are numerous examples already showing how the controlled synthesis of nanoparticles and the incorporation of a radioisotope in the nanostructure offer new features beyond the simple addition of different components. Among the different nanomaterials, iron oxide-based nanoparticles are the most used in imaging because of their versatility. In this review, we will study the different radioisotopes for biomedical imaging, how to incorporate them within the nanoparticles, and what applications they can be used for. Our focus is directed towards what is new in this field, what the nanoparticles can offer to the field of nuclear imaging, and the radioisotopes hybridized with nanomaterials for use in molecular imaging.

Evaluation of Novel 64Cu-Labeled Theranostic Gadolinium-Based Nanoprobes in HepG2 Tumor-Bearing Nude Mice

Radiation therapy of liver cancer is limited by low tolerance of the liver to radiation. Radiosensitizers can effectively reduce the required radiation dose. AGuIX nanoparticles are small, multifunctional gadolinium-based nanoparticles that can carry radioisotopes or fluorescent markers for single-photon emission computed tomography (SPECT), positron emission tomography (PET), fluorescence imaging, and even multimodality imaging. In addition, due to the high atomic number of gadolinium, it can also serve as a tumor radiation sensitizer. It is critical to define the biodistribution and pharmacokinetics of these gadolinium-based nanoparticles to quantitate the magnitude and duration of their retention within the tumor microenvironment during radiotherapy. Therefore, in this study, we successfully labeled AGuIX with 64Cu through the convenient built-in chelator. The biodistribution studies indicated that the radiotracer 64Cu-AGuIX accumulates to high levels in the HepG2 xenograft of nude mice, suggesting that it would be a potential theranostic nanoprobe for image-guided radiotherapy in HCC. We also used a transmission electron microscope to confirm AGuIX uptake in the HepG2 cells. In radiation therapy studies, a decrease in 18F-FDG uptake was observed in the xenografts of the nude mice irradiated with AGuIX, which was injected 1 h before. These results provide proof-of-concept that AGuIX can be used as a theranostic radiosensitizer for PET imaging to guide radiotherapy for liver cancer.

68Ga-radiolabeled AGuIX nanoparticles as dual-modality imaging agents for PET/MRI-guided radiation therapy

Aim: The aim of this study was to develop a dual-modality positron emission tomography/magnetic resonance (PET/MR) imaging probe by radiolabeling gadolinium-containing AGuIX derivatives with the positron-emitter Gallium-68 (68Ga). Materials & methods: AGuIX@NODAGA nanoparticles were labeled with 68Ga at high efficiency. Tumor accumulation in an appropriate disease model was assessed by ex vivo biodistribution and in vivo PET/MR imaging. Results: 68Ga-AGuIX@NODAGA was proven to passively accumulate in U87MG human glioblastoma tumor xenografts. Metabolite assessment in serum, urine and tumor samples showed that 68Ga-AGuIX@NODAGA remains unmetabolized up to at least 60 min postinjection. Conclusion: This study demonstrates that 68Ga-AGuIX@NODAGA can be used as a dual-modality PET/MR imaging agent with passive accumulation in the diseased area, thus showing great potential for PET/MR image-guided radiation therapy.