Nanomaterial Probes for Nuclear Imaging

PET-Based Dual-Modal Probes for In Vivo Imaging

Molecular imaging has significantly advanced the detection and analysis of in vivo metabolic processes, while single-modal techniques remain limited. Dual-modal imaging, particularly positron emission tomography (PET)-based combinations has emerged as a powerful solution, offering enhanced capabilities through integration with magnetic resonance imaging (MRI) or near-infrared fluorescence (NIRF) imaging. This review highlights recent progress in PET-based dual-modal imaging, focusing on the development of various bimodal probes derived from antibodies, nanoparticles, and peptides, and key applications including image-guided surgery and disease assessment. PET-based dual-modal imaging holds substantial potential for advancing research and diagnostics by improving resolution and providing functional insights. By combining complementary modalities, these systems deliver a more comprehensive view of disease processes, leading to more accurate diagnoses and targeted treatments. Future research prioritizes optimizing probe design for enhanced biocompatibility and safety, facilitating clinical translation, and broadens applications beyond cancer. Through interdisciplinary collaboration, PET-based dual-modal probes are poised to play a pivotal role in improving patient outcomes, particularly in diagnosing and managing complex diseases.

Application of rare earth elements in dual-modality molecular probes

The unique 4f subshell electronic structure of rare earth elements endows them with exceptional properties in electrical, magnetic, and optical domains. These properties include prolonged fluorescence lifetimes, large Stokes shifts, distinctive spectral bands, and strong resistance to photobleaching, making them ideal for the synthesis of molecular probes. Each imaging technique possesses unique advantages and specific applicabilities but also inherent limitations due to its operational principles. Dual-modality molecular probes effectively address these limitations, particularly in applications involving high-resolution Magnetic Resonance Imaging (MRI) such as MRI/OI, MRI/PET, MRI/CT, and MRI/US. This review summarizes the applications, advantages, challenges, and current research status of rare earth elements in these four dual imaging modalities, providing a theoretical basis for the future development and application of rare earth elements in the field of dual-modality molecular probes.

Exosomes as targeted diagnostic biomarkers: Recent studies and trends

Different categories of extracellular vesicles (EVs) are identified based on their origin and formation processes. Among these, exosomes (EXOs) originate from endosomal compartments merging with the plasma membrane, forming small lipid vesicles that transport a range of molecular cargo such as nucleic acids, proteins, and lipids. The composition of EXOs varies depending on their cellular source, encompassing various cell types, including neutrophils, dendritic cells, and even tumor cells. Remarkably, EXOs possess inherent stability, low immunogenicity, and compatibility, making them efficient nano vectors for drug delivery. Imaging techniques like bioluminescence, fluorescence, and nuclear imaging are crucial in non-invasively tracking EXOs within living organisms. This process requires the attachment of radionuclides to the EXO's structure without altering its essential characteristics. Real-time imaging of EXOs is vital for their clinical application, and recent advancements in labeling and tracking methodologies provide insights into biodistribution, functionality, and potential pathways for EXO-mediated drug delivery. This review presents updated progress in the diverse applications of EXOs in targeted imaging across various modalities, where they function as contrast agents facilitating tissue visualization and disease tracking. Consequently, EXOs emerge as promising entities in medical diagnostics and imaging.

Exploring the Potential of Nanogels: From Drug Carriers to Radiopharmaceutical Agents

Nanogels open up access to a wide range of applications and offer among others hopeful approaches for use in the field of biomedicine. This review provides a brief overview of current developments of nanogels in general, particularly in the fields of drug delivery, therapeutic applications, tissue engineering, and sensor systems. Specifically, cyclodextrin (CD)-based nanogels are important because they have exceptional complexation properties and are highly biocompatible. Nanogels as a whole and CD-based nanogels in particular can be customized in a wide range of sizes and equipped with a desired surface charge as well as containing additional molecules inside and outside, such as dyes, solubility-mediating groups or even biological vector molecules for pharmaceutical targeting. Currently, biological investigations are mainly carried out in vitro, but more and more in vivo applications are gaining importance. Modern molecular imaging methods are increasingly being used for the latter. Due to an extremely high sensitivity and the possibility of obtaining quantitative data on pharmacokinetic and pharmacodynamic properties, nuclear methods such as single photon emission computed tomography (SPECT) and positron emission tomography (PET) using radiolabeled compounds are particularly suitable here. The use of radiolabeled nanogels for imaging, but also for therapy, is being discussed.

Tyrosinase-activated Nanocomposites for Double-Modals Imaging Guided Photodynamic and Photothermal Synergistic Therapy

Tyrosinase (TYR) is an important biomarker of melanoma. The exploration of fluorescent pr-obes-based composites is beneficial to build an integrative platform for the diagnosis and treatment of melanoma. Herein, a multifunctional nanocomposite IOBOH@BSA activated by TYR is developed for selective imaging and ablation of melanoma. The chemical structure of IOBOH enables the fluorescence (FL) imaging activated by TYR, photoacoustic (PA) imaging, and photodynamic-photothermal activity by regulating the balance between radiative decay and non-radiative decay. IOBOH combined with bovine serum albumin (IOBOH@BSA) presents the response to TYR and realizes FL imaging with mitochondria-targeting in melanoma. Moreover, IOBOH@BSA shows excellent photothermal ability and is applied for PA imaging. After IOBOH@BSA is activated by TYR, the singlet oxygen generation increases obviously. IOBOH@BSA can realize TYR-activated imaging and photodynamic-photothermal therapy of melanoma. The development of TYR-activated multifunctional nanocomposites promotes the precise imaging and improves the therapeutic effect of melanoma.

Development of a Radiolabeled Folate-Mediated Drug Delivery System for Effective Delivery of Docetaxel

Many preclinical studies are carried out with the aim of developing new formulations for the effective delivery of taxane class drugs, one of the most important anticancer drugs used clinically today. In this study, a radiolabeled folate-mediated solid lipid magnetic nanoparticle (SLMNP) system was developed by loading superparamagnetic iron oxide nanoparticles (MNP) and docetaxel (DTX) into the solid lipid nanoparticles as a drug delivery system that will function both in cancer treatment and diagnosis. For this purpose, first, SLMNP was synthesized by the hot homogenization method, and the surface of the particles was modified with a folate derivative to carry the particles to tissues with folate receptors. The synthesized magnetic solid lipid nanoparticles were loaded with DTX, and then radiolabeling was carried out with technetium-99 m (^99mTc-DTX-SLMNP). Structural characteristics of these nanoparticles were determined by characterization methods. According to the TEM images of MNPs, SLN, and SLMNPs, MNPs were observed between 25and 35 nm, SLNs between 400 and 500 nm, and SLMNPs between 350 and 450 nm. The drug entrapment efficiency of SLMNPs loaded with DTX was found to be 19%, and the percentage efficiency of radiolabeling was found to be 98.0 ± 2.0%. The biological behavior of this radiolabeled system was investigated in vitro and in vivo. Folate receptor-positive SKOV-3 and folate receptor-negative A549 cancer cell lines were studied. The IC₅₀ values of DTX-SLMNP in SKOV-3 and A549 cells were 50.21 and 172.27 μM at 48 h, respectively. Gamma camera imaging studies of ^99mTc-DTX-SLMNP and magnetically applied ^99mTc-DTX-SLMNP compounds were performed on tumor-bearing CD-1 nude mice. The uptake in the folate receptor-positive tumor region was higher than that in the folate receptor negative tumor region. We proposed that the drug delivery system we prepared in this study be evaluated for preclinical studies of new drug carrier formulations of the taxane class of anticancer drugs.

Recent Innovations and Nano-Delivery of Actinium-225: A Narrative Review

The actinium-225 (²²⁵Ac) radioisotope exhibits highly attractive nuclear properties for application in radionuclide therapy. However, the ²²⁵Ac radionuclide presents multiple daughter nuclides in its decay chain, which can escape the targeted site, circulate in plasma, and cause toxicity in areas such as kidneys and renal tissues. Several ameliorative strategies have been devised to circumvent this issue, including nano-delivery. Alpha-emitting radionuclides and nanotechnology applications in nuclear medicine have culminated in major advancements that offer promising therapeutic possibilities for treating several cancers. Accordingly, the importance of nanomaterials in retaining the ²²⁵Ac daughters from recoiling into unintended organs has been established. This review expounds on the advancements of targeted radionuclide therapy (TRT) as an alternative anticancer treatment. It discusses the recent developments in the preclinical and clinical investigations on ²²⁵Ac as a prospective anticancer agent. Moreover, the rationale for using nanomaterials in improving the therapeutic efficacy of α-particles in targeted alpha therapy (TAT) with an emphasis on ²²⁵Ac is discussed. Quality control measures in the preparation of ²²⁵Ac-conjugates are also highlighted.

Radiolabeled Liposomes for Nuclear Imaging Probes

Quantitative nuclear imaging techniques are in high demand for various disease diagnostics and cancer theranostics. The non-invasive imaging modality requires radiotracing through the radioactive decay emission of the radionuclide. Current preclinical and clinical radiotracers, so-called nuclear imaging probes, are radioisotope-labeled small molecules. Liposomal radiotracers have been rapidly developing as novel nuclear imaging probes. The physicochemical properties and structural characteristics of liposomes have been elucidated to address their long circulation and stability as radiopharmaceuticals. Various radiolabeling methods for synthesizing radionuclides onto liposomes and synthesis strategies have been summarized to render them biocompatible and enable specific targeting. Through a variety of radionuclide labeling methods, radiolabeled liposomes for use as nuclear imaging probes can be obtained for in vivo biodistribution and specific targeting studies. The advantages of radiolabeled liposomes including their use as potential clinical nuclear imaging probes have been highlighted. This review is a comprehensive overview of all recently published liposomal SPECT and PET imaging probes.

Direct Radiolabeling of Trastuzumab-Targeting Triblock Copolymer Vesicles with 89Zr for Positron Emission Tomography Imaging

Radiolabeled drug nanocarriers that can be easily imaged via positron emission tomography (PET) are highly significant as their in vivo outcome can be quantitatively PET-traced with high sensitivity. However, typical radiolabeling of most PET-guided theranostic vehicles utilizes modification with chelator ligands, which presents various challenges. In addition, unlike passive tumor targeting, specific targeting of drug delivery vehicles via binding affinity to overexpressed cancer cell receptors is crucial to improve the theranostic delivery to tumors. Herein, we developed 89Zr-labeled triblock copolymer polymersomes of 60 nm size through chelator-free radiolabeling. The polymersomes are assembled from poly(N-vinylpyrrolidone)5-b-poly(dimethylsiloxane)30-b-poly(N-vinylpyrrolidone)5 (PVPON5-PDMS30-PVPON5) triblock copolymers followed by adsorption of a degradable tannin, tannic acid (TA), on the polymersome surface through hydrogen bonding. TA serves as an anchoring layer for both 89Zr radionuclide and targeting recombinant humanized monoclonal antibody, trastuzumab (Tmab). Unlike bare PVPON5-PDMS30-PVPON5 polymersomes, TA- and Tmab-modified polymersomes demonstrated a high radiochemical yield of more than 95%. Excellent retention of 89Zr by the vesicle membrane for up to 7 days was confirmed by PET in vivo imaging. Animal biodistribution using healthy BALB/c mice confirmed the clearance of 89Zr-labeled polymersomes through the spleen and liver without their accumulation in bone, unlike the free nonbound 89Zr radiotracer. The 89Zr-radiolabeled polymersomes were found to specifically target BT474 HER2-positive breast cancer cells via the Tmab-TA complex on the vesicle surface. The noncovalent Tmab anchoring to the polymersome membrane can be highly advantageous for nanoparticle modification compared to currently developed covalent methods, as it allows easy and quick integration of a broad range of targeting proteins. Given the ability of these polymersomes to encapsulate and release anticancer therapeutics, they can be further expanded as precision-targeted therapeutic carriers for advancing human health through highly effective drug delivery strategies.

In Vitro Hemocompatibility and Genotoxicity Evaluation of Dual-Labeled [99mTc]Tc-FITC-Silk Fibroin Nanoparticles for Biomedical Applications

Nuclear imaging is a highly sensitive and noninvasive imaging technique that has become essential for medical diagnosis. The use of radiolabeled nanomaterials capable of acting as imaging probes has shown rapid development in recent years as a powerful, highly sensitive, and noninvasive tool. In addition, quantitative single-photon emission computed tomography (SPECT) images performed by incorporating radioisotopes into nanoparticles (NPs) might improve the evaluation and the validation of potential clinical treatments. In this work, we present a direct method for [99mTc]Tc-radiolabeling of FITC-tagged silk fibroin nanoparticles (SFN). NPs were characterized by means of dynamic light scattering and scanning electron microscopy. In vitro studies were carried out, including the evaluation of stability in biological media and the evaluation of hemocompatibility and genotoxicity using the cytokinesis block micronucleus (CBMN) assay. The radiolabeling method was reproducible and robust with high radiolabeling efficiency (∼95%) and high stability in biological media. Hydrodynamic properties of the radiolabeled NPs remain stable after dual labeling. The interaction of SFN with blood elicits a mild host response, as expected. Furthermore, CBMN assay did not show genotoxicity induced by [99mTc]Tc-FITC-SFN under the described conditions. In conclusion, a feasible and robust dual-labeling method has been developed whose applicability has been demonstrated in vitro, showing its value for further investigations of silk fibroin NPs biodistribution in vivo.