Molecular Magnetic Resonance Imaging with Gd(III)-Based Contrast Agents: Challenges and Key Advances

Binuclear Lanthanide Complexes as Magnetic Resonance and Optical Imaging Probes for Redox Sensing

We report a family of lanthanide(III) complexes that act as redox probes via both magnetic resonance (MR) and luminescence outputs. The ligands are functionalized with nitro, azobenzene and azide groups which are reduced to a common aniline product, and each responds to both chemical and biocatalytic reductive conditions at different cathodic onset potentials. By judicious choice of complexed Ln(III), the probes can be optimized either for use in MR imaging (Ln = Gd), or as highly efficient turn-on luminescence probes (Ln = Tb). The Tb(III) analogues are essentially nonemissive, until reductive generation of the aniline affords a complex which when excited by visible light (488 nm) emits green light with a quantum yield of 45% and millisecond long luminescent lifetimes (ms). The tunable redox response and imaging modalities of these versatile complexes have the potential to open up new approaches to redox sensing, such as the imaging of hypoxic environments in biology.

Beyond Gadolinium: The Potential of Manganese Nanosystems in MRI and Multimodal Imaging Agents

Manganese-based nanoparticles (Mn-NPs) hold great promise as MRI contrast agents and components of theranostic nanoplatforms, serving as a promising alternative to the more established gadolinium(III)-based nanosystems. This potential stems from their unique physicochemical properties and improved safety profile. This review introduces the fundamental principles of relaxation to highlight the key physicochemical characteristics of Mn-based nanosystems that influence their effectiveness. We primarily examine two oxidation states of manganese, Mn(II) and Mn(III), to demonstrate the efficacy of Mn-NPs as relaxation probes, with a brief discussion of one Mn(IV) system. Subsequently, we review recent studies on Mn-NP-based MRI contrast agents, focusing on the correlation between nanoparticle structure and the oxidation state of the paramagnetic centre. For Mn(II), the most common strategy involves utilizing stable Mn-chelates anchored to or encapsulated within the nanoparticles. In contrast, for the higher oxidation state, Mn(III), Mn(III)-porphyrin and phthalocyanine NPs are the primary non-Mn oxide nanosystems of choice. Regarding nanoplatform composition, Mn(II)-based platforms utilizing lipids (micelles or liposomes), polysaccharides (nanogels), dendrimers, metal-organic frameworks, inorganic NPs, and silicas are among the most frequently investigated. While numerous in vitro and in vivo animal MRI studies of Mn nanoplatforms have been reported, none have yet received clinical approval. We describe innovative surface modification and functionalization procedures designed to improve NP characteristics (e.g., size, stability, dispersibility, relaxivity, targeting, and toxicity) and impart multifunctionality for multimodal imaging. These strategies may provide valuable guidance for the development of Mn-NPs toward future clinical applications, particularly in cancer theranostics. STATEMENT OF SIGNIFICANCE: This review provides a critical analysis of the current landscape of Mn-based nanoparticles, which are increasingly being explored as MRI contrast agents and for multimodal imaging. This growing interest is largely driven by concerns over the potential toxicity and environmental impact of traditional Gd-based systems. The review introduces the key structural and dynamic parameters that determine the effectiveness of these nanosystems, highlighting their direct relationship with molecular design. It also examines the crucial stability and kinetic inertness requirements that influence their development. By critically discussing selected recent examples across a diverse range of nanosystems, including micelles, liposomes, silica-based platforms, and MOFs, this review identifies existing challenges and provides key insights to guide their future clinical translation.

Porous Silica Nanoparticle Entrapped Small Gd(III) and Mn(II) Complexes as MRI Contrast Agents

Among the in vivo imaging techniques, magnetic resonance imaging (MRI) provides soft-tissue images with high spatial resolution without using any harmful ionizing radiation. Prior to in vivo imaging, the administration of a bolus injection of paramagnetic species, coined as contrast agents (CAs), has become almost routine to facilitate conspicuous imaging in a relatively short measurement period. The contrast agents are mainly small Gd(III)-complexes of macrocyclic and acyclic organic ligands with polar pendant arms. Nonetheless, reports on some adverse effects due to the accumulation of bare Gd(III) ions in the human body from the used gadolinium-based contrast agents necessitate extensive investigations on Mn(II)-complexes to engender potential alternatives. While thermodynamically stable and kinetically inert Mn-complexes with inner-sphere water molecule(s) have been developed and tested as CAs, the enhancement in the relaxivity value beyond 3.5 mM-1 s-1 has been intriguing. This review discloses the recent strategies for incorporating paramagnetic small Gd(III) and Mn(II) complexes within the porous nanosystems, the physicochemical properties, and stability and contrast efficiency improvement after confinement. The generation of "smart" and environmentally responsive contrasting probes by incorporating appropriate functional groups onto the surface of the robust nanosystems is also presented herein.

Advancements in molecular imaging for the diagnosis and treatment of pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a highly malignant tumor characterized by poor overall patient survival and prognosis, largely due to challenges in early diagnosis, limited surgical options, and a high propensity for therapy resistance. The integration of various imaging modalities through molecular imaging techniques, particularly multimodal molecular imaging, offers the potential to provide more precise and comprehensive information about the lesion. With advances in nanomedicine, new imaging and drug delivery approaches that allow the development of multifunctional theranostic agents offer opportunities for improving pancreatic cancer treatment using precision oncology. Herein, we review the diagnostic and therapeutic applications of molecular imaging for PDAC and discuss the adoption of multimodal imaging approaches that combine the strengths of different imaging techniques to enhance diagnostic accuracy and therapeutic efficacy. We emphasize the significant role of nanomedicine technology in advancing multimodal molecular imaging and theranostics, and their potential impact on PDAC management. This comprehensive review aims to serve as a valuable reference for researchers and clinicians, offering insights into the current state of molecular imaging in PDAC and outlining future directions for improving early diagnosis, combination therapies, and prognostic evaluations.

Magnetic-susceptibility-dependent ratiometric probes for enhancing quantitative MRI

In magnetic resonance imaging (MRI), quantitative measurements of analytes are hindered by difficulties in distinguishing the MRI signals of activation of the probe by the analyte from those of the accumulation of the intact probe. Here we show that imaging sensitivity and quantitation can be enhanced by ratiometric MRI probes with a high relaxivity-ratio change (more than 2.5-fold at 7 T) via magnetic-susceptibility-dependent magnetic resonance tuning. Specifically, polymeric probes that incorporate paramagnetic Mn-porphyrin and superparamagnetic iron oxide nanoparticles inducing opposite changes in the longitudinal and transverse magnetic relaxivities responded to analyte concentration independently of probe concentration. In mice, the probes allowed for quantitative real-time dynamic imaging of H2O2, H2S or pH in subcutaneous tumours, in livers with drug-induced injury and in orthotropic gliomas. The ratiometric MRI probes may be advantageously used to obtain molecular insight into pathological processes and to circumvent interference from dynamic changes in probe concentration within the body while providing anatomical information.

Recent advances in bioresponsive macrocyclic gadolinium(III) complexes for MR imaging and therapy

Magnetic resonance (MR) imaging is a non-invasive clinical diagnostic modality that provides anatomical and physiological information with sub-millimetre spatial resolution at the organ and tissue levels. It utilizes the relaxation times (T1 and T2) of protons in water to generate MR images. However, the intrinsic MR contrast produced by water relaxation in organs and tissues is limited. To enhance the sensitivity and specificity of MR imaging, about 30%-45% of all clinical MR diagnoses need to use contrast media. Currently, all clinically approved MR contrast agents are linear or macrocyclic gadolinium(III) (Gd(III)) complexes, which are not specific to particular biological events. Due to the relatively high potential for releasing toxic free Gd(III), linear Gd(III) complexes raise safety concerns, making macrocyclic Gd(III) probes the preferred choice for clinical MR imaging without acute safety issues. To enhance the capability of MR imaging for detecting dynamic biological processes and conditions, many bioresponsive macrocyclic Gd(III) complexes capable of targeting diverse biomarkers have been developed. This review provides a concise and timely summary of bioresponsive macrocyclic Gd(III) contrast agents, particularly those developed between 2019 and 2024. We focus on three major types of Gd(III) agent that respond specifically to changes in pH, chemicals, and enzymes, highlighting their molecular design strategies, proton-relaxivity responses, and applications in in vitro and in vivo MR imaging for monitoring specific biomedical conditions and therapies.

Chiral Switch of Gadopiclenol: New Standards in MRI Probes

Magnetic Resonance Imaging (MRI) plays a vital role in the accurate diagnosis of numerous human diseases and disorders, with Gd(III)-based contrast agents (GBCAs) being used in ≈30%-40% of procedures, resulting in ≈30 million doses administered annually worldwide. The careful design of a rigid macrocyclic chelator featuring a highly hydrophilic periphery leads to the development of gadopiclenol, the first bis-hydrated Gd(III)-based MRI contrast agent, recently approved for clinical use by both the FDA and EMA. The stereochemistry of the coordinating arms is found to play a crucial role in the remarkable thermodynamic stability and inertness of the Gd(III)-complex with the RRR/SSS-stereoisomer of this heptadentate chelating agent, ensuring its safety in vivo. The exceptional stability of the most effective gadopiclenol enantiomeric pair (RRR/SSS), coupled with a relaxivity 2 to 3 times higher than that of currently used GBCAs, has enabled the use of reduced doses while ensuring non-inferior image contrast.

Nitroxide radical contrast agents for safe magnetic resonance imaging: progress, challenges, and perspectives

Magnetic resonance imaging (MRI) is considered one of the most valuable diagnostic technologies in the 21st century. To enhance the image contrast of anatomical features, MRI contrast agents have been widely used in clinical MRI diagnosis, especially those based on gadolinium, manganese, and iron oxide. However, these metal-based MRI contrast agents show potential toxicity to patients, which urges researchers to develop novel MRI contrast agents that can replace metal-based MRI contrast agents. Metal-free nitroxide radical contrast agents (NRCAs) effectively overcome the shortcomings of metal-based contrast agents and also have many advantages, including good biocompatibility, prolonged systemic circulation time, and easily functionalized structures. Importantly, since NRCAs acquire MRI signals with standard tissue water 1H relaxation mechanisms, they have great potential to realize clinical translation among many metal-free MRI contrast agents. At present, NRCAs have been proposed as an effective substitute for metal-based MRI contrast agents. Herein, this review first briefly introduces NRCAs, including their composition, classification, mechanism of action, application performances and advantages. Then, this review highlights the progress of NRCAs, including small molecule-based NRCAs and polymer-based NRCAs. Finally, this review also discusses the challenges and future perspectives of NRCAs.

Quantitative Interpretation of Transverse Spin Relaxation by Translational Diffusion in Liquids

Intermolecular spin relaxation by translational diffusion of spin pairs has been widely used to study the properties of biomolecules in liquids. Notably, solvent paramagnetic relaxation enhancement (sPRE) arising from paramagnetic cosolutes has gained significant attention for various applications in structural biology, including the structural refinement of intrinsically disordered proteins, the elucidation of the molecular mechanisms driving cosolute-induced protein denaturation, and the characterization of residue-specific effective near-surface electrostatic potentials (ENS). Furthermore, sPRE has been extensively applied in magnetic resonance imaging (MRI), where paramagnetic ions, such as Gd(III)-based ions, are used as contrast agents. Among these applications, the transverse sPRE rate (Γ2) has predominantly been interpreted empirically as being proportional to the average interspin distance ⟨r-6⟩norm. In this study, we present a rigorous theoretical interpretation of Γ2 for spherically symmetric intermolecular potentials, demonstrating that it is proportional to ⟨r-4⟩norm. We provide an explicit formula for calculating ⟨r-4⟩norm without any adjustable parameters, offering valuable insights into the interaction potential independent of the type or strength of interactions. It has broad applicability, including the precise interpretation of the relaxation properties of the MRI contrast agents and calculation of the ENS.

MRI detection of free-contrast agent nanoparticles

PURPOSE

The integration of nanotechnology into biomedical imaging has significantly advanced diagnostic and theranostic capabilities. However, nanoparticle detection in imaging relies on functionalization with appropriate probes. In this work, a new approach to visualize free-label nanoparticles using MRI and MRS techniques is described, consisting of detecting by 1H CSI specific proton signals belonging to the components naturally present in most of the nanosystems used in preclinical and clinical research.

METHODS

Three different nanosystems, namely lipid-based micelles, liposomes, and perfluorocarbon-based nanoemulsions, were synthesized, characterized by high resolution NMR and then visualized by 1H CSI at 300 MHz. Subsequently the best 1H CSI performing system was administered to murine models of cancer to evaluate the possibility of tracking the nanosystem by looking at its proton associated signal. Furthermore, an in vitro comparison between 1H CSI and 19F MRI was carried out.

RESULTS

The study successfully demonstrates the feasibility of detecting nanoparticles using MRI/MRS without probe functionalization, employing 1H CSI. Among the nanosystems tested, the perfluorocarbon-based nanoemulsion exhibited the highest SNR. Consequently, it was evaluated in vivo, where its detection was achievable within tumors and inflamed regions via 1H CSI, and in lymph nodes via PRESS.

CONCLUSIONS

These findings present a promising avenue for nanoparticle imaging in biomedical applications, offering potential enhancements to diagnostic and theranostic procedures. This non-invasive approach has the capacity to advance imaging techniques and expand the scope of nanoparticle-based biomedical research. Further exploration is necessary to fully explore the implications and applications of this method.

Water-Soluble Mn(III)-Porphyrins with High Relaxivity and Photosensitization

Three water-soluble Mn(III)-porphyrin complexes with cationic pyridyl side groups bearing COOH- or OH-terminated carbon chains in the meta or para positions have been synthesized as probes for both magnetic resonance imaging (MRI) and photodynamic therapy (PDT). The complexes Mn-1, Mn-2, and Mn-3 are highly water-soluble, and their relaxivities range between 10 and 15 mM-1 s-1, at 20-80 MHz and 298 K, 2-3 times higher than that of commercial Gd(III)-based agents. The complexes containing carboxylate (Mn-2) or alcoholic (Mn-3) side chains in the para position are endowed with higher relaxivities and have also shown efficient photoinduced DNA cleavage and singlet oxygen (1O2) generation. Mn-3 with stronger photoinduced DNA cleavage has also revealed stabilizing and binding activities for G4 DNA, at a similar level as the known G4 binder Mn-TMPyP4. Nevertheless, the G4-binding activity of Mn-3 was nonspecific. Preliminary tests evidenced photocytotoxicity of Mn-3 on HeLa cells without a significant effect in the absence of light. Altogether, these results underline the potential of such water-soluble Mn(III)-porphyrins for the development of multimodal approaches combining MRI and PDT.

A Single-Chain Peptide Probe Targeting Pathological Collagen for Precise Staging of Hepatic Fibrosis by MR Imaging

Hepatic fibrosis, a chronic liver response to injury with potential severe outcomes like cirrhosis and liver cancer, necessitates urgent noninvasive diagnostic techniques to halt disease progression. We herein for the first time developed a single-chain peptide probe targeting pathological collagen for in vivo magnetic resonance imaging (MRI) of hepatic fibrosis. The novel (GhypO)10 probe, distinguished by its unique monomeric conformation achieved through Pro to (2S,4S)-hydroxyproline (hyp) substitution and subsequent disruption of hydrogen bonding, exhibits selectivity for pathological collagen over its intact counterpart in connective tissues. Fluorescence imaging of liver specimens from fibrotic models displayed a discernible relationship between pathological collagen levels and fibrosis stage. Moreover, T1-weighted MR images post Gd-GhypO administration revealed progressive signal enhancement congruent with fibrosis severity, corroborated by a corresponding increase in the contrast-to-noise ratio (ΔCNR). Biodistribution analysis indicates that Gd-GhypO has low Gd retention in the main organs 24 h postinjection, ensuring the probe's safety for molecular imaging. The Gd-GhypO probe therefore emerges as a potent tool for the precise, noninvasive delineation of hepatic fibrosis stages, offering significant implications for the diagnosis and management of liver fibrosis.

MR Imaging Reveals Dynamic Aggregation of Multivalent Glycoconjugates in Aqueous Solution

Glycoconjugates forming from the conjugation of carbohydrates to other biomolecules, such as proteins, lipids, or other carbohydrates, are essential components of mammalian cells and are involved in numerous biological processes. Due to the capability of sugars to form multiple hydrogen bonds, many synthetic glycoconjugates are desirable biocompatible platforms for imaging, diagnostics, drugs, and supramolecular self-assemblies. Herein, we present a multimeric galactose functionalized paramagnetic gadolinium (Gd(III)) chelate that displays spontaneous dynamic aggregation in aqueous conditions. The dynamic aggregation of the Gd(III) complex was shown by the concentration-dependent magnetic resonance (MR) relaxation measurements, nuclear magnetic resonance dispersion (NMRD) analysis, and dynamic light scattering (DLS). Notably, these data showed a nonlinear relationship between magnetic resonance relaxation rate and concentrations (0.03-1.35 mM), and a large DLS hydrodynamic radius was observed in the high-concentration solutions. MR phantom images were acquired to visualize real-time dynamic aggregation behaviors in aqueous solutions. The in situ visualization of the dynamic self-assembling process of multivalent glycoconjugates has rarely been reported.

Electrochemical Method for the Design of New Possible Gadolinium-Based Contrast Agents

Magnetic resonance imaging (MRI) is a technique that employs strong magnetic fields and radio frequencies to generate detailed images of the body's interior. In oncology patients, gadolinium-based contrast agents (GBCAs) are frequently administered to enhance the visualization of tumors. Those contrast agents are gadolinium chelates, characterized by high stability that prevents the release of the toxic gadolinium ion into the body. This work is part of the research for alternative nanoscaled GBCAs. Following the synthesis and characterization of zinc hexacyanoferrate nanoparticles, gadolinium ions were successfully incorporated into a hexacyanoferrate-based matrix, deposited on FTO-coated glass used as working electrode in a gadolinium salt solution, by applying a fixed potential determined through cyclic voltammetry studies. The presence of gadolinium inside the matrix was confirmed by EDX.

Aptamer-Gadolinium Conjugates for Targeted Magnetic Resonance Imaging of Early-Stage Bladder Cancer

Bladder cancer (BCa) poses a significant threat to human health, with early-stage diagnosis being particularly valuable yet challenging due to the limited availability of highly efficient targeted contrast agents. In this study, we have developed a novel aptamer-gadolinium conjugate (Apt-Gd) designed as a targeted contrast agent for the magnetic resonance imaging (MRI) of early-stage BCa. The synthesis of Apt-Gd involved the direct conjugation of aptamers with chelating agents through a bioorthogonal reaction, followed by gadolinium chelation. Notably, Apt-Gd exhibited high longitudinal relaxivity, exceptional BCa specificity, and good biocompatibility. Furthermore, our research revealed that intravesical instillation of Apt-Gd effectively enhanced the stability of aptamers and boosted the local contrast enhancement in BCa-bearing mice. The utilization of Apt-Gd yielded a satisfactory signal-to-noise ratio during BCa imaging and significantly prolonged the imaging time window. On the whole, the accurate detection of early-stage BCa using Apt-Gd was achieved for the first time, making a breakthrough in BCa diagnosis with promising potential for practical clinical applications.

Manganese Oxide Nanoparticles for MRI-Based Multimodal Imaging and Theranostics

Manganese-based MRI contrast agents have recently attracted much attention as an alternative to Gd-based compounds. Various nanostructures have been proposed for potential applications in in vivo diagnostics and theranostics. This review is focused on the discussion of different types of Mn oxide-based nanoparticles (MnxOy NPs) obtained at the +2, +3 and +4 oxidation states for MRI, multimodal imaging or theranostic applications. These NPs show favorable magnetic properties, good biocompatibility, and an improved toxicity profile relative to Gd(III)-based nanosystems, showing that the Mn paramagnetic ions offer advantages for the next generation of nanoscale MRI and theranostic contrast agents. Their potential for enhancing relaxivity and MRI contrast effects is illustrated through discussion of selected examples published in the past decade.

Synthesis and relaxivity of gadolinium-based DOTAGA conjugated 3-phosphoglycerate

The synthesis and characterization of a gadolinium-based contrast agent conjugated to 3-phosphoglycerate (Gd-3PG) are reported. The synthetic steps are optimized to incorporate a selective deprotection strategy for a primary tert-butyl dimethyl silyl (TBS) hydroxyl over a secondary one. The relaxivity of Gd-3PG shows characteristic improvement, likely due to secondary sphere effects and/or an increase in molecular weight (5.39 ± 0.14 mM-1 s-1 at 1.4 T and 37 °C). Michaelis-Menten enzymatic kinetics was measured on the modified 3PG-arm and it showed similar activity to the native 3PG metabolite, Km = 240 ± 30 μM. This agent and future versions of this type of GBCA, which are conjugated to glycolytic metabolites, were designed to monitor in vivo allosteric regulatory events in glycolytic processes.

Multifunctional nanoparticles potentiate in-situ tumor vaccines via reversing insufficient Photothermal therapy by disrupting tumor vasculature

Photothermal therapy can trigger immunogenic cell death and release personalized in-situ tumor vaccine, activating immune responses to eliminate systemic tumors beyond the irradiated zone. However, the immune response of the in-situ tumor vaccines is often undermined by the residual tumor cells and their induced immunosuppressive tumor microenvironment (TME), which is attributed to insufficient photothermal effects stemming from the limited accumulation of photosensitizers. To overcome these limitations, we developed multi-functional nanoparticles (VI@Gd-NPs) that integrate a tumor vasculature-specific disrupting agent (Vadimezan, Phase III clinical drug), a photosensitizer (Indocyanine Green, ICG), and a magnetic resonance imaging contrast agent (Gadolinium, Gd) through chemical self-assembly. By selectively disrupting the tumor vasculature, these nanoparticles enhance the intratumoral delivery of photosensitizers (ICG and blood cells), and Gd. With the guidance of Gd-enhanced MRI, the improved delivery facilitates comprehensive photothermal ablation and regulates the TME, further initiating the in-situ tumor vaccine. Notably, this approach significantly enhances anti-tumor immune responses, improves survival rates, and reduces tumor recurrence and metastasis in various animal models. Moreover, depleting CD8+ T cells reverses these therapeutic benefits, highlighting the critical role of adaptive T cell immunity. Therefore, the VI@Gd-NPs treatment holds great potential for reigniting the in-situ tumor vaccine of photothermal therapy.

Quantitative in Vivo Molecular MRI

Molecular magnetic resonance imaging (MRI) combines chemistry, chemical biology, and imaging techniques to track molecular events non-invasively. Quantitative molecular MRI aims to provide meaningful, reproducible numerical measurements of molecular processes or biochemical targets within the body. In this review, the classifications of molecular MRI probes based on their signal-generating mechanism and functionality are first described. From there, the primary considerations for in vitro characterization and in vivo validation of molecular MRI probes, including how to avoid pitfalls and biases are discussed. Then, recommendations on imaging acquisition protocols and analysis methods to establish quantitative relationships between MRI signal change induced by the probes and the molecular processes of interest are provided. Finally, several representative case studies are highlighted that incorporate these features. Quantitative molecular MRI is a multidisciplinary research area incorporating expertise in chemical biology, inorganic chemistry, molecular probes, imaging physics, drug development, pathobiology, and medicine. The purpose of this review is to provide guidance to chemists developing MR imaging probes and methods in terms of in vitro and in vivo validation to accelerate the translation of these new quantitative tools for non-invasive imaging of biological processes.

Construction of New MRI Contrast Agents for Spatiotemporal Visualization of Nitric Oxide in Ischemia/Reperfusion Organs

Noninvasive and real-time nitric oxide (NO) visualization in vivo is still a challenge. Herein, we constructed a series of NO-responsive magnetic resonance imaging (MRI) contrast agents Gd1b-e by modifying Gd-DO3A using a bis-pyridyl-ethylamine side chain as a signal-amplifying moiety and o-phenylenediamine as a NO-responsive linker. It was found that Gd1b, d, and e can form macromolecular ternary complexes (Gd-Zn2+-HSA) with high longitudinal relaxivity (r1) (12.2-16.2 mM-1 s-1). Once reacting with NO, the o-phenylenediamine linker was hydrolyzed to produce a small molecular Gd complex with sharply decreased r1 (4.7-6.3 mM-1 s-1). Among them, Gd1d with a desirable pharmacokinetic profile (t1/2 = 5.91 h) could clearly distinguish the ischemia-reperfusion (IR) liver with excessive NO in rats. Meanwhile, the temporarily reduced amount of NO in the IR liver and brain by the NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl could enhance the signal of Gd1d, suggesting anticipated NO-responsive property. This research offers a new avenue for insight into the NO spatiotemporal property in multiple IR organs.

A robust collagen-targeting MRI peptide contrast agent for in vivo imaging of hepatic fibrosis

We herein report the construction of a robust MRI peptide contrast agent Gd-ICTP with superior selectivity for type I collagen, enabling the accurate and non-invasive detection of hepatic fibrosis in vivo.

A Facile NMR Method for Pre-MRI Evaluation of Trigger-Responsive T1 Contrast Enhancement

There is a growing interest in developing paramagnetic nanoparticles as responsive magnetic resonance imaging (MRI) contrast agents, which feature switchable T1 image contrast of water protons upon biochemical cues for better discerning diseases. However, performing an MRI is pragmatically limited by its cost and availability. Hence, a facile, routine method for measuring the T1 contrast is highly desired in early-stage development. This work presents a single-point inversion recovery (IR) nuclear magnetic resonance (NMR) method that can rapidly evaluate T1 contrast change by employing a single, optimized IR pulse sequence that minimizes water signal for "off-state" nanoparticles and allows for sensitively measuring the signal change with "switch-on" T1 contrast. Using peptide-induced liposomal gadopentetic acid (Gd3+-DTPA) release and redox-sensitive manganese oxide (MnO2) nanoparticles as a demonstration of generality, this method successfully evaluates the T1 shortening of water protons caused by liposomal Gd3+-DTPA release and Mn2+ formation from MnO2 reduction. Furthermore, the NMR measurement is highly correlated to T1-weighted MRI scans, suggesting its feasibility to predict the MRI results at the same field strength. This NMR method can be a low-cost, time-saving alternative for pre-MRI evaluation for a diversity of responsive T1 contrast systems.

Relaxivity Modulation of Gd-HPDO3A-like Complexes by Introducing Polar and Protic Peripheral Groups

In the last three decades, high-relaxivity Magnetic Resonance Imaging (MRI) contrast agents (CAs) have been intensively sought, aiming at a reduction in the clinically injected dose while maintaining the safety of the CA and obtaining the same pathological information. Thus, four new Gd(III) complexes based on modified 10-(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (HP-DO3A) macrocyclic structure were designed and synthesized by introducing further polar and protic functional groups (amides, phosphonates, and diols) adjacent to the metal-coordinated hydroxyl group. A detailed 1H NMR relaxometric analysis allowed us to investigate the effect of these functional groups on the relaxivity, which showed a 20-60% increase (at 0.5 T, 298 K, and pH 7.4) with respect to that of clinically approved CAs. The contribution of the water molecules H-bonded to these peripheral functional groups on the relaxivity was evaluated in terms of the second sphere effect or prototropic exchange of labile protons.

Rational Design of a Hetero-multinuclear Gadolinium(III)-Copper(II) Complex: Integrating Magnetic Resonance Imaging, Photoacoustic Imaging, Mild Photothermal Therapy, Chemotherapy and Immunotherapy of Cancer

For more accurate diagnosis and effective treatment of cancer, we proposed to develop a hetero-multinuclear metal complex based on the property of apoferritin (AFt) for targeting tumor theranostics by integrating dual-modality imaging diagnosis and multimodality therapy. To this end, we rational designed and synthesized a trinuclear Gd(III)-Cu(II) thiosemicarbazone complex (Gd-2Cu) and then constructed a Gd-2Cu@AFt nanoparticle (NP) delivery system. Gd-2Cu/Gd-2Cu@AFt NPs not only had significant T1-weighted magnetic resonance imaging and photoacoustic imaging of the tumor but also effectively inhibited tumor growth through a combination of mild photothermal therapy, chemotherapy, and immunotherapy. Gd-2Cu@AFt NPs optimized the behavior of imaging diagnosis and therapy of Gd-2Cu, improved its targeting ability, and reduced the side effects in vivo. Besides, we revealed and clarified the anticancer mechanism of Gd-2Cu: interrupting energy metabolism of the tumor cell, inducing apoptosis of the tumor cell, and activating a systemic immune response by inducing immunogenic cell death of cancer cells.

Hyperbranched Polymeric 19F MRI Contrast Agents with Long T2 Relaxation Time Based on β-Cyclodextrin and Phosphorycholine

19F magnetic resonance imaging (19F MRI) is gaining attention as an emerging diagnostic technology. Effective 19F MRI contrast agents (CAs) for in vivo applications require a long transverse (or spin-spin) relaxation time (T2), short longitudinal (or spin-lattice) relaxation time (T1), high fluorine content, and excellent biocompatibility. Here, we present a novel hyperbranched polymeric 19F MRI CA based on β-cyclodextrin and phosphorylcholine. The influence of the branching degree and fluorine content on T2 was thoroughly investigated. Results demonstrated a maximum fluorine content of 11.85% and a T2 of 612 ms. This hyperbranched polymeric 19F MRI CA exhibited both great biocompatibility against cells and organs of mice and high-performance imaging capabilities both in vitro and in vivo. The research provides positive insights into the synthesis strategies, topological design, and selection of fluorine tags for 19F MRI CAs.

Advancements in manganese complex-based MRI agents: Innovations, design strategies, and future directions

This review focuses on the advancements in manganese (Mn) complex-based magnetic resonance imaging (MRI) agents for imaging different diseases. Here we emphasize the unique redox properties of Mn to deliver innovative MRI contrast agents, including small molecules, nanoparticles (NPs), metal-organic frameworks (MOFs), and polymer hybrids. Aspects of their rational design have been discussed, including size dependence, morphology tuning, surface property enhancement, etc., while also discussing the existing challenges and potential solutions. The present work will inspire and motivate scientists to emphasize MRI-guided applications and bring clinical success in the coming years.

Stimuli-responsive linkers and their application in molecular imaging

Molecular imaging is a non-invasive imaging method that is widely used for visualization and detection of biological events at cellular or molecular levels. Stimuli-responsive linkers that can be selectively cleaved by specific biomarkers at desired sites to release or activate imaging agents are appealing tools to improve the specificity, sensitivity, and efficacy of molecular imaging. This review summarizes the recent advances of stimuli-responsive linkers and their application in molecular imaging, highlighting the potential of these linkers in the design of activatable molecular imaging probes. It is hoped that this review could inspire more research interests in the development of responsive linkers and associated imaging applications.

Recent progress in quantitative analysis of self-assembled peptides

Self-assembled peptides have been among the important biomaterials due to its excellent biocompatibility and diverse functions. Over the past decades, substantial progress and breakthroughs have been made in designing self-assembled peptides with multifaceted biomedical applications. The techniques for quantitative analysis, including imaging-based quantitative techniques, chromatographic technique and computational approach (molecular dynamics simulation), are becoming powerful tools for exploring the structure, properties, biomedical applications, and even supramolecular assembly processes of self-assembled peptides. However, a comprehensive review concerning these quantitative techniques remains scarce. In this review, recent progress in techniques for quantitative investigation of biostability, cellular uptake, biodistribution, self-assembly behaviors of self-assembled peptide etc., are summarized. Specific applications and roles of these techniques are highlighted in detail. Finally, challenges and outlook in this field are concluded. It is believed that this review will provide technical guidance for researchers in the field of peptide-based materials and pharmaceuticals, and facilitate related research for newcomers in this field.

Decoration of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) with N-oxides increases the T1 relaxivity of Gd-complexes

High complex stability and longitudinal relaxivity of Gd-based contrast agents are important requirements for magnetic resonance imaging (MRI) because they ensure patient safety and contribute to measurement sensitivity. Charged and zwitterionic Gd3+-complexes of the well-known chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) provide an excellent basis for the development of safe and sensitive contrast agents. In this report, we describe the synthesis of DOTA-NOx, a DOTA derivative with four N-oxide functionalities via "click" functionalization of the tetraazide DOTAZA. The resulting complexes Gd-DOTA-NOx and Eu-DOTA-NOx are stable compounds in aqueous solution. NMR-spectroscopic characterization revealed a high excess of the twisted square antiprismatic (TSAP) coordination geometry over square antiprismatic (SAP). The longitudinal relaxivity of Gd-DOTA-NOx was found to be r1=7.7 mm-1 s-1 (1.41 T, 37 °C), an unusually high value for DOTA complexes of comparable weight. We attribute this high relaxivity to the steric influence and an ordering effect on outer sphere water molecules surrounding the complex generated by the strongly hydrated N-oxide groups. Moreover, Gd-DOTA-NOx was found to be stable against transchelation with high excess of EDTA (200 eq) over a period of 36 h, and it has a similar in vitro cell toxicity as clinically used DOTA-based GBCAs.

Advances in Noninvasive Molecular Imaging Probes for Liver Fibrosis Diagnosis

Liver fibrosis is a wound-healing response to chronic liver injury, which may lead to cirrhosis and cancer. Early-stage fibrosis is reversible, and it is difficult to precisely diagnose with conventional imaging modalities such as magnetic resonance imaging, positron emission tomography, single-photon emission computed tomography, and ultrasound imaging. In contrast, probe-assisted molecular imaging offers a promising noninvasive approach to visualize early fibrosis changes in vivo, thus facilitating early diagnosis and staging liver fibrosis, and even monitoring of the treatment response. Here, the most recent progress in molecular imaging technologies for liver fibrosis is updated. We start by illustrating pathogenesis for liver fibrosis, which includes capillarization of liver sinusoidal endothelial cells, cellular and molecular processes involved in inflammation and fibrogenesis, as well as processes of collagen synthesis, oxidation, and cross-linking. Furthermore, the biological targets used in molecular imaging of liver fibrosis are summarized, which are composed of receptors on hepatic stellate cells, macrophages, and even liver collagen. Notably, the focus is on insights into the advances in imaging modalities developed for liver fibrosis diagnosis and the update in the corresponding contrast agents. In addition, challenges and opportunities for future research and clinical translation of the molecular imaging modalities and the contrast agents are pointed out. We hope that this review would serve as a guide for scientists and students who are interested in liver fibrosis imaging and treatment, and as well expedite the translation of molecular imaging technologies from bench to bedside.

Dynamics of Coordinated Phosphonate Group Directly Observed by 17O-NMR in Lanthanide(iii) Complexes of a Mono(ethyl phosphonate) DOTA Analogue

Biological phosphates can coordinate metal ions and their complexes are common in living systems. Dynamics of mutual oxygen atom exchange in the tetrahedral group in complexes has not been investigated. Here, we present a direct experimental proof of exchange ("phosphonate rotation") in model Ln(III) complexes of monophosphonate H4dota analogue which alters phosphorus atom chirality of coordinated phosphonate monoester. Combination of macrocycle-based isomerism with P-based chirality leads to several diastereoisomers. (Non)-coordinated oxygen atoms were distinguished through 17O-labelled phosphonate group and their mutual exchange was followed by various NMR techniques and DFT calculations. The process is sterically demanding and occurs through bulky bidentate (κ2-PO2)- coordination and was observed only in twisted-square antiprism (TSA) diastereoisomer of large Ln(III) ions. Its energy demands increase for smaller Ln(III) ions (298ΔG≠(exp./DFT)=51.8/52.1 and 61.0/71.5 kJ mol-1 for La(III) and Eu(III), respectively). These results are helpful in design of such complexes as MRI CA and for protein paramagnetic NMR probes. It demonstrates usefulness of 17O NMR to study solution dynamics in complexes involving phosphorus acid derivatives and it may inspire use of this method to study dynamics of phosphoric acid derivatives (as e. g. phosphorus acid-based inhibitors of metalloenzymes) in different areas of chemistry.

Oligomeric amyloid-β targeted contrast agent for MRI evaluation of Alzheimer's disease mouse models

Background

Oligomeric amyloid beta (oAβ) is a toxic factor that acts in the early stage of Alzheimer's disease (AD) and may initiate the pathologic cascade. Therefore, detecting oAβ has a crucial role in the early diagnosis, monitoring, and treatment of AD.

Purpose

The purpose of this study was to evaluate MRI signal changes in different mouse models and the time-dependent signal changes using our novel gadolinium (Gd)-dodecane tetraacetic acid (DOTA)- ob5 aptamer contrast agent.

Methods

We developed an MRI contrast agent by conjugating Gd-DOTA-DNA aptamer called ob5 to evaluate its ability to detect oAβ deposits in the brain using MRI. A total of 10 control mice, 9 3xTg AD mice, and 11 APP/PS/Tau AD mice were included in this study, with the age of each model being 16 or 36 weeks. A T1-weighted image was acquired at the time points before (0 min) and after injection of the contrast agent at 5, 10, 15, 20, and 25 min. The analyses were performed to compare MRI signal differences among the three groups and the time-dependent signal differences in different mouse models.

Results

Both 3xTg AD and APP/PS/Tau AD mouse models had higher signal enhancement than control mice at all scan-time points after injection of our contrast media, especially in bilateral hippocampal areas. In particular, all Tg AD mouse models aged 16 weeks showed a higher contrast enhancement than those aged 36 weeks. For 3xTg AD and APP/PS/Tau AD groups, the signal enhancement was significantly different among the five time points (0 min, 5 min, 10 min, 15 min, 20 min, and 25 min) in multiple ROI areas, typically in the bilateral hippocampus, left thalamus, and left amygdala.

Conclusion

The findings of this study suggest that the expression of the contrast agent in different AD models demonstrates its translational flexibility across different species. The signal enhancement peaked around 15-20 min after injection of the contrast agent. Therefore, our novel contrast agent targeting oAβ has the potential ability to diagnose early AD and monitor the progression of AD.

Recent advances in ratiometric fluorescence imaging of enzyme activity in vivo

Among molecular imaging modalities that can monitor enzyme activity in vivo, optical imaging provides sensitive, molecular-level information at low-cost using safe and non-ionizing wavelengths of light. Yet, obtaining quantifiable optical signals in vivo poses significant challenges. Benchmarking using ratiometric signals can overcome dependence on dosing, illumination variability, and pharmacokinetics to provide quantitative in vivo optical data. This review highlights recent advances using fluorescent probes that are processed by enzymes to induce photophysical changes that can be monitored by ratiometric imaging. These diverse strategies include caged fluorophores that change photophysical properties upon enzymatic cleavage, as well as multi-fluorophore systems that are triggered by enzymatic cleavage to alter optical outputs in one or more fluorescent channels. The strategies discussed here have great potential for further development as well as potential broad applications for targeting diverse enzymes important for a wide range of human diseases.

Development of Ln(III) Derivatives as 19F Parashift Probes

19F parashift probes with paramagnetically shifted reporter nuclei provide attractive platforms to develop molecular imaging probes. These probes enable ratiometric detection of molecular disease markers using a direct detection technique. Here, we describe a series of trivalent lanthanide (Ln(III)) complexes that are structural analogues of the clinically approved MR contrast agent (CA) ProHance to obtain LnL 19F parashift probes. We evaluated trans-gadolinium paramagnetic lanthanides compared to diamagnetic YL for 19F chemical shift and relaxation rate enhancement. The paramagnetic contribution to chemical shift (δPCS) for paramagnetic LnL exhibited either shifts to lower frequency (δPCS < 0 for TbL, DyL, and HoL) or shifts to higher frequency (δPCS > 0 for ErL, TmL, and YbL) compared to YL 19F spectroscopic signal. Zero-echo time pulse sequences achieved 56-fold sensitivity enhancement for DyL over YL, while developing probe-specific pulse sequences with fast delay times and acquisition times achieved 0.6-fold enhancement in limit of detection for DyL. DyL provides an attractive platform to develop 19F parashift probes for ratiometric detection of enzymatic activity.

Chiral Pyclen-Based Heptadentate Chelates as Highly Stable MRI Contrast Agents

In recent years, pyclen-based complexes have attracted a great deal of interest as magnetic resonance imaging (MRI) contrast agents (CAs) and luminescent materials, as well as radiopharmaceuticals. Remarkably, gadopiclenol, a Gd(III) bishydrated complex featuring a pyclen-based heptadentate ligand, received approval as a novel contrast agent for clinical MRI application in 2022. To maximize stability and efficiency, two novel chiral pyclen-based chelators and their complexes were developed in this study. Gd-X-PCTA-2 showed significant enhancements in both thermodynamic and kinetic stabilities compared to those of the achiral parent derivative Gd-PCTA. 1H NMRD profiles reveal that both chiral gadolinium complexes (Gd-X-PCTA-1 and Gd-X-PCTA-2) have a higher relaxivity than Gd-PCTA, while variable-temperature 17O NMR studies show that the two inner-sphere water molecules have distinct residence times τMa and τMb. Furthermore, in vivo imaging demonstrates that Gd-X-PCTA-2 enhances the signal in the heart and kidneys of the mice, and the chiral Gd complexes exhibit the ability to distinguish between tumors and normal tissues in a 4T1 mouse model more efficiently than that of the clinical agent gadobutrol. Biodistribution studies show that Gd-PCTA and Gd-X-PCTA-2 are primarily cleared by a renal pathway, with 24 h residues of Gd-X-PCTA-2 in the liver and kidney being lower than those of Gd-PCTA.

Targeted Nanotheransotics: Integration of Preclinical MRI and CT in the Molecular Imaging and Therapy of Advanced Diseases

The integration of preclinical magnetic resonance imaging (MRI) and computed tomography (CT) methods has significantly enhanced the area of therapy and imaging of targeted nanomedicine. Nanotheranostics, which make use of nanoparticles, are a significant advancement in MRI and CT imaging. In addition to giving high-resolution anatomical features and functional information simultaneously, these multifunctional agents improve contrast when used. In addition to enabling early disease detection, precise localization, and personalised therapy monitoring, they also enable early disease detection. Fusion of MRI and CT enables precise in vivo tracking of drug-loaded nanoparticles. MRI, which provides real-time monitoring of nanoparticle distribution, accumulation, and release at the cellular and tissue levels, can be used to assess the efficacy of drug delivery systems. The precise localization of nanoparticles within the body is achievable through the use of CT imaging. This technique enhances the capabilities of MRI by providing high-resolution anatomical information. CT also allows for quantitative measurements of nanoparticle concentration, which is essential for evaluating the pharmacokinetics and biodistribution of nanomedicine. In this article, we emphasize the integration of preclinical MRI and CT into molecular imaging and therapy for advanced diseases.

Putting Hybrid Nanomaterials to Work for Biomedical Applications

Hybrid nanomaterials have found use in many biomedical applications. This article provides a comprehensive review of the principles, techniques, and recent advancements in the design and fabrication of hybrid nanomaterials for biomedicine. We begin with an introduction to the general concept of material hybridization, followed by a discussion of how this approach leads to materials with additional functionality and enhanced performance. We then highlight hybrid nanomaterials in the forms of nanostructures, nanocomposites, metal-organic frameworks, and biohybrids, including their fabrication methods. We also showcase the use of hybrid nanomaterials to advance biomedical engineering in the context of nanomedicine, regenerative medicine, diagnostics, theranostics, and biomanufacturing. Finally, we offer perspectives on challenges and opportunities.

Kilogram scale facile synthesis and systematic characterization of a Gd-macrochelate as T1-weighted magnetic resonance imaging contrast agent

To overcome the problems of commercial magnetic resonance imaging (MRI) contrast agents (CAs) (i.e., small molecule Gd chelates), we have proposed a new concept of Gd macrochelates based on the coordination of Gd3+ and macromolecules, e.g., poly(acrylic acid) (PAA). To further decrease the r2/r1 ratio of the reported Gd macrochelates that is an important factor for T1 imaging, in this study, a superior macromolecule hydrolyzed polymaleic anhydride (HPMA) was found to coordinate Gd3+. The synthesis conditions were optimized and the generated Gd-HPMA macrochelate was systematically characterized. The obtained Gd-HPMA29 synthesized in a 100 L of reactor has a r1 value of 16.35 mM-1 s-1 and r2/r1 ratio of 2.05 at 7.0 T, a high Gd yield of 92.7% and a high product weight (1074 g), which demonstrates the feasibility of kilogram scale facile synthesis. After optimization of excipients and sterilization at a high temperature, the obtained Gd-HPMA30 formulation has a pH value of 7.97, osmolality of 691 mOsmol/kg water, density of 1.145 g/mL, and viscosity of 2.2 cP at 20 ℃ or 1.8 cP at 37 ℃, which meet all specifications and physicochemical criteria for clinical injections indicating the immense potential for clinical applications.

Kilogram-Scale Synthesis of Extremely Small Gadolinium Oxide Nanoparticles as a T1-Weighted Contrast Agent for Magnetic Resonance Imaging

Magnetic resonance imaging contrast agents are frequently used in clinics to enhance the contrast between diseased and normal tissues. The previously reported poly(acrylic acid) stabilized exceedingly small gadolinium oxide nanoparticles (ES-GdON-PAA) overcame the problems of commercial Gd chelates, but limitations still exist, i.e., high r2/r1 ratio, long blood circulation half-life, and no data for large scale synthesis and formulation optimization. In this study, polymaleic acid (PMA) is found to be an ideal stabilizer to synthesize ES-GdONs. Compared with ES-GdON-PAA, the PMA-stabilized ES-GdON (ES-GdON-PMA) has a lower r2/r1 ratio (2.05, 7.0 T) and a lower blood circulation half-life (37.51 min). The optimized ES-GdON-PMA-9 has an exceedingly small particle size (2.1 nm), excellent water dispersibility, and stability. A facile, efficient, and environmental friendly synthetic method is developed for large-scale synthesis of the ES-GdONs-PMA. The weight of the optimized freeze-dried ES-GdON-PMA-26 synthesized in a 20 L of reactor reaches the kilogram level. The formulation optimization is also finished, and the concentrated ES-GdON-PMA-26 formulation (CGd = 100 mm) after high-pressure steam sterilization possesses eligible physicochemical properties (i.e., pH value, osmolality, viscosity, and density) for investigational new drug application.

Biocompatible and bioactivable terpolymer-lipid-MnO2 Nanoparticle-based MRI contrast agent for improving tumor detection and delineation

Early and precise detection of solid tumor cancers is critical for improving therapeutic outcomes. In this regard, magnetic resonance imaging (MRI) has become a useful tool for tumor diagnosis and image-guided therapy. However, its effectiveness is limited by the shortcomings of clinically available gadolinium-based contrast agents (GBCAs), i.e. poor tumor penetration and retention, and safety concerns. Thus, we have developed a novel nanoparticulate contrast agent using a biocompatible terpolymer and lipids to encapsulate manganese dioxide nanoparticles (TPL-MDNP). The TPL-MDNP accumulated in tumor tissue and produced paramagnetic Mn2+ ions, enhancing T1-weight MRI contrast via the reaction with H2O2 rich in the acidic tumor microenvironment. Compared to the clinically used GBCA, Gadovist®1.0, TPL-MDNP generated stronger T1-weighted MR signals by over 2.0-fold at 30 % less of the recommended clinical dose with well-defined tumor delineation in preclinical orthotopic tumor models of brain, breast, prostate, and pancreas. Importantly, the MRI signals were retained for 60 min by TPL-MDNP, much longer than Gadovist®1.0. Biocompatibility of TPL-MDNP was evaluated and found to be safe up to 4-fold of the dose used for MRI. A robust large-scale manufacturing process was developed with batch-to-batch consistency. A lyophilization formulation was designed to maintain the nanostructure and storage stability of the new contrast agent.

Neutrophils-mediated bioinspired nanoagents for noninvasive monitoring of inflammatory recruitment dynamics and navigating phototherapy in rheumatoid arthritis

Neutrophils play a crucial role in inflammatory immune responses, but their in vivo homing to inflammatory lesions remains unclear, hampering precise treatment options. In this study, we employed a biomineralization-inspired multimodal nanoagent to label neutrophils, enabling noninvasive monitoring of the dynamic process of inflammatory recruitment and guiding photothermal therapy in rheumatoid arthritis. Our nanoagents allowed visualization of neutrophil fate through magnetic resonance imaging, photoacoustic imaging, and fluorescence imaging in the first and second near-infrared windows. Histopathology and immunofluorescence analysis revealed pronounced inflammatory cell infiltration in rheumatoid arthritis compared to the normal limb. Furthermore, the recruitment quantity of neutrophils positively correlated with the inflammatory stage. Additionally, the inherent photothermal effect of the nanoagents efficiently ablated inflammatory cells during the optimal homing time and inflammatory phase. This neutrophil imaging-guided photothermal therapy precisely targeted inflammatory nuclei in rheumatoid arthritis and downregulated pro-inflammatory cytokines in serum. These results demonstrate that in vivo tracking of inflammatory immune response cells can significantly optimize the treatment of inflammatory diseases, including rheumatoid arthritis.

Magnetic Resonance Angiography with Hour-Scale Duration after Single Low-Dose Administration of Biocompatible Gadolinium Oxide Nanoprobe

Long-term contrast-enhanced angiography offers significant advantages in theranostics for diverse vascular diseases, particularly in terms of real-time dynamic monitoring during acute vascular events; However, achieving vascular imaging with a duration of hours through a single administration of low-dose contrast agent remains challenging. Herein, a hyaluronic acid-templated gadolinium oxide (HA@Gd2O3) nanoprobe-enhanced magnetic resonance angiography (MRA) is proposed to address this bottleneck issue for the first time. The HA@Gd2O3 nanoprobe synthesized from a facile one-pot biomineralization method owns ultrasmall size, good biocompatibility, optimal circulation half-life (≈149 min), and a relatively high T1 relaxivity (r1) under both clinical 3 T (8.215 mM-1s-1) and preclinical 9.4 T (4.023 mM-1s-1) equipment. The HA@Gd2O3 nanoprobe-enhanced MRA highlights major vessels readily with significantly improved contrast, extended imaging duration for at least 2 h, and ultrahigh resolution of 0.15 mm under 9.4 T, while only requiring half clinical dosage of Gd. This technique can enable rapid diagnosis and real-time dynamic monitoring of vascular changes in a model of acute superior mesenteric vein thrombosis with only a single injection of nanoprobe. The HA@Gd2O3 nanoprobe-enhanced MRA provides a sophisticated approach for long-term (hour scale) vascular imaging with ultrahigh resolution and high contrast through single administration of low-dose contrast agent.

TEMPO-conjugated tobacco mosaic virus as a magnetic resonance imaging contrast agent for detection of superoxide production in the inflamed liver

Superoxide, an anionic dioxygen molecule, plays a crucial role in redox regulation within the body but is implicated in various pathological conditions when produced excessively. Efforts to develop superoxide detection strategies have led to the exploration of organic-based contrast agents for magnetic resonance imaging (MRI). This study compares the effectiveness of two such agents, nTMV-TEMPO and kTMV-TEMPO, for detecting superoxide in a mouse liver model with lipopolysaccharide (LPS)-induced inflammation. The study demonstrates that kTMV-TEMPO, with a strategically positioned lysine residue for TEMPO attachment, outperforms nTMV-TEMPO as an MRI contrast agent. The enhanced sensitivity of kTMV-TEMPO is attributed to its more exposed TEMPO attachment site, facilitating stronger interactions with water protons and superoxide radicals. EPR kinetics experiments confirm kTMV-TEMPO's faster oxidation and reduction rates, making it a promising sensor for superoxide in inflamed liver tissue. In vivo experiments using healthy and LPS-induced inflamed mice reveal that reduced kTMV-TEMPO remains MRI-inactive in healthy mice but becomes MRI-active in inflamed livers. The contrast enhancement in inflamed livers is substantial, validating the potential of kTMV-TEMPO for detecting superoxide in vivo. This research underscores the importance of optimizing contrast agents for in vivo imaging applications. The enhanced sensitivity and biocompatibility of kTMV-TEMPO make it a promising candidate for further studies in the realm of medical imaging, particularly in the context of monitoring oxidative stress-related diseases.

Different anion (NO3- and OAc-)-controlled construction of dysprosium clusters with different shapes

The complex hydrolysis process and strong uncertainty of self-assembly rules have led to the precise synthesis of lanthanide clusters still being in the "blind-box" stage and simplifying the self-assembly process and developing reliable regulation strategies have attracted widespread attention. Herein, different anions are used to induce the construction of a series of dysprosium clusters with different shapes and connections. When the selected anion is NO3-, it blocks the coordination of metal sites around the cluster through the terminal group coordination mode, thereby controlling the growth of the cluster. When NO3- was changed to OAc-, OAc- adopted a bridging mode to induce modular units to build dysprosium clusters through an annular growth mechanism. Specifically, we selected 2-amino-6-methoxybenzoic acid, 2-hydroxybenzaldehyde, and Dy(NO3)3·6H2O to react under solvothermal conditions to obtain a pentanuclear dysprosium cluster (1). The five Dy(III) ions in 1 are distributed in upper and lower planes and are formed by the tight connection of nitrogen and oxygen atoms, and μ3-OH- bridges on the ligand. Next, octa-nuclear dysprosium cluster (2) were obtained by only regulating ligand substituents. The eight Dy(III) ions in 2 are tightly connected through ligand oxygen atoms, μ2-OH-, and μ3-OH- bridges, forming an elliptical {Dy/O} cluster core. Furthermore, only by changing NO3- to OAc-, a wheel-shaped tetradeca-nuclear dysprosium cluster (3) was obtained. Cluster 3 is composed of OAc- bridged multiple template Dy3L3 units and pulling of these template units connected by an annular growth mechanism forms a wheel-shaped cluster. The angle of the coordination site on NO3- is ∠ONO = 115°, which leads to the further extension of the metal sites on the periphery of clusters 1 and 2 through the terminal group coordination mode, thereby regulating the structural connection of the clusters. However, the angle of the coordination site on OAc- is ∠OCO = 128°, and a slightly increased angle leads to the formation of a ring-shaped cluster 3 by connecting the template units through bridging. This is a rare example of the controllable construction of lanthanide clusters with different shapes induced by the regulation of different anions, which provides a new method for the precise construction of lanthanide clusters with special shapes.

Engineering a Dual-Receptor Targeted Multivalent Probe for Enhanced Magnetic Resonance Imaging of Metastatic Cancer

Noninvasive monitoring of cancer metastasis is essential to improving clinical outcomes. Molecular MRI (mMRI) is a special implementation of noninvasive molecular imaging that promises to offer a powerful means for early detection and analysis of pathological states of cancer by tracking molecular markers. However, this is often hindered by the challenging issue of obtaining transformable mMRI contrast agents with high sensitivity, specificity, and broad applicability, given the high tumor heterogeneity and complex metastatic features. Herein, we present a dual-receptor targeted, multivalent recognition strategy and report a new class of mMRI probes for enhanced imaging of metastatic cancer. This probe is designed by covalently conjugating Gd-chelate with phenylboronic acid and an aptamer via an affordable polymerization chemistry to concurrently target two different cell-membrane receptors that are commonly overexpressed and highly implicated in both tumorigenesis and metastasis. Moreover, the polymerization chemistry allows the probe to contain a bunch of targeting ligands and signal reporters in a single chain, which not only leads to more than 2-fold enhancement in T1 relaxivity at 1.5 T compared to the commercial contrast agent but also enables it to actively target tumor cells in a multivalent recognition manner, contributing to a much higher imaging contrast than single-receptor targeted probes and the commercial agent in mouse models with lung metastases, yet without inducing systemic side effects. We expect this study to offer a useful molecular tool to promote transformable applications of mMRI and a better understanding of molecular mechanisms involved in cancer development.

Recent Advances in Synergistic Effect of Nanoparticles and Its Biomedical Application

The synergistic impact of nanomaterials is critical for novel intracellular and/or subcellular drug delivery systems of minimal toxicity. This synergism results in a fundamental bio/nano interface interaction, which is discussed in terms of nanoparticle translocation, outer wrapping, embedding, and interior cellular attachment. The morphology, size, surface area, ligand chemistry and charge of nanoparticles all play a role in translocation. In this review, we suggest a generalized mechanism to characterize the bio/nano interface, as we discuss the synergistic interaction between nanoparticles and cells, tissues, and other biological systems. Novel perceptions are reviewed regarding the ability of nanoparticles to improve hybrid nanocarriers with homogeneous structures to enhance multifunctional biomedical applications, such as bioimaging, tissue engineering, immunotherapy, and phototherapy.

Harnessing the power of goat milk-derived extracellular vesicles for medical breakthroughs: A review

Research into goat milk-derived extracellular vesicles (GMVs) has grown in popularity in recent years owing to their potential uses in several sectors, including medicine. GMVs are tiny, lipid-bound structures that cells secrete and use to transport bioactive substances like proteins, lipids, and nucleic acids. They may be extracted from different body fluids, including blood, urine, and milk, and have been found to play crucial roles in cell-to-cell communication. GMVs are a promising field of study with applications in preventing and treating various disorders. Their immune-modulating properties, for instance, have been investigated, and they have shown promise in treating autoimmune illnesses and cancer. They may be loaded with therapeutic compounds and directed to particular cells or tissues, but they have also been studied for their potential use as drug-delivery vehicles. Goat milk extracellular vesicles are an intriguing study topic with many possible benefits. Although more study is required to thoroughly understand their functioning and prospective applications, they provide a promising path for creating novel medical treatments and technology.

H-ferritin-nanocaged gadolinium nanoparticles for ultra-sensitive MR molecular imaging

Rationale: Magnetic resonance imaging (MRI) is a powerful diagnostic technology by providing high-resolution imaging. Although MRI is sufficiently valued in its resolving morphology, it has poor sensitivity for tracking biomarkers. Therefore, contrast agents are often used to improve MRI diagnostic sensitivity. However, the clinically used Gd chelates are limited in improving MRI sensitivity owing to their low relaxivity. The objective of this study is to develop a novel contrast agent to achieve a highly sensitive tracking of biomarkers in vivo. Methods: A Gd-based nanoprobe composed of a gadolinium nanoparticle encapsulated within a human H-ferritin nanocage (Gd-HFn) has been developed. The specificity and sensitivity of Gd-HFn were evaluated in vivo in tumor-bearing mice and apolipoprotein E-deficient mice (Apoe-/-) by MRI. Results: The Gd-HFn probe shows extremely high relaxivity values (r1 = 549 s-1mM-1, r2 = 1555 s-1mM-1 under a 1.5-T magnetic field; and r1 = 428 s-1mM-1 and r2 = 1286 s-1mM-1 under a 3.0-T magnetic field), which is 175-fold higher than that of the clinically standard Dotarem (Gd-DOTA, r1 =3.13 s-1mM-1) under a 1.5-T magnetic field, and 150-fold higher under a 3.0-T magnetic field. Owing to the substantially enhanced relaxivity values, Gd-HFn achieved a highly sensitive tracking for the tumor targeting receptor of TfR1 and enabled the in vivo MRI visualization of tumors approaching the angiogenic switch. Conclusions: The developed Gd-HFn contrast agent makes MRI a more powerful tool by simultaneously providing functional and morphological imaging information, which paves the way for a new perspective in molecular imaging.

Preparation and performance of biocompatible gadolinium polymer as liver-targeting magnetic resonance imaging contrast agent

A biocompatible macromolecule-conjugated gadolinium chelate complex (PAV2-EDA-DOTA-Gd) as a new liver-specific contrast agent for magnetic resonance imaging (MRI) was synthesized and evaluated. An aspartic acid-valine copolymer was used as a carrier and ethylenediamine as a chemical linker, and the aspartic acid-valine copolymer was covalently linked to the small molecule MRI contrast agent Gd-DOTA (Dotarem) to synthesize a large molecule contrast agent. In vitro MR relaxation showed that the T1-relaxivity of PAV2-EDA-DOTA-Gd (13.7 mmol-1 L s-1) was much higher than that of the small-molecule Gd-DOTA (4.9 mmol-1 L s-1). In vivo imaging of rats showed that the enhancement effect of PAV2-EDA-DOTA-Gd (55.37 ± 2.80%) on liver imaging was 2.6 times that of Gd-DOTA (21.12 ± 3.86%), and it produced a longer imaging window time (40-70 min for PAV2-EDA-DOTA-Gd and 10-30 min for Gd-DOTA). Preliminary safety experiments, such as cell experiments and tissue sectioning, showed that PAV2-EDA-DOTA-Gd had low toxicity and satisfactory biocompatibility. The results of this study indicated that PAV2-EDA-DOTA-Gd had high potential as a liver-specific MRI contrast agent.

Pharmacokinetics and Tolerability of the Cancer-Targeting MRI Contrast Agent MT218 in Healthy Males

OBJECTIVE

The aim of this study was to evaluate the pharmacokinetics and safety profile of MT218, a peptide-targeted gadolinium-based contrast agent, in healthy males.

MATERIALS AND METHODS

This was a double-blind, randomized, placebo-controlled, single-ascending-dose study including 30 healthy male subjects. In each dose group (0.01, 0.02, 0.04, and 0.08 mmol/kg), 4 subjects received MT218 and 2 subjects received placebo (saline) in bolus injections. The highest dose group (0.08 mmol/kg) was assessed in 2 cohorts, 1 fasted and 1 nonfasted. Clinical laboratory tests, vital signs, and electrocardiograms were investigated. Gadolinium concentrations were measured in plasma samples collected before administration and over a 24-hour period postinjection, and in urine specimens collected until 22 days. A noncompartmental model was used for pharmacokinetic analysis. A clinical and biological safety follow-up was carried out for up to 6 months.

RESULTS

No clinically significant modifications in biochemistry, hematology, urinalysis, electrocardiogram parameters, or vital signs were reported at any time point for any treatment group. No serious adverse events were observed in any dose group. Transient dizziness, hyperhidrosis, and injection site coldness were the main adverse events reported in both the MT218 and placebo groups. The mean total apparent clearance decreased slightly with increasing dose, and the median plasma t 1/2 ranged from 1.7 hours in the 0.01 mmol/kg group to 2.7 hours in the 0.08 mmol/kg nonfasted group. MT218 was rapidly excreted via renal filtration with 42.9% to 52.8% of the injected dose measured in urine within the first hour after administration, and 92.5% to 117.3% in urine within 24 hours. No Gd was detected by inductively coupled plasma mass spectrometry in urine after 21 days.

CONCLUSION

Single intravenous administration of MT218 was safely tolerated in the healthy males. Its pharmacokinetic parameters and safety profile are well aligned with those of other gadolinium-based contrast agents.