Macromolecules, dendrimers, and nanomaterials in magnetic resonance imaging: the interplay between size, function, and pharmacokinetics

Visualizing enterohepatic circulation in vivo by sensitive 19F MRI with a fluorinated ferrous chelate-based small molecule probe

Enterohepatic circulation (EHC) is a critical biological process for the normal regulation of many endogenous biomolecules and the increased retention of various exogenous substances. The status of EHC is closely related to the ordinary functioning of several digestive organs. However, it remains a challenge to achieve in vivo real-time visualization of this process. Herein, we rationally design and synthesize a ferrous chelate, DO3A-Fe(II)-9F, with high fluorine content and favorable water solubility for visualizing EHC via19F magnetic resonance imaging (MRI). The assessments on imaging performance reveal an 18-time increase in signal intensity compared to the fluorinated ligand alone. This probe's capability of entering EHC via the mediation of organic anion transporting polypeptides (OATPs) is validated with ex vivo bio-distribution analysis and in vivo uptake-blocking imaging experiments, which allows short-time sensitive 19F MRI of EHC in healthy mice. Additionally, we illustrate its capacity for clearly imaging tampered EHC in the mice with inflammatory bowel diseases (IBD), drug-induced liver injury (DILI) or orthotopic hepatocellular carcinoma (HCC). These results illustrate the promising potential of this probe for in vivo visualization of EHC under different conditions, especially disease conditions, which is beneficial for the study, diagnosis, or even stratification of various diseases.

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.

Nitroxides: Chemistry, Antioxidant Properties, and Biomedical Applications

Nitroxides are stable organic free radicals with a wide range of applications. They have found applications in chemistry, biochemistry, biophysics, molecular biology, and biomedicine as EPR/NMR imaging techniques. As spin labels and probes, they are used in electron paramagnetic resonance (EPR) spectroscopy in the study of proteins, lipids, nucleic acids, and enzymes, as well as for measuring oxygen concentration in cells and cellular organelles, as well as tissues and intracellular pH. Their unique redox properties have allowed them to be used as exogenous antioxidants. In this review, we have discussed the chemical properties of nitroxides and their antioxidant properties. Furthermore, we have considered their use as radioprotectors and protective agents in ischemia/reperfusion in vivo and in vitro. We also presented other applications of nitroxides in protecting cells and tissues from oxidative stress and in protein studies and discussed their use in EPR/MRI.

Bioengineered nanomaterials for dynamic diagnostics in vivo

In vivo diagnostics obtains real-time physiological information directly from the site of interest in a patient's body, providing more accurate disease diagnosis compared with ex vivo diagnostics. Particularly, in vivo dynamic diagnostics allows the continuous monitoring of physiological signals over a period of time, offering deeper insights into disease pathogenesis and progression. However, achieving in situ dynamic diagnostics in deep tissues presents challenges related to energy and signal penetration as well as dynamic monitoring. Bioengineered nanomaterials serve as an ideal platform for in vivo dynamic diagnostics, leveraging energy conversion and biofunctionalization to enable continuous acquisition of physiological information across temporal and spatial scales. In this review, with reference to the studies from the last five years, we summarize the fundamental components that are essential for dynamic diagnosis in vivo. Firstly, an input energy source with high tissue penetration is needed, such as near-infrared (NIR) light, X-rays, magnetic field and ultrasound. Secondly, a nanomaterial class that is responsive to such an energy source to provide a readable output signal is chosen. Thirdly, bioengineered nanoprobes are designed to exhibit spatial, temporal or spatiotemporal changes in the output signal. Finally, different methods are used to analyse the output signal of nanoprobes, such as detecting changes in optical, radiation, magnetic and ultrasound signals. This review also discusses the obstacles and potential solutions for advancing these bioengineered nanomaterials toward clinical translational applications.

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.

Gadolinium Complex with Tris-Hydroxypyridinone as an Input for New Imaging Probes: Thermodynamic Stability, Molecular Modeling and Biodistribution

The development of gadolinium-based magnetic resonance imaging (MRI) contrast agents (CAs) is a highly challenging and demanding research field in metal-coordination medicinal chemistry. The recognized high capacity of hydroxypyridinone (HOPO)-based compounds to coordinate Gd (III) led us to evaluate the set of physic-chemical-biological properties of a new Gd (III) complex with a hexadentate tripodal ligand (H3L) containing three 3,4-HOPO chelating moieties attached to an anchoring cyclohexane backbone. In particular, the thermodynamic stability constants of the complex were evaluated by potentiometry, showing the formation of a highly stable (1:1) Gd-L complex (log βGdL = 26.59), with full coordination even in an acid-neutral pH under the experimental conditions used. Molecular simulations of the Gd (III) complex revealed a minimum energy structure with somewhat-distorted octahedral geometry, involving full metal hexa-coordination by the three bidentate moieties of the ligand arms, indicating that an extra water molecule should be coordinated to the metal ion, an important feature for the CAs (and the required enhancement of water proton relaxivity). In vivo biodistribution studies with the 67Ga complex, as a surrogate of the corresponding Gd complex, showed in vivo stability and rapid excretion from the animal body. Though deserving further investigation, these results may give an input on future perspectives towards new MRI diagnostic agents.

Magnetic resonance imaging contrast agents based on albumin nanoparticles

Despite the potential safety hazards and side effects, small molecular magnetic resonance imaging (MRI) contrast agents have been generally used in clinical medical imaging. The development of stable, but low-toxicity and high-efficiency magnetic resonance contrast agents has been receiving continuous attention and research interest. With the deepening of studies, the combination of small molecular magnetic resonance contrast agents and albumin-based carriers is an effective strategy to obtain new MRI contrast agents with safety, low toxicity, high relaxation efficiency and targeting capability. In particular, the relaxivity values of some albumin-based nano-magnetic resonance contrast agents are greater than 100 mM-1 s-1, which is much higher than the relaxivity values of some small molecule MRI contrast agents. Therefore, herein, current research on albumin nanoparticle related MRI contrast agents is summarized, which is of great significance for clarifying the development direction of contrast agents.

Artificially Engineered Nanoprobes for Ultrasensitive Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is a noninvasive and radiation-free technique used for soft tissue. However, there are some limitations of the MRI modality, such as low sensitivity and poor image resolution. Artificially engineered magnetic nanoprobes have been extensively explored as a versatile platform for ultrasensitive MRI contrast agents due to their unique physiochemical characteristics and tunable magnetic properties. In this review, the emphasis is on recent progress in MRI nanoprobes with different structures and elements, including gadolinium-, iron-, manganese-based and metal-free nanoprobes. The key influencing factors and advanced engineering strategies for modulating the relaxation ratio of MRI nanoprobes are systematically condensed. Furthermore, the widespread and noninvasive visualization applications of MRI nanoprobes for real time monitoring of major organs and accurate disease diagnosing, such as cerebrovascular, ischemia, Alzheimer's disease, liver fibrosis, whole-body tumors, inflammation, as well as multi-mode imaging applications are summarized. Finally, the challenges and prospects for the future development of MRI nanoprobes are discussed, and promising strategies are specifically emphasized for improving biocompatibility, precisely engineering of optimal size, AI-driven prediction and design, and multifunctional self-assembly to enhance diagnostics. This review will provide new inspiration for artificial engineering and nanotechnology-based molecular probes for medical diagnosis and therapy with ultrasensitive MRI.

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.

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.

One-Pot Fabrication of Kinetically Inert Ultrasmall Manganese(II) Chelate-Backboned Polymer Contrast Agents for High-Performance Magnetic Resonance Imaging

Traditional macromolecules or nanoscale Mn2+ chelate-based magnetic resonance imaging (MRI) contrast agents (CAs) suffer from complicated and laborious synthesis processes, relatively low kinetic stability and T1 relaxivity, limiting their clinical applications. Herein, we fabricated a series of kinetically inert Mn2+ chelate-backboned polymers, P(MnL-PEG), through a facile and one-pot polymerization process. Particularly, P(MnL-PEG)-3 demonstrates a significantly higher T1 relaxivity of 23.9 Mn mM-1 s-1 at 1.5 T than that of previously reported small molecules and macromolecules or nanoscale Mn2+ chelate-based CAs. Due to its high T1 relaxivity, extended blood circulation, hepatocyte-specific uptake, and kidneys metabolism, P(MnL-PEG)-3 presents significantly enhanced contrast in blood vessel, liver, and kidneys imaging compared to clinical Gd3+-based CAs (Gd-EOB-DTPA and Gd-DOTA) at a dosage of 0.05 mmol Mn/Gd kg-1 BW, and can accurately diagnose orthotopic H22 liver tumors in vivo in animal models. We anticipate that this work will promote the development of clinically relevant MRI CAs.

Synthesis of Antifouling Poly(ethylene glycol) Brushes via "Grafting to" Approach for Improved Biodistribution

Polyethylene glycol (PEG) modification of materials has been identified to mitigate the challenge of biofouling. However, the practical application of PEGylation has been hampered by a low PEGylation density on the material surface. Therefore, developing efficient strategies to promote the PEGylation density is crucial. In this study, PEG brushes (PBs) with various structures were synthesized and their physicochemical properties and biomedical applications were investigated. Compared to benzaldehyde (BA), o-phthalaldehyde (OPA) exhibited higher reactivity with amine groups, resulting in increased grafting density (as high as 96.3%) and improved antifouling properties of PEG brushes. Bottlebrushes fabricated by PEG-OPA and polylysine demonstrated a prolonged circulation time in blood and enhanced potential for magnetic resonance imaging of tumors. Furthermore, the rigidity of the backbone was found to be crucial for the antifouling properties of PEG brushes both in vitro and in vivo. These findings are significant and provide valuable insights into designing biomaterials with superior antifouling performance.

Curcumin Coated Ultra-Small Iron Oxide Nanoparticles as T1 Contrast Agents for Magnetic Resonance Imaging of Cancer Cells

Background

The application of nanotechnology in the molecular diagnosis and treatment of cancer is essential.

Objective

This study aimed to investigate the influence of curcumin-coated ultra-small superparamagnetic iron oxide (USPIO) as a T1 contrast agent in Magnetic Resonance Imaging (MRI).

Material and Methods

In this experimental study, the influence of curcumin-coated USPIO (Fe3O4@C) on the diagnosis of the cancer cell line was investigated. After synthesis, characterization, and relaxation of Fe3O4@C, the contrast changes in T1-weight MRI to mouse colon carcinoma 26 cell line were evaluated in vitro.

Results

Fe3O4@C nanoparticles (NPs) are good at imaging; based on a relaxometry test, the r1 and r2 relaxivities of Dotarem were 3.139 and 0.603 mM-1s-1, respectively. Additionally, the r1 and r2 relaxivities of Fe3O4@C were 3.792 and 1.3 mM-1s-1, respectively, with the rate of 2.155 of r2/r1 NPs.

Conclusion

The NPs can be identified as a positive contrast agent with a weight of T1 in MRI. The coresh-ell Fe3O4@C NPs can be effective in cancer treatment and diagnosis because of the therapeutic effects of curcumin and the properties of USPIO.

A Gd(III)-labelled self-assembling peptide as a potential pH-responsive MRI contrast agent

A marine-derived peptide labelled with a Gd(III)-chelate was found to self-assemble depending on the solution pH, accompanied by changes in T1-relaxivity (r1) values when in the dispersed or self-assembled form. Such pH-responsive behavior can be advantageous in the development of macromolecular magnetic resonance imaging (MRI) contrast agents which monitor the tissue physiology.

Novel Gd-DTPA-peptide for targeted breast tumor magnetic resonance imaging

The prevalence of breast cancer underscores the imperative for early diagnosis in guiding treatment decisions. This study introduces a novel contrast agent, Gd-DTPA-VGB3, derived from the peptide VGB3 targeting vascular endothelial growth factor receptor-1 (VEGFR1) and VEGFR2, to enhance the contrast of conventional drug Magnevist in breast tumor MRI. The MRI contrast agent was synthesized on rink amide resin via Fmoc strategy, incorporating amino acids, and coupling to diethylenetriaminepentaacetic acid (DTPA). Gadolinium (Gd)-DTPA-VGB3 displayed specific binding to VEGFR1/2 in a displacement binding assay. Gd-DTPA-VGB3 exhibited minimal cytotoxicity to normal MCF-10 cells while inhibiting 4T1 mammary carcinoma cell proliferation. Compared to Magnevist, Gd-DTPA-VGB3 demonstrated a 2.8-fold increase in contrast-to-noise ratio (CNR) (355 vs. 125). Gd-DTPA-VGB3 exhibited enhanced accumulation in 4T1 tumor-bearing mice, resulting in significant signal intensity improvement. The findings highlight Gd-DTPA-VGB3's specific binding to VEGFRs, substantiating its potential as a candidate for enhancing MRI contrast in breast cancer diagnostics.

Light-responsive functional nanomaterials as pioneering therapeutics: a paradigm shift to combat age-related disorders

Aging, marked by dysregulated cellular systems, gives rise to a spectrum of age-related disorders, including neurodegeneration, atherosclerosis, immunosenescence, and musculoskeletal issues. These conditions contribute significantly to the global disease burden, posing challenges to health span and economic resources. Current therapeutic approaches, although diverse in mechanism, often fall short in targeting the underlying cellular pathologies. They fail to address the issues compounded by altered pharmacokinetics in the elderly. Nanotechnology emerges as a transformative solution, offering tissue-specific targeted therapies through nanoparticles. Functional nanomaterials (FNMs) respond to internal or external stimuli, with light-responsive nanomaterials gaining prominence. Harnessing the benefits of deep tissue penetration and ease of manipulation particularly in the near-infrared spectrum, light-responsive FNMs present innovative strategies for age-related comorbidities. This review comprehensively summarizes the potential of light-responsive FNM-based approaches for targeting cellular environments in age-related disorders, and also emphasizes the advantages over traditional treatment modalities. Specifically, it focuses on the development of various classes of light-responsive functional nanomaterials including plasmonic nanomaterials, nanomaterials as carriers, upconversion nanomaterials, 2D nanomaterials, transition metal oxide and dichalcogenide nanomaterials and carbon-based nanomaterials against age related diseases. We foresee that such advanced developments in the field of nanotechnology could provide a new hope for clinical diagnosis and treatment of age-related disorders.

Interacting Trimagnetic Ensembles for Enhanced Magnetic Resonance Transverse Relaxivity

An ensemble of nanosystems can be considered to improve magnetic resonance imaging (MRI) transverse relaxivity. Herein, an interacting superparamagnetic competing structure of an isotropic-anisotropic trimagnetic hybrid nanosystem, γ-Fe2O3@δ-MnO2@NiFe2O4, is considered for MRI relaxivity exploration. The interacting superparamagnetic system reveals fascinating dynamic magnetic behavior, where flower-shaped two-dimensional flakes are decorated over nanoparticles. The hybrid nanosystem exhibits modulated shape anisotropy with spin blocking and energy barrier broadening, which help in achieving faster MR transverse relaxivity. The hierarchical architecture ensemble of the trimagnetic landscape shows effective MR transverse relaxivity with a transverse (r2)/longitudinal (r1) relaxivity of 61.5 and potential cell viability. The competing trimagnetic system with regulated activation energy is found to be the underlying reason for such signal enhancement in MRI contrast efficiency. Hence, this study displays a novel pathway correlating MR transverse relaxivity with dynamic magnetic behavior and competing landscape of hierarchical trimagnetic ensembles.

Ultra-small Janus nanoparticle-induced activation of ferroptosis for synergistic tumor immunotherapy

Ferroptosis induced by lipid peroxide (LPO) accumulation is an effective cell death pathway for cancer therapy. However, how to effectively induce ferroptosis at tumor sites and improve its therapeutic effectiveness remains challenging. Here, MnFe2O4@NaGdF4@NLG919@HA (MGNH) nanocomplex with tumor-specific targeting and TME response is constructed to overcome immunosuppressive tumor microenvironment (TME) to potentiate the curative effect of ferroptosis by coupling the immune checkpoint indoleamine 2,3-dioxygenase (IDO) inhibitor, NLG919, and hyaluronic acid (HA) to novel ultra-small MnFe2O4@NaGdF4 (MG) nanoparticles with a Janus structure. Firstly, tumor site-precise delivery of MG and NLG919 is achieved with HA targeting. Secondly, MG acts as a magnetic resonance imaging contrast agent, which not only has a good photothermal effect to realize tumor photothermal therapy, but also depletes glutathione and catalyzes the production of reactive oxygen species from endogenous H2O2, which effectively promotes the accumulation of LPO and inhibits the expression of glutathione peroxidase 4, achieving enhanced ferroptosis. Thirdly, NLG919 inhibits the differentiation of Tregs by blocking the tryptophan/kynurenine immune escape pathway, thereby reversing immunosuppressive TME together with the Mn2+-activated cGAS-STING pathway. This work contributes new perspectives for the development of novel ultra-small Janus nanoparticles to reshape immunosuppressive TME and ferroptosis activation. STATEMENT OF SIGNIFICANCE: The Janus structured MnFe2O4@NaGdF4@NLG919@HA (MGNH) nanocomplex was synthesized, which can realize the precise delivery of T1/T2 contrast agents MnFe2O4@NaGdF4 (MG) and NLG919 at the tumor site under the ultra-small Janus structural characteristics and targeted molecule HA. The production of ROS, consumption of GSH, and photothermal properties of MGNH make it possible for CDT/PTT activated ferroptosis, and synergistically disrupt and reprogram tumor growth and immunosuppressive tumor microenvironment with NLG919 and Mn2+-mediated activation of cGAS-STING pathway, achieving CDT/PTT/immunotherapy activated by ferroptosis. Meanwhile, ultra-small structural properties of MGNH facilitate subsequent metabolic clearance by the body, allowing for the minimization of potential biotoxicity associated with its prolonged retention.

Cyclodextrin-conjugated low-molecular-weight polyethyleneimine as a macromolecular contrast agent for tumor-targeted magnetic resonance imaging

Macromolecular contrast agents (CAs) usually possess excellent contrast ability and tumor-targeting ability in comparison with small-molecule CAs, especially for early tumor detection. Herein, cyclodextrin-conjugated low-molecular-weight polyethyleneimine was synthesized as a macromolecular backbone. Afterward, a linear polymer with adamantane terminal and Gd chelates was synthesized, followed by conjugating with the backbone via host-guest interaction. Finally, folic acid was conjugated onto the as-prepared CAs through bioorthogonal chemistry, which endowed the CAs with the capability to accumulate into the tumor region. Compared to Magnevist (r1 = 4.25 mM-1 s-1) used in clinic, the PC/Ad-PEG2000-PLL(DTPA-Gd)-FA exhibited higher longitudinal relaxivity (r1 = 11.62 mM-1 s-1) with excellent biocompatibility. Furthermore, in vivo experiments demonstrated that PC/Ad-PEG2000-PLL(DTPA-Gd)-FA could effectively accumulate in the tumor region and produce a brighter image than that of Magnevist. The H&E staining and metabolic data further illustrated that this CA possessed excellent biocompatibility in vivo. Finally, these results above suggest that this macromolecular CA could be a potential candidate as a MRI CA for tumor-targeted diagnosis.

Simple hybrid polymeric nanostructures encapsulating macro-cyclic Gd/Eu based complexes: luminescence properties and application as MRI contrast agent

Lanthanide-based macrocycles are successfully incorporated into hybrid polyionic complexes, formed by adding a mixture of zirconium ions to a solution of a double-hydrophilic block copolymer. The resulting nanoobjects with an average radius of approximately 10-15 nm present good colloidal and chemical stability in physiological media even in the presence of competing ions such as phosphate or calcium ions. The final optical and magnetic properties of these objects benefit from both their colloidal nature and the specific properties of the complexes. Hence these new nanocarriers exhibit enhanced T1 MRI contrast, when administered intravenously to mice.

Multivalent Fluorinated Nanorings for On-Cell 19F NMR

The design of imaging agents with a high fluorine content is necessary for overcoming the challenges of low sensitivity in 19F magnetic resonance imaging (MRI)-based molecular imaging. Chemically self-assembled nanorings (CSANs) provide a strategy to increase the fluorine content through multivalent display. We previously reported an 19F NMR-based imaging tracer, in which case a CSAN-compatible epidermal growth factor receptor (EGFR)-targeting protein E1-dimeric dihydrofolate (E1-DD) was bioconjugated to a highly fluorinated peptide. Despite good 19F NMR performance in aqueous solutions, a limited signal was observed in cell-based 19F NMR using this monomeric construct, motivating further design. Here, we design several new E1-DD proteins bioconjugated to peptides of different fluorine contents. Flow cytometry analysis was used to assess the effect of variable fluorinated peptide sequences on the cellular binding characteristics. Structure-optimized protein, RTC-3, displayed an optimal spectral performance with high affinity and specificity for EGFR-overexpressing cells. To further improve the fluorine content, we next engineered monomeric RTC-3 into CSAN, η-RTC-3. With an approximate eightfold increase in the fluorine content, multivalent η-RTC-3 maintained high cellular specificity and optimal 19F NMR spectral behavior. Importantly, the first cell-based 19F NMR spectra of η-RTC-3 were obtained bound to EGFR-expressing A431 cells, showing a significant amplification in the signal. This new design illustrated the potential of multivalent fluorinated CSANs for future 19F MRI molecular imaging applications.

A Gadolinium(III) Complex Based on Pyridoxine Molecule with Single-Ion Magnet and Magnetic Resonance Imaging Properties

Pyridoxine (pyr) is a versatile molecule that forms part of the family of B vitamins. It is used to treat and prevent vitamin B6 deficiency and certain types of metabolic disorders. Moreover, the pyridoxine molecule has been investigated as a suitable ligand toward metal ions. Nevertheless, the study of the magnetic properties of metal complexes containing lanthanide(III) ions and this biomolecule is unexplored. We have synthesized and characterized a novel pyridoxine-based GdIII complex of formula [GdIII(pyr)2(H2O)4]Cl3 · 2 H2O (1) [pyr = pyridoxine]. 1 crystallizes in the triclinic system and space group Pī. In its crystal packing, cationic [Gd(pyr)2(H2O)4]3+ entities are connected through H-bonding interactions involving non-coordinating water molecules and chloride anions. In addition, Hirshfeld surfaces of 1 were calculated to further investigate their intermolecular interactions in the crystal lattice. Our investigation of the magnetic properties of 1, through ac magnetic susceptibility measurements, reveals the occurrence of a slow relaxation in magnetization in this mononuclear GdIII complex, indicating an unusual single-ion magnet (SIM) behavior for this pseudo-isotropic metal ion at very low temperatures. We also studied the relaxometric properties of 1, as a potential contrast agent for high-field magnetic resonance imaging (MRI), from solutions of 1 prepared in physiological serum (0.0-3.2 mM range) and measured at 3 T on a clinical MRI scanner. The values of relaxivity obtained for 1 are larger than those of some commercial MRI contrast agents based on mononuclear GdIII systems.

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.

Modular Self-Assembling Dendrimer Nanosystems for Magnetic Resonance and Multimodality Imaging of Tumors

Bioimaging is a powerful tool for diagnosing tumors but remains limited in terms of sensitivity and specificity. Nanotechnology-based imaging probes able to accommodate abundant imaging units with different imaging modalities are particularly promising for overcoming these limitations. In addition, the nanosized imaging agents can specifically increase the contrast of tumors by exploiting the enhanced permeability and retention effect. A proof-of-concept study is performed on pancreatic cancer to demonstrate the use of modular amphiphilic dendrimer-based nanoprobes for magnetic resonance (MR) imaging (MRI) or MR/near-infrared fluorescence (NIRF) multimodality imaging. Specifically, the self-assembly of an amphiphilic dendrimer bearing multiple Gd3+ units at its terminals, generates a nanomicellar agent exhibiting favorable relaxivity for MRI with a good safety profile. MRI reveals an up to two-fold higher contrast enhancement in tumors than in normal muscle. Encapsulating the NIRF dye within the core of the nanoprobe yields an MR/NIRF bimodal imaging agent for tumor detection that is efficient both for MRI, at Gd3+ concentrations 1/10 the standard clinical dose, and for NIRF imaging, allowing over two-fold stronger fluorescence intensities. These self-assembling dendrimer nanosystems thus constitute effective probes for MRI and MR/NIRF multimodality imaging, offering a promising nanotechnology platform for elaborating multimodality imaging probes in biomedical applications.

Integrative Modulation of Magnetic Resonance Transverse and Longitudinal Relaxivity in a Cell-Viable Bimagnetic Ensemble, γ-Fe2O3@ZnFe2O4

The potential application of magnetic nanosystems as magnetic resonance imaging (MRI) contrast agents has been thoroughly investigated. This work seeks to attain robust MRI-contrast efficiency by designing an interacting landscape of a bimagnetic ensemble of zinc ferrite nanorods and maghemite nanoparticles, γ-Fe2O3@ZnFe2O4. Because of competing spin clusters and structural anisotropy triggered by isotropic γ-Fe2O3 and anisotropic ZnFe2O4, γ-Fe2O3@ZnFe2O4 undergoes the evolution of cluster spin-glass state as evident from the critical slowing down law. Such interacting γ-Fe2O3@ZnFe2O4 with spin flipping of 1.2 × 10-8 s and energy barrier of 8.2 × 10-14 erg reflects enhanced MRI-contrast signal. Additionally, γ-Fe2O3@ZnFe2O4 is cell-viable to noncancerous HEK 293 cell-line and shows no pro-tumorigenic activity as observed in MDA-MB-231, an extremely aggressive triple-negative breast cancer cell line. As a result, γ-Fe2O3@ZnFe2O4 is a feasible option for an MRI-contrast agent having longitudinal relaxivity, r1, of 0.46 s-1mM-1 and transverse relaxivity, r2, of 15.94 s-1mM-1, together with r2/r1 of 34.65 at 1.41 T up to a modest metal concentration of 0.1 mM. Hence, this study addresses an interacting isotropic/anisotropic framework with faster water proton decay in MR-relaxivity resulting in phantom signal amplification.

Research Status of Dendrimer Micelles in Tumor Therapy for Drug Delivery

Dendrimers are a family of polymers with highly branched structure, well-defined composition, and extensive functional groups, which have attracted great attention in biomedical applications. Micelles formed by dendrimers are ideal nanocarriers for delivering anticancer agents due to the explicit study of their characteristics of particle size, charge, and biological properties such as toxicity, blood circulation time, biodistribution, and cellular internalization. Here, the classification, preparation, and structure of dendrimer micelles are reviewed, and the specific functional groups modified on the surface of dendrimers for tumor active targeting, stimuli-responsive drug release, reduced toxicity, and prolonged blood circulation time are discussed. In addition, their applications are summarized as various platforms for biomedical applications related to cancer therapy including drug delivery, gene transfection, nano-contrast for imaging, and combined therapy. Other applications such as tissue engineering and biosensor are also involved. Finally, the possible challenges and perspectives of dendrimer micelles for their further applications are discussed.

Reticular Chemistry of the Fcu-Type Gd(III)-Doped Metal-Organic Framework for T1 -Weighted Magnetic Resonance Imaging

Nanoscale metal-organic frameworks (nanoMOFs) are emerging as an important class of nanomaterials for the systematical investigation of biomedically relevant structure-property relationship (SPR) due to their highly tailorable features. In this work, the reticular chemistry approach is shown to explore the SPR of a fcu-type Zr(IV)-nanoMOF for T1 -weighted magnetic resonance imaging (MRI). Isoreticular replacement of the eight-coordinated square-antiprismatic Zr(IV) by nine-coordinated Gd(III) brings a stoichiometric water capped on the square-antiprismatic site, enabling the relaxation transfer in the inner-sphere, giving the r1 value of 4.55 mM-1 ·s-1 at the doping ratio of Gd : Zr = 1 : 1. Then, these isoreticular engineering studies provide feasible ways to facilitate the relaxation transfer in the second- and outer-sphere of the Gd(III)-doped Zr-oxo cluster for the relaxation respectively. Finally, these in vitro and in vivo MRI studies revealed that the Gd(III)-doped Zr-oxo cluster aggregated underlying the fcu-type framework surpasses its discrete molecular cluster for MRI. These results demonstrated that there is plenty of room inside MOFs for T1 -weighted MRI by reticular chemistry.

Redox Properties and in Vivo Magnetic Resonance Imaging of Cyclodextrin-Polynitroxides Contrast Agents

This paper reports the synthesis, characterization and in vivo application of water-soluble supramolecular contrast agents (Mw: 5-5.6 kDa) for MRI obtained from β-cyclodextrin functionalized with different kinds of nitroxide radicals, both with piperidine structure (CD2 and CD3) and with pyrrolidine structure (CD4 and CD5). As to the stability of the radicals in presence of ascorbic acid, CD4 and CD5 have low second order kinetic constants (≤0.05 M-1  s-1 ) compared to CD2 (3.5 M-1  s-1 ) and CD3 (0.73 M-1  s-1 ). Relaxivity (r1 ) measurements on compounds CD3-CD5 were carried out at different magnetic field strength (0.7, 3, 7 and 9.4 T). At 0.7 T, r1 values comprised between 1.5 mM-1  s-1 and 1.9 mM-1  s-1 were found while a significant reduction was observed at higher fields (r1 ≈0.6-0.9 mM-1  s-1 at 9.4 T). Tests in vitro on HEK293 human embryonic kidney cells, L929 mouse fibroblasts and U87 glioblastoma cells indicated that all compounds were non-cytotoxic at concentrations below 1 μmol mL-1 . MRI in vivo was carried out at 9.4 T on glioma-bearing rats using the compounds CD3-CD5. The experiments showed a good lowering of T1 relaxation in tumor with a retention of the contrast for at least 60 mins confirming improved stability also in vivo conditions.

Novel Nanogels Loaded with Mn(II) Chelates as Effective and Biologically Stable MRI Probes

Here it is described nanogels (NG) based on a chitosan matrix, which are covalently stabilized by a bisamide derivative of Mn-t-CDTA (t-CDTA = trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid). the Mn(II) complex acts both as a contrast medium and as a cross-linking agent. These nanogels are proposed as an alternative to the less stable paramagnetic nanogels obtained by electrostatic interactions between the polymeric matrix and paramagnetic Gd(III) chelates. The present novel nanogels show: i) relaxivity values seven times higher than that of typical monohydrated Mn(II) chelates at the clinical fields, thanks to the combination of a restricted mobility of the complex with a fast exchange of the metal-bound water molecule; ii) high stability of the formulation over time at pH 5 and under physiological conditions, thus excluding metal leaking or particles aggregation; iii) good extravasation and accumulation, with a maximum contrast achieved at 24 h post-injection in mice bearing subcutaneous breast cancer tumor; iv) high T1 contrast (1 T) in the tumor 24 h post-injection. These improved properties pave the way for the use of these paramagnetic nanogels as promising magnetic resonance imaging (MRI) probes for in vitro and in vivo preclinical applications.

Design of Highly Fluorinated Peptides for Cell-based 19F NMR

The design of imaging agents with high fluorine content is essential for overcoming the challenges associated with signal detection limits in 19F MRI-based molecular imaging. In addition to perfluorocarbon and fluorinated polymers, fluorinated peptides offer an additional strategy for creating sequence-defined 19F magnetic resonance imaging (MRI) imaging agents with a high fluorine signal. Our previously reported unstructured trifluoroacetyllysine-based peptides possessed good physiochemical properties and could be imaged at high magnetic field strength. However, the low detection limit motivated further improvements in the fluorine content of the peptides as well as removal of nonspecific cellular interactions. This research characterizes several new highly fluorinated synthetic peptides composed of highly fluorinated amino acids. 19F NMR analysis of peptides TB-1 and TB-9 led to highly overlapping, intense fluorine resonances and acceptable aqueous solubility. Flow cytometry analysis and fluorescence microscopy further showed nonspecific binding could be removed in the case of TB-9. As a preliminary experiment toward developing molecular imaging agents, a fluorinated EGFR-targeting peptide (KKKFFKK-βA-YHWYGYTPENVI) and an EGFR-targeting protein complex E1-DD bioconjugated to TB-9 were prepared. Both bioconjugates maintained good 19F NMR performance in aqueous solution. While the E1-DD-based imaging agent will require further engineering, the success of cell-based 19F NMR of the EGFR-targeting peptide in A431 cells supports the potential use of fluorinated peptides for molecular imaging.

Designing Smart Iron Oxide Nanoparticles for MR Imaging of Tumors

Iron oxide nanoparticles (IONPs) possess unique magnetism and good biocompatibility, and they have been widely applied as contrast agents (CAs) for magnetic resonance imaging (MRI). Traditional CAs typically show a fixed enhanced signal, thus exhibiting the limitations of low sensitivity and a lack of specificity. Nowadays, the progress of stimulus-responsive IONPs allows alteration of the relaxation signal in response to internal stimuli of the tumor, or external stimuli, thus providing an opportunity to overcome those limitations. This review summarizes the current status of smart IONPs as tumor imaging MRI CAs that exhibit responsiveness to endogenous stimuli, such as pH, hypoxia, glutathione, and enzymes, or exogenous stimuli, such as magnets, light, and so on. We discuss the challenges and future opportunities for IONPs as MRI CAs and comprehensively illustrate the applications of these stimuli-responsive IONPs. This review will help provide guidance for designing IONPs as MRI CAs and further promote the reasonable design of magnetic nanoparticles and achieve early and accurate tumor detection.

Metal-Assembled Collagen Peptide Microflorettes as Magnetic Resonance Imaging Agents

Magnetic resonance imaging (MRI) is a medical imaging technique that provides detailed information on tissues and organs. However, the low sensitivity of the technique requires the use of contrast agents, usually ones that are based on the chelates of gadolinium ions. In an effort to improve MRI signal intensity, we developed two strategies whereby the ligand DOTA and Gd(III) ions are contained within Zn(II)-promoted collagen peptide (NCoH) supramolecular assemblies. The DOTA moiety was included in the assembly either via a collagen peptide sidechain (NHdota) or through metal–ligand interactions with a His-tagged DOTA conjugate (DOTA-His6). SEM verified that the morphology of the NCoH assembly was maintained in the presence of the DOTA-containing peptides (microflorettes), and EDX and ICP-MS confirmed that Gd(III) ions were incorporated within the microflorettes. The Gd(III)-loaded DOTA florettes demonstrated higher intensities for the T1-weighted MRI signal and higher longitudinal relaxivity (r1) values, as compared to the clinically used contrast agent Magnevist. Additionally, no appreciable cellular toxicity was observed with the collagen microflorettes loaded with Gd(III). Overall, two peptide-based materials were generated that have potential as MRI contrast agents.

Revealing the In Situ Behavior of Aggregation-Induced Emission Nanoparticles and Their Biometabolic Effects via Mass Spectrometry Imaging

Simultaneous imaging of exogenous nanomaterials and endogenous metabolites in situ remains challenging and is beneficial for a systemic understanding of the biological behavior of nanomaterials at the molecular level. Here, combined with label-free mass spectrometry imaging, visualization and quantification of the aggregation-induced emission nanoparticles (NPs) in tissue were realized as well as related endogenous spatial metabolic changes simultaneously. Our approach enables us to identify the heterogeneous deposition and clearance behavior of nanoparticles in organs. The accumulation of nanoparticles in normal tissues results in distinct endogenous metabolic changes such as oxidative stress as indicated by glutathione depletion. The low passive delivery efficiency of nanoparticles to tumor foci suggested that the enrichment of NPs in tumors did not benefit from the abundant tumor vessels. Moreover, spatial-selective metabolic changes upon NPs mediated photodynamic therapy was identified, which enables understanding of the NPs induced apoptosis in the process of cancer therapy. This strategy allows us to simultaneously detect exogenous nanomaterials and endogenous metabolites in situ, hence to decipher spatial selective metabolic changes in drug delivery and cancer therapy processes.

A Multifunctional Integrated Metal-Free MRI Agent for Early Diagnosis of Oxidative Stress in a Mouse Model of Diabetic Cardiomyopathy

Reactive oxygen species (ROS) are closely associated with the progression of diabetic cardiomyopathy (DCM) and can be regarded as one of its early biomarkers. Magnetic resonance imaging (MRI) is emerging as a powerful tool for the detection of cardiac abnormalities, but the sensitive and direct ROS-response MRI probe remains to be developed. This restricts the early diagnosis of DCM and prevents timely clinical interventions, resulting in serious and irreversible pathophysiological abnormalities. Herein, a novel ROS-response contrast-enhanced MRI nanoprobe (RCMN) is developed by multi-functionalizing fluorinated carbon nanosheets (FCNs) with multi-hydroxyl and 2,2,6,6-tetramethylpiperidin-1-oxyl groups. RCMNs capture ROS and then gather in the heart provisionally, which triggers MRI signal changes to realize the in vivo detection of ROS. In contrast to the clinical MRI agents, the cardiac abnormalities of disease mice is detected 8 weeks in advance with the assistance of RCMNs, which greatly advances the diagnostic window of DCM. To the best of the knowledge, this is the first ROS-response metal-free T2 -weighted MRI probe for the early diagnosis of DCM mice model. Furthermore, RCMNs can timely scavenge excessively produced ROS to alleviate oxidative stress.

High spin Fe(III)-doped nanostructures as T1 MR imaging probes

Magnetic Resonance Imaging (MRI) T₁ contrast agents based on Fe(III) as an alternative to Gd-based compounds have been under intense scrutiny in the last 6-8 years and a number of nanostructures have been designed and proposed for in vivo diagnostic and theranostic applications. Excluding the large family of superparamagnetic iron oxides widely used as T₂ -MR imaging agents that will not be covered by this review, a considerable number and type of nanoparticles (NPs) have been employed, ranging from amphiphilic polymer-based NPs, NPs containing polyphenolic binding units such as melanin-like or polycatechols, mixed metals such as Fe/Gd or Fe/Au NPs and perfluorocarbon nanoemulsions. Iron(III) exhibits several favorable magnetic properties, high biocompatibility and improved toxicity profile that place it as the paramagnetic ion of choice for the next generation of nanosized MRI and theranostic contrast agents. An analysis of the examples reported in the last decade will show the opportunities for relaxivity and MR-contrast enhancement optimization that could bring Fe(III)-doped NPs to really compete with Gd(III)-based nanosystems. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Diagnostic Tools > Diagnostic Nanodevices Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Radiolabeled Iron Oxide Nanoparticles as Dual Modality Contrast Agents in SPECT/MRI and PET/MRI

During the last decades, the utilization of imaging modalities such as single photon emission computed tomography (SPECT), positron emission tomography (PET), and magnetic resonance imaging (MRI) in every day clinical practice has enabled clinicians to diagnose diseases accurately at early stages. Radiolabeled iron oxide nanoparticles (RIONs) combine their intrinsic magnetic behavior with the extrinsic character of the radionuclide additive, so that they constitute a platform of multifaceted physical properties. Thus, at a practical level, RIONs serve as the physical parent of the so-called dual-modality contrast agents (DMCAs) utilized in SPECT/MRI and PET/MRI applications due to their ability to combine, at real time, the high sensitivity of SPECT or PET together with the high spatial resolution of MRI. This review focuses on the synthesis and in vivo investigation of both biodistribution and imaging efficacy of RIONs as potential SPECT/MRI or PET/MRI DMCAs.

The Potential of Gadolinium Ascorbate Nanoparticles as a Safer Contrast Agent

There have been health concerns raised against the use of gadolinium (Gd)-based magnetic resonance imaging contrast agents. The primary observation is that Gd ions are prone to leaking into the bloodstream, causing nephrogenic systemic fibrosis as one of the side effects. In addition, such leakage of the ions inhibits easy clearance from the body. Herein we propose that Gd-ascorbate nanoparticles could be one of the safer choices as they are rather stable in aqueous dispersion and they do not get affected by Zn or Fe ions in the medium. The magnetic properties of the ions are preserved in the nanoparticles, and particles when sufficiently small may be amenable to renal clearance from the human body. Thus, when an aqueous solution of Gd-acetate and ascorbic acid was left to evolve with time, a Gd-ascorbate complex was formed that led to the formation of nanoparticles with time. The sizes of the nanoparticles increased with time, and when the particles were sufficiently large, they precipitated out of the medium. In addition, smaller nanoparticles were consistently present at all times of observations. UV-vis, photoluminescence and FTIR spectroscopy, mass spectrometry, and transmission electron microscopy analyses confirmed the formation of nanoparticles of Gd-ascorbate complex. In addition, magnetic measurements confirmed the high relaxivity of the nanoparticles as compared to the parent salt, indicating the effectiveness of the nanoparticles as contrast agents. Density functional theory-based calculations of the molecular complex-based nanoparticles accounted for the experimental observations.

Lactose-modified enzyme-sensitive branched polymers as a nanoscale liver cancer-targeting MRI contrast agent

Signal enhancement of magnetic resonance imaging (MRI) in the diseased region is dependent on the molecular structure of the MRI contrast agent. In this study, a macromolecular contrast agent, Branched-LAMA-DOTA-Cy5.5-Gd (BLDCGd), was prepared to target liver cancer. Due to the affinity of lactose to the Asialoglycoprotein receptor (ASGPR) over-expressed on the surface of liver cancer cells, lactose was selected as the targeting moiety in the contrast agent. A cathepsin B-sensitive tetrapeptide, GFLG, was used as a linkage moiety to construct a cross-linked macromolecular structure of the contrast agent, and the contrast agent could be degraded into fragments for clearance. A small-molecular-weight molecule, DOTA-Gd, and a fluorescent dye, Cy5.5, were conjugated to the macromolecular structure via a thiol-ene click reaction. The contrast agent, BLDCGd, had a high molecular weight (81 kDa) and a small particle size (59 ± 12 nm). Its longitudinal relaxivity (12.62 mM^-1 s^-1) was 4-fold that of the clinical agent DTPA-Gd (3.42 mM^-1 s^-1). Signal enhancement of up to 184% was observed at the tumor site in an H22 cell-based mouse model. A high accumulation level of BLDCGd in the liver tumor observed from MRI was confirmed from the fluorescence images obtained from the same contrast agent. BLDCGd showed no toxicity to HUVECs and H22 cells in vitro, and low blood chemistry indexes and no distinct histopathological abnormalities were also observed in vivo after injection of BLDCGd since it could be metabolized through the kidneys according to the in vivo MRI results of major organs. Therefore, the branched macromolecule BLDCGd could have great potential as an efficacious and bio-safe nanoscale MRI contrast agent for clinical diagnosis of liver cancer.

c-Met-Targeting 19F MRI Nanoparticles with Ultralong Tumor Retention for Precisely Detecting Small or Ill-Defined Colorectal Liver Metastases

Purpose

Precisely detecting colorectal liver metastases (CLMs), the leading cause of colorectal cancer-associated mortality, is extremely important. ¹H MRI with high soft tissue resolution plays a key role in the diagnosing liver lesions; however, precise detecting CLMs by ¹H MRI is a great challenge due to the limited sensitivity. Even though contrast agents may improve the sensitivity, due to their short half-life, repeated injections are required to monitor the changes of CLMs. Herein, we synthesized c-Met-targeting peptide-functionalized perfluoro-15-crown-5-ether nanoparticles (AH111972-PFCE NPs), for highly sensitive and early diagnosis of small CLMs.

Methods

The size, morphology and optimal properties of the AH111972-PFCE NPs were characterized. c-Met specificity of the AH111972-PFCE NPs was validated by in vitro experiment and in vivo ¹⁹F MRI study in the subcutaneous tumor murine model. The molecular imaging practicability and long tumor retention of the AH111972-PFCE NPs were evaluated in the liver metastases mouse model. The biocompatibility of the AH111972-PFCE NPs was assessed by toxicity study.

Results

AH111972-PFCE NPs with regular shape have particle size of 89.3 ± 17.8 nm. The AH111972-PFCE NPs exhibit high specificity, strong c-Met-targeting ability, and precise detection capability of CLMs, especially small or ill-defined fused metastases in ¹H MRI. Moreover, AH111972-PFCE NPs could be ultralong retained in metastatic liver tumors for at least 7 days, which is conductive to the implementation of continuous therapeutic efficacy monitoring. The NPs with minimal side effects and good biocompatibility are cleared mainly via the spleen and liver.

Conclusion

The c-Met targeting and ultralong tumor retention of AH111972-PFCE NPs will contribute to increasing therapeutic agent accumulation in metastatic sites, laying a foundation for CLMs diagnosis and further c-Met targeted treatment integration. This work provides a promising nanoplatform for the future clinical application to patients with CLMs.

Facile Synthesis of Weakly Ferromagnetic Organogadolinium Macrochelates-Based T1 -Weighted Magnetic Resonance Imaging Contrast Agents

To surmount the major concerns of commercial small molecule Gd chelates and reported Gd-based contrast agents (GBCAs) for magnetic resonance imaging (MRI), a new concept of organogadolinium macrochelates (OGMCs) constructed from the coordination between Gd3+ and macromolecules is proposed. A library of macromolecules were screened for Gd3+ coordination, and two candidates [i.e., poly(acrylic acid) (PAA), and poly(aspartic acid) (PASP)] succeeded in OGMC formation. Under optimized synthesis conditions, both Gd-PAA12 and Gd-PASP11 OGMCs are outstanding T1 -weighted CAs owing to their super high r1 values (> 50 mm-1  s-1 , 3.0 T) and ultralow r2 /r1 ratios (< 1.6, 3.0 T). The ferromagnetism of OGMCs is completely different from the paramagnetism of commercial and reported GBCAs. The ferromagnetism is very weak (Ms  < 1.0 emu g-1 ) leading to a low r2 , which is preferred for T1 MRI. Gd3+ is not released from the OGMC Gd-PAA12 and Gd-PASP11, ensuring biosafety for in vivo applications. The safety and T1 -weighted MRI efficiencies of the OGMC Gd-PAA12 and Gd-PASP11 are tested in cells and mice. The synthesis method of the OGMCs is facile and easy to be scaled up. Consequently, the OGMC Gd-PAA12 and Gd-PASP11 are superior T1 -weighted CAs with promising translatability to replace the commercial Gd chelates.

Preparation of Temperature-Responsive Antibody–Nanoparticles by RAFT-Mediated Grafting from Polymerization

Herein, we report the preparation of temperature-responsive antibody–nanoparticles by the direct polymerization of N-isopropylacrylamide (NIPAAm) from immunoglobulin G (IgG). To this end, a chain transfer agent (CTA) was introduced into IgG, followed by the precipitation polymerization of NIPAAm in an aqueous medium via reversible addition–fragmentation chain transfer polymerization above the lower critical solution temperature (LCST). Consequently, antibody–polymer particles with diameters of approximately 100–200 nm were formed. Owing to the entanglement of the grafted polymers via partial chemical crosslinking, the antibody–nanoparticles maintained their stability even at temperatures below the LCST. Further, the dispersed nanoparticles could be collected by thermal precipitation above the LCST. Additionally, the antibody–nanoparticles formulation could maintain its binding constant and exhibited a good resistance against enzymatic treatment. Thus, the proposed antibody–nanoparticles can be useful for maximizing the therapeutic potential of antibody–drug conjugates or efficacies of immunoassays and antibody recovery and recycling.

Molecular Parameters Promoting High Relaxivity in Cluster-Nanocarrier Magnetic Resonance Imaging Contrast Agents

We have investigated the mechanism of relaxivity for two magnetic resonance imaging contrast agents that both employ a cluster-nanocarrier design. The first system termed Mn8Fe4-coPS comprises the cluster Mn8Fe4O12(L)16(H2O)4 or Mn8Fe4 (1) (L = carboxylate) co-polymerized with polystyrene to form ∼75 nm nanobeads. The second system termed Mn3Bpy-PAm used the cluster Mn3(O2CCH3)6(Bpy)2 or Mn3Bpy (2) where Bpy = 2,2'-bipyridine, entrapped in ∼180 nm polyacrylamide nanobeads. Here, we investigate the rate of water exchange of the two clusters, and corresponding cluster-nanocarriers, in order to elucidate the mechanism of relaxivity in the cluster-nanocarrier. Swift-Connick analysis of O-17 NMR was used to determine the water exchange rates of the clusters and cluster-nanocarriers. We found distinct differences in the water exchange rate between Mn8Fe4 and Mn8Fe4-coPS, and we utilized these differences to elucidate the nanobead structure. Using the transverse relaxivity from O-17 NMR line widths, we were able to determine the hydration state of the Mn3Bpy (2) cluster as well as Mn3Bpy-PAm. Using these hydration states in the Swift-Connick analysis of O-17 NMR, we found the water exchange rate to be extremely close in value for the cluster Mn3Bpy and cluster-nanocarrier Mn3Bpy-PAm.

A dual initiator approach for oxygen tolerant RAFT polymerization

Reversible-deactivation radical polymerizations are privileged approaches for the synthesis of functional and hybrid materials. A bottleneck for conducting these processes is the need to maintain oxygen free conditions. Herein we report a broadly applicable approach to "polymerize through" oxygen using the synergistic combination of two radical initiators having different rates of homolysis. The in situ monitoring of the concentrations of oxygen and monomer simultaneously provided insight into the function of the two initiators and enabled the identification of conditions to effectively remove dissolved oxygen and control polymerization under open-to-air conditions. By understanding how the surface area to volume ratio of reaction vessels influence open-to-air polymerizations, well-defined polymers were produced using acrylate, styrenic, and methacrylate monomers, which each represent an expansion of scope for the "polymerizing through" oxygen approach. Demonstration of this method in tubular reactors using continuous flow chemistry provided a more complete structure-reactivity understanding of how reaction headspace influences PTO RAFT polymerizations.

Synthesis of Carbosilane and Carbosilane-Siloxane Dendrons Based on Limonene

In this work, carbosilane dendrons of the first, second, and third generations were obtained on the basis of a natural terpenoid, limonene. Previously, we have shown the possibility of selective hydrosilylation and hydrothiolation of limonene. It is proved that during hydrosilylation, only the isoprenyl double bond reacts, while the cyclohexene double bond does not undergo into the hydrosilylation reaction. However, the cyclohexene double bond reacts by hydrothiolation. This selectivity makes it possible to use limonene as a dendron growth center, while maintaining a useful function—a double bond at the focal point. Thus, the sequence of hydrosilylation and Grignard reactions based on limonene formed carbosilane dendrons. After that, the end groups were blocked by heptamethyltrisiloxane or butyllithium. The obtained substances were characterized using NMR spectroscopy, elemental analysis and GPC. Thus, the proposed methodology for the synthesis of carbosilane dendrons based on the natural terpenoid limonene opens up wide possibilities for obtaining various macromolecules: dendrimers, Janus dendrimers, dendronized polymers, and macroinitiators.

History of Technological Advancements towards MR-Linac: The Future of Image-Guided Radiotherapy

Image-guided radiotherapy (IGRT) enables optimal tumor targeting and sparing of organs-at-risk, which ultimately results in improved outcomes for patients. Magnetic resonance imaging (MRI) revolutionized diagnostic imaging with its superior soft tissue contrast, high spatiotemporal resolution, and freedom from ionizing radiation exposure. Over the past few years there has been burgeoning interest in MR-guided radiotherapy (MRgRT) to overcome current challenges in X-ray-based IGRT, including but not limited to, suboptimal soft tissue contrast, lack of efficient daily adaptation, and incremental exposure to ionizing radiation. In this review, we present an overview of the technologic advancements in IGRT that led to MRI-linear accelerator (MRL) integration. Our report is organized in three parts: (1) a historical timeline tracing the origins of radiotherapy and evolution of IGRT, (2) currently available MRL technology, and (3) future directions and aspirations for MRL applications.

Dendrimers as nanoscale vectors: Unlocking the bars of cancer therapy

Chemotherapy is the first choice in the treatment of cancer and is always preferred to other approaches such as radiation and surgery, but it has never met the need of patients for a safe and effective drug. Therefore, new advances in cancer treatment are now needed to reduce the side effects and burdens associated with chemotherapy for cancer patients. Targeted treatment using nanotechnology are now being actively explored as they could effectively deliver therapeutic agents to tumor cells without affecting normal cells. Dendrimers are promising nanocarriers with distinct physiochemical properties that have received considerable attention in cancer therapy studies, which is partly due to the numerous functional groups on their surface. In this review, we discuss the progress of different types of dendrimers as delivery systems in cancer therapy, focusing on the challenges, opportunities, and functionalities of the polymeric molecules. The paper also reviews the various role of dendrimers in their entry into cells via endocytosis, as well as the molecular and inflammatory pathways in cancer. In addition, various dendrimers-based drug delivery (e.g., pH-responsive, enzyme-responsive, redox-responsive, thermo-responsive, etc.) and lipid-, amino acid-, polymer- and nanoparticle-based modifications for gene delivery, as well as co-delivery of drugs and genes in cancer therapy with dendrimers, are presented. Finally, biosafety concerns and issues hindering the transition of dendrimers from research to the clinic are discussed to shed light on their clinical applications.