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.

Glutathione-triggered prodrugs: Design strategies, potential applications, and perspectives

The burgeoning prodrug strategy offers a promising avenue toward improving the efficacy and specificity of cytotoxic drugs. Elevated intracellular levels of glutathione (GSH) have been regarded as a hallmark of tumor cells and characteristic feature of the tumor microenvironment. Considering the pivotal involvement of elevated GSH in the tumorigenic process, a diverse repertoire of GSH-triggered prodrugs has been developed for cancer therapy, facilitating the attenuation of deleterious side effects associated with conventional chemotherapeutic agents and/or the attainment of more efficacious therapeutic outcomes. These prodrug formulations encompass a spectrum of architectures, spanning from small molecules to polymer-based and organic-inorganic nanomaterial constructs. Although the GSH-triggered prodrugs have been gaining increasing interests, a comprehensive review of the advancements made in the field is still lacking. To fill the existing lacuna, this review undertakes a retrospective analysis of noteworthy research endeavors, based on a categorization of these molecules by their diverse recognition units (i.e., disulfides, diselenides, Michael acceptors, and sulfonamides/sulfonates). This review also focuses on explaining the distinct benefits of employing various chemical architecture strategies in the design of these prodrug agents. Furthermore, we highlight the potential for synergistic functionality by incorporating multiple-targeting conjugates, theranostic entities, and combinational treatment modalities, all of which rely on the GSH-triggering. Overall, an extensive overview of the emerging field is presented in this review, highlighting the obstacles and opportunities that lie ahead. Our overarching goal is to furnish methodological guidance for the development of more efficacious GSH-triggered prodrugs in the future. By assessing the pros and cons of current GSH-triggered prodrugs, we expect that this review will be a handful reference for prodrug design, and would provide a guidance for improving the properties of prodrugs and discovering novel trigger scaffolds for constructing GSH-triggered prodrugs.

Key Insights on the Classification and Theranostic Applications of Magnetic Resonance Imaging Contrast Agents

Magnetic resonance imaging (MRI) is a non-invasive molecular imaging tool being extensively employed in clinical and biomedical research for the detection of a broad spectrum of diseases. This technique offers remarkable spatial resolution, good tissue penetration and a high soft tissue contrast. Contrast agents (CAs) have been regularly used in MRI tests to enhance the resolution of MR images and to visualize the diseased sites in the body. In the past years, considerable efforts have been devoted towards developing new theranostic MRI agents that can be tailored to integrate the targeting and therapeutic functions in a single agent. In this review, we have underlined the role of the MRI CAs in the developing field of 'theranostics' and their recent applications in the combined imaging and therapy of different types of tumors. In addition, this review also outlines the different categories of MRI CAs and their comprehensive classification based on different criteria such as chemical composition, relaxation mechanism and biodistribution with clinically relevant examples.

Developing a Hetero-Trinuclear Erbium(III)-Copper(II) Complex Based on Apoferritin: Targeted Photoacoustic Imaging and Multimodality Therapy of Tumor

For the integration of targeted diagnosis and treatment of tumor, we innovatively designed and synthesized a single-molecule hetero-multinuclear Er(III)-Cu(II) complex (ErCu2) and then constructed an ErCu2@apoferritin (AFt) nanoparticle (NP) delivery system. ErCu2 and ErCu2@AFt NPs not only provided an evident photoacoustic imaging (PAI) signal of the tumor but also effectively inhibited tumor growth by integrating photothermal therapy, chemotherapy, and immunotherapy. ErCu2@AFt NPs improved the targeting ability and decreased the systemic toxicity of ErCu2 in vivo. Furthermore, we confirmed that ErCu2 and ErCu2@AFt NPs inhibited tumor growth by inducing apoptosis and autophagy of tumor cells and activating the immune system. The study not only provides a novel strategy to develop therapeutic metal agents but also reveals their potential for targeted accurate diagnosis and multimodality therapy of cancer.

Constructing sequence-controlled heterolayered dendritic lanthanide chelates via a one-pot strategy using orthogonal chemistry

The construction of sequence-controlled heterometallic lanthanide complexes is challenging despite their intriguing physical/chemical properties and enormous potential applications. Here we report a one-pot strategy that exploits orthogonal chemical reactions for modular assembly, which allows for rapid preparation of sequence-controlled heterolayered lanthanide-complex dendritic structures.

Structure modification: a successful tool for prodrug design

Prodrug strategy is critical for innovative drug development. Structural modification is the most straightforward and effective method to develop prodrugs. Improving drug defects and optimizing the physical and chemical properties of a drug, such as lipophilicity and water solubility, changing the way of administration can be achieved through specific structural modification. Designing prodrugs by linking microenvironment-responsive groups to the prototype drugs is of great help in enhancing drug targeting. In the meantime, making connections between prodrugs and suitable drug delivery systems could realize drug loading increases, greater stability, bioavailability and drug release control. In this paper, lipidic, water-soluble, pH-responsive, redox-sensitive and enzyme-activatable prodrugs are reviewed on the basis of structural modification.

Flavonoid-Conjugated Gadolinium Complexes as Anti-Inflammatory Theranostic Agents

In this study, we designed, synthesized, and evaluated gadolinium compounds conjugated with flavonoids as potential theranostic agents for the treatment of inflammation. These novel theranostic agents combine a molecular imaging agent and one of three flavonoids (galangin, chrysin, and 7-hydroxyflavone) as anti-inflammatory drugs as a single integrated platform. Using these agents, MR imaging showed contrast enhancement (>10 in CNR) at inflamed sites in an animal inflammation model, and subsequent MR imaging used to monitor the therapeutic efficacy of these integrated agents revealed changes in inflamed regions. The anti-inflammatory effects of these agents were demonstrated both in vitro and in vivo. Furthermore, the antioxidant efficacy of the agents was evaluated by measuring their reactive oxygen species scavenging properties. For example, Gd-galangin at 30 μM showed a three-fold higher ROS scavenging of DPPH. Taken together, our findings provide convincing evidence to indicate that flavonoid-conjugated gadolinium compounds can be used as potentially efficient theranostic agents for the treatment of inflammation.

Low-Molecular-Weight Fe(III) Complexes for MRI Contrast Agents

Fe(III) complexes have again attracted much attention for application as MRI contrast agents in recent years due to their high thermodynamic stability, low long-term toxicity, and large relaxivity at a higher magnetic field. This mini-review covers the recent progress on low-molecular-weight Fe(III) complexes, which have been considered as one of the promising alternatives to clinically used Gd(III)-based contrast agents. Two kinds of complexes including mononuclear Fe(III) complexes and multinuclear Fe(III) complexes are summarized in sequence, with a specific highlight of the structural relationships between the complexes and their relaxivity and thermodynamic stability. In additional, the future perspectives for the design of low-molecular-weight Fe(III) complexes for MRI contrast agents are suggested.

An Activatable 19 F MRI Molecular Probe for Sensing and Imaging of Norepinephrine

Norepinephrine (NE), acting as both a neurotransmitter and hormone, plays a significant role in regulating the action of the brain and body. Many studies have demonstrated a strong correlation between mental disorders and aberrant NE levels. Therefore, it is of urgent demand to develop in vivo analytical methods of NE for diagnostic assessment and mechanistic investigations of mental diseases. Herein, we report a 19 F MRI probe (NRFP) for sensing and imaging NE, which is constructed by conjugating a gadolinium chelate to a fluorine-containing moiety through a NE-responsive aromatic thiocarbonate linkage. The capacity and specificity of NRFP for detecting NE is validated with in vitro detecting/imaging experiments. Furthermore, the feasibility of NRFP for visualizing NE in animals is illustrated by ex vivo and in vivo imaging experiments, demonstrating the promising potential of NRFP for selective detection and specific imaging of NE in deep tissues of living subjects.

Tandem Chemoimmunotherapy by a Cascade-Responsive Molecular Prodrug

The limited therapeutic effects of immunotherapy for most types of cancer stimulates the pursuit for efficient methods to improve its response rate. Herein we report the design and synthesis of a cascade-responsive molecular prodrug for tandem chemoimmunotherapy. This molecular prodrug first releases doxorubicin (DOX) in the mildly acidic tumor microenvironment (TME) to induce immunogenic cell death (ICD) of tumor cells. Caspase 3/7 released during tumor cell apoptosis liberates NLG919 from the prodrug, which inhibits the activity of indoleamine 2,3-dioxygenase (IDO) and results in relief of TME immunosuppression. Meanwhile, tumor-associated antigens and immune stimulatory cytokines released during ICD activate the immune response against the tumor, leading to synergistic chemoimmunotherapy. The efficacy of this prodrug is validated by in vitro and in vivo experiments, demonstrating the success of this strategy for cancer treatment.

Mesoporous Silica Nanoparticles-Embedded Lanthanide Organic Polyhedra for Enhanced Stability, Luminescence and Cell Imaging

We report here a simple but efficient “ship-in-a-bottle” synthetic strategy for increasing the stability and luminescence performance of LOPs by embedding them into mesoporous silica nanoparticles (MSNs). Three types of...

A dual-responsive doxorubicin-indoximod conjugate for programmed chemoimmunotherapy

Herein we report a dual-responsive doxorubicin–indoximod conjugate (DOXIND) for programmed chemoimmunotherapy. This conjugate is able to release doxorubicin and indoximod upon exposure to appropriate stimuli for synergistic chemotherapy and immunotherapy, respectively. We demonstrate its promoting effects on immune response and inhibiting effects on tumor growth through a series of in vitro and in vivo experiments.

A dual-responsive doxorubicin–indoximod conjugate was developed, which allows for sequential on-demand release of doxorubicin and indoximod for programmed chemoimmunotherapy.

Porous Silica Nanospheres with a Confined Mono(aquated) Mn(II)-Complex: A Potential T1-T2 Dual Contrast Agent for Magnetic Resonance Imaging

Magnetic resonance imaging has emerged as an indispensable imaging modality for the early-stage diagnosis of many diseases. The imaging in the presence of a contrast agent is always advantageous, as it mitigates the low-sensitivity issue of the measurements and provides excellent contrast in the acquired images even in a short acquisition time. However, the stability and high relaxivity of the contrast agents remained a challenge. Here, molecules of a mononuclear, mono(aquated), thermodynamically stable [log K_MnL = 14.80(7) and pMn = 8.97] Mn(II)-complex (1), based on a hexadentate pyridine-picolinate unit-containing ligand (H₂PyDPA), were confined within a porous silica nanosphere in a noncovalent fashion to render a stable nanosystem, complex 1@SiO₂NP. The entrapped complex 1 (complex 1@SiO₂) exhibited r₁ = 8.46 mM^-1 s^-1 and r₂ = 33.15 mM^-1 s^-1 at pH = 7.4, 25 °C, and 1.41 T in N-(2-hydroxyethyl)piperazine-N'-ethanesulfonic acid buffer. The values were about 2.9 times higher compared to the free (unentrapped)-complex 1 molecules. The synthesized complex 1@SiO₂NP interacted significantly with albumin protein and consequently boosted both the relaxivity values to r₁ = 24.76 mM^-1 s^-1 and r₂ = 63.96 mM^-1 s^-1 at pH = 7.4, 37 °C, and 1.41 T. The kinetic inertness of the entrapped molecules was established by recognizing no appreciable change in the r₁ value upon challenging complex 1@SiO₂NP with 30 and 40 times excess of Zn(II) ions at pH 6 and 25 °C. The water molecule coordinated to the Mn(II) ion in complex 1@SiO₂ was also impervious to the physiologically relevant anions (bicarbonate, biphosphate, and citrate) and pH of the medium. Thus, it ensured the availability of the inner-coordination site of complex 1 for the coordination of water molecules in the biological media. The concentration-dependent changes in image intensities in T₁- and T₂-weighted phantom images and uptake of the nanoparticles by the HeLa cell put forward the biocompatible complex 1@SiO₂NP as a potential dual-mode MRI contrast agent, an alternative to Gd(III)-containing contrast agents.

Activatable Multiplexed 19F Magnetic Resonance Imaging Visualizes Reactive Oxygen and Nitrogen Species in Drug-Induced Acute Kidney Injury

In vivo levels of reactive oxygen species (ROS) and reactive nitrogen species (RNS) are critical to many physiological and pathological processes. Because of the distinct differences in their biological generation and effects, simultaneously visualizing both of them could help deepen our insights into the mechanistic details of these processes. However, real-time and deep-tissue imaging and differentiation of ROS- and RNS-related molecular events in living subjects still remain a challenge. Here, we report the development of two activatable ¹⁹F magnetic resonance imaging (MRI) molecular probes with different ¹⁹F chemical shifts and specific responsive behaviors for simultaneous in vivo detection and deep-tissue imaging of O₂^•- and ONOO^-. These probes are capable of real-time visualization and differentiation of O₂^•- and ONOO^- in living mice with drug-induced acute kidney injury by interference-free multiplexed hot-spot ¹⁹F MRI, illustrating the potential of this technique for background-free real-time imaging of diverse biological processes, accurate diagnosis of various diseases in deep tissues, and rapid toxicity evaluation of assorted drugs.

An Integrated Fluorescent Probe for Ratiometric Detection of Glutathione in the Golgi Apparatus and Activated Organelle-Targeted Therapy

Cancer is a serious threat to human health, and there is an urgent need to develop new treatment methods to overcome it. Organelle targeting therapy, as a highly effective and less toxic side effect treatment strategy, has great research significance and development prospects. Being an essential organelle, the Golgi apparatus plays a particularly major role in the growth of cancer cells. Acting as an indispensable and highly expressed antioxidant in cancer cells, glutathione (GSH) also contributes greatly during the Golgi oxidative stress. Therefore, it counts for much to track the changes of GSH concentration in Golgi for monitoring the occurrence and development of tumor cells, and exploring Golgi-targeted therapy is also extremely important for effective treatment of cancer. In this work, we designed and synthesized a simple Golgi-targeting fluorescent probe GT-GSH for accurately detecting GSH. The probe GT-GSH reacting with GSH decomposes toxic substances to Golgi, thereby killing cancer cells. At the same time, the ratiometric fluorescent probe can detect the concentration changes of GSH in Golgi stress with high sensitivity and selectivity in living cells. Therefore, such a GSH-responsive fluorescent probe with a Golgi-targeted therapy effect gives a new method for accurate treatment of cancer.

Deep-tissue real-time imaging of drug-induced liver injury with peroxynitrite-responsive 19F MRI nanoprobes

Peroxynitrite is an important biomarker for assessing drug-induced liver injury (DILI), which is critical for the development and use of drugs. Herein, we report the development of peroxynitrite-responsive self-assembled ¹⁹F MRI nanoprobes, which enable the sensitive imaging of peroxynitrite in L02 cells subjected to oxidative stress and living mice with DILI.

Smart magnetic resonance imaging-based theranostics for cancer

Smart theranostics are dynamic platforms that integrate multiple functions, including at least imaging, therapy, and responsiveness, in a single agent. This review showcases a variety of responsive theranostic agents developed specifically for magnetic resonance imaging (MRI), due to the privileged position this non-invasive, non-ionising imaging modality continues to hold within the clinical imaging field. Different MRI smart theranostic designs have been devised in the search for more efficient cancer therapy, and improved diagnostic efficiency, through the increase of the local concentration of therapeutic effectors and MRI signal intensity in pathological tissues. This review explores novel small-molecule and nanosized MRI theranostic agents for cancer that exhibit responsiveness to endogenous (change in pH, redox environment, or enzymes) or exogenous (temperature, ultrasound, or light) stimuli. The challenges and obstacles in the design and in vivo application of responsive theranostics are also discussed to guide future research in this interdisciplinary field towards more controllable, efficient, and diagnostically relevant smart theranostics agents.

A simple and feasible atom-precise biotinylated Cu(i) complex for tumor-targeted chemodynamic therapy

A simple and feasible atom-precise biotinylated Cu(i) complex, which can catalyze H₂O₂ overexpressed commonly in the tumor microenvironment to produce ˙OH through a Fenton-like reaction, was prepared and employed as an effective agent for tumor-targeted chemodynamic therapy.

Hypoxia-Activated Prodrug Enabling Synchronous Chemotherapy and HIF-1α Downregulation for Tumor Treatment

The overexpression of HIF-1α in solid tumors due to hypoxia is closely related to drug resistance and consequent treatment failure. Herein, we constructed a hypoxia-activated prodrug named as YC-Dox. This prodrug could be activated under hypoxic conditions and undergo self-immolation to release doxorubicin (Dox) and YC-1 hemisuccinate (YCH-1), which could execute chemotherapy and result in HIF-1α downregulation, respectively. This prodrug is capable of specifically releasing Dox and YCH-1 in response to hypoxia, leading to a substantial synergistic potency and a remarkable cytotoxic selectivity (>8-fold) for hypoxic cancer cells over normoxic healthy cells. The in vivo experiments reveal that this prodrug can selectively aim at hypoxic cancer cells and avoid undesired targeting of normal cells, leading to elevated therapeutic efficacy for tumor treatment and minimized adverse effects on normal tissues.

Precise Cancer Anti-acid Therapy Monitoring Using pH-Sensitive MnO2@BSA Nanoparticles by Magnetic Resonance Imaging

Microfluctuations in a pH gradient create a harsh microenvironment in tumors, leaving behind the most aggressive, invasive, and drug-resistant tumor cells. Directly visualizing the spatiotemporal distribution of pH variations and accurately quantifying the dynamic acid-base changes during cancer treatment are critical to estimate prognosis and to evaluate therapeutic efficacy. However, the quantification of subtle pH variations dynamically and noninvasively remains challenging. The purpose of this study is to determine and visualize dynamic acid-base changes in solid tumors during anti-acid treatments by magnetic resonance imaging (MRI) using pH-sensitive nanoparticles. We report the development of pH-sensitive nanoparticles, MnO₂@BSA, that rapidly and strongly amplify the MR contrast signal in response to the extracellular acidic environment of solid tumors. The spatiotemporal distribution and dynamic fluctuations of pH heterogeneity in NCI-H460 lung tumors were observed with MnO₂@BSA at different time points after an anti-acid treatment with esomeprazole, which directly interferes with the acidic microenvironment of the tumor. Imaging results were validated using a pH microsensor. MRI of pH-sensitive MnO₂@BSA nanoparticles provided direct readouts of the kinetics of pH gradient fluctuations during esomeprazole treatment. A significant MR signal reduction was observed at the 48 h time point after treatment. The manipulated extracellular pH changes detected noninvasively by MRI coincided with the extracellular pH fluctuations measured with a pH microsensor (pH 6.12-6.63). Immunofluorescence and Western blot analyses confirmed the expression of V-ATPase in NCI-H460 lung cancer cells, which could be inhibited by esomeprazole, as detected by ELISA assay. Overall, these results demonstrate that MnO₂@BSA MRI has great potential as a noninvasive tool to accurately monitor pH fluctuations, thereby paving the way for the dynamic detection of acidic microenvironments in vivo without the need for pH microsensors.

Recent Advancements in Stimuli Responsive Drug Delivery Platforms for Active and Passive Cancer Targeting

The tumor-specific targeting of chemotherapeutic agents for specific necrosis of cancer cells without affecting the normal cells poses a great challenge for researchers and scientists. Though extensive research has been carried out to investigate chemotherapy-based targeted drug delivery, the identification of the most promising strategy capable of bypassing non-specific cytotoxicity is still a major concern. Recent advancements in the arena of onco-targeted therapies have enabled safe and effective tumor-specific localization through stimuli-responsive drug delivery systems. Owing to their promising characteristic features, stimuli-responsive drug delivery platforms have revolutionized the chemotherapy-based treatments with added benefits of enhanced bioavailability and selective cytotoxicity of cancer cells compared to the conventional modalities. The insensitivity of stimuli-responsive drug delivery platforms when exposed to normal cells prevents the release of cytotoxic drugs into the normal cells and therefore alleviates the off-target events associated with chemotherapy. Contrastingly, they showed amplified sensitivity and triggered release of chemotherapeutic payload when internalized into the tumor microenvironment causing maximum cytotoxic responses and the induction of cancer cell necrosis. This review focuses on the physical stimuli-responsive drug delivery systems and chemical stimuli-responsive drug delivery systems for triggered cancer chemotherapy through active and/or passive targeting. Moreover, the review also provided a brief insight into the molecular dynamic simulations associated with stimuli-based tumor targeting.

Gadolinium theranostics for the diagnosis and treatment of cancer

Combining therapeutic and diagnostic tools into a single ‘theranostic’ platform lies at the forefront of cancer research. Some of the most promising theranostics exploit the unique nuclear and electronic properties of the lanthanoid metal gadolinium.

Coordination-Assembled Water-Soluble Anionic Lanthanide Organic Polyhedra for Luminescent Labeling and Magnetic Resonance Imaging

Lanthanide-containing functional complexes have found a variety of applications in materials science and biomedicine because of their unique electroptical and magnetic properties. However, the poor stability and solubility in water of multicomponent lanthanide organic assemblies significantly limit their practical applications. We report here a series of water-stable anionic Ln_2nL_3n-type (n = 2, 3, 4, and 5) lanthanide organic polyhedra (LOPs) constructed by deprotonation self-assembly of three fully conjugated ligands (H₄L¹ and H₄L^2a/b) featuring a 2,6-pyridine bitetrazolate chelating moiety. The outcomes of the LOPs formation reactions were found to be very sensitive toward the reaction conditions including base, metal source, solvents, and concentrations as characterized by a combination of NMR, high-resolution ESI-MS and X-ray crystallography. Ligands H₄L^2a/b manifested an excellent sensitization toward lanthanide ions (Ln = Eu^III and Tb^III), with high luminescent quantum yields for Tb₈L^2a₁₂ (Φ = 11.2% in water) and Eu₈L^2b₁₂ (Φ = 76.8% in DMSO) measured in polar solvents. Furthermore, due to the giant molecular weight and rigidity of the polyhedral skeleton, Gd₈L^2b₁₂ showed a very high longitudinal relaxivity (r₁) of 400.53 mM^-1S^-1. The performance of Gd₈L^2b₁₂ as potential magnetic resonance imaging contrast agents (CAs) in vivo was evaluated with much longer retention time in the tumor sites compared with the commercial Gd^III-based CAs. Dual-modal imaging potential has also been demonstrated with the mixed Eu/Gd LOPs. Our results not only provide a new design route toward water-stable multinuclear lanthanide organic assemblies but also offer potential candidates of supramolecular-edifices for bioimaging and drug delivery.

Functional gadolinium-based nanoscale systems for cancer theranostics

Cancer theranostics is a new strategy for combating cancer that integrates cancer imaging and treatment through theranostic agents to provide an efficient and safe way to improve cancer prognosis. Design and synthesis of these cancer theranostic agents are crucial since these agents are required to be biocompatible, tumor-specific, imaging distinguishable and therapeutically efficacious. In this regard, several types of gadolinium (Gd)-based nanomaterials have been introduced to combine different therapeutic agents with Gd to enhance the efficacy of therapeutic agents. At the same time, the entire treatment procedure could be monitored via imaging tools due to incorporation of Gd ions, Gd chelates and Gd/other imaging probes in the theranostic agents. This review aims to overview recent advances in the Gd-based nanomaterials for cancer theranostics and perspectives for Gd nanomaterial-based cancer theranostics are provided.

Iron and Chelation in Biochemistry and Medicine: New Approaches to Controlling Iron Metabolism and Treating Related Diseases

Iron is essential for all living organisms. Many iron-containing proteins and metabolic pathways play a key role in almost all cellular and physiological functions. The diversity of the activity and function of iron and its associated pathologies is based on bond formation with adjacent ligands and the overall structure of the iron complex in proteins or with other biomolecules. The control of the metabolic pathways of iron absorption, utilization, recycling and excretion by iron-containing proteins ensures normal biologic and physiological activity. Abnormalities in iron-containing proteins, iron metabolic pathways and also other associated processes can lead to an array of diseases. These include iron deficiency, which affects more than a quarter of the world's population; hemoglobinopathies, which are the most common of the genetic disorders and idiopathic hemochromatosis. Iron is the most common catalyst of free radical production and oxidative stress which are implicated in tissue damage in most pathologic conditions, cancer initiation and progression, neurodegeneration and many other diseases. The interaction of iron and iron-containing proteins with dietary and xenobiotic molecules, including drugs, may affect iron metabolic and disease processes. Deferiprone, deferoxamine, deferasirox and other chelating drugs can offer therapeutic solutions for most diseases associated with iron metabolism including iron overload and deficiency, neurodegeneration and cancer, the detoxification of xenobiotic metals and most diseases associated with free radical pathology.

Lanthanide conjugates as versatile instruments for therapy and diagnostics

Lanthanides have demonstrated outstanding properties in many fields of research including biology and medicinal chemistry. Their unique luminescence and magnetic properties make them the metals of choice for next generation theranostics that efficiently combine the two central pillars of medicine - diagnostics and therapy. Attached to targeting units, lanthanide complexes pave the way for real-time imaging of drug uptake and distribution as well as specific regulation of subcellular processes with few side effects. This enables individualized treatment options for severe diseases characterized by altered cell expression. The highly diverse results achieved as well as insights into the challenges that research in this area has to face in the upcoming years will be summarized in the present review.

Co-encapsulating CoFe2O4 and MTX for hyperthermia

Magnetic manotheranostics can be a fascinating charm to diagnose a tumour with MRI, and treatment through hyperthermia. This study aims to synthesise and characterise magnetically responsive polymer colloids (MRPCs). Healthy tissue damage done by chemotherapy session could be minimised by MRPCs. For the colloidal formulation of MRPCs, the oil in water emulsion technique was employed with the aid of sonication and stirring. The organic phase of emulsion contained methotrexate (MTX) drug, Eudragit E100 and CoFe2O4 (synthesised by co-precipitation) in ethanol, and the aqueous phase contained tween 80 in deionised water. The emulsion was optimised by studying/adjusting two different parameters, i.e. the concentration of constituents and sonication cycles. Multiple formulations were produced at sonication amplitude of 60% at 20 kHz, followed by centrifugation and lyophilisation. Characterisation of MRPCs was done for morphology, size measurement (23-25 nm), surface charge (∼15.12), coercivity (∼1549.6 G), magnetisation (2.6 emu) and retentivity (1.34 emu). Drug release in simulating physiological environment (pH = 7.4), was observed for up to 48 h, and, to determine the best release kinetic mechanism results were compared with kinetic models. Magnetic hyperthermia studies showed that MRPCs achieved an acceptable temperature of 42°C, for hyperthermia treatments in cancer patients.

Cascaded Multiresponsive Self-Assembled 19F MRI Nanoprobes with Redox-Triggered Activation and NIR-Induced Amplification

Molecular probes featuring promising capabilities including specific targeting, high signal-to-noise ratio, and in situ visualization of deep tissues are in great demand for tumor diagnosis and therapy. ¹⁹F magnetic resonance imaging (MRI) techniques incorporating stimuli-responsive probes are anticipated to be highly beneficial for specific detection and imaging of tumors because of negligible background and deep tissue penetration. Herein, we report a cascaded multiresponsive self-assembled nanoprobe, which enables sequential redox-triggered and near-infrared (NIR) irradiation-induced ¹⁹F MR signal activation/amplification for sensing and imaging. Specifically, we designed and synthesized a cascaded multiresponsive ¹⁹F-bearing nanoprobe based on the self-assembly of amphiphilic redox-responsive ¹⁹F-containing polymers and NIR-absorbing indocyanine green (ICG) molecules. It could realize the activation of ¹⁹F signals in the reducing tumor microenvironment and subsequent signal amplification via the photothermal process. This stepwise two-stage activation/amplification of ¹⁹F signals was validated by ¹⁹F NMR and MRI both in vitro and in vivo. The multiresponsive ¹⁹F nanoprobes capable of cascaded ¹⁹F signal activation/amplification and photothermal effect exertion can provide accurate sensing and imaging of tumors.

DOTA-Branched Organic Frameworks as Giant and Potent Metal Chelators

Multinuclear complexes as metallo-agents for clinical use have caught extensive attention. In this paper, using 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) as both a functioning unit and a constructing junction, we build a series of DOTA-branched organic frameworks with multiple chelating holes by organizing DOTA layer by layer. These giant chelators are well characterized, which reveals their nanosized and soft structures. Further experiments demonstrate that they could efficiently hold abundant metal ions with much higher kinetic stabilities than the conventional small DOTA chelator. Their corresponding polynuclear complexes containing Gd³⁺, Tb³⁺, or both show superior imaging properties, excellent feasibility for peripheral modification, and unusual kinetic stability. This work can be easily extended to the fabrication of diverse homomultinuclear complexes and core/shell heteromultinuclear complexes with multifunctional properties. We expect that this new type of giant molecules and the ligand-branching strategy would open up a new avenue for the design and construction of next-generation polymetallic agents with high performance and stabilities for biomedical applications.

Intracellular GSH-responsive camptothecin delivery systems

Smart GSH-responsive camptothecin delivery systems for treatment of tumors and real-time monitoring in vivo and in vitro were described.

A fluorinated bihydrazide conjugate for activatable sensing and imaging of hypochlorous acid by 19F NMR/MRI

A fluorinated bihydrazide conjugate as a ¹⁹F NMR/MRI probe with a “turn-on” character for activatable sensing and imaging of HClO was reported.