Covalent assembly of nanoparticles as a peptidase-degradable platform for molecular MRI

In Vivo PET Detection of Lung Micrometastasis in Mice by Targeting Endothelial VCAM-1 Using a Dual-Contrast PET/MRI Probe

Current clinical diagnostic imaging methods for lung metastases are sensitive only to large tumours (1-2 mm cross-sectional diameter), and early detection can dramatically improve treatment. We have previously demonstrated that an antibody-targeted MRI contrast agent based on microparticles of iron oxide (MPIO; 1 μm diameter) enables the imaging of endothelial vascular cell adhesion molecule-1 (VCAM-1). Using a mouse model of lung metastasis, upregulation of endothelial VCAM-1 expression was demonstrated in micrometastasis-associated vessels but not in normal lung tissue, and binding of VCAM-MPIO to these vessels was evident histologically. Owing to the lack of proton MRI signals in the lungs, we modified the VCAM-MPIO to include zirconium-89 (89Zr, t1/2 = 78.4 h) in order to allow the in vivo detection of lung metastases by positron emission tomography (PET). Using this new agent (89Zr-DFO-VCAM-MPIO), it was possible to detect the presence of micrometastases within the lung in vivo from ca. 140 μm in diameter. Histological analysis combined with autoradiography confirmed the specific binding of the agent to the VCAM-1 expressing vasculature at the sites of pulmonary micrometastases. By retaining the original VCAM-MPIO as the basis for this new molecular contrast agent, we have created a dual-modality (PET/MRI) agent for the concurrent detection of lung and brain micrometastases.

MRI-based microthrombi detection in stroke with polydopamine iron oxide

In acute ischemic stroke, even when successful recanalization is obtained, downstream microcirculation may still be obstructed by microvascular thrombosis, which is associated with compromised brain reperfusion and cognitive decline. Identifying these microthrombi through non-invasive methods remains challenging. We developed the PHySIOMIC (Polydopamine Hybridized Self-assembled Iron Oxide Mussel Inspired Clusters), a MRI-based contrast agent that unmasks these microthrombi. In a mouse model of thromboembolic ischemic stroke, our findings demonstrate that the PHySIOMIC generate a distinct hypointense signal on T2*-weighted MRI in the presence of microthrombi, that correlates with the lesion areas observed 24 hours post-stroke. Our microfluidic studies reveal the role of fibrinogen in the protein corona for the thrombosis targeting properties. Finally, we observe the biodegradation and biocompatibility of these particles. This work demonstrates that the PHySIOMIC particles offer an innovative and valuable tool for non-invasive in vivo diagnosis and monitoring of microthrombi, using MRI during ischemic stroke.

MicroRNAs as regulators of immune checkpoints in cancer immunotherapy: targeting PD-1/PD-L1 and CTLA-4 pathways

Immunotherapy has revolutionized cancer treatment by harnessing the power of the immune system to eliminate tumors. Immune checkpoint inhibitors (ICIs) block negative regulatory signals that prevent T cells from attacking cancer cells. Two key ICIs target the PD-1/PD-L1 pathway, which includes programmed death-ligand 1 (PD-L1) and its receptor programmed death 1 (PD-1). Another ICI targets cytotoxic T-lymphocyte-associated protein 4 (CTLA-4). While ICIs have demonstrated remarkable efficacy in various malignancies, only a subset of patients respond favorably. MicroRNAs (miRNAs), small non-coding RNAs that regulate gene expression, play a crucial role in modulating immune checkpoints, including PD-1/PD-L1 and CTLA-4. This review summarizes the latest advancements in immunotherapy, highlighting the therapeutic potential of targeting PD-1/PD-L1 and CTLA-4 immune checkpoints and the regulatory role of miRNAs in modulating these pathways. Consequently, understanding the complex interplay between miRNAs and immune checkpoints is essential for developing more effective and personalized immunotherapy strategies for cancer treatment.

Realization of High Magnetization in Artificially Designed Ni/NiO Layers through Exchange Coupling

High-magnetization materials play crucial roles in various applications. However, the past few decades have witnessed a stagnation in the discovery of new materials with high magnetization. In this work, Ni/NiO nanocomposites are fabricated by depositing Ni and NiO thin layers alternately, followed by annealing at specific temperatures. Both the as-deposited samples and those annealed at 373 K exhibit low magnetization. However, the samples annealed at 473 K exhibit a significantly enhanced saturation magnetization exceeding 607 emu cm-3 at room temperature, surpassing that of pure Ni (480 emu cm-3 ). Material characterizations indicate that the composite comprises NiO nanoclusters of size 1-2 nm embedded in the Ni matrix. This nanoclustered NiO is primarily responsible for the high magnetization, as confirmed by density functional theory calculations. The calculations also indicate that the NiO clusters are ferromagnetically coupled with Ni, resulting in enhanced magnetization. This work demonstrates a new route toward developing artificial high-magnetization materials using the high magnetic moments of nanoclustered antiferromagnetic materials.

In vivo methods for imaging blood-brain barrier function and dysfunction

The blood-brain barrier (BBB) is the interface between the central nervous system and systemic circulation. It tightly regulates what enters and is removed from the brain parenchyma and is fundamental in maintaining brain homeostasis. Increasingly, the BBB is recognised as having a significant role in numerous neurological disorders, ranging from acute disorders (traumatic brain injury, stroke, seizures) to chronic neurodegeneration (Alzheimer's disease, vascular dementia, small vessel disease). Numerous approaches have been developed to study the BBB in vitro, in vivo, and ex vivo. The complex multicellular structure and effects of disease are difficult to recreate accurately in vitro, and functional aspects of the BBB cannot be easily studied ex vivo. As such, the value of in vivo methods to study the intact BBB cannot be overstated. This review discusses the structure and function of the BBB and how these are affected in diseases. It then discusses in depth several established and novel methods for imaging the BBB in vivo, with a focus on MRI, nuclear imaging, and high-resolution intravital fluorescence microscopy.

Surface-Mediated Production of Complexed •OH Radicals and FeO Species as a Mechanism for Iron Oxide Peroxidase-Like Nanozymes

Fe₃ O₄ nanoparticles (NPs) with intrinsic peroxidase-like properties have attracted significant interest, although limited information is available on the definite catalytic mechanism. Here, it is shown that both complexed hydroxyl radicals (•OH) and high-valent FeO species are attributed primarily to the peroxidase-like catalytic activity of Fe₃ O₄ NPs under acid conditions rather than only being caused by free •OH radicals generated through the iron-driven Fenton/Haber-Weiss reactions as previously thought. The low energy barrier of OO bond dissociation of H₂ O₂ /•OOH (0.14 eV) and the high oxidation activity of surface FeO (0 eV) due to the reduced state of Fe on the surface of Fe₃ O₄ NPs thermodynamically favor both the •OH and FeO pathways. By contrast, high-valent FeO species are the key intermediates in the catalytic cycles of natural peroxidase enzymes. Moreover, it is demonstrated that the enzyme-like activity of Fe₃ O₄ NPs can be rationally regulated by modulating the size, surface structure, and valence of active metal atoms in the light of this newly proposed nanozyme catalytic mechanism.

MRI techniques for immunotherapy monitoring

MRI is a widely available clinical tool for cancer diagnosis and treatment monitoring. MRI provides excellent soft tissue imaging, using a wide range of contrast mechanisms, and can non-invasively detect tissue metabolites. These approaches can be used to distinguish cancer from normal tissues, to stratify tumor aggressiveness, and to identify changes within both the tumor and its microenvironment in response to therapy. In this review, the role of MRI in immunotherapy monitoring will be discussed and how it could be utilized in the future to address some of the unique clinical questions that arise from immunotherapy. For example, MRI could play a role in identifying pseudoprogression, mixed response, T cell infiltration, cell tracking, and some of the characteristic immune-related adverse events associated with these agents. The factors to be considered when developing MRI imaging biomarkers for immunotherapy will be reviewed. Finally, the advantages and limitations of each approach will be discussed, as well as the challenges for future clinical translation into routine clinical care. Given the increasing use of immunotherapy in a wide range of cancers and the ability of MRI to detect the microstructural and functional changes associated with successful response to immunotherapy, the technique has great potential for more widespread and routine use in the future for these applications.

Tracking the immune response by MRI using biodegradable and ultrasensitive microprobes

Molecular magnetic resonance imaging (MRI) holds great promise for diagnosis and therapeutic monitoring in a wide range of diseases. However, the low intrinsic sensitivity of MRI to detect exogenous contrast agents and the lack of biodegradable microprobes have prevented its clinical development. Here, we synthetized a contrast agent for molecular MRI based on a previously unknown mechanism of self-assembly of catechol-coated magnetite nanocrystals into microsized matrix-based particles. The resulting biodegradable microprobes (M3P for microsized matrix-based magnetic particles) carry up to 40,000 times higher amounts of superparamagnetic material than classically used nanoparticles while preserving favorable biocompatibility and excellent water dispersibility. After conjugation to monoclonal antibodies, targeted M3P display high sensitivity and specificity to detect inflammation in vivo in the brain, kidneys, and intestinal mucosa. The high payload of superparamagnetic material, excellent toxicity profile, short circulation half-life, and widespread reactivity of the M3P particles provides a promising platform for clinical translation of immuno-MRI.

Micro/Nanosystems for Magnetic Targeted Delivery of Bioagents

Targeted delivery of pharmaceuticals is promising for efficient disease treatment and reduction in adverse effects. Nano or microstructured magnetic materials with strong magnetic momentum can be noninvasively controlled via magnetic forces within living beings. These magnetic carriers open perspectives in controlling the delivery of different types of bioagents in humans, including small molecules, nucleic acids, and cells. In the present review, we describe different types of magnetic carriers that can serve as drug delivery platforms, and we show different ways to apply them to magnetic targeted delivery of bioagents. We discuss the magnetic guidance of nano/microsystems or labeled cells upon injection into the systemic circulation or in the tissue; we then highlight emergent applications in tissue engineering, and finally, we show how magnetic targeting can integrate with imaging technologies that serve to assist drug delivery.

Redox-Activated Contrast-Enhanced T1-Weighted Imaging Visualizes Glutathione-Mediated Biotransformation Dynamics in the Liver

GSH-mediated liver biotransformation is a crucial physiological process demanding efficient research tools. Here, we report a type of amorphous Fe_xMn_yO nanoparticles (AFMO-ZDS NPs) as redox-activated probes for in vivo visualization of the dynamics of GSH-mediated biotransformation in liver with T₁-weighted magnetic resonance imaging (MRI). This imaging technique reveals the periodic variations in GSH concentration during the degradation of AFMO-ZDS NPs due to the limited transportation capacity of GSH carriers in the course of GSH efflux from hepatocytes to perisinusoidal space, providing direct imaging evidence for this important carrier-mediated process during GSH-mediated biotransformation. Therefore, this technique offers an effective method for in-depth investigations of GSH-related biological processes in liver under various conditions as well as a feasible means for the real-time assessment of liver functions, which is highly desirable for early diagnosis of liver diseases and prompt a toxicity evaluation of pharmaceuticals.

Design and Preparation of "corn-like" SPIONs@DFK-SBP-M13 Assembly for Improvement of Effective Internalization

Purpose

Superparamagnetic iron oxide nanoparticles (SPIONs) have exhibited preeminent diagnosis and treatment performances, but their low internalization severely limits predesigned functions. The low cell internalization is now an urgent bottleneck problem for almost all nanomaterials. To achieve more internalization of SPIONS, recombinant M13 phage was designed for targeted delivery and smart release.

Methods

M13 phages were designed to co-express exogenous SPARC binding peptide (SBP) and cathepsin B cleavage peptide (DFK), formed recombinant DFK-SBP-M13. 3.37± 0.06 nm of SPIONs were modified by 3, 4-dihydroxyhydrocinnamic acid (DHCA) to gain 10.80 ± 0.21 nm of DHCA-coated SPIONs, i.e., DHCA@SPIONs. Upon adjusting the proportions of DHCA@SPIONs and DFK-SBP-M13, the multi-carboxyl SPIONs assembled onto recombinant M13 phages via covalent bonding. The assemblies were co-cultured with MDA-MB-231 cells to interpret their internalization and smart release.

Results

The “corn-like” SPIONs@DFK-SBP-M13 (261.47±3.30 nm) assemblies have not been reported previously. The assembly was stable, dispersible, superparamagnetic and biocompatible. After co-cultivation with MDA-MB-231 cells, the SPIONs@DFK-SBP-M13 assemblies quickly bond to the cell surface and are internalized. The enrichment rate of SPIONs@DFK-SBP-M13 assembly was 13.9 times higher than free SPIONs at 0.5 h, and intracellular Fe content was 3.6 times higher at 1 h. Furthermore, the DFK peptides favored cathepsin B to cleave SPIONs from the M13 templates resulting in release of SPIONs inside cells.

Conclusion

The novel SPIONs@DFK-SBP-M13 assembly can rapidly deliver SPIONs to the targeted sites and enabled smart release. The combination of genetic recombination and nanotechnology is beneficial for designing and optimizing some new nanomaterials with special functions to achieve wider applications.

Molecular MRI of Neuroinflammation: Time to Overcome the Translational Roadblock

The ability to detect a molecular target in the central nervous system non-invasively and at high spatial resolution using magnetic resonance imaging (MRI) has attracted the interest of researchers for several decades. Yet, molecular MRI studies remain restricted to the preclinical stage and the path to clinical translation remains unclear. The focus of molecular MRI of neuroinflammation has moved from parenchymal to vascular targets, that are more easily reachable by intravenously injected probes. This has allowed the use of large superparamagnetic probes, such as micro-sized particles of iron oxide (MPIO), that dramatically improved the sensitivity of molecular MRI compared to smaller contrast agents. In particular, recent studies demonstrated the feasibility of unraveling inflammation in the brain by MRI using MPIO able to bind activated endothelial cells with potential applications in neurovascular, neuroinflammatory and neurodegenerative disorders. In the present review, we present the most striking advances in the field and the remaining challenges that must be overcome before clinical use of molecular MRI of neuroinflammation.

Bioinspired Magnetic Nanochains for Medicine

Superparamagnetic iron oxide nanoparticles (SPIONs) have been widely used for medicine, both in therapy and diagnosis. Their guided assembly into anisotropic structures, such as nanochains, has recently opened new research avenues; for instance, targeted drug delivery. Interestingly, magnetic nanochains do occur in nature, and they are thought to be involved in the navigation and geographic orientation of a variety of animals and bacteria, although many open questions on their formation and functioning remain. In this review, we will analyze what is known about the natural formation of magnetic nanochains, as well as the synthetic protocols to produce them in the laboratory, to conclude with an overview of medical applications and an outlook on future opportunities in this exciting research field.

A novel molecular magnetic resonance imaging agent targeting activated leukocyte cell adhesion molecule as demonstrated in mouse brain metastasis models

Molecular magnetic resonance imaging (MRI) allows visualization of biological processes at the molecular level. Upregulation of endothelial ALCAM (activated leukocyte cell adhesion molecule) is a key element for leukocyte recruitment in neurological disease. The aim of this study, therefore, was to develop a novel molecular MRI contrast agent, by conjugating anti-ALCAM antibodies to microparticles of iron oxide (MPIO), for detection of endothelial ALCAM expression in vivo. Binding specificity of ALCAM-MPIO was demonstrated in vitro under static and flow conditions. Subsequently, in a proof-of-concept study, mouse models of brain metastasis were induced by intracardial injection of brain-tropic human breast carcinoma, lung adenocarcinoma or melanoma cells to upregulate endothelial ALCAM. At selected time-points, mice were injected intravenously with ALCAM-MPIO, and ALCAM-MPIO induced hypointensities were observed on T2*-weighted images in all three models. Post-gadolinium MRI confirmed an intact blood-brain barrier, indicating endoluminal binding. Correlation between endothelial ALCAM expression and ALCAM-MPIO binding was confirmed histologically. Statistical analysis indicated high sensitivity (80-90%) and specificity (79-83%) for detection of endothelial ALCAM in vivo with ALCAM-MPIO. Given reports of endothelial ALCAM upregulation in numerous neurological diseases, this advance in our ability to image ALCAM in vivo may yield substantial improvements for both diagnosis and targeted therapy.

Inorganic nanomaterials with rapid clearance for biomedical applications

Inorganic nanomaterials that have inherently exceptional physicochemical properties (e.g., catalytic, optical, thermal, electrical, or magnetic performance) that can provide desirable functionality (e.g., drug delivery, diagnostics, imaging, or therapy) have considerable potential for application in the field of biomedicine. However, toxicity can be caused by the long-term, non-specific accumulation of these inorganic nanomaterials in healthy tissues, preventing their large-scale clinical utilization. Over the past several decades, the emergence of biodegradable and clearable inorganic nanomaterials has offered the potential to prevent such long-term toxicity. In addition, a comprehensive understanding of the design of such nanomaterials and their metabolic pathways within the body is essential for enabling the expansion of theranostic applications for various diseases and advancing clinical trials. Thus, it is of critical importance to develop biodegradable and clearable inorganic nanomaterials for biomedical applications. This review systematically summarizes the recent progress of biodegradable and clearable inorganic nanomaterials, particularly for application in cancer theranostics and other disease therapies. The future prospects and opportunities in this rapidly growing biomedical field are also discussed. We believe that this timely and comprehensive review will stimulate and guide additional in-depth studies in the area of inorganic nanomedicine, as rapid in vivo clearance and degradation is likely to be a prerequisite for the future clinical translation of inorganic nanomaterials with unique properties and functionality.

New Approaches in Nanomedicine for Ischemic Stroke

Ischemic stroke, caused by the interruption of blood flow to the brain and subsequent neuronal death, represents one of the main causes of disability in developed countries. Therapeutic methods such as recanalization approaches, neuroprotective drugs, or recovery strategies have been widely developed to improve the patient's outcome; however, important limitations such as a narrow therapeutic window, the ability to reach brain targets, or drug side effects constitute some of the main aspects that limit the clinical applicability of the current treatments. Nanotechnology has emerged as a promising tool to overcome many of these drug limitations and improve the efficacy of treatments for neurological diseases such as stroke. The use of nanoparticles as a contrast agent or as drug carriers to a specific target are some of the most common approaches developed in nanomedicine for stroke. Throughout this review, we have summarized our experience of using nanotechnology tools for the study of stroke and the search for novel therapies.

Improving anti-PD-L1 therapy in triple negative breast cancer by polymer-enhanced immunogenic cell death and CXCR4 blockade

Triple negative breast cancer (TNBC) with highly metastatic features generally does not respond to anti-programmed cell death 1 ligand 1 (PD-L1) therapy due to multiple immunosuppressive mechanisms to exclude and disable T cells. Here, we develop a polymer-based combinatory approach consisting of both immunogenic cell death (ICD)-inducing and CXCR4-inhibiting function to prime tumor microenvironment and improve anti-PD-L1 therapy in TNBC. Our findings revealed that the combination therapy was able to spur the T cell response in primary tumors by increasing the tumor immunogenicity to recruit T cells, removing the physiological barriers of intratumoral fibrosis and collagen to increase T cell infiltration, and reducing the immunosuppressive cells to revive T cells. Meanwhile, such approach efficiently inhibited the formation of pre-metastatic niche in abscopal lung. Because of the significant promotion of anti-tumor and anti-metastasis immunity, the non-responding TNBC gained robust responsiveness to anti-PD-L1 therapy which resulted in complete eradication of orthotopic tumors, inhibition of pulmonary metastasis, and durable memory effects against tumor recurrence. Our work provided a generalizable approach of simultaneous ICD induction and CXCR4 blockade to apply anti-PD-L1 therapy in TNBC.

Imaging Extracellular Acidification and Immune Activation in Cancer

Metabolism reveals pathways by which cells, in healthy and disease tissues, use nutrients to fuel their function and (re)growth. However, gene-centric views have dominated cancer hallmarks, relegating metabolic reprogramming that all cells in the tumor niche undergo as an incidental phenomenon. Aerobic glycolysis in cancer is well known, but recent evidence suggests that diverse symbolic traits of cancer cells are derived from oncogene-directed metabolism required for their sustenance and evolution. Cells in the tumor milieu actively metabolize different nutrients, but proficiently secrete acidic by-products using diverse mechanisms to create a hostile ecosystem for host cells, and where local immune cells suffer collateral damage. Since metabolic interactions between cancer and immune cells hold promise for future cancer therapies, here we focus on translational magnetic resonance methods enabling in vivo and simultaneous detection of tumor habitat acidification and immune activation - innovations for monitoring personalized treatments.

Rational Design of All-Organic Nanoplatform for Highly Efficient MR/NIR-II Imaging-Guided Cancer Phototheranostics

Organic theranostic nanomedicine has precision multimodel imaging capability and concurrent therapeutics under noninvasive imaging guidance. However, the rational design of desirable multifunctional organic theranostics for cancer remains challenging. Rational engineering of organic semiconducting nanomaterials has revealed great potential for cancer theranostics largely owing to their intrinsic diversified biophotonics, easy fabrication of multimodel imaging platform, and desirable biocompatibility. Herein, a novel all-organic nanotheranostic platform (TPATQ-PNP NPs) is developed by exploiting the self-assembly of a semiconducting small molecule (TPATQ) and a new synthetic high-density nitroxide radical-based amphiphilic polymer (PNP). The nitroxide radicals act as metal-free magnetic resonance imaging agent through shortened longitudinal relaxation times, and the semiconducting molecules enable ultralow background second near-infrared (NIR-II, 1000-1700 nm) fluorescence imaging. The as-prepared TPATQ-PNP NPs can light up whole blood vessels of mice and show precision tumor-locating ability with synergistic (MR/NIR-II) imaging modalities. The semiconducting molecules also undergo highly effective photothermal conversion in the NIR region for cancer photothermal therapy guided by complementary tumor diagnosis. The designed multifunctional organic semiconducting self-assembly provides new insights into the development of a new platform for cancer theranostics.

Histone Deacetylase Inhibitor-loaded Calcium Alginate Microspheres for Acute Kidney Injury Treatment

The protective effects of histone deacetylase (HDAC) inhibitors were highlighted in the treatment of kidney diseases, especially acute kidney injury (AKI). However, the currently available HDAC inhibitor cannot be delivered to the kidney properly because of its poor solubility in aqueous solutions. Therefore, calcium alginate (Ca-ALG) microspheres were proposed as microcarriers for the delivery of HDAC inhibitors in this study. First, Ca-ALG microspheres with high sphericity were obtained by a single-emulsion microfluidic strategy. Then, we selected suitable Ca-ALG microspheres for HDAC inhibitor loading by analyzing the swelling ratio and the release property using different parameters. Besides, thermal stimulation will change the drug release property of Ca-ALG microspheres in in vitro experiments. Furthermore, the HDAC inhibitor-loaded microspheres were delivered to the kidney by renal subcapsular injection for evaluating the treatment effects in mice with ischemia-reperfusion-induced AKI. The in vivo results showed that the HDAC inhibitor-loaded Ca-ALG microspheres could effectively reduce the renal regional inflammatory response and macrophage infiltration. Taken together, we proposed a promising therapy with an effective kidney-targeted drug delivery for the treatment of AKI.

Ultrasensitive molecular imaging of intestinal mucosal inflammation using leukocyte-mimicking particles targeted to MAdCAM-1 in mice

Mucosal tissues play critical roles in health and disease as the primary barrier between the external world and the inner body, lining the digestive, respiratory, urinary, mammary, and reproductive tracts. Clinical evaluation of mucosal tissues is currently performed using endoscopy, such as ileocolonoscopy for the intestinal mucosa, which causes substantial patient discomfort and can lead to organ damage. Here, we developed a contrast agent for molecular magnetic resonance imaging (MRI) that is targeted to mucosal vascular addressin cell adhesion molecule 1 (MAdCAM-1), an adhesion molecule overexpressed by inflamed mucosal tissues. We investigated the diagnostic performance of molecular MRI of MAdCAM-1 to detect mucosal inflammation in several models of acute and chronic intestinal inflammation in mice. We demonstrated that molecular MRI of MAdCAM-1 reveals disease activity and can evaluate the response to inflammatory treatments along the whole intestinal mucosa in clinically relevant models of inflammatory bowel diseases. We also provide evidence that this technique can detect low, subclinical mucosal inflammation. Molecular MRI of MAdCAM-1 has potential applications in early diagnosis, longitudinal follow-up, and therapeutic response monitoring in diseases affecting mucosal tissues, such as inflammatory bowel diseases.

Cardiovascular magnetic resonance imaging for inflammatory heart diseases

Inflammatory myocardial diseases represent a diverse group of conditions in which abnormal inflammation within the myocardium is the primary driver of cardiac dysfunction. Broad causes of myocarditis include infection by cardiotropic viruses or other infectious agents, to systemic autoimmune disease, or to toxins. Myocarditis due to viral aetiologies is a relatively common cause of acute chest pain syndromes in younger and middle-aged patients and often has a benign prognosis, though this and other forms of myocarditis also cause serious sequelae, including heart failure, arrhythmia and death. Endomyocardial biopsy remains the gold standard tool for tissue diagnosis of myocarditis in living individuals, although new imaging technologies have a crucial and complementary role. This review outlines the current state-of-the-art and future experimental cardiovascular magnetic resonance (CMR) imaging approaches for the detection of inflammation and immune cell activity in the heart. Multiparametric CMR, particularly with novel quantitative T1- and T2-mapping, is a valuable and widely-available tool for the non-invasive assessment of inflammatory heart diseases. Novel CMR molecular contrast agents will enable a more targeted assessment of immune cell activity and may be useful in guiding the development of novel therapeutics for myocarditis.

Magnetic Nanoparticles as MRI Contrast Agents

Iron oxide nanoparticles (IONPs) have emerged as a promising alternative to conventional contrast agents (CAs) for magnetic resonance imaging (MRI). They have been extensively investigated as CAs due to their high biocompatibility and excellent magnetic properties. Furthermore, the ease of functionalization of their surfaces with different types of ligands (antibodies, peptides, sugars, etc.) opens up the possibility of carrying out molecular MRI. Thus, IONPs functionalized with epithelial growth factor receptor antibodies, short peptides, like RGD, or aptamers, among others, have been proposed for the diagnosis of various types of cancer, including breast, stomach, colon, kidney, liver or brain cancer. In addition to cancer diagnosis, different types of IONPs have been developed for other applications, such as the detection of brain inflammation or the early diagnosis of thrombosis. This review addresses key aspects in the development of IONPs for MRI applications, namely, synthesis of the inorganic core, functionalization processes to make IONPs biocompatible and also to target them to specific tissues or cells, and finally in vivo studies in animal models, with special emphasis on tumor models.

Improved detection of molecularly targeted iron oxide particles in mouse brain using B0 field stabilised high resolution MRI

PURPOSE

High resolution multi-gradient echo (MGE) scanning is typically used for detection of molecularly targeted iron oxide particles. The images of individual echoes are often combined to generate a composite image with improved SNR from the early echoes and boosted contrast from later echoes. In 3D implementations prolonged scanning at high gradient duty cycles induces a B0 shift that predominantly affects image alignment in the slow phase encoding dimension of 3D MGE images. The effect corrupts the composite echo image and limits the image resolution that is realised. A real-time adaptive B0 stabilisation during respiration gated 3D MGE scanning is shown to reduce image misalignment and improve detection of molecularly targeted iron oxide particles in composite images of the mouse brain.

METHODS

An optional B0 measurement block consisting of a 16 μs hard pulse with FA 1°, an acquisition delay of 3.2 ms, followed by gradient spoiling in all three axes was added to a respiration gated 3D MGE scan. During the acquisition delay of each B0 measurement block the NMR signal was routed to a custom built B0 stabilisation unit which mixed the signal to an audio frequency nominally centred around 1000 Hz to enable an Arduino based single channel receiver to measure frequency shifts. The frequency shift was used to effect correction to the main magnetic field via the B0 coil. The efficacy of B0 stabilisation and respiration gating was validated in vivo and used to improve detection of molecularly targeted microparticles of iron oxide (MPIO) in a mouse model of acute neuroinflammation.

RESULTS

Without B0 stabilisation 3D MGE image data exhibit varying mixtures of translation, scaling and blurring, which compromise the fidelity of the composite image. The real-time adaptive B0 stabilisation minimises corruption of the composite image as the images from the different echoes are properly aligned. The improved detection of molecularly targeted MPIO easily compensates for the scan time penalty of 14% incurred by the B0 stabilisation method employed. Respiration gating of the B0 measurement and the MRI scan was required to preserve high resolution detail, especially towards the back of the brain.

CONCLUSIONS

High resolution imaging for the detection of molecularly targeted iron oxide particles in the mouse brain requires good stabilisation of the main B0 field, and can benefit from a respiration gated image acquisition strategy.

Improving Delineation of True Tumor Volume With Multimodal MRI in a Rat Model of Brain Metastasis

PURPOSE

Brain metastases are almost universally lethal with short median survival times. Despite this, they are often potentially curable, with therapy failing only because of local relapse. One key reason relapse occurs is because treatment planning did not delineate metastasis margins sufficiently or accurately, allowing residual tumor to regrow. The aim of this study was to determine the extent to which multimodal magnetic resonance imaging (MRI), with a simple and automated analysis pipeline, could improve upon current clinical practice of single-modality, independent-observer tumor delineation.

METHODS AND MATERIALS

We used a single rat model of brain metastasis (ENU1564 breast carcinoma cells in BD-IX rats), with and without radiation therapy. Multimodal MRI data were acquired using sequences either in current clinical use or in clinical trial and included postgadolinium T1-weighted images and maps of blood flow, blood volume, T1 and T2 relaxation times, and apparent diffusion coefficient.

RESULTS

In all cases, independent observers underestimated the true size of metastases from single-modality gadolinium-enhanced MRI (85 ± 36 μL vs 131 ± 40 μL histologic measurement), although multimodal MRI more accurately delineated tumor volume (132 ± 41 μL). Multimodal MRI offered increased sensitivity compared with independent observer for detecting metastasis (0.82 vs 0.61, respectively), with only a slight decrease in specificity (0.86 vs 0.98). Blood flow maps conferred the greatest improvements in margin detection for late-stage metastases after radiation therapy. Gadolinium-enhanced T1-weighted images conferred the greatest increase in accuracy of detection for smaller metastases.

CONCLUSIONS

These findings suggest that multimodal MRI of brain metastases could significantly improve the visualization of brain metastasis margins, beyond current clinical practice, with the potential to decrease relapse rates and increase patient survival. This finding now needs validation in additional tumor models or clinical cohorts.

Inhibition of Immunosuppressive Tumors by Polymer-Assisted Inductions of Immunogenic Cell Death and Multivalent PD-L1 Crosslinking

Checkpoint blockade immunotherapies harness the host's own immune system to fight cancer, but only work against tumors infiltrated by swarms of pre-existing T cells. Unfortunately, most cancers to date are immune-deserted. Here, we report a polymer-assisted combination of immunogenic chemotherapy and PD-L1 degradation for efficacious treatment in originally non-immunogenic cancer. "Priming" tumors with backbone-degradable polymer-epirubicin conjugates elicits immunogenic cell death and fosters tumor-specific CD8+ T cell response. Sequential treatment with a multivalent polymer-peptide antagonist to PD-L1 overcomes adaptive PD-L1 enrichment following chemotherapy, biases the recycling of PD-L1 to lysosome degradation via surface receptor crosslinking, and produces prolonged elimination of PD-L1 rather than the transient blocking afforded by standard anti-PD-L1 antibodies. Together, these findings established the polymer-facilitated tumor targeting of immunogenic drugs and surface crosslinking of PD-L1 as a potential new therapeutic strategy to propagate a long-term antitumor immunity, which might broaden the application of immunotherapy to immunosuppressive cancers.

Ten-Gram-Scale Facile Synthesis of Organogadolinium Complex Nanoparticles for Tumor Diagnosis

The market of available contrast agents for clinical magnetic resonance imaging (MRI) has been dominated by gadolinium (Gd) chelates based T₁ contrast agents for decades. However, there are growing concerns about their safety because they are retained in the body and are nephrotoxic, which necessitated a warning by the U.S. Food and Drug Administration against the use of such contrast agents. To ameliorate these problems, it is necessary to improve the MRI efficiency of such contrast agents to allow the administration of much reduced dosages. In this study, a ten-gram-scale facile method is developed to synthesize organogadolinium complex nanoparticles (i.e., reductive bovine serum albumin stabilized Gd-salicylate nanoparticles, GdSalNPs-rBSA) with high r₁ value of 19.51 mm^-1 s^-1 and very low r₂ /r₁ ratio of 1.21 (B₀ = 1.5 T) for high-contrast T₁ -weighted MRI of tumors. The GdSalNPs-rBSA nanoparticles possess more advantages including low synthesis cost (≈0.54 USD per g), long in vivo circulation time (t_1/2 = 6.13 h), almost no Gd³⁺ release, and excellent biosafety. Moreover, the GdSalNPs-rBSA nanoparticles demonstrate excellent in vivo MRI contrast enhancement (signal-to-noise ratio (ΔSNR) ≈ 220%) for tumor diagnosis.

Extracellular vesicle integrins act as a nexus for platelet adhesion in cerebral microvessels

Circulating extracellular vesicles (EVs) regulate signaling pathways via receptor-ligand interactions and content delivery, after attachment or internalization by endothelial cells. However, they originate from diverse cell populations and are heterogeneous in composition. To determine the effects of specific surface molecules, the use of synthetic EV mimetics permits the study of specific EV receptor-ligand interactions. Here, we used endogenous EVs derived from the circulation of rats, as well as ligand-decorated synthetic microparticles (MPs) to examine the role of integrin αvβ3 in platelet adhesion under flow in structurally intact cerebral arteries. At an intraluminal pressure of 50 mmHg and flow rate of 10 µl/min, platelets were delivered to the artery lumen and imaged with whole-field fluorescent microscopy. Under basal conditions very few platelets bound to the endothelium. However, adhesion events were markedly increased following the introduction of arginine-glycine-aspartate (RGD)-labelled synthetic MPs or endogenously-derived EVs from experimental stroke animals carrying excess RGD proteins, including vitronectin, CD40-ligand and thrombospondin-1. These data, which were generated in a dynamic and physiologically relevant system, demonstrate the importance of vesicle-carried RGD ligands in platelet adherence to the cerebrovascular endothelium and highlight the ability of synthetic EVs to isolate and identify key components of the molecular handshake between EVs and their targets.

Exceedingly Small Gadolinium Oxide Nanoparticles with Remarkable Relaxivities for Magnetic Resonance Imaging of Tumors

Gd chelates have occupied most of the market of magnetic resonance imaging (MRI) contrast agents for decades. However, there have been some problems (nephrotoxicity, non-specificity, and low r₁ ) that limit their applications. Herein, a wet-chemical method is proposed for facile synthesis of poly(acrylic acid) (PAA) stabilized exceedingly small gadolinium oxide nanoparticles (ES-GON-PAA) with an excellent water dispersibility and a size smaller than 2.0 nm, which is a powerful T₁ -weighted MRI contrast agent for diagnosis of diseases due to its remarkable relaxivities (r₁ = 70.2 ± 1.8 mM^-1 s^-1 , and r₂ /r₁ = 1.02 ± 0.03, at 1.5 T). The r₁ is much higher and the r₂ /r₁ is lower than that of the commercial Gd chelates and reported gadolinium oxide nanoparticles (GONs). Further ES-GON-PAA is developed with conjugation of RGD2 (RGD dimer) (i.e., ES-GON-PAA@RGD2) for T₁ -weighted MRI of tumors that overexpress RGD receptors (i.e., integrin α_v β₃ ). The maximum signal enhancement (ΔSNR) for T₁ -weighted MRI of tumors reaches up to 372 ± 56% at 2 h post-injection of ES-GON-PAA@RGD2, which is much higher than commercial Gd-chelates (<80%). Due to the high biocompatibility and high tumor accumulation, ES-GON-PAA@RGD2 with remarkable relaxivities is a promising and powerful T₁ -weighted MRI contrast agent.

VCAM-1 Density and Tumor Perfusion Predict T-cell Infiltration and Treatment Response in Preclinical Models

Cancer immunotherapies have demonstrated durable responses in a range of different cancers. However, only a subset of patients responds to these therapies. We set out to test if non-invasive imaging of tumor perfusion and vascular inflammation may be able to explain differences in T-cell infiltration in pre-clinical tumor models, relevant for treatment outcomes. Tumor perfusion and vascular cell adhesion molecule (VCAM-1) density were quantified using magnetic resonance imaging (MRI) and correlated with infiltration of adoptively transferred and endogenous T-cells. MRI biomarkers were evaluated for their ability to detect tumor rejection 3 days after T-cell transfer. Baseline levels of these markers were used to assess their ability to predict PD-L1 treatment response. We found correlations between MRI-derived VCAM-1 density and infiltration of endogenous or adoptively transferred T-cells in some preclinical tumor models. Blocking T-cell binding to endothelial cell adhesion molecules (VCAM-1/ICAM) prevented T-cell mediated tumor rejection. Tumor rejection could be detected 3 days after adoptive T-cell transfer prior to tumor volume changes by monitoring the extracellular extravascular volume fraction. Imaging tumor perfusion and VCAM-1 density before treatment initiation was able to predict the response of MC38 tumors to PD-L1 blockade. These results indicate that MRI based assessment of tumor perfusion and VCAM-1 density can inform about the permissibility of the tumor vasculature for T-cell infiltration which may explain some of the observed variance in treatment response for cancer immunotherapies.

Cellular magnetic resonance imaging: in vivo tracking of gastric cancer cells and detecting of lymph node metastases using microparticles of iron oxide in mice

Background

Monitoring the fate of implanted cells over time in an experimental animal may provide a new way to track the metastatic process. Lymph node metastase is of extremely importance for the prognostic prediction of gastric carcinoma. The aim of this study was to assess the feasibility of magnetic resonance imaging (MRI), using micron-sized superparamagnetic iron oxide particles (MPIO), for monitoring of the fate of gastric cancer cells and detecting the migration of gastric cancer cells through the lymphatic system in a mouse model.

Methods

SGC-7901 gastric cancer cells were labeled with green fluorescent MPIO. The cells were monitored in vitro at multiple time points by staining for iron-labeled cells and by flow cytometric detection of the fluorescent MPIO. MPIO-labeled cells were implanted subcutaneously into nude mice, and cellular MRI was performed at different time points until 35 days postinjection.

Results

The potential for retention of the iron particles in vitro was evaluated. Our results showed that the labeling and uptake efficiency of MPIO reached 90.0% after 24 hrs of incubation, and a small percentage of cells that retained MPIO could be examined until 16 days after labeling. In vivo MRI-based tracking over several weeks in mice revealed regions of signal loss in the primary tumors for up to 5 weeks. Furthermore, small regions of signal void were detected in images of the inguinal lymph nodes in three mice at day 28 postinjection or later, and histological assays confirmed the presence of iron-labeled cancer cells.

Conclusion

This study supports MPIO-based cell tracking is a useful tool for monitoring the fate of gastric cancer cells in mice over time, which may facilitate progress in understanding the mechanisms of early regional lymph node micrometastases.

Dynamically Reversible Iron Oxide Nanoparticle Assemblies for Targeted Amplification of T1-Weighted Magnetic Resonance Imaging of Tumors

Smart magnetic resonance (MR) contrast agents, by which MR contrast can be selectively enhanced under acidic tumor microenvironment, are anticipated to significantly improve the diagnostic accuracy. Here, we report pH-sensitive iron oxide nanoparticle assemblies (IONAs) that are cross-linked by small-molecular aldehyde derivative ligands. The dynamic formation and cleavage of hydrazone linkages in neutral and acidic environments, respectively, allow the reversible response of the nanoassemblies to pH variations. At neutral pH, IONAs are structurally robust due to the cross-linking by the strong hydrazone bonds. In acidic tumor microenvironment, the hydrazone bonds are cleaved so that the IONAs are quickly disassembled into a large number of hydrophilic extremely small-sized iron oxide nanoparticles (ESIONs). As a result, significantly enhanced T1MR contrast is achieved, as confirmed by the measurement of r1 values at different pH conditions. Such acidity-targeting MR signal amplification by the pH-sensitive IONAs was further validated in vivo, demonstrating a novel T1 magnetic resonance imaging (MRI) strategy for highly sensitive imaging of acidic tumors.

VCAM-1-targeted MRI Enables Detection of Brain Micrometastases from Different Primary Tumors

PURPOSE

A major issue for the effective treatment of brain metastasis is the late stage of diagnosis with existing clinical tools. The aim of this study was to evaluate the potential of vascular cell adhesion molecule 1 (VCAM-1)-targeted MRI for early detection of brain micrometastases in mouse models across multiple primary tumor types.Experimental Design: Xenograft models of brain micrometastasis for human breast carcinoma (MDA231Br-GFP), lung adenocarcinoma (SEBTA-001), and melanoma (H1_DL2) were established via intracardiac injection in mice. Animals (n = 5-6/group) were injected intravenously with VCAM-1-targeted microparticles of iron oxide (VCAM-MPIO) and, subsequently, underwent T 2*-weighted MRI. Control groups of naïve mice injected with VCAM-MPIO and tumor-bearing mice injected with nontargeting IgG-MPIO were included.

RESULTS

All models showed disseminated micrometastases in the brain, together with endothelial VCAM-1 upregulation across the time course. T 2*-weighted MRI of all tumor-bearing mice injected with VCAM-MPIO showed significantly more signal hypointensities (P < 0.001; two-sided) than control cohorts, despite a lack of blood-brain barrier (BBB) impairment. Specific MPIO binding to VCAM-1-positive tumor-associated vessels was confirmed histologically. VCAM-1 expression was demonstrated in human brain metastasis samples, across all three primary tumor types.

CONCLUSIONS

VCAM-1-targeted MRI enables the detection of brain micrometastases from the three primary tumor types known to cause the majority of clinical cases. These findings represent an important step forward in the development of a broadly applicable and clinically relevant imaging technique for early diagnosis of brain metastasis, with significant implications for improved patient survival.

Triply Loaded Nitroxide Brush-Arm Star Polymers Enable Metal-Free Millimetric Tumor Detection by Magnetic Resonance Imaging

Nitroxides occupy a privileged position among plausible metal-free magnetic resonance imaging (MRI) contrast agents (CAs) due to their inherently low-toxicity profiles; nevertheless, their translational development has been hindered by a lack of appropriate contrast sensitivity. Nanostructured materials with high nitroxide densities, where each individual nitroxide within a macromolecular construct contributes to the image contrast, could address this limitation, but the synthesis of such materials remains challenging. Here, we report a modular and scalable synthetic approach to nitroxide-based brush-arm star polymer (BASP) organic radical CAs (ORCAs) with high nitroxide loadings. The optimized ∼30 nm diameter "BASP-ORCA3" displays outstanding T2 sensitivity with a very high molecular transverse relaxivity ( r2 > 1000 mM-1 s-1). BASP-ORCA3 further exhibits excellent stability in vivo, no acute toxicity, and highly desirable pharmacokinetic and biodistribution profiles for longitudinal detection of tumors by MRI. When injected intravenously into mice bearing subcutaneous plasmacytomas, BASP-ORCA3 affords distinct in vivo visualization of tumors on translationally relevant time scales. Leveraging its high sensitivity, BASP-ORCA3 enables efficient mapping of tumor necrosis, which is an important biomarker to predict therapeutic outcomes. Moreover, BASP-ORCA3 allows for detection of millimetric tumor implants in a disseminated murine model of advanced-stage human ovarian cancer that possess genetic, histological, and vascular characteristics that are similar to those seen in patients. This work establishes BASP-ORCA3 as a promising metal-free spin contrast agent for MRI.

Optimization of molecularly targeted MRI in the brain: empirical comparison of sequences and particles

BACKGROUND

Molecular MRI is an evolving field of research with strong translational potential. Selection of the appropriate MRI sequence, field strength and contrast agent depend largely on the application. The primary aims of the current study were to: 1) assess the sensitivity of different MRI sequences for detection of iron oxide particles in mouse brain; 2) determine the effect of magnetic field strength on detection of iron oxide particles in vivo; and 3) compare the sensitivity of targeted microparticles of iron oxide (MPIO) or ultra-small superparamagnetic iron oxide (USPIO) for detection of vascular cell adhesion molecule-1 (VCAM-1) in vivo.

METHODS

Mice were injected intrastriatally with interleukin 1β to induce VCAM-1 expression on the cerebral vasculature. Subsequently, animals were injected intravenously with either VCAM-MPIO or VCAM-USPIO and imaged 1 or 13 hours post-injection, respectively. MRI was performed at 4.7, 7.0, or 9.4 T, using three different T2*-weighted sequences: single gradient echo 3D (GE3D), multi-gradient echo 3D (MGE3D) and balanced steady-state free precession 3D (bSSFP3D).

RESULTS

MGE3D yielded the highest signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) for the detection of iron oxide particles. All sequences showed a significant increase in SNR and CNR from 4.7 to 7.0 T, but no further improvement at 9.4 T. However, whilst targeted MPIO enabled sensitive detection of VCAM-1 expression on the cerebral vasculature, the long half-life (16.5 h vs 1.2 min) and lower relaxivity per particle (1.29×10-14 vs 1.18×10-9 Hz L/particle) of USPIO vs. MPIO rendered them impractical for molecular MRI.

CONCLUSION

These findings demonstrate clear advantages of MPIO compared to USPIO for molecularly-targeted MRI, and indicate that the MGE3D sequence is optimal for MPIO detection. Moreover, higher field strengths (7.0/9.4 T) showed enhanced sensitivity over lower field strengths (4.7 T). With the development of biodegradable MPIO, these agents hold promise for clinical translation.

Dotted Core-Shell Nanoparticles for T1 -Weighted MRI of Tumors

Gd-based T 1 -weighted contrast agents have dominated the magnetic resonance imaging (MRI) contrast agent market for decades. Nevertheless, they are reported to be nephrotoxic and the U.S. Food and Drug Administration has issued a general warning concerning their use. In order to reduce the risk of nephrotoxicity, the MRI performance of the Gd-based T 1 -weighted contrast agents needs to be improved to allow a much lower dosage. In this study, novel dotted core-shell nanoparticles (FeGd-HN3-RGD2) with superhigh r 1 value (70.0 mM-1 s-1 ) and very low r 2 /r 1 ratio (1.98) are developed for high-contrast T 1 -weighted MRI of tumors. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and histological analyses show good biocompatibility of FeGd-HN3-RGD2. Laser scanning confocal microscopy images and flow cytometry demonstrate active targeting to integrin αv β3 positive tumors. MRI of tumors shows high tumor ΔSNR for FeGd-HN3-RGD2 (477 ± 44%), which is about 6-7-fold higher than that of Magnevist (75 ± 11%). MRI and inductively coupled plasma results further confirm that the accumulation of FeGd-HN3-RGD2 in tumors is higher than liver and spleen due to the RGD2 targeting and small hydrodynamic particle size (8.5 nm), and FeGd-HN3-RGD2 is readily cleared from the body by renal excretion.

Molecular Magnetic Resonance Imaging of Endothelial Activation in the Central Nervous System

Endothelial cells of the central nervous system over-express surface proteins during neurological disorders, either as a cause, or a consequence, of the disease. Since the cerebral vasculature is easily accessible by large contrast-carrying particles, it constitutes a target of choice for molecular magnetic resonance imaging (MRI). In this review, we highlight the most recent advances in molecular MRI of brain endothelial activation and focus on the development of micro-sized particles of iron oxide (MPIO) targeting adhesion molecules including intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1), P-Selectin and E-Selectin. We also discuss the perspectives and challenges for the clinical application of this technology in neurovascular disorders (ischemic stroke, intracranial hemorrhage, subarachnoid hemorrhage, diabetes mellitus), neuroinflammatory disorders (multiple sclerosis, brain infectious diseases, sepsis), neurodegenerative disorders (Alzheimer's disease, vascular dementia, aging) and brain cancers (primitive neoplasms, metastasis).

Prediction of disease activity in models of multiple sclerosis by molecular magnetic resonance imaging of P-selectin

New strategies for detecting disease activity in multiple sclerosis are being investigated to ameliorate diagnosis and follow-up of patients. Today, although magnetic resonance imaging (MRI) is widely used to diagnose and monitor multiple sclerosis, no imaging tools exist to predict the evolution of disease and the efficacy of therapeutic strategies. Here, we show that molecular MRI targeting the endothelial adhesion molecule P-selectin unmasks the pathological events that take place in the spinal cord of mice subjected to chronic or relapsing experimental autoimmune encephalomyelitis. This approach provides a quantitative spatiotemporal follow-up of disease course in relation to clinical manifestations. Moreover, it predicts relapse in asymptomatic mice and remission in symptomatic animals. Future molecular MRI targeting P-selectin may be used to improve diagnosis, follow-up of treatment, and management of relapse/remission cycles in multiple sclerosis patients by providing information currently inaccessible through conventional MRI techniques.