A Novel Histochemical Staining Approach for Rare-Earth-Based Nanoprobes

Hypersensitive MR angiography based on interlocking stratagem for diagnosis of cardiac-cerebral vascular diseases

Magnetic resonance (MR) angiography is one of the main diagnostic approaches for cardiac-cerebral vascular diseases. Nevertheless, the non-contrast-enhanced MR angiography suffers from its intrinsic problems derived from the blood flow-dependency, while the clinical Gd-chelating contrast agents are limited by their rapid vascular extravasation. Herein, we report a hypersensitive MR angiography strategy based on interlocking stratagem of zwitterionic Gd-chelate contrast agents (PAA-Gd). The longitudinal molar relaxivity of PAA-Gd was 4.6-times higher than that of individual Gd-chelates as well as appropriate blood half-life (73.8 min) and low immunogenicity, enabling sophisticated micro-vessels angiography with a resolution at the order of hundred micrometers. A series of animal models of cardiac-cerebrovascular diseases have been built for imaging studies on a 7.0 T MRI scanner, while the clinical translation potential of PAA-Gd has been evaluated on swine on a 3.0 T clinical MRI scanner. The current studies offer a promising strategy for precise diagnosis of vascular diseases.

A robust MRI contrast agent for specific display of the interstitial stream

Experimental and clinical studies have reported phenomena of long-range fluid flow in interstitial space. However, its behaviours and functions are yet to be addressed. The imaging of the interstitial stream in vivo can clarify its transportation route and allow further understanding of physiological mechanisms and clinical relevance. Here to illustrate the route of the interstitial stream leading to the kidney, we design and synthesize a magnetic resonance imaging (MRI) contrast agent PAA-g-(DTPA-gadolinium). This MRI agent has a high longitudinal relaxivity for higher MRI contrast and large size to avoid leakage across the interstitial space. Using dynamic contrast enhanced MRI, histochemical staining, and trace element analysis of gadolinium, we track the nano-scale PAA-g-(DTPA-gadolinium) transported in the interstitial stream. The agent can be applied for a wide range of imaging and analysis of tissues and organs, thereby enabling advances in the fields of physiology, pathology, and pharmacology.

Histochemistry for nanomedicine: Novelty in tradition

During the last two centuries, histochemistry has provided significant advancements in many fields of life sciences. After a period of neglect due to the great development of biomolecular techniques, the histochemical approach has been reappraised and is now widely applied in the field of nanomedicine. In fact, the novel nanoconstructs intended for biomedical purposes must be visualized to test their interaction with tissue and cell components. To this aim, several long-established staining methods have been re-discovered and re-interpreted in an unconventional way for unequivocal identification of nanoparticulates at both light and transmission electron microscopy.

An atherosclerotic plaque-targeted single-chain antibody for MR/NIR-II imaging of atherosclerosis and anti-atherosclerosis therapy

Background

Oxidation-specific epitopes (OSEs) are rich in atherosclerotic plaques. Innate and adaptive immune responses to OSEs play an important role in atherosclerosis. The purpose of this study was to develop novel human single-chain variable fragment (scFv) antibody specific to OSEs to image and inhibit atherosclerosis.

Results

Here, we screened a novel scFv antibody, named as ASA6, from phage-displayed human scFv library. ASA6 can bind to oxidized LDL (Ox-LDL) and atherosclerotic plaques. Meanwhile, ASA6 can also inhibit the uptake of Ox-LDL into macrophage to reduce macrophage apoptosis. The atherosclerotic lesion area of ApoE^−/− mice administrated with ASA6 antibody was significantly reduced. Transcriptome analysis reveals the anti-atherosclerosis effect of ASA6 is related to the regulation of fatty acid metabolism and inhibition of M1 macrophage polarization. Moreover, we conjugated ASA6 antibody to NaNdF₄@NaGdF₄ nanoparticles for noninvasive imaging of atherosclerotic plaques by magnetic resonance (MR) and near-infrared window II (NIR-II) imaging.

Conclusions

Together, these data demonstrate the potential of ASA6 antibody in targeted therapy and noninvasive imaging for atherosclerosis.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-01047-4.

An MRI contrast agent based on a zwitterionic metal-chelating polymer for hepatorenal angiography and tumor imaging

MRI contrast agents such as paramagnetic Gd(iii)-chelates, can improve the ability of MRI in differentiating diseased and healthy tissues, and have been widely used in clinical diagnosis. However, the enhancement effect of small molecular MRI contrast agents is unsatisfied due to their relative high rotation rates. Furthermore, the small molecular contrast agents also suffer from the short blood half-life and nonspecific extracellular diffusion in tissues, which also restricts their applications. To address these issues, we developed a macromolecular MRI contrast agent based on a zwitterionic metal-chelating polymer. Poly(acrylic acid) (PAA) was chosen as the main chain, and diethylenetriamine pentaacetic acid (DTPA) as the metal-chelating group was coupled through the carboxyl groups of PAA using diethylenetriamine (DET) as a linker. The macromolecular MRI contrast agent constructed by chelating with Gd3+ (Gd-PAA) exhibited a much higher longitudinal relaxation rate (r1) than the clinical contrast agent Gd-DTPA. Importantly, due to the stealth ability of the zwitterionic structure, Gd-PAA can reside in the blood long enough without any microvascular leakage in the extracellular space of normal tissues, which allows it to be used for precise blood MR imaging, such as hepatorenal angiography, but also for tumor imaging because of the enhanced permeability and retention (EPR) effecta. Besides, the result of long-term toxicity tests highlights the safety feature of the current contrast agent. Hence, the current contrast agent overcomes the defect of traditional small molecular Gd(iii)-based T1-weighted contrast agents and shows great prospects for future clinical applications.

Boosting often overlooked long wavelength emissions of rare-earth nanoparticles for NIR-II fluorescence imaging of orthotopic glioblastoma

Rare-earth nanoparticles (RE NPs) with narrow long wavelength emissions have been recently investigated for their potential application for fluorescence imaging in the second near-infrared window (NIR-II). Previously these RE NPs have a very limited application in the diagnosis and treatment of deep-seated tumors such as brain tumors, due to their weak fluorescence in the range of 1300-1700 nm. Herein, we report a significant enhancement of more than 10 times regular emission of NaNdF₄ nanoparticles at 1340 nm wavelength by coating them with an inert layer of NaLuF₄, followed by sensitizing with a near-infrared dye (IR-808). We deliver these highly bright nanoparticles into the brain by using focused ultrasound to temporarily open the blood-brain barrier (BBB), and then detect the orthotopic glioblastoma by fluorescence imaging at 1340 nm. The images obtained from long wavelength fluorescence (i.e. 1340 nm) exhibited better resolution and contrast compared to the short wavelength fluorescence (i.e. 1060 nm). Our study not only provides insights for enhancing often overlooked emissions of rare-earth nanoparticles for NIR-II fluorescence imaging of deep-seated tumors, but also demonstrates great potential of focused ultrasound based technology in delivering nanotheranostic agents.

Coordinatively Unsaturated Fe3+ Based Activatable Probes for Enhanced MRI and Therapy of Tumors

Exogenous Fe^III can be used for cancer magnetic resonance (MR) imaging and potentially for cancer treatment by a ferroptosis pathway or photothermal ablation. To achieve this, effective and accurate delivery of Fe^III to cancerous sites is critical, requiring a balance of release kinetics of Fe³⁺ in tumorous and normal tissues. A nanoprobe is described consisting of upconversion luminescence (UCL) nanoparticles as a core and a coordinatively unsaturated Fe^III -containing Fe³⁺ /gallic acid complex as a shell. Owing to the introduction of an unsaturated coordination structure, Fe^III in the nanoprobe can be released only in the tumor microenvironment in response to the lightly acidic pH. The multiple UCLs are used for quantitatively visualizing the release of Fe³⁺ in vivo, whilst the release resultant serves as a photothermal agent. This nanoprobe exhibited ligand-free tumor targeting ability, activatable MR imaging performance, and efficacious therapeutic effects against tumors in vivo.

Detection of lymph node metastasis with near-infrared upconversion luminescent nanoprobes

The detection of lymph node metastasis is of great importance for therapy planning and prognosis of cancers, but remains challenging in the clinic. In the current study, we report a tumor-specific imaging probe constructed with NaGdF4:Yb,Tm,Ca@NaLuF4 core@shell upconversion nanoparticles showing distinctive near infrared emission. The following studies revealed that the characteristic Tm dopant emission at 804 nm showed a penetration depth up to 7.7 mm through multi-layered mice skin tissues, substantially greater than emissions at 655 nm and 541 nm typically from the widely used Er dopant, which is apparently favorable for sensitive tumor diagnosis. The cell binding assay further revealed that the anti-HER2 antibodies covalently attached on the particle surface endowed the nanoprobe with excellent binding specificity in targeting HER2-positive cancer cells in vitro, which further enabled the detection of lymph node metastasis of breast cancer in vivo in mice. In addition, the pharmacokinetics of the resulting nanoprobes were intensively studied through both upconversion luminescence imaging and SPECT imaging for comparing with that of the mother particles. The results obtained through both approaches were well consistent and revealed that the surface conjugation of antibodies largely altered the pharmacokinetic behaviors and substantially prolonged the blood half-life of the underlying nanoparticles, which was never reported before.