Perfluoro-tert-butanol: a cornerstone for high performance fluorine-19 magnetic resonance imaging

Magnetic Particle Imaging: From Tracer Design to Biomedical Applications in Vasculature Abnormality

Magnetic particle imaging (MPI) is an emerging non-invasive tomographic technique based on the response of magnetic nanoparticles (MNPs) to oscillating drive fields at the center of a static magnetic gradient. In contrast to magnetic resonance imaging (MRI), which is driven by uniform magnetic fields and projects the anatomic information of the subjects, MPI directly tracks and quantifies MNPs in vivo without background signals. Moreover, it does not require radioactive tracers and has no limitations on imaging depth. This article first introduces the basic principles of MPI and important features of MNPs for imaging sensitivity, spatial resolution, and targeted biodistribution. The latest research aiming to optimize the performance of MPI tracers is reviewed based on their material composition, physical properties, and surface modifications. While the unique advantages of MPI have led to a series of promising biomedical applications, recent development of MPI in investigating vascular abnormalities in cardiovascular and cerebrovascular systems, and cancer are also discussed. Finally, recent progress and challenges in the clinical translation of MPI are discussed to provide possible directions for future research and development.

Synthesis and Detection of BODIPY-, Biotin-, and 19 F- Labeled Single-Entity Dendritic Heparan Sulfate Mimetics

Heparin and heparan sulfate (HS) are naturally occurring mammalian glycosaminoglycans, and their synthetic and semi-synthetic mimetics have attracted significant interest as potential therapeutics. However, understanding the mechanism of action by which HS, heparin, and HS mimetics have a biological effect is difficult due to their highly charged nature, broad protein interactomes, and variable structures. To address this, a library of novel single-entity dendritic mimetics conjugated to BODIPY, Fluorine-19 (19 F), and biotin was synthesized for imaging and localization studies. The novel dendritic scaffold allowed for the conjugation of labeling moieties without reducing the number of sulfated capping groups, thereby better mimicking the multivalent nature of HS-protein interactions. The 19 F labeled mimetics were assessed in phantom studies and were detected at concentrations as low as 5 mM. Flow cytometric studies using a fluorescently labeled mimetic showed that the compound associated with immune cells from tumors more readily than splenic counterparts and was directed to endosomal-lysosomal compartments within immune cells and cancer cells. Furthermore, the fluorescently labeled mimetic entered the central nervous system and was detectable in brain-infiltrating immune cells 24 hours after treatment. Here, we report the enabling methodology for rapidly preparing various labeled HS mimetics and molecular probes with diverse potential therapeutic applications.

Design of fluorinated stealth poly(ε-caprolactone) nanocarriers

The covalent functionalization of polymers with fluorinated moieties represents a promising strategy for the development of multimodal systems. Moreover, polymer fluorination often endows the resulting nanocarriers with improved colloidal stability in the biological environment. In this work, we developed fluorinated pegylated (PEG) biodegradable poly(ε-caprolactone) (PCL) drug nanocarriers showing both high colloidal stability and stealth properties, as well as being (19F)-Nuclear Magnetic Resonance (NMR) detectable. The optimized nanocarriers were obtained mixing a PEG-PCL block copolymer with a nonafluoro-functionalized PCL polymer. The role of PEGylation and fluorination on self-assembly and colloidal behavior of the obtained nanoparticles (NPs) was investigated, as well as their respective role on stealth properties and colloidal stability. To prove the feasibility of the developed NPs as potential 19F NMR detectable drug delivery systems, a hydrophobic drug was successfully encapsulated, and the maintenance of the relevant 19F NMR properties evaluated. Drug-loaded fluorinated NPs still retained a sharp and intense 19F NMR signal and good relaxivity parameters (i.e., T1 and T2 relaxation times) in water, which were not impaired by drug encapsulation.

Perfluoro-tert-butyl Group-Derived Capmatinib: Synthesis, Biological Evaluation and Its Application in 19 F Magnetic Resonance Imaging

Capmatinib is an FDA-approved drug to treat metastatic non-small cell lung cancer with MET-exon 14 skipping. Herein, the perfluoro-tert-butyl group, which possesses nine chemically identical fluorine atoms, was introduced on Capmatinib to afford a targeted 19 F magnetic resonance imaging (MRI) probe, perfluoro-tert-butyl group-derived Capmatinib (9F-CAP). The 19 F MRI concentration limit was found to be 25 mM in FLASH sequence. Molecular docking simulation, surface plasmon resonance (SPR) (with a Kd of 40.7 μM), half-inhibitory concentration (with a IC50 of 168 nM), Annexin V, and cytotoxicity assays jointly demonstrated that the 9F-CAP targeted cMET protein specifically. Therefore, the targeted imaging capability of 9F-CAP is of great significance for the preoperative diagnosis of specific cancers.

Fluorinated Human Serum Albumin as Potential 19F Magnetic Resonance Imaging Probe

Fluorinated human serum albumin conjugates were prepared and tested as potential metal-free probes for ¹⁹F magnetic resonance imaging (MRI). Each protein molecule was modified by several fluorine-containing compounds via the N-substituted natural acylating reagent homocysteine thiolactone. Albumin conjugates retain the protein's physical and biological properties, such as its 3D dimensional structure, aggregation ability, good solubility, proteolysis efficiency, biocompatibility, and low cytotoxicity. A dual-labeled with cyanine 7 fluorescence dye and fluorine reporter group albumin were synthesized for simultaneous fluorescence imaging and ¹⁹F MRI. The preliminary in vitro studies show the prospects of albumin carriers for multimodal imaging.

Self-Assembly of Precisely Fluorinated Albumin for Dual Imaging-Guided Synergistic Chemo-Photothermal-Photodynamic Cancer Therapy

Although albumin has been extensively used in nanomedicine, it is still challenging to fluorinate albumin into fluorine-19 magnetic resonance imaging (¹⁹F MRI)-traceable theranostics because existing strategies lead to severe ¹⁹F signal splitting, line broadening, and low ¹⁹F MRI sensitivity. To this end, 34-cysteine-selectively fluorinated bovine serum albumins (BSAs) with a sharp singlet ¹⁹F peak have been developed as ¹⁹F MRI-sensitive and self-assembled frameworks for cancer theranostics. It was found that fluorinated albumin with a non-binding fluorocarbon and a long linker is crucial for avoiding ¹⁹F signal splitting and line broadening. With the fluorinated BSAs, paclitaxel (PTX) and IR-780 were self-assembled into stable, monodisperse, and multifunctional nanoparticles in a framework-promoted self-emulsion way. The high tumor accumulation, efficient cancer cell uptake, and laser-triggered PTX sharp release of the BSA nanoparticles enabled ¹⁹F MRI-near infrared fluorescence imaging (NIR FLI)-guided synergistic chemotherapy (Chemo), photothermal and photodynamic therapy of xenograft MCF-7 cancer with a high therapeutical index in mice. This study developed a rational synthesis of ¹⁹F MRI-sensitive albumin and a framework-promoted self-emulsion of multifunctional BSA nanoparticles, which would promote the development of protein-based high-performance biomaterials for imaging, diagnosis, therapy, and beyond.

Spatial characterization of redox processes and speciation of Ru(III) anticancer complexes by 19F magnetic resonance imaging

The application of CF₃-labeled Ru(III) anticancer complexes to magnetic resonance (MR) imaging of tumour tissues is demonstrated. By combining anatomical chemical-shift selective (CHESS) imaging with ¹⁹F chemical-shift imaging (CSI) MR methods, we show that oxidation states and ligand-exchange processes of the complexes can be spatially encoded. Measurements on different tissue models, including a human breast adenocarcinoma tumour, validate the application of these complexes as MR theranostics for the sensing and targeting of hypoxia.

19F MRI-fluorescence imaging dual-modal cell tracking with partially fluorinated nanoemulsions

As a noninvasive “hot-spot” imaging technology, fluorine-19 magnetic resonance imaging (19F MRI) has been extensively used in cell tracking. However, the peculiar physicochemical properties of perfluorocarbons (PFCs), the most commonly used 19F MRI agents, sometimes cause low sensitivity, poor cell uptake, and misleading results. In this study, a partially fluorinated agent, perfluoro-tert-butyl benzyl ether, was used to formulate a 19F MRI-fluorescence imaging (FLI) dual-modal nanoemulsion for cell tracking. Compared with PFCs, the partially fluorinated agent showed considerably improved physicochemical properties, such as lower density, shorter longitudinal relaxation times, and higher solubility to fluorophores, while maintaining high 19F MRI sensitivity. After being formulated into stable, monodisperse, and paramagnetic Fe3+-promoted nanoemulsions, the partially fluorinated agent was used in 19F MRI-FLI dual imaging tracking of lung cancer A549 cells and macrophages in an inflammation mouse model.

Partially fluorinated nanoemulsions for 19F MRI-fluorescence dual imaging cell tracking

Fluorine-19 magnetic resonance imaging (¹⁹F MRI) has been a technology of choice for in vivo cell tracking, in which perfluorocarbons (PFCs) nanoemulsions are the most used ¹⁹F MRI agents. However, the peculiar physicochemical properties of PFCs may lead to poor cell uptake and misleading cell tracking results. Herein, we employed partially fluorinated aromatic agents to formulate paramagnetic nanoemulsions as novel ¹⁹F MRI-fluorescence (FL) dual imaging agents for cell tracking. With the intramolecular π-π interaction, low density and fluorine content, the partially fluorinated agents enable considerable solubilities of functional agents and short relaxation times, which facilitates convenient preparation of stable, biocompatible, and multifunctional nanoemulsions with high ¹⁹F MRI sensitivity. Replacing PFCs in ¹⁹F MRI nanoemulsions with readily available partially fluorinated aromatic agents may address many issues associated with PFCs and provide a novel strategy for high-performance ¹⁹F MRI agents of broad biomedical applications.

Synthesis of trifluoromethylated aza-BODIPYs as fluorescence-19F MRI dual imaging and photodynamic agents

Dual-imaging agents with highly sensitive fluorescence (FL) imaging and highly selective fluorine-19 magnetic resonance imaging (¹⁹F MRI) are valuable for biomedical research. At the same time, photosensitizers with a high reactive oxygen species (ROS) generating capability are crucial for photodynamic therapy (PDT) of cancer. Herein, a series of tetra-trifluoromethylated aza-boron dipyrromethenes (aza-BODIPYs) were conveniently synthesized from readily available building blocks and their physicochemical properties, including ultraviolet-visible (UV-Vis) absorption, FL emission, photothermal efficacy, ROS generating efficacy, and ¹⁹F MRI sensitivity, were systematically investigated. An aza-BODIPY with 12 symmetrical fluorines was identified as a potent FL-¹⁹F MRI dual-imaging traceable photodynamic agent. It was found that the selective introduction of trifluoromethyl (CF₃) groups into aza-BODIPYs may considerably improve their UV absorption, FL emission, photothermal efficacy, and ROS generating properties, which lays the foundation for the rational design of trifluoromethylated aza-BODIPYs in biomedical applications.

Nanotechnology as a Versatile Tool for 19F-MRI Agent’s Formulation: A Glimpse into the Use of Perfluorinated and Fluorinated Compounds in Nanoparticles

Simultaneously being a non-radiative and non-invasive technique makes magnetic resonance imaging (MRI) one of the highly sought imaging techniques for the early diagnosis and treatment of diseases. Despite more than four decades of research on finding a suitable imaging agent from fluorine for clinical applications, it still lingers as a challenge to get the regulatory approval compared to its hydrogen counterpart. The pertinent hurdle is the simultaneous intrinsic hydrophobicity and lipophobicity of fluorine and its derivatives that make them insoluble in any liquids, strongly limiting their application in areas such as targeted delivery. A blossoming technique to circumvent the unfavorable physicochemical characteristics of perfluorocarbon compounds (PFCs) and guarantee a high local concentration of fluorine in the desired body part is to encapsulate them in nanosystems. In this review, we will be emphasizing different types of nanocarrier systems studied to encapsulate various PFCs and fluorinated compounds, headway to be applied as a contrast agent (CA) in fluorine-19 MRI (¹⁹F MRI). We would also scrutinize, especially from studies over the last decade, the different types of PFCs and their specific applications and limitations concerning the nanoparticle (NP) system used to encapsulate them. A critical evaluation for future opportunities would be speculated.

Hydrofluorocarbons Nanoparticles for 19F MRI-Fluorescence Dual Imaging and Chemo-Photodynamic Therapy

The synergistic chemotherapy and photodynamic therapy (PDT) may significantly improve cancer therapeutic efficacy, in which fluorinated nanoemulsions are highly advantageous for their ability to deliver oxygen to hypoxic tumors and...

19 F MRI Probes for Multimodal Imaging*

Magnetic resonance imaging (MRI) is one of the most powerful imaging tools today, capable of displaying superior soft-tissue contrast. This review discusses developments in the field of ¹⁹ F MRI multimodal probes in combination with optical fluorescence imaging (OFI), ¹ H MRI, chemical exchange saturation transfer (CEST) MRI, ultrasonography (USG), X-ray computed tomography (CT), single photon emission tomography (SPECT), positron emission tomography (PET), and photoacoustic imaging (PAI). In each case, multimodal ¹⁹ F MRI probes compensate for the deficiency of individual techniques and offer improved sensitivity or accuracy of detection over unimodal counterparts. Strategies for designing ¹⁹ F MRI multimodal probes are described with respect to their structure, physicochemical properties, biocompatibility, and the quality of images.