Fluorine-19 Magnetic Resonance Research Articles

Self-Assembled Fluorinated Nanoparticles as Sensitive and Biocompatible Theranostic Platforms for 19 F MRI.

Theranostics is a novel paradigm integrating therapy and diagnostics, thereby providing new prospects for overcoming the limitations of traditional treatments. In this context, perfluorocarbons (PFCs) are the most widely used tracers in preclinical fluorine-19 magnetic resonance (19 F MR), primarily for their high fluorine content. However, PFCs are extremely hydrophobic, and their solutions often display reduced biocompatibility, relative instability, and subpar 19 F MR relaxation times. This study aims to explore the potential of micellar 19 F MR imaging (MRI) tracers, synthesized by polymerization-induced self-assembly (PISA), as alternative theranostic agents for simultaneous imaging and release of the non-steroidal antileprotic drug clofazimine. In vitro, under physiological conditions, these micelles demonstrate sustained drug release. In vivo, throughout the drug release process, they provide a highly specific and sensitive 19 F MRI signal. Even after extended exposure, these fluoropolymer tracers show biocompatibility, as confirmed by the histological analysis. Moreover, the characteristics of these polymers can be broadly adjusted by design to meet the wide range of criteria for preclinical and clinical settings. Therefore, micellar 19 F MRI tracers display physicochemical properties suitable for in vivo imaging, such as relaxation times and non-toxicity, and high performance as drug carriers, highlighting their potential as both diagnostic and therapeutic tools.

Fluorinated rotaxanes as sensitive 19F MRI agents: Threading for higher sensitivity

As a promising imaging technology, the low sensitivity of fluorine-19 magnetic resonance imaging (19F MRI) severely hinders its biomedical applications. Herein, we have developed an unprecedented rotaxane-based strategy to improve the sensitivity of 19F MRI agents. By threading the fluorinated macrocycle into 2-blade pinwheel [2]rotaxanes, the 19F longitudinal relaxation rate R1 was dramatically increased, resulting in a significant 19F MRI signal intensity enhancement of up to 79%. Through comparative molecular dynamics studies using a series of solution and solid-state 1H/19F nuclear magnetic resonance (1H/19F NMR) and molecular dynamics simulations, it was found that the formation of mechanical bonds dramatically restricts the motion of the wheel fluorines and thus increasing the R1 for higher 19F MRI sensitivity. Besides a novel strategy for improving 19F MRI sensitivity, this study has established 19F NMR/MRI as a valuable technology for monitoring the molecular dynamics of rotaxanes, which may shed new light on high-performance 19F MRI agents and molecular devices.

All-in-One Heptamethine Cyanine Amphiphiles for Dual Imaging-Guided Chemo-Photodynamic-Photothermal Therapy of Breast Cancer.

Developing a theranostic system that integrates multimodal imaging, synergistic therapeutic, and formulation entities is a promising strategy for efficient cancer treatment. However, the complexity and safety concerns of multiple functional entities hinder their clinical translation. Herein, versatile "all-in-one" heptamethine cyanine amphiphiles (PEG-Cy-Fs) with multiple favorable capabilities, including fluorine-19 magnetic resonance imaging (19 F MRI), near-infrared fluorescence imaging (NIR FLI), photodynamic therapy (PDT), photothermal therapy (PTT), polyethylene glycolation (PEGylation) and high biocompatibility, are developed for the convenient construction of theranostic platforms. Amphiphiles PEG-Cy-Fs are synthesized on a multi-hundred-milligram scale with high efficacy, which self-assembled with a chemotherapy drug tamoxifen (TAM) into monodisperse and stable nanoparticles (SoFoTm/PEG-Cy-F18 ) with "turned on" FLI, sensitive 19 F MRI, mitochondria-targeting ability, high PDT and PTT efficacy, and PEGylation-optimized pharmacokinetics. The selective accumulation of SoFoTm/PEG-Cy-F18 in xenograft MCF-7 tumor with a long retention time (>10 days) enabled 19 F MRI-NIR FLI-guided chemo-photodynamic-photothermal therapy (chemo-PDT-PTT) of breast cancer with high therapeutical index in mice. The "all-in-one" heptamethine cyanine amphiphile may facilitate the convenient and standardized preparation of high-performance theranostics systems for clinical translation.

Method for estimation of apoptotic cell fraction of cytotherapy using in vivo fluorine-19 magnetic resonance: pilot study in a patient with head and neck carcinoma receiving tumor-infiltrating lymphocytes labeled with perfluorocarbon nanoemulsion

BackgroundAdoptive transfer of T cells is a burgeoning cancer therapeutic approach. However, the fate of the cells, once transferred, is most often unknown. We describe the first clinical experience with...

Preparation of PFPE-Based Polymeric Nanoparticles via Polymerization-Induced Self-Assembly as Contrast Agents for 19F MRI.

Fluorine-19 magnetic resonance imaging (19F MRI) probes have received considerable research interest as imaging contrast agents (CAs), but they remain neglected and underutilized due to the limited fluorine content or poor performance of fluorinated tracers. Here, we present polymeric nanoparticles (NPs) as 19F MRI CAs with a simple synthesis method and promising imaging performance. First, hydrophilic random copolymers were synthesized from oligo(ethylene glycol) methyl ether acrylate and perfluoropolyether methacrylate by reversible addition-fragmentation chain transfer (RAFT) polymerization. The optimal fluorine content, polymer concentration, and cytotoxicity as 19F MRI CAs were investigated in detail. Then, the optimal copolymer was selected as the macromolecular chain transfer agent, and the chain extension was performed with 2-(perfluorooctyl ethyl methacrylate). Subsequently, the NPs with different morphologies, such as ellipsoidal, spherical nanoparticles and vesicles, were prepared in situ by the RAFT-mediated polymerization-induced self-assembly method. In addition, the 19F MRI signal and cytotoxicity studies further confirmed that these polymeric NPs are nontoxic and have great potential as promising 19F MRI CAs for biological applications.

Water-Soluble Chemically Precise Fluorinated Molecular Clusters for Interference-Free Multiplex 19F MRI in Living Mice.

Fluorine-19 magnetic resonance imaging (19F MRI) is gaining widespread interest from the fields of biomolecule detection, cell tracking, and diagnosis, benefiting from its negligible background, deep tissue penetration, and multispectral capacity. However, a wide range of 19F MRI probes are in great demand for the development of multispectral 19F MRI due to the limited number of high-performance 19F MRI probes. Herein, we report a type of water-soluble molecular 19F MRI nanoprobe by conjugating fluorine-containing moieties with a polyhedral oligomeric silsesquioxane (POSS) cluster for multispectral color-coded 19F MRI. These chemically precise fluorinated molecular clusters are of excellent aqueous solubility with relatively high 19F contents and of single 19F resonance frequency with suitable longitudinal and transverse relaxation times for high-performance 19F MRI. We construct three POSS-based molecular nanoprobes with distinct 19F chemical shifts at -71.91, -123.23, and -60.18 ppm and achieve interference-free multispectral color-coded 19F MRI of labeled cells in vitro and in vivo. Moreover, in vivo 19F MRI reveals that these molecular nanoprobes could selectively accumulate in tumors and undergo rapid renal clearance afterward, illustrating their favorable in vivo behavior for biomedical applications. This study provides an efficient strategy to expand the 19F probe libraries for multispectral 19F MRI in biomedical research.

Quantitative assessment of angioplasty-induced vascular inflammation with 19F cardiovascular magnetic resonance imaging

BackgroundMacrophages play a pivotal role in vascular inflammation and predict cardiovascular complications. Fluorine-19 magnetic resonance imaging (19F MRI) with intravenously applied perfluorocarbon allows a background-free direct quantification of macrophage abundance in experimental vascular disease models in mice. Recently, perfluorooctyl bromide-nanoemulsion (PFOB-NE) was applied to effectively image macrophage infiltration in a pig model of myocardial infarction using clinical MRI scanners. In the present proof-of-concept approach, we aimed to non-invasively image monocyte/macrophage infiltration in response to carotid artery angioplasty in pigs using 19F MRI to assess early inflammatory response to mechanical injury. MethodsIn eight minipigs, two different types of vascular injury were conducted: a mild injury employing balloon oversize angioplasty only (BA, n = 4) and a severe injury provoked by BA in combination with endothelial denudation (BA + ECDN, n = 4). PFOB-NE was administered intravenously three days after injury followed by 1H and 19F MRI to assess vascular inflammatory burden at day six. Vascular response to mechanical injury was validated using X-ray angiography, intravascular ultrasound and immunohistology in at least 10 segments per carotid artery. ResultsAngioplasty was successfully induced in all eight pigs. Response to injury was characterized by positive remodeling with predominantly adventitial wall thickening and concomitant infiltration of monocytes/macrophages. No severe adverse reactions were observed following PFOB-NE administration. In vivo 19F signals were only detected in the four pigs following BA + ECDN with a robust signal-to-noise ratio (SNR) of 14.7 ± 4.8. Ex vivo analysis revealed a linear correlation of 19F SNR to local monocyte/macrophage cell density. Minimum detection limit of infiltrated monocytes/macrophages was estimated at approximately 410 cells/mm2. ConclusionsIn this proof-of-concept study, 19F MRI enabled quantification of monocyte/macrophage infiltration after vascular injury with sufficient sensitivity. This may provide the opportunity to non-invasively monitor vascular inflammation with MRI in patients after angioplasty or even in atherosclerotic plaques.

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.

First in vivo fluorine-19 magnetic resonance imaging of the multiple sclerosis drug siponimod.

Theranostic imaging methods could greatly enhance our understanding of the distribution of CNS-acting drugs in individual patients. Fluorine-19 magnetic resonance imaging (19F MRI) offers the opportunity to localize and quantify fluorinated drugs non-invasively, without modifications and without the application of ionizing or other harmful radiation. Here we investigated siponimod, a sphingosine 1-phosphate (S1P) receptor antagonist indicated for secondary progressive multiple sclerosis (SPMS), to determine the feasibility of in vivo 19F MR imaging of a disease modifying drug. Methods: The 19F MR properties of siponimod were characterized using spectroscopic techniques. Four MRI methods were investigated to determine which was the most sensitive for 19F MR imaging of siponimod under biological conditions. We subsequently administered siponimod orally to 6 mice and acquired 19F MR spectra and images in vivo directly after administration, and in ex vivo tissues. Results: The 19F transverse relaxation time of siponimod was 381 ms when dissolved in dimethyl sulfoxide, and substantially reduced to 5 ms when combined with serum, and to 20 ms in ex vivo liver tissue. Ultrashort echo time (UTE) imaging was determined to be the most sensitive MRI technique for imaging siponimod in a biological context and was used to map the drug in vivo in the stomach and liver. Ex vivo images in the liver and brain showed an inhomogeneous distribution of siponimod in both organs. In the brain, siponimod accumulated predominantly in the cerebrum but not the cerebellum. No secondary 19F signals were detected from metabolites. From a translational perspective, we found that acquisitions done on a 3.0 T clinical MR scanner were 2.75 times more sensitive than acquisitions performed on a preclinical 9.4 T MR setup when taking changes in brain size across species into consideration and using equivalent relative spatial resolution. Conclusion: Siponimod can be imaged non-invasively using 19F UTE MRI in the form administered to MS patients, without modification. This study lays the groundwork for more extensive preclinical and clinical investigations. With the necessary technical development, 19F MRI has the potential to become a powerful theranostic tool for studying the time-course and distribution of CNS-acting drugs within the brain, especially during pathology.

Multibranched-Based Fluorinated Materials: Tailor-Made Design of 19F-MRI Probes

ConspectusFuture medicine is primarily aiming at the development of novel approaches for an early diagnosis of diseases and a personalized therapy for patients. For achieving these objectives, a key role is played by medical imaging. Among available noninvasive imaging techniques, Fluorine-19 (19F) Magnetic Resonance Imaging (MRI) is emerging as a powerful quantitative detection modality for clinical use both for molecular imaging and for cell tracking.The strength of using 19F-MRI is mainly related to the lack of endogenous organic fluorine in tissues, with no background, enabling the visualization of fluorinated tracers as hot-spot images, adding secondary independent information to the anatomical features provided by the grayscale 1H-MRI. The main challenge for 19F-MRI clinical application is the intrinsic reduced sensitivity of MRI. To improve sensitivity, undoubtedly the use of a high field MRI scanner and cryogenic radiofrequency probes is advantageous, but there is a clear need of developing increasingly effective fluorinated tracers.The ideal tracer should bear as many as possible magnetically equivalent fluorine atoms and show optimal magnetic resonance relaxivity properties (i.e., T1 and T2), which enable reduced acquisition time with the possibility to apply fast imaging methods. Moreover, it should be biocompatible with reduced tendency to bioaccumulate in tissues, which is one of the main drawbacks in using perfluorocarbons (PFCs), together with their difficulty to be chemically modified with functional groups. In fact, PFCs such as perfluorooctyl bromide (PFOB), perfluoro-15-crown-5-ether (PFCE), and linear perfluoropolyethers (PFPE) are currently the most used tracers in 19F-MRI preclinical and clinical studies, with the above-mentioned limitations. In this regard, molecules bearing short branched fluorinated chains gained a lot of attention for their high number of equivalent fluorines and expected capability of reducing bioaccumulation concerns. A valuable building block for branched fluorinated tracers is perfluoro-tert-butanol (PFTB), with nine magnetically equivalent fluorines and easy availability and modification.In this Account we will discuss the main challenges that 19F-MRI has to overcome for increasing its clinical use, highlighting on one hand the need of developing customized fluorinated materials for increasing sensitivity and enabling multimodal properties, and on the other hand, the importance of the ultrastructure of the final formulation for the final biological response (i.e., clearance). In this context, our group has been focusing on the synthesis and development of branched fluorinated tracers, for which the originator is a molecule called PERFECTA (from suPERFluorinatEdContrasT Agent), bearing 36 equiv 19F atoms, which showed not only optimal relaxometry properties but also a very specific and intense Raman signal. Thus, PERFECTA and its derivatives represent a new family of multimodal tracers enabling multiscale analysis, from whole body imaging (19F-MRI) to microscopic detection at the cellular/tissue level (Raman microscopy). We believe that our proposed PFTB strategy can strongly promote the production of increasingly effective 19F-MRI materials with additional functionalities, facilitating the clinical translation of this imaging modality.

Thermoresponsive Triblock Copolymers as Widely Applicable 19F Magnetic Resonance Imaging Tracers

Fluorine-19 magnetic resonance imaging (19F MRI) has emerged as a promising noninvasive diagnostic tool, broadening the diagnostic possibilities of commonly used proton MRI. Despite the potential of 19F MRI, an ideal tracer paving the way toward the entry of this method into common medical practice is yet to be developed. In this study, we report on a series of polymeric systems based on thermoresponsive poly[N-(2,2-difluoroethyl)acrylamide] (PDFEA), a polymer considered to be an ideal tracer for 19F MRI. The described systems are designed as BAB triblock copolymers, where B corresponds to thermoresponsive PDFEA blocks and A is a hydrophilic poly(ethylene glycol) block. These BAB triblock copolymers are able to form nanoparticles in dilute aqueous solutions, which undergo a transition into physically cross-linked hydrogels upon increasing the polymer concentration. Since thermoresponsive particle- and hydrogel-based systems are applicable in a wide range of biomedical applications, we created a diagnostic system with potential therapeutic properties (theranostic) as a widely tunable platform through straightforward synthesis while serving a multitude of applications. We analyzed the effect of the BAB block ratio on the self-assembly, thermoresponsiveness, and mechanical properties of the studied hydrogels, together with their suitability for 19F MRI. Finally, their biocompatibility was assessed on a relevant cell line.

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.

Optimization of superfluorinated PLGA nanoparticles for enhanced cell labelling and detection by 19F-MRI

Fluorine-19 (19F) Magnetic Resonance Imaging (MRI) is an emergent imaging technique for molecular imaging and cell tracking. Lack of intrinsic 19F signals in tissues allows unambiguous in vivo detection of exogenous fluorinated probes, complementary to the anatomical and multiparametric information obtained by standard 1H-MRI. However, the intrinsic low sensitivity of MRI technique requires the need of designing increasingly effective fluorinated tracers. PERFECTA, with its 36 magnetically equivalent 19F atoms and a designed branched molecular structure, represents an excellent superfluorinated tracer. In this paper, we report the development of PERFECTA loaded PLGA NPs stabilized by different coatings as promising 19F-MRI probes. The results clearly show the optimal cellular uptake of the produced colloidally stable PERFECTA loaded PLGA NPs without impact on cells viability. Importantly, NPs stabilization with the anionic surfactant sodium cholate (NaC) clearly enhances NPs internalization within cells with respect to PVA-coated NPs. Moreover, the optimized NPs are characterized by shorter T1 relaxation times with respect to other PERFECTA formulations that would allow the increase of 19F-MRI sensitivity with fast imaging acquisitions.

Fluorine labelling of therapeutic human tolerogenic dendritic cells for 19F-magnetic resonance imaging.

Tolerogenic dendritic cell (tolDC) therapies aim to restore self-tolerance in patients suffering from autoimmune diseases. Phase 1 clinical trials with tolDC have shown the feasibility and safety of this approach, but have also highlighted a lack of understanding of their distribution in vivo. Fluorine-19 magnetic resonance imaging (19F-MRI) promises an attractive cell tracking method because it allows for detection of 19F-labelled cells in a non-invasive and longitudinal manner. Here, we tested the suitability of nanoparticles containing 19F (19F-NP) for labelling of therapeutic human tolDC for detection by 19F-MRI. We found that tolDC readily endocytosed 19F-NP with acceptable effects on cell viability and yield. The MRI signal-to-noise ratios obtained are more than sufficient for detection of the administered tolDC dose (10 million cells) at the injection site in vivo, depending on the tissue depth and the rate of cell dispersal. Importantly, 19F-NP labelling did not revert tolDC into immunogenic DC, as confirmed by their low expression of typical mature DC surface markers (CD83, CD86), low secretion of pro-inflammatory IL-12p70, and low capacity to induce IFN-γ in allogeneic CD4+ T cells. In addition, the capacity of tolDC to secrete anti-inflammatory IL-10 was not diminished by 19F-NP labelling. We conclude that 19F-NP is a suitable imaging agent for tolDC. With currently available technologies, this imaging approach does not yet approach the sensitivity required to detect small numbers of migrating cells, but could have important utility for determining the accuracy of injecting tolDC into the desired target tissue and their efflux rate.

Multiresponsive fluorinated polymers as a theranostic platform using 19F MRI

Drug delivery systems (DDSs) can significantly improve the biodistribution and pharmacokinetics of various drugs. Herein, we describe diblock polymers of poly(2-methyloxazoline) and N-(2,2′-difluoroethyl)acrylamide with N-[2-(ferrocenylcarboxamido)ethyl]acrylamide that can be used as advanced DDSs. These thermoresponsive diblock copolymers self-assemble when heated to body temperature but disassemble when exposed to oxidative conditions (reactive oxygen species, ROS), releasing their cargo. Moreover, our polymers are not prone to spontaneous oxidation by air or hydrogen peroxide under physiological conditions but are highly sensitive to ROS under acidic conditions. Advantageously, the biodistribution of our DDS can be monitored with fluorine-19 magnetic resonance imaging (19F MRI). Therefore, our polymers could be used in both local and systemic drug delivery systems in ROS-rich environments, such as tumors or inflamed tissues. Additionally, the properties of our polymers could be widely modified to meet the demands of various clinical applications. Overall, we demonstrate that our copolymers (i) release their cargo preferentially in an ROS-rich environment, (ii) are biocompatible, and (iii) can be easily visualized in vivo.

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.

Enhanced detection of paramagnetic fluorine-19 magnetic resonance imaging agents using zero echo time sequence and compressed sensing.

Fluorine-19 (19 F) magnetic resonance imaging (MRI) is an emerging technique offering specific detection of labeled cells in vivo. Lengthy acquisition times and modest signal-to-noise ratio (SNR) makes three-dimensional spin-density-weighted 19 F imaging challenging. Recent advances in tracer paramagnetic metallo-perfluorocarbon (MPFC) nanoemulsion probes have shown multifold SNR improvements due to an accelerated 19 F T1 relaxation rate and a commensurate gain in imaging speed and averages. However, 19 F T2 -reduction and increased linewidth limit the amount of metal additive in MPFC probes, thus constraining the ultimate SNR. To overcome these barriers, we describe a compressed sampling (CS) scheme, implemented using a "zero" echo time (ZTE) sequence, with data reconstructed via a sparsity-promoting algorithm. Our CS-ZTE scheme acquires k-space data using an undersampled spherical radial pattern and signal averaging. Image reconstruction employs off-the-shelf sparse solvers to solve a joint total variation and -norm regularized least square problem. To evaluate CS-ZTE, we performed simulations and acquired 19 F MRI data at 11.7T in phantoms and mice receiving MPFC-labeled dendritic cells. For MPFC-labeled cells in vivo, we show SNR gains of ~6.3×with 8-fold undersampling. We show that this enhancement is due to three mechanisms including undersampling and commensurate increase in signal averaging in a fixed scan time, denoising attributes from the CS algorithm, and paramagnetic reduction of T1 . Importantly, 19 F image intensity analyses yield accurate estimates of absolute quantification of 19 F spins. Overall, the CS-ZTE method using MPFC probes achieves ultrafast imaging, a substantial boost in detection sensitivity, accurate 19 F spin quantification, and minimal image artifacts.

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.

Visualizing CAR-T cell Immunotherapy Using 3 Tesla Fluorine-19 MRI

PurposeChimeric antigen receptor (CAR) T cell cancer immunotherapies have shown remarkable results in patients with hematological malignancies and represent the first approved genetically modified cellular therapies. However, not all blood cancer patients respond favorably, serious side effects have been reported, and the treatment of solid tumors has been a challenge. An imaging tool for visualizing the variety of CAR-T cell products in use and being explored could provide important patient-specific data on CAR-T cell location to inform on potential success or failure of treatment as well as off-target toxicities. Fluorine-19 (19F) magnetic resonance imaging (MRI) allows for the noninvasive detection of 19F perfluorocarbon (PFC) labeled cells. Our objective was to visualize PFC-labeled (PFC +) CAR-T cells in a mouse model of leukemia using clinical field strength (3 Tesla) 19F MRI and compare the cytotoxicity of PFC + versus unlabeled CAR-T cells.ProceduresNSG mice (n = 17) received subcutaneous injections of CD19 + human B cell leukemia cells (NALM6) expressing firefly luciferase in their left hind flank (1 × 106). Twenty-one days later, each mouse received an intratumoral injection of 10 × 106 PFC + CD19-targeted CAR-T cells (n = 6), unlabeled CD19-targeted CAR-T cells (n = 3), PFC + untransduced T cells (n = 5), or an equivalent volume of saline (n = 3). 19F MRI was performed on mice treated with PFC + CAR-T cells days 1, 3, and 7 post-treatment. Bioluminescence imaging (BLI) was performed on all mice days − 1, 5, 10, and 14 post-treatment to monitor tumor response.ResultsPFC + CAR-T cells were successfully detected in tumors using 19F MRI on days 1, 3, and 7 post-injection. In vivo BLI data revealed that mice treated with PFC + or PFC − CAR-T cells had significantly lower tumor burden by day 14 compared to untreated mice and mice treated with PFC + untransduced T cells (p < 0.05). Importantly, mice treated with PFC + CAR-T cells showed equivalent cytotoxicity compared to mice receiving PFC − CAR-T cells.ConclusionsOur studies demonstrate that clinical field strength 19F MRI can be used to visualize PFC + CAR-T cells for up to 7 days post–intratumoral injection. Importantly, PFC labeling did not significantly affect in vivo CAR-T cell cytotoxicity. These imaging tools may have broad applications for tracking emerging CAR-T cell therapies in preclinical models and may eventually be useful for the detection of CAR-T cells in patients where localized injection of CAR-T cells is being pursued.

The sensitivity of magnetic particle imaging and fluorine-19 magnetic resonance imaging for cell tracking

Magnetic particle imaging (MPI) and fluorine-19 (19F) MRI produce images which allow for quantification of labeled cells. MPI is an emerging instrument for cell tracking, which is expected to have superior sensitivity compared to 19F MRI. Our objective is to assess the cellular sensitivity of MPI and 19F MRI for detection of mesenchymal stem cells (MSC) and breast cancer cells. Cells were labeled with ferucarbotran or perfluoropolyether, for imaging on a preclinical MPI system or 3 Tesla clinical MRI, respectively. Using the same imaging time, as few as 4000 MSC (76 ng iron) and 8000 breast cancer cells (74 ng iron) were reliably detected with MPI, and 256,000 MSC (9.01 × 1016 19F atoms) were detected with 19F MRI, with SNR > 5. MPI has the potential to be more sensitive than 19F MRI for cell tracking. In vivo sensitivity with MPI and 19F MRI was evaluated by imaging MSC that were administered by different routes. In vivo imaging revealed reduced sensitivity compared to ex vivo cell pellets of the same cell number. We attribute reduced MPI and 19F MRI cell detection in vivo to the effect of cell dispersion among other factors, which are described.