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The search for alternatives to Gd-containing magnetic resonance imaging (MRI) contrast agents addresses the field of Fe(III)-bearing species with the expectation that the use of an essential metal ion may avoid the issues raised by the exogenous Gd. Attention is currently devoted to highly stable Fe(III) complexes with hexacoordinating ligands, although they may lack any coordinated water molecule. We found that the hexacoordinated Fe(III) complex with two units of deferasirox, a largely used iron sequestering agent, owns properties that can make it a viable alternative to Gd-based agents. Fe(deferasirox)2 displays an outstanding thermodynamic stability, a high binding affinity to human serum albumin (three molecules of complex are simultaneously bound to the protein), and a good relaxivity that increases in the range 20-80 MHz. The relaxation enhancement is due to second sphere water molecules likely forming H-bonds with the coordinating phenoxide oxygens. A further enhancement was observed upon the formation of the supramolecular adduct with albumin. The binding sites of Fe(deferasirox)2 on albumin were characterized by relaxometric competitive assays. Preliminary in vivo imaging studies on a tumor-bearing mouse model indicate that, on a 3 T MRI scanner, the contrast ability of Fe(deferasirox)2 is comparable to the one shown by the commercial Gd(DTPA) agent. ICP-MS analyses on blood samples withdrawn from healthy mice administered with a dose of 0.1 mmol/kg of Fe(deferasirox)2 showed that the complex is completely removed in 24 h.

Objectives The targeting of tumor cells and their visualization with magnetic resonance imaging (MRI) is an important task in biomedicine. The low sensitivity of this technique is a significant drawback and one that may hamper the detection of the imaging reporters used.To overcome this sensitivity issue, this work explores the synergy between 2 strategies: (1) arginine, glycine, aspartic acid peptide (RGD)-functionalized giant unilamellar vesicles (GUVs) loaded with Gd complexes to accumulate large amounts of MRI contrast agent at the targeting site; and (2) the use of magnetization transfer contrast (MTC), which is a sensitive MRI technique for the detection of Gd complexes in the tumor region. Materials and methods Giant unilamellar vesicles were prepared using the gentle swelling method, and the cyclic RGD targeting moiety was introduced onto the external membrane. Paramagnetic Gd-containing complexes and the fluorescent probe rhodamine were both part of the vesicle membranes and Gd-complexes were also the payload within the inner aqueous cavity. Giant unilamellar vesicles that were loaded with the imaging reporters, but devoid of the RGD targeting moiety, were used as controls. U-87 MG human glioblastoma cells, which are known to overexpress the targets for RGD moieties, were used. In the in vivo experiments, U-87 MG cells were subcutaneously injected into nu/nu mice, and the generated tumors were imaged using MRI, 15 days after cell administration. Magnetic resonance imaging was carried out at 7 T, and T2W, T1W, and MTC/Z-spectra were acquired. Confocal microscopy images and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) were used for result validation. Results In vitro results show that RGD GUVs specifically bind to U-87 MG cells. Microscopy demonstrates that (1) RGD GUVs were anchored onto the external surface of the tumor cells without any internalization; (2) a low number of GUVs per cell were clustered at specific regions; and (3) there is no evidence for macrophage uptake or cell toxicity. The MRI of cell pellets after incubation with RGD GUVs and untargeted ctrl-GUVs was performed. No difference in T1 signal was detected, whereas a 15% difference in MT contrast is present between the RGD GUV-treated cells and the ctrl-GUV-treated cells.Magnetic resonance imaging scans of tumor-bearing mice were acquired before and after (t = 0, 4 hours and 24 hours) the administration of RGD GUVs and ctrl-GUVs. A roughly 16% MTC difference between the 2 groups was observed after 4 hours. Immunofluorescence analyses and ICP-MS analyses (for Gd-detection) of the explanted tumors confirmed the specific accumulation of RGD GUVs in the tumor region. Conclusions RGD GUVs seem to be interesting carriers that can facilitate the specific accumulation of MRI contrast agents at the tumor region. However, the concentration achieved is still below the threshold needed for T1w-MRI visualization. Conversely, MTC proved to be sufficiently sensitive for the visualization of detectable contrast between pretargeting and posttargeting images.

8-Hydroxypyrene-1,3,6-trisulfonate (HPTS) is a small, hydrophilic fluorescent molecule. Since the pKa of the hydroxyl group is close to neutrality and quickly responds to pH changes, it is widely used as a pH-reporter in cell biology for measurements of intracellular pH. HPTS fluorescence (both excitation and emission spectra) at variable pH was measured in pure water in the presence of NaCl solution or in the presence of different buffers (PBS or hepes in the presence or not of NaCl) and in a solution containing BSA. pKa values have been obtained from the sigmoidal curves. Herein, we investigated the effect of mono-, di-, and trivalent cations (Na

Changes in metabolism is an hallmark that characterizes tumour cells from healthy ones. Their detection can be highly relevant for staging the tumor and for monitoring the response to therapeutic treatments. Herein it is shown the readout of these changes can be achieved either by assessing the pH of the extracellular space in the tumour region and by monitoring real time transformations of hyperpolarized C-13 labelled substrates. Mapping pH in a MR image is possible by measuring the CEST response of an administered contrast agent such as Iopamidol that can provide accurate measurements of the heterogeneity of tumour acidosis. Direct detection of relevant enzymatic activities have been acquired by using Pyruvate and Fumarate hyperpolarized by the incorporation of a molecule of para-H

This work aims to investigate the supramolecular binding interactions that occur between iodinated X-ray contrast agents (CAs) and macrocyclic gadolinium (Gd)-based MRI contrast agents (GBCAs). This study provides some new insights in the renal excretion pathways of the two types of imaging probes.The water-proton relaxivities (rA significant increase in rThe reported results show that it is possible to detect the co-presence of iodinated agents and macrocyclic GBCAs in contrast-enhanced MR images. The new information may be useful in the design of novel experiments toward improved diagnostic outcomes.

International audience; Dysfunctional elastin turnover plays a major role in the progression of atherosclerotic plaques. Failure of tropoelastin cross-linking into mature elastin leads to the accumulation of tropoelastin within the growing plaque, increasing its instability. Here we present Gd4-TESMA, an MRI contrast agent specifically designed for molecular imaging of tropoelastin within plaques. Gd4-TESMA is a tetrameric probe composed of a tropoelastin-binding peptide (the VVGS-peptide) conjugated with four Gd(III)-DOTA-monoamide chelates. It shows a relaxivity per molecule of 34.0 ± 0.8 mM-1 s-1 (20 MHz, 298 K, pH 7.2), a good binding affinity to tropoelastin (KD = 41 ± 12 μM), and a serum half-life longer than 2 h. Gd4-TESMA accumulates specifically in atherosclerotic plaques in the ApoE-/- murine model of plaque progression, with 2 h persistence of contrast enhancement. As compared to the monomeric counterpart (Gd-TESMA), the tetrameric Gd4-TESMA probe shows a clear advantage regarding both sensitivity and imaging time window, allowing for a better characterization of atherosclerotic plaques.

The search for alternatives to Gd-containing magnetic resonance imaging (MRI) contrast agents addresses the field of Fe(III)-bearing species with the expectation that the use of an essential metal ion may avoid the issues raised by the exogenous Gd. Attention is currently devoted to highly stable Fe(III) complexes with hexacoordinating ligands, although they may lack any coordinated water molecule. We found that the hexacoordinated Fe(III) complex with two units of deferasirox, a largely used iron sequestering agent, owns properties that can make it a viable alternative to Gd-based agents. Fe(deferasirox)

This study is focused on the development of innovative sensors to non-invasively monitor the tissue implant status by Fast-Field-Cycling Magnetic Resonance Imaging (FFC-MRI). These sensors are based on oligo-histidine moieties that are conjugated to PLGA polymers representing the structural matrix for cells hosting scaffolds. The presence of 14N atoms of histidine causes a quadrupolar relaxation enhancement (also called Quadrupolar Peak, QP) at 1.39 MHz. This QP falls at a frequency well distinct from the QPs generated by endogenous semisolid proteins. The relaxation enhancement is pH dependent in the range 6.5-7.5, thus it acts as a reporter of the scaffold integrity as it progressively degrades upon lowering the microenvironmental pH. The ability of this new sensors to generate contrast in an image obtained at 1.39 MHz on a FFC-MRI scanner is assessed. A good biocompatibility of the histidine-containing scaffolds is observed after its surgical implantation in healthy mice. Over time the scaffold is colonized by endogenous fibroblasts and this process is accompanied by a progressive decrease of the intensity of the relaxation peak. In respect to the clinically used contrast agents this material has the advantage of generating contrast without the use of potentially toxic paramagnetic metal ions.

Herein, the synthesis and an extensive characterization of two novel Gd(AAZTA) (AAZTA=6-amino-6-methylperhydro-1,4-diazepine tetra acetic acid) derivatives functionalized with short (C

ProceduresTo preliminary assess the relationship between Manganese Enhanced Magnetic Resonance Imaging (MEMRI) and the expression of calcium receptors in human prostate and breast cancer animal models.MethodsNOD/SCID mice were inoculated with MDA-MB-231 breast cancer cells and prostate PC3 cancer cells to develop orthotopic or pseudometastatic cancer animal models. Mice were studied on a clinical 3T scanner by using a prototype birdcage coil before and after intravenous injection of MnCl2. Assessment of receptor's status was carried out after the MR images acquisition by immunohistochemistry on excised tumours.ResultsManganese contrast enhancement in breast or prostate cancer animal models well correlated with CaSR expression (pConclusionOur preliminary results suggest that MEMRI appears an efficient tool to characterize human breast and prostate cancer animal models in the presence of different expression level of calcium receptors.

Nanotheranostic reagents that integrate magnetic resonance imaging (MRI) and photothermal therapy (PTT) offer a promising strategy for the treatment of human disease. However, classic gadolinium (Gd)-based T(1)-MRI contrast agents are limited by their low relaxivity. To address this, we produced Gd-loaded Tobacco mosaic virus (TMV) particles coated with the mussel-inspired biopolymer polydopamine (PDA). Such biocompatible nanotheranostic reagents can be used to facilitate PTT, guided by multimodal magnetic resonance/photoacoustic imaging. The r(1)-relaxivity of the Gd-TMV-PDA particles at 60 MHz was ~80 mM(−1)s(−1), compared to 13.63 mM(−1)s(−1) for the uncoated Gd-TMV particles. The Gd-TMV-PDA particles also promoted strong near-infrared absorption with high photothermal conversion efficiency (28.9%) and demonstrated excellent photoacoustic contrast. Multimodal imaging and PTT resulted in the effective killing of PC-3 prostate cancer cells. Gd-TMV-PDA nanoparticles therefore offer a promising theranostic approach that can now be tested in vivo in cancer models.

The relaxivity of Gd(HP-DO3A) was studied as a function of pH and buffer composition in order to identify the main factors of the observed relaxation enhancement due to the exchange of the coordinated hydroxyl proton. It was established that the paramagnetic relaxation time, T1M, of the coordinated hydroxyl proton is about 50% shorter than that of the protons in the coordinated water molecule. The control of the p K of the coordinated alcoholic -OH moiety in the ligand is fundamental to utilize the proton exchange enhanced relaxivity under physio/pathologic conditions. A new derivative of Gd(HP-DO3A) was synthesized by replacing the -CH3 group with a -CF3 moiety. In this complex, the -OH group becomes more acidic. Consequently, the maximum contribution of the proton exchange to the relaxivity is shifted to a lower pH region with the fluorinated ligand.

Magnetic Resonance Imaging (MRI) enables to provide anatomical, functional and molecular information of pathological angiogenesis when used with properly tailored imaging probes. Functional studies have been the domain of Dynamic Contrast Enhancement (DCE) -MRI protocols from which it is possible to extract quantitative estimations on key parameters such as the volumes of vascular and extracellular compartments and the rates of the bidirectional exchange of the imaging reporters across the endothelial barrier. Whereas paramagnetic Gd-complexes able to reversibly bind to serum albumin act better than the clinically used small-sized, hydrophilic species, new findings suggest that an accurate assessment of the vascular volume is possible by analyzing images acquired upon the i.v. administration of Gd-labelled Red Blood Cells (RBCs). As far as it concerns molecular MRI, among the many available biomarkers, αvβ3 integrins are the most investigated ones. The low expression of these targets makes mandatory the use of nano-sized systems endowed with the proper signal enhancing capabilities. A number of targeted nano-particles have been investigated including micelles, liposomes, iron oxides and perfluorocarbon containing systems. Finally, a growing attention is devoted to the design and testing of "theranostic" agents based on the exploitation of MRI to monitor drug delivery processes and therapeutic outcome.

Chemical Exchange Saturation Transfer (CEST) approach is a novel tool within magnetic resonance imaging (MRI) that allows visualization of molecules possessing exchangeable protons with water. Many molecules, employed as excipients for the formulation of finished drug products, are endowed with hydroxyl, amine or amide protons, thus can be exploitable as MRI-CEST contrast agents. Their high safety profiles allow them to be injected at very high doses. Here we investigated the MRI-CEST properties of several excipients (ascorbic acid, sucrose, N-acetyl-D-glucosamine, meglumine and 2-pyrrolidone) and tested them as tumor-detecting agents in two different murine tumor models (breast and melanoma cancers). All the investigated molecules showed remarkable CEST contrast upon i.v. administration in the range 1-3 ppm according to the type of mobile proton groups. A marked increase of CEST contrast was observed in tumor regions up to 30 min post injection. The combination of marked tumor contrast enhancement and lack of toxicity make these molecules potential candidates for the diagnosis of tumors within the MRI-CEST approach. (C) 2017 Elsevier B.V. All rights reserved.

The properties of LnIII -HPDO3A complexes as relaxation enhancers and paraCEST agents are essentially related to the hydroxylpropyl moiety. A series of three HPDO3A derivatives, with small modifications to the hydroxyl arm, were herein investigated to understand how heightened control can be gained over the parameters involved in the design of these agents. A full 1 H and 17 O-NMR relaxometric analysis was conducted and demonstrated that increasing the length of the OH group from the lanthanide centre significantly enhanced the water exchange rate of the gadolinium complex, but with a subsequent reduction in kinetic stability. Alternatively, the introduction of an additional methyl group, which increased the steric bulk around the OH moiety, resulted in the formation of almost exclusively the TSAP isomer (95 %) as identified by 1 H-NMR of the europium complex. The gadolinium analogue of this complex also exhibited a very fast water exchange rate, but with no detectable loss of kinetic stability. This complex therefore demonstrates a notable improvement over Gd-HPDO3A.

Objectives Being administered intravenously, the tissue that gadolinium-based contrast agents (GBCAs) for magnetic resonance imaging mostly encounter is blood. Herein, it has been investigated how much Gd is internalized by cellular blood components upon the in vitro incubation of GBCAs in human blood or upon intravenous administration of GBCAs to healthy mice. We report results that show how the superb sensitivity of inductively coupled plasma-mass spectrometry (ICP-MS) allows the detection of very tiny amounts of GBCAs entering red blood cells (RBCs) and white blood cells (WBCs). This finding may introduce new insights in the complex matter relative to excretion and retention pathway of administered GBCAs. Materials and methods The study was tackled by 2 independent approaches. First, human blood was incubated in vitro with 5 mM of GBCAs (gadoteridol, gadobenate dimeglumine, gadodiamide, and gadopentetate dimeglumine) for variable times (30 minutes, 1 hour, 2 hours, and 3 hours) at 37°C. Then, blood cell components were isolated by using the Ficoll Histopaque method, washed 3 times, mineralized, and analyzed by ICP-MS for total Gd quantification. Furthermore, blood components derived from human blood incubated with gadodiamide or gadoteridol underwent UPLC-MS (ultra performance liquid chromatography-mass spectrometry) analysis for determination of the amount of intact Gd-DTPA-BMA and Gd-HPDO3A. Second, the distribution of Gd in the blood components of healthy CD-1 mice was administered intravenously with a single dose (1.2 mmol/kg) of gadodiamide or gadoteridol. Blood samples were separated and processed at different time points (24 hours, 48 hours, 96 hours, and 10 days after GBCA administration). As for human blood, ICP-MS quantification of total Gd and UPLC-MS determination of the amount of intact GBCAs were carried out. Results The amount of Gd taken up by RBCs and WBCs was well detectable by ICP-MS. The GBCAs seem to be able to cross the membrane by diffusion (RBCs) or, possibly, by macropinocytosis (WBCs). Ex vivo studies allowed it to be established that the structure of the different GBCAs were not relevant to determine the amount of Gd internalized in the cells. Although the amount of Gd steadily decreases over time in gadoteridol-labeled cells, in the case of gadodiamide, the amount of Gd in the cells does not decrease (even 10 days after the administration of the GBCA). Moreover, while gadoteridol maintains its structural integrity upon cellular uptake, in the case of gadodiamide, the amount of intact complex markedly decreases over time. Conclusions The detection of significant amounts of Gd in RBCs and WBCs indicates that GBCAs can cross blood cell membranes. This finding may play a role in our understanding of the processes that are at the basis of Gd retention in the tissues of patients who have received the administration of GBCAs.

Breast Cancer is the most diffuse cancer among women and the treatment outcome is largely determined by its early detection. MRI at fixed magnetic field is already widely used for cancer detection. Herein it is shown that the acquisition of proton T1 at different magnetic fields adds further advantages. In fact, Fast Field Cycling Nuclear Magnetic Resonance Dispersion (FFC-NMRD) profiles have been shown to act as a high –sensitivity tool for cancer detection and staging in ex vivo murine breast tissues collected from Balb/NeuT mice. From NMRD profiles it was possible to extract two new cancer biomarkers, namely: (i) the appearance of 14N-quadrupolar peaks (QPs) reporting on tumor onset and (ii) the slope of the NMRD profile reporting on the progression of the tumor. By this approach it was possible to detect the presence of tumor in transgenic NeuT mice at a very early stage (5–7 weeks), when the disease is not yet detectable by using conventional high field (7 T) MRI and only minimal abnormalities are present in histological assays. These results show that, NMRD profiles may represent a useful tool for early breast cancer detection and for getting more insight into an accurate tumor phenotyping, highlighting changes in composition of the mammary gland tissue (lipids/proteins/water) occurring during the development of the neoplasia.

The work aimed at developing a novel MRI-based theranostic protocol for improving the anticancer efficacy of a Doxil-like liposomal formulation. The goal was achieved stimulating the intratumor release of the drug from the nanocarrier and favoring its diffusion in the lesion by the sequential application of low-intensity pulsed ultrasound. The protocol was tested on mice bearing a syngeneic breast cancer model. The combination of acoustic waves with different characteristics allowed for: i) the release of the drug and the co-encapsulated MRI agent (Gadoteridol) from the liposomes in the vessels of the tumor region, and ii) the extravasation of the released material, as well as intact liposomes, in the tumor stroma. The MR-T1 contrast enhancement measured in the tumor reported on the delivery and US-triggered release of Doxorubicin. The developed protocol resulted in a marked increase in the intratumor drug concentration that, in turn, led to the complete regression of the lesion. The protocol has a good clinical translatability because all the components of the theranostic agent (Doxorubicin, liposomes, Gadoteridol) are approved for human use.

The discussed topic about gadolinium-based contrast agents (GBCA) safety has recently been revived due to the evidence of hyperintensities observed in the dentate nucleus (DN) and globus pallidus (GP) in the brain of patients with normal kidney function. Several preclinical studies have been conducted to understanding how the use of GBCAs can promote the gadolinium deposition in the brain. Here, we evaluate the impact of chronic cerebral hypoperfusion on gadolinium presence. T1 hyperintensities and BBB integrity were evaluated by MRI in chronically hypoperfused and healthy rats injected with either gadodiamide or hypertonic saline. Additionally, the assessment of glucose metabolism by PET imaging and the gadolinium content by ICP-MS was performed after the last MR scan. Chronically hypoperfused rats displayed a greater MRI T1w signal in the DCN and hippocampus compared to Sham-operated animals, suggesting gadolinium accumulation. Dynamic contrast-enhanced (DCE) MRI assessment of BBB permeability revealed loss of integrity (high Ktrans) after rat injury in the dentate nuclei and hippocampus. Ex vivo tissue analysis showed greater gadolinium retention in the cerebellum and subcortical regions, supporting the imaging finding. FDG-PET imaging of the cerebellum did not reveal abnormal uptake in the DCN after chronic cerebral hypoperfusion. Higher signal intensity followed by higher Gd concentration observed in DCN and hippocampus of animals subjected to cerebral injury can be associated with an increase in BBB permeability due to the applied vascular dementia animal model. Nonetheless, no glucose metabolism abnormalities were detected in chronically hypoperfused cerebellum.

The synthesis of poly[N,N-bis(3-aminopropyl)glycine] (PAPGly) dendrons Gd-based contrast agents (GdCAs) via an orthogonal protection of the different functional groups and an activation/coupling strategy wherein a specific number of synthetic steps add a generation to the existing dendron has been described. The aim of this protocol is to build up two different generations of dendrons (G-0 or dendron's core, and G-1) with peripheral NH2 groups to conjugate a 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) derivative and afterwards to chelate with Gd3+ paramagnetic ions. These complexes, which have a well-defined molecular weight, are of relevance to MRI as an attempt to gain higher H-1 relaxivity by slowing down the rotation of molecule compared to monomeric Gd(III) complexes used as contrast agents and to increase the number of paramagnetic centers present in one molecular structure. From the study of their water H-1 longitudinal relaxation rate at different magnetic fields (NMRD, Nuclear Magnetic Relaxation Dispersion) and by evaluating the variable temperature O-17-NMR data we determined the parameters characterizing the water exchange rate and the rotational correlation time of each complex, both affecting H-1 relaxivity. Furthermore, these two novel PAPGly GdCAs were objects of i) an in vivo study to determine their biodistributions in healthy C57 mice at several time points, and ii) the Dynamic Contrast-Enhanced MRI (DCE-MRI) approach to assess their contrast efficiency measured in the tumor region of C57BL/6 mice transplanted subcutaneously with B16-F10 melanoma cells. The aim of the comparison of these two dendrons GdCAs, having different molecular weights (MW), is to understand how MW and relaxivity may influence the contrast enhancement capabilities in vivo at low magnetic field (1 T). Significant contrast enhancement was observed in several organs (vessel, spleen and liver), already at 5 min post-injection, for the investigated CAs. Moreover, these CAs induced a marked contrast enhancement in the tumor region, thanks to the enhanced permeability retention effect of those macromolecular structures.

The dentate nuclei of the cerebellum are the areas where gadolinium predominantly accumulates. It is not yet known whether gadolinium deposition affects brain functions.To assess whether gadolinium-dependent high signal intensity of the cerebellum on TObservational, cross-sectional.Fifteen patients affected by Crohn's disease were compared with 16 healthy age- and gender-matched control subjects. All participants underwent neurological, neurocognitive-psychological assessment, and blood sampling.1.5-T magnet blood oxygenation level-dependent (BOLD) functional MRI.High signal intensity on TAn unpaired two-sample t-test (age and sex were nuisance variables) was used to investigate between-group differences in cerebellar and dentate nucleus functional connectivity. Z-statistical images were set using clusters determined by Z 2.3 and a familywise error (FWE)-corrected cluster significance threshold of P = 0.05.Dentate nuclei RSFC was not different (P = n.s.) between patients with gadolinium-dependent high signal intensity on TCrohn's disease patients with gadolinium-dependent hyperintense dentate nuclei on unenhanced T2 Technical Efficacy Stage: 5 J. Magn. Reson. Imaging 2019;50:445-455.

Prostate Cancer (PCa) is the second most common and fifth cause of cancer-related mortality in males in Western Countries. The development of innovative tools for an early, more precise and noninvasive diagnosis is a medical need. Vascular volume (Vv) and hypoxia are two of the most important tumor hallmarks. Herein, they have been assessed in TRAMP mice by using MRI. Their quantification has been carried out by injecting autologous Red Blood Cells (RBCs), ex vivo labelled with Gd-HPDO3A or Gd-DOTP complexes, respectively. Gd-labelled-RBCs are stably confined in the intravascular space, also in presence of a very leaky tumor endothelium, thus representing efficient probes for vascular space analysis. Vv enhancement and hypoxia onset have been demonstrated to be present at early stages of PCa and their expression largely increases with tumor development. Moreover, also Diffusion weighted MRI and Amide Proton Transfer MRI have been herein applied to characterize PCa. The herein applied multiparametric MRI (mpMRI) analysis allows a detailed in vivo characterization of PCa, in which each histotype and cancer stage displays a specific MRI pattern. This provides an unprecedented opportunity to feature prostate tumor, making possible a non-invasive, precise and early diagnosis, which could direct treatments towards a more personalized medicine.

The aim of this work was to investigate, by five different administration protocols, the impact of the dosage, the time passed after the last injection and the frequency of injections, on accumulation and distribution of Gd-containing species in the body tissues of healthy mice upon repeated injections of Gadolinium Based Contrast Agents (GBCAs). Gadodiamide and Gadoteridol have been compared. The amount of Gd retained in several tissues/organs (cerebrum, cerebellum, spleen, liver, kidneys, eyes, skin, bone and muscle) has been assessed by ICP-MS upon administration of the GBCAs i) at three weeks or three months after the last administration, ii) when one, three or twelve doses of GBCA were administered and iii) when administrations were made every two weeks. Gd was found in all tissues after the administration of Gadodiamide. Conversely, in the case of Gadoteridol, Gd was detected only in spleen, kidneys, liver and bone. The amounts of Gd found in spleen, liver and kidneys markedly decrease upon increasing the time that has passed after the last administration, whereas, in the case of Gadodiamide, the decrease of Gd found in bone, cerebrum and cerebellum appears to occur at a much slower rate. Overall, areas of long term deposition appear to be bone and spleen for both GBCAs. In conclusion, our findings demonstrate that intravenous multiple administrations of GBCAs is associated with extensive multiorgan retention which is reduced but not eliminated by the use of the macrocyclic Gadoteridol as well as by adopting reduced and/or less frequent dosing.

From the early days of CEST agents' disclosure, it was evident that their potential for in vivo applications was strongly hampered by the intrinsic low sensitivity. Therefore, much work has been devoted to seek out suitable routes to achieve strong CEST contrast enhancement. The use of nanosized systems turned out to be a strategic choice, because a very large amount of CEST agents can be delivered at the site of interest. However, the breakthrough innovation in term of increase of sensitivity was found by designing the lipoCEST agents. The naturally inspired, liposomes vesicles, when loaded with paramagnetic lanthanide-based shift reagents, can be transformed into CEST probes. The large number of water molecules entrapped inside the inner cavity of the nanovesicles represents an enormous pool of exchanging protons for the generation of CEST contrast, whereas the presence of the shift reagent increases the separation in chemical shift of their nuclear magnetic resonance signal from that of the bulk water, thus allowing for a proper exchange regime for the activation of CEST contrast. From lipoCEST, it has been rather straightforward to evolve to cellCEST in order to exploit the cytoplasmatic water molecules as source of the CEST effect, once cells have been loaded with the proper shift reagent. The red blood cells were found to be particularly suitable for the development of the cellCEST concept. Finally, an understanding of the main determinants of the CEST effects in nanosized and cellular-sized agents has allowed the design of innovative lipoCEST/RBC aggregates for potential theranostic applications. WIREs Nanomed Nanobiotechnol 2016, 8:602-618. doi: 10.1002/wnan.1385 For further resources related to this article, please visit the WIREs website.

Theranostic delivery systems are nanostructures that combine the modality of therapy and diagnostic imaging. Polymeric micro- and nanobubbles, spherical vesicles containing a gas core, have been proposed as new theranostic carriers for MRI-guided therapy. In this study, chitosan nanobubbles were purposely tuned for the co-delivery of prednisolone phosphate and a Gd(III) complex, as therapeutic and MRI diagnostic agent, respectively. Perfluoropentane was used for filling up the internal core of the formulation. These theranostic nanobubbles showed diameters of about 500nm and a positive surface charge that allows the interaction with the negatively charged Gd-DOTP complex. Pluronic F68 was added to the nanobubble aqueous suspension as stabilizer agent. The encapsulation efficiency was good for both the active compounds, and a prolonged drug release profile was observed in vitro. The effect of ultrasound stimulation on prednisolone phosphate release was evaluated at 37°C. A marked increase on drug release kinetics with no burst effect was obtained after the exposure of the system to ultrasound. Furthermore, the relaxivity of the MRI probe changed upon incorporation in the nanobubble shell, thereby offering interesting opportunity in dual MRI-US experiments. The ultrasound characterization showed a good in vitro echogenicity of the theranostic nanobubbles. In summary, chitosan drug-loaded nanobubbles with Gd(III) complex bound to their shell might be considered a new platform for imaging and drug delivery with the potential of improving anti-cancer treatments.

OBJECTIVES The aim of the study was to explore the role of the stability of metal complexes in the processes that lead to the metal retention in the brain and other tissues of mice administered with lanthanides-based contrast agents. This issue was tackled by the simultaneous injection of gadolinium (Gd)-diethylentriamminopentaacetate (DTPA) and lanthanum-DTPA, which have the same charge and structure but differ in their thermodynamic stability by 3 orders of magnitude. MATERIALS AND METHODS A total of 20 healthy BALB/c mice were administered by a single intravenous injection with a dose consisting of 0.6 mmol La-DTPA/kg and 0.6 mmol Gd-DTPA/kg. Then the animals were killed at different time points: 4, 24, 48, and 96 hours (5 mice each group).In an additional protocol, 5 mice were administered with 9 doses of 0.3 mmol La-DTPA/kg and 0.3 mmol of Gd-DTPA/kg every 2 days over a period of 3 weeks. The sacrifice time was set to 3 weeks after the last administration. After sacrifice, the Gd and La content in liver, spleen, kidney, muscle, cerebrum, cerebellum, bone, eye, skin, blood, and urine was determined by inductively coupled plasma-mass spectrometry. RESULTS A general decrease in the content of both the lanthanides was observed upon delaying the sacrifice time. At relatively short times after the injection (up to 96 hours), in the spleen, kidney, muscle, skin, and eye, almost the same content of La and Gd was detected, whereas in the cerebrum, cerebellum, bones, and liver, the amount of retained La decreased much slower than that of Gd, yielding a progressive increase in La/Gd ratio. The amount of retained La in the various tissues 21 days after the last of 9 administrations of La-DTPA and Gd-DTPA was always significantly higher than that of Gd. The concentration of both La and Gd decreased rapidly both in blood and in urine samples. DISCUSSION The departure from the 1:1 ratio in the amounts of La and Gd determined in the investigated tissues has been used to gain information on the role of the complex stability and "wash-out" kinetics. The behavior of the less s` La-DTPA highlights processes occurring for Gd-DTPA at a slower rate.The herein obtained results support the view that most of the La/Gd retained in the brain arises from the intact chelate that has extravasated immediately after the intravenous administration. Long-term deposition of metal ions from internal reservoirs seems particularly relevant for liver and spleen.

Molecular imaging requires the specific accumulation of contrast agents at the target. To exploit the superb resolution of MRI for applications in molecular imaging, gadolinium chelates, as the MRI contrast agents (CA), have to be conjugated to a specific vector able to recognize the epitope of interest. Several Gd(III)-chelates can be chemically linked to the same binding vector in order to deliver multiple copies of the CA (multimers) in a single targeting event thus increasing the sensitivity of the molecular probe. Herein three novel bifunctional agents, carrying one functional group for the bioconjugation to targeting vectors and four Gd(III)-AAZTA chelate functions for MRI contrast enhancement (AAZTA = 6-amino-6-methylperhydro-1,4-diazepinetetraacetic acid), are reported. The relaxivity in the tetrameric derivatives is 16.4 ± 0.2 mMGd–1 s–1 at 21.5 MHz and 25 °C, being 2.4-fold higher than that of parent, monomeric Gd(III)-AAZTA. These compounds can be used as versatile building blocks to insert pre...

In this work the selective uptake of native horse spleen ferritin and apoferritin loaded with MRI contrast agents has been assessed in human breast cancer cells (MCF-7 and MDA-MB-231). The higher expression of L-ferritin receptors (SCARA5) led to an enhanced uptake in MCF-7 as shown in T2 and T1 weighted MR images, respectively. The high efficiency of ferritin internalization in MCF-7 has been exploited for the simultaneous delivery of curcumin, a natural therapeutic molecule endowed with antineoplastic and anti-inflammatory action, and the MRI contrast agent Gd-HPDO3A. This theranostic system is able to treat selectively breast cancer cells over-expressing ferritin receptors. By entrapping in apoferritin both Gd-HPDO3A and curcumin, it was possible to deliver a therapeutic dose of 167 μg ml−1 (as calculated by MRI) of this natural drug to MCF-7 cells, thus obtaining a significant reduction of cell proliferation. Fil: Geninatti Crich, S.. Universitã â Di Torino; Italia Fil: Cadenazzi, M.. Universitã â Di Torino; Italia Fil: Lanzardo, S.. Universitã â Di Torino; Italia Fil: Conti, L.. Universitã â Di Torino; Italia Fil: Ruiu, R.. Universitã â Di Torino; Italia Fil: Alberti, D.. Universitã â Di Torino; Italia Fil: Cavallo, F.. Universitã â Di Torino; Italia Fil: Cutrin, Juan Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Cardiológicas (i); Argentina. Università  Di Torino; Italia Fil: Aime, S.. Universitã â Di Torino; Italia

Accurate mapping of small changes in pH is essential to the diagnosis of diseases such as cancer. The difficulty in mapping pH accurately in vivo resides in the need for the probe to have a ratiometric response so as to be able to independently determine the concentration of the probe in the body independently from its response to pH. The complex Fe

Purpose To evaluate the speciation of gadolinium-containing species after multiple administrations of the gadolinium-based contrast agents (GBCAs) gadodiamide and gadoteridol and to quantify the amount of intact gadolinium complexes and insoluble gadolinium-containing species. Materials and Methods A total dose of 13.2 mmol per kilogram of body weight of each GBCA was administered in healthy Wistar rats over a period of 8 weeks. Three days after the final administration, rats were sacrificed, and the brains were excised and divided into three portions. Each portion of brain homogenate was divided into two parts, one for determination of the total gadolinium concentration with inductively coupled plasma mass spectrometry and one for determination of the amount of intact GBCA and gadolinium-containing insoluble species. Relaxometric measurements of gadodiamide and gadolinium trichloride in the presence of polysialic acid were also performed. Results The mean total gadolinium concentrations for gadodiamide and gadoteridol, respectively, were 0.317 μg/g ± 0.060 (standard deviation) and 0.048 μg/g ± 0.004 in the cortex, 0.418 μg/g ± 0.078 and 0.051 μg/g ± 0.009 in the subcortical brain, and 0.781 μg/g ± 0.079 and 0.061 μg/g ± 0.012 in the cerebellum. Gadoteridol comprised 100% of the gadolinium species found in rats treated with gadoteridol. In rats treated with gadodiamide, the largest part of gadolinium retained in brain tissue was insoluble species. In the cerebellum, the amount of intact gadodiamide accounts for 18.2% ± 10.6 of the total gadolinium found therein. The mass balance found for gadolinium implies the occurrence of other soluble gadolinium-containing species (approximately 30%). The relaxivity of the gadolinium polysialic acid species formed in vitro was 97.8 mM/sec at 1.5 T and 298 K. Conclusion Gadoteridol was far less retained, and the entire detected gadolinium was intact soluble GBCA, while gadodiamide yielded both soluble and insoluble gadolinium-containing species, with insoluble species dominating.

Commercial Gd-containing complexes are often used as MRI reporters in cellular labeling procedures as they are internalized into endosomes by pinocytosis. A methodology has been applied to assess the relative stability of three commercial Gd contrast agents following cellular uptake in fibroblasts and macrophages. It has been found that the acyclic series of Gd MRI contrast agents are degraded much more rapidly than their macrocyclic analogues, following endosomal internalization into living cells. This helps to explain their causal role in the development of nephrogenic systemic fibrosis in renally impaired patients. The methodology has also been applied to assess the fate of Gd-DTPA-BMA-loaded liposomes upon their endosomal internalization. Resistant liposomes prevent the degradation of the complex, whereas liposomes designed to release their payload in the acidic environments show a loss of integrity of Gd-DTPA-BMA analogous to the one observed upon internalization of the free complex.

Apoferritin has been exploited to deliver simultaneously therapeutic and imaging agents (loaded into its internal cavity) to hepatocytes as this protein is efficiently taken up from blood by hepatocyte scavenger receptor class A type 5 via the ferritin transporting route. To this purpose the protein has been loaded with the magnetic resonance imaging (MRI) contrast agent GdHPDO3A and curcumin, a polyphenolic substance endowed with multiple pharmacological actions, namely: antioxidant, anti-inflammatory, antineoplastic. Curcumin and GdHPDO3A loaded apoferritin has been used with the aim to attenuate the thioacetamide-induced hepatitis together with the evaluation by MRI of drug delivery efficiency. Mice pretreated by intraperitoneal administration showed significantly attenuated hepatic injury as assessed by measuring alanine aminotransferase (ALT) activity in plasma and by histology assessment. The encapsulation of curcumin inside the apoferritin cavity significantly increases its stability and bioavailability while maintaining its therapeutic anti-inflammatory properties. Fil: Cutrin, Juan Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Cardiológicas (i); Argentina. Universita di Torino; Italia Fil: Geninatti Crich, Simonetta. Universitã â Di Torino; Italia Fil: Burghelea, Diana. Universitã â Di Torino; Italia Fil: Dastrù, Walter. Universitã â Di Torino; Italia Fil: Aime, Silvio. Universitã â Di Torino; Italia

Novel contrast agent based systems, which selectively visualize specific cells, e.g., neurons in the brain, would be of substantial importance for the fast developing field of molecular magnetic resonance imaging (MRI). We report here the synthesis and in vitro validation of a Gd(III)-based contrast agent designed to act as an MRI responsive probe for imaging the activity of the enzyme glutamic acid decarboxylase (GAD) present in neurons. Upon the action of the enzyme, the Gd(III) complex increases its hydration sphere and takes on a residual positive charge that promotes its binding to endogenous macromolecules. Both effects contribute in a synergic way to generate a marked relaxation enhancement, which directly reports enzyme activity and will allow activity detection of GAD positive cells in vitro and in vivo selectively.

PolyLactic and Glycolic Acid nanoparticles (PLGA-NPs), coated with L-Ferritin,are exploited for the simultaneous delivery of paclitaxel and an amphiphilic Gd based MRI contrast agent into breast cancer cells (MCF7). L-Ferritin has been covalently conjugated to the external surface of PLGA-NPs exploiting NHS activated carboxylic groups. The results confirmed that nanoparticles decorated with L-Ferritin have many advantages with respect both albumin-decorated and non-decorated particles. Ferritin moieties endow PLGA-NPs with targeting capability, exploiting SCARA5 receptors overexpressed by these tumour cells, that results in an increased paclitaxel cytotoxicity. Moreover, protein coating increased nanoparticle stability thus reducing the fast and aspecific drug release before reaching the target. The theranostic potentiality of the nanoparticles has been demonstrated by evaluating the signal intensity enhancement on T1-weighted MRI images of labelled MCF7 cells. The results werecompared with that obtained with MDA cells used as negative control due to their lower SCARA5 expression. Fil: Turino, Ludmila Noelia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Ruggiero, Maria R.. Universita di Torino; Italia Fil: Stefanìa, Rachele. Universita di Torino; Italia Fil: Cutrin, Juan C.. Universita di Torino; Italia Fil: Aime, Silvio. Universita di Torino; Italia Fil: Geninatti Crich, Simonetta. Universita di Torino; Italia

Accurate mapping of small changes in pH is essential to the diagnosis of diseases such as cancer. The difficulty in mapping pH accurately in vivo resides in the need for the probe to have a ratiometric response so as to be able to independently determine the concentration of the probe in the body independently from its response to pH. The complex FeII-DOTAm-F12 behaves as an MRI contrast agent with dual 19F and CEST modality. The magnitude of its CEST response is dependent both on the concentration of the complex and on the pH, with a significant increase in saturation transfer between pH 6.9 and 7.4, a pH range that is relevant to cancer diagnosis. The signal-to-noise ratio of the 19F signal of the probe, on the other hand, depends only on the concentration of the contrast agent and is independent of pH. As a result, the complex can ratiometrically map pH and accurately distinguish between pH 6.9 and 7.4. Moreover, the iron(II) complex is stable in air at room temperature and adopts a rare 8-coordinate g...

To dissect the contributions to the longitudinal relaxivity (rLongitudinal relaxation rates RIn v-SBF or in the presence of HSA, rThe major contributions to r

Most metastatic gastrointestinal stromal tumors (GISTs) develop resistance to the first-line imatinib treatment. Recently, increased vessel density and angiogenic markers were reported in GISTs with a poor prognosis, suggesting that angiogenesis is implicated in GIST tumor progression and resistance. The purpose of this study was to investigate the relationship between tumor vasculature and imatinib resistance in different GIST mouse models using a noninvasive magnetic resonance imaging (MRI) functional approach. Immunodeficient mice (n = 8 for each cell line) were grafted with imatinib-sensitive (GIST882 and GIST-T1) and imatinib-resistant (GIST430) human cell lines. Dynamic contrast-enhanced MRI (DCE-MRI) was performed on GIST xenografts to quantify tumor vessel permeability (K trans) and vascular volume fraction (v p). Microvessel density (MVD), permeability (mean dextran density, MDD), and angiogenic markers were evaluated by immunofluorescence and western blot assays. Dynamic contrast-enhanced magnetic resonance imaging showed significantly increased vessel density (P

A new approach to enzyme-responsive MRI agents based on the use of liposomes loaded with a high number of paramagnetic metal complexes (Gd-HPDO3A) is presented. It relies on the disruption of low relaxivity aggregates formed by liposomes and a macromolecular substrate that is selectively cleaved by the enzyme of interest. The interaction of anionic liposomes composed of POPC:CHOL:DPGS and the cationic protein protamine yields a poorly soluble supramolecular assembly endowed with a low relaxivity. The action of the serine protease trypsin causes the digestion of protamine and the consequent de-assembly of the supramolecular adduct. The process is accompanied by an overall relaxation enhancement of solvent water protons as consequence of the dissolution of the aggregated liposomes. The observed increase of relaxivity is linearly dependent on the enzyme concentration. An illustrative example of the possible use of the herein presented responsive agent has been reported. It consists of the entrapment of the supramolecular assembly in alginate microcapsules that have often been used as envelopes for in vivo applications of stem cells and pancreatic islets. The change in the observed longitudinal relaxation rate R 1 (leading to an hyperintense signal in the corresponding MR images) may act as a sensor of the protease activity in the biological environment in which the capsules is located.

Hyperpolarization provides a strong enhancement of the MR signal and allows the acquisition of images from nuclei other than protons. Besides vascular imaging and perfusion studies the use of hyperpolarized molecules has allowed the visualization of real-time substrate uptake and metabolism in vivo. Metabolic imaging is an outstanding field of research that aims at providing the clinicians with the possibility of interrogating real-time complex metabolic pathways that give a direct insight into the cellular state and activity.

The peculiar properties of osmotically shrunken liposomes acting as magnetic resonance imaging-chemical exchange saturation transfer (MRI-CEST) contrast agents have been investigated. Attention has been primarily devoted to assessing the contribution arising from encapsulated and incorporated paramagnetic lanthanide(III)-based shift reagents in determining the chemical shift of the intraliposomal water protons, which is a relevant factor for generating the CEST contrast. It is demonstrated that a highly shifted resonance for the encapsulated water can be attained by increasing the percentage of the amphiphilic shift reagent incorporated in the liposome bilayer. It is also demonstrated that the shift contribution arising from the bulk magnetic susceptibility can be optimized through the modulation of the osmotic shrinkage. In terms of sensitivity, it is shown that the saturation transfer efficiency can be significantly improved by increasing the size of the vesicle, thus allowing a high number of exchangeable protons to be saturated. In addition, the role played by the intensity of the saturating radiofrequency field has also been highlighted.

There is an ongoing desire to produce high-relaxivity, Gd-based magnetic resonance imaging (MRI) contrast agents. These may allow for lower doses to be used, which is especially important in view of the current safety concerns surrounding Gd in patients. Here we report the synthesis of a high-relaxivity MRI contrast agent, by incorporating Gd-chelating lipids that coordinate two water molecules into high-density lipoprotein (q = 2 HDL). We compared the properties of q = 2 HDL with those of an analogous HDL particle labeled with Gd-chelating lipids that coordinate only one water molecule (q = 1 HDL). We found that the q = 2 HDL possessed an elevated r(1) of 41 mM(-1) s(-1) compared to 9 mM(-1) s(-1) for q = 1 HDL at 20 MHz, but the q = 2 HDL exhibited high R(2)* values at high fields, precluding imaging above 128 MHz. While carrying out this investigation we observed that enlarged, disrupted particles were formed when the synthesis was carried out above the lipid critical micelle concentration (cmc), indicating the importance of synthesis below the cmc when modifying lipoproteins in this manner. The high relaxivity of q = 2 HDL means it will be an efficacious contrast agent for future MR imaging studies.

The Gd(III) complexes of three new octadentate chelators, prepared by substitution of four, two, and one carboxylate groups of EGTA with phosphonate groups, have been investigated by 1H and 17O NMR relaxometric techniques in aqueous solutions. The analysis of the solvent proton relaxivity data as a function of pH, temperature, and magnetic field strength (nuclear magnetic relaxation dispersion (NMRD) profiles) in combination with the 17O transverse relaxation rate data at variable temperature allowed assessing the hydration state of the complexes, the occurrence of pH-dependent oligomerization processes for the tetraphosphonate derivative, the presence of a well-defined second sphere of hydration that markedly contributes to the relaxivity, and the values of the structural and dynamic relaxation parameters. In addition, in the case of the monophosphonate derivative the presence of a coordinated water molecule has allowed evaluation of the kinetic parameters of the exchange process, highly relevant for the possible use of this Gd(III) complex as an MRI probe. The rate of exchange of the water molecule, (298)k(ex) = 4.2 x 10(8)s(-1), is one of the highest measured so far for a nonacoordinate Gd(III) chelate and optimal for developing contrast-enhancing probes of high efficacy at high magnetic fields.

This article illustrates some innovative applications of liposomes loaded with paramagnetic lanthanide-based complexes in MR molecular imaging field. When a relatively high amount of a Gd(III) chelate is encapsulated in the vesicle, the nanosystem can simultaneously affect both the longitudinal (R(1)) and the transverse (R(2)) relaxation rate of the bulk H2O H-atoms, and this finding can be exploited to design improved thermosensitive liposomes whose MRI response is not longer dependent on the concentration of the probe. The observation that the liposome compartmentalization of a paramagnetic Ln(III) complex induce a significant R(2) enhancement, primarily caused by magnetic susceptibility effects, prompted us to test the potential of such agents in cell-targeting MR experiments. The results obtained indicated that these nanoprobes may have a great potential for the MR visualization of cellular targets (like the glutamine membrane transporters) overexpressing in tumor cells. Liposomes loaded with paramagnetic complexes acting as NMR shift reagents have been recently proposed as highly sensitive CEST MRI agents. The main peculiarity of CEST probes is to allow the MR visualization of different agents present in the same region of interest, and this article provides an illustrative example of the in vivo potential of liposome-based CEST agents.

Nanosized contrast agents have great potential in magnetic resonance molecular imaging applications for clinical diagnosis. This study proposes new nanoparticles spontaneously formed under mild conditions and composed of a noncovalent adduct between a gadolinium complex, a polymer of beta-cyclodextrin (pbetaCD: MW 1.5 x 10(6) g mol(-1)) and a dextran grafted with alkyl chains (MD). The formation of this supramolecular nanoassembly is based upon a "lock-and-key" recognition process in which the hydrophobic alkyl chains of MD and the adamantyl moieties of macrocyclic Gd(III) chelates are included in the cavities of pbetaCD. The large number of betaCDs contained in the pbetaCD resulted in the formation of 200 nm diameter nanoparticles, each entrapping 1.8 x 10(5) molecules of a low-molecular-weight Gd complex. This system, which exhibits a great relaxivity enhancement (48.4 mM(-1) s(-1), at 20 MHz and 37 degrees C) compared to the Gd(III) chelate itself (5.2 mM(-1) s(-1)), appears to be a promising strategy for the in vivo targeted delivery of Gd(III) complexes. The mechanisms of particle formation, conjugation strategies, and relaxometric characterizations in the field of contrast-enhanced magnetic resonance imaging are discussed.

One of the major advantages of the CEST methodology deals with the possibility of visualizing more probes in the same MR image voxels. This is a unique property within the contrast media that act on the 1H-NMR signal of water protons, and it might considerably improve the potential of the technique. In addition to displaying sufficiently different resonance frequencies of their mobile protons, it is also important that the CEST agents designed for this application are highly sensitive. LIPOCEST agents represent the most sensitive class of CEST systems developed so far. On this basis, two LIPOCEST samples, a spherical one and an osmotically shrunken nonspherical one, endowed with markedly different resonance frequencies of their intraliposomal water protons, 3 ppm and 15 ppm, respectively, were prepared and tested both in vitro and in ex-vivo on a bovine muscle used as tissue-surrogate. The response of the two agents did not interfere each other, thus allowing the multiple visualization of the two agents present at nanomolar concentrations in the same image voxels. Copyright © 2008 John Wiley & Sons, Ltd.

The use of [1-(13) C]pyruvate hyperpolarized by means of dynamic nuclear polarization provides a direct way to track the metabolic transformations of this metabolite in vivo and in cell cultures. The identification of the intra- and extracellular contributions to the (13) C NMR resonances is not straightforward. In order to obtain information about the rate of pyruvate and lactate transport through the cellular membrane, we set up a method that relies on the sudden 'quenching' of the extracellular metabolites' signal. The paramagnetic Gd-tetraazacyclododecane triacetic acid (Gd-DO3A) complex was used to dramatically decrease the longitudinal relaxation time constants of the (13) C-carboxylate resonances of both pyruvate and lactate. When Gd-DO3A was added to an MCF-7 cellular culture, which had previously received a dose of hyperpolarized [1-(13) C]pyruvate, the contributions of the extracellular pyruvate and lactate signals were deleted. From the analysis of the decay curves of the (13) C-carboxylate resonances of pyruvate and lactate it was possible to extract information about the exchange rate of the two metabolites across the cellular membrane. In particular, it was found that, in the reported experimental conditions, the lactate transport from the intra- to the extracellular space is not much lower than the rate of lactate formation. The method reported herein is non-destructive and it could be translated to in vivo studies. It opens a route for the use of hyperpolarized pyruvate to assess altered activity of carboxylate transporter proteins that may occur in pathological conditions. Copyright © 2016 John WileySons, Ltd.

A novel MRI blood-pool contrast agent (Gd-AAZTA-MADEC) has been compared with established blood pool agents for tumor contrast enhanced images and angiography. Synthesis, relaxometric properties, albumin binding affinity and pharmacokinetic profiles are reported. For in vivo studies, angiographic images and tumor contrast enhanced images were acquired on mice with benchtop 1T-MRI scanners and compared with MS-325, B22956/1 and B25716/1. The design of this contrast agent involved the elongation of the spacer between the targeting deoxycholic acid moiety and the Gd-AAZTA imaging reporting unit that drastically changed either the binding affinity to albumin (KA(HSA) = 8.3 × 10(5) M(-1)) and the hydration state of the Gd ion (q = 2) in comparison to the recently reported B25716/1. The very markedly high binding affinity towards mouse and human serum albumins resulted in peculiar pharmacokinetics and relaxometric properties. The NMRD profiles clearly indicated that maximum efficiency is attainable at magnetic field strength of 1 T. In vivo studies showed high enhancement of the vasculature and a prolonged accumulation inside tumor. The herein reported pre-clinical imaging studies show that a great benefit arises from the combination of a benchtop MRI scanner operating at 1 T and the albumin-binding Gd-AAZTA-MADEC complex, for pursuing enhanced angiography and improved characterization of tumor vascular microenvironment.