Fabio Tedoldi

In vivo and in vitro liver cancer metabolism observed with hyperpolarized [5-13C]glutamine

Glutamine metabolism is, with its many links to oncogene expression, considered a crucial step in cancer metabolism and it is thereby a key target for alteration in cancer development. In particular, strong correlations have been reported between oncogene expression and expression and activity of the enzyme glutaminase. This mitochondrial enzyme, which is responsible for the deamidation of glutamine to form glutamate, is overexpressed in many tumour tissues. In animal models, glutaminase expression is correlated with tumour growth rate and it is readily possible to limit tumour growth by suppression of glutaminase activity. In principle, hyperpolarized (13)C MR spectroscopy can provide insight to glutamine metabolism and should hence be a valuable tool to study changes in glutaminase activity as tumours progress. However, no such successful in vivo studies have been reported, even though several good biological models have been tested. This may, at least partly, be due to problems in preparing glutamine for hyperpolarization. This paper reports a new and improved preparation of hyperpolarized [5-(13)C]glutamine, which provides a highly sensitive (13)C MR marker. With this preparation of hyperpolarized [5-(13)C]glutamine, glutaminase activity in vivo in a rat liver tumour was investigated. Moreover, this marker was also used to measure response to drug treatment in vitro in cancer cells. These examples of [5-(13)C]glutamine used in tumour models warrant the new preparation to allow metabolic studies with this conditionally essential amino acid.

Relevance of electron spin dissipative processes to dynamic nuclear polarization via thermal mixing

The available theoretical approaches aiming at describing Dynamic Nuclear spin Polarization (DNP) in solutions containing molecules of biomedical interest and paramagnetic centers are not able to model the behaviour observed upon varying the concentration of trityl radicals or the polarization enhancement caused by moderate addition of gadolinium complexes. In this manuscript, we first show experimentally that the nuclear steady state polarization reached in solutions of pyruvic acid with 15 mM trityl radicals is substantially independent on the average internuclear distance. This evidences a leading role of electron (over nuclear) spin relaxation processes in determining the ultimate performances of DNP. Accordingly, we have devised a variant of the Thermal Mixing model for inhomogenously broadened electron resonance lines which includes a relaxation term describing the exchange of magnetic anisotropy energy of the electron spin system with the lattice. Thanks to this additional term, the dependence of the nuclear polarization on the electron concentration can be properly accounted for. Moreover, the model predicts a strong increase of the final polarization upon shortening the electron spin-lattice relaxation time, providing a possible explanation for the effect of gadolinium doping.

Hyperpolarized 13C‐labelled anhydrides as DNP precursors of metabolic MRI agents

The extraordinary enhancement of the nuclear magnetic resonance (NMR) signal that can be obtained by dynamic nuclear polarization (DNP) techniques is prompting new avenues of research based on the in vivo detection of metabolic abnormalities associated with the onset and progression of human diseases. (13) C-labelled short-chain fatty acids appear to be interesting candidates for this novel class of metabolic-active contrast agents (MCAs), as they have been shown to report on metabolic differences between healthy and ischaemic tissues in mice. In spite of their promising biological efficacy, the formulations of short-chain fatty acids that fulfil the many technical constraints of the DNP procedure, as it is today, may limit their clinical potential. New solutions have been sought to circumvent technology-related challenges and facilitate clinical translation of these molecules. In particular, it has been shown that, by using symmetric anhydrides as chemical precursors for short-chain fatty acids, no glass-forming additives are needed in the DNP formulations. Furthermore, novel esterified trityl radicals and lipophilic gadolinium complexes allow easy removal of the polarization-promoting additives at the end of the DNP process. By applying the three concepts reported, we have succeeded in preparing aqueous formulations of short-chain fatty acids for pharmaceutical use that have favourable properties compared with those obtained from current procedures. The use of organic derivatives as chemical precursors of the MCA of interest appears to be a generally valid concept, not restricted to symmetric anhydrides of fatty acids, which can markedly improve the clinical potential of other (13) C-labelled compounds.

Differences in gadolinium retention after repeated injections of macrocyclic MR contrast agents to rats

To compare the levels of gadolinium in the blood, cerebrum, cerebellum, liver, femur, kidneys, and skin after multiple exposure of rats to the macrocyclic gadolinium‐based contrast agents (GBCAs) gadoterate, gadobutrol, and gadoteridol.

Hyperpolarized [1,3‐13C2]ethyl acetoacetate is a novel diagnostic metabolic marker of liver cancer

An increased prevalence of liver diseases such as hepatitis C and nonalcoholic fatty liver results in an augmented incidence of the most common form of liver cancer, hepatocellular carcinoma (HCC). HCC is most often found in the cirrhotic liver and it can therefore be challenging to rely on anatomical information alone when diagnosing HCC. Valuable information on specific cellular metabolism can be obtained with high sensitivity thanks to an emerging magnetic resonance (MR) technique that uses 13C labeled hyperpolarized molecules. Our interest was to explore potential new high contrast metabolic markers of HCC using hyperpolarized 13C‐MR. This work led to the identification of a class of substrates, low molecular weight ethyl‐esters, which showed high specificity for carboxyl esterases and proved in many cases to possess good properties for signal enhancement. In particular, hyperpolarized [1,3‐13C2]ethyl acetoacetate (EAA) was shown to provide a metabolic fingerprint of HCC. Using this substrate a liver cancer implanted in rats was diagnosed as a consequence of an ∼4 times higher metabolic substrate‐to‐product ratio than in the surrounding healthy tissue, (p = 0.009). Unregulated cellular uptake as well as cosubstrate independent enzymatic conversion of EAA, made this substrate highly useful as a hyperpolarized 13C‐MR marker. This could be appreciated by the signal‐to‐noise (SNR) obtained from EAA, which was comparable to the SNR reported in a literature liver cancer study with state‐of‐the‐art hyperpolarized substrate, [1‐13C]pyruvate. Also, the contrast‐to‐noise (CNR) in the EAA based metabolic ratio images was significantly improved compared with the CNR in equivalent images reported using [1‐13C]pyruvate.

The role of the glassy dynamics and thermal mixing in the dynamic nuclear polarization and relaxation mechanisms of pyruvic acid

The temperature dependence of (1)H and (13)C nuclear spin-lattice relaxation rate 1/T1 has been studied in the 1.6-4.2 K temperature range in pure pyruvic acid and in pyruvic acid containing trityl radicals at a concentration of 15 mM. The temperature dependence of 1/T1 is found to follow a quadratic power law for both nuclei in the two samples. Remarkably the same temperature dependence is displayed also by the electron spin-lattice relaxation rate 1/T1e in the sample containing radicals. These results are explained by considering the effect of the structural dynamics on the relaxation rates in pyruvic acid. Dynamic nuclear polarization experiments show that below 4 K the (13)C build up rate scales with 1/T1e, in analogy to (13)C 1/T1 and consistently with a thermal mixing scenario where all the electrons are collectively involved in the dynamic nuclear polarization process and the nuclear spin reservoir is in good thermal contact with the electron spin system.

Macrocyclic paramagnetic agents for MRI: Determinants of relaxivity and strategies for their improvement

To dissect the contributions to the longitudinal relaxivity (r1) of two commercial contrast agents (CAs), Gd‐DOTA and Gd‐HP‐DO3A, and to synthesize/characterize a novel macrocyclic agent (Gd‐Phen‐DO3A) having superior r1.

On-site magnetization in open antiferromagnetic chains: A classical analysis versus NMR experiments in a spin-1 compound

The response of an open spin chain with isotropic antiferromagnetic interactions to a uniform magnetic field is studied by classical Monte Carlo simulations. It is observed how the induced on-site magnetization is nonuniform, due to the occurrence of edge staggered terms which decay exponentially over a distance equal to the zero-field correlation length of the infinite chain. The total magnetic moment associated to each staggered term is found to be about half of the original single-spin magnitude and to decrease as the inverse of temperature (i.e., to behave as a Curie-like moment). The numerical results are compared to recent NMR findings in spinless-doped

Nuclear magnetic resonance studies of DNP-ready trehalose obtained by solid state mechanochemical amorphization

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Non-clinical assessment of safety and gadolinium deposition after cumulative administration of gadobenate dimeglumine (MultiHance®) to neonatal and juvenile rats

the remarkable agreement found shows that, for temperatures above the Haldane gap, the classical approach gives a correct picture of the boundary effects observed in the Heisenberg