A nitroxides-based macromolecular MRI contrast agent with an extraordinary longitudinal relaxivity for tumor imaging via clinical T1WI SE sequence

Contrast Agents Based on Human Serum Albumin and Nitroxides for 1H-MRI and Overhauser-Enhanced MRI

In cancer diagnostics, magnetic resonance imaging (MRI) uses contrast agents to enhance the distinction between the target tissue and background. Several promising approaches have been developed to increase MRI sensitivity, one of which is Overhauser dynamic nuclear polarization (ODNP)-enhanced MRI (OMRI). In this study, a macromolecular construct based on human serum albumin and nitroxyl radicals (HSA-NIT) was developed using a new synthesis method that significantly increased the modification to 21 nitroxide residues per protein. This was confirmed by electron paramagnetic resonance (EPR) spectroscopy and matrix-assisted laser desorption/ionization time-of-flight (MALDI ToF) mass spectrometry. Gel electrophoresis and circular dichroism showed no significant changes in the structure of HSA-NITs, and no oligomers were formed during modification. The cytotoxicity of HSA-NITs was comparable to that of native albumin. HSA-NITs were evaluated as potential "metal-free" organic radical relaxation-based contrast agents for 1H-MRI and as hyperpolarizing contrast agents for OMRI. Relaxivities (longitudinal and transversal relaxation rates r1 and r2) for HSA-NITs were measured at different magnetic field strengths (1.88, 3, 7, and 14 T). Phantoms were used to demonstrate the potential use of HSA-NIT as a T1- and T2-weighted relaxation-based contrast agent at 3 T and 14 T. The efficacy of 1H Overhauser dynamic nuclear polarization (ODNP) in liquids at an ultralow magnetic field (ULF, B0 = 92 ± 0.8 μT) was investigated for HSA-NIT conjugates. The HSA-NITs themselves did not show ODNP enhancement; however, under the proteolysis conditions simulating cancer tissue, HSA-NIT conjugates were cleaved into lower-molecular-weight (MW) protein fragments that activate ODNP capabilities, resulting in a maximum achievable enhancement |Emax| of 40-50 and a radiofrequency power required to achieve half of Emax, P1/2, of 21-27 W. The HSA-NIT with a higher degree of modification released increased the number of spin probes upon biodegradation, which significantly enhanced the Overhauser effect. Thus, HSA-NITs may represent a new class of MRI relaxation-based contrast agents as well as novel cleavable conjugates for use as hyperpolarizing contrast agents (HCAs) in OMRI.

TEMPO-conjugated tobacco mosaic virus as a magnetic resonance imaging contrast agent for detection of superoxide production in the inflamed liver

Superoxide, an anionic dioxygen molecule, plays a crucial role in redox regulation within the body but is implicated in various pathological conditions when produced excessively. Efforts to develop superoxide detection strategies have led to the exploration of organic-based contrast agents for magnetic resonance imaging (MRI). This study compares the effectiveness of two such agents, nTMV-TEMPO and kTMV-TEMPO, for detecting superoxide in a mouse liver model with lipopolysaccharide (LPS)-induced inflammation. The study demonstrates that kTMV-TEMPO, with a strategically positioned lysine residue for TEMPO attachment, outperforms nTMV-TEMPO as an MRI contrast agent. The enhanced sensitivity of kTMV-TEMPO is attributed to its more exposed TEMPO attachment site, facilitating stronger interactions with water protons and superoxide radicals. EPR kinetics experiments confirm kTMV-TEMPO's faster oxidation and reduction rates, making it a promising sensor for superoxide in inflamed liver tissue. In vivo experiments using healthy and LPS-induced inflamed mice reveal that reduced kTMV-TEMPO remains MRI-inactive in healthy mice but becomes MRI-active in inflamed livers. The contrast enhancement in inflamed livers is substantial, validating the potential of kTMV-TEMPO for detecting superoxide in vivo. This research underscores the importance of optimizing contrast agents for in vivo imaging applications. The enhanced sensitivity and biocompatibility of kTMV-TEMPO make it a promising candidate for further studies in the realm of medical imaging, particularly in the context of monitoring oxidative stress-related diseases.

Redox Properties and in Vivo Magnetic Resonance Imaging of Cyclodextrin-Polynitroxides Contrast Agents

This paper reports the synthesis, characterization and in vivo application of water-soluble supramolecular contrast agents (Mw: 5-5.6 kDa) for MRI obtained from β-cyclodextrin functionalized with different kinds of nitroxide radicals, both with piperidine structure (CD2 and CD3) and with pyrrolidine structure (CD4 and CD5). As to the stability of the radicals in presence of ascorbic acid, CD4 and CD5 have low second order kinetic constants (≤0.05 M-1  s-1 ) compared to CD2 (3.5 M-1  s-1 ) and CD3 (0.73 M-1  s-1 ). Relaxivity (r1 ) measurements on compounds CD3-CD5 were carried out at different magnetic field strength (0.7, 3, 7 and 9.4 T). At 0.7 T, r1 values comprised between 1.5 mM-1  s-1 and 1.9 mM-1  s-1 were found while a significant reduction was observed at higher fields (r1 ≈0.6-0.9 mM-1  s-1 at 9.4 T). Tests in vitro on HEK293 human embryonic kidney cells, L929 mouse fibroblasts and U87 glioblastoma cells indicated that all compounds were non-cytotoxic at concentrations below 1 μmol mL-1 . MRI in vivo was carried out at 9.4 T on glioma-bearing rats using the compounds CD3-CD5. The experiments showed a good lowering of T1 relaxation in tumor with a retention of the contrast for at least 60 mins confirming improved stability also in vivo conditions.

Mitochondrial targeted ROS Scavenger based on nitroxide for Treatment and MRI imaging of Acute Kidney Injury

INTRODUCTION

Overproduction of reactive oxygen species (ROS) during oxidative stress is a hallmark of acute kidney injure (AKI), which induced the damage to the renal cells and mitochondrial injury.

PURPOSE

In this contribution, we prepared mitochondrial targeted nitroxide, which linked 3-carboxy-2,2,5,5-tetramethylpyrrolidine 1-oxyl (carboxy-PROXYL) with (2-aminoethyl)triphenylphosphonium bromide (TPP), named TPP-PROXYL to eliminate the ROS in situ and image the oxidative stress reaction by MRI.

METHODS

2,7-Dichlorodihydrofluorescein diacetate (DCFH-DA) staining, mitochondrial membrane potential assay (JC-1) staining and transmission electron microscope (TEM) experiments were processed to verify that TPP-PROXYL could target mitochondria, scavenge the ROS, and prevent damage to mitochondria in live cells. Contrast enhanced MRI also been used to monitor these redox reaction in AKI model.

RESULTS

TPP-PROXYL demonstrated excellent ROS T₁-weighted magnetic resonance imaging (MRI) enhancement in vitro and in vivo, with r₁ value about 0.190 mM^-1·s^-1. In vivo AKI treatment experiments proved that TPP-PROXYL could improve the survival rate of mice and inhibit kidney damage. Moreover, the great ROS scavenging capability and the renal damage reduction during AKI treatment of TPP-PROXYL was verified via MR imaging technology.

CONCLUSION

Collectively, this research provides TPP-PROXYL would serve as a powerful platform to realize ROS scavenging, treatment and MR imaging of AKI.