Highly Specific and Sensitive Radioiodinated Agent for In Vivo Imaging of Superoxide through Superoxide-Initiated Retention

Innovations in Nuclear Medicine Imaging for Reactive Oxygen Species: Applications and Radiopharmaceuticals

Reactive oxygen species (ROS) are generated during normal cellular energy production and play a critical role in maintaining cellular function. However, excessive ROS can damage cells and tissues, contributing to the development of diseases such as cardiovascular, inflammatory, and neurodegenerative disorders. This review explores the potential of nuclear medicine imaging techniques for detecting ROS and evaluates various radiopharmaceuticals used in these applications. Radiopharmaceuticals, which are drugs labeled with radionuclides, can bind to specific biomarkers, facilitating their identification in vivo using nuclear medicine equipment, i.e., positron emission tomography and single photon emission computed tomography, for diagnostic purposes. This review includes a comprehensive search of PubMed, covering radiopharmaceuticals such as analogs of fluorescent probes and antioxidant vitamin C, and biomarkers targeting mitochondrial complex I or cystine/glutamate transporter.

Ex Tenebris Lux: Illuminating Reactive Oxygen and Nitrogen Species with Small Molecule Probes

Reactive oxygen and nitrogen species are small reactive molecules derived from elements in the air─oxygen and nitrogen. They are produced in biological systems to mediate fundamental aspects of cellular signaling but must be very tightly balanced to prevent indiscriminate damage to biological molecules. Small molecule probes can transmute the specific nature of each reactive oxygen and nitrogen species into an observable luminescent signal (or even an acoustic wave) to offer sensitive and selective imaging in living cells and whole animals. This review focuses specifically on small molecule probes for superoxide, hydrogen peroxide, hypochlorite, nitric oxide, and peroxynitrite that provide a luminescent or photoacoustic signal. Important background information on general photophysical phenomena, common probe designs, mechanisms, and imaging modalities will be provided, and then, probes for each analyte will be thoroughly evaluated. A discussion of the successes of the field will be presented, followed by recommendations for improvement and a future outlook of emerging trends. Our objectives are to provide an informative, useful, and thorough field guide to small molecule probes for reactive oxygen and nitrogen species as well as important context to compare the ecosystem of chemistries and molecular scaffolds that has manifested within the field.

Detecting Validated Intracellular ROS Generation with 18F-dihydroethidine-Based PET

PURPOSE

To determine the sensitivity of the 18F-radiolabelled dihydroethidine analogue ([18F]DHE) to ROS in a validated ex vivo model of tissue oxidative stress.

PROCEDURES

The sensitivity of [18F]DHE to various ROS-generating systems was first established in vitro. Then, isolated rat hearts were perfused under constant flow, with contractile function monitored by intraventricular balloon. Cardiac uptake of infused [18F]DHE (50-150 kBq.min-1) was monitored by γ-detection, while ROS generation was invoked by menadione infusion (0, 10, or 50 μm), validated by parallel measures of cardiac oxidative stress.

RESULTS

[18F]DHE was most sensitive to oxidation by superoxide and hydroxyl radicals. Normalised [18F]DHE uptake was significantly greater in menadione-treated hearts (1.44 ± 0.27) versus control (0.81 ± 0.07) (p < 0.05, n = 4/group), associated with concomitant cardiac contractile dysfunction, glutathione depletion, and PKG1α dimerisation.

CONCLUSION

[18F]DHE reports on ROS in a validated model of oxidative stress where perfusion (and tracer delivery) is unlikely to impact its pharmacokinetics.

Radiotracers for Nuclear Imaging of Reactive Oxygen Species: Advances Made So Far

Reactive oxygen species (ROS) are a cluster of highly reactive and short-lived oxygen-containing molecules that lead to metabolic disorders where production exceeds catabolism in an organism. Many specific radiotracers for positron/single-photon emission tomography have been developed to reveal the discrepancy of ROS levels in normal and damaged tissues and further clarify the relationship between ROS and diseases. This review summarizes the advances achieved for the development of ROS radiotracers to date. The structure design, radiosynthesis, and imaging performance of existing radiotracers are discussed with the individual ROS-response mechanisms highlighted.

Redox Monitoring in Nuclear Medical Imaging

Significance: The imbalance in redox homeostasis is known as oxidative stress, which is relevant to many diseases such as cancer, arteriosclerosis, and neurodegenerative disorders. Overproduction of reactive oxygen species (ROS) is one of the factors that trigger the redox state imbalance in vivo. The ROS have high reactivity and impair biomolecules, whereas antioxidants and antioxidant enzymes, such as ascorbate and glutathione, reduce the overproduction of ROS to rectify the redox imbalance. Owing to this, redox monitoring tools have been developed to understand the redox fluctuations in oxidative stress-related diseases. Recent Advances: In an attempt to monitor redox substances, including ROS and radical species, versatile modalities have been developed, such as electron spin resonance, chemiluminescence, and fluorescence. In particular, many fluorescent probes have been developed that are selective for ROS. This has significantly contributed to understanding the relevance of ROS in disease onset and progression. Critical Issues: To date, the dynamics of ROS and radical fluctuation in in vivo redox states remain unclear, and there are a few methods for the in vivo detection of redox fluctuations. Future Directions: In this review, we summarize the development of radiolabeled probes for monitoring redox-relevant species by nuclear medical imaging that is applicable in vivo. In the future, translational research is likely to be advanced through the development of highly sensitive and in vivo applicable detection methods, such as nuclear medical imaging, to clarify the underlying dynamics of ROS, radicals, and redox substances in many diseases. Antioxid. Redox Signal. 36, 797-810.

Direct 18F-Labeling of Biomolecules via Spontaneous Site-Specific Nucleophilic Substitution by F- on Phosphonate Prostheses

We describe a high radiochemical yield late-stage direct ¹⁸F-labeling of bare biomolecules containing common active groups. Spontaneity and site-selectivity are attributed to the remarkably higher rates of nucleophilic substitution reactions on phosphonates than on other electrophiles by F^- at various hydrogen bond forms. Rapid access to many medicinally significant ¹⁸F-labeled biomolecules is achieved at 21-68% radiochemical yields and 35.9-55.1 GBq μmol^-1 molar activities both manually or automatically.

Synthesis of 18 F-radiolabeled organophosphine fluorides for thiol-chemoselective peptide conjugation

Two 18 F-radiolabeled organofluorophosphine fluorides ([18 F]4 and [18 F]7) for chemoselective thiol-conjugation were designed and synthesized via 18 F-19 F isotopic exchange reaction. This simple and rapid radiofluorination produced both 18 F-radiolabeled fluorides in excellent radiochemical yields (>94%) and radiochemical purity. The optimal reaction conditions are 0.05-mg substrate, 0.69 mg of potassium carbonate, and dried [18 F]F- were mixed in 100-μl anhydrous acetonitrile at room temperature for 5 min. Both of [18 F]4 and [18 F]7 showed specificity for thiol-conjugation with cysteine and have been used in the radiosynthesis of c (RGDfC). The [18 F]7 with an adamantanyl-hindered substituent displayed superior in vitro and in vivo stability.

Oxygen Vacancy-Enhanced Electrochemiluminescence Sensing Strategy Using Luminol Thermally Encapsulated in Apoferritin as a Transducer for Biomarker Immunoassay

Oxygen vacancies (OVs) enhanced electrochemiluminescence (ECL) biosensing strategy using luminol thermally encapsulated in apoferritin (Lum@apoFt) as an efficient transducer was investigated for ultrasensitive biomarker detection. By applying the oxygen-defect engineering (ODE) strategy, the OVs enriched cobalt-iron oxide (r-CoFe₂O₄) was fabricated as the sensing substrate to boost the electron mobility and catalyze the generation of superoxide anion radical (O₂^•-) for signal amplification. It should be noted that r-CoFe₂O₄ with higher OVs density dramatically accelerated the ECL reaction between O₂^•- and luminol anionic radicals, achieving 6.5-fold stronger ECL output than CoFe₂O₄ with no or low OVs density. Moreover, facile encapsulation of approximate 412 luminol molecules in a single apoFt cavity was first realized by an efficient thermal-induction method. The obtained Lum@apoFt complexes exhibited well-maintained ECL efficiency and excellent biocompatibility for biological modifications. On this basis, a biosensor was developed for early diagnostics of squamous cell carcinomas by detecting its representative biomarker named cytokeratin 19 fragment 21-1 (CYFRA 21-1), from which excellent linearity was achieved in 0.5 pg/mL to 50 ng/mL with a detection limit of 0.14 pg/mL. This work not only put forward a novel idea of creating OVs enriched sensing interface with excellent signal-amplification function but also proposes a facile and robust methodology to design apoFt-based transducers for developing more practical nanoscale biosensors in early diagnostics of diseases.