in-vivo-epr-assessment-ph-po2-redox-status-concentrations-phosphate

In Vivo EPR Assessment of pH, pO2, Redox Status, and Concentrations of Phosphate and Glutathione in the Tumor Microenvironment

This protocol demonstrates the capability of low-field electron paramagnetic resonance (EPR)-based techniques in combination with functional paramagnetic ...

West Virginia University

West Virginia University School of Medicine

Stable triarylmethyl radicals are ideal spin labels used for biomedical electron paramagnetic resonance applications. Previously reported structures exhibit polar charged functions for water solubilization preventing them from crossing the cell membrane. We report the synthesis of a triarylmethyl radical conjugated to poly-arginine peptide allowing intracellular delivery of the paramagnetic label.

Poly-arginine conjugated triarylmethyl radical as intracellular spin label.

Superoxide radical is involved in numerous physiological and pathophysiological processes. Tetrathiatriarylmethyl (TAM) radicals are known to react with superoxide allowing measurement of superoxide production in biological media. We report the synthesis of a Nitro conjugated TAM radical showing a rate constant of 7 × 10 M swhich is two order of magnitude higher than other TAMs, allowing high sensitivity measurement of superoxide.

Nitro-Triarylmethyl Radical as Dual Oxygen and Superoxide Probe.

Noninvasive in vivo assessment of chemical tumor microenvironment (TME) parameters such as oxygen (pO), extracellular acidosis (pH), and concentration of interstitial inorganic phosphate (Pi) may provide unique insights into biological processes in solid tumors. In this work, we employ a recently developed multifunctional trityl paramagnetic probe and electron paramagnetic resonance (EPR) technique for in vivo concurrent assessment of these TME parameters in various mouse models of cancer. While the data support the existence of hypoxic and acidic regions in TME, the most dramatic differences, about 2-fold higher concentrations in tumors vs. normal tissues, were observed for interstitial Pi - the only parameter that also allowed for discrimination between non-metastatic and highly metastatic tumors. Correlation analysis between [Pi], pO, pHand tumor volumes reveal an association of high [Pi] with changes in tumor metabolism and supports different mechanisms of protons and Pi accumulation in TME. Our data identifies interstitial inorganic phosphate as a new TME marker for tumor progression. Pi association with tumor metabolism, buffer-mediated proton transport, and a requirement of high phosphorus content for the rapid growth in the "growth rate hypothesis" may underline its potential role in tumorigenesis and tumor progression.

Interstitial Inorganic Phosphate as a Tumor Microenvironment Marker for Tumor Progression.

This Feature overviews the basic principles of using stable organic radicals involved in reversible exchange processes as functional paramagnetic probes. We demonstrate that these probes in combination with electron paramagnetic resonance (EPR)-based spectroscopy and imaging techniques provide analytical tools for quantitative mapping of critical parameters of local chemical microenvironment. The Feature is written to be understandable to people who are laymen to the EPR field in anticipation of future progress and broad application of these tools in biological systems, especially in vivo, over the next years.

Exchange Phenomena in the Electron Paramagnetic Resonance Spectra of the Nitroxyl and Trityl Radicals: Multifunctional Spectroscopy and Imaging of Local Chemical Microenvironment.

Superoxide radical represents one of the most biologically relevant reactive oxygen species involved in numerous physiological and pathophysiological processes. Superoxide measurement through the decay of an electron paramagnetic resonance (EPR) signal of a triarylmethyl (TAM) radical possesses the advantage of a high selectivity and relatively high rate constant of TAM reaction with the superoxide. Hereby we report a straightforward synthesis and characterization of a TAM-TAM biradical showing a high reactivity with superoxide (second-order rate constant, (6.7 ± 0.2) × 10Ms) enabling the measurement of superoxide radical by following the increase of a sharp EPR signal associated with the formation of a TAM-quinone-methide monoradical product.

Article	Year
Poly-arginine conjugated triarylmethyl radical as intracellular spin label. Bioorganic & medicinal chemistry letters\| PubMed ID: 26923698	2016
Nitro-Triarylmethyl Radical as Dual Oxygen and Superoxide Probe. Cell biochemistry and biophysics\| PubMed ID: 27206803	2017
Interstitial Inorganic Phosphate as a Tumor Microenvironment Marker for Tumor Progression. Scientific reports\| PubMed ID: 28117423	2017
Exchange Phenomena in the Electron Paramagnetic Resonance Spectra of the Nitroxyl and Trityl Radicals: Multifunctional Spectroscopy and Imaging of Local Chemical Microenvironment. Analytical chemistry\| PubMed ID: 28363027	2017
Triarylmethyl-based biradical as a superoxide probe. Free radical research\| PubMed ID: 28817975	2017

Benoit Driesschaert

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