Interstitial Inorganic Phosphate as a Tumor Microenvironment Marker for Tumor Progression

Andrey A Bobko,Ilirian Dhimitruka,Valery V Khramtsov,Benoit Driesschaert,Jason Evans,Mikhail M Dikov,Rahman Mohammad,Timothy D Eubank,Elena E Tchekneva

doi:10.1038/srep41233

Abstract

Noninvasive in vivo assessment of chemical tumor microenvironment (TME) parameters such as oxygen (pO2), extracellular acidosis (pHe), 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], pO2, pHe and 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.

Highlights

tumor microenvironment (TME) acidosis has been proposed to be selectively more toxic to normal parenchymal tissues compared with invading cancers[7]
A positive correlation is found between pO2 and pHe in agreement with a higher contribution of glycolysis in tissue energy metabolism at lower pO2 resulting in interstitial lactic acidosis
We designed a trityl paramagnetic probe[9,10] with unique spectral properties that allows for simultaneous monitoring of tissue pO2, pHe and [Pi]. This probe was successfully used in vivo in animal models of cancer using low-field L-band electron paramagnetic resonance (EPR) spectroscopy that allowed for a few cm tissue depth penetration of microwave field

Summary

Introduction

TME acidosis has been proposed to be selectively more toxic to normal parenchymal tissues compared with invading cancers[7]. Noninvasive in vivo assessment of TME parameters such as oxygen (pO2) and extracellular acidosis (pHe) may provide unique insights into biological processes in tumors, tumor progression, aggressiveness and efficacy of anticancer therapies. We employ an electron paramagnetic resonance (EPR) technique for in vivo concurrent assessment of pO2, extracellular pH (pHe) and concentration of interstitial inorganic phosphate (Pi) in TME in animal models of cancer. This technique is based on application of a recently developed soluble multifunctional paramagnetic probe providing unsurpassed opportunity for in vivo multiparameter measurements[9,10] (see Fig. 1). The associate of [Pi] with tumor metabolism[11,12], buffer-mediated proton transport[13], and a requirement of high phosphorus content for the rapid growth in the “growth rate hypothesis14” may underline its potential role in tumorigenesis, tumor progression and metastasis

Methods

Results

Conclusion