Abstract 4158: Non-invasive mapping of acidosis and extracellular lactosis for assessing tumor invasion in vivo
Authors: Choffart Anais , Chiaffarelli Remy , Zimmermann Max , Kuebler Laura , Martins André 
Published: March 2024

Abstract
Tumor cells typically display a hyperglycolytic metabolic phenotype characterized by increased lactate production, known as the Warburg effect. This drift in oxidative metabolism often results in a more acidic microenvironment. This adverse microenvironment represents a unique metabolic signature in cancer cells with more invasive phenotypes. However, to date, there are no effective methods available to evaluate cancer progression and metastatic potential in vivo. To bridge this gap, we have developed a molecular imaging technique (CEST-MRI) that can track extracellular pH (pHe; acidoCEST) and extracellular lactate levels (shiftCEST) simultaneously to discern different cancer phenotypes.
In this study we have generated and selected in vivo two PyMT derived murine breast cancer cell lines, a parental and a G6 metastatic. We first characterized the cell’s metabolism by analyzing key biomarkers with qPCR, Western Blot and microscopy, and confirmed their distinct metabolic profiles with Seahorse and RNA Sequencing. Notably, the metastatic PyMT exhibited a more active metabolism, aligning with the invasive phenotype observed by spheroid invasion assay. Herein, we combined the injection of iopamidol and shift reagent (SR) to perform quasi-simultaneous acidoCEST and shiftCEST. First, we assessed the approach in vitro by introducing iopamidol and SR into phantoms containing the individual contrast agents, and the combination in pure water and cells supernatants at different pHe and lactate levels. We performed LDH assays to cross-validate the extracellular concentrations and monitored the pH with a micro pH meter (Mettler-Toledo). In vivo, the cells were injected orthotopically in the 4th mammary fat pad of C57BL/6N mice. Hybrid shift/acidoCEST sequences were optimized and acquired following the injection of the iopamidol+SR solution. Preclinical shift/acidoCEST enabled the simultaneous and accurate determination of extracellular acidosis and lactosis, revealing increased acidification in the metastatic models despite lower lactate secretion. Metastatic tumors exhibited a negative correlation between tumor volume and pHe, indicating the significance of acidity in mutagenesis and invasion. In contrast, no correlation was observed for the parental non-metastatic tumor. Additionally, the metastatic tumors had lower levels of lactate than the parental tumors, which could be attributed to their higher mitochondrial activity, reflecting a diverted metabolic fitness.
In summary, our study highlights the efficacy of shift/acidoCEST as a reliable method for non-invasive metabolic imaging, enabling the simultaneous detection of extracellular acidity and lactate production by MRI. This research introduces a unique platform for assessing the metabolic aggressiveness of cancer, emphasizing the significance of acidity and lactate production as crucial biomarkers in cancer invasion.
Citation Format: Anais Choffart, Remy Chiaffarelli, Max Zimmermann, Laura Kuebler, André Martins. Non-invasive mapping of acidosis and extracellular lactosis for assessing tumor invasion in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4158.