In vivo spectroscopy to concurrently characterize five metabolic and vascular endpoints relevant to aggressive breast cancer

Abstract

Discovery We describe a novel method leveraging quantitative fluorescence spectroscopy to characterize oxidative phosphorylation, glucose uptake, fatty acid uptake, total hemoglobin, and oxygen saturation concurrently in healthy and tumor-bearing in vivo murine tissue. ABSTRACT. Significance: Emerging evidence that aggressive breast tumors rely on various substrates including lipids and glucose to proliferate and recur necessitates the development of tools to track multiple metabolic and vascular endpoints concurrently in vivo . Aim: Our quantitative spectroscopy technique provides time-matched measurements of the three major axes of breast cancer metabolism as well as tissue vascular properties in vivo . Approach: We leverage exogenous fluorophores to quantify oxidative phosphorylation, glucose uptake, and fatty acid oxidation, and endogenous contrast for measurements of hemoglobin and oxygen saturation. An inverse Monte Carlo algo-rithm corrects for aberrations resulting from tissue optical properties, allowing the unmixing of spectrally overlapping fluorophores. Results: Implementation of our inverse Monte Carlo resulted in a linear relationship of fluorophore intensity with concentration ( R 2 < 0 . 99 ) in tissue-mimicking phantom validation studies. We next sequenced fluorophore delivery to faithfully recapitulate independent measurement of each fluorophore. The ratio of Bodipy FL C16/2-NBDG administered to a single animal is not different from that in paired animals receiving individual fluorophores ( p ¼ n : s : ). Clustering of five variables was effective in distinguishing tumor from mammary tissue (sensitivity = 0.75, specificity = 0.83, and accuracy = 0.79). Conclusions: Our system can measure major axes of metabolism and associated vascular endpoints, allowing for future study of tumor metabolic flexibility.