Metabolic MRI for quantifying aerobic glycolysis and immune function in gliomas

University Of California Los Angeles, Los Angeles CA

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Abstract

PROJECT SUMMARY Abnormal metabolism is a hallmark of cancer and results in altered immune function. Notably, glycolysis is of- ten enhanced in cancers, even in the presence of abundant oxygen (i.e. the Warburg effect). This form of ?aer- obic glycolysis? results in a dramatic decrease in tumor acidity due to increased concentration of lactic acid, which comes with dramatic consequences, as this is directly linked to increased tumor aggressiveness, in- creased invasion, increased genetic mutations, increased resistance to therapy, increased angiogenesis, and decreased immune function. Extensive scientific evidence supports the hypothesis that aerobic glycolysis plays an important role in gliomagenesis and altered tumor-infiltrating CD8+ T lymphocytes (TIL)-cell function; how- ever, there remains a critical gap in our understanding of the role of extracellular acidosis and oxygen metabo- lism in altering immune function in human gliomas due to the lack of a robust non-invasive tool for measuring low pH and oxygen consumption. Thus, the purpose of the current project is to validate a new imaging tech- nique that can provide high-resolution images of regions of aerobic glycolysis, or high lactic acid production but low oxygen consumption, and explore the association between this new measurement and measures of both tumor and TIL metabolic function. The current study will investigate the central hypotheses that 1) tumor tissue undergoing high aerobic glycolysis defined by low pH and low O2 consumption can be reliably detected using multi-echo amine CEST imaging; 2) regions with high ?aerobic glycolytic index? (AGI) on MRI will have elevat- ed hypoxic and glycolytic expression levels independent of the concentration of immune cells; 3) tumors with high in vivo AGI using MRI will have high ex vivo measurements of AGI in tumor, but not immune cells; and 4) TILs extracted from tumors with high in vivo AGI measurements will have lower glucose consumption and cy- tokine production, suggestive of functional impairment. To accomplish this we will first verify the specificity of to areas of the tumor undergoing abnormal metabolism using tissue from image-guided biopsies. We hypothesize the AGI will provide high specificity for tumor and high levels of AGI will correlate with a high expression of fea- tures involved in aerobic glycolysis, including hypoxia inducible factor (HIF)-1?, GLUT3, and HK2. Next, we will explore the association between in vivo AGI and ex vivo AGI in both tumor and TILs using a functional assay and extracellular flux analysis estimates of the extracellular acidification rate (ECAR) and oxygen consumption rate (OCR) during metabolic manipulations of tissue extracted using image-guided biopsy. We theorize the MRI-derived AGI will show a strong positive association with the ex vivo AGI estimate of glycolytic potential in tumor but no association in TILs. Lastly, we will test whether tumors with an elevated in vivo AGI measured with MRI have dampened glucose utilization and cytokine production through ex vivo metabolic manipulation.