In Vivo 13 C NMR spectroscopy of glucose metabolism of RIF‐1 tumors

An efficient method for measuring in vivo 13 C NMR spectra of tumors has been developed and employed to monitor glucose metabolism in radiation‐induced fibrosarcomas (RIF‐1) subcutaneously implanted in C3H/HeN mice. [1‐ 13 C]Glucose was injected directly into the tumors at a dose of 1 g/kg body wt. Spectra were obtained with a Bruker AM 360‐WB spectrometer (8.4 T/8.9 cm bore) employing a homebuilt probe equipped with a four‐turn solenoidal coil (1.5 cm outer diameter) for detection of 13 C signals and a Helmholtz coil (two 3‐cm turns separated by a 3‐cm gap, oriented orthogonally to the 13 C coil) for 1 H decoupling. In addition to the natural abundance 13 C resonances of the tumors, signals were detected from the α‐and β‐anomers of labeled glucose. Within 15 min following injection of labeled glucose [3‐ 13 C]lactate and [3‐ 13 C]alanine were detected. Lactate labeling approached steady state levels within about 50 min after glucose injection; in contrast, alanine labeling increased continuously over the duration of the experiment (70 min). Sixty minutes after glucose injection, the ratio of the intensity of [3‐ 13 C]lactate to the principal lipid methylene resonance (30 ppm from external tetramethylsilane), which served as an internal intensity reference, was correlated with tumor size, whereas the corresponding ratio of the [3‐ 13 C] alanine resonance was not. Labeling of glutamate was below the level of detection in the in vivo spectra; however, labeling of C 4 ‐glutamate at a level approximately 50‐fold lower than the level of [3‐ 13 C]lactate was detected in perchloric acid extracts. Incorporation of 13 C label into C 2 ‐and C 3 ‐glutamate and C 2 ‐lactate was also observed. © 1991 Academic Press, Inc.