Nonglycolytic Acidification of Murine Radiation-induced Fibrosarcoma 1 Tumor via 3-O-Methyl-D-glucose Monitored by JH, 2H, 13C,and 31PNuclear Magnetic Resonance Spectroscopy1

The effects of 3-O-methyl-D-glucose (3-OMG) on subcutaneously implanted murine radiation-induced fibrosarcoma 1 tumor were examined with 'H, "(.', and "I" nuclear magnetic resonance (NMR) in situ. Using 31P NMR, changes in tumor high-energy phosphate metabolism were monitored for 2.5 h after i.p. administration of 3-OMG (8.1 g/kg body weight); tumor pH decreased by a mean maximum of 0.52 ±0.05 (SE) («= 10), |PCr| decreased by 54%, [NTP| decreased by 35%, and [P¡] increased by 36%. Tumor blood flow, as measured by 2H NMR monitor ing of D2O washout kinetics, decreased by 40% at l h and by 47% at 2 h after 3-OMG injection (n = 4). This substantial tumor acidification (pH decrease » 0.1), expected to require a glycolytic substrate (Hwang et al., Cancer Res., 51: 3108-3118, 1991), is surprising in light of the previously documented metabolically inert nature of 3-OMG. In situ "< NMR spectroscopy, following |6-"( |3-OM(, i.p. injection, examined the possibility of the glycolytic metabolism of 3-OMG. However, only the C-6 resonance of 3-OMG was detected (n = 6); no resonances from (613C]3-OMG-6-phosphate or |3-13C]lactate were observed. These results confirmed that 3-OMG was not metabolized in radiation-induced fibro sarcoma 1 tumor. At the completion of the ¡nsitu "(.' NMR experiments, tumors were freeze clamped, and perchloric acid extraction was per formed. High-resolution 'H NMR measurement of lactate concentrations showed no statistically significant difference in control tumor extracts (from mice not receiving i.p. injection; n = 5) and ¡ntumor extracts from mice administered i.p. [6-'3C]3-OMG (n = 5), indicating that there was no significant increase in lactate level in the tumor extracts from mice administered i.p. 3-OMG due to increased plasma glucose concentration. The results of these 'H and "( ' NMR studies indicated that the radiationinduced fibrosarcoma 1 tumor acidification caused by i.p. administration of 3-OMG was not due to a direct (3-OMG —¿ » lactate) or an indirect (systemic glucose —¿ > lactate) increase in tumor lactic acid levels.