Nonglycolytic Acidification of Murine Radiation-induced Fibrosarcoma 1 Tumor via 3-O-Methyl-d-glucose Monitored by ¹H, ²H, ¹³C, and ³¹P Nuclear 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 ²H, ¹³C, and ³¹P 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) (n = 10), [PCr] decreased by 54%, [NTP] decreased by 35%, and [P₁] increased by 36%. Tumor blood flow, as measured by ²H NMR monitoring of D₂O washout kinetics, decreased by 40% at 1 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 ¹³C NMR spectroscopy, following [6-¹³C]3-OMG 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 [6-¹³C]3-OMG-6-phosphate or [3-¹³C]lactate were observed. These results confirmed that 3-OMG was not metabolized in radiation-induced fibrosarcoma 1 tumor. At the completion of the in situ ¹³C NMR experiments, tumors were freeze clamped, and perchloric acid extraction was performed. High-resolution ¹H NMR measurement of lactate concentrations showed no statistically significant difference in control tumor extracts (from mice not receiving i.p. injection; n = 5) and in tumor extracts from mice administered i.p. [6-¹³C]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 ¹H and ¹³C NMR studies indicated that the radiation-induced 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.