Nuclear Magnetic Resonance of the Subcutaneously Implanted 9L Glioma

The effects of chemotherapy [25 mg/kg 1,3-bis(2-chloroethyl)-1-nitrosourea administered with a single i.p. injection] on cellular energetics by P nuclear magnetic resonance (NMR) spectroscopy, total tissue sodium by single-quantum (SQ) Na NMR spectroscopy, and intracellular sodium by triple-quantum-filtered (TQF) Na NMR spectroscopy were studied in the s.c. 9L glioma. Animals were studied by NMR 2 days before therapy and 1 and 5 days after therapy. Destructive chemical analysis was also performed 5 days after therapy to validate the origin of changes in SQ and TQF Na signals. One day after treatment, there was no significant difference between control and treated tumors in terms of tumor size or Na and P spectral data. Five days after therapy, treated tumors had 28 6 16% (P < 0.1) lower SQ Na signal intensity, 46 6 20% (P < 0.05) lower TQF Na signal intensity, 125 6 51% (P < 0.05) higher ATP:Pi ratio, 186 6 69% (P < 0.05) higher phosphocreatine:Pi ratio, and 0.17 6 0.06 pH units (P < 0.05) higher intracellular pH compared with control tumors. No significant differences in TQF Na relaxation times were seen between control and treated tumors at any time point. Destructive chemical analysis showed that the relative extracellular space of control and treated tumors was identical, but the treated tumors had 21 6 8% (P < 0.05) lower total tissue Na concentration and 60 6 24% (P < 0.05) lower intracellular Na concentration compared with the controls. The higher phosphocreatine:Pi and ATP:Pi ratios after 1,3-bis(2chloroethyl)-1-nitrosourea treatment indicate improved bioenergetic status in the surviving tumor cells. The decrease in SQ and multiple-quantum-filtered Na signal intensity was largely attributable to a decrease in Nai 1 because the treatment did not change the relative extracellular space. The improved energy metabolism could decrease the intracellular concentration of Na by increasing the activity of Na-K-ATPase and decreasing the activity of Na/H. Although both Na and P spectra were consistent with improved cellular metabolism in treated tumors, the Na methods may be better suited for monitoring response to therapy because of higher signal:noise ratio and ease of imaging the single Na resonance.