Changes in 31P nuclear magnetic resonance with tumor growth in radioresistant and radiosensitive tumors

In vivo 31P nuclear magnetic resonance (31P NMR) spectroscopy has been used to compare metabolic profiles with tumor radiosensitivity. A radioresistant mammary carcinoma (MCa) and a radiosensitive methylcholanthrene-induced fibrosarcoma (Meth-A) were studied by 31P NMR spectroscopy in the tumor volume range of approximately 100-1200 mm3. The MCa showed a constant pH in this volume range; the ratio of phosphocreatine to inorganic phosphate (PCr/Pi) for 160-300 mm3 tumors was 0.33 +/- 0.11 (mean +/- standard deviation) and did not change (0.29 +/- .09) for tumors in the volume range of 600-1200 mm3. In comparison, the Meth-A showed a decrease in tumor pH as volume increased from 160-300 mm3 (pH 7.16 +/- 0.4) to 600-1200 mm3 (pH 6.94 +/- .07). Tumor PCr/Pi decreased from 0.70 +/- .16 (160-300 mm3) to 0.33 +/- .16 (600-1200 mm3). The radiation doses for control of MCa-induced tumors in 50% of the treated tumors ranged from 65 (150-250 mm3) to 71 Gy (1000-1300 mm3) and for the Meth-A-induced tumors ranged from 35 (150-250 mm3) to 38 Gy (1000-1300 mm3). These results suggest that 31P NMR spectra may be a qualitative predictor of tumor hypoxia, although further studies of human and rodent tumors are necessary to support this hypothesis.