Use of high-resolution 31P-labeled topical magnetic resonance spectroscopy to monitor in vivo tumor metabolism in rats.

A probe using a single-tuned solenoid coil has been constructed to study in vivo metabolism of rats in a wide-bore Bruker nuclear magnetic resonance spectrometer. Transplantable rat mammary adenocarcinomas (estrogen receptor negative) were implanted into the hind leg muscle of 8-week-old rats. The other leg without tumor was used as a control. Tumor metabolism could be distinguished from that of surrounding muscle by the appearance of inorganic phosphate and sugar phosphate resonances, reflecting tissue necrosis, and increased glycolysis. Tumor growth was accompanied by an increase in the size of these peaks, and the chemical shifts of the inorganic phosphate peak indicated that the intracellular pH became more acidic. Administration of methotrexate (i.v.) reversed these patterns and decreased tumor volume. Changes in the phosphocreatine peaks indicated changes in tumor volume rather than in tumor metabolism. These studies show that topical magnetic resonance not only can monitor the growth of tumors in vivo but can be also used to evaluate the efficacy of chemotherapeutic drugs.