Effects of oxygen on the metabolism of murine tumors using in-vivo P-31 NMR

The effect of 100% inspired oxygen on in vivo tumor metabolism was examined using /sup 31p/. Isotransplants of murine tumors, MCaIV (mammary adenocarcinoma) and FSaII, (fibrosarcoma), were used. Tumor volumes ranged from 30 to 1800 mm/sup 3/. Both tumors have a high hypoxic cell fraction at >250mm/sup 3/. NMR spectra were obtained using a narrow bore superconducting magnet operating at 145.587 MHz for Phosphorus-31. Tumors were implanted in the hind food dorsum to assure all detected mobile phosphates were of tumor origin. PCr/Pi ratios of tumors >250mm/sup 3/ were reduced compared with tumors <250mm/sup 3/ of the same histology. Response to 100% inspired oxygen was greater for large tumors, and for tumors with lower baseline PCr/Pi ratios. Respiration of 10% oxygen increased Pi and decreased PCr and ATP. The response to 10% oxygen was observed in both large and small tumors of both histologies. The fractional increase in PCr/Pi ratio after 100% oxygen breathing appears to be a non-invasive method of detecting tumor hypoxia