Magnetic resonance spectroscopy studies on experimental murine and human tumors: comparison of changes in phosphorus metabolism with induced changes in vascular volume.

The responses of two experimental murine tumors and two human tumor xenografts to the vasodilator hydralazine were compared using two magnetic resonance spectroscopy endpoints. Changes in tumor metabolism were determined using 31P MRS where inorganic phosphate levels relative to total phosphate (Pi/total) were measured, and alteration in tumor blood volume was examined using 19F MRS with perfluorooctylbromide (PFOB) as tracer. The integrated 19F signal from PFOB is dose dependent and stable for at least 2 hr after injection. The murine tumors SCCVII/Ha and KHT both showed changes in tumor metabolism after hydralazine, as an increase in Pi/total. However, hydralazine reduced vascular volume in the KHT tumor, demonstrated by reduced 19F signal from PFOB, but no such reduction was seen in the SCCVII/Ha tumor. In contrast, hydralazine had no effect on phosphorus metabolism in the HT29 and HX118 human tumor xenografts, but reduced vascular volume in both tumors. These results demonstrate that the effects of vasoactive agents such as hydralazine on tumor phosphorus metabolism are only partially consistent with changes in vascular volume, measured by the 19F MRS technique.