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Purpose: BW 589C induces severe tumor hypoxia by modifying the affinity of oxyhemoglobin, causing a left shift of the oxygen-hemoglobin dissociation curve. 31 P magnetic resonance spectra (MRS) was used to monitor the effects of BW 589C on tumor energy metabolism in three experimental tumor models. Methods and Materials: HT-29 colon xenograft, murine transplantable RIF-1 fibrosarcoma and KHT sarcoma were studied in unanesthetised mice. 31 P MR spectra were acquired on a 4.7 Tesla magnet before administering oral BW 589C (250 mg/kg) and after 3, 6, and 24 h. Samples of tail vein blood were then taken for 2,3 DPG levels for RIF-1 and HT-29 tumors. Results: Doubling of inorganic phosphorus (P i ) to total phosphorus was observed 5–6 h after BW 589C for all three tumor types. Although the left shift due to BW 589C persists at 24 h, the level of P i to total phosphorus returned to baseline with no significant difference from control values for the RIF-1 and HT-29 tumors. These results suggest that there was cellular metabolic adaptation to the reduction of oxygen delivery by BW 589C. This does not appear to involve 2,3 DPG as there was no significant alteration in tumor levels. The death of hypoxic cells may, also, have contributed to the recovery of Pi to total phosphorus. Conclusion: The efficacy of bioreductive drugs can be enhanced by increasing the severity of tumor hypoxia. 31 P MRS in conjunction with other techniques for assessing the intratumor environment could play an important role in planning cancer therapy.

Large phosphomonoester (PME) signals are detected in the phosphorus magnetic resonance spectra (31P MRS) of many neoplastic and rapidly dividing tissues. In addition, alterations in phosphodiester (PDE) signals are sometimes seen. The present study of a murine lymphoma growing in liver showed a positive correlation between the hepatic PME/PDE ratio measured in vivo by 31P MRS at 4.7 T and the degree of lymphomatous infiltration in the liver, quantified by histology. High-resolution 31P MRS of liver extracts at 9.7 T showed that the PME peak consists largely of phosphoethanolamine (PE) and to a lesser extent of phosphocholine (PC). The concentration of both PE and PC increased positively with lymphomatous infiltration of the liver. In vivo, the PDE peak contains signals from phospholipids (mostly phosphatidylethanolamine and phosphatidylcholine) and the phospholipid breakdown products glycerophosphoethanolamine (GPE) and glycerophosphocholine (GPC). Low levels of GPE and GPC were detected in the aqueous extracts of the control and infiltrated livers; their concentrations remained unchanged as the infiltration increased. The total concentration of phospholipids measured by 31P MRS of organic extracts decreased about 3-fold as the infiltration increased to 70%. Thus, our data showed that the increased PME/PDE ratio in vivo is due to both an increase in the PME metabolites and a decrease in the PDE metabolites. We propose that this ratio can be used as a non-invasive measure of the degree of lymphomatous infiltration in vivo. Images Figure 2

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 31 P MRS where inorganic phosphate levels relative to total phosphate (Pi/total) were measured, and alteration in tumor blood volume was examined using 19 F MRS with perfluorooctylbromide (PFOB) as tracer. The integrated 19 F signal from PFOB is dose dependent and stable for at least 2 hr after injection. The murine tumors SCCVH/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 19 F 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.

Flunarizine and nicotinamide have previously been shown to increase blood perfusion to experimental mouse tumors and consequently, to increase their sensitivity to X rays. These agents were examined for their ability to alter metabolism, measured by 31P magnetic resonance spectroscopy, in the SCCVII/Ha carcinoma and the KHT sarcoma. Flunarizine at 5 mg/kg I.P. produced a 45% reduction in the ratio of inorganic phosphate to total phosphate (Pi/total) in the SCCVII/Ha tumor but only a 24% reduction in this ratio in the KHT tumor. These effects were seen 45 min after drug administration, and ratios returned to control levels by 90 min. In the SCCVII/Ha tumor, nicotinamide at 1000 mg/kg I.P. reduced Pi/total by 56% from 30 min to at least 2 hr after injection, and the ratio was reduced by 59% in the KHT tumor at 30 min after injection, returning to control levels by 2 hr. For the SCCVII/Ha tumor, the time course for the effects of flunarizine and nicotinamide on the inorganic phosphate ratio coincided with that previously reported for radiosensitization.

BACKGROUND One method of evaluating the mechanism of action of agents which alter tumor oxygenation is to determine their effects on tumor blood flow. PURPOSE This study tests applicability of a new approach using an emulsion of the inert fluorocarbon perfluorooctylbromide (PFOB) at nontoxic doses as a tracer in fluorine-19 (19F) nuclear magnetic resonance (NMR) spectroscopy to evaluate dynamic changes in vascular perfusion volume in transplanted tumors. METHODS The PFOB emulsion (100% wt/vol) was injected into the tail vein in tumor-bearing C3H/He or nu/nu mice immobilized in a magnet interfaced to a spectrometer, either as a single bolus injection of 8 mL/kg body weight or in multiple injections to a total dose of 24 mL/kg. A 7-mm external surface coil was placed over the tumor. Signal from the PFOB in the tumor volume seen by the coil rapidly reached equilibrium and was maintained for at least 2 hours, and multiple doses of PFOB emulsion resulted in a linear increase in 19F signal strength. Since the 19F signal strength was directly proportional to the perfusion volume of the tumor vasculature, reduction of signal intensity should correspond directly to any reduction in volume caused by a change in the tumor blood flow. To investigate this hypothesis, the vasoactive agent hydralazine (5 mg/kg) was injected intravenously after administering the PFOB emulsion to induce changes in tumor blood supply. KHT and RIF-1 murine sarcomas, the HT29 human colon carcinoma, and the HX118 human melanoma tumors were studied. In a comparative analysis of changes in blood flow induced by hydralazine, we studied Xe-133 clearance in KHT murine sarcoma and SCCVII/Ha (SCCVII) murine squamous cell carcinoma. RESULTS Hydralazine significantly reduced the 19F signal intensity in the murine tumors RIF-1 and KHT and in the HT29 human tumor, with little reduction in the SCCVII/Ha murine and HX118 human tumors. Hydralazine induced a statistically significant 64% decrease in mean clearance rate in the KHT tumor, while SCCVII/Ha tumors showed no significant change, indicating that hydralazine restricted blood flow to a greater extent in the tumor type that showed reduced 19F signal from the PFOB emulsion. CONCLUSION These data demonstrate the potential of PFOB emulsion as a tracer in NMR spectroscopy for studying tumor vasculature.

The biological response of some anti-cancer therapeutic agents is mediated via the tumour vasculature. These agents included photodynamic therapy (PDT), endocrine therapy, immunotherapy, hyperthermia, radio- and chemotherapies [1].

The effect of hydralazine on tumours appears to vary depending on tumour type. Blood flow and radiation sensitivity decrease more in murine tumours than human tumour xenografts. In this study a comparison between various tumour types has been made using in vivo 31P nuclear magnetic resonance spectroscopy (NMRS) to follow the metabolic responses occurring after clamping or intravenous administration of hydralazine (5 mg kg-1). Large increases in the Pi/total phosphate ratio were found with the murine sarcomas, KHT and RIF-1 implanted into C3H/He mice. However little or no effect was seen for the two human xenografted tumours, HX118 and HT29 implanted in MFI nu/nu/01a mice. An intermediate response was observed for KHT tumours grown in nu/nu mice. All tumours showed a large response to clamping. The anaesthetic Hypnorm/Hypnovel has a great influence on the response of the tumour metabolism to hydralazine appearing to both prolong and increase the changes induced. There is evidence to support the theory that the changes in 31P spectra are related to the oxygen status of the tumours.