The energy metabolism of RIF-1 tumours following hydralazine

Phosphorus-31 Magnetic Resonance Spectroscopy (MRS) was used to observe the effect of two doses of the vasodilator hydralazine on the energy status of RIF-1 tumours. An intravenous dose of 5 mg/kg hydralazine reduced the high energy phosphate metabolites PCr and ATP, lowered pHMRS and raised the levels of inorganic phosphate of tumours within 20 min of administering the drug. The levels of high energy metabolites continued to decrease for at least 24 h. Normal muscle spectra obtained up to 1 h after drug administration remained unchanged. An intravenous dose of 0.5 mg/kg hydralazine also reduced NTP/Pi and PCr/Pi levels of tumours up to at least 5 h after drug administration, but the effect was smaller than for the higher dose. Blood flow measurements and measurements of systemic blood pressure demonstrated that 5 mg/kg of hydralazine produced a reduction in both systemic blood pressure and tumour blood flow relative to most normal tissues investigated. It is concluded that the changes in the P-31 MRS spectra of tumours were due to a reduction in tumour vascular perfusion following administration of hydralazine.     

Early radiation effects in highly apoptotic murine lymphoma xenografts monitored by P magnetic resonance spectroscopy

Purpose: Phosphorus-31 magnetic resonance spectra (³¹P-MRS) were obtained from highly apoptotic murine lymphoma xenografts before and up to 24 hr following graded doses of radiation ranging from 2 to 30 Gy. Radiation-induced apoptosis was also estimated up to 24 hr by scoring apoptotic cells in tumor tissue.Methods and Materials: Highly apoptotic murine lymphoma cells, EL4, were subcutaneously transplanted into C57/BL mice. At 7 days after transplantation, radiation was given to the tumor with a single dose at 3, 10, and 30 Gy. The β-ATP/Pi, PME/Pi, and β-ATP/PME values were calculated from the peak area of each spectrum. Radiation-induced apoptosis was scored with counting apoptotic cells on hematoxylin and eosin stained specimens (%apoptosis).Results: The values of % apoptosis 4, 8, and 24 hr after radiation were 21.8, 19.6, and 4.6% at 3 Gy, 35.1, 25.6, and 14.8% at 10 Gy, 38.4, 38.0, and 30.6% at 30 Gy, respectively (cf. 4.4% in control). There was no correlation between early change in β-ATP/Pi and % apoptosis at 4 hr after radiation when most of the apoptosis occurred. An early decrease in PME/Pi was observed at 4 hr after radiation dose at 30 Gy. For each dose, the values of β-ATP/Pi 24 hr after radiation were inversely related to radiation dose.Conclusion: The increase in β-ATP/Pi observed by ³¹P-MRS was linked to the degree of histological recovery from radiation-induced apoptosis.     

Early radiation effects in highly apoptotic murine lymphoma xenografts monitored by 31P magnetic resonance spectroscopy

Purpose: Phosphorus-31 magnetic resonance spectra (³¹P-MRS) were obtained from highly apoptotic murine lymphoma xenografts before and up to 24 hr following graded doses of radiation ranging from 2 to 30 Gy. Radiation-induced apoptosis was also estimated up to 24 hr by scoring apoptotic cells in tumor tissue.Methods and Materials: Highly apoptotic murine lymphoma cells, EL4, were subcutaneously transplanted into C57/BL mice. At 7 days after transplantation, radiation was given to the tumor with a single dose at 3, 10, and 30 Gy. The β-ATP/Pi, PME/Pi, and β-ATP/PME values were calculated from the peak area of each spectrum. Radiation-induced apoptosis was scored with counting apoptotic cells on hematoxylin and eosin stained specimens (%apoptosis).Results: The values of % apoptosis 4, 8, and 24 hr after radiation were 21.8, 19.6, and 4.6% at 3 Gy, 35.1, 25.6, and 14.8% at 10 Gy, 38.4, 38.0, and 30.6% at 30 Gy, respectively (cf. 4.4% in control). There was no correlation between early change in β-ATP/Pi and % apoptosis at 4 hr after radiation when most of the apoptosis occurred. An early decrease in PME/Pi was observed at 4 hr after radiation dose at 30 Gy. For each dose, the values of β-ATP/Pi 24 hr after radiation were inversely related to radiation dose.Conclusion: The increase in β-ATP/Pi observed by ³¹P-MRS was linked to the degree of histological recovery from radiation-induced apoptosis.     

Correlations between in vivo tumor weight,oxygen pressure, 31P NMR spectroscopy,hypoxic microenvironment marking by beta-D-iodinated azomycin galactopyranoside (beta-D-IAZGP), and radiation sensitivity

PURPOSE: The purpose of this study is to evaluate the amount of hypoxic fraction in a rodent tumor by means of polarographic oxygen electrode, phosphorus-31 magnetic resonance spectroscopy (31P-MRS), and a newly synthesized hypoxic marker, beta-D-iodinated azomycin galactopyranoside (beta-D-IAZGP). We also investigated the radiosensitivity for tumors of different weights. METHODS AND MATERIALS: Murine mammary carcinoma cells, FM3A, were subcutaneously implanted into the back of 5-week-old male C3H/He mice. beta-D-IAZGP radiolabeled with 123I or with 125I was injected intravenously into tumor-bearing mice, and marker distribution was measured by nuclear medicine procedures. Radiosensitivity of the tumor was measured by the in vivo/in vitro clonogenic assay. Tumor oxygenation status was also measured directly by polarographic oxygen electrodes and indirectly estimated from 31P-MR spectra. RESULTS: Higher accumulation of 123I-beta-D-IAZGP was observed in the tumors than in normal tissues at 24 h after administration. As to biodistribution of 125I-beta-D-IAZGP, the tumor/blood ratio varied widely, but correlated significantly with tumor weight. Mean oxygen pressure (pO2) values and ratios of nucleoside triphosphate beta to inorganic phosphate (beta-ATP/Pi) and of phosphocreatine to inorganic phosphate (PCr/Pi) decreased significantly with the increase in tumor volume. As tumor volume increased, the surviving fraction of cells from tumors irradiated in vivo increased significantly. CONCLUSIONS: The increase in tumor volume was significantly correlated with a reduction in mean pO2, a decrease in the ratios of beta-ATP/Pi or PCr/Pi, an increase in uptake of beta-D-IAZGP, and an increase in radioresistance. Because the uptake of beta-D-IAZGP can be measured noninvasively by nuclear medicine techniques, it could be clinically useful for monitoring hypoxia in human tumors.     

Correlations between in vivo 31P NMR spectroscopy measurements, tumor size, hypoxic fraction and cell survival after radiotherapy

Phosphorus metabolite levels were measured non-invasively using 31P magnetic resonance spectroscopy (MRS) in SCCVII/SF tumors, subcutaneously transplanted into the legs of unanesthetized C3Hf/Sed mice. Shortly after MRS measurements, tumors were irradiated with a single dose of 20 Gy, and cell survival and radiobiologic hypoxic fraction were determined with an in vitro cloning assay. Significant correlations were found between tumor size and surviving fraction, hypoxic fraction, pH, and phosphorus metabolite ratios. With increase of tumor size, surviving fraction and hypoxic fraction both increased, the ratios of inorganic phosphate and phosphomonoesters to nucleoside triphosphates (Pi/NTP and PME/NTP, respectively) and inorganic phosphate to phosphocreatine (Pi/PCr) increased and pH decreased. However, considerable heterogeneity of MRS spectral parameters, even in tumors of similar size, precluded accurate prediction of hypoxic fraction and cell survival after radiotherapy.     

Quantitative changes in tumor metabolism, partial pressure of oxygen, and radiobiological oxygenation status postradiation.

Hypoxia is considered to be a major cause of tumor radioresistance. Reoxygenation of previously hypoxic areas after a priming dose of radiation is associated with an increase in tumor radiosensitivity. In a study of a hypoxic mammary carcinoma, 31P nuclear magnetic resonance spectra showed statistically significant increases in metabolite ratios (phosphocreatine/Pi and nucleotide triphosphate/Pi) after 65 and 32 Gy. The maximum changes in metabolite ratios after 32 Gy occurred at 48 h, although significant changes were detected at 24 h. A corresponding increase in the mean tumor pO2 (polarographic microelectrode measurements) and a decrease in hypoxic cell fraction [changes in paired (clamped versus unclamped) tumor control dose for 50% of tumors] were also shown to occur 48 h after a priming dose of 32 Gy. A significant increase in the mean tumor pO2, phosphocreatine/Pi, and nucleotide triphosphate/Pi, compared to initial values, was noted at 24, 48, and 96 h post 65-Gy radiation. An increase in the downfield component of the phosphomonoester peak relative to the upfield component (phosphoethanolamine), is also noted after doses of 65 and 32 Gy. These are likely to be due to cell kill and/or decreased cell proliferation. In this tumor model, 31P nuclear magnetic resonance spectroscopic changes postradiation are temporally coincident with and may be indicative of tumor reoxygenation as measured by the tumor control dose for 50% of tumors and oxygen-sensitive microelectrodes.     

Different early effect of irradiation in brain and small cell lung cancer examined by in vivo 31P-magnetic resonance spectroscopy.

Early effects of irradiation were evaluated by non-invasive in vivo 31P-magnetic resonance spectroscopy (31P-MRS) of two small cell lung cancer (SCLC) tumor lines CPH SCCL 54A and 54B, in nude mice. The tumors were originally derived from the same patient and have similar morphology and growth characteristics, but a different radiosensitivity. The 54A tumors are twice as radiosensitive as the 54B's. In the present study the tumors were treated with 2.5, 10, and 40 Gy. For comparison, nude mice were given cranial irradiation at the same three doses, and the effect was evaluated by in vivo 31P-MRS. No effect was observed in brain at any dose level. In contrast, 40 Gy induced a statistically significant reduction in ATP/Pi ratio during the 12-h post-irradiation period. This effect was more pronounced in 54A than in 54B. Some reduction was observed following 10 Gy, whereas 2.5 Gy induced no changes in ATP/Pi. The differential effect on tumors and brain might be relevant for monitoring irradiation effects by in vivo 31P-MRS in patients with brain metastases.     

In vivo 31P-nuclear magnetic resonance study of the response of a murine mammary tumor to different doses of gamma-radiation

The response of the s.c. implanted murine mammary carcinoma NU-82 to 10 and 20 Gy of gamma-radiation was followed by in vivo 31P-nuclear magnetic resonance spectroscopy on 48 mice during a period of 2 days. During the first 8 h after a dose of 10 Gy, the ratio of ATP/inorganic phosphate increases to a value of 120 +/- 15% (SE) of the control value. This rise is followed by a decrease of the ratio to 74 +/- 12% after 47 h. However treatment with 20 Gy causes the ratio of ATP/Pi to decrease gradually to a level of 45 +/- 7% after 47 h. Histological investigations demonstrated that radiation-induced necrosis largely contributes to this phenomenon. During the time of observation irradiated tumors displayed no changes in size and intracellular pH. After treatment with 10 Gy as well as with 20 Gy, the phosphodiester resonance decreased in intensity. By 31P-nuclear magnetic resonance spectroscopy on extracts of the NU-82 tumor, two phosphodiesters were identified, glycerophosphocholine and glycerophosphoethanolamine.     

Effects of hydralazine on in vivo tumor energy metabolism, hematopoietic radiation sensitivity, and cardiovascular parameters

Energy metabolism of murine FSaII foot tumors was studied by in vivo 31P-MRS in C3Hf/Sed mice. Spectroscopy was performed following exposure to escalating doses of hydralazine (HYD) ip. At 0.25 mg/kg, HYD caused a 20% increase in PCr/Pi and had no significant effect on mean arterial blood pressure. HYD doses greater than or equal to 2 mg/kg lead to hypotension which was associated with a decrease in PCr, NTP, pH, and an increase in Pi (p less than 0.01 for control vs 10 mg/kg HYD). When mice were given ip injections of HYD (0.25, 1, 2 and 10 mg/kg) 10 min prior to whole body irradiation, spleen stem cell survival after 6 Gy was increased (2.19 colonies in control animals vs 6.74 colonies per spleen in animals treated with greater than or equal to 2 mg/kg HYD), as was the LD50/30 dose (6.49 Gy [control] vs 9.00 Gy [10 mg/kg HYD]). The data provide evidence that PCr/Pi is a useful indicator of perfusion efficiency (and indirectly of hypoxic cell fraction) in FSaII tumors. These observations suggest that HYD may be a useful adjuvant for hyperthermic treatment of tumors and for potentiation of agents specifically toxic to hypoxic or nutrient-deprived cancer cells. HYD should be used with care in patients receiving radiation treatments or other therapies for which hypoxia can unfavorably affect treatment outcome.     

Monitoring of tumor reoxygenation following irradiation by 31P magnetic resonance spectroscopy: an experimental study of human melanoma xenografts.

BACKGROUND AND PURPOSE: Inadequate tumor reoxygenation during radiation therapy may cause local treatment failure. This study was aimed at investigating the potential usefulness of 31P-MRS in monitoring tumor reoxygenation following radiation treatment. MATERIALS AND METHODS: Tumors of two human melanoma xenograft lines (BEX-t and HUX-t) were exposed to 15.0 Gy, and then the fraction of radiobiologically hypoxic cells, measured by using the paired survival curve method, or tumor bioenergetic status, measured by 31P-MRS as the (PCr + NTPbeta)/Pi resonance ratio, was determined versus time after the radiation exposure. RESULTS: Untreated BEX-t and HUX-t tumors showed similar fractions of radiobiologically hypoxic cells and similar bioenergetic status, whereas both parameters differed substantially between the lines in irradiated tumors. A close association was found between radiation-induced changes in tumor bioenergetic status and radiation-induced changes in the fraction of radiobiologically hypoxic cells. CONCLUSION: 31P-MRS is a potentially useful method for monitoring tumor reoxygenation following radiation treatment.     

Tumor size dependent changes in a murine fibrosarcoma: use of in vivo 31P NMR for non-invasive evaluation of tumor metabolic status

Tumor tissue contains viable hypoxic regions that are radioresistant and often chemoresistant and may therefore be responsible for some treatment failures. A subject of general interest has been the development of non-invasive means of monitoring tissue oxygen. Pulse Fourier transform 31P NMR spectroscopy can be used to estimate intracellular nucleotide triphosphates (NTP), phosphocreatinine (PCr), inorganic phosphate (Pi) and pH. We have obtained 31P NMR spectra as an indirect estimate of tissue oxygen and metabolic status in a C3H mouse fibrosarcoma FSaII. Sequential spectra were studied during tumor growth in a cohort of animals and peak area ratios for several metabolites were computed digitally by computer. During growth, tumors showed a progressive loss of PCr with increasing Pi, and most tumors greater than 250 mm3 in volume had little or no measurable PCr. The smallest tumors (38 mm3 average volume) had PCr/Pi ratios of 1.03 +/- .24, whereas tumors 250 mm3 or more had an average PCr/Pi ratio of 0.15 +/- .04. Similarly derived NTP/Pi ratios decreased with tumor size, but this change was not significant (p = .17). Radiobiologic hypoxic cell fractions were estimated using the radiation dose required to control tumor in 50% of animals (TCD50) or by the lung colony technique. Tumors less than 100 mm3 had a hypoxic cell fraction of 4% (TCD50) while tumors 250 mm3 had a 40% hypoxic cell fraction (lung colony assay). These hypoxic fraction determinations correlated well with the depletion of PCr and decline in NTP/Pi ratios seen at 250 mm3 tumor volumes. Tumor spectral changes with acute ischemia were studied after ligation of the tumor bearing limb and were similar to changes seen with tumor growth. PCr was lost within 7 minutes, with concurrent increase in Pi and loss of NTP. Complete loss of all high energy phosphates occurred by 40 minutes of occlusion. In vivo tumor 31P NMR spectroscopy can be used to estimate tissue metabolic status and may be useful in non-invasive prediction of hypoxic cell fraction, reoxygenation, and radiation treatment response.     

31Phosphorus-magnetic resonance spectroscopy to assess histologic tumor response noninvasively after isolated limb perfusion for soft tissue tumors

BACKGROUND: In patients with unresectable soft tissue sarcoma of the extremities, isolated limb perfusion (ILP) has been reported to result in significant tumor regression enabling limb-sparing resection in the majority of patients. However, clinical tumor response as evaluated by imaging and histopathology (extent of tumor necrosis) often differ significantly. The current study was initiated to evaluate prospectively the role of 31phosphorus-magnetic resonance spectroscopy (31P-MRS) in the noninvasive assessment of histologic response in patients treated with ILP. METHODS: Thirty-two patients with locally advanced and unresectable soft tissue tumors (sarcoma in 28 patients and bulky melanoma in 4 patients) were treated by ILP with recombinant human tumor necrosis factor-alpha and melphalan or with cytostatics. 31P-MRS was performed prior to treatment and at regular intervals after ILP until definite tumor resection. Clinical response parameters according to the World Health Organization as well as the histopathologic necrosis rate of the resection specimen were correlated with changes in the energy-rich phosphorous metabolites phosphocreatine (PCR); alpha-, beta-, gamma-adenosine triphosphate (ATP); phosphomonoesters (PME); and inorganic phosphate (Pi). RESULTS: Clinically, 15 of 32 patients (response rate [RR] of 47%) demonstrated a partial response (PR). The ratios of PME/PCR and PME/beta-ATP decreased significantly after ILP in comparison with preoperative values (P < 0.001). The changes in the PME/beta-ATP ratio were significantly different between clinical responders and nonresponders (P < 0.02) in contrast with the PME/PCR ratios (P < 0.09). Histologic necrosis of > 90% (pathologic (p) PR) was present in 17 resection specimens, 7 of which demonstrated no clinical response. Seven tumors demonstrated a pathologic complete response (pCR). When combining PR, pPR, and pCR (RR of 68%), 31P-MRS was able to predict response with a specificity of 94% and a sensitivity of 68% (P < 0.006, by the chi-square test). CONCLUSIONS: The considerable difference between clinical and pathologic RR after ILP underlines the shortcomings of established response criteria. Utilizing changes in PME/beta-ATP ratios, 31P-MRS is a highly specific tool with which to predict histologic response in this setting. This finding may be of major value in those patients in whom the decision to perform a major resection or amputation must be made for local tumor control.     

Size dependent changes in tumor phosphate metabolism after radiation therapy as detected by 31P NMR spectroscopy

In Vivo 31P NMR spectroscopy was used to study changes in phosphate metabolism that occur after irradiation of the C3H fibrosarcoma, FSaII. Previously, we have shown that small FSaII tumors (less than 250 mm3) have a greater phosphocreatinine/inorganic phosphate (PCr/Pi) ratio and a lower hypoxic cell fraction (HCF) than large FSaII tumors (greater than 250 mm3). Six small tumors (113 +/- 26 mm3) were treated with radiation doses chosen to induce local control in greater than 50% of animals, (70-100 Gy, single fraction). Minimal changes in the tumor 31P NMR spectrum were seen over eight days of monitoring. During this interval, tumor regression began a minimum of 36 hours after radiation. This contrasted with large tumors (650-1000 mm3) wherein a significant increase in the Pcr/Pi ratio was seen 44 hr after irradiation. In tumors of this size range, a tumor growth delay of 4 to 7 days is obtained after a single 70 Gy fraction of radiation. Since small FSaII tumors have a minimal HCF (approximately equal to 4%), radiation induced reoxygenation would not be expected to have a large effect on their average cellular metabolism. Large tumors of this histology have a high HCF (greater than or equal to 40%), and may therefore be expected to have a significant average change in tumor cell metabolism with reoxygenation. The 31P NMR observations of small and large tumors after irradiation are compatible with radiation induced reoxygenation in the larger tumors.     

Enhancement of antitumor effect of hyperthermia with glucose administration in murine mammary carcinoma

Antitumor effects of hyperthermia are enhanced by lowering the pH in the tumor tissue with administration of glucose. This decreased pH in the tumor tissue with glucose administration was determined using mouse experimental tumors. 31P-MRS microelectrodes were used for the measurement of pH. By using these two measurement methods, time course change in the tumor tissue was determined in the controls and the groups treated with 6 g/kg of intraperitoneal glucose. The determination of pH with 31P-MRS was calculated from the chemical shift of the peak of creatine phosphate (Pcr) and that of inorganic phosphate (Pi). Following glucose administration, the tumor tissue showed a decrease of 0.3 pH units with the microelectrode method, but did not show any significant decrease in pH with the MRS determination. This finding suggested that 31P-MRS showed intracellular pH (pHi) due to the localization of Pi and that the microelectrode indicated interstitial or extracellular pH (pHe). The ATP/Pi ratio obtained in tumor tissue 24 h after heat treatment (with, without glucose) was correlated with tumor inhibition.     

Integrated magnetic resonance imaging and phosphorus spectroscopy of soft tissue tumors

Eighteen patients with soft tissue masses underwent integrated magnetic resonance imaging (MRI) and phosphorus spectroscopy (31P-MRS) to evaluate benign and malignant tumor morphology and metabolism. Spectra from soft tissue tumors had a significantly higher proportion of phosphate in the low-energy portion of the 31P spectrum (P less than 0.001) with a concomitant decrease in phosphocreatine (P less than 0.01) compared with 31P spectra from normal muscle. Malignant tumors had a mean pH of 7.35 +/- 0.13 which was greater than that of muscle tissue with a mean pH of 7.08 +/- 0.07 (P less than 0.001). All tumors had greater relative levels of phosphomonoesters, inorganic phosphate, and phosphodiesters compared with those in muscle tissue but considerable variability among tumors was noted due to tumor size, extent of tumor necrosis, and muscle contamination. Integrated MRI/MRS studies are necessary to provide exact localization of the tumor and a more correct interpretation of the 31P-MRS data.     

Megavoltage external beam irradiation of craniopharyngiomas: analysis of tumor control and morbidity

From 1971 to 1985, 21 patients received megavoltage external beam radiation therapy at the University of Pittsburgh for control of craniopharyngioma. Minimum tumor doses prescribed to the 95% isodose volume ranged between 51.3 to 70.0 Gy. Median total dose was 60.00 Gy and median dose per fraction was 1.83 Gy. Three deaths occurred from intercurrent disease and no deaths from tumor progression. Actuarial overall survival was 89% and 82% at 5 and 10 years. Actuarial local control was 95% at 5 and 10 years. Radiation related complications included one patient with optic neuropathy, one with brain necrosis, and one that developed optic neuropathy followed by brain necrosis. The high dose group of patients who received a NSD or Neuret equivalent of greater than 60 Gy at 1.8 Gy per fraction had a significantly greater risk of radiation complications (p = .024). The actuarial risk at 5 years for optic neuropathy was 30% and brain necrosis was 12.5% in the high dose group. Tumor control in the high dose group was not shown to be significantly better. Any possible benefit in tumor control in treating patients with craniopharyngioma with doses above 60 Gy at 1.8 Gy per fraction appears to be offset by the increased risk of radiation injury.     

Measurements of in vivo 31P nuclear magnetic resonance spectra in neuroectodermal tumors for the evaluation of the effects of chemotherapy

The effects of chemotherapy on living tumor tissue in hamsters and rats were investigated by measuring the 31P nuclear magnetic resonance spectra using topical magnetic resonance. Human neuroblastoma, human glioblastoma, and rat glioma tumor cells were inoculated s.c. in the lumbar region of the animals. After the diameter of the tumors increased to 1.5 cm, in vivo 31P nuclear magnetic resonance spectra were measured selectively in the tumors with a TMR-32 spectrometer. Adenosine triphosphate, inorganic phosphate (Pi), phosphodiester, and phosphomonoester peaks were observed. The phosphocreatine peak was hardly detectable, adenosine triphosphate and phosphomonoester peaks were high, and tissue pH, calculated from the chemical shift of Pi, declined. Regardless of the tumor origin or the histological type, the spectral pattern of each neuroectodermal tumor was found to be essentially the same. After i.v. injection of a large dose of a chemotherapeutic agent, adenosine triphosphate peaks decreased and Pi increased gradually, resulting in a dominant Pi peak pattern after 6 to 12 hours. However, during the same period, there were no observable changes in the spectra of normal organs. These findings indicated that the drugs have a selective and direct action on the energy metabolism of tumor cells. With lower drug doses, no remarkable changes were seen in the spectrum. Measurement of in vivo 31P nuclear magnetic resonance spectra is valuable not only to investigate the energy metabolism in tumor tissue but also to evaluate the effects of chemotherapy.     

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.     

Modification of the 31P magnetic resonance spectra of a rat tumour using vasodilators and its relationship to hypotension

The effects of different doses of hydralazine and prostacyclin on the 31P magnetic resonance spectra of the LBDS1 fibrosarcoma were investigated and related to their effects on mean arterial blood pressure (MABP) and heart rate. The effect of reducing MABP by bleeding the animals, via the tail artery, was also investigated. Tumour spectral changes following high dose drug treatment (an increase in inorganic phosphate, a reduction in nucleotide triphosphates and a reduction in pH) were consistent with nutrient deprivation. These changes were dose dependent. Changes in MABP and heart rate were consistent with vasodilatation in normal tissues. However, for the same fall in MABP, hydralazine produced a greater rise in tumour inorganic phosphate (Pi) and a greater fall in tumour pH than did prostacyclin. Controlled bleeding was effective in reducing MABP. It also reduced tumour pH but had no significant effect on tumour Pi. The clinical application of the two drugs for reducing tumour blood flow and pH for therapy is likely to be limited by the large degree of hypotension necessary to produce an effect. The differential effect of the two drugs for the same fall in MABP may be related to different degrees of direct tumour vasodilatation or to a direct effect of hydralazine on tumour energy metabolism. The observation that controlled bleeding does not change tumour Pi is further evidence indicating that the degree of arterial hypotension is not the sole factor in determining tumour energy status.     

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

The effect of 100% inspired oxygen on in vivo tumor metabolism was examined using phosphorus-31 (31P) NMR spectroscopy. Isotransplants of two murine tumor histologies, designated MCaIV (C3H mammary adenocarcinoma) and FSaII (C3H fibrosarcoma), were used in syngeneic mice. Tumor volumes ranged from 30 to 1,800 mm3. Both tumor histologies are known to have a high hypoxic cell fraction when tumor volumes exceed 250 mm3. 31P nuclear magnetic resonance (NMR) spectra were obtained at 145.587 MHz, and the signal was detected using a 1.4 cm diameter, single loop coil designed to localize the signal from only the tumor. Spectral parameters for optimal signal-to-noise ratio (SNR) included a 60 degrees pulse and a 2-second recycle delay. Tumors were implanted in the hindfoot dorsum to assure that all detected mobile phosphates were of tumor origin. Phosphocreatine/inorganic phosphate (PCr/Pi) ratios of large tumors (greater than 250 mm3) were reduced compared with small tumors (less than 250 mm3) of the same histology. The increased PCr/Pi response to 100% inspired oxygen was greater for large tumors and for tumors with lower baseline PCr/Pi ratios. When host animals were given 10% oxygen for respiration, there was an increase in Pi and a decrease in both PCr and ATP. The response to 10% oxygen was observed in both large and small tumors of both tumor histologies studied. Resting skeletal muscle exhibited no alteration in the NMR spectrum during either 100 or 10% oxygen breathing. We conclude that the fractional increase in PCr/Pi ratio that occurs after 100% oxygen breathing is a sensitive, noninvasive method of detecting tumor hypoxia.