The energy metabolism of RIF-1 tumours following hydralazine

Hydralazine-augmented contrast ultrasound imaging improves the detection of hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) detection with B-mode and contrast-enhanced ultrasound (CUS) imaging often varies between subjects, especially in patients with background cirrhosis. Various factors contribute to this variability, including the tumor blood flow, tumor size, internal echoes, and its location in livers with diffuse fibro-cirrhotic changes.

OBJECTIVE

Towards improving lesion detection, this study evaluates a vasodilator, hydralazine, to enhance the visibility of HCC by reducing its blood flow relative to the surrounding liver tissue.

METHODS

HCC were analyzed for tumor visibility measured for B-mode, CUS, and hydralazine-augmented-contrast ultrasound (HyCUS) in an autochthonous HCC rat model. 21 tumors from 12 rats were studied. B-mode and CUS images were acquired before hydralazine injection. Rats received an intravenous hydralazine injection of 5 mg/kg, then images were acquired 20 min later. Four rats were used as controls. The difference in echo intensity of the lesion and the surrounding tissue was used to determine the visibility index (VI).

RESULTS

The visibility index for HCC was found to be significantly improved with the use of HyCUS imaging compared to traditional B-mode and CUS imaging. The visibility index for HCC was 16.5 ± 2.8 for HyCUS, compared to 5.3 ± 4.8 for B-mode and 4.1 ± 3.8 for CUS. The differences between HyCUS and the other imaging modalities were statistically significant, with p-values of 0.001 and 0.02, respectively. Additionally, when compared to control cases, HyCUS showed higher discrimination of HCC (VI = 6.4 ± 1.2) with a p-value of 0.003, while B-mode (VI = 6.7 ± 1.4, p = 0.5) and CUS (VI = 6.4 ± 1.2, p = 0.3) showed lower discrimination.

CONCLUSION

Vascular blood flow modulation by hydralazine enhances the visibility of HCC. HyCUS offers a potential problem-solving method for detecting HCC when B-mode and CUS are unsuccessful, especially with background fibro-cirrhotic liver disease. Future evaluation of the approach in humans will determine its translatability for clinical applications.

Deuterium MR Spectroscopy at 4.7 T

Deuterium MR spectroscopy was used for the determination of tissue blood flow (TBF). The tracer D2O was injected into the tissue of interest, and tracer washout was followed using a 4.7 T spectroscopy/imaging unit. Normal subcutaneous tissue in rats was studied, as well as tissue influenced by vasoactive agents (papaverine and adrenaline). The vasoactive agents introduced changes of 40% in TBF, compared with normal tissue. Normal tissue measurements were repeated using various D2O injection volumes (5–400 μl). The injection volume 5 μl gave TBF 11.7 ± 2.0 ml/100 g·min (mean ± 1 SD). This value was 40% higher than corresponding values observed at larger injection volumes (200–400 μl). This injection volume effect is probably partly due to a capillary dilution caused by tracer administration, and partly related to the non-physiological deuterium signal decrease observed in dead rats. Blood flow measurements in human colon tumours implanted in nude mice showed a rather poor reproducibility, not improved by the use of a multiple site injection technique.

Evaluation of the "steal" phenomenon on the efficacy of hypoxia activated prodrug TH-302 in pancreatic cancer

Pancreatic ductal adenocarcinomas are desmoplastic and hypoxic, both of which are associated with poor prognosis. Hypoxia-activated prodrugs (HAPs) are specifically activated in hypoxic environments to release cytotoxic or cytostatic effectors. TH-302 is a HAP that is currently being evaluated in a Phase III clinical trial in pancreatic cancer. Using animal models, we show that tumor hypoxia can be exacerbated using a vasodilator, hydralazine, improving TH-302 efficacy. Hydralazine reduces tumor blood flow through the "steal" phenomenon, in which atonal immature tumor vasculature fails to dilate in coordination with normal vasculature. We show that MIA PaCa-2 tumors exhibit a "steal" effect in response to hydralazine, resulting in decreased tumor blood flow and subsequent tumor pH reduction. The effect is not observed in SU.86.86 tumors with mature tumor vasculature, as measured by CD31 and smooth muscle actin (SMA) immunohistochemistry staining. Combination therapy of hydralazine and TH-302 resulted in a reduction in MIA PaCa-2 tumor volume growth after 18 days of treatment. These studies support a combination mechanism of action for TH-302 with a vasodilator that transiently increases tumor hypoxia.

Molecular Imaging of Cancer: Applications of Magnetic Resonance Methods

Cancer is a complex disease exhibiting a host of phenotypic diversities. Noninvasive multinuclear magnetic resonance imaging (MRI) and spectroscopic imaging (MRSI) provide an array of capabilities to characterize and understand several of the vascular, metabolic, and physiological characteristics unique to cancer. The availability of targeted contrast agents has widened the scope of MR techniques to include the detection of receptor and gene expression. In this paper, we have highlighted the application of several MR techniques in imaging and understanding cancer.

Effects of nicotinamide and carbogen on tumour oxygenation, blood flow, energetics and blood glucose levels

Both host carbogen (95% oxygen/5% carbon dioxide) breathing and nicotinamide administration enhance tumour radiotherapeutic response and are being re-evaluated in the clinic. Non-invasive magnetic resonance imaging (MRI) and 31P magnetic resonance spectroscopy (MRS) methods have been used to give information on the effects of nicotinamide alone and in combination with host carbogen breathing on transplanted rat GH3 prolactinomas. Gradient recalled echo (GRE) MRI, sensitive to blood oxygenation changes, and spin echo (SE) MRI, sensitive to perfusion/flow, showed large signal intensity increases with carbogen breathing. Nicotinamide, thought to act by suppressing the transient closure of small blood vessels that cause intermittent tumour hypoxia, induced a small increase in blood oxygenation but no detectable change in perfusion/flow. Carbogen combined with nicotinamide was no more effective than carbogen alone. Both carbogen and nicotinamide caused significant increases in the nucleoside triphosphate/inorganic phosphate (betaNTP/Pi) ratio, implying that the tumour cells normally receive sub-optimal substrate supply, and is consistent with either increased glycolysis and/or a switch to more oxidative metabolism. The most striking observation was the marked increase in blood glucose (twofold) induced by both nicotinamide and carbogen. Whether this may play a role in tumour radiosensitivity has yet to be determined.

pH and drug resistance in tumors

Uptake of weakly ionizing drugs by tumours is greatly influenced by the interstitial and intracellular pH, and the ionization properties of the drug. Extracellular pH in tumors is acidic, while the intracellular pH is in the neutral-to-alkaline range. Tumors of the bladder, kidney and gastrointestinal system in particular are exposed to extremes of pH. Strategies for exhancing and exploiting acid-outside plasmalemmal pH gradients to drive the uptake of weak acid drugs into tumors are discussed, as are techniques for alkalinizing tissues to improve response to weak base drugs. The participation of acidic intracellular vesicles in non-specific drug resistance is explored. Copyright 2000 Harcourt Publishers Ltd.

Localized in vivo 1H NMR spectroscopy of murine tumours: effect of blood flow reduction

Single voxel 1H localized spectroscopy (PRESS at 300 MHz) was used to monitor physiological and biochemical changes induced by hydralazine (5 mg/kg, i.p.) in murine C3H mammary tumours. In addition to a significant increase (by 52%, maximal at 30 min) in the intensity of the 1.32 ppm signal (predominantly from lactate, consistent with a selective reduction in tumour blood supply by hydralazine), downfield shifts in the resonance frequencies of 1H signals were observed. In particular, the signal initially at 3.24 ppm (total choline, tCho) shifted by 0.050 ppm (maximal at 13 min), whereas water shifted by 0.086 ppm. Lactate intensity and water and tCho resonance frequencies returned to control values at approximately 100 min after treatment. No significant changes in the resonance frequencies of water or tCho were observed over this time period in the tumours of mice given saline. In vitro studies showed that, while the resonance frequency of water was temperature dependent, the main components of the tCho signal (choline, phosphorylcholine and glycerophosphorylcholine) were more than 30-fold less sensitive to temperature. It was concluded that the shift in the water resonance frequency was due to the combined effects of tumour temperature reduction and a paramagnetic shift from increased deoxyhaemoglobin levels, whereas the tCho signal was only affected by the paramagnetic shifts.

Hypoxic cell cytotoxin tirapazamine induces acute changes in tumor energy metabolism and pH: a 31P magnetic resonance spectroscopy study

Tirapazamine is a hypoxic cell cytotoxin in phase II/III trials. To further understand its mechanism of action in vivo, we examined the effect of tirapazamine on tumor energy metabolism and pH. RIF-1 and SCCVII tumors were grown subcutaneously in the flanks of C3H mice. Tumor energy metabolism, expressed as the ratio of inorganic phosphate to nucleotide triphosphate (Pi/NTP), and intracellular pH (pHi), were measured by 31P magnetic resonance spectroscopy (MRS). In RIF-1 and SCCVII tumors, tirapazamine increased the Pi/NTP ratio by 2.6-fold and 3-fold, respectively, within the first hour after an intraperitoneal dose of 0.3 mmol/kg. A corresponding decrease in pHi from 7.05+/-0.07 to 6.48+/-0.06, and 7.21+/-0.09 to 6.45+/-0.02 in RIF-1 and SCCVII tumors, respectively, was observed. The decrease in tumor 31P bioenergetics and pH was reversible, as exemplified by RIF-1 tumors, which showed a further increase in Pi/NTP ratio of 3.5-fold by 5-8 hr, returning to normal range at 24 hr. Corresponding pHi of RIF-1 tumors was 6.88+/-0.05 at 5-8 hr and 7.16+/-0.05 at 24 hr. We concluded that tirapazamine induces acute changes in tumor energy metabolism and pHi. These findings are relevant to the rational selection and optimal timing of coadministered therapy.

31P-magnetic resonance spectroscopy and 2H-magnetic resonance imaging studies of a panel of early-generation transplanted murine tumour models

The objective of this study was first to determine whether three slowly growing early-generation murine transplantable tumours, the T40 fibrosarcoma, T115 mammary carcinoma and T237 lung carcinoma, exhibit patterns of energetics and blood flow during growth that are different from those of the faster growing RIF-1 fibrosarcoma. Serial measurements were made with 31P-magnetic resonance spectroscopy (MRS), relating to nutritive blood flow and 2H-magnetic resonance imaging (MRI), which is sensitive to both nutritive and large-vessel (non-nutritive) flow. All four tumour lines showed a decrease in betaNTP/Pi and pH with growth; however, each line showed a different pattern of blood flow that did not correlate with the decrease in energetics. Qualitative histological analysis strongly correlated with the 2H-MRI. Second, their response to 5 mg kg(-1) hydralazine i.v. was monitored by 31P-MRS. A marked decrease in betaNTP/Pi and pH was observed in both the RIF-1 fibrosarcoma and the third-generation T115 mammary carcinoma after hydralazine challenge. In contrast, the fourth generation T40 fibrosarcoma and T237 lung carcinoma showed no change in 31P-MRS parameters. However, a fifth-generation T237 cohort, which grew approximately three times faster than fourth-generation T237 cohorts, exhibited a significant deterioration in betaNTP/Pi and pH in response to hydralazine. These data are consistent with a decoupling between large-vessel and nutritive blood flow and indicate that early-generation transplants that have a slow growth rate and vascular tone are more appropriate models of human tumour vasculature than more rapidly growing, repeatedly transplanted tumours.

Nuclear magnetic resonance spectroscopy of cancer

Nuclear magnetic resonance spectroscopy (MRS) offers a non-invasive approach for studying tumour biochemistry and physiology. This review highlights NMR nuclei (31P, 1H, 19F, 13C, 2H) that have been observed in both pre-clinical and clinical spectroscopic studies of cancer.

Effects of blood flow modifiers on tumor metabolism observed in vivo by proton magnetic resonance spectroscopic imaging

Perfusion plays a key role in tumor proliferation and therapeutic response. Tumor heterogeneity necessitates use of the highest spatial resolution to monitor metabolic correlates of blood flow changes. This is best achieved with 1H NMR spectroscopy, which permits noninvasive acquisition of high resolution spectroscopic images (SI) of subcutaneous tumors in a relatively short scan time (e.g., 12-25 microliters voxels with signal-to-noise ratio 7:1 in 30 min at 4.7 T). This study seeks to identify 1H spectroscopic indices of tumor blood flow. Proton SI of subcutaneous murine RIF-1 tumors were recorded (a) before and after administration of nicotinamide (1 g/kg) to increase blood flow, and (b) before and after hydralazine (10 mg/kg) to decrease flow. Nicotinamide produced a significant decrease in the total choline peak amplitudes, which subsequent high resolution NMR spectroscopy of tumor extracts revealed to be due to decreases in phosphocholine and glycerophosphocholine. The deamidation of nicotinamide to nicotinic acid, which is known to have hypolipidemic effects and to stimulate the formation of prostaglandins, may have sufficiently altered lipid metabolism to affect the in vivo concentration of the NMR-visible choline-containing compounds. The main effect of hydralazine was a significant increase of lactate, which is consistent with a reduction of tumor blood flow.

The chronic administration of drugs that inhibit the regulation of intracellular pH: in vitro and anti-tumour effects

Mean values of extracellular pH (pHe) in tumours tend to be about 0.5 pH units lower than in normal tissues, whereas values of intracellular pH (pHi) in tumours and normal tissues are similar. Previous studies have shown that drugs that acidify cells at lower pHe such as nigericin, used alone or with agents that inhibit the regulation of pHi, have toxicity to cultured cells at pHe < 6.5 in short-term exposure; these agents also lead to modest anti-tumour effects in mice when given acutely. To evaluate the long-term effects of these drugs at levels of pHe that might occur commonly in tumours, we exposed cells for up to 72h at pHe 6.8 or 7.2 in vitro. Nigericin (0.033 microM) caused time-dependent cell killing of murine KHT and EMT-6 cells at pHe 6.8 (but not at pHe 7.2) with a surviving fraction approximately 5 x 10(-3) after 72 h exposure. Cell killing was increased in the presence of 4,4-diisothiocyanstilbene 2,2-disulphonic acid (DIDS), an inhibitor of Na+-dependent HCO3-/CI- exchange, and to a lesser extent in the presence of 5-(N-ethyl-N-isopropyl) amiloride (EIPA), an inhibitor of Na+/H+ exchange. Cell killing was exquisitely sensitive to the level of pHe. Osmotic pumps were used to obtain a 72 h continuous infusion of nigericin in mice; this led to dose-dependent killing of cells in KHT tumours with surviving fraction of approximately 0.1 at maximum tolerated doses. Hydralazine, which may cause tumour hypoxia and lower pHi as well as pHe, caused cytotoxity when given alone by chronic infusion, and enhanced the cytotoxicity due to nigericin. The addition of DIDS and/or EIPA (using two pumps) further enhanced anti-tumour toxicity, with a surviving fraction of approximately 0.002 at tolerated doses of the four drugs used to treat KHT tumours. The experiments demonstrate the activity of drugs that inhibit the regulation of pHi against murine tumours when delivered by chronic infusion.

Acidic pH enhances the invasive behavior of human melanoma cells

As a consequence of poor perfusion and elevated acid production, the extracellular pH (pHex) of tumors is generally acidic. Despite this, most in vitro experiments are still performed at the relatively alkaline pHex of 7.4. This is significant, because slight changes in pHex can have profound effects on cell phenotype. In this study we examined the effects of mildly acidic conditions on the in vitro invasive potential of two human melanoma cell lines; the highly invasive C8161, and poorly invasive A375P. We observed that culturing of either cell line at acidic pH (6.8) caused dramatic increases in both migration and invasion, as measured with the Membrane Invasion Culture System (MICS). This was not due to a direct effect of pH on the invasive machinery, since cells cultured at normal pH (7.4) and tested at acidic pH did not exhibit increased invasive potential. Similarly, cells cultured at acidic pH were more aggressive than control cells when tested at the same medium pH. These data indicate that culturing of cells at mildly acidic pH induces them to become more invasive. Since acid pH will affect the intracellular pH (pHin) and intracellular calcium ([Ca2+]in), we examined the effect of these parameters on invasion. While changes in [Ca2+]in were not consistent with invasive potential, the changes in pHin were. While these conditions decrease the overall amount of gelatinases A and B secreted by these cells, there is a consistent and significant increase in the proportion of the activated form of gelatinase B.

Direct evidence that hydralazine can induce hypoxia in both transplanted and spontaneous murine tumours

Hydralazine can substantially decrease blood flow and increase hypoxia in transplanted tumours. Previous indirect studies have suggested that hydralazine does not induce such effects in spontaneous tumours. We have now directly investigated the ability of hydralazine to increase hypoxia in both transplanted and spontaneous murine tumours by measuring tumour oxygen partial pressure (pO2) distributions using an Eppendorf oxygen electrode. Spontaneous tumours arose at different sites in CDF1 mice, while transplanted tumours were produced by implanting a C3H mouse mammary carcinoma on the backs of the same mouse strain. Measurements of pO2 were made in anaesthetised mice immediately before and 45 min after an intravenous injection of 5 mg kg-1 hydralazine. In the transplanted tumours hydralazine significantly decreased tumour oxygenation, such that the percentage of pO2 values < or = 5 mmHg increased from 45% to 87%, and median pO2 decreased from 5 to 3 mmHg. Similar significant changes were induced by hydralazine in the spontaneous tumours, the percentage of pO2 values < or = 5 mmHg increasing from 60% to 94% while the median pO2 values decreased from 8 to 2 mmHg. These results clearly show that there is no difference in the response of transplanted and spontaneous mouse tumours to hydralazine.

Reduced blood flow increases the in vivo ammonium ion concentration in the RIF-1 tumor

PURPOSE

Previous studies from our laboratory have suggested that pooling of ammonium in tumor tissues may be caused by its inefficient removal due to the poor vasculature commonly found in tumors. The purpose of these experiments was to validate the relationship between tumor ammonium ion concentration and tumor blood flow, and to determine whether large concentrations of ammonium ion detected by Nuclear Magnetic Resonance (NMR) spectroscopy are either produced within the tumor or simply imported into the tumor through the blood stream.

METHODS AND MATERIALS

To test this hypothesis, we reduced blood flow in subcutaneously grown Radiation Induced Fibrosarcoma-1 (RIF-1) tumors, either by creating partial ischemia with a bolus injection of hydralazine or by occlusion with surgical sutures. 14N and 31P NMR spectroscopy were used to detect the presence of ammonium, and to assess the bioenergetic status of the tumors, respectively.

RESULTS

A correlation between ammonium ion concentration and PCr/Pi ratio was established for untreated tumors. An increase in the in vivo tumor ammonium ion concentration was observed for every tumor that experienced a reduction in blood flow caused by either hydralazine injection or suture ligation. Changes in ammonium ion concentration paralleled changes in the bioenergetics of hydralazine-treated tumors.

CONCLUSION

Our results support the hypothesis that a reduction in tumor blood flow is responsible for the accumulation of ammonium in tumors, and that detected ammonium originated from within the tumor.

The effects of isoflurane and halothane on blood flow and 31P NMR spectra in murine RIF-1 tumors

The principal aim of these studies was to evaluate the utility of isoflurane and halothane for NMR investigations of tumor physiology. In vivo 31P and 2H NMR were used to examine RIF-1 tumors before, during, and (for 31P) after anesthesia. In tumors, halothane decreases blood flow, [PCR]:[NTP], and pH indicated by the Pi chemical shift (pHnmr), while it increases [Pi]:[NTP]; effects consistent with well-established cardiovascular effects of halothane. Isoflurane does not affect tumor blood flow or [PCr]:[NTP], but increases tumor [Pi]:[NTP] and decreases tumor pHnmr. In vivo 31P NMR measurements of normal mouse liver (upper abdomen) indicate that isoflurane has a similar effect in the liver. Although the mechanism for these effects is unknown, observation of a split Pi peak during isoflurane anesthesia suggests that a pool of Pi in a lower pH environment may become evident under isoflurane anesthesia. Regardless of the cause for increased [Pi]:[NTP] and decreased pHnmr, the utility of isoflurane anesthesia for 31P NMR studies of energy metabolism is limited.

Glucose metabolism in RIF-1 tumors after reduction in blood flow: an in vivo 13C and 31P NMR study

Low pH appears to enhance the effectiveness of therapeutic hyperthermia. 13C and 31P NMR spectroscopy have been employed to examine the possibility that elevating glucose in a solid tumor while simultaneously reducing tumor blood flow would induce a more profound acidosis than either treatment alone. When blood flow in RIF-1 tumors was acutely reduced by administration of hydralazine and additional glucose was delivered locally by intratumoral injection, tumor acidosis (as determined by 31P NMR spectroscopy) during the period of reduced blood flow was not enhanced, relative to administration of hydralazine alone. Tumor NTP/P1 ratios decreased significantly within 20 min of hydralazine administration, whether or not glucose was injected, although NTP/P1 ratios were slightly higher in tumors that received extra glucose. Tumor lactate concentrations were not significantly different in glucose-supplemented tumors, despite glucose concentrations that were 4 to 5 times higher. When the added glucose was labeled with 13C, no correlation was detected between the pH in an individual tumor and the intensity of the 3-[13C]-lactate resonance in the same tumor.

Hydralazine at thermoradiotherapy: tumor size and blood flow effects

PURPOSE

This study was aimed to assess the dependence on tumor size and blood flow of the efficacy of a vasoactive drug hydralazine with thermoradiotherapy.

METHODS AND MATERIALS

Experiments were performed on mice bearing SCC-VII tumors with volumes of about 85 and 340 mm3 (7-8 or 11-12 days after transplantation, respectively). Local hyperthermia (water bath, 43 degrees C, 0.5 h) was started 3 h after irradiation of tumors. Hydralazine (2.5 mg/kg, IP) was given 0.5 h before heating. Tumor blood flow was evaluated by laser Doppler flowmetry before, during and up to 2 days after the treatments.

RESULTS

It was shown that hydralazine and hyperthermia, even in combination with each other, had very weak anti-tumor effect, especially for 85 mm tumors. The agents also insignificantly enhanced the efficacy of radiotherapy excluding the case of polyradiomodification for 340 mm3 tumors when a dose modifying factor of about 2.0 was achieved. Thermometry showed only a small improvement by HDZ in heating patterns of tumors of both sizes. Meanwhile, the therapeutic efficacy of hydralazine and heat was correlated with the changes in tumor blood flow, first of all with the delayed effects. The radiomodifiers induced only minor and transient suppression of perfusion in the smaller tumors, and more markedly and for longer time decreased blood flow in the larger tumors. In the latter case, the inhibiting effect of the drug plus hyperthermia remained for at least 48 h after the treatment.

CONCLUSION

(a) The combined use of hydralazine and heat seems to be advisable only at radiotherapy of rather large advanced tumors; (b) the efficacy of such radiomodification is correlated with prolonged inhibition of tumor blood flow by these agents; and (c) hydralazine and hyperthermia are likely to kill selectively both acutely and chronically hypoxic radioresistant cancer cells.

From hydralazine to CGRP to man?

Attempts to selectively reduce tumour blood flow have, in the past, concentrated on the use of hydralazine. However, although this vasodilator can be highly effective in experimental animals, it is only at such high concentration as to result in a severe and clinically unacceptable reduction in systemic blood pressure. At clinically acceptable levels, the drug appears to produce a small increase in tumour blood flow. We have used the techniques of magnetic resonance spectroscopy as indicators of metabolism and blood flow in a search for vasoactive drugs that would produce an effective reduction in tumour blood flow without causing severe hypotension or other serious side effects. Single injections of either prazosin or CGRP are shown to be substantially more effective than hydralazine in causing a reduction in tumour blood flow without massive reduction in blood pressure. Even more effective was CGRP given by continuous infusion. In this case a three-fold reduction in tumour blood flow could be obtained with a reduction of only 15-20% in systemic blood pressure. All these studies, however, have been made with transplanted animal tumours. Using high-dose hydralazine and primary tumours that were either radiation or chemically induced, we obtained a success rate of only about a 35% in causing selective reduction in blood flow. In contrast, in a transplanted tumour line derived from one of the non-responding radiation-induced primary lesions, the success rate was about 95%, consistent with the majority of animal studies using transplanted tumours.(ABSTRACT TRUNCATED AT 250 WORDS)

Spatial heterogeneity of the metabolic response of RIF-1 tumors to a vasoactive agent evaluated in vivo by one-dimensional 31P chemical-shift imaging

Localized 31P NMR spectroscopy was used to evaluate the spatial heterogeneity of the metabolic response of RIF-1 tumors to hydralazine. Volume localized 31P spectra were obtained from subcutaneous RIF-1 tumors using one-dimensional chemical-shift imaging, before and 20 min after treatment with 5 mg/kg hydralazine, administered intravenously. Following treatment all of the tumors showed an overall decrease in the ratio of nucleoside triphosphate (NTP) to inorganic phosphate (Pi) and a decrease in pH. However, spatial localization revealed that the reduction in NTP/Pi was not uniform within some tumors. This was partly due to regional differences in the levels of metabolites existing before treatment. Normal tissue adjacent to the tumor did not show a significant decrease in high-energy metabolites or pH.

Comparative effects of hydralazine on perfusion of KHT tumor, kidney and liver and on renal function in mice

Hydralazine has been widely used to reduce tumor blood flow in mice. It has an application in the deliberate creation of reducing environments within tumors and has been used in conjunction with both bioreductive and cytotoxic drugs. We have compared the dose-response to hydralazine of relative tissue perfusion of KHT tumor, kidney and liver, assayed by 86Rb extraction, over the dose range 0.2 to 5.0 mgkg-1 and shown that doses of 1.0 mgkg-1 and higher cause significant reductions in perfusion of all three tissues but 0.2 mgkg-1 has no effect. Tumor perfusion (+/- 2 se) was reduced to 80 +/- 8% of control by 1.0 mgkg-1, to 38 +/- 13% by 2.5 mgkg-1 and to 35 +/- 7% by 5.0 mgkg-1. Relative kidney perfusion was reduced to 83 +/- 11% of control by 1.0 mgkg-1 and to 73 +/- 9% by 5.0 mgkg-1; relative liver perfusion was reduced to 71 +/- 10% of control by 1.0 mgkg-1 and to 64 +/- 10% by 5.0 mgkg-1. This reduction in kidney and liver perfusion may indicate that there would be impairment of elimination and/or metabolism of co-administered drugs. We have therefore also measured the dose-response of the effect of hydralazine on glomerular filtration rate and effective renal plasma flow, assayed by clearance of 51CrEDTA and 125I-iodohippurate, respectively. 5.0 mgkg-1 hydralazine blocks clearance of EDTA for 40 min, slows subsequent clearance by a factor (+/- 2 se) of 2.4 +/- 1.2, and slows 125I-iodohippurate clearance by a factor of 5.5 +/- 0.8; 1.0 mgkg-1 hydralazine slows EDTA clearance by a factor of 1.5 +/- 0.3. The time-course of the effect of 5.0 mgkg-1 hydralazine on isotope clearance was measured and this dose was shown to affect isotope clearance at times up to 4 h after administration. These data confirm that hydralazine at doses effective at reducing tumor blood flow also impairs renal function, and is therefore likely to affect the pharmacokinetics of any co-administered drug that is cleared by the kidney.

Energy metabolism, pH changes, and lactate production in RIF-1 tumors following intratumoral injection of glucose

The metabolic consequences of increased glucose availability were examined in subcutaneous RIF-1 tumors in vivo, using 13C and 31P NMR spectroscopy. Significant increases in the levels of nucleotide triphosphates and phosphocreatine relative to low energy phosphates and in tumor pH were observed within 30 min following injection of 1 g/kg of glucose directly into the tumor. These changes did not occur following an equivalent intratumoral dose of the non-metabolizable sugar alcohol, mannitol. When [1-13C]-glucose was administered, [3-13C]-lactate and [3-13C]-alanine were the only labeled metabolites detected in the in vivo 13C NMR spectra during the period of bioenergetic improvement. Biochemical analysis revealed a substantial increase in tumor and plasma glucose concentration, but no increase in either tumor or plasma lactate, consistent with the absence of acidosis. Evaluation of the distribution of glucose in the tumor by quantitative autoradiography of [1-14C]-2-deoxyglucose administered with the glucose indicated that, on average, 7 mM of the added glucose distributed over the entire tumor within 10 min. The significant improvement in overall metabolic status of the tumors following glucose administration is attributed to the existence of substrate limited regions within the tumor.

In vivo 31P nuclear magnetic resonance spectroscopy of experimental murine tumours and human tumour xenografts: effects of blood flow modification

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.

The potential for prazosin and calcitonin gene-related peptide (CGRP) in causing hypoxia in tumours

Using 31P NMR spectroscopy, changes in tumour metabolic status were studied in a transplanted rat fibrosarcoma following the administration of vasodilators. Mean Arterial Blood Pressure (MABP) was monitored simultaneously. Two vasodilators were studied, prazosin and CGRP, which altered the NMR parameters Pi/sigma P, beta NTP,Pi, PCr/Pi and PME/Pi in a dose dependent manner. There was a good correlation between the various NMR parameters; for analysis, Pi/sigma P was used for convenience. With increasing doses of vasodilator, Pi/sigma P increased and the MABP decreased. Reduction in pHNMR showed a correlation with decreasing MABP following the administration of prazosin but not after CGRP. Both prazosin and CGRP produced changes in 31P NMR spectra consistent with a reduction in tumour blood flow. The results for prazosin and CGRP were comparable and showed a 15-20% increase in Pi/sigma P for a 20% reduction in MABP. These results were compared with those from hydralazine. With hydralazine an acceptable reduction in blood pressure (up to approximately 25%) has little effect and may even alter NMR parameters consistent with an increase in blood flow, a reduction of approximately 40% is required for a significant decrease in flow. Both prazosin and CGRP are shown to be far more effective than hydralazine in causing tumour hypoxia at a clinically acceptable reduction in blood pressure. CGRP may be the more suitable for clinical use because of its short half life, its capability to achieve controlled hypotension and the relatively few side effects associated with its use.