Local disposition kinetics of floxuridine after intratumoral and subcutaneous injection as monitored by [19F]-nuclear magnetic resonance spectroscopy in vivo

Purpose: To test the utility of [¹⁹F]-nuclear magnetic resonance (NMR) spectroscopy for studying the kinetics of local drug disposition after interstitial application in vivo. Methods: Floxuridine at 30 μmol (2.5% of the reported i.p. 50% lethal dose, LD₅₀) was injected into rats either intratumorally (Morris hepatoma M3924A) or s.c. [¹⁹F]-NMR spectra were obtained at the site of administration for up to 5 h after injection using a 2-cm diameter surface coil at 2.0 T. Signal-time data obtained for floxuridine and the metabolite 5-fluorouracil were analyzed using linear compartment models. Results: The lower limit for the quantitation of drug remaining at the site of administration was 1 μmol for tumors and 0.2 μmol for the s.c. injection site. Local drug disposition was biexponential in four of six tumors where the half-lives of the fast and slow components of disposition ranged from 4 to 26 and from 33 to 289 min, respectively. It was monoexponential in the remaining two tumors (half-lives 49 and 128 min) and in the s.c. injection experiments (n = 4, half-life 6–9 min). 5-Fluorouracil could be quantitated in three of six tumors; the estimated fraction of floxuridine converted intratumorally into 5-fluorouracil was 11–23%. α-Fluoro-β-alanine was detected in the sum spectra of three of the six tumours. Conclusions: Local drug-disposition kinetics after interstitial application can be monitored noninvasively by in vivo [¹⁹F]-NMR spectroscopy. Disposition kinetics after local injection is highly variable and has a slow component in this tumor, whereas it is much less variable and relatively fast in subcutaneous tissue. The results suggest that NMR spectroscopy may be useful for in vivo studies of drug release from depot preparations designed for interstitial application. Received: 7 August 1998 / Accepted: 17 December 1998     

Demonstration of tumor-selective retention of fluorinated nitroimidazole probes by 19F magnetic resonance spectroscopy in vivo

We have evaluated two fluorinated misonidazole analogues, Ro 07-0741 and CCI-103F, as potential probes for the non-invasive identification of hypoxic tumor cells by 19F magnetic resonance spectroscopy (MRS) in vivo. The equipment used was a 1.9 T Oxford Research Systems TMR-32 spectrometer, fitted with a 15 mm diameter surface coil. Signal was readily detectable, with similar intensity from EMT6 tumor, liver, and brain at early times (1-2 hr) after i.v. injection in BALB/c mice, indicative of an initial uniform biodistribution of parent probes. At later times (5-10 hr) there was a progressive reduction in signal intensity from brain and liver, but tumor levels remained constant or declined more slowly. This is illustrated by tumor/brain ratios at 6-7 hr of 2.9 (Ro 07-0741) and 4.2 (CCI-103F). In 4/5 mice analyzed at 20-24 hr after Ro 07-0741, and 1/2 following CCI-103F, tumor signal remained detectable. This occurred in the absence of parent probe as measured by HPLC, suggesting the involvement of a product of nitroreductive bioactivation. Studies with KHT and RIF-1 tumors in C3H/He mice showed a similar trend but retention in RIF-1 was less dramatic, and this was consistent with the known hypoxic fractions and comparative in vivo nitroreductase activities. These promising results support the continuing development of 19F nitroimidazole probes for non-invasive identification of hypoxic cells in vivo.     

1H magnetic resonance spectroscopy of prostate cancer: biomarkers for tumor characterization

Proton Magnetic Resonance Spectroscopic Imaging (MRSI) permits a non-invasive assessment of metabolites in the prostate gland. This article reviews the assessment of choline-containing compounds, citrate, and polyamines as markers for prostate tumor detection and aggressiveness.     

Human tumor fluorouracil trapping: clinical correlations of in vivo 19F nuclear magnetic resonance spectroscopy pharmacokinetics

We previously reported that fluorouracil (5FU) accumulation and metabolism in human livers and tumors can be studied by in vivo nuclear magnetic resonance spectroscopy (NMRS). We have extended these observations by evaluating the pharmacokinetics of 5FU in the tumors of 11 patients with carcinoma of the breast, colon, endometrium, cervix, and kidney, using 19F-NMRS in a 1.5 Magnetom (Siemens Medical Systems, Cerrito, CA) magnetic resonance imaging unit (MRI). These NMRS measurements detected a long-lived tumor pool of 5FU in six of 11 tumors in our patients including carcinomas in the pelvis, breast, lung, and liver. The half-life (T1/2) of this tumor pool of "trapped" 5FU was 0.33 to 1.3 hours (20 to 78 minutes), much longer than the T1/2 of 5FU in blood (5 to 15 minutes). Neither the anabolites of 5FU (fluorinated nucleosides, nucleotides, 5FU-RNA, or 5FU-thymidylate synthase) nor the catabolites (eg, fluorobetaalanine [FBAL]) were detectable by 19F NMRS. Patient response to chemotherapy appeared to correlate with the extent of trapping of free 5FU in the human tumors: in the seven patients receiving 5FU, or 5FU or FUdR plus leucovorin, four of four patients whose tumors trapped 5FU responded to fluorinated pyrimidine chemotherapy, whereas three patients in whom there was a failure to detect tumor trapping were resistant to 5FU. We conclude that NMRS is clinically feasible, and enables investigators to study 5FU pharmacokinetics and metabolism in tumors in vivo. 19F-NMRS of 5FU allows for in vivo evaluation of 5FU metabolic modulation and might be able to guide therapeutic decisions.     

Nonglycolytic acidification of murine radiation-induced fibrosarcoma 1 tumor via 3-O-methyl-D-glucose monitored by 1H, 2H, 13C, and 31P nuclear magnetic resonance spectroscopy.

The effects of 3-O-methyl-D-glucose (3-OMG) on subcutaneously implanted murine radiation-induced fibrosarcoma 1 tumor were examined with 2H, 13C, and 31P nuclear magnetic resonance (NMR) in situ. Using 31P NMR, changes in tumor high-energy phosphate metabolism were monitored for 2.5 h after i.p. administration of 3-OMG (8.1 g/kg body weight); tumor pH decreased by a mean maximum of 0.52 +/- 0.05 (SE) (n = 10), [PCr] decreased by 54%, [NTP] decreased by 35%, and [Pi] increased by 36%. Tumor blood flow, as measured by 2H NMR monitoring of D2O washout kinetics, decreased by 40% at 1 h and by 47% at 2 h after 3-OMG injection (n = 4). This substantial tumor acidification (pH decrease much greater than 0.1), expected to require a glycolytic substrate (Hwang et al., Cancer Res., 51: 3108-3118, 1991), is surprising in light of the previously documented metabolically inert nature of 3-OMG. In situ 13C NMR spectroscopy, following [6-13C]3-OMG i.p. injection, examined the possibility of the glycolytic metabolism of 3-OMG. However, only the C-6 resonance of 3-OMG was detected (n = 6); no resonances from [6-13C]3-OMG-6-phosphate or [3-13C]lactate were observed. These results confirmed that 3-OMG was not metabolized in radiation-induced fibrosarcoma 1 tumor. At the completion of the in situ 13C NMR experiments, tumors were freeze clamped, and perchloric acid extraction was performed. High-resolution 1H NMR measurement of lactate concentrations showed no statistically significant difference in control tumor extracts (from mice not receiving i.p. injection; n = 5) and in tumor extracts from mice administered i.p. [6-13C]3-OMG (n = 5), indicating that there was no significant increase in lactate level in the tumor extracts from mice administered i.p. 3-OMG due to increased plasma glucose concentration. The results of these 1H and 13C NMR studies indicated that the radiation-induced fibrosarcoma 1 tumor acidification caused by i.p. administration of 3-OMG was not due to a direct (3-OMG----lactate) or an indirect (systemic glucose----lactate) increase in tumor lactic acid levels.     

Modulation of murine radiation-induced fibrosarcoma-1 tumor metabolism and blood flow in situ via glucose and mannitol administration monitored by 31P and 2H nuclear magnetic resonance spectroscopy

The hyperglycemia-induced in situ metabolism and blood flow changes produced in s.c. implanted murine radiation-induced fibrosarcoma-1 tumors, grown on the flanks of female C3H/HeJ mice, were examined with 31P and 2H nuclear magnetic resonance. Initial experiments verified a hyperglycemic tumor acidification similar to that reported earlier with a different substrain of mice, C3H/AnF (J.L. Evelhoch et al., Proc. Natl. Acad. Sci. USA, 81: 6496-6500, 1984). Changes in the tumor pH, phosphorus metabolites, and blood flow were then compared after administration of saline, glucose, or mannitol (a nonmetabolizable glucose analogue) using a mole-equivalent dose of the sugars (i.e., 0.8 mmol/20g mouse). Neither saline (n = 8) nor mannitol (n = 6) administration had any marked effect upon tumor pH, whereas glucose administration produced a mean maximum tumor pH reduction of 0.74 +/- 0.09 (SE; n = 9) during the 2.5 h post-glucose injection. No significant changes in high energy phosphate concentrations were observed during the same period after saline injection. After glucose injection, the [phosphocreatine] gradually decreased by 64% (P = 0.0001). After the initial 1 h post-glucose injection, the [inorganic phosphate] increased by 58% (P = 0.0001), and the [nucleoside triphosphates] decreased by 29% (P = 0.0001) during the following 1.5 h. After mannitol injection, while there was no change in [inorganic phosphate] over time (P = 0.37), the [phosphocreatine] decreased by 33% (P = 0.0001) and the [nucleoside triphosphates] decreased by 21% (P = 0.0015) within 20 min, then both the [phosphocreatine] and [nucleoside triphosphates] remained at constant levels during the following 2 h. In parallel experiments, the volumetric rate of tumor blood flow and perfusion was measured by 2H nuclear magnetic resonance monitoring of 2H2O washout kinetics (S-G. Kim and J. J. H. Ackerman, Cancer Res., 48: 3449-3453, 1988); tumor blood flow decreased by 80% (P = 0.0001, n = 11), 60% (P = 0.0031, n = 4), and 20% (P = 0.058, n = 10) at 2 h after glucose, mannitol, or saline injections, respectively. These results suggest that anaerobic glycolysis is a requirement for hyperglycemic tumor acidification. However, the decrease in tumor blood flow accompanying hyperglycemic acidification suggests that flow reduction also may be a contributing or a required cofactor for acidification via inhibition of lactic acid egress.(ABSTRACT TRUNCATED AT 400 WORDS)     

19F magnetic resonance spectroscopy studies of the metabolism of 5-fluorouracil in murine RIF-1 tumors and liver

The metabolism of 5-fluorouracil (5FU) in tumors and livers of RIF-1 tumor-bearing C3H mice given i.p. injections of 5FU was serially monitored by 19F magnetic resonance spectroscopy. The levels of 5FU and fluoronucleotide detected in the tumors after a dose of 130 mg/kg (n = 13) were less than one-third of those after 260-mg/kg 5FU (n = 14). During the days after these doses, tumor size decreased by 24 +/- 3 and 52 +/- 6 SEM%, respectively. A second 130-mg/kg dose, given at day 7 after the first 130-mg/kg dose, resulted in still lower tumor fluorine levels and little change in tumor size. There was a significant correlation between the magnetic resonance spectroscopy-detected fluoronucleotide levels and the shrinkage of tumors after the 260-mg/kg dose (r = 0.44; P = 0.024). In mouse liver, the degradation of 5FU to alpha-fluoro-beta-ureidoprobionic acid and alpha-fluoro-beta-alanine after the 260-mg dose (n = 13) was slower than after a dose of 130 mg/kg (n = 14). For the respective doses, the half-life of 5FU was 59 +/- 7 versus 28 +/- 2 SEM min (P less than 0.0001). There was a negative correlation between the levels of 5FU catabolite (alpha-fluoro-beta-ureidoprobionic acid and alpha-fluoro-beta-alanine) in liver and fluoronucleotide in tumor (r = -0.80; P = 0.0020), which indicates that the degradation in liver and the activation of 5FU in tumor are competing processes.     

Metabolism of tegafur in rat liver observed by in vivo 19F magnetic resonance spectroscopy and chromatography.

Metabolism of tegafur in the rat liver was observed by in-vivo 19F magnetic resonance spectroscopy (MRS). After MRS observation, tegafur and q-fluorouracil (5-FU) in the liver were determined by a chromatographic method for comparison with the results of 19F-MRS. Rats were divided into 3 groups: 1) CCl4-induced liver injury group, 2) uracil combined group, 3) control group. Catabolism to fluoro-beta-alanine was suppressed in both the liver injury group and the uracil combined group. Low peaks of 5-FU and fluoronucleotides could be found only in the uracil combined group. The result of 19F MRS observation of each group was in agreement with the result of determination of tegafur and 5-FU by chromatography. This showed that substances which could be observed by 19F-MRS were in proportion to all intracellular fluoro-containing substances. 19F-MRS can provide direct information on the metabolism of fluoropyimidines non-invasively and it might be a useful aid in choosing suitable chemotherapy for patients.     

Metabolites of 5-fluorouracil in plasma and urine, as monitored by 19F nuclear magnetic resonance spectroscopy, for patients receiving chemotherapy with or without methotrexate pretreatment

19F NMR spectroscopy at 470 MHz (11.7 Tesla) has been used to directly measure the levels of 5-fluorouracil (FU) and its fluorine-containing catabolites in plasma and urine of colon cancer patients after i.v. infusion (10 min) of 60-230 mumol (8-30 mg) FU/kg, either with or without pretreatment with methotrexate (5.1-12.5 mg/kg). With a 1.5-ml sample the minimum metabolite concentration that can be quantified is approximately 15 +/- 5 microM within 30 min and 3 +/- 1 microM within 12 h of data acquisition. The first and second catabolites of FU, dihydrofluorouracil and alpha-fluoro-beta-ureidopropanoic acid, exhibit steady-state behavior with dose-dependent plasma concentrations of 5-40 microM for approximately 10-90 min after infusion (12 patients, 16 treatments). The final catabolite alpha-fluoro-beta-alanine (FBAL) was detected in plasma after 5-15 min, and the rate at which its concentration increased was independent of FU dose, while the maximum concentration reached at about the time FU disappeared (FU less than 5 microM in 1-2 h) was dose-dependent. The area under the time curve for FU in plasma increased more than linearly with dose. Several patients showed elevated levels of free fluoride anion (F-) in plasma (63 samples: median, 5 microM; maximum, 33 microM). In urine all of the above catabolites and F- could be observed. In samples with pH greater than or equal to 7.3 (methotrexate patients, due to bicarbonate infusion) N-carboxy-FBAL was also found in significant amounts. Urinary excretion of FU and catabolites amounted to 2.6-30% of the dose within 2 h (14 patients, 18 treatments) and 60-66% within 24 h (three patients). The ratio FU/creatinine in 2-h urine increased more than linearly with FU dose. Urinary fluoride concentration reached a maximum during the first day after FU infusion and returned to normal background levels after 2-3 days (four patients). The pattern of FU catabolites observed in plasma or urine did not differ significantly between responders and nonresponders to therapy or between patients with FU monotherapy and patients with methotrexate pretreatment. Cytotoxic FU anabolites, i.e., nucleotides, were not detected in plasma or urine (i.e., are less than 3 microM). Their detection in tumor tissue will be required for an assessment of individual responsiveness to FU. Possible toxic metabolic products derivable from FBAL, e.g., 2-fluoroacetate or 2-fluorocitrate, were not detected (i.e., are less than 3 microM) in plasma or urine.(ABSTRACT TRUNCATED AT 400 WORDS)     

Flavone acetic acid (NSC 347512)-induced modulation of murine tumor physiology monitored by in vivo nuclear magnetic resonance spectroscopy

Flavone acetic acid (FAA), a new drug with broad activity against transplanted solid tumors of mice, induces nonrepairable DNA single strand breaks that correlate with therapeutic efficacy. To test the hypothesis that the inability of the cells to repair single strand breaks is associated with a disruption of tumor energy metabolism, in vivo 31P nuclear magnetic resonance (NMR) spectra were acquired from s.c. implanted Glasgow osteogenic sarcomas in C57BL/6 x DBA/2 F1 mice both before and after treatment with FAA i.v. at 100, 150, or 200 mg/kg and from a control (no treatment) group (n = 4 in each group). While FAA produced a dose-dependent decrease in both the nucleoside triphosphates level and pH, only treatment with an efficacious dose of 200 mg/kg resulted in both a reduction in pH and a complete loss of nucleoside triphosphates from the NMR spectrum at 4 h with no recovery until 48 h and little recovery out to 72 h. The ATP concentration determined by high pressure liquid chromatography in a parallel set of experiments was 5.59 +/- 1.16 (SE) mumol/g (wet weight) in control tumors (n = 9) and 0.24 +/- 0.12 mumol/g (wet weight) at 4 h after 200 mg/kg FAA (n = 7). To examine the possibility that the loss of ATP and decreased pH are associated with a reduction in tumor blood flow, we used 2H NMR to monitor the washout of D2O injected directly into the tumor both before and 4 h after treatment with 200 mg/kg FAA. The pretreatment tumor blood flow of 12.4 +/- 1.7 ml/min/100 g was reduced to 1.9 +/- 0.5 ml/min/100 g at 4 h after treatment (n = 3). The FAA-induced reduction of both tumor blood flow and ATP may play an important role in its mechanism of action and should be considered in the combination of FAA with other drugs or therapeutic modalities. In addition, because 31P NMR can be used clinically, it should provide a nonambiguous early indicator of activity for clinical trials of FAA.     

Response of radiation-induced fibrosarcoma-1 in mice to cyclophosphamide monitored by in vivo 31P nuclear magnetic resonance spectroscopy

In vivo 31P nuclear magnetic resonance spectroscopy has been used to examine the RIF-1 fibrosarcoma in mice during untreated growth and following chemotherapy with cyclophosphamide. Levels of inorganic phosphate increase relative to phosphocreatine or nucleoside triphosphates during early untreated growth. After the tumor reaches a volume of approximately 1 g, no further decrease in energy level is observed. Following treatment with cyclophosphamide, tumor phosphorus metabolite ratios and pH are significantly altered, compared to untreated age-matched controls. During the growth delay period following chemotherapy there is a significant reduction in the ratio of inorganic phosphate to other phosphate metabolites, compared to age-matched controls. In addition, a more alkaline pH is observed in the tumors of treated animals. When the growth delay period ends, nuclear magnetic resonance spectra return to pretreatment patterns. The magnitude of the differences in 31P nuclear magnetic resonance spectral parameters between treated animals and untreated controls is dose dependent. However, doses of cyclophosphamide above 200 mg/kg do not result in earlier spectroscopic alterations, nor in larger effects by Day 3 after treatment, even though clonogenic cell killing and growth delay are greater at these higher doses.     

Glucose metabolism in drug-sensitive and drug-resistant human breast cancer cells monitored by magnetic resonance spectroscopy

Glucose utilization and lactate production have been monitored as a function of time using 13C magnetic resonance spectroscopy and [13C1]-glucose with perfused wild type MCF-7 human breast cancer cells and a drug-resistant (AdrR) cell line derived from them. Compared to wild type cells, AdrR cells exhibited an enhanced (3-fold) rate of glycolysis, indicating an increased demand for ATP production. We have investigated the effects of glucose depletion and azide, an inhibitor of oxidative phosphorylation, on the levels of intracellular phosphates (Pi, ATP) and intracellular pH using 31P magnetic resonance spectroscopy and on the rates of glycolysis. In both cell lines, ATP levels and the rates of glucose utilization and lactate production were invariant in the presence of azide. ATP production, especially in AdrR cells, was highly dependent on active glucose metabolism. The results of these direct measurements confirm that these cells survive by predominantly utilizing glycolysis. Glutamate and myo-inositol were observed in 13C spectra of acid extracts of AdrR but not wild type cells. Both metabolites are potential substrates in drug detoxification. These differences in rates of glycolysis, ATP production, and the production of certain metabolites may reflect metabolic adaptations associated with the development of drug resistance.     

pH dependence of 5-fluorouracil uptake observed by in vivo 31P and 19F nuclear magnetic resonance spectroscopy

Multinuclear nuclear magnetic resonance spectroscopy was used to follow the metabolism and kinetics of 5-fluorouracil (5FU) after i.v. administration at a dose of 100 mg/kg on Wistar rats. 31P spectra allow one to determine both the energetic status and the pH of the tissues under investigation, while serial 19F spectra reveal the drug clearance. Analyses of 5FU kinetics show that the half-life of 5FU elimination is about 35 min in tissue with a pH of 7.3. However, this half-life increases 2.5-fold when the local pH decreases below 6.9. Thus, acidification seems to induce a local retention of 5FU, which tends to prove the existence of active transport. This retention of the drug may have significant clinical implications for assessing and improving chemotherapy alone or in combination.     

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.     

N-ethyl-N-nitrosourea induced brain tumors in rats monitored by nuclear magnetic resonance imaging, plasma proton nuclear magnetic resonance spectroscopy and microscopy.

Characteristic slow growing brain gliomas were induced in rats by a single subcutaneous injection of N-ethyl-N-nitrosourea (ENU) within 24 h of birth. A parallel control group of rats was injected with saline. Seven treated rats developed gliomas within 2 years. Periodic nuclear magnetic resonance imaging (MRI) of the brain in 3-mm slices at 1.5 Tesla and monthly plasma sampling for proton magnetic resonance spectroscopy (MRS) at 360 MHz were started 6 months after the injection of ENU. In the MRS experiments, the Fossel index, average of the line widths of the methylene and methyl peaks at 360 MHz, was determined from half-line widths of methyl and methylene peaks at 0.8 ppm and 1.3 ppm. In five of the ENU injected animals that developed histologically verified brain tumors, these were also observed by MRI without contrast agents. There was no consistent correlation between the imaged tumors and the Fossel index obtained through MRS during the course of the study where repeated observations were performed on individual animals, nor was there any consistent statistical difference in the Fossel index between ENU-treated and control animals. The results of this study demonstrate that slowly developing carcinogen-induced brain tumors in rats can be successfully and reliably monitored noninvasively by MRI but not by MRS of plasma.     

Noninvasive detection of temozolomide in brain tumor xenografts by magnetic resonance spectroscopy

Poor drug delivery to brain tumors caused by aberrant tumor vasculature and a partly intact blood-brain barrier (BBB) and blood-brain tumor barrier (BTB) can significantly impair the efficacy of chemotherapy. Determining drug delivery to brain tumors is a challenging problem, and the noninvasive detection of drug directly in the tumor can be critically important for accessing, predicting, and eventually improving effectiveness of therapy. In this study, in vivo magnetic resonance spectroscopy (MRS) was used to detect an anticancer agent, temozolomide (TMZ), in vivo in murine xenotransplants of U87MG human brain cancer. Dynamic magnetic resonance imaging (MRI) with the low-molecular-weight contrast agent, gadolinium diethylenetriaminepentaacetic acid (GdDTPA), was used to evaluate tumor vascular parameters. Carbon-13-labeled TMZ ([¹³C]TMZ, 99%) was intraperitoneally administered at a dose of ∼140 mg/kg (450 mg/m², well within the maximal clinical dose of 1000 mg/m² used in humans) during the course of in vivo MRS experiments. Heteronuclear multiple-quantum coherence (HMQC) MRS of brain tumors was performed before and after i.p. administration of [¹³C]TMZ. Dynamic MRI experiments demonstrated slower recovery of MRI signal following an intravenous bolus injection of GdDTPA, higher vascular flow and volume obtained by T*₂-weighted MRI, as well as enhanced uptake of the contrast agent in the brain tumor compared with normal brain detected by T₁-weighted MRI. These data demonstrate partial breakdown of the BBB/BTB and good vascularization in U87MG xenografts. A [¹³C]TMZ peak was detected at 3.9 ppm by HMQC from a selected volume of about 0.15 cm³ within the brain tumor with HMQC pulse sequences. This study clearly demonstrates the noninvasive detection of [¹³C]TMZ in xenografted U87MG brain tumors with MRS. Noninvasive tracking of antineoplastic agents using MRS can have a significant impact on brain tumor chemotherapy.     

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.     

A phase I study of the nitroimidazole hypoxia marker SR4554 using 19F magnetic resonance spectroscopy

Background:

SR4554 is a fluorine-containing 2-nitroimidazole, designed as a hypoxia marker detectable with ¹⁹F magnetic resonance spectroscopy (MRS). In an initial phase I study of SR4554, nausea/vomiting was found to be dose-limiting, and 1400 mg m⁻² was established as MTD. Preliminary MRS studies demonstrated some evidence of ¹⁹F retention in tumour. In this study we investigated higher doses of SR4554 and intratumoral localisation of the ¹⁹F MRS signal.

Methods:

Patients had tumours ⩾3 cm in diameter and ⩽4 cm deep. Measurements were performed using ¹H/¹⁹F surface coils and localised ¹⁹F MRS acquisition. SR4554 was administered at 1400 mg m⁻², with subsequent increase to 2600 mg m⁻² using prophylactic metoclopramide. Spectra were obtained immediately post infusion (MRS no. 1), at 16 h (MRS no. 2) and 20 h (MRS no. 3), based on the SR4554 half-life of 3.5 h determined from a previous study. ¹⁹Fluorine retention index (%) was defined as (MRS no. 2/MRS no. 1)*100.

Results:

A total of 26 patients enrolled at: 1400 (n=16), 1800 (n=1), 2200 (n=1) and 2600 mg m⁻² (n=8). SR4554 was well tolerated and toxicities were all ⩽grade 1; mean plasma elimination half-life was 3.7±0.9 h. SR4554 signal was seen on both unlocalised and localised MRS no. 1 in all patients. Localised ¹⁹F signals were detected at MRS no. 2 in 5 out of 9 patients and 4 out of 5 patients at MRS no. 3. The mean retention index in tumour was 13.6 (range 0.6–43.7) compared with 4.1 (range 0.6–7.3) for plasma samples taken at the same times (P=0.001) suggesting ¹⁹F retention in tumour and, therefore, the presence of hypoxia.

Conclusion:

We have demonstrated the feasibility of using ¹⁹F MRS with SR4554 as a potential method of detecting hypoxia. Certain patients showed evidence of ¹⁹F retention in tumour, supporting further development of this technique for detection of tumour hypoxia.     

In vivo proton (H1) magnetic resonance spectroscopy for cervical carcinoma

Proton magnetic resonance spectroscopy (MRS) may be a useful tool in both the initial diagnosis of cervical carcinoma and the subsequent surveillance after radiation therapy, particularly when other standard diagnostic methods are inconclusive. Single voxel magnetic resonance (MR) spectral data were acquired from 8 normal volunteers, 16 patients with cervical cancer before radiation therapy, and 18 patients with cervical cancer after radiation therapy using an external pelvic coil at a 1.5-T on a Signa system. The presence or absence of various resonances within each spectrum was evaluated for similarities within each patient group and for spectral differences between groups. Resonances corresponding to lipid and creatine dominated the spectrum for the eight normal volunteers without detection of a choline resonance. Spectra from 16 pretreatment patients with biopsy-proven cervical cancer revealed strong resonances at a chemical shift of 3.25 ppm corresponding to choline. Data acquired from the 18 posttreatment setting studies was variable, but often correlated well with the clinical findings. Biopsy confirmation was obtained in seven patients. H1 MRS of the cervix using a noninvasive pelvic coil consistently demonstrates reproducible spectral differences between normal and neoplastic cervical tissue in vivo. However, signal is still poor for minimal disease recurrence. Further study is needed at intervals before, during, and after definitive irradiation with biopsy confirmation to validate the accuracy of MRS in distinguishing persistence or recurrence of disease from necrosis and fibrosis.