In vivo detection of ifosfamide by 31P-MRS in rat tumours: increased uptake and cytotoxicity induced by carbogen breathing in GH3 prolactinomas

Investigating the Vascular Phenotype of Subcutaneously and Orthotopically Propagated PC3 Prostate Cancer Xenografts Using Combined Carbogen Ultrasmall Superparamagnetic Iron Oxide MRI

The aim of this study was to use the combined carbogen-ultrasmall superparamagnetic iron oxide (CUSPIO) magnetic resonance imaging (MRI) method, which uses spatial correlations in independent susceptibility imaging biomarkers, to investigate and compare the impact of tumor size and anatomical site on vascular structure and function in vivo. Mice bearing either subcutaneous or orthotopic PC3 LN3 prostate tumors were imaged at 7 T, using a multi-gradient echo sequence to quantify R2, before and during carbogen (95% O2/5% CO2) breathing, and subsequently following intravenous administration of USPIO particles. Carbogen and USPIO-induced changes in R2 were used to inform on hemodynamic vasculature and fractional blood volume (%), respectively. The CUSPIO imaging data were also segmented to identify and assess five categories of R2 response. Small and large subcutaneous and orthotopic tumor cohorts all exhibited significantly (P < 0.05) different median baseline R2, ΔR2carbogen, and fractional blood volume. CUSPIO imaging showed that small subcutaneous tumors predominantly exhibited a negative ΔR2carbogen followed by a positive ΔR2USPIO, consistent with a well perfused tumor vasculature. Large subcutaneous tumors exhibited a small positive ΔR2carbogen and relatively low fractional blood volume, suggesting less functional vasculature. Orthotopic tumors revealed a large, positive ΔR2carbogen, consistent with vascular steal, and which may indicate that vascular function is more dependent on site of implantation than tumor size. Regions exhibiting significant ΔR2carbogen, but no significant ΔR2USPIO, suggesting transient vascular shutdown over the experimental timecourse, were apparent in all 3 cohorts. CUSPIO imaging can inform on efficient drug delivery via functional vasculature in vivo, and on appropriate tumor model selection for pre-clinical therapy trials.

Involvement of MEK/ERK1/2 and PI3K/Akt pathways in the refractory behavior of GH3B6 pituitary tumor cells to the inhibitory effect of TGFβ1

Pituitary tumor cells have a poor response to the growth inhibitory effect of TGFβ1, possibly resulting from the cross talk of TGFβ/Smads signal with other signaling pathways, an undescribed mechanism in these tumoral cells. To address this hypothesis, we investigated whether the mitogen-activated extracellular signal-regulated kinase (MEK)/ERK1/2 and phosphoinositide-3 kinase/protein kinase B (PI3K/Akt) pathways were able to regulate the antimitogenic effect of TGFβ1 on GH3B6 cells. TGFβ1 treatment decreased the cell proliferation and induced an activation of mothers against decapentaplegic homolog 2/3 (Smad2/3), effects that were potentiated by MEK and PI3K inhibitors, thus indicating the existence of a cross talk between TGFβ1/Smad with the MEK/ERK1/2 or PI3K/Akt pathways. In addition, through immunoprecipitation assays, a direct interaction was observed between Smad2/3-ERK1/2 and Smad2/3-Akt, which decreased when the GH3B6 cells were incubated with TGFβ1 in the presence of MEK or PI3K inhibitors, thereby suggesting that the ERK1/2- and Akt-activated states were involved. These Smad2/3-ERK1/2 and Smad2/3-Akt associations were also confirmed by confocal and transmission electron microscopy. These findings indicate that the TGFβ1-antimitogenic effect in GH3B6 cells was attenuated by the MEK/ERK1/2 and PI3K/Akt pathways via modulating Smad2/3 phosphorylation. This molecular mechanism could explain in part the refractory behavior of pituitary tumor cells to the inhibitory effect of TGFβ1.

Magnetic resonance spectroscopy of cancer metabolism and response to therapy

Magnetic resonance spectroscopy allows noninvasive in vivo measurements of biochemical information from living systems, ranging from cultured cells through experimental animals to humans. Studies of biopsies or extracts offer deeper insights by detecting more metabolites and resolving metabolites that cannot be distinguished in vivo. The pharmacokinetics of certain drugs, especially fluorinated drugs, can be directly measured in vivo. This review briefly describes these methods and their applications to cancer metabolism, including glycolysis, hypoxia, bioenergetics, tumor pH, and tumor responses to radiotherapy and chemotherapy.

Magnetic resonance methods and applications in pharmaceutical research

This review presents an overview of some recent magnetic resonance (MR) techniques for pharmaceutical research. MR is noninvasive, and does not expose subjects to ionizing radiation. Some methods that have been used in pharmaceutical research MR include magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) methods, among them, diffusion-weighted MRI, perfusion-weighted MRI, functional MRI, molecular imaging and contrast-enhance MRI. Some applications of MR in pharmaceutical research include MR in metabonomics, in vivo MRS, studies in cerebral ischemia and infarction, degenerative joint diseases, oncology, cardiovascular disorders, respiratory diseases and skin diseases. Some of these techniques, such as cardiac and joint imaging, or brain fMRI are standard, and are providing relevant data routinely. Skin MR and hyperpolarized gas lung MRI are still experimental. In conclusion, considering the importance of finding and characterizing biomarkers for improved drug evaluation, it can be expected that the use of MR techniques in pharmaceutical research is going to increase in the near future.

Molecular imaging in drug development

Molecular imaging can allow the non-invasive assessment of biological and biochemical processes in living subjects. Such technologies therefore have the potential to enhance our understanding of disease and drug activity during preclinical and clinical drug development, which could aid decisions to select candidates that seem most likely to be successful or to halt the development of drugs that seem likely to ultimately fail. Here, with an emphasis on oncology, we review the applications of molecular imaging in drug development, highlighting successes and identifying key challenges that need to be addressed for successful integration of molecular imaging into the drug development process.

Carbogen breathing differentially enhances blood plasma volume and 5-fluorouracil uptake in two murine colon tumor models with a distinct vascular structure

For the systemic treatment of colorectal cancer, 5-fluorouracil (FU)-based chemotherapy is the standard. However, only a subset of patients responds to chemotherapy. Breathing of carbogen (95% O2 and 5% CO2) may increase the uptake of FU through changes in tumor physiology. This study aims to monitor in animal models in vivo the effects of carbogen breathing on tumor blood plasma volume, pH, and energy status, and on FU uptake and metabolism in two colon tumor models C38 and C26a, which differ in their vascular structure and hypoxic status. Phosphorus-31 magnetic resonance spectroscopy (MRS) was used to assess tumor pH and energy status, and fluorine-19 MRS was used to follow FU uptake and metabolism. Advanced magnetic resonance imaging methods using ultrasmall particles of iron oxide were performed to assess blood plasma volume. The results showed that carbogen breathing significantly decreased extracellular pH and increased tumor blood plasma volume and FU uptake in tumors. These effects were most significant in the C38 tumor line, which has the largest relative vascular area. In the C26a tumor line, carbogen breathing increased tumor growth delay by FU. In this study, carbogen breathing also enhanced systemic toxicity by FU.

The C-neu mammary carcinoma in Oncomice; characterization and monitoring response to treatment with herceptin by magnetic resonance methods

To characterize spontaneously occurring c-neu/HER2 overexpressing tumours in oncomice and their response to herceptin by non-invasive magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI). Oncomice were monitored by localized 31P MRS during unperturbed growth and before and after treatment with 10 mg/kg herceptin (Hoffman La Roche) intraperitoneally for up to 21 days post-treatment. Vascular morphology and function was assessed by quantitation of tumour magnetic resonance (MR) relaxation rates R2* and R2 prior to and either during carbogen (95% O2/5% CO2) breathing or following administration of the blood-pool contrast agent NC100150 (Clariscan, Amersham Health). Immunohistochemistry showed strong membrane staining for HER2 protein overexpression. The 31P MRS showed only a significant (p<0.01) increase of phosphomonoester / total phosphate ratio over 21 days of growth. Herceptin increased the tumour volume doubling time compared to untreated tumours and significantly increased the phosphomonoester / beta-nucleoside triphosphate ratio 2 days after treatment (p=0.01). Tumours showed a highly heterogeneous yet significant (p<0.01) decrease or increase in R2* in response to carbogen or NC100150 respectively. The absence of a decline in tumour bioenergetics with growth, commonly seen in 31P MRS studies of transplanted rodent tumour models, coupled with the heterogeneous blood volume revealed by 1H MRI, suggest a metabolic and vascular phenotype similar to that found in human tumours.

Investigations in vivo of the effects of carbogen breathing on 5-fluorouracil pharmacokinetics and physiology of solid rodent tumours

PURPOSE

We have shown previously that carbogen (95% 0(2), 5% CO(2)) breathing by rodents can increase uptake of anticancer drugs into tumours. The aim of this study was to extend these observations to other rodent models using the anticancer drug 5-fluorouracil (5FU). 5FU pharmacokinetics in tumour and plasma and physiological effects on the tumour by carbogen were investigated to determine the locus of carbogen action on augmenting tumour uptake of 5FU.

METHODS

Two different tumour models were used, rat GH3 prolactinomas xenografted s.c. into nude mice and rat H9618a hepatomas grown s.c. in syngeneic Buffalo rats. Uptake and metabolism of 5FU in both tumour models with or without host carbogen breathing was studied non-invasively using fluorine-19 magnetic resonance spectroscopy ((19)F-MRS), while plasma samples from Buffalo rats were used to construct a NONMEM pharmacokinetic model. Physiological effects of carbogen on tumours were studied using (31)P-MRS for energy status (NTP/Pi) and pH, and gradient-recalled echo magnetic resonance imaging (GRE-MRI) for blood flow and oxygenation.

RESULTS

In both tumour models, carbogan-induced GRE-MRI signal intensity increases of approximately 60% consistent with an increase in tumour blood oxygenation and/or flow. In GH3 xenografts, (19)F-MRS showed that carbogen had no significant effect on 5FU uptake and metabolism by the tumours, and (31)P-MRS showed there was no change in the NTP/Pi ratio. In H9618a hepatomas, (19)F-MRS showed that carbogen had no effect on tumour 5FU uptake but significantly ( p=0.0003) increased 5FU elimination from the tumour (i.e. decreased the t(1/2)) and significantly ( p=0.029) increased (53%) the rate of metabolism to cytotoxic fluoronucleotides (FNuct). The pharmacokinetic analysis showed that carbogen increased the rate of tumour uptake of 5FU from the plasma but also increased the rate of removal. (31)P-MRS showed there were significant ( p<or=0.02) increases in the hepatoma NTP/Pi ratio of 49% and transmembrane pH gradient of 0.11 units.

CONCLUSIONS

We suggest that carbogen can transiently increase tumour blood flow, but this effect alone may not increase uptake of anticancer drugs without a secondary mechanism operating. In the case of the hepatoma, the increase in tumour energy status and pH gradient may be sufficient to augment 5FU metabolism to cytotoxic FNuct, while in the GH3 xenografts this was not the case. Thus carbogen breathing does not universally lead to increased uptake of anticancer drugs.

[Use of contrast agent in high-field MRI (3 T)]

The basic diagnostic efficacy of MR contrast medium in the evaluation of primary brain tumors and its clinical usefulness in the detection of brain metastases with single and cumulative triple-dose was compared using a high-field 3 T MR unit and a 1.5 T MR unit. Additionally, the effect of contrast agent on high-resolution MR venography based on the BOLD effect was evaluated at both field strengths. Tumor-brain contrast after gadodiamide administration, as assessed by means of statistical evaluation of MP-RAGE scans and T1-SE images, was significantly higher at 3 T than at 1.5 T. The subjective assessment of cumulative triple-dose 3 T images obtained the best results in the detection of brain metastases, followed by 1.5 T cumulative triple-dose enhanced images. Due to higher spatial resolution, contrast-enhanced MR venography at 3 T showed more details in and around tumors than at 1.5 T, additionally enhanced by stronger susceptibility weighting and higher signal-to-noise ratio at 3 T. In summary, administration of gadolinium-based contrast agent produces higher contrast between tumor and normal brain at 3 T than at 1.5 T, helps to detect more cerebral metastases at 3 T than at 1.5 T in single and cumulative triple dose, and improves MR venography at 3 T with increase in spatial resolution within the same measurement time, thus providing more detailed information.

MR Contrast Agent at High-Field MRI (3 Tesla)

Tumor-to-brain contrast after gadolinium administration using MP-RAGE and T1-SE scans in patients with primary and secondary brain tumors was significantly higher at 3 T than at 1.5 T. The subjective assessment of cumulative triple-dose 3 Tesla images obtained the best results in the detection of brain metastases compared with other sequences followed by 1.5 T cumulative triple-dose enhanced images. In macroadenomas of the hypophysis, contrast-enhanced 3 T MRI was superior to standard MRI in the diagnosis of cavernous sinus infiltration and in visualization of cranial nerves within the cavernous sinus. Due to higher spatial resolution, contrast-enhanced MR venography at 3 T showed more details in and around tumors than at 1.5 T, additionally enhanced by stronger susceptibility weighting and higher signal-to-noise ratio at 3 T. In summary, administration of gadolinium-based contrast agent produces higher contrast between tumor and normal brain at 3 T than at 1.5 T, helps to detect more cerebral metastases at 3 T versus 1.5 T in single and cumulative triple dose, improves the evaluation of macroadenomas of the hypophysis, and makes MR venography at 3 T clinically attractive with increase in spatial resolution within the same measurement time, thus providing more detailed information.

Correlation between 5-fluorouracil metabolism and treatment response in two variants of C26 murine colon carcinoma

Following an i.p. dose of 150 mg x kg(-1) 5-fluorouracil (5-FU), drug uptake and metabolism over a 2-h period were studied by in vivo (19)F magnetic resonance spectroscopy (MRS) for the murine colon carcinoma lines C26-B (5-FU-insensitive; n=11) and C26-10 (5-FU-sensitive; n=15) implanted s.c. in Balb/C mice. Time courses for tumour growth, intracellular levels of FdUMP, thymidylate synthase (TS) activity, and 5-FU in RNA were also determined, and the effects of a 9.5-min period of carbogen breathing, starting 1 min before drug administration, on MRS-detected 5-FU metabolism and tumour growth curves were examined. Both tumour variants generated MRS-detectable 5-FU nucleotides and showed similar initial growth inhibition after treatment. However, the growth rate of C26-B tumours returned to normal, while the sensitive C26-10 tumours, which produced larger fluoronucleotide pools, still showed moderate growth inhibition. Carbogen breathing did not significantly influence 5-FU uptake or fluoronucleotide production but did significantly enhance growth inhibition in C26-10 tumours. While both tumour variants exhibited incorporation of 5-FU into RNA and inhibition of TS via FdUMP, clearance of 5-FU from RNA and recovery of TS activity were greater for the insensitive C26-B line, indicating that these processes, in addition to 5-FU uptake and metabolism, may be important determinants of drug sensitivity and treatment response.

High-resolution three-dimensional contrast-enhanced blood oxygenation level-dependent magnetic resonance venography of brain tumors at 3 Tesla: first clinical experience and comparison with 1.5 Tesla

RATIONALE AND OBJECTIVES

To evaluate the clinical potential of high-resolution 3D contrast-enhanced blood oxygenation level-dependent MR-Venography (CE-MRV) for primary brain tumors and metastases at 3 Tesla (T) in comparison to 1.5 T.

METHODS

Eighteen patients with brain tumors were examined using CE-MRV after application of a standard dose of MRI contrast agent (0.1 mmol/kg gadodiamide). CE-MRV is based on a high-resolution 3D flow-compensated gradient-echo sequence with long echo times that uses the contrast-enhanced blood oxygenation level-dependent effect. This technique was performed using the same volume coverage and acquisition time at both field strengths after performing standard imaging sequences.

RESULTS

The higher spatial resolution of CE-MRV at 3 T showed more details within and around tumors than at 1.5 T. Visibility was enhanced by stronger susceptibility weighting and higher intrinsic signal-to-noise at 3 T. Compared with standard imaging protocols, additional information characterized as tubular and nontubular hypointense structures were found within or around lesions on CE-MRV images.

CONCLUSIONS

Acquisition of CE-MRV data at 3 T enables spatial resolution to be increased within the same measurement time and with the same volume coverage compared with 1.5 T, thus providing more detailed information. The method may also show the potential to estimate oxygen supply of tumors, especially at high field strengths.

Increased tumour extracellular pH induced by Bafilomycin A1 inhibits tumour growth and mitosis in vivo and alters 5-fluorouracil pharmacokinetics

The aim was to determine if a specific inhibitor of vacuolar H(+)-ATPases (V-ATPases), Bafilomycin A1 (BFM), could increase the low extracellular pH (pHe) typical of solid tumours and thus inhibit their growth in vivo. BFM inhibited the proliferation of various human cells and rat pituitary GH3 tumour cells in vitro (IC50: 2.5-19.2 nM), and flow cytometry on GH3 cells showed a marked increase in S and G2M phases after 16-48 h, but no evidence of increased apoptosis. BFM caused significant inhibition of GH3 xenograft growth, and histomorphometry showed a 30% decrease in mitosis but no change in apoptosis. 31P-magnetic resonance spectroscopy (MRS) in vivo of GH3 xenografts showed that BFM increased pHe, but did not affect pHi, resulting in a decrease in the negative pH gradient (-delta pH). BFM decreased lactate formation suggesting a reduction in glycolysis. We suggest that BFM reduces extracellular H(+)-transport by inhibition of V-ATPases leading to an increase in pHe and decreased glycolysis, and thus reduced tumour cell proliferation. 19F-MRS in vivo showed that a smaller -delta pH was associated with decreased retention of 5-fluorouracil (5FU) which was consistent with our previous data in vivo implying the -delta pH controls tumour retention of 5 FU.

Enhanced uptake of ifosfamide into GH3 prolactinomas with hypercapnic hyperoxic gases monitored in vivo by (31)P MRS

Previously, (31)P magnetic resonance spectroscopy (MRS) has been used to detect ifosfamide (IF) in vivo and to show that breathing carbogen (5% CO(2)/95% O(2)) enhances the uptake and increases the efficacy of IF in rat GH3 prolactinomas [Rodrigues LM, Maxwell RJ, McSheehy PMJ, Pinkerton CR, Robinson SP, Stubbs M, and Griffiths JR (1997). In vivo detection of ifosfamide by (31)P MRS in rat tumours; increased uptake and cytotoxicity induced by carbogen breathing in GH3 prolactinomas. Br J Cancer 75, 62-68]. We now show that other hypercapnic and/or hyperoxic (5% CO(2) in air, 2.5% CO(2) in O(2)) gas mixtures also increase the uptake of IF into tumors, measured by (31)P MRS. All gases caused an increased uptake (C(max)) of IF compared to air breathing, with carbogen inducing the largest increase (85% (P<.02) compared to 46% with 2.5% CO(2) in O(2) (P<.004) and 48% with 5% CO(2) in air (P<.004)). The T(max) (time of maximum concentration in tumor posintravenous injection of IF) was significantly (P<.04) later in the cohort that breathed 5% CO(2) in air. The increased uptake of IF with carbogen breathing was selective to tumor tissue and there were no significant increases in any of the normal tissues studied, suggesting that any host tissue toxicity would be minimal. Carbogen breathing by patients causes breathlessness. There was no significant difference in IF uptake between breathing carbogen and 2.5% CO(2) in O(2) and, therefore, the ability of 2.5% CO(2) in O(2) to also increase IF uptake may be clinically useful as it causes less patient discomfort.

Pharmacokinetic imaging: a noninvasive method for determining drug distribution and action

Advances in positron emission tomography (PET), single photon emission computed tomography (SPECT) and magnetic resonance spectroscopy (MRS), and the ability to label a wide variety of compounds for in vivo use in humans, have created a new technology for making precise physiological and pharmacological measurements. Due to the noninvasive nature of these approaches, repetitive and/or continuous measurements have become possible. Thus far, these techniques have been primarily used for one-time assessments of individuals. However, experience suggests that a major use of this technology will be in the evaluation of new drug therapies. Already, these techniques have been used to measure precisely and noninvasively the pharmacokinetics of a variety of antimicrobial, antineoplastic and CNS agents. In the case of CNS drugs, imaging techniques (particularly PET) have been used to define the classes of neuroreceptors with which the drug interacts. The physiological, pharmacological and biochemical measurements that can be performed noninvasively using modern imaging techniques can greatly facilitate the evaluation of new therapies. These measurements are most likely to be useful during drug development in preclinical studies and in phase I/II human studies. Preclinically, new drugs can be precisely compared with standard therapies, or a series of analogues can be screened for further development on the basis of performance in animal models. In Phase I/II, imaging measurements can be combined with classical pharmacokinetic data to establish optimal administration schedules, evaluate the utility of interventions in specific clinical situations, and aid in the design of Phase III trials.

Issues of normal tissue toxicity in patient and animal studies--effect of carbogen breathing in rats after 5-fluorouracil treatment

Non-invasive magnetic resonance spectroscopy (MRS) can be used in the clinic to monitor the pharmacokinetics of the chemotherapeutic drug 5-fluorouracil (5-FU) and the effects of modifiers. We report two studies of 5-FU toxicity in normal tissue--one with patients and the other an animal study. 1) 19F MRS signals from fluoronucleotides, cytotoxic anabolites of 5-FU metabolism, were observed in the livers of two patients treated with 5-FU for colorectal cancer, shown by computed tomography (CT) and ultrasound (US) to have no liver metastases. This is the first report of non-invasive monitoring of toxic 5-FU metabolites in normal human tissues. 2) In animals, carbogen-breathing enhances tumour uptake and the efficacy of 5-FU, and the method is under trial in patients. This study demonstrates that there were no significant effects of carbogen breathing on the levels of 5-FU and its metabolites in normal rat tissues, or on the histology of the tissues assessed after treatment.

Oxygen tension in primary gynaecological tumours: the influence of carbon dioxide concentration

BACKGROUND AND PURPOSE

To assess the effect of inhalation of various high oxygen content gases (HOCG) with different carbon dioxide concentrations on the tumour oxygen tension in patients with primary gynaecological malignancies.

MATERIALS AND METHODS

Tumour oxygen tension was assessed on two protocols in those patients with locally advanced visible or palpable primary gynaecological malignancies. Patients were assessed initially while breathing room air (R/A). After 4 min of inhaling the first HOCG, a second assessment of the oxygen tension within the tumour was made. After a 10 min rest period while inhaling R/A, the second HOCG was administered for 4 min after which the third set of measurements were obtained. Protocol A involved assessing the tumour oxygen tension in 12 patients while breathing R/A, 100% oxygen (O(2)) and 5% carbogen (95% O(2), 5% CO(2)). For protocol B, tumour oxygen tension assessments of 13 patients while breathing R/A, 2.5% carbogen (97.5% O(2), 2.5% CO(2)), and 5% carbogen. Median pO(2) and percentage of values </=2.5 mmHg were assessed.

RESULTS

Regarding protocol A, the median of the median pO(2) values increased from 5 mmHg when breathing R/A to 47 mmHg for 100% O(2) and to 105 mmHg for 5% carbogen inhalation. The median of the percentage of values </=2. 5 mmHg decreased: 17% for R/A vs. 16% for 100% O(2) (P=ns) vs. 0% for 5% carbogen (P=0.015). In protocol B, the median of the median pO(2) values increased from 3 mmHg when breathing R/A to 73 mmHg when inhaling 2.5% carbogen and to 72 mmHg for 5% carbogen inhalation. The median of the percentage of values </=2.5 mmHg decreased with both carbogen mixtures compared with room air: 42% for R/A vs. 0% for 2.5% carbogen (P=0.05) and 3% for 5% carbogen (P=0.015). No statistically significant difference in this parameter was found between the two carbogen concentrations.

CONCLUSION

Oxygen tension as measured with an Eppendorf pO(2) histograph, increased with inhalation of the oxygen and carbon dioxide gas mixtures tested. While 100% oxygen inhalation increased the median pO(2) compared with R/A a significantly greater increase in oxygen tension was seen with inhalation of either carbogen gas mixture. Pure oxygen inhalation did not decrease the percentage of values </=2.5 mmHg whereas inhalation of either 2.5 and 5% carbogen gas resulted in a significant decrease in this parameter. Both carbogen concentrations appear equal at increasing the oxygen tension in primary gynaecological tumours as measured with the Eppendorf pO(2) histograph.

Initial measurements of ifosfamide and cyclophosphamide in patients using (31)P MRS: pulse-and-acquire, decoupling, and polarization transfer

Ifosfamide and cyclophosphamide are (31)P-containing alkylating agents used widely in the treatment of cancer. In this communication it is demonstrated that signals from these agents may be detected in the livers of patients undergoing treatment using (31)P MRS at 1.5 T. In vitro, signals are enhanced 4-fold by use of (1)H-decoupling, with a B(1) field of 100 Hz at -150 Hz relative to water. Polarization transfer (BINEPT) enhances signals in vitro by a further factor of 5.5. Preliminary results using the double-resonance methods in vivo show that the technique is practicable although enhancements may be less than observed in vitro. Factors affecting signal enhancement in vivo are evaluated. Magn Reson Med 44:180-184, 2000.

Effect of carbogen breathing on the pharmacodynamics of 5-fluorouracil in a murine colon carcinoma

To determine whether carbogen breathing has an effect on 5-fluorouracil (5-FU) uptake, retention and metabolism in C38 murine colon tumours grown in C57Bl/6 mice, we used in vivo 19F nuclear magnetic resonance (NMR) spectroscopy. Eleven tumour-bearing mice were treated with 150 mg/kg of 5-FU given intraperitoneally (i.p.). Five mice received carbogen gas (95% O(2) and 5% CO(2)) for 9.5 min, starting 1 min before 5-FU administration. We found increased levels of 5-FU and its anabolites and catabolites by sequential ¿19F NMR spectroscopy in the group treated with 5-FU in combination with carbogen compared with the group treated with 5-FU alone. The maximum of normalised values of 5-FU and its metabolites, reached after carbogen breathing, was almost 2-fold higher than after treatment with 5-FU alone. Despite these increased concentrations no significant effect of carbogen on growth inhibition of the tumour by 5-FU was observed, which may be related to the size as well as the well vascularised and perfused conditions of the tumours studied.

Monitoring pharmacokinetics of anticancer drugs: non-invasive investigation using magnetic resonance spectroscopy

Magnetic resonance spectroscopy (MRS) offers the unique advantage of detecting, identifying and quantifying chemicals deep within the living body in a totally non-invasive manner. In studies on pharmacology and toxicology of anticancer drugs, MRS and the closely related technique magnetic resonance imaging (MRI) have many uses. MRS in particular, despite its low sensitivity, offers unique insights into pharmacokinetics (the changing concentration of the drug at its site of action) which can be monitored, and metabolism (both activation and detoxification) can be detected in real time. This review considers some recent work on (19)F, (31)P, (1)H and (13)C MRS of anticancer drugs. Future possibilities for (13)C MRS and (1)H MRS studies of drugs and their metabolites are considered in detail.

Applications of magnetic resonance in model systems: tumor biology and physiology

A solid tumor presents a unique challenge as a system in which the dynamics of the relationship between vascularization, the physiological environment and metabolism are continually changing with growth and following treatment. Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) studies have demonstrated quantifiable linkages between the physiological environment, angiogenesis, vascularization and metabolism of tumors. The dynamics between these parameters continually change with tumor aggressiveness, tumor growth and during therapy and each of these can be monitored longitudinally, quantitatively and non-invasively with MRI and MRS. An important aspect of MRI and MRS studies is that techniques and findings are easily translated between systems. Hence, pre-clinical studies using cultured cells or experimental animals have a high connectivity to potential clinical utility. In the following review, leaders in the field of MR studies of basic tumor physiology using pre-clinical models have contributed individual sections according to their expertise and outlook. The following review is a cogent and timely overview of the current capabilities and state-of-the-art of MRI and MRS as applied to experimental cancers. A companion review deals with the application of MR methods to anticancer therapy.

In vivo magnetic resonance methods in pharmaceutical research: current status and perspectives

In the last decade, in vivo MR methods have become established tools in the drug discovery and development process. In this review, several successful and potential applications of MRI and MRS in stroke, rheumatoid and osteo-arthritis, oncology and cardiovascular disorders are dealt with in detail. The versatility of the MR approach, allowing the study of various pathophysiological aspects in these disorders, is emphasized. New indication areas, for the characterization of which MR methods have hardly been used up to now, such as respiratory, gastro-intestinal and skin diseases, are outlined in a subsequent section. A strength of MRI, being a non-invasive imaging modality, is the ability to provide functional, i.e. physiological, readouts. Functional MRI examples discussed are the analysis of heart wall motion, perfusion MRI, tracer uptake and clearance studies, and neuronal activation studies. Functional information may also be derived from experiments using target-specific contrast agents, which will become important tools in future MRI applications. Finally the role of MRI and MRS for characterization of transgenic and knock-out animals, which have become a key technology in modern pharmaceutical research, is discussed. The advantages of MRI and MRS are versatility, allowing a comprehensive characterization of a diseased state and of the drug intervention, and non-invasiveness, which is of relevance from a statistical, economical and animal welfare point of view. Successful applications in drug discovery exploit one or several of these aspects. In addition, the link between preclinical and clinical studies makes in vivo MR methods highly attractive methods for pharmaceutical research.

Improvement in human tumour oxygenation with carbogen of varying carbon dioxide concentrations

BACKGROUND AND PURPOSE

Carbogen (95%O2, 5%CO2) is being used in clinical trials as a hypoxic radiosensitiser. Tolerance to carbogen can be a problem, this study compares tumour oxygenation during inhalation of hyperoxic gas containing either 2% or 5% CO2.

MATERIALS AND METHODS

Tumour pO2 was measured in 16 patients using the Eppendorf pO2 histograph.

RESULTS

After breathing gas containing either 5% or 2% CO2 an increase in median pO2 was measured in every tumour, the frequency of low pO2 values ( < or = 10 mmHg) fell from 47% to 29% in the 5% group and from 55% to 17% in the 2% group.

CONCLUSIONS

This study confirms that breathing 2% CO2 and 98% O2 is well tolerated and effective in increasing tumour oxygenation.

The effects of host carbogen (95% oxygen/5% carbon dioxide) breathing on metabolic characteristics of Morris hepatoma 9618a

Characteristics of the tumour metabolic profile play a role in both the tumour-host interaction and in resistance to treatment. Because carbogen (95% oxygen/5% carbon dioxide) breathing can both increase sensitivity to radiation and improve chemotherapeutic efficacy, we have studied its effects on the metabolic characteristics of Morris hepatoma 9618a. Host carbogen breathing increased both arterial blood pCO2 and pO2, but decreased blood pH. A fourfold increase in tumour pO2 (measured polarographically) and a twofold increase in image intensity [measured by gradient recalled echo magnetic resonance (MR) imaging sensitive to changes in oxy/deoxyhaemoglobin] were observed. No changes were seen in blood flow measured by laser Doppler flowmetry. Tumour intracellular pH remained neutral, whereas extracellular pH decreased significantly (P < 0.01). Nucleoside triphosphate/inorganic phosphate (NTP/Pi), tissue and plasma glucose increased twofold and lactate decreased in both intra- and extracellular compartments, suggesting a change to a more oxidative metabolism. The improvement in energy status of the tumour was reflected in changes in tissue ions, including Na+, through ionic equilibria. The findings suggest that the metabolic profile of hepatoma 9618a is defined partly by intrinsic tumour properties caused by transformation and partly by tissue hypoxia, but that it can respond to environmental changes induced by carbogen with implications for improvements in therapeutic efficacy.

Magnetic resonance imaging techniques for monitoring changes in tumor oxygenation and blood flow

The application of functional magnetic resonance (MR) imaging techniques to the measurement of oxygenation and blood flow in tumors is described. Gradient recalled echo MR imaging (GRE-MRI) offers a real-time noninvasive method for monitoring tumor response to vasomodulators such as carbogen (95% O2/5% CO2) breathing in attempts to overcome tumor hypoxia and improve treatment efficacy. Although the response is tumor-type dependent, increases in signal intensity of up to 100% have been observed in several animal tumor types. Responses are also seen in human tumors. The observed increases in GRE-MRI signal intensity are due to a combination of a reduction of deoxyhemoglobin in the blood causing changes in the MR imaging relaxation time T2* and changes in blood flow and may also reflect the capillary density. Thus, the magnitude of the GRE image intensity change gives an indication of the potential response of an individual tumor to treatments that aim to improve tissue oxygenation and therefore how the tumor may respond to therapy. In addition, carbogen breathing by the host has been shown to increase the uptake and efficacy of chemotherapeutic agents in animal tumors.

Modification of tumor blood flow: current status and future directions

Suboptimal drug distribution and hypoxia, which can contribute to treatment failure, are a direct consequence of the spatial and temporal heterogeneity in perfusion that occurs in solid tumors. Therefore, improvements in tumor blood flow have wide-ranging therapeutic importance. Paradoxically, controlled decreases in tumor blood flow can also be exploited and, if permanent, induce extensive tumor cell death on their own. We review the current knowledge of the factors controlling tumor blood flow with emphasis on the roles of the endogeneous vasodilator nitric oxide and the endogenous vasoconstrictor endothelin-1. The potential importance and application of approaches that irreversibly damage vascular function, so-called vascular targeting, are also discussed. Emphasis is given to the drug-based approaches to vascular targeting that are now entering clinical evaluation. There is no doubt that increased understanding of the processes that determine blood flow in tumors, coupled with the availability of techniques to monitor blood flow noninvasively in the clinic, will enable strategies for selectively modifying tumor blood flow to be transferred from the laboratory to the clinical setting.

Assessment of glucosylifosfamide mustard biodistribution in rats with prostate adenocarcinomas by means of in vivo 31P NMR and in vitro uptake experiments

A combined in vitro/in vivo study was performed to evaluate the possible application of phosphorus (31P) NMR spectroscopy for therapy monitoring and to investigate glucosylifosfamide mustard (Glc-IPM) transport and biodistribution by radiotracer techniques. Dynamic in vivo 31P NMR measurements were performed in rats with prostate adenocarcinoma after i.v. injection of 1 mmol/kg body weight (bw) of ifosfamide (IFO) (n = 4) and 1 mmol/kg bw (n = 4) or 2.15 mmol/kg bw (n = 9) of Glc-IPM. In a biodistribution study with 14C-labeled Glc-IPM and a final dose of 0.8 mmol Glc-IPM/kg bw, the animals were killed 5, 30, 60, and 120 min after drug administration, an ethanol extraction was performed from several tissues, and the dose per g tissue was calculated. The same tumor cell line was used in saturation and competition experiments to further elucidate the transport mechanism. The 31P NMR signals of IFO and Glc-IPM showed no overlap with the endogenous phosphorus peaks. A rapid washout with a half-life between 25.9 +/- 5.6 min for the lower dose and 34.3 +/- 4.2 min for the higher dose of Glc-IPM was observed in the tumor. No statistically significant change of the pH value was observed during the examination period. The beta-nucleoside 5'-triphosphate (NTP)/inorganic phosphate (Pi) signal intensity ratio showed a tendency to decrease but without statistical significance. A rapid elimination was demonstrated by both the noninvasive NMR technique and the biodistribution study. No saturation was found in vitro for the Glc-IPM uptake, even at the concentration of 5 mM. Furthermore, the Glc-IPM uptake was not inhibited by the presence of 2-deoxyglucose and vice versa. The data show that the pharmacokinetics of Glc-IPM in the tumor can be followed in vivo by 31P NMR. The results presented are evidence for diffusion as the transport mechanism for Glc-IPM in this tumor model. However, the better visualization of Glc-IPM as compared to ifosfamide may be due to metabolic trapping of a negatively charged metabolite after deglycosylation.

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.

The response of human tumors to carbogen breathing, monitored by Gradient-Recalled Echo Magnetic Resonance Imaging

PURPOSE

Gradient-Recalled Echo (GRE) Magnetic Resonance Imaging (MRI), which detects changes in blood vessel deoxyhaemoglobin content, has been investigated as a noninvasive monitor of changes in human tumor oxygenation and blood flow, in response to carbogen (95% O2, 5% CO2) breathing.

METHODS AND MATERIALS

GRE images (TE = 60 ms, TR = 200 ms, alpha = 40 degrees, 256[2] matrix) were acquired from 31 patients with primary and metastatic disease, prior to and during carbogen breathing. Three patients underwent a follow-up examination after radiotherapy.

RESULTS

Seventeen out of 34 tumors showed enhanced image intensity, consistent with an improvement in tumor oxygenation and blood flow, while 11 showed no response; 6 studies were technical failures. In one patient a metastatic node that had eluded orthodox investigation was visualized. A reduction in response was observed in the three patients studied postradiotherapy.

CONCLUSION

This method, which can be performed on a standard clinical MRI instrument, provides a noninvasive measurement of tumor response to oxygenation/blood flow modification. In principle, this should enable the clinician to optimize treatment protocols, such as carbogen breathing, for individual radiotherapy patients.