Magnetic resonance spectroscopy studies on experimental murine and human tumors: comparison of changes in phosphorus metabolism with induced changes in vascular volume

Acute effects of vascular modifying agents in solid tumors assessed by noninvasive laser Doppler flowmetry and near infrared spectroscopy

The potential of noninvasive laser Doppler flowmetry (LDF) and near infrared spectroscopy (NIRS) to detect acute effects of different vascular-modifying agents on perfusion and blood volume in tumors was evaluated. C3H mouse mammary carcinomas (approximately 200 mm(3)) in the rear foot of CDF1 mice were treated with flavone acetic acid (FAA, 150 mg/kg), 5,6-dimethylxanthenone-4-acetic acid (DMXAA, 20 mg/kg), combretastatin A-4 disodium phosphate (CA4DP, 250 mg/kg), hydralazine (HDZ, 5 mg/kg), or nicotinamide (NTA, 500 mg/kg). Tumor perfusion before and after treatment was evaluated by noninvasive LDF, using a 41 degrees C heated custom-built LDF probe with four integrated laser/receiver units, and tumor blood volume was estimated by NIRS, using light guide coupled reflectance measurements at 800+/-10 nm. FAA, DMXAA, CA4DP, and HDZ significantly decreased tumor perfusion by 50%, 47%, 73%, and 78%, respectively. In addition, FAA, DMXAA, and HDZ significantly reduced the blood volume within the tumor, indicating that these compounds to some degree shunted blood from the tumor to adjacent tissue, HDZ being most potent. CA4DP caused no change in the tumor blood volume, indicating that the mechanism of action of CA4DP was vascular shut down with the blood pool trapped in the tumor. NTA caused no change in either tumor perfusion or tumor blood volume. We conclude that noninvasive LDF and NIRS can determine acute effects of vascular modifying agents on tumor perfusion and blood volume.

Issues in flow and oxygenation dependent contrast (FLOOD) imaging of tumours

The sensitivity of blood oxygenation level dependent (BOLD) contrast techniques to changes to tumour deoxyhaemoglobin concentration is of relevance to many strategies in cancer treatments. In the context of tumour studies, which frequently involve the use of agents to modify blood flow, there are underlying physiological changes different to those of BOLD in the brain. Hence we use the term, flow and oxygenation dependent (FLOOD) contrast, to emphasize this difference and the importance of flow effects. We have measured the R(2)* changes in a prolactinoma tumour model for a variety of vasoactive challenges [carbogen, 100% oxygen and 100% nitrogen as different breathing gases, and administration of tumour blood flow modifiers such as calcitonin gene related peptide (CGRP), hydralazine and nicotinamide]. In addition we have measured other relevant physiological parameters, such as bioenergetic status from (31)P MRS, and blood pH and glucose, that may change during a vasoactive challenge. Here we discuss how they relate to our understanding of FLOOD contrast in tumours. We frequently observe R(2)* changes that match the expected action of the vascular stimulus: R(2)* decreases with agents expected to improve tumour oxygenation and blood flow, and increases with agents designed to increase tumour hypoxia. Unlike most normal tissues, tumours have a chaotic and poorly regulated blood supply, and a mix of glycolytic and oxidative metabolism; thus the response to a vasoactive challenge is not predictable. Changes in blood volume can counteract the effect of blood oxygenation changes, and changes in blood pH and glucose levels can alter oxygen extraction. This can lead to R(2)* changes that are smaller or the reverse of those expected. To properly interpret FLOOD contrast changes these effects must be accounted for.

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

BACKGROUND AND PURPOSE

Inadequate tumor reoxygenation during radiation therapy may cause local treatment failure. This study was aimed at investigating the potential usefulness of 31P-MRS in monitoring tumor reoxygenation following radiation treatment.

MATERIALS AND METHODS

Tumors of two human melanoma xenograft lines (BEX-t and HUX-t) were exposed to 15.0 Gy, and then the fraction of radiobiologically hypoxic cells, measured by using the paired survival curve method, or tumor bioenergetic status, measured by 31P-MRS as the (PCr + NTPbeta)/Pi resonance ratio, was determined versus time after the radiation exposure.

RESULTS

Untreated BEX-t and HUX-t tumors showed similar fractions of radiobiologically hypoxic cells and similar bioenergetic status, whereas both parameters differed substantially between the lines in irradiated tumors. A close association was found between radiation-induced changes in tumor bioenergetic status and radiation-induced changes in the fraction of radiobiologically hypoxic cells.

CONCLUSION

31P-MRS is a potentially useful method for monitoring tumor reoxygenation following radiation treatment.

31P-nuclear magnetic resonance spectroscopy in vivo of four human melanoma xenograft lines: spin-lattice relaxation times

Phosphorus spin-lattice relaxation times (T1s) were measured in vivo by 31P-nuclear magnetic resonance spectroscopy in tumors from four amelanotic human melanoma xenograft lines grown subcutaneously in BALB/c-nu/nu mice. The T1s were analyzed in relation to tumor volume, fractional tumor water content, and fraction of necrotic tumor tissue. The following resonances were studied: phosphomonoesters (PME), inorganic phosphate (Pi), phosphodiesters (PDE), phosphocreatine (PCr), and nucleoside triphosphates gamma, alpha, and beta (NTP gamma, alpha, and beta). Two different techniques were used to measure the T1s: superfast inversion recovery (SUFIR) and conventional inversion recovery (IR). The SUFIR and IR methods gave similar results. Tumors in the volume range 100-3000 mm3 were studied. The PME, Pi, PDE, and PCr resonances showed significantly longer T1s than the NTP gamma, alpha, and beta resonances at small tumor volumes. The T1s at small tumor volumes also differed significantly between the tumor lines. The T1s either decreased or remained unchanged with increasing tumor volume; the volume-dependence of the T1s differed significantly between the tumor lines but not between the resonances. Calculations based on the T1s measured here indicated that the errors in PCr/Pi and NTP beta/Pi resonance ratios due to partial saturation can vary with tumor volume but are usually < 20% at a repetition time of 2.0 s and < 15% at a repetition time of 3.0 s. There was no correlation between the T1s and fractional tumor water content.(ABSTRACT TRUNCATED AT 250 WORDS)

Phosphorus metabolism during growth of lymphoma in mouse liver: a comparison of 31P magnetic resonance spectroscopy in vivo and in vitro

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

Platinum drug delivery and radiation for locally advanced prostate cancer

Combined therapies of cisplatin and radiation have resulted in clinical reports of apparent efficacious control of locoregional cancer and enhanced survival. Mechanisms of interaction between platinum and radiation that may explain these clinical observations all have in common the prediction that higher concentrations of platinum in all tumor cells close in time to irradiation should lead to greater potentiation of radiation-induced killing of those cells. Cisplatin is thus viewed as providing some radiation-equivalent, or a radiation dose-effect factor, for sterilization of tumors. One disease site that has not been well investigated for response to cisplatin plus radiation therapy, but that could benefit from it, is locally advanced prostate cancer. A body of literature now supports the view that local control of stage C (T3, N0, M0) prostate cancer is correlated with disease-free survival. This correlation makes prostate cancer a candidate for potentially achieving improved cure rates following local tumor sterilization by combining cisplatin with radiation therapy. The need and approaches to optimize delivery of cisplatin within tumor tissue is explored. Increasing cisplatin concentration to all the cells of a tumor, i.e., homogeneously delivering systemic high-dose cisplatin, should benefit the efficacious response otherwise expected for cisplatin combined with radiation. Strategies to increase the homogeneity of cisplatin delivery to a tumor are considered to be those that increase perfusion to that tumor. Vasoactive agents used in anticancer protocols are especially considered for their potential value in serving to increase tumor perfusion. These protocol-inclusive agents include certain cytokines and L-arginine antagonists, and should be better managed and accepted in practice compared to other vasoactive agents that need to be developed as specific additives to protocol designs.

Stable bioenergetic status despite substantial changes in blood flow and tissue oxygenation in a rat tumour

Experiments on s.c. rat tumours (DS sarcoma) were performed to determine whether chronic or acute changes in tumour perfusion necessarily lead to changes in tissue oxygenation and bioenergetic status since, as a rule, blood flow is thought to be the ultimate determinant of the tumour bioenergetic status. Based on this study, there is clear experimental evidence that growth-related or acute (following i.v. administration of tumour necrosis factor alpha) decreases in tumour blood flow are accompanied by parallel alterations in tissue oxygenation. In contrast, tumour energy status remains stable as long as flow values do not fall below 0.4-0.5 ml g-1 min-1, and provided that glucose as the main substrate can be recruited from the enlarged interstitial compartment. Perfusion rate seems to play a paramount role in determining energy status only in low-flow tumours or low-flow tissue areas.

In vivo 31P MRS of experimental tumours

More than 50% of cancers fail to respond to any individual treatment and tumour follow-up after treatment plays a major role in routine therapy planning and pharmacological research. Today, MRS is the only technological approach providing non-invasive access to tumour biochemistry. Ten years ago, expectations were raised concerning 31P MRS as an exciting and promising technical approach to the study of tumours. However the expectations have not always come to fruition. How close are we now to seeing routine 31P NMR in clinical oncology? This review of the 127 published papers shows spectroscopy results in more than 150 experimental animal tumour models. These tumour/host/treatment systems provide us with a useful basis to evaluate the current state of the art, summarize the basic knowledge presently available, determine the key points underlying the present disappointment of some clinical oncologists and stimulate new basic research. The information collected concerns the discussion of the reliability of experimental models in oncology, the technical improvement of magnetic resonance technology and the monitoring of bioenergetic status, pH regulation and phospholipid metabolism in treated and untreated tumours. Recent advances (two-thirds of the papers have been published in the last 5 years) seem to provide more optimistic perspectives than those generally accepted a few years ago, in the depressing period following early pioneering work.