The assessment of treatment response in non-Hodgkin's lymphoma by image guided 31P magnetic resonance spectroscopy

Impact of cannabis use on brain metabolism using 31P and 1H magnetic resonance spectroscopy

PURPOSE

This prospective cross-sectional study investigated the influence of regular cannabis use on brain metabolism in young cannabis users by using combined proton and phosphorus magnetic resonance spectroscopy.

METHODS

The study was performed in 45 young cannabis users aged 18-30, who had been using cannabis on a regular basis over a period of at least 2 years and in 47 age-matched controls. We acquired 31P MRS data in different brain regions at 3T with a double-resonant 1H/31P head coil, anatomic images, and 1H MRS data with a standard 20-channel 1H head coil. Absolute concentration values of proton metabolites were obtained via calibration from tissue water as an internal reference, whereas a standard solution of 75 mmol/l KH2PO4 was used as an external reference for the calibration of phosphorus signals.

RESULTS

We found an overall but not statistically significant lower concentration level of several proton and phosphorus metabolites in cannabis users compared to non-users. In particular, energy-related phosphates such as adenosine triphosphate (ATP) and inorganic phosphate (Pi) were reduced in all regions under investigation. Phosphocreatine (PCr) showed lowered values mainly in the left basal ganglia and the left frontal white matter.

CONCLUSION

The results suggest that the increased risk of functional brain disorders observed in long-term cannabis users could be caused by an impairment of the energy metabolism of the brain, but this needs to be verified in future studies.

Cancer insights from magnetic resonance spectroscopy of cells and excised tumors

Multinuclear ex vivo magnetic resonance spectroscopy (MRS) of cancer cells, xenografts, human cancer tissue, and biofluids is a rapidly expanding field that is providing unique insights into cancer. Starting from the 1970s, the field has continued to evolve as a stand-alone technology or as a complement to in vivo MRS to characterize the metabolome of cancer cells, cancer-associated stromal cells, immune cells, tumors, biofluids and, more recently, changes in the metabolome of organs induced by cancers. Here, we review some of the insights into cancer obtained with ex vivo MRS and provide a perspective of future directions. Ex vivo MRS of cells and tumors provides opportunities to understand the role of metabolism in cancer immune surveillance and immunotherapy. With advances in computational capabilities, the integration of artificial intelligence to identify differences in multinuclear spectral patterns, especially in easily accessible biofluids, is providing exciting advances in detection and monitoring response to treatment. Metabolotheranostics to target cancers and to normalize metabolic changes in organs induced by cancers to prevent cancer-induced morbidity are other areas of future development.

Early detection of changes in phospholipid metabolism during neoadjuvant chemotherapy in breast cancer patients using phosphorus magnetic resonance spectroscopy at 7T

The purpose of this work was to investigate whether noninvasive early detection (after the first cycle) of response to neoadjuvant chemotherapy (NAC) in breast cancer patients was possible. ³¹ P-MRSI at 7 T was used to determine different phosphor metabolites ratios and correlate this to pathological response. ³¹ P-MRSI was performed in 12 breast cancer patients treated with NAC. ³¹ P spectra were fitted and aligned to the frequency of phosphoethanolamine (PE). Metabolic signal ratios for phosphomonoesters/phosphodiesters (PME/PDE), phosphocholine/glycerophosphatidylcholine (PC/GPtC), phosphoethanolamine/glycerophosphoethanolamine (PE/GPE) and phosphomonoesters/in-organic phosphate (PME/Pi) were determined from spectral fitting of the individual spectra and the summed spectra before and after the first cycle of NAC. Metabolic ratios were subsequently related to pathological response. Additionally, the correlation between the measured metabolic ratios and Ki-67 levels was determined using linear regression. Four patients had a pathological complete response after treatment, five patients a partial pathological response, and three patients did not respond to NAC. In the summed spectrum after the first cycle of NAC, PME/Pi and PME/PDE decreased by 18 and 13%, respectively. A subtle difference among the different response groups was observed in PME/PDE, where the nonresponders showed an increase and the partial and complete responders a decrease (P = 0.32). No significant changes in metabolic ratios were found. However, a significant association between PE/Pi and the Ki-67 index was found (P = 0.03). We demonstrated that it is possible to detect subtle changes in ³¹ P metabolites with a 7 T MR system after the first cycle of NAC treatment in breast cancer patients. Nonresponders showed different changes in metabolic ratios compared with partial and complete responders, in particular for PME/PDE; however, more patients need to be included to investigate its clinical value.

Comparison of three reference methods for the measurement of intracellular pH using 31P MRS in healthy volunteers and patients with lymphoma

31P magnetic resonance spectroscopy (31P MRS) can measure intracellular pH (pHi) using the chemical shift difference between pH-dependent inorganic phosphate (Pi) and a pH-independent reference peak. This study compared three different frequency reference peaks [phosphocreatine (PCr), α resonance of adenosine triphosphate (αATP) and water (using 1H MRS)] in a cohort of 10 volunteers and eight patients with non-Hodgkin's lymphoma (NHL). Well-resolved chemical shift imaging (CSI) spectra were acquired on a 1.5T scanner for muscle, liver and tumour. The pH was calculated for all volunteers and patients using the available methods. The consistency of the resulting pH was evaluated. The direct Pi–PCr method was best for those spectra with a very well-defined PCr, such as muscle (pH=7.05 ± 0.02). In liver, the Pi–αATP method gave more consistent results (pH=7.30 ± 0.06) than the calibrated water-based method (pH=7.27 ± 0.11). In NHL nodes, the measured pH using the Pi–αATP method was 7.25 ± 0.12. Given that the measured range includes some biological variation in individual patients, treatment-related changes of the order of 0.1 pH units should be detectable.

Early detection of radiation therapy response in non-Hodgkin's lymphoma xenografts by in vivo 1H magnetic resonance spectroscopy and imaging

The purpose of the study was to investigate the capability of (1)H MRS and MRI methods for detecting early response to radiation therapy in non-Hodgkin's lymphoma (NHL). Studies were performed on the WSU-DLCL2 xenograft model in nude mice of human diffuse large B-cell lymphoma, the most common form of NHL. Radiation treatment was applied as a single 15 Gy dose to the tumor. Tumor lactate, lipids, total choline, T(2) and apparent diffusion coefficients (ADC) were measured before treatment and at 24 h and 72 h after radiation. A Hadamard-encoded slice-selective multiple quantum coherence spectroscopy sequence was used for detecting lactate (Lac) while a stimulated echo acquisition mode sequence was used for detection of total choline (tCho) and lipids. T(2)- and diffusion-weighted imaging sequences were used for measuring T(2) and ADC. Within 24 h after radiation, significant changes were observed in the normalized integrated resonance intensities of Lac and the methylenes of lipids. Lac/H(2)O decreased by 38 +/- 15% (p = 0.03), and lipid (1.3 ppm, CH(2))/H(2)O increased by 57 +/- 14% (p = 0.01). At 72 h after radiation, tCho/H(2)O decreased by 45 +/- 14% (p = 0.01), and lipid (2.8 ppm, polyunsaturated fatty acid)/H(2)O increased by 970 +/- 36% (p = 0.001). ADC increased by 14 +/- 2% (p = 0.003), and T(2) did not change significantly. Tumor growth delay and regression were observed thereafter. This study enabled comparison of the relative sensitivities of various (1)H MRS and MRI indices to radiation and suggests that (1)H MRS/MRI measurements detect early responses to radiation that precede tumor volume changes.

In vivo MRS markers of response to CHOP chemotherapy in the WSU-DLCL2 human diffuse large B-cell lymphoma xenograft

To identify 1H-MRS molecular biomarkers of early clinical therapeutic response in non-Hodgkin's lymphoma, an in vivo longitudinal study was performed on human non-Hodgkin's diffuse large B-cell lymphoma xenografts (WSU-DLCL2) grown in the flanks of female SCID mice. 31P-MRS measurements, which have been demonstrated to be prognostic clinical indices of response (Arias-Mendoza et al. Acad. Radiol. 2004; 11: 368-376) but which provide lower spatial resolution, were included for comparison. The animals received CHOP (cyclophosphamide, hydroxydoxorubicin, oncovin and prednisone) chemotherapy for three 1-week cycles, resulting in stable disease based on tumor volume. Localization of total choline and phosphorus metabolites in vivo was achieved with stimulated echo acquisition mode and image selected in vivo spectroscopy sequences, respectively. Significant decreases in lactate were detected by the selective multiple quantum coherence spectral editing technique after the first cycle of CHOP, whereas total choline and the phosphomonoester/nucleoside triphosphate ratio did not change until the third cycle. Ex vivo extract MRS of tumors corroborated the in vivo results. Histological staining with antibodies to Ki67 revealed a decrease in proliferation rate in CHOP-treated tumors that coincided with the decrease in lactate. This study demonstrates the utility of lactate as an early proliferation-sensitive indicator of therapeutic response in a mouse model of non-Hodgkin's lymphoma and serves as a basis for future clinical implementation of these methods.

Extracellular pH and P-31 magnetic resonance spectroscopic variables are related to outcome in canine soft tissue sarcomas treated with thermoradiotherapy

PURPOSE

The objective was to test whether tumor pH and (31)P magnetic resonance spectroscopic end points were related to treatment outcome in pet canine patients with spontaneous soft tissue sarcomas treated with thermoradiotherapy.

EXPERIMENTAL DESIGN

Forty-two dogs with evaluable (31)P magnetic resonance spectroscopic end points and pH data were included in this study. Tumor variables (grade and volume), extracellular pH (pHe), T(2) relaxation times, intracellular pH, and selected phosphometabolite ratios were examined for correlation with clinical outcome.

RESULTS

From 39 dogs, pHe was a predictor of metastasis-free survival (MFS), with hazard ratio (HR, 0.29; P = 0.005) and overall survival (OS) with (HR, 0.36; P = 0.013). Tumor volume (>19 cm(3)) was related to MFS (HR, 2.14; P = 0.04), time to local failure (HR, 3.4; P = 0.025), and OS (HR, 2.27; P = 0.03). There was no association between T(2) or intracellular pH and clinical outcome. Tumor grade (high versus low/intermediate) and phosphodiester/betaATP ratio were identified as significant predictors for MFS, with (HR, 2.66; P = 0.009) and (HR, 0.75; P = 0.027), respectively, and as predictors of OS with (HR, 2.66; P = 0.009) and (HR, 0.76; P = 0.03), respectively. The phosphodiester/phosphocreatinine ratio predicted time to local failure (HR, 1.24; P = 0.017).

CONCLUSIONS

pHe was predictive of metastasis and OS in canine spontaneous sarcomas. To our knowledge, this is the first time that pHe has been shown to be predictive of clinical outcome. The results suggest that additional studies should be considered evaluating the prognostic significance of this variable. Phospholipid resonances, related to membrane metabolism, were related to clinical outcome, confirming recent results reported in human patients with soft tissue sarcomas treated with thermoradiotherapy.

Potential role of magnetic resonance spectroscopy in assessment of tumour response in childhood cancer

This brief review considers to what extent Magnetic Resonance Spectroscopy (MRS) can play a role in monitoring early tumour response with examples of preclinical studies and selected clinical studies in tumours of children and young adults. An early non-invasive indicator of tumour response to therapy would provide useful information regarding the effectiveness of therapy. This might be a relevant prognostic factor in new patients and in phase II studies could facilitate recommendations at an early stage as to whether to continue treatment. This review suggests that several markers and ratios are emerging as potential prognostic markers, but larger prospective studies are needed before translating this into clinical practice.

Tumour phospholipid metabolism

Following the impetus of early clinical and experimental investigations, in vivo and in vitro MRS studies of tumours pointed in the eighties to the possible significance of signals arising from phospholipid (PL) precursors and catabolites as novel biochemical indicators of in vivo tumour progression and response to therapy. In the present decade, MRS analyses of individual components contributing to the 31P PME (phosphomonoester) and PDE (phosphodiester) resonances, as well as to the 1H 'choline peak', have reinforced some of these expectations. Moreover, the absolute quantification of these signals provided the basis for addressing more specific (although still open) questions on the biochemical mechanisms responsible for the formation of intracellular pools of PL derivatives in tumours, under different conditions of cell proliferative status and/or malignancy level. This article is aimed at providing an overview on: (a) quantitative MRS measurements on the contents of phosphocholine (PCho), phosphoethanolamine (PEtn) and their glycerol derivatives ģlycerol 3-phosphocholine (GPC) and glycerol 3-phosphoethanolamine (GPE)[ in human tumours and cells (with particular attention to breast and brain cancer and lymphomas), as well as in normal mammalian tissues (including developing organs and rapidly proliferating tissues); (b) possible correlations of MRS parameters like PEtn/PCho and PCho/GPC ratios with in vitro cell growth status and/or cell tumorigenicity; and (c) current and new hypotheses on the role and interplay of biosynthetic and catabolic pathways of the choline and ethanolamine cycles in modulating the intracellular sizes of PCho and PEtn pools, either in response to mitogenic stimuli or in relation to malignant transformation.

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 beta-ATP/Pi, PME/Pi, and beta-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 beta-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 beta-ATP/Pi 24 hr after radiation were inversely related to radiation dose.

CONCLUSION

The increase in beta-ATP/Pi observed by 31P-MRS was linked to the degree of histological recovery from radiation-induced apoptosis.

Tumor pH: implications for treatment and novel drug design

Although limited data exist, electrode-measured pH values of human tumors and adjacent normal tissues, which are concurrently obtained by the same investigator in the same patient, consistently show that the electrode pH (believed to represent tissue extracellular pH primarily) is substantially and consistently lower in tumor than in normal tissue. In contrast, the 31P-magnetic resonance spectroscopy-estimated intracellular pH is essentially identical or slightly more basic in tumor compared with normal tissue. As a consequence, the cellular pH gradient is substantially reduced or reversed in these tissues. This difference provides an exploitable avenue for the treatment of cancer. The extent to which drugs exhibiting weakly acid or basic properties are ionized depends on their ionization potential (pKa) and the pH of their milieu. Weakly acidic drugs that are lipid soluble in their nonionized state diffuse freely across the cell membrane and on entering a relatively basic intracellular compartment become trapped and accumulate within the cell. This may lead to substantial (10-fold or more) differences in the intracellular-to-extracellular drug distribution between tumor and normal tissue for cytotoxics, hypoxic cell sensitizers, or other drugs exhibiting appropriate pKa. Experimental in vitro evaluation of these predictions confirms both the predicted pH gradient-dependent changes in cellular drug accumulation and toxicity.

Treatment-induced changes in 31P-MRS (magnetic resonance spectroscopy) spectra of sera from patients with acute leukemia

31P-nuclear magnetic resonance (NMR) spectra were obtained in vitro from sera of 40 healthy volunteers and 30 patients with acute leukemia (AL) at the time of diagnosis and repeated up to 2-13 times during therapy. All spectra consisted of inorganic phosphate (Pi) peak (used as a reference peak) and two peaks from phospholipids (PL): one peak due to phosphatidylethanolamine and sphingomyelin (PE + SM) and second peak due to phosphatidylcholine (PC). Prior to initiation of therapy 31P spectra of sera of patients with acute leukemia differed from spectra of sera of normal individuals. Peak intensities of the PL were low in relation to Pi. During therapy leading to remission, resonance from PL progressively increased approximately to the spectral pattern in normal sera. Contrary to that, in non-responders the intensities of the phospholipids peaks remained unchanged. Long-term follow-up 31P-MRS studies showed not only a good correlation between this 31P-MRS evolution of sera and the response to the therapy but also showed changes in phospholipids' levels in the following days during and after therapy. Moreover, correlations were found between high-density lipoprotein (HDL), cholesterol (CHOL) and low-density lipoprotein (LDL) concentrations measured by conventional techniques and peak intensities of PC and of PE + SM acquired by 31P-MRS.

Characterization of a murine lymphoma cell line by 31P-NMR spectroscopy: in vivo monitoring of the local anti-tumor effects of systemic immune cell transfer

The intradermal ESb-MP murine T-cell lymphoma in syngeneic DBA/2 mice has been used as a model for adoptive immunotherapy (ADI). Cultured ESb-MP cells were characterized in suspension by 31P-NMR spectroscopy (MRS) at 11.7 T, and solid primary tumors were examined by 31P-MRS in vivo at 7.0 Tesla using surface-coil techniques. Growing tumors contained relatively high levels of phosphomonoesters (PME, predominantly phosphoethanolamine), nucleotides (NTP) and Pi, low levels of phosphodiesters (PDE) and no phosphocreatine. Mean tissue pH was found to be 6.7-6.9. The spectra of ESb-MP cells cultured in RPMI medium (containing choline but no ethanolamine) also showed low PDE and no phosphocreatine at an intracellular pH of 7.4; however, only a trace amount of phosphoethanolamine was detected and significant levels of nucleoside mono- and diphosphates were observed. The complete ADI treatment protocol involved low-dose irradiation (5 Gy) followed by i.v. transfer of immune spleen cells from allogeneic B10.D2 donors and resulted in 100% remission (responders); no treatment or incomplete ADI (irradiation or immune cell transfer alone) resulted in no remissions (nonresponders). In vivo MRS could best discriminate between responders and non-responders on the basis of tissue pH, which increased in responders to 7.0 by day 5-6 after complete ADI. Following therapy, the sum of PME + Pi (both absolute and as a percent of total phosphates) decreased significantly only for responders but only after a visible decrease in tumor volume was apparent.

Phospholipid metabolites, prognosis and proliferation in human breast carcinoma

The content of the phospholipid metabolites, phosphocholine, phosphoethanolamine, glycerophosphorylcholine and glycerophosphorylethanolamine was measured in chemical extracts from 46 human breast carcinoma using 31P NMR spectroscopy. Some patients had received therapy prior to tumour resection. The data were therefore stratified into two groups: (i) all tumours; and (ii) untreated tumours. Three indices of tumour proliferation i.e., mitotic index, Ki67 and S-phase fraction were determined on tissue from the same tumours and were found not to correlate with the content of any of these metabolites. In addition oestrogen-receptor status and density, tumour grade and DNA ploidy were obtained on some tumours. The phosphocholine content was higher in high grade tumours when compared with low grade tumours. There was no apparent relationship between DNA ploidy and the content of any of these metabolites. Glycerophosphorylcholine content of oestrogen-receptor positive tumours correlated with receptor density. However, there was no significant difference between receptor positive and negative tumours in the content of any of the phospholipid metabolites measured.

Studies of human tumors by MRS: a review

The literature describing 31P, 1H, 13C, 23Na and 19F MRS in vivo in human cancers is reviewed. Cancers have typical metabolic characteristics in 31P and 1H MRS including high levels of phospholipid metabolites and a cellular pH more alkaline than normal. These alone are not specific for cancer but are diagnostic in appropriate clinical settings. Some metabolic characteristics appear to be prognostic indices and correlation with treatment response is emerging as an important potentially cost-effective use of MRS in oncology. 19F MRS examines pharmacokinetics of 5-fluorouracil and by demonstrating its retention predicts response of a cancer to treatment. Current needs include improvement of diagnostic specificity by use of techniques like multivoxel MRS, proton decoupling of 31P, short echo time and fat-suppressed 1H MRS, 13C MRS direct or via 1H-observe, and statistical analysis of multiple spectral features. Trials in large populations in well defined clinical settings are needed to determine if MRS can provide independent prognostic indices useful in cancer management.

Tumour pH and response to chemotherapy: an in vivo 31P magnetic resonance spectroscopy study in non-Hodgkin's lymphoma

Serial image-localized 31P magnetic resonance spectroscopy studies were performed in nine patients with newly diagnosed non-Hodgkin's lymphoma (NHL) during the early part of treatment with chemotherapy. The pre-treatment intracellular pH (pHi) of the tumours ranged from 6.97 to 7.61 for high-grade NHL (n = 3), and 7.16 to 7.39 for low-grade NHL (n = 5). A pH of 7.24 was recorded in a patient with intermediate-grade NHL. Slice-to-slice variation in tumour pHi in spectra obtained with a one-dimensional chemical shift imaging (1D-CSI) technique varied from zero to 0.5 pH units. The largest variation was seen in high-grade tumours. Slice-to-slice variation may reflect tumour heterogeneity. Alkaline shifts in tumour pHi of 0.14 to 0.45 pH units were seen in six patients following chemotherapy. Maximal change in tumour pH was related temporally to increases in the phosphodiester/beta-adenosine triphosphate ratio, and occurred before alterations in tumour size were documented. Cell death and necrosis may be associated with an alkaline shift in pHi due to cessation of H(+)-producing processes and release of basic components of proteins. An alkaline shift in tumour pHi may therefore be an early metabolic marker of response to chemotherapy.