Magnetic resonance detects changes in phosphocholine associated with Ras activation and inhibition in NIH 3T3 cells

Imaging biomarkers of TERT or GABPB1 silencing in TERT-positive glioblastoma

BACKGROUND

TERT promoter mutations are observed in 80% of wild-type IDH glioblastoma (GBM). Moreover, the upstream TERT transcription factor GABPB1 was recently identified as a cancer-specific therapeutic target for tumors harboring a TERT promoter mutation. In that context, noninvasive imaging biomarkers are needed for the detection of TERT modulation.

METHODS

Multiple GBM models were investigated as cells and in vivo tumors and the impact of TERT silencing, either directly or by targeting GABPB1, was determined using 1H and hyperpolarized 13C magnetic resonance spectroscopy (MRS). Changes in associated metabolic enzymes were also investigated.

RESULTS

1H-MRS revealed that lactate and glutathione (GSH) were the most significantly altered metabolites when either TERT or GABPB1 was silenced, and lactate and GSH levels were correlated with cellular TERT expression. Consistent with the drop in lactate, 13C-MRS showed that hyperpolarized [1-13C]lactate production from [1-13C]pyruvate was also reduced when TERT was silenced. Mechanistically, the reduction in GSH was associated with a reduction in pentose phosphate pathway flux, reduced activity of glucose-6-phosphate dehydrogenase, and reduced NADPH. The drop in lactate and hyperpolarized lactate were associated with reductions in glycolytic flux, NADH, and expression/activity of GLUT1, monocarboxylate transporters, and lactate dehydrogenase A.

CONCLUSIONS

Our study indicates that MRS-detectable GSH, lactate, and lactate production could serve as metabolic biomarkers of response to emerging TERT-targeted therapies for GBM with activating TERT promoter mutations. Importantly these biomarkers are readily translatable to the clinic, and thus could ultimately improve GBM patient management.

MR-detectable metabolic biomarkers of response to mutant IDH inhibition in low-grade glioma

Mutations in isocitrate dehydrogenase 1 (IDH1mut) are reported in 70-90% of low-grade gliomas and secondary glioblastomas. IDH1mut catalyzes the reduction of α-ketoglutarate (α-KG) to 2-hydroxyglutarate (2-HG), an oncometabolite which drives tumorigenesis. Inhibition of IDH1mut is therefore an emerging therapeutic approach, and inhibitors such as AG-120 and AG-881 have shown promising results in phase 1 and 2 clinical studies. However, detection of response to these therapies prior to changes in tumor growth can be challenging. The goal of this study was to identify non-invasive clinically translatable metabolic imaging biomarkers of IDH1mut inhibition that can serve to assess response. Methods: IDH1mut inhibition was confirmed using an enzyme assay and 1H- and 13C- magnetic resonance spectroscopy (MRS) were used to investigate the metabolic effects of AG-120 and AG-881 on two genetically engineered IDH1mut-expressing cell lines, NHAIDH1mut and U87IDH1mut. Results:1H-MRS indicated a significant decrease in steady-state 2-HG following treatment, as expected. This was accompanied by a significant 1H-MRS-detectable increase in glutamate. However, other metabolites previously linked to 2-HG were not altered. 13C-MRS also showed that the steady-state changes in glutamate were associated with a modulation in the flux of glutamine to both glutamate and 2-HG. Finally, hyperpolarized 13C-MRS was used to show that the flux of α-KG to both glutamate and 2-HG was modulated by treatment. Conclusion: In this study, we identified potential 1H- and 13C-MRS-detectable biomarkers of response to IDH1mut inhibition in gliomas. Although further studies are needed to evaluate the utility of these biomarkers in vivo, we expect that in addition to a 1H-MRS-detectable drop in 2-HG, a 1H-MRS-detectable increase in glutamate, as well as a hyperpolarized 13C-MRS-detectable change in [1-13C] α-KG flux, could serve as metabolic imaging biomarkers of response to treatment.

Application of in vivo MR methods in the study of breast cancer metabolism

In the last two decades, various in vivo MR methodologies have been evaluated for their potential in the study of cancer metabolism. During malignant transformation, metabolic alterations occur, leading to morphological and functional changes. Among various MR methods, in vivo MRS has been extensively used in breast cancer to study the metabolism of cells, tissues or whole organs. It provides biochemical information at the metabolite level. Altered choline, phospholipid and energy metabolism has been documented using proton (¹ H), phosphorus (³¹ P) and carbon (¹³ C) isotopes. Increased levels of choline-containing compounds, phosphomonoesters and phosphodiesters in breast cancer, which are indicative of altered choline and phospholipid metabolism, have been reported using in vivo, in vitro and ex vivo NMR studies. These changes are reversed on successful therapy, which depends on the treatment regimen given. Monitoring the various tumor intermediary metabolic pathways using nuclear spin hyperpolarization of ¹³ C-labeled substrates by dynamic nuclear polarization has also been recently reported. Furthermore, the utility of various methods such as diffusion, dynamic contrast and perfusion MRI have also been evaluated to study breast tumor metabolism. Parameters such as tumor volume, apparent diffusion coefficient, volume transfer coefficient and extracellular volume ratio are estimated. These parameters provide information on the changes in tumor microstructure, microenvironment, abnormal vasculature, permeability and grade of the tumor. Such changes seen during cancer progression are due to alterations in the tumor metabolism, leading to changes in cell architecture. Due to architectural changes, the tissue mechanical properties are altered; this can be studied using magnetic resonance elastography, which measures the elastic properties of tissues. Moreover, these structural MRI methods can be used to investigate the effect of therapy-induced changes in tumor characteristics. This review discusses the potential of various in vivo MR methodologies in the study of breast cancer metabolism.

The relevance of tyrosine kinase inhibitors for global metabolic pathways in cancer

Tumor metabolism is a thrilling discipline that focuses on mechanisms used by cancer cells to earn crucial building blocks and energy to preserve growth and overcome resistance to various treatment modalities. At the same time, therapies directed specifically against aberrant signalling pathways driven by protein tyrosine kinases (TKs) involved in proliferation, metastasis and growth count for several years to promising anti-cancer approaches. In this respect, small molecule inhibitors are the most widely used clinically relevant means for targeted therapy, with a rising number of approvals for TKs inhibitors. In this review, we discuss recent observations related to TKs-associated metabolism and to metabolic feedback that is initialized as cellular response to particular TK-targeted therapies. These observations provide collective evidence that therapeutic responses are primarily linked to such pathways as regulation of lipid and amino acid metabolism, TCA cycle and glycolysis, advocating therefore the development of further effective targeted therapies against a broader spectrum of TKs to treat patients whose tumors display deregulated signalling driven by these proteins.

1H-NMR-based metabolic profiling of a colorectal cancer CT-26 lung metastasis model in mice

Lung metastasis is an important cause for the low 5-year survival rate of colorectal cancer patients. Understanding the metabolic profile of lung metastasis of colorectal cancer is important for developing molecular diagnostic and therapeutic approaches. We carried out the metabonomic profiling of lung tissue samples on a mouse lung metastasis model of colorectal cancer using 1H-nuclear magnetic resonance (1H-NMR). The lung tissues of mice were collected at different intervals after marine colon cancer cell line CT-26 was intravenously injected into BALB/c mice. The distinguishing metabolites of lung tissue were investigated using 1H-NMR-based metabonomic assay, which is a highly sensitive and non-destructive method for biomarker identification. Principal component analysis (PCA), partial least squares discriminant analysis (PLS-DA) and orthogonal partial least squares discriminant analysis (OPLS-DA) were applied to analyze 1H-NMR profiling data to seek potential biomarkers. All of the 3 analyses achieved excellent separations between the normal and metastasis groups. A total of 42 metabolites were identified, ~12 of which were closely correlated with the process of metastasis from colon to lung. These altered metabolites indicated the disturbance of metabolism in metastatic tumors including glycolysis, TCA cycle, glutaminolysis, choline metabolism and serine biosynthesis. Our findings firstly identified the distinguishing metabolites in mouse colorectal cancer lung metastasis models, and indicated that the metabolite disturbance may be associated with the progression of lung metastasis from colon cancer. The altered metabolites may be potential biomarkers that provide a promising molecular approach for clinical diagnosis and mechanistic study of colorectal cancer with lung metastasis.

Near infrared fluorescent imaging of choline kinase alpha expression and inhibition in breast tumors

Choline kinase alpha (ChoKα) overexpression is associated with an aggressive tumor phenotype. ChoKα inhibitors induce apoptosis in tumors, however validation of their specificity is difficult in vivo. We report the use of optical imaging to assess ChoKα status in cells and in vivo using JAS239, a carbocyanine-based ChoKα inhibitor with inherent near infrared fluorescence. JAS239 attenuated choline phosphorylation and viability in a panel of human breast cancer cell lines. Antibody blockade prevented cellular retention of JAS239 indicating direct interaction with ChoKα independent of the choline transporters and catabolic choline pathways. In mice bearing orthotopic MCF7 breast xenografts, optical imaging with JAS239 distinguished tumors overexpressing ChoKα from their empty vector counterparts and delineated tumor margins. Pharmacological inhibition of ChoK by the established inhibitor MN58b led to a growth inhibition in 4175-Luc+ tumors that was accompanied by concomitant reduction in JAS239 uptake and decreased total choline metabolite levels as measured using magnetic resonance spectroscopy. At higher therapeutic doses, JAS239 was as effective as MN58b at arresting tumor growth and inducing apoptosis in MDA-MB-231 tumors, significantly reducing tumor choline below baseline levels without observable systemic toxicity. These data introduce a new method to monitor therapeutically effective inhibitors of choline metabolism in breast cancer using a small molecule companion diagnostic.

Breast Tissue Metabolism by Magnetic Resonance Spectroscopy

Metabolic alterations are known to occur with oncogenesis and tumor progression. During malignant transformation, the metabolism of cells and tissues is altered. Cancer metabolism can be studied using advanced technologies that detect both metabolites and metabolic activities. Identification, characterization, and quantification of metabolites (metabolomics) are important for metabolic analysis and are usually done by nuclear magnetic resonance (NMR) or by mass spectrometry. In contrast to the magnetic resonance imaging that is used to monitor the tumor morphology during progression of the disease and during therapy, in vivo NMR spectroscopy is used to study and monitor tumor metabolism of cells/tissues by detection of various biochemicals or metabolites involved in various metabolic pathways. Several in vivo, in vitro and ex vivo NMR studies using ¹H and ³¹P magnetic resonance spectroscopy (MRS) nuclei have documented increased levels of total choline containing compounds, phosphomonoesters and phosphodiesters in human breast cancer tissues, which is indicative of altered choline and phospholipid metabolism. These levels get reversed with successful treatment. Another method that increases the sensitivity of substrate detection by using nuclear spin hyperpolarization of ¹³C-lableled substrates by dynamic nuclear polarization has revived a great interest in the study of cancer metabolism. This review discusses breast tissue metabolism studied by various NMR/MRS methods.

(1)H NMR studies distinguish the water soluble metabolomic profiles of untransformed and RAS-transformed cells

Metabolomic profiling is an increasingly important method for identifying potential biomarkers in cancer cells with a view towards improved diagnosis and treatment. Nuclear magnetic resonance (NMR) provides a potentially noninvasive means to accurately characterize differences in the metabolomic profiles of cells. In this work, we use (1)H NMR to measure the metabolomic profiles of water soluble metabolites extracted from isogenic control and oncogenic HRAS-, KRAS-, and NRAS-transduced BEAS2B lung epithelial cells to determine the robustness of NMR metabolomic profiling in detecting differences between the transformed cells and their untransformed counterparts as well as differences among the RAS-transformed cells. Unique metabolomic signatures between control and RAS-transformed cell lines as well as among the three RAS isoform-transformed lines were found by applying principal component analysis to the NMR data. This study provides a proof of principle demonstration that NMR-based metabolomic profiling can robustly distinguish untransformed and RAS-transformed cells as well as cells transformed with different RAS oncogenic isoforms. Thus, our data may potentially provide new diagnostic signatures for RAS-transformed cells.

Metabolite profiling in retinoblastoma identifies novel clinicopathological subgroups

BACKGROUND

Tumour classification, based on histopathology or molecular pathology, is of value to predict tumour behaviour and to select appropriate treatment. In retinoblastoma, pathology information is not available at diagnosis and only exists for enucleated tumours. Alternative methods of tumour classification, using noninvasive techniques such as magnetic resonance spectroscopy, are urgently required to guide treatment decisions at the time of diagnosis.

METHODS

High-resolution magic-angle spinning magnetic resonance spectroscopy (HR-MAS MRS) was undertaken on enucleated retinoblastomas. Principal component analysis and cluster analysis of the HR-MAS MRS data was used to identify tumour subgroups. Individual metabolite concentrations were determined and were correlated with histopathological risk factors for each group.

RESULTS

Multivariate analysis identified three metabolic subgroups of retinoblastoma, with the most discriminatory metabolites being taurine, hypotaurine, total-choline and creatine. Metabolite concentrations correlated with specific histopathological features: taurine was correlated with differentiation, total-choline and phosphocholine with retrolaminar optic nerve invasion, and total lipids with necrosis.

CONCLUSIONS

We have demonstrated that a metabolite-based classification of retinoblastoma can be obtained using ex vivo magnetic resonance spectroscopy, and that the subgroups identified correlate with histopathological features. This result justifies future studies to validate the clinical relevance of these subgroups and highlights the potential of in vivo MRS as a noninvasive diagnostic tool for retinoblastoma patient stratification.

Metabolic reprogramming in mutant IDH1 glioma cells

BACKGROUND

Mutations in isocitrate dehydrogenase (IDH) 1 have been reported in over 70% of low-grade gliomas and secondary glioblastomas. IDH1 is the enzyme that catalyzes the oxidative decarboxylation of isocitrate to α-ketoglutarate while mutant IDH1 catalyzes the conversion of α-ketoglutarate into 2-hydroxyglutarate. These mutations are associated with the accumulation of 2-hydroxyglutarate within the tumor and are believed to be one of the earliest events in the development of low-grade gliomas. The goal of this work was to determine whether the IDH1 mutation leads to additional magnetic resonance spectroscopy (MRS)-detectable changes in the cellular metabolome.

METHODS

Two genetically engineered cell models were investigated, a U87-based model and an E6/E7/hTERT immortalized normal human astrocyte (NHA)-based model. For both models, wild-type IDH1 cells were generated by transduction with a lentiviral vector coding for the wild-type IDH1 gene while mutant IDH1 cells were generated by transduction with a lentiviral vector coding for the R132H IDH1 mutant gene. Metabolites were extracted from the cells using the dual-phase extraction method and analyzed by 1H-MRS. Principal Component Analysis was used to analyze the MRS data.

RESULTS

Principal Component Analysis clearly discriminated between wild-type and mutant IDH1 cells. Analysis of the loading plots revealed significant metabolic changes associated with the IDH1 mutation. Specifically, a significant drop in the concentration of glutamate, lactate and phosphocholine as well as the expected elevation in 2-hydroxyglutarate were observed in mutant IDH1 cells when compared to their wild-type counterparts.

CONCLUSION

The IDH1 mutation leads to several, potentially translatable MRS-detectable metabolic changes beyond the production of 2-hydroxyglutarate.

Magnetic resonance spectroscopy for detection of choline kinase inhibition in the treatment of brain tumors

Abnormal choline metabolism is a hallmark of cancer and is associated with oncogenesis and tumor progression. Increased choline is consistently observed in both preclinical tumor models and in human brain tumors by proton magnetic resonance spectroscopy (MRS). Thus, inhibition of choline metabolism using specific choline kinase inhibitors such as MN58b may be a promising new strategy for treatment of brain tumors. We demonstrate the efficacy of MN58b in suppressing phosphocholine production in three brain tumor cell lines. In vivo MRS studies of rats with intracranial F98-derived brain tumors showed a significant decrease in tumor total choline concentration after treatment with MN58b. High-resolution MRS of tissue extracts confirmed that this decrease was due to a significant reduction in phosphocholine. Concomitantly, a significant increase in poly-unsaturated lipid resonances was also observed in treated tumors, indicating apoptotic cell death. MRI-based volume measurements demonstrated a significant growth arrest in the MN58b-treated tumors in comparison with saline-treated controls. Histologically, MN58b-treated tumors showed decreased cell density, as well as increased apoptotic cells. These results suggest that inhibition of choline kinase can be used as an adjuvant to chemotherapy in the treatment of brain tumors and that decreases in total choline observed by MRS can be used as an effective pharmacodynamic biomarker of treatment response.

Protein and nucleotide biosynthesis are coupled by a single rate-limiting enzyme, PRPS2, to drive cancer

Cancer cells must integrate multiple biosynthetic demands to drive indefinite proliferation. How these key cellular processes, such as metabolism and protein synthesis, crosstalk to fuel cancer cell growth is unknown. Here, we uncover the mechanism by which the Myc oncogene coordinates the production of the two most abundant classes of cellular macromolecules, proteins, and nucleic acids in cancer cells. We find that a single rate-limiting enzyme, phosphoribosyl-pyrophosphate synthetase 2 (PRPS2), promotes increased nucleotide biosynthesis in Myc-transformed cells. Remarkably, Prps2 couples protein and nucleotide biosynthesis through a specialized cis-regulatory element within the Prps2 5' UTR, which is controlled by the oncogene and translation initiation factor eIF4E downstream Myc activation. We demonstrate with a Prps2 knockout mouse that the nexus between protein and nucleotide biosynthesis controlled by PRPS2 is crucial for Myc-driven tumorigenesis. Together, these studies identify a translationally anchored anabolic circuit critical for cancer cell survival and an unexpected vulnerability for "undruggable" oncogenes, such as Myc. PAPERFLICK:

Silencing of the glycerophosphocholine phosphodiesterase GDPD5 alters the phospholipid metabolite profile in a breast cancer model in vivo as monitored by (31) P MRS

Abnormal choline phospholipid metabolism is an emerging hallmark of cancer, which is implicated in carcinogenesis and tumor progression. The malignant metabolic phenotype is characterized by high levels of phosphocholine (PC) and relatively low levels of glycerophosphocholine (GPC) in aggressive breast cancer cells. Phosphorus ((31) P) MRS is able to non-invasively detect these water-soluble metabolites of choline as well as ethanolamine phospholipid metabolism. Here we have investigated the effects of stably silencing glycerophosphoester diesterase domain containing 5 (GDPD5), which is an enzyme with glycerophosphocholine phosphodiesterase activity, in MDA-MB-231 breast cancer cells and orthotopic tumor xenografts. Tumors in which GDPD5 was stably silenced with GDPD5-specific shRNA contained increased levels of GPC and phosphoethanolamine (PE) compared with control tumors.

MR-detectable metabolic consequences of mitogen-activated protein kinase kinase (MEK) inhibition

Metabolic reprogramming is increasingly being viewed as a hallmark of cancer. Accordingly, metabolic readouts can serve as biomarkers of response to therapy. The goal of this study was to investigate some of the MRS-detectable metabolic consequences of mitogen-activated protein kinase kinase (MEK) inhibition. We investigated PC3 prostate cancer, MCF-7 breast cancer and A375 melanoma cells, and determined that, consistent with previous studies, MRS-detectable levels of phosphocholine decreased significantly in all cell lines (to 63%, 50% and 18% of the control, respectively) following MEK inhibition with U0126. This effect was mediated by a decrease in the expression of choline kinase α, the enzyme that catalyzes the phosphorylation of choline. In contrast, the impact of MEK inhibition on glycolysis was cell line dependent. A375 cells, which express mutant BRAF, demonstrated significant decreases in glucose uptake (to 36% of control) and lactate production (to 42% of control) in line with positron emission tomography data. In contrast, in PC3 and MCF-7 cells, increases in glucose uptake (to 198% and 192% of control, respectively) and lactate production (to 177% and 212% of control, respectively) were observed, in line with a previous hyperpolarized (13) C MRS study. This effect is probably mediated by the activation of the phosphoinositide 3-kinase pathway and AMP-activated protein kinase. Our findings demonstrate the value of translatable non-invasive MRS methods for the provision of information on cellular metabolism as an indication of the activation of potential feedback loops following MEK inhibition.

Monitoring response to cytostatic cisplatin in a HER2(+) ovary cancer model by MRI and in vitro and in vivo MR spectroscopy

Background:

Limited knowledge is available on alterations induced by cytostatic drugs on magnetic resonance spectroscopy (MRS) and imaging (MRI) parameters of human cancers, in absence of apoptosis or cytotoxicity. We here investigated the effects of a cytostatic cisplatin (CDDP) treatment on ¹H MRS and MRI of HER2-overexpressing epithelial ovarian cancer (EOC) cells and in vivo xenografts.

Methods:

High-resolution MRS analyses were performed on in vivo passaged SKOV3.ip cells and cell/tissue extracts (16.4 or 9.4 T). In vivo MRI/MRS quantitative analyses (4.7 T) were conducted on xenografts obtained by subcutaneous implantation of SKOV3.ip cells in SCID mice. The apparent diffusion coefficient (ADC) and metabolite levels were measured.

Results:

CDDP-induced cytostatic effects were associated with a metabolic shift of cancer cells towards accumulation of MRS-detected neutral lipids, whereas the total choline profile failed to be perturbed in both cultured cells and xenografts. In vivo MRI examinations showed delayed tumour growth in the CDDP-treated group, associated with early reduction of the ADC mean value.

Conclusion:

This study provides an integrated set of information on cancer metabolism and physiology for monitoring the response of an EOC model to a cytostatic chemotherapy, as a basis for improving the interpretation of non-invasive MR examinations of EOC patients.

Noninvasive phosphorus magnetic resonance spectroscopic imaging predicts outcome to first-line chemotherapy in newly diagnosed patients with diffuse large B-cell lymphoma

RATIONALE AND OBJECTIVES

Based on their association with malignant proliferation, using noninvasive phosphorus MR spectroscopic imaging ((31)P MRSI), we measured the tumor content of the phospholipid-related phosphomonoesters (PME), phosphoethanolamine and phospholcholine, and its correlation with treatment outcome in newly diagnosed patients with diffuse large B-cell lymphoma (DLBCL) receiving standard first-line chemotherapy.

EXPERIMENTAL DESIGN

The PME value normalized to nucleoside triphosphates (PME/NTP) was measured using (31)P MRSI in tumor masses of 20 patients with DLBCL before receiving standard first-line chemotherapy. Response at 6 months was complete in 13 patients and partial in seven. Time to treatment failure (TTF) was ≤11 months in eight patients, from 18 to 30 months in three, and ≥60 months in nine.

RESULTS

On a t test, the pretreatment tumor PME/NTP mean value (SD, n) of patients with a complete response at 6 months was 1.42 (0.41, 13), which was significantly different from the value of 2.46 (0.40, 7) in patients with partial response (P < .00001). A Fisher test significantly correlated the PME/NTP values with response at 6 months (sensitivity and specificity at 0.85, P < .004) while a Cox proportional hazards regression significantly correlated the PME/NTP values with TTF (hazard ratio = 5.21, P < .02). A Kaplan-Meier test set apart a group entirely composed of patients with TTF ≤ 11 months (hazard ratio = 8.66, P < .00001).

CONCLUSIONS

The pretreatment tumor PME/NTP values correlated with response to treatment at 6 months and time to treatment failure in newly diagnosed patients with DLBCL treated with first-line chemotherapy, and therefore they could be used to predict treatment outcome in these patients.

HDAC inhibition induces increased choline uptake and elevated phosphocholine levels in MCF7 breast cancer cells

Histone deacetylase (HDAC) inhibitors have emerged as effective antineoplastic agents in the clinic. Studies from our lab and others have reported that magnetic resonance spectroscopy (MRS)-detectable phosphocholine (PC) is elevated following SAHA treatment, providing a potential noninvasive biomarker of response. Typically, elevated PC is associated with cancer while a decrease in PC accompanies response to antineoplastic treatment. The goal of this study was therefore to elucidate the underlying biochemical mechanism by which HDAC inhibition leads to elevated PC. We investigated the effect of SAHA on MCF-7 breast cancer cells using ¹³C MRS to monitor [1,2-¹³C] choline uptake and phosphorylation to PC. We found that PC synthesis was significantly higher in treated cells, representing 154±19% of control. This was within standard deviation of the increase in total PC levels detected by ³¹P MRS (129±7% of control). Furthermore, cellular choline kinase activity was elevated (177±31%), while cytidylyltransferase activity was unchanged. Expression of the intermediate-affinity choline transporter SLC44A1 and choline kinase α increased (144% and 161%, respectively) relative to control, as determined by mRNA microarray analysis with protein-level confirmation by Western blotting. Taken together, our findings indicate that the increase in PC levels following SAHA treatment results from its elevated synthesis. Additionally, the concentration of glycerophosphocholine (GPC) increased significantly with treatment to 210±45%. This is likely due to the upregulated expression of several phospholipase A2 (PLA₂) isoforms, resulting in increased PLA₂ activity (162±18%) in SAHA-treated cells. Importantly, the levels of total choline (tCho)-containing metabolites, comprised of choline, PC and GPC, are readily detectable clinically using ¹H MRS. Our findings thus provide an important step in validating clinically translatable non-invasive imaging methods for follow-up diagnostics of HDAC inhibitor treatment.

Treatment with the MEK inhibitor U0126 induces decreased hyperpolarized pyruvate to lactate conversion in breast, but not prostate, cancer cells

Alterations in cell metabolism are increasingly being recognized as a hallmark of cancer and are being exploited for the development of diagnostic tools and targeted therapeutics. Recently, ¹³C MRS-detectable hyperpolarized pyruvate to lactate conversion has been validated in models as a noninvasive imaging method for the detection of tumors and treatment response, and has successfully passed phase I clinical trials. To date, response to treatment has been associated with a decrease in hyperpolarized lactate production. In this study, we monitored the effect of treatment with the mitogen-activated protein kinase (MEK) inhibitor U0126 in prostate and breast cancer cells. Following treatment, we observed a 31% decrease in the flux of hyperpolarized ¹³C label in treated MCF-7 breast cancer cells relative to controls. In contrast, and unexpectedly, the flux increased to 167% in treated PC3 prostate cancer cells. To mechanistically explain these observations, we investigated treatment-induced changes in the different factors known to affect the pyruvate to lactate conversion. NADH (nicotinamide adenine dinucleotide, reduced form) levels remained unchanged, whereas lactate dehydrogenase expression and activity, as well as intracellular lactate, increased in both cell lines, providing an explanation for the elevated hyperpolarized lactate observed in PC3 cells. The expression of MCT1, which mediates pyruvate transport, decreased in treated MCF-7, but not PC3, cells. This identifies pyruvate transport as rate limiting in U0126-treated MCF-7 cells and explains the decrease in hyperpolarized lactate observed in these cells following treatment. Our findings highlight the complexity of interactions between MEK and metabolism, and the need for mechanistic validation before hyperpolarized ¹³C MRS can be used to monitor treatment-induced molecular responses.

Metabolic consequences of treatment with AKT inhibitor perifosine in breast cancer cells

Activation of the PI3K/Akt pathway is associated with the development of numerous human cancers. As a result, many emerging therapies target this pathway. Previous studies have shown that targeting the PI3K/Akt pathway at the level of PI3K is associated with a drop in phosphocholine (PCho) and a reduction in hyperpolarized lactate production. However, the consequences of targeting downstream of PI3K at the level of Akt have not been investigated. Perifosine is an anticancer alkylphospholipid used in clinical trials. It acts by inhibiting phosphorylation of Akt and has been shown to inhibit CTP-phosphocholine cytidyltransferase (CT). The goal of this study was to identify the MRS-detectable metabolic consequences of treatment with perifosine in MCF-7 breast cancer cells. We found that perifosine treatment led to a 51 ± 5% drop in PCho from 30 ± 5 to 15 ± 1 fmol/cell and a comparable drop in de novo synthesized PCho. This was associated with a drop in choline kinase (ChoK) activity and ChoKα expression. CT inhibition could not be ruled out but likely did not contribute to the change in PCho. We also found that intracellular lactate levels decreased from 2.7 ± 0.5 to 1.5 ± 0.3 fmol/cell and extracellular lactate levels dropped by a similar extent. These findings were consistent with a drop in lactate dehydrogenase expression and associated with a drop in activity of the hypoxia inducible factor (HIF)-1α. The drops in PCho and lactate production following perifosine treatment are therefore mediated downstream of Akt by the drop in HIF-1α, which serves as the transcription factor for both ChoK and lactate dehydrogenase. The metabolic changes were confirmed in a second breast cancer cell line, MDA-MB-231. Taken together, these findings indicate that PCho and lactate can serve as noninvasive metabolic biomarkers for monitoring the effects of inhibitors that target the PI3K/Akt pathway, independent of the step that leads to inhibition of HIF-1α.

Prognostic value of metabolic response in breast cancer patients receiving neoadjuvant chemotherapy

BACKGROUND

Today's clinical diagnostic tools are insufficient for giving accurate prognosis to breast cancer patients. The aim of our study was to examine the tumor metabolic changes in patients with locally advanced breast cancer caused by neoadjuvant chemotherapy (NAC), relating these changes to clinical treatment response and long-term survival.

METHODS

Patients (n = 89) participating in a randomized open-label multicenter study were allocated to receive either NAC as epirubicin or paclitaxel monotherapy. Biopsies were excised pre- and post-treatment, and analyzed by high resolution magic angle spinning magnetic resonance spectroscopy (HR MAS MRS). The metabolite profiles were examined by paired and unpaired multivariate methods and findings of important metabolites were confirmed by spectral integration of the metabolite peaks.

RESULTS

All patients had a significant metabolic response to NAC, and pre- and post-treatment spectra could be discriminated with 87.9%/68.9% classification accuracy by paired/unpaired partial least squares discriminant analysis (PLS-DA) (p < 0.001). Similar metabolic responses were observed for the two chemotherapeutic agents. The metabolic responses were related to patient outcome. Non-survivors (< 5 years) had increased tumor levels of lactate (p = 0.004) after treatment, while survivors (≥ 5 years) experienced a decrease in the levels of glycine (p = 0.047) and choline-containing compounds (p ≤ 0.013) and an increase in glucose (p = 0.002) levels. The metabolic responses were not related to clinical treatment response.

CONCLUSIONS

The differences in tumor metabolic response to NAC were associated with breast cancer survival, but not to clinical response. Monitoring metabolic responses to NAC by HR MAS MRS may provide information about tumor biology related to individual prognosis.

Choline metabolism in malignant transformation

Abnormal choline metabolism is emerging as a metabolic hallmark that is associated with oncogenesis and tumour progression. Following transformation, the modulation of enzymes that control anabolic and catabolic pathways causes increased levels of choline-containing precursors and breakdown products of membrane phospholipids. These increased levels are associated with proliferation, and recent studies emphasize the complex reciprocal interactions between oncogenic signalling and choline metabolism. Because choline-containing compounds are detected by non-invasive magnetic resonance spectroscopy (MRS), increased levels of these compounds provide a non-invasive biomarker of transformation, staging and response to therapy. Furthermore, enzymes of choline metabolism, such as choline kinase, present novel targets for image-guided cancer therapy.

Magnetic resonance spectroscopy detectable metabolomic fingerprint of response to antineoplastic treatment

Targeted therapeutic approaches are increasingly being implemented in the clinic, but early detection of response frequently presents a challenge as many new therapies lead to inhibition of tumor growth rather than tumor shrinkage. Development of novel non-invasive methods to monitor response to treatment is therefore needed. Magnetic resonance spectroscopy (MRS) and magnetic resonance spectroscopic imaging are non-invasive imaging methods that can be employed to monitor metabolism, and previous studies indicate that these methods can be useful for monitoring the metabolic consequences of treatment that are associated with early drug target modulation. However, single-metabolite biomarkers are often not specific to a particular therapy. Here we used an unbiased 1H MRS-based metabolomics approach to investigate the overall metabolic consequences of treatment with the phosphoinositide 3-kinase inhibitor LY294002 and the heat shock protein 90 inhibitor 17AAG in prostate and breast cancer cell lines. LY294002 treatment resulted in decreased intracellular lactate, alanine fumarate, phosphocholine and glutathione. Following 17AAG treatment, decreased intracellular lactate, alanine, fumarate and glutamine were also observed but phosphocholine accumulated in every case. Furthermore, citrate, which is typically observed in normal prostate tissue but not in tumors, increased following 17AAG treatment in prostate cells. This approach is likely to provide further information about the complex interactions between signaling and metabolic pathways. It also highlights the potential of MRS-based metabolomics to identify metabolic signatures that can specifically inform on molecular drug action.

MRS and MRSI guidance in molecular medicine: targeting and monitoring of choline and glucose metabolism in cancer

MRS and MRSI are valuable tools for the detection of metabolic changes in tumors. The currently emerging era of molecular medicine, which is shaped by molecularly targeted anticancer therapies combined with molecular imaging of the effects of such therapies, requires powerful imaging technologies that are able to detect molecular information. MRS and MRSI are such technologies that are able to detect metabolites arising from glucose and choline metabolism in noninvasive in vivo settings and at higher resolution in tissue samples. The roles played by MRS and MRSI in the diagnosis of different types of cancer, as well as in the early monitoring of the tumor response to traditional chemotherapies, are reviewed. The emerging roles of MRS and MRSI in the development and detection of novel targeted anticancer therapies that target oncogenic signaling pathways or markers in choline or glucose metabolism are discussed.

MR evaluation of response to targeted treatment in cancer cells

The development of molecular technologies, together with progressive sophistication of molecular imaging methods, has allowed the further elucidation of the multiple mutations and dysregulatory effects of pathways leading to oncogenesis. Acting against these pathways by specifically targeted agents represents a major challenge for current research efforts in oncology. As conventional anatomically based pharmacological endpoints may be inadequate to monitor the tumor response to these targeted treatments, the identification and use of more appropriate, noninvasive pharmacodynamic biomarkers appear to be crucial to optimize the design, dosage and schedule of these novel therapeutic approaches. An aberrant choline phospholipid metabolism and enhanced flux of glucose derivatives through glycolysis, which sustain the redirection of mitochondrial ATP to glucose phosphorylation, are two major hallmarks of cancer cells. This review focuses on the changes detected in these pathways by MRS in response to targeted treatments. The progress and limitations of our present understanding of the mechanisms underlying MRS-detected phosphocholine accumulation in cancer cells are discussed in the light of gene and protein expression and the activation of different enzymes involved in phosphatidylcholine biosynthesis and catabolism. Examples of alterations induced in the MRS choline profile of cells exposed to different agents or to tumor environmental factors are presented. Current studies aimed at the identification in cancer cells of MRS-detected pharmacodynamic markers of therapies targeted against specific conditional or constitutive cell receptor stimulation are then reviewed. Finally, the perspectives of present efforts addressed to identify enzymes of the phosphatidylcholine cycle as possible novel targets for anticancer therapy are summarized.

Lipid profiling of cancerous and benign gallbladder tissues by 1H NMR spectroscopy

Qualitative and quantitative (1) H NMR analysis of lipid extracts of gallbladder tissue in chronic cholecystitis (CC, benign) (n = 14), xanthogranulomatous cholecystitis (XGC, intermediate) (n = 9) and gallbladder cancer (GBC, malignant) (n = 8) was carried out to understand the mechanisms involved in the transformation of benign gallbladder tissue to intermediate and malignant tissue. The results revealed alterations in various tissue lipid components in gallbladder in CC, XGC and GBC. The difference in the nature of lipid components in benign and malignant disease may aid in the identification of the biological pathways involved in the etiopathogenesis of GBC. This is the first study on lipid profiling of gallbladder tissue by (1) H NMR spectroscopy, and has possible implications for the development of future diagnostic approaches.

Metabolic effects of signal transduction inhibition in cancer assessed by magnetic resonance spectroscopy

Despite huge efforts in development of drugs targeting oncogenic signalling, the number of such drugs entering clinical practice to date remains limited. Rational use of biomarkers for drug candidate selection and early monitoring of response to therapy may accelerate this process. Magnetic resonance spectroscopy (MRS) can be used to assess metabolic effects of drug treatment both in vivo and in vitro, and technological advances are continuously increasing the utility of this non-invasive method. In this review, we summarise the use of MRS for monitoring the effect of targeted anticancer drugs, and discuss the potential role of MRS in the context of personalised cancer treatment.

The phosphoinositide 3-kinase inhibitor PI-103 downregulates choline kinase alpha leading to phosphocholine and total choline decrease detected by magnetic resonance spectroscopy

The phosphoinositide 3-kinase (PI3K) pathway is a major target for cancer drug development. PI-103 is an isoform-selective class I PI3K and mammalian target of rapamycin inhibitor. The aims of this work were as follows: first, to use magnetic resonance spectroscopy (MRS) to identify and develop a robust pharmacodynamic (PD) biomarker for target inhibition and potentially tumor response following PI3K inhibition; second, to evaluate mechanisms underlying the MRS-detected changes. Treatment of human PTEN null PC3 prostate and PIK3CA mutant HCT116 colon carcinoma cells with PI-103 resulted in a concentration- and time-dependent decrease in phosphocholine (PC) and total choline (tCho) levels (P < 0.05) detected by phosphorus ((31)P)- and proton ((1)H)-MRS. In contrast, the cytotoxic microtubule inhibitor docetaxel increased glycerophosphocholine and tCho levels in PC3 cells. PI-103-induced MRS changes were associated with alterations in the protein expression levels of regulatory enzymes involved in lipid metabolism, including choline kinase alpha (ChoK(alpha)), fatty acid synthase (FAS), and phosphorylated ATP-citrate lyase (pACL). However, a strong correlation (r(2) = 0.9, P = 0.009) was found only between PC concentrations and ChoK(alpha) expression but not with FAS or pACL. This study identified inhibition of ChoK(alpha) as a major cause of the observed change in PC levels following PI-103 treatment. We also showed the capacity of (1)H-MRS, a clinically well-established technique with higher sensitivity and wider applicability compared with (31)P-MRS, to assess response to PI-103. Our results show that monitoring the effects of PI3K inhibitors by MRS may provide a noninvasive PD biomarker for PI3K inhibition and potentially of tumor response during early-stage clinical trials with PI3K inhibitors.

Nuclear magnetic resonance detects phosphoinositide 3-kinase/Akt-independent traits common to pluripotent murine embryonic stem cells and their malignant counterparts

Pluripotent embryonic stem (ES) cells, a potential source of somatic precursors for cell therapies, cause tumors after transplantation. Studies of mammalian carcinogenesis using nuclear magnetic resonance (NMR) spectroscopy have revealed changes in the choline region, particularly increased phosphocholine (PCho) content. High PCho levels in murine ES (mES) cells have recently been attributed to cell pluripotency. The phosphoinositide 3-kinase (PI3K)/Akt pathway has been implicated in tumor-like properties of mES cells. This study aimed to examine a potential link between the metabolic profile associated with choline metabolism of pluripotent mES cells and PI3K/Akt signaling. We used mES (ES-D3) and murine embryonal carcinoma cells (EC-F9) and compared the metabolic profiles of 1) pluripotent mES (ESD0), 2) differentiated mES (ESD14), and 3) pluripotent F9 cells. Involvement of the PI3K/Akt pathway was assessed using LY294002, a selective PI3K inhibitor. Metabolic profiles were characterized in the extracted polar fraction by (1)H NMR spectroscopy. Similarities were found between the levels of choline phospholipid metabolites (PCho/total choline and PCho/glycerophosphocholine [GPCho]) in ESD0 and F9 cell spectra and a greater-than five-fold decrease of the PCho/GPCho ratio associated with mES cell differentiation. LY294002 caused no significant change in relative PCho levels but led to a greater-than two-fold increase in PCho/GPCho ratios. These results suggest that the PCho/GPCho ratio is a metabolic trait shared by pluripotent and malignant cells and that PI3K does not underlie its development. It is likely that the signature identified here in a mouse model may be relevant for safe therapeutic applications of human ES cells.

Noninvasive detection of target modulation following phosphatidylinositol 3-kinase inhibition using hyperpolarized 13C magnetic resonance spectroscopy

Numerous mechanism-based anticancer drugs that target the phosphatidylinositol 3-kinase (PI3K) pathway are in clinical trials. However, it remains challenging to assess responses by traditional imaging methods. Here, we show for the first time the efficacy of hyperpolarized (13)C magnetic resonance spectroscopy (MRS) in detecting the effect of PI3K inhibition by monitoring hyperpolarized [1-(13)C]lactate levels produced from hyperpolarized [1-(13)C]pyruvate through lactate dehydrogenase (LDH) activity. In GS-2 glioblastoma cells, PI3K inhibition by LY294002 or everolimus caused hyperpolarized lactate to drop to 42 +/- 12% and to 76 +/- 5%, respectively. In MDA-MB-231 breast cancer cells, hyperpolarized lactate dropped to 71 +/- 15% after treatment with LY294002. These reductions were correlated with reductions in LDH activity to 48 +/- 4%, 63 +/- 4%, and 69 +/- 12%, respectively, and were associated with a drop in levels of LDHA mRNA and LDHA and hypoxia-inducible factor-1alpha proteins. Supporting these findings, tumor growth inhibition achieved by everolimus in murine GS-2 xenografts was associated with a drop in the hyperpolarized lactate-to-pyruvate ratio detected by in vivo MRS imaging, whereas an increase in this ratio occurred with tumor growth in control animals. Taken together, our findings illustrate the application of hyperpolarized (13)C MRS of pyruvate to monitor alterations in LDHA activity and expression caused by PI3K pathway inhibition, showing the potential of this method for noninvasive imaging of drug target modulation.

Proton MRS detects metabolic changes in hormone sensitive and resistant human prostate cancer models CWR22 and CWR22r

17-Allylamino, 17-demethoxygeldanamycin (17-AAG), an effective inhibitor of the heat shock protein hsp90, preferentially inhibiting tumor hsp90 compared to hsp90 from normal cells, has shown promising results against several cancers, including hormone-resistant prostate cancer. Levels of several oncogenic proteins critical to tumor growth and progression, such as androgen receptor and HER2/neu, were reduced 4 h post 17-allylamino, 17-demethoxygeldanamycin treatment. Posttreatment metabolic changes have also been observed in several tumor cell lines. In this study, total choline distributions in hormone sensitive CWR22 and hormone resistant CWR22r prostate cancer xenograft tumors in mice were measured before and at 4 h and 48 h after a single-bolus 17-allylamino, 17-demethoxygeldanamycin treatment at 100 mg/kg, using proton MR spectroscopy. Our results show that tumor total choline levels declined 4 h after the treatment for CWR22 (P = 0.001) and 48 h post treatment for CWR22r (P = 0.003). Metabolic changes, in particular of total choline intensity detected by proton magnetic resonance spectroscopic imaging (MRSI), are consistent with the observed immunohistochemistry changes, tumor growth inhibition for CWR22r (P = 0.01 at 14 days post treatment), and a constant prostate specific antigen level versus increasing prostate specific antigen for control CWR22 (P = 0.01). Metabolic changes in total choline by proton MRSI can be used as an early biomarker of response for advanced-stage prostate cancer in targeted therapy such as 17-allylamino, 17-demethoxygeldanamycin.

Metabolic assessment of the action of targeted cancer therapeutics using magnetic resonance spectroscopy

Developing rational targeted cancer drugs requires the implementation of pharmacodynamic (PD), preferably non-invasive, biomarkers to aid response assessment and patient follow-up. Magnetic resonance spectroscopy (MRS) allows the non-invasive study of tumour metabolism. We describe the MRS-detectable PD biomarkers resulting from the action of targeted therapeutics, and discuss their biological significance and future translation into clinical use.

Use of nuclear magnetic resonance-based metabolomics in detecting drug resistance in cancer

Cancer cells possess a highly unique metabolic phenotype, which is characterized by high glucose uptake, increased glycolytic activity, decreased mitochondrial activity, low bioenergetic and increased phospholipid turnover. These metabolic hallmarks can be readily assessed by metabolic technologies - either in vitro or in vivo - to monitor responsiveness and resistance to novel targeted drugs, where specific inhibition of cell proliferation (cytostatic effect) occurs rather than direct induction of cell death (cytotoxicity). Using modern analytical technologies in combination with statistical approaches, 'metabolomics', a global metabolic profile on patient samples can be established and validated for responders and nonresponders, providing additional metabolic end points. Discovered metabolic end points should be translated into noninvasive metabolic imaging protocols.

Changes in choline metabolism as potential biomarkers of phospholipase C{gamma}1 inhibition in human prostate cancer cells

Phosphoinositide-specific phospholipase Cγ1 (PLCγ1) is activated downstream of many receptor tyrosine kinases to promote cell motility. Inhibition of this protein is being explored as a therapeutic strategy for blocking cancer cell invasion and metastasis. The clinical development of such cytostatic therapies requires the implementation of pharmacodynamic biomarkers of target modulation. In this study, we use magnetic resonance spectroscopy to explore metabolic biomarkers of PLCγ1 down-regulation in PC3LN3 prostate cancer cells. We show that inhibition of PLCγ1 via an inducible short hairpin RNA system causes a reduction in phosphocholine levels by up to 50% relative to the control as detected by (1)H and (31)P magnetic resonance spectroscopy analyses. This correlated with a rounded-up morphology and reduced cell migration. Interestingly, the fall in phosphocholine levels was not recorded in cells with constitutive PLCγ1 knockdown where the rounded-up phenotype was no longer apparent. This study reveals alterations in metabolism that accompany the cellular effects of PLCγ1 knockdown and highlights phosphocholine as a potential pharmacodynamic biomarker for monitoring the action of inhibitors targeting PLCγ1 signaling.

Modulation of choline kinase activity in human cancer cells observed by dynamic 31P NMR

Choline metabolites are widely studied in cancer research as biomarkers of malignancy and as indicators of therapeutic response. However, endogenous phosphocholine levels are determined by a number of processes that confound the interpretation of these measurements, including membrane transport rates and a series of enzyme catalysed reactions in the Kennedy pathway. Employing a dynamic (31)P NMR assay that is specific to choline kinase (ChoK) we have measured the rates of this enzyme reaction in cell lysates of MDA-MB-231 breast, PC-3 prostate and HeLa cervical cancer cells and in solutions of purified human ChoK. The rates are sensitive to inhibition by hemicholinium-3 (HC-3), a competitive ChoK inhibitor, and to N-[2-bromocinnamyl(amino)ethyl]-5-isoquinolinesulphonamide (H-89), an agent commercialized as a specific cyclic-AMP-dependent protein kinase A (PKA) inhibitor.

1H MRS identifies specific metabolite profiles associated with MYCN-amplified and non-amplified tumour subtypes of neuroblastoma cell lines

Neuroblastoma is the most common extracranial solid malignancy in children. The disease possesses a broad range of clinical phenotypes with widely varying prognoses. Numerous studies have sought to identify the associated genetic abnormalities in the tumour, resulting in the identification of useful prognostic markers. In particular, the presence of multiple copies of the MYCN oncogene (referred to as MYCN amplification) has been found to confer a poor prognosis. However, the molecular pathways involved are as yet poorly defined. Metabolite profiles generated by in vitro (1)H MRS provide a means of investigating the downstream metabolic consequences of genetic alterations and can identify potential targets for new agents. Thirteen neuroblastoma cell lines possessing multiple genetic alterations were investigated; seven were MYCN amplified and six MYCN non-amplified. In vitro magic angle spinning (1)H MRS was performed on cell suspensions, and the spectra analysed to obtain metabolite concentration ratios relative to total choline (tCho). A principal component analysis using these concentration ratios showed that MYCN-amplified and non-amplified cell lines form separate classes according to their metabolite profiles. Phosphocholine/tCho and taurine/tCho were found to be significantly raised (p < 0.05) and glycerophosphocholine/tCho significantly reduced (p < 0.05) in the MYCN-amplified compared with the MYCN non-amplified cell lines (two-tailed t test). (1)H MRS of the SH-EP1 cell line and an isogenic cell line transfected with the MYCN oncogene also showed that MYCN oncogene over-expression causes alterations in phosphocholine, glycerophosphocholine and taurine concentrations. Molecular pathways of choline and taurine metabolism are potential targets for new agents tailored to MYCN-amplified neuroblastoma.

Magnetic resonance imaging and spectroscopy of transgenic models of cancer

The complexity of cancer, where a single genetic alteration can have multiple functional effects, makes it a fascinating but humbling disease to study, and the necessity of investigating it in its entirety is more imperative than ever before. Advances in transgene technology have made it possible to create cancer cells, or mice with specific genetic alterations, and the application of an array of both functional and molecular non-invasive MR methods to these transgenic cancer cells and mice to characterize their phenotypic traits is revolutionizing our understanding of cancer. With the establishment of multi-modality molecular imaging centers within barrier or pathogen-free facilities, multi-parametric and multi-modality imaging of transgenic mouse models of human cancer are becoming increasingly prevalent. In this review, we outline some of the methods currently available for generating transgenic mice and cancer cell lines. We also present examples of the application of MR methods to transgenic models that are providing novel insights into the molecular and functional characteristics of cancer and are leading to an era of "non-invasive phenotyping" of the effects of specific molecular alterations in cancer.

Magnetic resonance spectroscopy suggests key differences in the metastatic behaviour of medulloblastoma

BACKGROUND

Metastatic medulloblastoma has a poorer prognosis than localised disease in part due to inherent properties of the tumour. 1H magnetic resonance spectroscopy (MRS) provides a powerful method for investigating tumour metabolism in vivo.

METHODS

Magnetic resonance imaging and short echo time (Te 30 ms) single voxel MRS were performed on the primary tumour of 16 children with medulloblastoma prior to surgical resection. Tumour volumes were calculated using a segmentation technique and the MRS was analysed using LCModel.

RESULTS

Patients with metastatic disease had primary tumours which were smaller (p=0.01), had higher levels of total choline (p=0.03) and lower levels of mobile lipids (p=0.04).

CONCLUSION

Metastatic medulloblastomas have metabolite profiles indicative of increased cell growth and decreased cell death compared with localised tumours reflecting intrinsic differences in underlying biology. Localised tumours with an MRS metabolite profile similar to those with metastatic disease may be at increased risk of metastatic relapse.

Choline metabolism in cancer: implications for diagnosis and therapy

Magnetic resonance studies from the last 10 years have conclusively demonstrated that choline metabolism is altered in a wide variety of cancers. In cancer, the choline metabolite profile is characterized by an elevation of phosphocholine and total choline-containing compounds. This elevation is increasingly being used as an endogenous biomarker of cancer. Importantly, the enzymes and pathways resulting in these distinct alterations in phosphocholine and total choline may provide novel molecular targets for specific, targeted anticancer therapies. In this article, we have summarized some of the magnetic resonance spectroscopy and positron emission tomography techniques that are currently available, or will be in the near future, for choline metabolism-based diagnosis, staging and therapy assessment in cancer patients. This review also outlines currently known molecular alterations that cause the aberrant choline metabolite profile in cancers and concludes with a summary of recent research findings that may, in the future, lead to novel anticancer therapies targeting choline metabolism.

Therapeutic targets and biomarkers identified in cancer choline phospholipid metabolism

Choline phospholipid metabolism is altered in a wide variety of cancers. The choline metabolite profile of tumors and cancer cells is characterized by an elevation of phosphocholine and total choline-containing compounds. Noninvasive magnetic resonance spectroscopy can be used to detect this elevation as an endogenous biomarker of cancer, or as a predictive biomarker for monitoring tumor response to novel targeted therapies. The enzymes directly causing this elevation, such as choline kinase, phospholipase C and phospholipase D may provide molecular targets for anticancer therapies. Signal transduction pathways that are activated in cancers, such as those mediated by the receptor tyrosine kinases breakpoint cluster region-abelson (Bcr-Abl), c-KIT or epidermal growth factor receptor (EGFR), correlate with the alterations in choline phospholipid metabolism of cancers, and also offer molecular targets for specific anticancer therapies. This review summarizes recently discovered molecular targets in choline phospholipid metabolism and signal transduction pathways, which may lead to novel anticancer therapies potentially being monitored by magnetic resonance spectroscopy techniques.

Mechanisms of indomethacin-induced alterations in the choline phospholipid metabolism of breast cancer cells

Human mammary epithelial cells (HMECs) exhibit an increase in phosphocholine (PC) and total choline-containing compounds, as well as a switch from high glycerophosphocholine (GPC)/low PC to low GPC/high PC, with progression to malignant phenotype. The treatment of human breast cancer cells with a nonsteroidal anti-inflammatory agent, indomethacin, reverted the high PC/low GPC pattern to a low PC/high GPC pattern indicative of a less malignant phenotype, supported by decreased invasion. Here, we have characterized mechanisms underlying indomethacin-induced alterations in choline membrane metabolism in malignant breast cancer cells and nonmalignant HMECs labeled with [1,2-13C]choline using 1H and 13C magnetic resonance spectroscopy. Microarray gene expression analysis was performed to understand the molecular mechanisms underlying these changes. In breast cancer cells, indomethacin treatment activated phospholipases that, combined with an increased choline phospholipid biosynthesis, led to increased GPC and decreased PC levels. However, in nonmalignant HMECs, activation of the anabolic pathway alone was detected following indomethacin treatment. Following indomethacin treatment in breast cancer cells, several candidate genes, such as interleukin 8, NGFB, CSF2, RHOB, EDN1, and JUNB, were differentially expressed, which may have contributed to changes in choline metabolism through secondary effects or signaling cascades leading to changes in enzyme activity.

Applications of magnetic resonance spectroscopy in radiotherapy treatment planning

Following advances in conformal radiotherapy, a key problem now facing radiation oncologists is target definition. While MRI and CT provide images of excellent spatial resolution, they do not always provide sufficient contrast to identify tumour extent or to identify regions of high cellular activity that might be targeted with boost doses. Magnetic resonance spectroscopy (MRS) is an alternative approach that holds great promise for aiding target definition for radiotherapy treatment planning, and for evaluation of response and recurrence. MRS is able to detect signals from low molecular weight metabolites such as choline and creatine that are present at concentrations of a few mM in tissue. Spectra may be acquired from single voxels, or from a 2D or 3D array of voxels using spectroscopic imaging. The current state of the art achieves a spatial resolution of 6-10 mm in a scan time of about 10-15 min. Co-registered MR images are acquired in the same examination. The method is currently under evaluation, in particular in brain (where MRS has been shown to differentiate between many tumour types and grades) and in prostate (where cancer may be distinguished from normal tissue and benign prostatic hypertrophy). The contrast achieved with MRS, based on tissue biochemistry, therefore provides a promising alternative for identifying tumour extent and regions of high metabolic activity. It is anticipated that MRS will become an essential tool for treatment planning where other modalities lack the necessary contrast.

Detection of histone deacetylase inhibition by noninvasive magnetic resonance spectroscopy

Histone deacetylase (HDAC) inhibitors are new and promising antineoplastic agents. Current methods for monitoring early response rely on invasive biopsies or indirect blood-derived markers. Our goal was to develop a magnetic resonance spectroscopy (MRS)-based method to detect HDAC inhibition. The fluorinated lysine derivative Boc-Lys-(Tfa)-OH (BLT) was investigated as a (19)F MRS molecular marker of HDAC activity together with (31)P MRS of endogenous metabolites. In silico modeling of the BLT-HDAC interaction and in vitro MRS studies of BLT cleavage by HDAC confirmed BLT as a HDAC substrate. BLT did not affect cell viability or HDAC activity in PC3 prostate cancer cells. PC3 cells were treated, in the presence of BLT, with the HDAC inhibitor p-fluoro-suberoylanilide hydroxamic acid (FSAHA) over the range of 0 to 10 micromol/L, and HDAC activity and MRS spectra were monitored. Following FSAHA treatment, HDAC activity dropped, reaching 53% of control at 10 micromol/L FSAHA. In parallel, a steady increase in intracellular BLT from 14 to 32 fmol/cell was observed. BLT levels negatively correlated with HDAC activity consistent with higher levels of uncleaved BLT in cells with inhibited HDAC. Phosphocholine, detected by (31)P MRS, increased from 7 to 16 fmol/cell following treatment with FSAHA and also negatively correlated with HDAC activity. Increased phosphocholine is probably due to heat shock protein 90 inhibition as indicated by depletion of client proteins. In summary, (19)F MRS of BLT, combined with (31)P MRS, can be used to monitor HDAC activity in cells. In principle, this could be applied in vivo to noninvasively monitor HDAC activity.

Evaluation of 31P high-resolution magic angle spinning of intact tissue samples

The first detailed evaluation is presented of high-resolution (31)P MRS using magic angle spinning (MAS) of intact tissue samples and comparison with the conventional method of studying tissue extracts. The main motivation is that MAS leaves the sample intact at the end of the study for histopathological evaluation. While MAS of tissue samples has previously been demonstrated for (1)H MRS, (31)P MRS is better suited to study of the phospholipid metabolites of importance in cancer. Samples of rhabdomyosarcoma and RIF-1 experimental tumours were maintained at 4 degrees C, spun at 3 kHz and measured in 28-min acquisitions at 11.7 and 14 T. Metabolite stability was evaluated using four sequential 28-min acquisitions. High-resolution MRS was performed on extracts of the same tissue samples. (31)P HR-MAS yielded well-resolved high-resolution spectra, showing peaks from phosphoethanolamine (PE), phosphocholine (PC), inorganic phosphate, glycerophosphoethanolamine and glycerophosphocholine, with linewidths in the range 3-20 Hz. In tumour samples there was no significant change in peak areas over a 2-h period, while peaks sensitive to pH (inorganic phosphate, PE and PC) showed a small change in chemical shift, corresponding to a change of 0.13 +/- 0.06 pH units. Tissue metabolite concentrations showed good agreement with concentrations measured from extracts of the same pieces of tissue. For calculation of metabolite concentrations, the measurement of a reference compound in a separate measurement is more robust than using the signal from a reference compound in the rotor with the sample. Compared with performing tissue extracts, use of MAS of intact tissue samples requires less preparation, is quicker and permits the same sample to be used for subsequent histopathology. The methodology has particular application in studying phospholipid metabolism in cancer and in monitoring tumour response to treatment, where concentrations of phospholipid-related metabolites are found to alter following response to a wide range of anti-cancer therapies.

Magnetic resonance spectroscopy (MRS) in the investigation of cancer at The Royal Marsden Hospital and The Institute of Cancer Research

Developments in magnetic resonance spectroscopy (MRS) at The Royal Marsden Hospital and The Institute of Cancer Research are reviewed in the context of preceding developments in nuclear magnetic resonance (NMR) and MRS, and some of the early developments in this field, particularly those leading to human measurements. The early development of technology, and associated techniques for human measurement and assessment will be discussed, with particular reference to experience at out institutions. Applications using particular nuclei will then be described and related to other experimental work where appropriate. Contributions to the development of MRS that have been published in Physics in Medicine and Biology will be discussed.

Minimally invasive pharmacokinetic and pharmacodynamic technologies in hypothesis-testing clinical trials of innovative therapies

Clinical trials of new cancer drugs should ideally include measurements of parameters such as molecular target expression, pharmacokinetic (PK) behavior, and pharmacodynamic (PD) endpoints that can be linked to measures of clinical effect. Appropriate PK/PD biomarkers facilitate proof-of-concept demonstrations for target modulation; enhance the rational selection of an optimal drug dose and schedule; aid decision-making, such as whether to continue or close a drug development project; and may explain or predict clinical outcomes. In addition, measurement of PK/PD biomarkers can minimize uncertainty associated with predicting drug safety and efficacy, reduce the high levels of drug attrition during development, accelerate drug approval, and decrease the overall costs of drug development. However, there are many challenges in the development and implementation of biomarkers that probably explain their disappointingly low implementation in phase I trials. The Pharmacodynamic/Pharmacokinetic Technologies Advisory committee of Cancer Research UK has found that submissions for phase I trials of new cancer drugs in the United Kingdom often lack detailed information about PK and/or PD endpoints, which leads to suboptimal information being obtained in those trials or to delays in starting the trials while PK/PD methods are developed and validated. Minimally invasive PK/PD technologies have logistic and ethical advantages over more invasive technologies. Here we review these technologies, emphasizing magnetic resonance spectroscopy and positron emission tomography, which provide detailed functional and metabolic information. Assays that measure effects of drugs on important biologic pathways and processes are likely to be more cost-effective than those that measure specific molecular targets. Development, validation, and implementation of minimally invasive PK/PD methods are encouraged.

Identification of magnetic resonance detectable metabolic changes associated with inhibition of phosphoinositide 3-kinase signaling in human breast cancer cells

Phosphoinositide 3-kinase (PI3K) is an attractive target for novel mechanism-based anticancer treatment. We used magnetic resonance (MR) spectroscopy (MRS) to detect biomarkers of PI3K signaling inhibition in human breast cancer cells. MDA-MB-231, MCF-7, and Hs578T cells were treated with the prototype PI3K inhibitor LY294002, and the (31)P MR spectra of cell extracts were monitored. In every case, LY294002 treatment was associated with a significant decrease in phosphocholine levels by up to 2-fold (P < 0.05). In addition, a significant increase in glycerophosphocholine levels by up to 5-fold was also observed (P <or= 0.05), whereas the content of glycerophosphoethanolamine, when detectable, did not change significantly. Nucleotide triphosphate levels did not change significantly in MCF-7 and MDA-MB-231 cells but decreased by approximately 1.3-fold in Hs578T cells (P = 0.01). The changes in phosphocholine and glycerophosphocholine levels seen in cell extracts were also detectable in the (31)P MR spectra of intact MDA-MB-231 cells following exposure to LY294002. When treated with another PI3K inhibitor, wortmannin, MDA-MB-231 cells also showed a significant decrease in phosphocholine content by approximately 1.25-fold relative to the control (P < 0.05), whereas the levels of the remaining metabolites did not change significantly. Our results indicate that PI3K inhibition in human breast cancer cells by LY294002 and wortmannin is associated with a decrease in phosphocholine levels.

RNA interference-mediated choline kinase suppression in breast cancer cells induces differentiation and reduces proliferation

Choline kinase is overexpressed in breast cancer cells and activated by oncogenes and mitogenic signals, making it a potential target for cancer therapy. Here, we have examined, for the first time, the effects of RNA interference (RNAi)-mediated down-regulation of choline kinase in nonmalignant and malignant human breast epithelial cell lines using magnetic resonance spectroscopy (MRS) as well as molecular analyses of proliferation and differentiation markers. RNAi knockdown of choline kinase reduced proliferation, as detected by proliferating cell nuclear antigen and Ki-67 expression, and promoted differentiation, as detected by cytosolic lipid droplet formation and expression of galectin-3. The functional importance of RNAi-mediated choline kinase down-regulation on choline phospholipid metabolism was confirmed by the significant reduction of phosphocholine detected by MRS. These results strongly support the targeting of choline kinase in breast cancer cells with RNAi and show the potential ability of noninvasive MRS to detect and evaluate future treatments incorporating such strategies.