Metabolite changes in HT-29 xenograft tumors following HIF-1alpha inhibition with PX-478 as studied by MR spectroscopy in vivo and ex vivo

2'-deoxy-2'-[18F] fluoro-D-glucose positron emission tomography, diffusion-weighted magnetic resonance imaging, and choline spectroscopy to predict the activity of cetuximab in tumor xenografts derived from patients with squamous cell carcinoma of the head and neck

We investigated changes on 2'-deoxy-2'-[18F]fluoro-D-glucose positron emission tomography (¹⁸FDG-PET), diffusion-weighted magnetic resonance imaging (DW-MRI), and choline spectroscopy as early markers of cetuximab activity in squamous cell carcinoma of the head and neck (SCCHN). SCCHN patient-derived tumor xenografts models were selected based on their cetuximab sensitivity. Three models were resistant to cetuximab and two were sensitive (one was highly sensitive and the other one was moderately sensitive). Cetuximab was infused on day 0 and 7. Maximal standardized uptake values (SUVmax), apparent diffusion coefficient (ADC), and total choline pool were measured at baseline and at day 8. To investigate the possible clinical relevance of our pre-clinical findings, we also studied the SUVmax and ADC modifications induced by cetuximab in five patients. Cetuximab induced a significant decrease in SUVmax and an increase in ADC at day 8 compared to baseline in the most cetuximab-sensitive model but not in the other models. At day 8, in one resistant model, SUVmax was decreased compared to baseline and was significantly lower than the controls. Choline spectroscopy was not able to predict cetuximab activity. The five patients treated with cetuximab had a ¹⁸FDG-PET partial response. One patient had a partial response according to RECISTv1.1. Interestingly, this last had also an increase in ADC value above 25%. Our preclinical data support the use of PDTX to investigate imaging techniques to detect early treatment response. Our pre-clinical and clinical data suggest that DW-MRI and ¹⁸FDG-PET should be further investigated to predict cetuximab activity.

Imaging markers of response to combined BRAF and MEK inhibition in BRAF mutated vemurafenib-sensitive and resistant melanomas

A majority of patients with a V600x melanoma respond quickly to BRAF/MEK inhibition (BRAFi/MEKi) and have an obvious clinical benefit. Nearly all the patients after this initial phase will develop resistance. Therefore, non-invasive early markers of response/non-response are needed in order to identify those patients who, due to intrinsic or acquired resistance, do not respond to treatment and would be eligible for alternative treatments.

The aim of this study was to investigate the value of magnetic resonance spectroscopy (¹H-MRS) of choline and diffusion-weighted magnetic resonance imaging (DW-MRI) as early markers of response to BRAF inhibition (BRAFi) with vemurafenib alone or in combination with MEK inhibition (MEKi) with trametinib, in BRAFi-sensitive and BRAFi-resistant melanoma xenografts.

Tumor response was significantly improved by the combination of BRAFi and MEKi, compared to BRAFi alone, only in sensitive xenografts; thus indicating that vemurafenib-resistant A375R xenografts were cross-resistant to the inhibition of MEK, as confirmed by immunohistochemistry analysis for phosphorylated ERK.

In vivo¹H-MRS showed that in sensitive melanoma xenografts, a significant blockage of ERK phosphorylation, but not a decrease in cell proliferation, was required to affect total choline (tCho) levels, thus suggesting that tCho could serve as a pharmacodynamic (PD) marker for agents targeting the MAPK cascade. In addition, early effects of the combination therapy on tumor cellularity could be detected via DW-MRI. In particular, skewness and kurtosis of the apparent diffusion coefficient (ADC) distribution may be useful to detect changes in the diffusional heterogeneity that might not affect the global ADC value.

Response Detection of Castrate-Resistant Prostate Cancer to Clinically Utilised and Novel Treatments by Monitoring Phospholipid Metabolism

Androgen receptor (AR) activation is the primary driving factor in prostate cancer which is initially responsive to castration but then becomes resistant (castration-resistant prostate cancer (CRPC)). CRPC cells still retain the functioning AR which can be targeted by other therapies. A recent promising development is the use of inhibitors (Epi-1) of protein-protein interaction to inhibit AR-activated signalling. Translating novel therapies into the clinic requires sensitive early response indicators. Here potential response markers are explored. Growth inhibition of prostate cancer cells with flutamide, paclitaxel, and Epi-1 was measured using the MTT assay. To simulate choline-PET scans, pulse-chase experiments were carried out with [³H-methyl]choline and proportion of phosphorylated activity was determined after treatment with growth inhibitory concentrations of each drug. Extracts from treated cells were also subject to ³¹P-NMR spectroscopy. Cells treated with flutamide demonstrated decreased [³H-methyl]choline phosphorylation, whilst the proportion of phosphorylated [³H-methyl]choline that was present in the lipid fraction was increased in Epi-1-treated cells. Phospholipid breakdown products, glycerophosphorylcholine and glycerophosphoethanolamine levels, were shown by 31P-NMR spectroscopy to be decreased to undetectable levels in cells treated with Epi-1. LNCaP cells responding to treatment with novel protein-protein interaction inhibitors suggest that ³¹P-NMR spectroscopy may be useful in detecting response to this promising therapy.

Identification of Gastric Cancer Biomarkers Using 1H Nuclear Magnetic Resonance Spectrometry

Existing gastric cancer diagnosing methods were invasive, hence, a reliable non-invasive gastric cancer diagnosing method is needed. As a starting point, we used 1H NMR for identifying gastric cancer biomarkers using a panel of gastric cancer spheroids and normal gastric spheroids. We were able to identify 8 chemical shift biomarkers for gastric cancer spheroids. Our data suggests that the cancerous and non-cancerous spheroids significantly differ in the lipid composition and energy metabolism. These results encourage the translation of these biomarkers into in-vivo gastric cancer detection methodology using MRI-MS.

Current opportunities and challenges of magnetic resonance spectroscopy, positron emission tomography, and mass spectrometry imaging for mapping cancer metabolism in vivo

Cancer is known to have unique metabolic features such as Warburg effect. Current cancer therapy has moved forward from cytotoxic treatment to personalized, targeted therapies, with some that could lead to specific metabolic changes, potentially monitored by imaging methods. In this paper we addressed the important aspects to study cancer metabolism by using image techniques, focusing on opportunities and challenges of magnetic resonance spectroscopy (MRS), dynamic nuclear polarization (DNP)-MRS, positron emission tomography (PET), and mass spectrometry imaging (MSI) for mapping cancer metabolism. Finally, we highlighted the future possibilities of an integrated in vivo PET/MR imaging systems, together with an in situ MSI tissue analytical platform, may become the ultimate technologies for unraveling and understanding the molecular complexities in some aspects of cancer metabolism. Such comprehensive imaging investigations might provide information on pharmacometabolomics, biomarker discovery, and disease diagnosis, prognosis, and treatment response monitoring for clinical medicine.

High-field small animal magnetic resonance oncology studies

This review focuses on the applications of high magnetic field magnetic resonance imaging (MRI) and spectroscopy (MRS) to cancer studies in small animals. High-field MRI can provide information about tumor physiology, the microenvironment, metabolism, vascularity and cellularity. Such studies are invaluable for understanding tumor growth and proliferation, response to treatment and drug development. The MR techniques reviewed here include (1)H, (31)P, chemical exchange saturation transfer imaging and hyperpolarized (13)C MRS as well as diffusion-weighted, blood oxygen level dependent contrast imaging and dynamic contrast-enhanced MRI. These methods have been proven effective in animal studies and are highly relevant to human clinical studies.

Multimodal imaging of tumor response to sorafenib combined with radiation therapy: comparison between diffusion-weighted MRI, choline spectroscopy and 18F-FLT PET imaging

The purpose of this study was to determine the value of different imaging modalities, that is, magnetic resonance imaging/spectroscopy (MRI/MRS) and positron emission tomography (PET), to assess early tumor response to sorafenib with or without radiotherapy. Diffusion-weighted (DW)-MRI, choline (1)H MRS at 11.7 T, and (18)F-FLT PET imaging were used to image fibrosarcoma (FSaII) tumor-bearing mice over time. The imaging markers were compared with apoptosis cell death and cell proliferation measurements assessed by histology. Anti-proliferative effects of sorafenib were evidenced by (1)H MRS and (18)F-FLT PET after 2 days of treatment with sorafenib, with no additional effect of the combination with radiation therapy, results that are in agreement with Ki67 staining. Apparent diffusion coefficient calculated using DW-MRI was not modified after 2 days of treatment with sorafenib, but showed significant increase 24 h after 2 days of sorafenib treatment combined with consecutive irradiation. The three imaging markers were able to show early tumor response as soon as 24 h after treatment initiation, with choline MRS and (18)F-FLT being sensitive to sorafenib in monotherapy as well as in combined therapy with irradiation, whereas DW-MRI was only sensitive to the combination of sorafenib with radiotherapy.

Metabolomics in cancer biomarker discovery: current trends and future perspectives

Cancer is one of the most devastating human diseases that causes a vast number of mortalities worldwide each year. Cancer research is one of the largest fields in the life sciences and despite many astounding breakthroughs and contributions over the past few decades, there is still a considerable amount to unveil on the function of cancer. It is well known that cancer metabolism differs from that of normal tissue and an important hypothesis published in the 1950s by Otto Warburg proposed that cancer cells rely on anaerobic metabolism as the source for energy, even under physiological oxygen levels. Following this, cancer central carbon metabolism has been researched extensively and beyond respiration, cancer has been found to involve a wide range of metabolic processes, and many more are still to be unveiled. Studying cancer through metabolomics could reveal new biomarkers for cancer that could be useful for its future prognosis, diagnosis and therapy. Metabolomics is becoming an increasingly popular tool in the life sciences since it is a relatively fast and accurate technique that can be applied with either a particular focus or in a global manner to reveal new knowledge about biological systems. There have been many examples of its application to reveal potential biomarkers in different cancers that have employed a range of different analytical platforms. In this review, approaches in metabolomics that have been employed in cancer biomarker discovery are discussed and some of the most noteworthy research in the field is highlighted.

Quantitative (31)P HR-MAS MR spectroscopy for detection of response to PI3K/mTOR inhibition in breast cancer xenografts

PURPOSE

Phospholipid metabolites are of importance in cancer studies, and have been suggested as candidate metabolic biomarkers for response to targeted anticancer drugs. The purpose of this study was to develop a phosphorus ((31) P) high resolution magic angle spinning magnetic resonance spectroscopy protocol for quantification of phosphorylated metabolites in intact cancer tissue.

METHODS

(31) P spectra were acquired on a 14.1 T spectrometer with a triplet (1) H/(13) C/(31) P MAS probe. Quantification of metabolites was performed using the PULCON principle. Basal-like and luminal-like breast cancer xenografts were treated with the dual PI3K/mTOR inhibitor BEZ235, and the impact of treatment on the concentration of phosphocholine, glycerophosphocholine, phosphoethanolamine and glycerophosphoethanolamine was evaluated.

RESULTS

In basal-like xenografts, BEZ235 treatment induced a significant decrease in phosphoethanolamine (-25.6%, P = 0.01) whilst phosphocholine (16.5%, P = 0.02) and glycerophosphocholine (37.3%, P < 0.001) were significantly increased. The metabolic changes could partially be explained by increased levels of phospholipase A2 group 4A (PLA2G4A).

CONCLUSION

(31) P high resolution magic angle spinning magnetic resonance spectroscopy is a useful method for quantitative assessment of metabolic responses to PI3K inhibition. Using the PULCON principle for quantification, the levels of phosphocholine, glycerophosphocholine, phosphoethanolamine, and glycerophosphoethanolamine could be evaluated with high precision and accuracy.

Selective inhibition of hypoxia-inducible factor 1α ameliorates adipose tissue dysfunction

Hypoxia-inducible factor 1α (HIF1α) induction in adipocytes is a critical component of the "fibrotic response," directly linked to metabolic dysfunction in adipose tissues under hypoxic conditions. We reasoned that inhibition of HIF1α may ameliorate the negative aspects of the obesity-associated fat pad expansion. We used the selective HIF1α inhibitor PX-478, whose effectiveness has previously been established in tumor models. We demonstrate that PX-478 treatment effectively suppresses the high-fat-diet (HFD)-induced HIF1α activation in adipose tissue. HIF1α inhibition causes a reduction of weight gain in mice on an HFD but not on a chow diet. Treatment increases energy expenditure and prompts resistance to HFD-mediated deterioration of metabolic parameters. Moreover, PX-478-treated mice have reduced fibrosis and fewer inflammatory infiltrates in their adipose tissues. We confirm the metabolic effects obtained with PX-478 treatment using an adipose tissue-specific, doxycycline-inducible dominant negative HIF1α mutant (dn-HIF1α). Consistent with the pharmacological results, genetic inhibition of endogenous HIF1α activity prompts similar metabolic improvements in HFD-fed mice. Collectively, our results demonstrate that HIF1α inhibition in the adipocyte leads to significant metabolic improvements, suggesting that selective HIF1α inhibition in adipose tissue may be an effective therapeutic avenue in the context of metabolic dysfunction.

The HIF-pathway inhibitor NSC-134754 induces metabolic changes and anti-tumour activity while maintaining vascular function

Background:

Hypoxia-inducible factor-1 (HIF-1) mediates the transcriptional response to hypoxic stress, promoting tumour progression and survival. This study investigated the acute effects of the small-molecule HIF-pathway inhibitor NSC-134754.

Methods:

Human PC-3LN5 prostate cancer cells were treated with NSC-134754 for 24 h in hypoxia. Orthotopic prostate tumour-bearing mice were treated with a single dose of NSC-134754 for 6, 24 or 48 h. Treatment response was measured using magnetic resonance spectroscopy and imaging. Ex-vivo histological validation of imaging findings was also sought.

Results:

In vitro, NSC-134754 significantly reduced lactate production and glucose uptake (P<0.05), while significantly increasing intracellular glucose (P<0.01) and glutamine uptake/metabolism (P<0.05). Increased glutamine metabolism was independent of c-Myc, a factor also downregulated by NSC-134754. In vivo, a significantly higher tumour apparent diffusion coefficient was determined 24 h post-treatment (P<0.05), with significantly higher tumour necrosis after 48 h (P<0.05). NSC-134754-treated tumours revealed lower expression of HIF-1α and glucose transporter-1, at 6 and 24 h respectively, while a transient increase in tumour hypoxia was observed after 24 h. Vessel perfusion/flow and vascular endothelial growth factor levels were unchanged with treatment.

Conclusion:

NSC-134754 induces metabolic alterations in vitro and early anti-tumour activity in vivo, independent of changes in vascular function. Our data support the further evaluation of NSC-134754 as an anti-cancer agent.

Multimodal assessment of early tumor response to chemotherapy: comparison between diffusion-weighted MRI, 1H-MR spectroscopy of choline and USPIO particles targeted at cell death

The aim of this study was to determine the value of different magnetic resonance (MR) protocols to assess early tumor response to chemotherapy. We used a murine tumor model (TLT) presenting different degrees of response to three different cytotoxic agents. As shown in survival curves, cyclophosphamide (CP) was the most efficient drug followed by 5-fluorouracil (5-FU), whereas the etoposide treatment had little impact on TLT tumors. Three different MR protocols were used at 9.4 Tesla 24 h post-treatment: diffusion-weighted (DW)-MRI, choline measurement by (1) H MRS, and contrast-enhanced MRI using ultrasmall iron oxide nanoparticles (USPIO) targeted at phosphatidylserine. Accumulation of contrast agent in apoptotic tumors was monitored by T(2) -weighted images and quantified by EPR spectroscopy. Necrosis and apoptosis were assessed by histology. Large variations were observed in the measurement of choline peak areas and could not be directly correlated to tumor response. Although the targeted USPIO particles were able to significantly differentiate between the efficiency of each cytotoxic agent and best correlated with survival endpoint, they present the main disadvantage of non-specific tumor accumulation, which could be problematic when transferring the method to the clinic. DW-MRI presents a better compromise by combining longitudinal studies with a high dynamic range; however, DW-MRI was unable to show any significant effect for 5-FU. This study illustrates the need for multimodal imaging in assessing tumor response to treatment to compensate for individual limitations.

Magnetic resonance spectroscopy of cancer metabolism and response to therapy

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

Reduced phosphocholine and hyperpolarized lactate provide magnetic resonance biomarkers of PI3K/Akt/mTOR inhibition in glioblastoma

The phosphatidylinositol-3-kinase/Akt/mammalian target of rapamycin (PI3K/Akt/mTOR) signaling pathway is activated in more than88% of glioblastomas (GBM). New drugs targeting this pathway are currently in clinical trials. However, noninvasive assessment of treatment response remains challenging. By using magnetic resonance spectroscopy (MRS), PI3K/Akt/mTOR pathway inhibition was monitored in 3 GBM cell lines (GS-2, GBM8, and GBM6; each with a distinct pathway activating mutation) through the measurement of 2 mechanistically linked MR biomarkers: phosphocholine (PC) and hyperpolarized lactate.(31)P MRS studies showed that treatment with the PI3K inhibitor LY294002 induced significant decreases in PC to 34 %± 9% of control in GS-2 cells, 48% ± 5% in GBM8, and 45% ± 4% in GBM6. The mTOR inhibitor everolimus also induced a significant decrease in PC to 62% ± 14%, 57% ± 1%, and 58% ± 1% in GS-2, GBM8, and GBM6 cells, respectively. Using hyperpolarized (13)C MRS, we demonstrated that hyperpolarized lactate levels were significantly decreased following PI3K/Akt/mTOR pathway inhibition in all 3 cell lines to 51% ± 10%, 62% ± 3%, and 58% ± 2% of control with LY294002 and 72% ± 3%, 61% ± 2%, and 66% ± 3% of control with everolimus in GS-2, GBM8, and GBM6 cells, respectively. These effects were mediated by decreases in the activity and expression of choline kinase α and lactate dehydrogenase, which respectively control PC and lactate production downstream of HIF-1. Treatment with the DNA damaging agent temozolomide did not have an effect on either biomarker in any cell line. This study highlights the potential of PC and hyperpolarized lactate as noninvasive MR biomarkers of response to targeted inhibitors in GBM.

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.

Metabolic imaging: a link between lactate dehydrogenase A, lactate, and tumor phenotype

PURPOSE

We compared the metabolic profiles and the association between LDH-A expression and lactate production in two isogenic murine breast cancer cell lines and tumors (67NR and 4T1). These cell lines were derived from a single mammary tumor and have different growth and metabolic phenotypes.

EXPERIMENTAL DESIGN

LDH-A expression, lactate concentration, glucose utilization, and oxygen consumption were measured in cells, and the potential relationship between tumor lactate levels [measured by magnetic resonance spectroscopic imaging (MRSI)] and tumor glucose utilization [measured by [(18)F]2-deoxy-2-fluoro-D-glucose positron emission tomography ([(18)F]FDG-PET)] was assessed in orthotopic breast tumors derived from these cell lines.

RESULTS

We show a substantial difference in LDH-A expression between 67NR and 4T1 cells under normoxia and hypoxia. We also show that small orthotopic 4T1 tumors generate 10-fold more lactate than corresponding 67NR tumors. The high lactate levels in small primary 4T1 tumors are associated with intense pimonidazole staining (a hypoxia indicator). Less-intense hypoxia staining was observed in the larger 67NR tumors and is consistent with the gradual increase and plateau of lactate concentration in enlarging 67NR tumors.

CONCLUSIONS

Lactate-MRSI has a greater dynamic range than [(18)F]FDG-PET and may be a more sensitive measure with which to evaluate the aggressive and metastatic potential of primary breast tumors.

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.

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.

17-allyamino-17-demethoxygeldanamycin treatment results in a magnetic resonance spectroscopy-detectable elevation in choline-containing metabolites associated with increased expression of choline transporter SLC44A1 and phospholipase A2

Introduction

17-allyamino-17-demethoxygeldanamycin (17-AAG), a small molecule inhibitor of Hsp90, is currently in clinical trials in breast cancer. However, 17-AAG treatment often results in inhibition of tumor growth rather than shrinkage, making detection of response a challenge. Magnetic resonance spectroscopy (MRS) and spectroscopic imaging (MRSI) are noninvasive imaging methods than can be used to monitor metabolic biomarkers of drug-target modulation. This study set out to examine the MRS-detectable metabolic consequences of Hsp90 inhibition in a breast cancer model.

Methods

MCF-7 breast cancer cells were investigated, and MRS studies were performed both on live cells and on cell extracts. ³¹P and ¹H MRS were used to determine total cellular metabolite concentrations and ¹³C MRS was used to probe the metabolism of [1,2-¹³C]-choline. To explain the MRS metabolic findings, microarray and RT-PCR were used to analyze gene expression, and in vitro activity assays were performed to determine changes in enzymatic activity following 17-AAG treatment.

Results

Treatment of MCF-7 cells with 17-AAG for 48 hours caused a significant increase in intracellular levels of choline (to 266 ± 18% of control, P = 0.05) and phosphocholine (PC; to 181 ± 10% of control, P = 0.001) associated with an increase in expression of choline transporter SLC44A1 and an elevation in the de novo synthesis of PC. We also detected an increase in intracellular levels of glycerophosphocholine (GPC; to 176 ± 38% of control, P = 0.03) associated with an increase in PLA2 expression and activity.

Conclusions

This study determined that in the MCF-7 breast cancer model inhibition of Hsp90 by 17-AAG results in a significant MRS-detectable increase in choline, PC and GPC, which is likely due to an increase in choline transport into the cell and phospholipase activation. ¹H MRSI can be used in the clinical setting to detect levels of total choline-containing metabolite (t-Cho, composed of intracellular choline, PC and GPC). As Hsp90 inhibitors enter routine clinical use, t-Cho could thus provide an easily detectable, noninvasive metabolic biomarker of Hsp90 inhibition in breast cancer patients.

Hypoxia-induced metabolic shifts in cancer cells: moving beyond the Warburg effect

Hypoxia has been recognized to play a role in promoting the invasive and metastatic behaviour of cancer cells. Largely via the transcription factor, hypoxia-induced factor 1, hypoxia exerts significant effects on cellular metabolism, with numerous downstream consequences. Energetically there is a significant shift away from oxidative phosphorylation in mitochondria towards glycolysis, a state also involved in the 'Warburg effect'. The proteins involved in mediating the altered metabolic pathways seen in tumour cells thus represent new targets for potential therapeutic intervention. Hypoxia has been associated with the development of aggressive phenotypes in cancer cells, and can be accompanied by changes in carbohydrate and lipid metabolism that impact tumour cell proliferation, adhesion, and angiogenesis. Herein, we examine glycolytic and other less investigated metabolic pathways in relation to cancer and hypoxia, with a focus on emerging tools for large-scale metabolite profiling ('metabolomics'). Metabolomic technologies permit the measurement of a wide range of metabolites in an untargeted manner, however, to date, this technology has been relatively under utilized for studying cellular responses to hypoxia. We detail some of the common experimental approaches employed in metabolomics experiments, including nuclear magnetic resonance and new mass spectrometry-based methods of analysis. Selected examples of the application of these technologies to the study of metabolic alterations brought about by hypoxia are provided, particularly as they relate to energy, carbohydrate, and lipid metabolism. Finally, the potential for therapeutic targeting of metabolic processes activated by hypoxia is presented.

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.

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.

Targeting metabolic transformation for cancer therapy

Cancer therapy has long relied on the rapid proliferation of tumour cells for effective treatment. However, the lack of specificity in this approach often leads to undesirable side effects. Many reports have described various 'metabolic transformation' events that enable cancer cells to survive, suggesting that metabolic pathways might be good targets. There are currently several drugs under development or in clinical trials that are based on specifically targeting the altered metabolic pathways of tumours. This Review highlights pathways against which there are already drugs in different stages of development and also discusses additional druggable targets.

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.

Targeting the hypoxia-inducible factor (HIF) pathway in cancer

The central component of hypoxia sensing in the cell is the hypoxia-inducible factor (HIF) transcriptional complex. HIF activity is deregulated in many human cancers, especially those that are highly hypoxic. Hypoxic tumour cells are usually resistant to radiotherapy and most conventional chemotherapeutic agents, rendering them highly aggressive and metastatic. Overexpression of HIF-alpha, the regulatory subunit of HIF, is associated with increased vascular density, severity of tumour grade, treatment failure and a poor prognostic outcome with conventional therapies. Therefore HIF is an attractive, although challenging, therapeutic target, and several different strategies have been developed to target HIF directly or indirectly in recent years. This review outlines the preclinical and clinical advances in this arena and discusses which cancers may benefit from HIF-targeted therapy.

In vivo (1)H MRS of WSU-DLCL2 human non-Hodgkin's lymphoma xenografts: response to rituximab and rituximab plus CHOP

In order to identify early (1)H MRS metabolic markers of response to rituximab immunotherapy and to rituximab plus CHOP (cyclophosphamide, hydroxydoxorubicin, vincristine, and prednisone) combination therapy, we performed an in vivo MRS investigation of a non-Hodgkin's lymphoma (NHL) xenograft model. Human WSU-DLCL2 NHL cells were subcutaneously implanted into flanks of female severe combined immunodeficient mice. When tumor volumes reached approximately 600 mm(3), rituximab was administered for three weekly cycles at a dose of 25 mg/kg per cycle with or without CHOP. Before and after treatment, tumor lactate (Lac) and total choline (tCho) were detected using the selective multiple quantum coherence sequence and the stimulated echo acquisition mode sequence, respectively. Rituximab produced a small tumor growth delay ( approximately 5 days), whereas treatment with rituximab plus CHOP (RCHOP) led to approximately 20% tumor regression after three cycles of therapy. After one cycle of rituximab, the tCho/H(2)O ratio had decreased significantly (5%, P = 0.003), whereas the Lac/H(2)O ratio had not changed (P = 0.58). Both Lac/H(2)O and tCho/H(2)O had decreased after one cycle of RCHOP treatment (26%, P = 0.001; 10%, P = 0.016, respectively). After two cycles of RCHOP, Ki67 assay of histological tumor specimens indicated approximately 40% decrease in proliferation (P < 0.001) in the RCHOP-treated tumors; no change was detected after treatment with rituximab alone. This study suggests that decreases in tCho/H(2)O are more sensitive indices of response to rituximab, whereas decreases in Lac/H(2)O are more sensitive to response to CHOP combination therapy.

Metabolomics of cancer

Metabolomics, one of the "omic" sciences in systems biology, is the global assessment and validation of endogenous small-molecule biochemicals (metabolites) within a biologic system. Initially, putative quantitative metabolic biomarkers for cancer detection and/or assessment of efficacy of anticancer treatment are usually discovered in a preclinical setting (using animal and human cell cultures), followed by translational validation of these biomarkers in biofluid or tumor tissue. Based on the tumor origin, various biofluids, such as blood, urine, and expressed prostatic secretions, can be used for validating metabolic biomarkers noninvasively in cancer patients. Metabolite detection and quantification is usually carried out by nuclear magnetic resonance (NMR) spectroscopy, while mass spectrometry (MS) provides another highly sensitive metabolomics technology. Usually, sophisticated statistical analyses are carried out either on spectroscopic or on quantitative metabolic data sets to provide meaningful information about the metabolic makeup of the sample. Various metabolic biomarkers, related to glycolysis, mitochondrial citric cycle acid, choline and fatty acid metabolism, were recently reported to play important roles in cancer development and responsiveness to anticancer treatment using NMR-based metabolic profiling.Carefully designed and validated protocols for sample handling and sample extraction followed by appropriate NMR techniques and statistical analyses, which are required to establish quantitative (1)H-NMR-based metabolomics as a reliable analytical tool in the area of cancer biomarker discovery, are discussed in the present chapter.

Metabolomic studies of human lung carcinoma cell lines using in vitro (1)H NMR of whole cells and cellular extracts

We report principal component analysis (PCA) of (1)H NMR spectra recorded for a group of human lung carcinoma cell lines in culture and (1)H NMR analysis of extracts from the same samples. The samples studied were cells of lung tumour origin with different chemotherapy drug resistance patterns. For whole cells, it was found that the statistically significant causes of spectral variation were an increase in the choline and a decrease in the methylene mobile lipid (1)H resonance intensities, which correlate with our knowledge of the level of resistance displayed by the different cells. Similarly, in the (1)H NMR spectra of the aqueous and lipophilic extracts, significant quantitative differences in the metabolite distributions were apparent, which are consistent with the PCA results.

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.

Using metabolomics to monitor anticancer drugs

The metabolome of a cancer cell is likely to show changes after responding to an anticancer drug. These changes could be used to decide whether to continue treatment or, in the context of a drug trial, to indicate whether the drug is working and perhaps its mechanism of action. (Nuclear) magnetic resonance spectroscopy (NMR/MRS) methods can offer important insights into novel anticancer agents in order to accelerate the drug development process including time-course studies on the effect of a drug on its site of action (termed pharmacodynamics), in this case the cancer. In addition, some classes of anticancer agents currently under development (e.g. antiangiogenics) are designed to be used in combination with other drugs and will not cause tumour shrinkage when used as single agents in Phase 1 clinical trials. Thus NMR/MRS may have a special role in monitoring the pharmacodynamic actions of such drugs in early-phase clinical trials. This review focuses on the use of ex vivo NMR and in vivo MRS methods for monitoring the effect of some novel anticancer drugs on the cancer metabolome. Ex vivo NMR methods are complementary to in vivo measurements, as they can provide additional information and help in the interpretation of the in vivo data.

Response of choline metabolites to docetaxel therapy is quantified in vivo by localized (31)P MRS of human breast cancer xenografts and in vitro by high-resolution (31)P NMR spectroscopy of cell extracts

Choline-containing compounds (CCCs) are elevated in breast cancer, and detected in vivo by the (1)H MRS total choline (tCho) resonance (3.25 ppm) and the (31)P MRS phosphomonoester (PME) resonance (3.8 ppm). Both the tCho and PME resonances decrease early after initiation of successful therapy. The single major component of these composite resonances, phosphocholine (PCho), also responds to therapy by decreasing. The ability to resolve and quantify PCho in vivo would thus increase the sensitivity of this biomarker for early detection of therapeutic response. Herein, the in vivo resolution and quantification of PCho is reported in human mouse xenograft tumors of the human breast cancer cell lines MCF-7 and MDA-mb-231. Significant decreases in tumor PCho are observed within 2 to 4 d posttreatment with the antimicrotubule drug, docetaxel. To determine whether these decreases are a general tumor response or an intracellular metabolic response, high-resolution NMR spectroscopy was performed on extracts of cells treated with docetaxel. Significant decreases in intracellular PCho and increases in glycerophosphocholine (GPC) were observed. These decreases are coincident with other tumor and cellular responses such as tumor growth delay (TGD), cell-cycle arrest, and modes of cell death such as mitotic catastrophe, necrosis, and apoptosis, with mitotic catastrophe predominating.

In vivo mouse imaging and spectroscopy in drug discovery

Imaging modalities such as micro-computed tomography (micro-CT), micro-positron emission tomography (micro-PET), high-resolution MRI, optical imaging, and high-resolution ultrasound have become invaluable tools in preclinical pharmaceutical research. They can be used to non-invasively investigate, in vivo, rodent biology and metabolism, disease models, and pharmacokinetics and pharmacodynamics of drugs. The advantages and limitations of each approach usually determine its application, and therefore a small-rodent imaging laboratory in a pharmaceutical environment should ideally provide access to several techniques. In this paper we aim to illustrate how these techniques may be used to obtain meaningful information for the phenotyping of transgenic mice and for the analysis of compounds in murine models of disease.

Promise and Progress for Functional and Molecular Imaging of Response to Targeted Therapies

Biomarkers to predict or monitor therapy response are becoming essential components of drug developer's armamentaria. Molecular and functional imaging has particular promise as a biomarker for anticancer therapies because it is non-invasive, can be used longitudinally and provides information on the whole patient or tumor. Despite this promise, molecular or functional imaging endpoints are not routinely incorporated into clinical trial design. As the costs of clinical trials and drug development become prohibitively more expensive, the need for improved biomarkers has become imperative and thus, the relatively high cost of imaging is justified. Imaging endpoints, such as Diffusion-Weighted MRI, DCE-MRI and FDG-PET have the potential to make drug development more efficient at all phases, from discovery screening with in vivo pharmacodynamics in animal models through the phase III enrichment of the patient population for potential responders. This review focuses on the progress of imaging responses to new classes of anti-cancer therapies targeted against PI3 kinase/AKT, HIF-1alpha and VEGF. The ultimate promise of molecular and functional imaging is to theragnostically predict response prior to commencement of targeted therapy.

The role of hypoxia inducible factor-1 in cell metabolism--a possible target in cancer therapy

In many cancer types, intratumoural hypoxia is linked to increased expression and activity of the transcription factor hypoxia-inducible factor (HIF-1alpha), which is associated with poor patient prognosis. This increased the interest in HIF-1alpha as a cancer drug target. Further, HIF-1alpha has also a central role in the adaptive cellular programme responding to hypoxia in normal tissues. Many of the HIF-1alpha-regulated genes encode enzymes of metabolic pathways. Therefore, studying the link and the feedback mechanisms between metabolism and HIF-1alpha is of major importance to find new and specific therapeutic strategies.

Advances in methods for assessing tumor hypoxia in vivo: implications for treatment planning

Tumor hypoxia and its downstream effects have remained of considerable interest for decades due to its negative impact on response to various cancer therapies and promotion of metastasis. Diagnosing hypoxia non-invasively can provide a significant advancement in cancer treatment and is the dire necessity for implementing specific targeted therapies now emerging to treat different aspects of cancer. A variety of techniques are being proposed to do so. However, none of them has yet been established in the clinical arena. This review summarizes the methods currently available to assess tumor hypoxia in vivo and their respective advantages and shortcomings. It also points out the impedances that need to be overcome to establish any particular method in the clinic, along with a broad overview of requirements for further advancement in this sphere of cancer research.

The response of RIF-1 fibrosarcomas to the vascular-disrupting agent ZD6126 assessed by in vivo and ex vivo 1H magnetic resonance spectroscopy

The response of radiation-induced fibrosarcoma 1 (RIF-1) tumors treated with the vascular-disrupting agent (VDA) ZD6126 was assessed by in vivo and ex vivo 1H magnetic resonance spectroscopy (MRS) methods. Tumors treated with 200 mg/kg ZD6126 showed a significant reduction in total choline (tCho) in vivo 24 hours after treatment, whereas control tumors showed a significant increase in tCho. This response was investigated further within both ex vivo unprocessed tumor tissues and tumor tissue metabolite extracts. Ex vivo high-resolution magic angle spinning (HRMAS) and 1H MRS of metabolite extracts revealed a significant reduction in phosphocholine and glycerophosphocholine in biopsies of ZD6126-treated tumors, confirming in vivo tCho response. ZD6126-induced reduction in choline compounds is consistent with a reduction in cell membrane turnover associated with necrosis and cell death following disruption of the tumor vasculature. In vivo tumor tissue water diffusion and lactate measurements showed no significant changes in response to ZD6126. Spin-spin relaxation times (T2) of water and metabolites also remained unchanged. Noninvasive 1H MRS measurement of tCho in vivo provides a potential biomarker of tumor response to VDAs in RIF-1 tumors.