Positron Emission Tomography Imaging of Tumor Cell Metabolism and Application to Therapy Response Monitoring

The Role of Total-Body PET in Drug Development and Evaluation: Status and Outlook

Total-body PET, an emerging technique, enables high-quality simultaneous total-body dynamic PET acquisition and accurate kinetic analysis. It has the potential to facilitate the study of multiple tracers while minimizing radiation dose and improving tracer-specific imaging. This advancement holds promise for enhancing the development and clinical evaluation of drugs, particularly radiopharmaceuticals. Multiple clinical trials are using a total-body PET scanner to explore existing and innovative radiopharmaceuticals. However, challenges persist, along with the opportunities, with regard to the use of total-body PET in drug development and evaluation. Specifically, considerations relate to the role of total-body PET in clinical pharmacologic evaluations and its integration into the theranostic paradigm. In this review, state-of-the-art total-body PET and its potential roles in pharmaceutical research are explored.

ImmunoPET provides a novel way to visualize the CD103+ tissue-resident memory T cell to predict the response of immune checkpoint inhibitors

BACKGROUND

Immune checkpoint inhibitors (ICIs) have made significant progress in oncotherapy improving survival of patients. However, the benefits are limited to only a small subgroup of patients who could achieve durable responses. Early prediction of response may enable treatment optimization and patient stratification. Therefore, developing appropriate biomarkers is critical to monitoring efficacy and assessing patient response to ICIs.

MAIN BODY

Herein, we first introduce a new potential biomarker, CD103, expressed on tissue-resident memory T cells, and discuss the potential application of CD103 PET imaging in predicting immune checkpoint inhibitor treatment. In addition, we describe the current targets of ImmunoPET and compare these targets with CD103. To assess the benefit of PET imaging, a comparative analysis between ImmunoPET and other imaging techniques commonly employed for tumor diagnosis was performed. Additionally, we compare ImmunoPET and immunohistochemistry (IHC), a widely utilized clinical method for biomarker identification with respect to visualizing the immune targets.

CONCLUSION

CD103 ImmunoPET is a promising method for determining tumor-infiltrating lymphocytes (TILs) load and response to ICIs, thereby addressing the lack of reliable biomarkers in cancer immunotherapy. Compared to general T cell markers, CD103 is a specific marker for tissue-resident memory T cells, which number increases during successful ICI therapy. ImmunoPET offers noninvasive, dynamic imaging of specific markers, complemented by detailed molecular information from immunohistochemistry (IHC). Radiomics can extract quantitative features from traditional imaging methods, while near-infrared fluorescence (NIRF) imaging aids tumor detection during surgery. In the era of precision medicine, combining such methods will offer a more comprehensive approach to cancer diagnosis and treatment.

Label-free spatially maintained measurements of metabolic phenotypes in cells

Metabolic reprogramming at a cellular level contributes to many diseases including cancer, yet few assays are capable of measuring metabolic pathway usage by individual cells within living samples. Here, autofluorescence lifetime imaging is combined with single-cell segmentation and machine-learning models to predict the metabolic pathway usage of cancer cells. The metabolic activities of MCF7 breast cancer cells and HepG2 liver cancer cells were controlled by growing the cells in culture media with specific substrates and metabolic inhibitors. Fluorescence lifetime images of two endogenous metabolic coenzymes, reduced nicotinamide adenine dinucleotide (NADH) and oxidized flavin adenine dinucleotide (FAD), were acquired by a multi-photon fluorescence lifetime microscope and analyzed at the cellular level. Quantitative changes of NADH and FAD lifetime components were observed for cells using glycolysis, oxidative phosphorylation, and glutaminolysis. Conventional machine learning models trained with the autofluorescence features classified cells as dependent on glycolytic or oxidative metabolism with 90%-92% accuracy. Furthermore, adapting convolutional neural networks to predict cancer cell metabolic perturbations from the autofluorescence lifetime images provided improved performance, 95% accuracy, over traditional models trained via extracted features. Additionally, the model trained with the lifetime features of cancer cells could be transferred to autofluorescence lifetime images of T cells, with a prediction that 80% of activated T cells were glycolytic, and 97% of quiescent T cells were oxidative. In summary, autofluorescence lifetime imaging combined with machine learning models can detect metabolic perturbations between glycolysis and oxidative metabolism of living samples at a cellular level, providing a label-free technology to study cellular metabolism and metabolic heterogeneity.

Prospective validation of 18F-Fluoroethylcholine as a tracer in PET/MRI for the evaluation of breast lesions and prediction of lymph node status

PURPOSE

To assess 18F-Fluoroethylcholine (18F-FEC) as a PET/MRI tracer in the evaluation of breast lesions, breast cancer aggressiveness, and prediction of lymph node status.

MATERIALS AND METHODS

This prospective, monocentric study was approved by the ethics committee and patients gave written, informed consent. This clinical trial was registered in the EudraCT database (Number 2017-003089-29). Women who presented with suspicious breast lesions were included. Histopathology was used as reference standard. Simultaneous 18F-FEC PET/MRI of the breast was performed in a prone position with a dedicated breast coil. MRI was performed using a standard protocol before and after contrast agent administration. A simultaneous read by nuclear medicine physicians and radiologists collected the imaging data of MRI-detected lesions, including the maximum standardized 18F-FEC-uptake value of breast lesions (SUV_maxT) and axillary lymph nodes (SUV_maxLN). Differences in SUV_max were evaluated with the Mann-Whitney U test. To calculate diagnostic performance, the area under the receiver operating characteristics curve (ROC) was used.

RESULTS

There were 101 patients (mean age 52.3 years, standard deviation 12.0) with 117 breast lesions included (30 benign, 7 ductal carcinomas in situ, 80 invasive carcinomas). 18F-FEC was well tolerated by all patients. The ROC to distinguish benign from malignant breast lesions was 0.846. SUV_maxT was higher if lesions were malignant (p < 0.001), had a higher proliferation rate (p = 0.011), and were HER2-positive (p = 0.041). SUV_maxLN was higher in metastatic lymph nodes, with an ROC of 0.761 for SUV_maxT and of 0.793 for SUV_maxLN. CONCLUSION: Simultaneous 18F-FEC PET/MRI is safe and has the potential to be used for the evaluation of breast cancer aggressiveness, and prediction of lymph node status.

Application of Metabolic Reprogramming to Cancer Imaging and Diagnosis

Cellular metabolism governs the signaling that supports physiological mechanisms and homeostasis in an individual, including neuronal transmission, wound healing, and circadian clock manipulation. Various factors have been linked to abnormal metabolic reprogramming, including gene mutations, epigenetic modifications, altered protein epitopes, and their involvement in the development of disease, including cancer. The presence of multiple distinct hallmarks and the resulting cellular reprogramming process have gradually revealed that these metabolism-related molecules may be able to be used to track or prevent the progression of cancer. Consequently, translational medicines have been developed using metabolic substrates, precursors, and other products depending on their biochemical mechanism of action. It is important to note that these metabolic analogs can also be used for imaging and therapeutic purposes in addition to competing for metabolic functions. In particular, due to their isotopic labeling, these compounds may also be used to localize and visualize tumor cells after uptake. In this review, the current development status, applicability, and limitations of compounds targeting metabolic reprogramming are described, as well as the imaging platforms that are most suitable for each compound and the types of cancer to which they are most appropriate.

Development of 89Zr-anti-CD103 PET imaging for non-invasive assessment of cancer reactive T cell infiltration

PURPOSE

CD103, an integrin specifically expressed on the surface of cancer-reactive T cells, is significantly increased during successful immunotherapy across human malignancies. In this study, we describe the generation and zirconium-89 (⁸⁹Zr) radiolabeling of monoclonal antibody (mAb) clones that specifically recognize human CD103 for non-invasive immune positron-emission tomography (PET) imaging of T cell infiltration as potential biomarker for effective anticancer immune responses.

EXPERIMENTAL DESIGN

First, to determine the feasibility of anti-CD103 immuno-PET to visualize CD103-positive cells at physiologically and clinically relevant target densities, we developed an ⁸⁹Zr-anti-murine CD103 PET tracer. Healthy, non-tumor bearing C57BL/6 mice underwent serial PET imaging after intravenous injection, followed by ex vivo biodistribution. Tracer specificity and macroscopic tissue distribution were studied using autoradiography combined with CD103 immunohistochemistry. Next, we generated and screened six unique mAbs that specifically target human CD103 positive cells. Optimal candidates were selected for ⁸⁹Zr-anti-human CD103 PET development. Nude mice (BALB/cOlaHsd-Foxn1nu) with established CD103 expressing Chinese hamster ovary (CHO) or CHO wild-type xenografts were injected with ⁸⁹Zr-anti-human CD103 mAbs and underwent serial PET imaging, followed by ex vivo biodistribution.

RESULTS

⁸⁹Zr-anti-murine CD103 PET imaging identified CD103-positive tissues at clinically relevant target densities. For human anti-human CD103 PET development two clones were selected based on strong binding to the CD103⁺ CD8⁺ T cell subpopulation in ovarian cancer tumor digests, non-overlapping binding epitopes and differential CD103 blocking properties. In vivo, both ⁸⁹Zr-anti-human CD103 tracers showed high target-to-background ratios, high target site selectivity and a high sensitivity in human CD103 positive xenografts.

CONCLUSION

CD103 immuno-PET tracers visualize CD103 T cells at relevant densities and are suitable for future non-invasive assessment of cancer reactive T cell infiltration.

PET Use in Cancer Diagnosis, Treatment, and Prognosis

Tumorigenesis is a multistep process marked by variations in numerous metabolic pathways that affect cellular architectures and functions. Cancer cells reprogram their energy metabolism to enable several basic molecular functions, including membrane biosynthesis, receptor regulations, bioenergetics, and redox stress. In recent years, cancer diagnosis and treatment strategies have targeted these specific metabolic changes and the tumor's interactions with its microenvironment. Positron emission tomography (PET) captures all molecular alterations leading to abnormal function and cancer progression. As a result, the development of PET radiotracers increasingly focuses on irregular biological pathways or cells that overexpress receptors that have the potential to function as biomarkers for early diagnosis and treatment measurements as well as research. This chapter reviews both established and evolving PET radiotracers used to image tumor biology. We have also included a few advantages and disadvantages of the routinely used PET radiotracers in cancer imaging.

Economical Production of Radiopharmaceuticals for Preclinical Imaging Using Microdroplet Radiochemistry

The short-lived radiolabeled "tracers" needed for performing whole body imaging in animals or patients with positron-emission tomography (PET) are generally produced via automated "radiosynthesizers". Most current radiosynthesizers are designed for routine production of relatively large clinical batches and are very wasteful when only a small batch of a tracer is needed, such as is the case for preclinical in vivo PET imaging studies. To overcome the prohibitively high cost of producing small batches of PET tracers, we developed a droplet microreactor system that performs radiochemistry at the 1-10μL scale instead of the milliliter scale of conventional technologies. The overall yield for the droplet-based production of many PET tracers is comparable to conventional approaches, but 10-100× less reagents are consumed, the synthesis can be completed in much less time (<30 min), and only a small laboratory footprint and minimal radiation shielding are needed. By combining these advantages, droplet microreactors enable the economical production of small batches PET tracers on demand. Here, we describe the fabrication method of the droplet microreactor and the droplet-based synthesis of an example radiotracer ([¹⁸F]fallypride).

Imaging modalities for monitoring acute therapeutic effects after near-infrared photoimmunotherapy in vivo

Near-infrared photoimmunotherapy (NIR-PIT) induces immediate cell death after irradiation with near-infrared (NIR) light. Acute therapeutic effects caused by NIR-PIT before the change of tumor size is essential to be monitored by imaging modalities. We summarized and compared the imaging modalities for evaluating acute therapeutic effects after NIR-PIT, and aimed to provide a better understanding of advantages and disadvantages of each modality for evaluation in clinical applications. Fluorescence imaging and fluorescence lifetime, with high resolution, remains high accumulation of fluorescence dyes in the normal organs. High resolution and noninvasiveness are the major advantages of magnetic resonance imaging, while ¹⁸ F-fluorodeoxyglucose positron emission tomography provides information about the glucose metabolism. Optical coherence tomography provided more information about the blood vessels. Thus, all of the imaging modalities play an important role in evaluating acute therapeutic effects after NIR-PIT. Clinicians should choose suitable modality according to specific purpose and conditions in clinical application.

Development and Validation of a PET/SPECT Radiopharmaceutical in Oncology

In oncology, biomarker research aimed to provide insights on cancer biology via positron emission tomography (PET) and single photon emission tomography (SPECT) imaging has seen an incredible growth in the past two decades. Despite the increased number of publications on PET/SPECT radiopharmaceuticals, the field lacked standardization of in vitro and in vivo parameters necessary for the characterization of any radiotracer. Through the efforts of the World Molecular Imaging Society Education Committee, this white paper lays down validation studies that are essential to chemically and biologically characterize new radiopharmaceuticals derived from small molecules, peptides or proteins. Finally, a brief overview of the steps toward translation is also presented.Herein, we discuss the following: Chemistry and radiochemistry metrics to establish the identity of the imaging agent. In vitro and in vivo studies to examine the radiotracer's mechanism of action, which includes target specificity, pharmacokinetics and in vivo metabolism.

Intracellular Water Lifetime as a Tumor Biomarker to Monitor Doxorubicin Treatment via FFC-Relaxometry in a Breast Cancer Model

This study aims to explore whether the water exchange rate constants in tumor cells can act as a hallmark of pathology status and a reporter of therapeutic outcomes. It has been shown, using 4T1 cell cultures and murine allografts, that an early assessment of the therapeutic effect of doxorubicin can be detected through changes in the cellular water efflux rate constant kio. The latter has been estimated by analyzing the magnetization recovery curve in standard NMR T1 measurements when there is a marked difference in the proton relaxation rate constants (R1) between the intra- and the extra-cellular compartments. In cellular studies, T1 measurements were carried out on a relaxometer working at 0.5 T, and the required difference in R1 between the two compartments was achieved via the addition of a paramagnetic agent into the extracellular compartment. For in-vivo experiments, the large difference in the R1 values of the two-compartments was achieved when the T1 measurements were carried out at low magnetic field strengths. This task was accomplished using a Fast Field Cycling (FFC) relaxometer that was properly modified to host a mouse in its probe head. The decrease in kio upon the administration of doxorubicin is the result of the decreased activity of Na+/K+-ATPase, as shown in an independent test on the cellular uptake of Rb ions. The results reported herein suggest that kio can be considered a non-invasive, early and predictive biomarker for the identification of responsive patients immediately from the first doxorubicin treatment.

Economical droplet-based microfluidic production of [18F]FET and [18F]Florbetaben suitable for human use

Current equipment and methods for preparation of radiopharmaceuticals for positron emission tomography (PET) are expensive and best suited for large-scale multi-doses batches. Microfluidic radiosynthesizers have been shown to provide an economic approach to synthesize these compounds in smaller quantities, but can also be scaled to clinically-relevant levels. Batch microfluidic approaches, in particular, offer significant reduction in system size and reagent consumption. Here we show a simple and rapid technique to concentrate the radioisotope, prior to synthesis in a droplet-based radiosynthesizer, enabling production of clinically-relevant batches of [18F]FET and [18F]FBB. The synthesis was carried out with an automated synthesizer platform based on a disposable Teflon-silicon surface-tension trap chip. Up to 0.1 mL (4 GBq) of radioactivity was used per synthesis by drying cyclotron-produced aqueous [18F]fluoride in small increments directly inside the reaction site. Precursor solution (10 µL) was added to the dried [18F]fluoride, the reaction chip was heated for 5 min to perform radiofluorination, and then a deprotection step was performed with addition of acid solution and heating. The product was recovered in 80 µL volume and transferred to analytical HPLC for purification. Purified product was formulated via evaporation and resuspension or a micro-SPE formulation system. Quality control testing was performed on 3 sequential batches of each tracer. The method afforded production of up to 0.8 GBq of [18F]FET and [18F]FBB. Each production was completed within an hour. All batches passed quality control testing, confirming suitability for human use. In summary, we present a simple and efficient synthesis of clinically-relevant batches of [18F]FET and [18F]FBB using a microfluidic radiosynthesizer. This work demonstrates that the droplet-based micro-radiosynthesizer has a potential for batch-on-demand synthesis of 18F-labeled radiopharmaceuticals for human use.

Supply and demand: Cellular nutrient uptake and exchange in cancer

Nutrient supply and demand delineate cell behavior in health and disease. Mammalian cells have developed multiple strategies to secure the necessary nutrients that fuel their metabolic needs. This is more evident upon disruption of homeostasis in conditions such as cancer, when cells display high proliferation rates in energetically challenging conditions where nutritional sources may be scarce. Here, we summarize the main routes of nutrient acquisition that fuel mammalian cells and their implications in tumorigenesis. We argue that the molecular mechanisms of nutrient acquisition not only tip the balance between nutrient supply and demand but also determine cell behavior upon nutrient limitation and energetic stress and contribute to nutrient partitioning and metabolic coordination between different cell types in inflamed or tumorigenic environments.

Circulating tumor cell profiling for precision oncology

Analysis of circulating tumor cells (CTCs) collected from patient's blood offers a broad range of opportunities in the field of precision oncology. With new advances in profiling technology, it is now possible to demonstrate an association between the molecular profiles of CTCs and tumor response to therapy. In this Review, we discuss mechanisms of tumor resistance to therapy and their link to phenotypic and genotypic properties of CTCs. We summarize key technologies used to isolate and analyze CTCs and discuss recent clinical studies that examined CTCs for genomic and proteomic predictors of responsiveness to therapy. We also point out current limitations that still hamper the implementation of CTCs into clinical practice. We finally reflect on how these shortcomings can be addressed with the likely contribution of multiparametric approaches and advanced data analytics.

Spatial heterogeneity of radiolabeled choline positron emission tomography in tumors of patients with non-small cell lung cancer: first-in-patient evaluation of [18F]fluoromethyl-(1,2-2H4)-choline

Purpose: The spatio-molecular distribution of choline and its metabolites in tumors is highly heterogeneous. Due to regulation of choline metabolism by hypoxic transcriptional signaling and other survival factors, we envisage that detection of such heterogeneity in patient tumors could provide the basis for advanced localized therapy. However, non-invasive methods to assess this phenomenon in patients are limited. We investigated such heterogeneity in Non-Small Cell Lung Cancer (NSCLC) with [18F]fluoromethyl-(1,2-2H4) choline ([18F]D4-FCH) and positron emission tomography/computed tomography (PET/CT). Experimental design: [18F]D4-FCH (300.5±72.9MBq [147.60-363.6MBq]) was administered intravenously to 17 newly diagnosed NSCLC patients. PET/CT scans were acquired concurrently with radioactive blood sampling to permit mathematical modelling of blood-tissue transcellular rate constants. Comparisons were made with biopsy-derived choline kinase-α (CHKα) expression and diagnostic [18F]fluorodeoxyglucose ([18F]FDG) scans. Results: Oxidation of [18F]D4-FCH to [18F]D4-fluorobetaine was suppressed (48.58±0.31% parent at 60 min) likely due to the deuterium isotope effect embodied within the design of the radiotracer. Early (5 min) and late (60 min) images showed specific uptake of tracer in all 51 lesions (tumors, lymph nodes and metastases) from 17 patients analyzed. [18F]D4-FCH-derived uptake (SUV60max) in index primary lesions (n=17) ranged between 2.87-10.13; lower than that of [18F]FDG PET [6.89-22.64]. Mathematical modelling demonstrated net irreversible uptake of [18F]D4-FCH at steady-state, and parametric mapping of the entire tumor showed large intratumorally heterogeneity in radiotracer retention, which is likely to have influenced correlations with biopsy-derived CHKα expression. Conclusions: [18F]D4-FCH is detectable in NSCLC with large intratumorally heterogeneity, which could be exploited in the future for targeting localized therapy.

Carbon Nanomaterials for Sorption of 68Ga for Potential Using in Positron Emission Tomography

In present work, carbon nanomaterials (CNMs) are investigated as potential carriers of ⁶⁸Ga, which is widely used in positron emission tomography (PET) in nuclear medicine. Sorption behavior of ⁶⁸Ga was studied onto CNMs of various structures and chemical compositions: nanodiamonds (ND), reduced graphite oxide (rGiO) and multi-walled carbon nanotubes (MWCNT), as well as their oxidized (ND–COOH) or reduced (rGiO–H, MWCNT–H) forms. The physicochemical properties of the nanoparticles were determined by high resolution transmission electron microscopy, x-ray photoelectron spectroscopy, dynamic light scattering and potentiometric titration. The content of ⁶⁸Ga in the solutions during the study of sorption was determined by gamma-ray spectrometry. The highest degree of ⁶⁸Ga sorption was observed on ND and ND–COOH samples, and the optimal sorption conditions were determined: an aqueous solution with a pH of 5–7, m/V ratio of 50 μg/mL and a room temperature (25 °C). The ⁶⁸Ga@ND and ⁶⁸Ga@ND–COOH conjugates were found to be stable in a model blood solution—phosphate-buffered saline with a pH of 7.3, containing 40 g/L of bovine serum albumin: ⁶⁸Ga desorption from these samples in 90 minutes was no more than 20% at 25 °C and up to 30% at 37 °C. Such a quantity of desorbed ⁶⁸Ga does not harm the body and does not interfere with the PET imaging process. Thus, ND and ND–COOH are promising CNMs for using as carriers of ⁶⁸Ga for PET diagnostics.

Imaging DNA Damage Repair In Vivo After 177Lu-DOTATATE Therapy

Molecular radiotherapy using 177Lu-DOTATATE is a most effective treatment for somatostatin receptor-expressing neuroendocrine tumors. Despite its frequent and successful use in the clinic, little or no radiobiologic considerations are made at the time of treatment planning or delivery. On positive uptake on octreotide-based PET/SPECT imaging, treatment is usually administered as a standard dose and number of cycles without adjustment for peptide uptake, dosimetry, or radiobiologic and DNA damage effects in the tumor. Here, we visualized and quantified the extent of DNA damage response after 177Lu-DOTATATE therapy using SPECT imaging with 111In-anti-γH2AX-TAT. This work was a proof-of-principle study of this in vivo noninvasive biodosimeter with β-emitting therapeutic radiopharmaceuticals. Methods: Six cell lines were exposed to external-beam radiotherapy (EBRT) or 177Lu-DOTATATE, after which the number of γH2AX foci and the clonogenic survival were measured. Mice bearing CA20948 somatostatin receptor-positive tumor xenografts were treated with 177Lu-DOTATATE or sham-treated and coinjected with 111In-anti-γH2AX-TAT, 111In-IgG-TAT control, or vehicle. Results: Clonogenic survival after external-beam radiotherapy was cell-line-specific, indicating varying levels of intrinsic radiosensitivity. Regarding in vitro cell lines treated with 177Lu-DOTATATE, clonogenic survival decreased and γH2AX foci increased for cells expressing high levels of somatostatin receptor subtype 2. Ex vivo measurements revealed a partial correlation between 177Lu-DOTATATE uptake and γH2AX focus induction between different regions of CA20948 xenograft tumors, suggesting that different parts of the tumor may react differentially to 177Lu-DOTATATE irradiation. Conclusion:111In-anti-γH2AX-TAT allows monitoring of DNA damage after 177Lu-DOTATATE therapy and reveals heterogeneous damage responses.

Metabolomics for Investigating Physiological and Pathophysiological Processes

Metabolomics uses advanced analytical chemistry techniques to enable the high-throughput characterization of metabolites from cells, organs, tissues, or biofluids. The rapid growth in metabolomics is leading to a renewed interest in metabolism and the role that small molecule metabolites play in many biological processes. As a result, traditional views of metabolites as being simply the "bricks and mortar" of cells or just the fuel for cellular energetics are being upended. Indeed, metabolites appear to have much more varied and far more important roles as signaling molecules, immune modulators, endogenous toxins, and environmental sensors. This review explores how metabolomics is yielding important new insights into a number of important biological and physiological processes. In particular, a major focus is on illustrating how metabolomics and discoveries made through metabolomics are improving our understanding of both normal physiology and the pathophysiology of many diseases. These discoveries are yielding new insights into how metabolites influence organ function, immune function, nutrient sensing, and gut physiology. Collectively, this work is leading to a much more unified and system-wide perspective of biology wherein metabolites, proteins, and genes are understood to interact synergistically to modify the actions and functions of organelles, organs, and organisms.

Imaging of cancer lipid metabolism in response to therapy

Lipids represent a diverse array of molecules essential to the cell's structure, defense, energy, and communication. Lipid metabolism can often become dysregulated during tumor development. During cancer therapy, targeted inhibition of cell proliferation can likewise cause widespread and drastic changes in lipid composition. Molecular imaging techniques have been developed to monitor altered lipid profiles as a biomarker for cancer diagnosis and treatment response. For decades, MRS has been the dominant non-invasive technique for studying lipid metabolite levels. Recent insights into the oncogenic transformations driving changes in lipid metabolism have revealed new mechanisms and signaling molecules that can be exploited using optical imaging, mass spectrometry imaging, and positron emission tomography. These novel imaging modalities have provided researchers with a diverse toolbox to examine changes in lipids in response to a wide array of anticancer strategies including chemotherapy, radiation therapy, signal transduction inhibitors, gene therapy, immunotherapy, or a combination of these strategies. The understanding of lipid metabolism in response to cancer therapy continues to evolve as each therapeutic method emerges, and this review seeks to summarize the current field and areas of unmet needs.

Metabolism of Stem and Progenitor Cells: Proper Methods to Answer Specific Questions

Stem cells can stay quiescent for a long period of time or proliferate and differentiate into multiple lineages. The activity of stage-specific metabolic programs allows stem cells to best adapt their functions in different microenvironments. Specific cellular phenotypes can be, therefore, defined by precise metabolic signatures. Notably, not only cellular metabolism describes a defined cellular phenotype, but experimental evidence now clearly indicate that also rewiring cells towards a particular cellular metabolism can drive their cellular phenotype and function accordingly. Cellular metabolism can be studied by both targeted and untargeted approaches. Targeted analyses focus on a subset of identified metabolites and on their metabolic fluxes. In addition, the overall assessment of the oxygen consumption rate (OCR) gives a measure of the overall cellular oxidative metabolism and mitochondrial function. Untargeted approach provides a large-scale identification and quantification of the whole metabolome with the aim to describe a metabolic fingerprinting. In this review article, we overview the methodologies currently available for the study of invitro stem cell metabolism, including metabolic fluxes, fingerprint analyses, and single-cell metabolomics. Moreover, we summarize available approaches for the study of in vivo stem cell metabolism. For all of the described methods, we highlight their specificities and limitations. In addition, we discuss practical concerns about the most threatening steps, including metabolic quenching, sample preparation and extraction. A better knowledge of the precise metabolic signature defining specific cell population is instrumental to the design of novel therapeutic strategies able to drive undifferentiated stem cells towards a selective and valuable cellular phenotype.

Involvement of increased p53 expression in the decrease of mitochondrial DNA copy number and increase of SUVmax of FDG-PET scan in esophageal squamous cell carcinoma

We appraised Warburg effect through analysis of mitochondrial DNA (mtDNA) copy number and maximum standard uptake value (SUV_max) of ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET) scan and their alterations in esophageal squamous cell carcinoma (ESCC). Later T-status and longer longitudinal tumor length were associated with lower mtDNA^ESCC copy number (p < .05) but higher SUV_max-ESCC (p < .05), respectively. Lower mtDNA^ESCC copy number correlated with higher SUV_max-ESCC, reciprocally (p < .05). ESCCs expressing mutant p53 protein had lower mtDNA^ESCC copy number (p = .056) but higher SUV_max-ESCC (p = .046). We conclude that mutant p53 protein may be involved in the Warburg effect of ESCC.

Genetic features associated with 18F-FDG uptake in intrahepatic cholangiocarcinoma

Purpose

In intrahepatic cholangiocarcinoma (iCCA), genetic characteristics on ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG)-PET scans are not yet clarified. If specific genetic characteristics were found to be related to FDG uptake in iCCA, we can predict molecular features based on the FDG uptake patterns and to distinguish different types of treatments. In this purpose, we analyzed RNA sequencing in iCCA patients to evaluate gene expression signatures associated with FDG uptake patterns.

Methods

We performed RNA sequencing of 22 cases iCCA who underwent preoperative ¹⁸F-FDG-PET, and analyzed the clinical and molecular features according to the maximum standard uptake value (SUVmax). Genes and biological pathway which are associated with SUVmax were analyzed.

Results

Patients with SUVmax higher than 9.0 (n = 9) had poorer disease-free survival than those with lower SUVmax (n = 13, P = 0.035). Genes related to glycolysis and gluconeogenesis, phosphorylation and cell cycle were significantly correlated with SUVmax (r ≥ 0.5). RRM2, which is related to the toxicity of Gemcitabine was positively correlated with SUVmax, and SLC27A2 which is associated with Cisplastin response was negatively correlated with SUVmax. According to the pathway analysis, cell cycle, cell division, hypoxia, inflammatory, and metabolism-related pathways were enriched in high SUVmax patients.

Conclusion

The genomic features of gene expression and pathways can be predicted by FDG uptake features in iCCA. Patients with high FDG uptake have enriched cell cycle, metabolism and hypoxic pathways, which may lead to a more rational targeted treatment approach.

How clinical imaging can assess cancer biology

Human cancers represent complex structures, which display substantial inter- and intratumor heterogeneity in their genetic expression and phenotypic features. However, cancers usually exhibit characteristic structural, physiologic, and molecular features and display specific biological capabilities named hallmarks. Many of these tumor traits are imageable through different imaging techniques. Imaging is able to spatially map key cancer features and tumor heterogeneity improving tumor diagnosis, characterization, and management. This paper aims to summarize the current and emerging applications of imaging in tumor biology assessment.

3D Growth of Cancer Cells Elicits Sensitivity to Kinase Inhibitors but Not Lipid Metabolism Modifiers

Tumor cells exhibit altered lipid metabolism compared with normal cells. Cell signaling kinases are important for regulating lipid synthesis and energy storage. How upstream kinases regulate lipid content, versus direct targeting of lipid-metabolizing enzymes, is currently unexplored. We evaluated intracellular lipid concentrations in prostate and breast tumor spheroids, treated with drugs directly inhibiting metabolic enzymes fatty acid synthase (FASN), acetyl-CoA carboxylase (ACC), diacylglyceride acyltransferase (DGAT), and pyruvate dehydrogenase kinase (PDHK), or cell signaling kinase enzymes PI3K, AKT, and mTOR with lipidomic analysis. We assessed whether baseline lipid profiles corresponded to inhibitors' effectiveness in modulating lipid profiles in three-dimensional (3D) growth and their relationship to therapeutic activity. Inhibitors against PI3K, AKT, and mTOR significantly inhibited MDA-MB-468 and PC3 cell growth in two-dimensional (2D) and 3D spheroid growth, while moderately altering lipid content. Conversely, metabolism inhibitors against FASN and DGAT altered lipid content most effectively, while only moderately inhibiting growth compared with kinase inhibitors. The FASN and ACC inhibitors' effectiveness in MDA-MB-468, versus PC3, suggested the former depended more on synthesis, whereas the latter may salvage lipids. Although baseline lipid profiles did not predict growth effects, lipid changes on therapy matched the growth effects of FASN and DGAT inhibitors. Several phospholipids, including phosphatidylcholine, were also upregulated following treatment, possibly via the Kennedy pathway. As this promotes tumor growth, combination studies should include drugs targeting it. Two-dimensional drug screening may miss important metabolism inhibitors or underestimate their potency. Clinical studies should consider serial measurements of tumor lipids to prove target modulation. Pretherapy tumor classification by de novo lipid synthesis versus uptake may help demonstrate efficacy.

Acetylcholine signaling system in progression of lung cancers

The neurotransmitter acetylcholine (ACh) acts as an autocrine growth factor for human lung cancer. Several lines of evidence show that lung cancer cells express all of the proteins required for the uptake of choline (choline transporter 1, choline transporter-like proteins) synthesis of ACh (choline acetyltransferase, carnitine acetyltransferase), transport of ACh (vesicular acetylcholine transport, OCTs, OCTNs) and degradation of ACh (acetylcholinesterase, butyrylcholinesterase). The released ACh binds back to nicotinic (nAChRs) and muscarinic receptors on lung cancer cells to accelerate their proliferation, migration and invasion. Out of all components of the cholinergic pathway, the nAChR-signaling has been studied the most intensely. The reason for this trend is due to genome-wide data studies showing that nicotinic receptor subtypes are involved in lung cancer risk, the relationship between cigarette smoke and lung cancer risk as well as the rising popularity of electronic cigarettes considered by many as a "safe" alternative to smoking. There are a small number of articles which review the contribution of the other cholinergic proteins in the pathophysiology of lung cancer. The primary objective of this review article is to discuss the function of the acetylcholine-signaling proteins in the progression of lung cancer. The investigation of the role of cholinergic network in lung cancer will pave the way to novel molecular targets and drugs in this lethal malignancy.

Comparison of [18F]Fluorocholine and [18F]Fluordesoxyglucose for assessment of progression, lung metastasis detection and therapy response in murine 4T1 breast tumor model

The [18F]Fluorocholine ([18F]FCH) tracer for PET imaging has been proven to be effective for several malignances. However, there are only a few studies related to its breast tumor applicability and they are still limited. The aim of this study was investigate the efficacy of [18F]FCH/PET compared to [18F]FDG/PET in a murine 4T1 mammary carcinoma model treated and nontreated. [18F]FCH/PET showed its applicability for primary tumor and lung metastasis detection and their use for response monitoring of breast cancer therapeutics at earlier stages.

Synthesis and evaluation of an N-[18F]fluorodeoxyglycosyl amino acid for PET imaging of tumor metabolism

INTRODUCTION

The limitations of [¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG), including producing false-positive or -negative results, low image contrast in brain tumor diagnosis and poor differentiation of tumor and inflammatory, necessitate the development of new radiopharmaceuticals. In the present study, a novel [¹⁸F]fluoroglycoconjugate tracer, [¹⁸F]FDGly-NH-Phe, for tumor metabolism imaging was prepared and evaluated.

METHODS

[¹⁸F]FDGly-NH-Phe was prepared by condensing [¹⁸F]FDG with L-4-aminophenylalanine in an acidic condition, and purified with semi-preparative-high performance liquid chromatography (HPLC). The in vitro stability study was conducted in phosphate-buffered saline (PBS, pH 4.0-9.18) at room temperature (RT) and in fetal bovine serum (FBS) at 37 °C. The preliminary cellular uptake studies were performed using Hep-2 cell. The bio-distribution studies, PET/CT imaging and metabolism studies were performed and compared with [¹⁸F]FDG on ICR or BALB/c nude model mice.

RESULTS

[¹⁸F]FDGly-NH-Phe was derived from a direct condensation of [¹⁸F]FDG with L-4-aminophenylalanine with high stability in FBS and PBS (pH of 6.5-9.18). In vitro cell experiments showed that [¹⁸F]FDGly-NH-Phe uptake in Hep-2 cells was primarily transported through amino acid transporters including Na⁺-dependent A system, ASC system, and system B^0,+ system. The bio-distribution of [¹⁸F]FDGly-NH-Phe in normal ICR mice showed faster blood radioactivity clearance, and lower uptake in brain and heart than [¹⁸F]FDG. The performance of PET/CT imaging for [¹⁸F]FDGly-NH-Phe in the mice model manifested excellent tumor visualization, high tumor-to-background ratios, and low accumulation in inflammatory lesions. Metabolism studies for [¹⁸F]FDGly-NH-Phe indicated high in vivo stability in plasma and urine and decomposition into [¹⁸F]FDG in the tumor microenvironment.

CONCLUSION

The results demonstrated that [¹⁸F]FDGly-NH-Phe as a novel amino acid PET tracer showed the capability to differentiate tumor from inflammation, and the potentials for future clinical applications.

Radiosynthesis and validation of (±)-[18F]-3-fluoro-2-hydroxypropionate ([18F]-FLac) as a PET tracer of lactate to monitor MCT1-dependent lactate uptake in tumors

Cancers develop metabolic strategies to cope with their microenvironment often characterized by hypoxia, limited nutrient bioavailability and exposure to anticancer treatments. Among these strategies, the metabolic symbiosis based on the exchange of lactate between hypoxic/glycolytic cancer cells that convert glucose to lactate and oxidative cancer cells that preferentially use lactate as an oxidative fuel optimizes the bioavailability of glucose to hypoxic cancer cells. This metabolic cooperation has been described in various human cancers and can provide resistance to anti-angiogenic therapies. It depends on the expression and activity of monocarboxylate transporters (MCTs) at the cell membrane. MCT4 is the main facilitator of lactate export by glycolytic cancer cells, and MCT1 is adapted for lactate uptake by oxidative cancer cells. While MCT1 inhibitor AZD3965 is currently tested in phase I clinical trials and other inhibitors of lactate metabolism have been developed for anticancer therapy, predicting and monitoring a response to the inhibition of lactate uptake is still an unmet clinical need. Here, we report the synthesis, evaluation and in vivo validation of (±)-[18F]-3-fluoro-2-hydroxypropionate ([18F]-FLac) as a tracer of lactate for positron emission tomography. [18F]-FLac offers the possibility to monitor MCT1-dependent lactate uptake and inhibition in tumors in vivo.

PET Scan Misses Cutaneous Melanoma Metastasis with Significant Tumour Size and Tumour Thickness

BACKGROUND

Although PET-scan is an advanced, innovative and widely used method for monitoring patients with different types of cancer diseases, it is important to note that its application in patients with cutaneous melanoma is limited and should be reconsidered.

CASE REPORT

To affirm this new statement, we are presenting a case from our clinical practice of a patient with melanoma of the interdigital space (with resected in sano primary melanoma and performed complete lymphadenectomy) that showed locoregional and systemic progression in two months post operation. The PET scan performed within the second hospitalization (and before the second operation) did not detect the presence of any cutaneous metastases, which were clinically and histologically verified after the second operative procedure.

CONCLUSIONS

This data suggests that shortly more reliable and sensitive imaging methods for monitoring patients with cutaneous melanoma should be found. Having in mind that our patient has been operated twice in the area of the primary lesion (as the surgical wound underwent secondary healing), theoretically, the abundant cicatrization could have led to reduced glucose uptake in the surrounded cancerous tissue. Monitoring of a larger number of patients with locoregional metastases and surgical interventions in different locations would shed light on the observations shared by us.

Rethinking cancer: current challenges and opportunities in cancer research

Cancer therapeutics currently have the lowest clinical trial success rate of all major diseases. Partly as a result of the paucity of successful anti-cancer drugs, cancer will soon be the leading cause of mortality in developed countries. As a disease embedded in the fundamentals of our biology, cancer presents difficult challenges that would benefit from uniting experts from a broad cross-section of related and unrelated fields. Combining extant approaches with novel ones could help in tackling this challenging health problem, enabling the development of therapeutics to stop disease progression and prolong patient lives. This goal provided the inspiration for a recent workshop titled ‘Rethinking Cancer’, which brought together a group of cancer scientists who work in the academic and pharmaceutical sectors of Europe, America and Asia. In this Editorial, we discuss the main themes emerging from the workshop, with the aim of providing a snapshot of key challenges faced by the cancer research community today. We also outline potential strategies for addressing some of these challenges, from understanding the basic evolution of cancer and improving its early detection to streamlining the thorny process of moving promising drug targets into clinical trials.

Summary: Pablo Meyer and Ross Cagan discuss the main themes emerging from a recent workshop ‘Rethinking Cancer’, highlighting the key challenges faced by the research community and outlining potential strategies to promote translation of basic findings.

Therapeutic potential of the metabolic modulator Metformin on osteosarcoma cancer stem-like cells

PURPOSE

Osteosarcoma is the most common primary bone tumour appearing in children and adolescents. Recent studies demonstrate that osteosarcoma possesses a stem-like cell subset, so-called cancer stem-like cells, refractory to conventional chemotherapeutics and pointed out as responsible for relapses frequently observed in osteosarcoma patients. Here, we explored the therapeutic potential of Metformin on osteosarcoma stem-like cells, alone and as a chemosensitizer of doxorubicin.

METHODS

Stem-like cells were isolated from human osteosarcoma cell lines, MNNG/HOS and MG-63, using the sphere-forming assay. Metformin cytotoxicity alone and combined with doxorubicin were evaluated using MTT/BrdU assays. Protein levels of AMPK and AKT were evaluated by Western Blot. Cellular metabolic status was assessed based on [¹⁸F]-FDG uptake and lactate production measurements. Sphere-forming efficiency and expression of pluripotency transcription factors analysed by qRT-PCR were tested as readout of Metformin effects on stemness features.

RESULTS

Metformin induced a concentration-dependent decrease in the metabolic activity and proliferation of sphere-forming cells and improved doxorubicin-induced cytotoxicity. This drug also down-regulated the expression of master regulators of pluripotency (OCT4, SOX2, NANOG), and decreased spheres' self-renewal ability. Metformin effects on mitochondria led to the activation and phosphorylation of the energetic sensor AMPK along with an upregulation of the pro-survival AKT pathway in both cell populations. Furthermore, Metformin-induced mitochondrial stress increased [¹⁸F]-FDG uptake and lactate production in parental cells but not in the quiescent stem-like cells, suggesting the inability of the latter to cope with the energy crisis induced by metformin.

CONCLUSIONS

This preclinical study suggests that Metformin may be a potentially useful therapeutic agent and chemosensitizer of osteosarcoma stem-like cells to doxorubicin.

Is FCH PET able to identify foci of infection superiorly to FDG PET?

We report a case of a brain abscess identified on fluorine-18 choline (FCH) positron emission tomography (PET) scan, which was not identified on fluorodeoxyglucose (FDG) PET scan. To our knowledge, there are no previous case reports of incidental brain abscess identified by FCH PET imaging. A 51-year-old man, with liver cirrhosis complicated by hepatocellular carcinoma (HCC) was enrolled in a research trial comparing HCC detection in FCH PET versus FDG PET. During the course of the trial, he underwent radiofrequency ablation (RFA) for HCC. A repeat FCH PET scan post-RFA incidentally revealed a 2.5 cm lesion with avid uptake in the left occipital area of the brain. The patient was asymptomatic. MRI suggested this was an abscess. A craniotomy and drainage was performed, with culture of Streptococcus intermedius (Smilleri group) from the thick-walled collection, a causative organism for previous episode of pneumonia. He successfully completed a 6 week course of antibiotics.

Clinical Applications of Small-molecule PET Radiotracers: Current Progress and Future Outlook

Radiotracers, or radiopharmaceuticals, are bioactive molecules tagged with a radionuclide used for diagnostic imaging or radiotherapy and, when a positron-emitting radionuclide is chosen, the radiotracers are used for PET imaging. The development of novel PET radiotracers in many ways parallels the development of new pharmaceuticals, and small molecules dominate research and development pipelines in both disciplines. The 4 decades since the introduction of [¹⁸F]FDG have seen the development of many small molecule PET radiotracers. Ten have been approved by the US Food and Drug Administration as of 2016, whereas hundreds more are being evaluated clinically. These radiotracers are being used in personalized medicine and to support drug discovery programs where they are greatly improving our understanding of and ability to treat diseases across many areas of medicine including neuroscience, cardiovascular medicine, and oncology.

Small Molecule PET Tracers for Transporter Imaging

As the field of PET has expanded and an ever-increasing number and variety of compounds have been radiolabeled as potential in vivo tracers of biochemistry, transporters have become important primary targets or facilitators of radiotracer uptake and distribution. A transporter can be the primary target through the development of a specific high-affinity radioligand: examples are the multiple high-affinity radioligands for the neuronal membrane neurotransmitter or vesicular transporters, used to image nerve terminals in the brain. The goal of a radiotracer might be to study the function of a transporter through the use of a radiolabeled substrate, such as the application of 3-O-[¹¹C]methyl]glucose to measure rates of glucose transport through the blood-brain barrier. In many cases, transporters are required for radiotracer distributions, but the targeted biochemistries might be unrelated: an example is the use of 2-deoxy-2-[¹⁸F]FDG for imaging glucose metabolism, where initial passage of the radiotracer through cell membranes requires the action of specific glucose transporters. Finally, there are transporters such as p-glycoprotein that function to extrude small molecules from tissues, and can effectively work against successful uptake of radiotracers. The diversity of structures and functions of transporters, their importance in human health and disease, and their role in therapeutic drug disposition suggest that in vivo imaging of transporter location and function will continue to be a point of emphasis in PET radiopharmaceutical development. In this review, the variety of transporters and their importance for in vivo PET radiotracer development and application are discussed. Transporters have thus joined the other major protein targets such as G-protein coupled receptors, ligand-gated ion channels, enzymes, and aggregated proteins as of high interest for understanding human health and disease.

Role of Imaging in the Era of Precision Medicine

Precision medicine is an emerging approach for treating medical disorders, which takes into account individual variability in genetic and environmental factors. Preventive or therapeutic interventions can then be directed to those who will benefit most from targeted interventions, thereby maximizing benefits and minimizing costs and complications. Precision medicine is gaining increasing recognition by clinicians, healthcare systems, pharmaceutical companies, patients, and the government. Imaging plays a critical role in precision medicine including screening, early diagnosis, guiding treatment, evaluating response to therapy, and assessing likelihood of disease recurrence. The Association of University Radiologists Radiology Research Alliance Precision Imaging Task Force convened to explore the current and future role of imaging in the era of precision medicine and summarized its finding in this article. We review the increasingly important role of imaging in various oncological and non-oncological disorders. We also highlight the challenges for radiology in the era of precision medicine.

Characterization of the Tumor Microenvironment and Tumor-Stroma Interaction by Non-invasive Preclinical Imaging

Tumors are often characterized by hypoxia, vascular abnormalities, low extracellular pH, increased interstitial fluid pressure, altered choline-phospholipid metabolism, and aerobic glycolysis (Warburg effect). The impact of these tumor characteristics has been investigated extensively in the context of tumor development, progression, and treatment response, resulting in a number of non-invasive imaging biomarkers. More recent evidence suggests that cancer cells undergo metabolic reprograming, beyond aerobic glycolysis, in the course of tumor development and progression. The resulting altered metabolic content in tumors has the ability to affect cell signaling and block cellular differentiation. Additional emerging evidence reveals that the interaction between tumor and stroma cells can alter tumor metabolism (leading to metabolic reprograming) as well as tumor growth and vascular features. This review will summarize previous and current preclinical, non-invasive, multimodal imaging efforts to characterize the tumor microenvironment, including its stromal components and understand tumor-stroma interaction in cancer development, progression, and treatment response.

Targeting amino acid metabolism for cancer therapy

To support sustained biomass accumulation, tumor cells undergo metabolic reprogramming. Nutrient transporters and metabolic enzymes are regulated by the same oncogenic signals that drive cell-cycle progression. Some of the earliest cancer therapies used antimetabolites to disrupt tumor metabolism, and there is now renewed interest in developing drugs that target metabolic dependencies. Many cancers exhibit increased demand for specific amino acids, and become dependent on either an exogenous supply or upregulated de novo synthesis. Strategies to exploit such 'metabolic addictions' include depleting amino acids in blood serum, blocking uptake by transporters and inhibiting biosynthetic or catabolic enzymes. Recent findings highlight the importance of using appropriate model systems and identifying target patient groups as potential therapies advance into the clinic.

Bone imaging in prostate cancer: the evolving roles of nuclear medicine and radiology

The bone scan continues to be recommended for both the staging and therapy response assessment of skeletal metastases from prostate cancer. However, it is widely recognised that bone scans have limited sensitivity for disease detection and is both insensitive and non-specific for determining treatment response, at an early enough time point to be clinically useful. We, therefore, review the evolving roles of nuclear medicine and radiology for this application. We have reviewed the published literature reporting recent developments in imaging bone metastases in prostate cancer, and provide a balanced synopsis of the state of the art. The development of single-photon emission computed tomography combined with computed tomography has improved detection sensitivity and specificity but has not yet been shown to lead to improvements in monitoring therapy. A number of bone-specific and tumour-specific tracers for positron emission tomography/computed tomography (PET/CT) are now available for advanced prostate cancer that show promise in both clinical settings. At the same time, the development of whole-body magnetic resonance imaging (WB-MRI) that incorporates diffusion-weighted imaging also offers significant improvements for detection and therapy response assessment. There are emerging data showing comparative SPECT/CT, PET/CT, and WB-MRI test performance for disease detection, but no compelling data on the usefulness of these technologies in response assessment have yet emerged.

In vivo Magnetic Resonance Metabolic and Morphofunctional Fingerprints in Experimental Models of Human Ovarian Cancer

Epithelial ovarian cancer (EOC) is the gynecological malignancy with the highest death rate, characterized by frequent relapse and onset of drug resistance. Disease diagnosis and therapeutic follow-up could benefit from application of molecular imaging approaches, such as magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS), able to monitor metabolic and functional alterations and investigate the underlying molecular mechanisms. Here, we overview the quantitative alterations that occur during either orthotopic or subcutaneous growth of preclinical EOC models. A common feature of (1)H MR spectra is the presence of a prominent peak due to total choline-containing metabolites (tCho), together with other metabolic alterations and MRI-detected morphofunctional patterns specific for different phenotypes. The tCho signal, already present at early stages of tumor growth, and changes of diffusion-weighted MRI parameters could serve as markers of malignancy and/or tumor response to therapy. The identification by MRS and MRI of biochemical and physiopathological fingerprints of EOC disease in preclinical models can represent a basis for further developments of non-invasive MR approaches in the clinical setting.

Choline Metabolism Alteration: A Focus on Ovarian Cancer

Compared with normal differentiated cells, cancer cells require a metabolic reprograming to support their high proliferation rates and survival. Aberrant choline metabolism is a fairly new metabolic hallmark reflecting the complex reciprocal interactions between oncogenic signaling and cellular metabolism. Alterations of the involved metabolic network may be sustained by changes in activity of several choline transporters as well as of enzymes such as choline kinase-alpha (ChoK-α) and phosphatidylcholine-specific phospholipases C and D. Of note, the net outcome of these enzymatic alterations is an increase of phosphocholine and total choline-containing compounds, a "cholinic phenotype" that can be monitored in cancer by magnetic resonance spectroscopy. This review will highlight the molecular basis for targeting this pathway in epithelial ovarian cancer (EOC), a highly heterogeneous and lethal malignancy characterized by late diagnosis, frequent relapse, and development of chemoresistance. Modulation of ChoK-α expression impairs only EOC but not normal ovarian cells, thus supporting the hypothesis that "cholinic phenotype" is a peculiar feature of transformed cells and indicating ChoK-α targeting as a novel approach to improve efficacy of standard EOC chemotherapeutic treatments.