Non-Invasive Glutamine PET Reflects Pharmacological Inhibition of BRAFV600E In Vivo

Reproducibility and repeatability of 18F-(2S, 4R)-4-fluoroglutamine PET imaging in preclinical oncology models

INTRODUCTION

Measurement of repeatability and reproducibility (R&R) is necessary to realize the full potential of positron emission tomography (PET). Several studies have evaluated the reproducibility of PET using 18F-FDG, the most common PET tracer used in oncology, but similar studies using other PET tracers are scarce. Even fewer assess agreement and R&R with statistical methods designed explicitly for the task. 18F-(2S, 4R)-4-fluoro-glutamine (18F-Gln) is a PET tracer designed for imaging glutamine uptake and metabolism. This study illustrates high reproducibility and repeatability with 18F-Gln for in vivo research.

METHODS

Twenty mice bearing colorectal cancer cell line xenografts were injected with ~9 MBq of 18F-Gln and imaged in an Inveon microPET. Three individuals analyzed the tumor uptake of 18F-Gln using the same set of images, the same image analysis software, and the same analysis method. Scans were randomly re-ordered for a second repeatability measurement 6 months later. Statistical analyses were performed using the methods of Bland and Altman (B&A), Gauge Reproducibility and Repeatability (Gauge R&R), and Lin's Concordance Correlation Coefficient. A comprehensive equivalency test, designed to reject a null hypothesis of non-equivalence, was also conducted.

RESULTS

In a two-way random effects Gauge R&R model, variance among mice and their measurement variance were 0.5717 and 0.024. Reproducibility and repeatability accounted for 31% and 69% of the total measurement error, respectively. B&A repeatability coefficients for analysts 1, 2, and 3 were 0.16, 0.35, and 0.49. One-half B&A agreement limits between analysts 1 and 2, 1 and 3, and 2 and 3 were 0.27, 0.47, and 0.47, respectively. The mean square deviation and total deviation index were lowest for analysts 1 and 2, while coverage probabilities and coefficients of the individual agreement were highest. Finally, the definitive agreement inference hypothesis test for equivalency demonstrated that all three confidence intervals for the average difference of means from repeated measures lie within our a priori limits of equivalence (i.e. ± 0.5%ID/g).

CONCLUSIONS

Our data indicate high individual analyst and laboratory-level reproducibility and repeatability. The assessment of R&R using the appropriate methods is critical and should be adopted by the broader imaging community.

Preclinical Evaluation of a Radiolabeled Pan-RAF Inhibitor for RAF-Specific PET/CT Imaging

Abnormalities in the RAS-RAF signaling pathway occur in many solid tumors, leading to aberrant tumor proliferation, invasion, and metastasis. Due to the elusive pharmacology of RAS, RAF inhibitors have become the main targeted therapeutic drugs. Naporafenib (LXH-254) is a high-affinity pan-RAF inhibitor with FDA Fast Track Qualification. We sought to develop an 18F-labeled molecular probe from LXH-254 for PET imaging of tumors overexpressing RAF to noninvasively screen patients for susceptibility to targeted RAF therapy. To reduce the lipid solubility, LXH-254 was designed with triethylene glycol di(p-toluenesulfonate) (TsO-PEG3-OTs) to obtain the precursor (LXH-254-OTs) and a nucleophilic substitution reaction with 18F to obtain the tracer ([18F]F-LXH-254). [18F]F-LXH-254 exhibited good molar activity (7.16 ± 0.81 GBq/μmol), radiochemical purity (>95%), and stability. Micro-PET imaging revealed distinct radioactivity accumulation of [18F]F-LXH-254 in tumors in the imaging groups, whereas in the blocked group, the tumor radioactivity level was consistent with the background tissue, illustrating the affinity and specificity of [18F]F-LXH-254 in targeting RAF. Overall, [18F]F-LXH-254 is a promising radiotracer for screening and diagnosing patients with RAF-related disease and monitoring their treatment. This is the first attempt at using an 18F-labeled RAF-specific radiotracer.

PET Imaging of Metabolism, Perfusion, and Hypoxia: FDG and Beyond

ABSTRACT

Imaging glucose metabolism with [18F]fluorodeoxyglucose positron emission tomography has transformed the diagnostic and treatment algorithms of numerous malignancies in clinical practice. The cancer phenotype, though, extends beyond dysregulation of this single pathway. Reprogramming of other pathways of metabolism, as well as altered perfusion and hypoxia, also typifies malignancy. These features provide other opportunities for imaging that have been developed and advanced into humans. In this review, we discuss imaging metabolism, perfusion, and hypoxia in cancer, focusing on the underlying biology to provide context. We conclude by highlighting the ability to image multiple facets of biology to better characterize cancer and guide targeted treatment.

Role of solute carrier transporters in regulating dendritic cell maturation and function

Dendritic cells (DCs) are specialized antigen-presenting cells that initiate and regulate innate and adaptive immune responses. Solute carrier (SLC) transporters mediate diverse physiological functions and maintain cellular metabolite homeostasis. Recent studies have highlighted the significance of SLCs in immune processes. Notably, upon activation, immune cells undergo rapid and robust metabolic reprogramming, largely dependent on SLCs to modulate diverse immunological responses. In this review, we explore the central roles of SLC proteins and their transported substrates in shaping DC functions. We provide a comprehensive overview of recent studies on amino acid transporters, metal ion transporters, and glucose transporters, emphasizing their essential contributions to DC homeostasis under varying pathological conditions. Finally, we propose potential strategies for targeting SLCs in DCs to bolster immunotherapy for a spectrum of human diseases.

Animal Models and Their Role in Imaging-Assisted Co-Clinical Trials

The availability of high-fidelity animal models for oncology research has grown enormously in recent years, enabling preclinical studies relevant to prevention, diagnosis, and treatment of cancer to be undertaken. This has led to increased opportunities to conduct co-clinical trials, which are studies on patients that are carried out parallel to or sequentially with animal models of cancer that mirror the biology of the patients' tumors. Patient-derived xenografts (PDX) and genetically engineered mouse models (GEMM) are considered to be the models that best represent human disease and have high translational value. Notably, one element of co-clinical trials that still needs significant optimization is quantitative imaging. The National Cancer Institute has organized a Co-Clinical Imaging Resource Program (CIRP) network to establish best practices for co-clinical imaging and to optimize translational quantitative imaging methodologies. This overview describes the ten co-clinical trials of investigators from eleven institutions who are currently supported by the CIRP initiative and are members of the Animal Models and Co-clinical Trials (AMCT) Working Group. Each team describes their corresponding clinical trial, type of cancer targeted, rationale for choice of animal models, therapy, and imaging modalities. The strengths and weaknesses of the co-clinical trial design and the challenges encountered are considered. The rich research resources generated by the members of the AMCT Working Group will benefit the broad research community and improve the quality and translational impact of imaging in co-clinical trials.

[18F]-(2S,4R)4-Fluoroglutamine PET Imaging of Glutamine Metabolism in Murine Models of Hepatocellular Carcinoma (HCC)

Purpose

Quantitative in vivo [¹⁸F]-(2S,4R)4-fluoroglutamine ([¹⁸F]4-FGln or more simply [¹⁸F]FGln) metabolic kinetic parameters are compared with activity levels of glutamine metabolism in different types of hepatocellular carcinoma (HCC).

Methods

For this study, we used two transgenic mouse models of HCC induced by protooncogenes, MYC, and MET. Biochemical data have shown that tumors induced by MYC have increased levels of glutamine metabolism compared to those induced by MET. One-hour dynamic [¹⁸F]FGln PET data were acquired and reconstructed for fasted MYC mice (n = 11 tumors from 7 animals), fasted MET mice (n = 8 tumors from 6 animals), fasted FVBN controls (n = 8 normal liver regions from 6 animals), nonfasted MYC mice (n = 16 tumors from 6 animals), and nonfasted FVBN controls (n = 8 normal liver regions from 3 animals). The influx rate constants (K₁) using the one-tissue compartment model were derived for each tumor with the left ventricular blood pool input function.

Results

Influx rate constants were significantly higher for MYC tumors (K₁ = 0.374 ± 0.133) than for MET tumors (K₁ = 0.141 ± 0.058) under fasting conditions (P = 0.0002). Rate constants were also significantly lower for MET tumors (K₁ = 0.141 ± 0.135) than normal livers (K₁ = 0.332 ± 0.179) under fasting conditions (P = 0.0123). Fasting conditions tested for MYC tumors and normal livers did not result in any significant difference with P values > 0.005.

Conclusion

Higher influx rate constants corresponded to elevated levels of glutamine metabolism as determined by biochemical assays. The data showed that there is a distinctive difference in glutamine metabolism between MYC and MET tumors. Our study has demonstrated the potential of [¹⁸F]FGln PET imaging as a tool to assess glutamine metabolism in HCC tumors in vivo with a caution that it may not be able to clearly distinguish HCC tumors from normal liver tissue.

First-in-Human PET Imaging and Estimated Radiation Dosimetry of l-[5-11C]-Glutamine in Patients with Metastatic Colorectal Cancer

Altered metabolism is a hallmark of cancer. In addition to glucose, glutamine is an important nutrient for cellular growth and proliferation. Noninvasive imaging via PET may help facilitate precision treatment of cancer through patient selection and monitoring of treatment response. l-[5-11C]-glutamine (11C-glutamine) is a PET tracer designed to study glutamine uptake and metabolism. The aim of this first-in-human study was to evaluate the radiologic safety and biodistribution of 11C-glutamine for oncologic PET imaging. Methods: Nine patients with confirmed metastatic colorectal cancer underwent PET/CT imaging. Patients received 337.97 ± 44.08 MBq of 11C-glutamine. Dynamic PET acquisitions that were centered over the abdomen or thorax were initiated simultaneously with intravenous tracer administration. After the dynamic acquisition, a whole-body PET/CT scan was acquired. Volume-of-interest analyses were performed to obtain estimates of organ-based absorbed doses of radiation. Results:11C-glutamine was well tolerated in all patients, with no observed safety concerns. The organs with the highest radiation exposure included the bladder, pancreas, and liver. The estimated effective dose was 4.46E-03 ± 7.67E-04 mSv/MBq. Accumulation of 11C-glutamine was elevated and visualized in lung, brain, bone, and liver metastases, suggesting utility for cancer imaging. Conclusion: PET using 11C-glutamine appears safe for human use and allows noninvasive visualization of metastatic colon cancer lesions in multiple organs. Further studies are needed to elucidate its potential for other cancers and for monitoring response to treatment.

Metabolic Phenotypes, Dependencies, and Adaptation in Lung Cancer

Lung cancer is a heterogeneous disease that is subdivided into histopathological subtypes with distinct behaviors. Each subtype is characterized by distinct features and molecular alterations that influence tumor metabolism. Alterations in tumor metabolism can be exploited by imaging modalities that use metabolite tracers for the detection and characterization of tumors. Microenvironmental factors, including nutrient and oxygen availability and the presence of stromal cells, are a critical influence on tumor metabolism. Recent technological advances facilitate the direct evaluation of metabolic alterations in patient tumors in this complex microenvironment. In addition, molecular alterations directly influence tumor cell metabolism and metabolic dependencies that influence response to therapy. Current therapeutic approaches to target tumor metabolism are currently being developed and translated into the clinic for patient therapy.

Correlation Between Prognostic Biomarker SLC1A5 and Immune Infiltrates in Various Types of Cancers Including Hepatocellular Carcinoma

Background

Solute carrier family 1 member 5 (SLC1A5) is a major glutamine transporter and plays a key role in tumor growth. The main objectives of this study were to visualize the prognostic landscape of SLC1A5 in multiple cancers and determine the relations between SLC1A5 expression and tumor immunity.

Methods

SLC1A5 expression and its effect on tumor prognosis were analyzed using multiple online tools Oncomine, Gene Expression Profiling Interactive Analysis, PrognoScan, and Kaplan-Meier plotter with their own datasets as well as the data from The Cancer Genome Atlas. The correlations between SLC1A5 and tumor immune infiltrates were determined via TIMER.

Results

SLC1A5 expression was significantly higher in several types of cancers, including hepatocellular carcinoma (HCC), compared with corresponding normal tissues. High SLC1A5 expression correlated with poor overall survival and with disease-free survival related to alcohol consumption. Moreover, SLC1A5 expression correlated positively with the numbers of tumor-infiltrating B cells, CD4⁺ T and CD8⁺ T cells, macrophages, neutrophils, and dendritic cells in HCC and in lower-grade glioma (LGG). Also, SLC1A5 expression showed strong correlations with diverse immune marker sets in HCC and LGG, indicating its role in regulating tumor immunity.

Conclusions

SLC1A5 represents a useful prognostic biomarker in multiple cancers, and its expression correlates highly with tumor immune-cell infiltration, especially in HCC and LGG.

Inhibition of the ʟ-glutamine transporter ASCT2 sensitizes plasma cell myeloma cells to proteasome inhibitors

Proteasome inhibitors (PIs), used in the treatment of plasma cell myeloma (PCM), interfere with the degradation of misfolded proteins leading to activation of unfolded protein response (UPR) and cell death. However, despite initial strong antimyeloma effects, PCM cells eventually develop acquired resistance to PIs. The pleiotropic role of ʟ-glutamine (Gln) in cellular functions makes inhibition of Gln metabolism a potentially good candidate for combination therapy. Here, we show that PCM cells, both sensitive and resistant to PIs, express membrane Gln transporter (ASCT2), require extracellular Gln for survival, and are sensitive to ASCT2 inhibitors (ASCT2i). ASCT2i synergistically potentiate the cytotoxic activity of PIs by inducing apoptosis and modulating autophagy. Combination of ASCT2 inhibitor V9302 and proteasome inhibitor carfilzomib upregulates the intracellular levels of ROS and oxidative stress markers and triggers catastrophic UPR as shown by upregulated spliced Xbp1 mRNA, ATF3 and CHOP levels. Moreover, analysis of RNA sequencing revealed that the PI in combination with ASCT2i reduced the levels of Gln metabolism regulators such as MYC and NRAS. Analysis of PCM patients' data revealed that upregulated ASCT2 and other Gln metabolism regulators are associated with advanced disease stage and with PIs resistance. Altogether, we identified a potent therapeutic approach that may prevent acquired resistance to PIs and may contribute to the improvement of treatment of patients suffering from PCM.

ASCT2 and LAT1 Contribution to the Hallmarks of Cancer: From a Molecular Perspective to Clinical Translation

The role of the amino acid transporters ASCT2 and LAT1 in cancer has been explored throughout the years. In this review, we report their impact on the hallmarks of cancer, as well as their clinical significance. Overall, both proteins have been associated with cell death resistance through dysregulation of caspases and sustainment of proliferative signaling through mTOR activation. Furthermore, ASCT2 appears to play an important role in cellular energetics regulation, whereas LAT1 expression is associated with angiogenesis and invasion and metastasis activation. The molecular impact of these proteins on the hallmarks of cancer translates into various clinical applications and both transporters have been identified as prognostic factors in many types of cancer. Concerning their role as therapeutic targets, efforts have been undertaken to synthesize competitive or irreversible ASCT2 and LAT1 inhibitors. However, JHP203, a selective inhibitor of the latter, is, to the best of our knowledge, the only compound included in a Phase 1 clinical trial. In conclusion, considering the usefulness of ASCT2 and LAT1 in a variety of cancer-related pathways and cancer therapy/diagnosis, the development and testing of novel inhibitors for these transporters that could be evaluated in clinical trials represents a promising approach to cancer prognosis improvement.

A glutamine 'tug-of-war': targets to manipulate glutamine metabolism for cancer immunotherapy

Within the tumour microenvironment (TME), there is a cellular 'tug-of-war' for glutamine, the most abundant amino acid in the body. This competition is most evident when considering the balance between a successful anti-tumour immune response and the uncontrolled growth of tumour cells that are addicted to glutamine. The differential effects of manipulating glutamine abundance in individual cell types is an area of intense research and debate. Here, we discuss some of the current strategies in development altering local glutamine availability focusing on inhibition of enzymes involved in the utilisation of glutamine and its uptake by cells in the TME. Further studies are urgently needed to complete our understanding of glutamine metabolism, to provide critical insights into the pathways that represent promising targets and for the development of novel therapeutic strategies for the treatment of advanced or drug resistant cancers.

Metabolic Evaluation of MYCN-Amplified Neuroblastoma by 4-[18F]FGln PET Imaging

PURPOSE

This study aims to explore whether 4-(2S,4R)-[¹⁸F]fluoroglutamine (4-[¹⁸F]FGln) positron emission tomography (PET) imaging is helpful in identifying and monitoring MYCN-amplified neuroblastoma by enhanced glutamine metabolism.

PROCEDURES

Cell uptake studies and dynamic small-animal PET studies of 4-[¹⁸F]FGln and 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) were conducted in human MYCN-amplified (IMR-32 and SK-N-BE (2) cells) and non-MYCN-amplified (SH-SY5Y cell) neuroblastoma cells and animal models. Subsequently, short hairpin RNA (shRNA) knockdown of alanine-serine-cysteine transporter 2 (ASCT2/SLC1A5) in IMR-32 cells and xenografts were investigated in vitro and in vivo. Western blot (WB), real-time polymerase chain reaction (RT-PCR), and immunofluorescence (IF) assays were used to measure the prevalence of ASCT2, Ki-67, and c-Caspase 3, respectively.

RESULTS

IMR-32 and SK-N-BE (2) cells showed high glutamine uptake in vitro (31.6 ± 1.7 and 21.6 ± 6.6 %ID/100 μg). In the in vivo study, 4-[¹⁸F]FGln was localized in IMR-32, SK-N-BE (2), and SH-SY5Y tumors with a high uptake (6.6 ± 0.3, 5.6 ± 0.2, and 3.7 ± 0.1 %ID/g). The maximum uptake (tumor-to-muscle, T/M) of the IMR-32 and SK-N-BE (2) tumors (3.71 and 2.63) was significantly higher than that of SH-SY5Y (1.54) tumors (P < 0.001, P < 0.001). The maximum uptake of 4-[¹⁸F]FGln in IMR-32 and SK-N-BE (2) tumors was 2.3-fold and 2.1-fold higher than that of [¹⁸F]FDG, respectively. Furthermore, in the in vitro and in vivo studies, the maximum uptake of 4-[¹⁸F]FGln in shASCT2-IMR-32 cells and tumors was 2.1-fold and 2.5-fold lower than that of the shControl-IMR-32. No significant difference in [¹⁸F]FDG uptake was found between shASCT2-IMR-32 and shControl-IMR-32 cells and tumors.

CONCLUSION

4-[¹⁸F]FGln PET can provide a valuable clinical tool in the assessment of metabolic glutamine uptake in MYCN-amplified neuroblastoma. ASCT2-targeted therapy may provide a supplementary method in MYCN-amplified neuroblastoma treatment.

Natural Products and Derivatives Targeting at Cancer Energy Metabolism: A Potential Treatment Strategy

In the 1920s, Dr Otto Warburg first suggested the significant difference in energy metabolism between malignant cancer cells and adjacent normal cells. Tumor cells mainly adopt the glycolysis as energy source to maintain tumor cell growth and biosynthesis under aerobic conditions. Investigation on energy metabolism pathway in cancer cells has aroused the interest of cancer researchers all around the world. In recent years, plentiful studies suggest that targeting the peculiar cancer energy metabolic pathways, including glycolysis, mitochondrial respiration, amino acid metabolism, and fatty acid oxidation may be an effective strategy to starve cancer cells by blocking essential nutrients. Natural products (NPs) are considered as the "treasure trove of small molecules drugs" and have played an extremely remarkable role in the discovery and development of anticancer drugs. And numerous NPs have been reported to act on cancer energy metabolism targets. Herein, a comprehensive overview about cancer energy metabolism targets and their natural-occurring inhibitors is prepared.

An anti-ASCT2 monoclonal antibody suppresses gastric cancer growth by inducing oxidative stress and antibody dependent cellular toxicity in preclinical models

Glutamine is a major nutrient for cancer cells during rapid proliferation. Alanine-serine-cysteine (ASC) transporter 2 (ASCT2; SLC1A5) mediates glutamine uptake in a variety of cancer cells. We previously reported that KM8094, a novel anti-ASCT2 humanized monoclonal antibody, possesses anti-tumor efficacy in gastric cancer patient-derived xenografts. The aim of this study was to investigate the molecular mechanism underlying the effect of KM8094 and to further substantiate the preclinical feasibility of using KM8094 as a potential therapeutic agent against gastric cancer. First, ASCT2 was found to be highly expressed in cancer tissues derived from gastric cancer patients by an immunohistochemical analysis. Next, we performed in vitro studies using multiple gastric cancer cell lines and observed that several gastric cancer cells expressing ASCT2 showed glutamine-dependent cell growth, which was repressed by KM8094. We found that KM8094 inhibited the glutamine uptake, leading to the reduction of glutathione (GSH) level and the elevation of oxidative stress. KM8094 suppressed the cell cycle progression and increased the apoptosis. Furthermore, KM8094 exerted antibody dependent cellular cytotoxicity (ADCC) against human gastric cancer cells in vitro. Finally, in vivo studies revealed that KM8094 suppressed tumor growth in several gastric cancer xenografts. This effect was enhanced by docetaxel, one of the agents commonly used in gastric cancer therapy. Thus, our findings suggest that KM8094 is a potential new therapeutic agent for gastric cancer expressing ASCT2, which blocks the cellular glutamine metabolism and possesses ADCC activity.

Pharmacological blockade of ASCT2-dependent glutamine transport leads to antitumor efficacy in preclinical models

The unique metabolic demands of cancer cells underscore potentially fruitful opportunities for drug discovery in the era of precision medicine. However, therapeutic targeting of cancer metabolism has led to surprisingly few new drugs to date. The neutral amino acid glutamine serves as a key intermediate in numerous metabolic processes leveraged by cancer cells, including biosynthesis, cell signaling, and oxidative protection. Herein we report the preclinical development of V-9302, a competitive small molecule antagonist of transmembrane glutamine flux that selectively and potently targets the amino acid transporter ASCT2. Pharmacological blockade of ASCT2 with V-9302 resulted in attenuated cancer cell growth and proliferation, increased cell death, and increased oxidative stress, which collectively contributed to antitumor responses in vitro and in vivo. This is the first study, to our knowledge, to demonstrate the utility of a pharmacological inhibitor of glutamine transport in oncology, representing a new class of targeted therapy and laying a framework for paradigm-shifting therapies targeting cancer cell metabolism.

Imaging Cancer Metabolism

It is widely accepted that altered metabolism contributes to cancer growth and has been described as a hallmark of cancer. Our view and understanding of cancer metabolism has expanded at a rapid pace, however, there remains a need to study metabolic dependencies of human cancer in vivo. Recent studies have sought to utilize multi-modality imaging (MMI) techniques in order to build a more detailed and comprehensive understanding of cancer metabolism. MMI combines several in vivo techniques that can provide complementary information related to cancer metabolism. We describe several non-invasive imaging techniques that provide both anatomical and functional information related to tumor metabolism. These imaging modalities include: positron emission tomography (PET), computed tomography (CT), magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS) that uses hyperpolarized probes and optical imaging utilizing bioluminescence and quantification of light emitted. We describe how these imaging modalities can be combined with mass spectrometry and quantitative immunochemistry to obtain more complete picture of cancer metabolism. In vivo studies of tumor metabolism are emerging in the field and represent an important component to our understanding of how metabolism shapes and defines cancer initiation, progression and response to treatment. In this review we describe in vivo based studies of cancer metabolism that have taken advantage of MMI in both pre-clinical and clinical studies. MMI promises to advance our understanding of cancer metabolism in both basic research and clinical settings with the ultimate goal of improving detection, diagnosis and treatment of cancer patients.

Approaches and techniques to characterize cancer metabolism in vitro and in vivo

Cancer metabolism is wired to sustain uncontrollable cell proliferation and ensure cell survival. Given the multitude of available approaches to study metabolic alterations it remains a challenging task to select the most appropriate method. In this mini-review we describe how cancer metabolism can be studied in vitro and in vivo providing an overview of available approaches and techniques, discussing their advantages and drawbacks and guiding through selection of an appropriate method to address particular research needs. This work is particularly intended to those cancer researchers who are new in the field but want to investigate metabolic alterations in their cancer model systems.

Glutamine Metabolism in Cancer: Understanding the Heterogeneity

Reliance on glutamine has long been considered a hallmark of cancer cell metabolism. However, some recent studies have challenged this notion in vivo, prompting a need for further clarifications on the role of glutamine metabolism in cancer. We find that there is ample evidence of an essential role for glutamine in tumors and that a variety of factors, including tissue type, the underlying cancer genetics, the tumor microenvironment and other variables such as diet and host physiology collectively influence the role of glutamine in cancer. Thus the requirements for glutamine in cancer are overall highly heterogeneous. In this review, we discuss the implications both for basic science and for targeting glutamine metabolism in cancer therapy.