Epithelial and mesenchymal tumor compartments exhibit in vivo complementary patterns of vascular perfusion and glucose metabolism

Iron commensalism of mesenchymal glioblastoma promotes ferroptosis susceptibility upon dopamine treatment

The heterogeneity of glioblastoma multiforme (GBM) leads to poor patient prognosis. Here, we aim to investigate the mechanism through which GBM heterogeneity is coordinated to promote tumor progression. We find that proneural (PN)-GBM stem cells (GSCs) secreted dopamine (DA) and transferrin (TF), inducing the proliferation of mesenchymal (MES)-GSCs and enhancing their susceptibility toward ferroptosis. PN-GSC-derived TF stimulates MES-GSC proliferation in an iron-dependent manner. DA acts in an autocrine on PN-GSC growth in a DA receptor D1-dependent manner, while in a paracrine it induces TF receptor 1 expression in MES-GSCs to assist iron uptake and thus enhance ferroptotic vulnerability. Analysis of public datasets reveals worse prognosis of patients with heterogeneous GBM with high iron uptake than those with other GBM subtypes. Collectively, the findings here provide evidence of commensalism symbiosis that causes MES-GSCs to become iron-addicted, which in turn provides a rationale for targeting ferroptosis to treat resistant MES GBM.

Glioblastoma stem-cell derived mesenchymal cells become reliant on iron but vulnerable to ferroptosis and within patients of heterogeneous glioblastoma multiforme prognosis for those with high iron uptake is poorer than other subtypes.

Cancer heterogeneity is not compatible with one unique cancer cell metabolic map

The Warburg effect and its accompanying metabolic features (anaplerosis, cataplerosis) are presented in textbooks and reviews as a hallmark (general characteristic): the metabolic map of cancer. On the other hand, research articles on specific tumors since a few years emphasize various biological features of different cancers, different cells in a cancer and the dynamic heterogeneity of these cells. We have analysed the research literature of the subject and show the generality of a dynamic, evolving biological and metabolic, spatial and temporal heterogeneity of individual cancers. We conclude that there is no one metabolic map of cancer but several and describe the two extremes of a panel from the hypoxic to the normoxic state. The implications for the significance of general 'omic' studies, and on therapeutic conclusions drawn from them and for the diagnostic use of fractional biopsies is discussed.

Metabolic plasticity in heterogeneous pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDA) is one of the most lethal malignant neoplasms. The recognized hallmarks of PDA are regarded to be downstream events of metabolic reprogramming. Because PDA is a heterogeneous disease that is influenced by genetic polymorphisms and changes in the microenvironment, metabolic plasticity is a novel feature of PDA. As intrinsic factors for metabolic plasticity, K-ras activation and mutations in other tumor suppressor genes induce abnormal mitochondrial metabolism and enhance glycolysis, with alterations in glutamine and lipid metabolism. As extrinsic factors, the acidic and oxygen/nutrient-deprived microenvironment also induces cancer cells to reprogram their metabolic pathway and hijack stromal cells (mainly cancer-associated fibroblasts and immunocytes) to communicate, thereby adapting to metabolic stress. Therefore, a better understanding of the metabolic features of PDA will contribute to the development of novel diagnostic and therapeutic strategies.

Energy sources identify metabolic phenotypes in pancreatic cancer

Metabolic reprogramming is one of the emerging hallmarks of cancers. As a highly malignant tumor, pancreatic ductal adenocarcinoma (PDA) is not only a metabolic disease but also a heterogeneous disease. Heterogeneity induces PDA dependence on distinct nutritive substrates, thereby inducing different metabolic phenotypes. We stratified PDA into four phenotypes with distinct types of energy metabolism, including a Warburg phenotype, a reverse Warburg phenotype, a glutaminolysis phenotype, and a lipid-dependent phenotype. The four phenotypes possess distinct metabolic features and reprogram their metabolic pathways to adapt to stress. The metabolic type present in PDA should prompt differential imaging and serologic metabolite detection for diagnosis and prognosis. The targeting of an individual metabolic phenotype with corresponding metabolic inhibitors is considered a promising therapeutic approach and, in combination with chemotherapy, is expected to be a novel strategy for PDA treatment.

Hypoxia, cancer metabolism and the therapeutic benefit of targeting lactate/H(+) symporters

Since Otto Warburg reported the 'addiction' of cancer cells to fermentative glycolysis, a metabolic pathway that provides energy and building blocks, thousands of studies have shed new light on the molecular mechanisms contributing to altered cancer metabolism. Hypoxia, through hypoxia-inducible factors (HIFs), in addition to oncogenes activation and loss of tumour suppressors constitute major regulators of not only the "Warburg effect" but also many other metabolic pathways such as glutaminolysis. Enhanced glucose and glutamine catabolism has become a recognised feature of cancer cells, leading to accumulation of metabolites in the tumour microenvironment, which offers growth advantages to tumours. Among these metabolites, lactic acid, besides imposing an acidic stress, is emerging as a key signalling molecule that plays a pivotal role in cancer cell migration, angiogenesis, immune escape and metastasis. Although interest in lactate for cancer development only appeared recently, pharmacological molecules blocking its metabolism are already in phase I/II clinical trials. Here, we review the metabolic pathways generating lactate, and we discuss the rationale for targeting lactic acid transporter complexes for the development of efficient and selective anticancer therapies.

CB1 cannabinoid receptor in SF1-expressing neurons of the ventromedial hypothalamus determines metabolic responses to diet and leptin

Metabolic flexibility allows rapid adaptation to dietary change, however, little is known about the CNS mechanisms regulating this process. Neurons in the hypothalamic ventromedial nucleus (VMN) participate in energy balance and are the target of the metabolically relevant hormone leptin. Cannabinoid type-1 (CB₁) receptors are expressed in VMN neurons, but the specific contribution of endocannabinoid signaling in this neuronal population to energy balance regulation is unknown. Here we demonstrate that VMN CB₁ receptors regulate metabolic flexibility and actions of leptin. In chow-fed mice, conditional deletion of CB₁ in VMN neurons (expressing the steroidogenic factor 1, SF1) decreases adiposity by increasing sympathetic activity and lipolysis, and facilitates metabolic effects of leptin. Conversely, under high-fat diet, lack of CB₁ in VMN neurons produces leptin resistance, blunts peripheral use of lipid substrates and increases adiposity. Thus, CB₁ receptors in VMN neurons provide a molecular switch adapting the organism to dietary change.

The SLC16A family of monocarboxylate transporters (MCTs)--physiology and function in cellular metabolism, pH homeostasis, and fluid transport

The SLC16A family of monocarboxylate transporters (MCTs) is composed of 14 members. MCT1 through MCT4 (MCTs 1-4) are H(+)-coupled monocarboxylate transporters, MCT8 and MCT10 transport thyroid hormone and aromatic amino acids, while the substrate specificity and function of other MCTs have yet to be determined. The focus of this review is on MCTs 1-4 because their role in lactate transport is intrinsically linked to cellular metabolism in various biological systems, including skeletal muscle, brain, retina, and testis. Although MCTs 1-4 all transport lactate, they differ in their transport kinetics and vary in tissue and subcellular distribution, where they facilitate "lactate-shuttling" between glycolytic and oxidative cells within tissues and across blood-tissue barriers. However, the role of MCTs 1-4 is not confined to cellular metabolism. By interacting with bicarbonate transport proteins and carbonic anhydrases, MCTs participate in the regulation of pH homeostasis and fluid transport in renal proximal tubule and corneal endothelium, respectively. Here, we provide a comprehensive review of MCTs 1-4, linking their cellular distribution to their functions in various parts of the human body, so that we can better understand the physiological roles of MCTs at the systemic level.

Potential role of combined FDG PET/CT & contrast enhancement MRI in a rectal carcinoma model with nodal metastases characterized by a poor FDG-avidity

PURPOSE

To investigate the additional role of MRI contrast enhancement (CE) in the primary tumor and the FDG uptake at PET in the lymph-node metastases.

MATERIALS AND METHODS

A model of colorectal cancer induced by orthotopic HT-29 cells microinjection, producing pelvic lymph node metastases, was assessed using CE-MRI and FDG-PET. Histology and GLUT-1 immunohistochemistry were performed on primary tumors and iliac lymph nodes.

RESULTS

Primary tumors were characterized by low FDG-uptake but high CE-MRI, particularly at tumor periphery. Undetectable FDG-uptake characterized the metastatic lymph-nodes. Histology revealed large stromal bundles at tumor periphery and a dense network of stromal fibers and neoplastic cells in the inner portion of the tumors. Both primary tumors and positive lymph nodes showed poor GLUT-1 staining.

CONCLUSION

Our data support the complementary role of MRI-CE and FDG PET in some types of carcinomas characterized by abundant cancer-associated stroma and poor FDG avidity consequent to poor GLUT-1 transported. In these tumors FDG-PET alone may be not completely adequate to obtain an adequate tumor radiotherapy planning, and a combination with dual CE-MRI is strongly recommended.

In vivo ¹⁸F-FDG tumour uptake measurements in small animals using Cerenkov radiation

PURPOSE

2-[(18)F]Fluoro-2-deoxy-D-glucose ((18)F-FDG) is a widely used PET radiotracer for the in vivo diagnosis of several diseases such as tumours. The positrons emitted by (18)F-FDG, travelling into tissues faster than the speed of light in the same medium, are responsible for Cerenkov radiation (CR) emission which is prevalently in the visible range. The purpose of this study is to show that CR escaping from tumour tissues of small living animals injected with (18)F-FDG can be detected with optical imaging (OI) techniques using a commercial optical instrument equipped with charge-coupled detectors (CCD).

METHODS

The theory behind the Cerenkov light emission and the source depth measurements using CR is first presented. Mice injected with (18)F-FDG or saline solution underwent dynamic OI acquisition and a comparison between images was performed. Multispectral analysis of the radiation was used to estimate the depth of the source of Cerenkov light. Small animal PET images were also acquired in order to compare the (18)F-FDG bio-distribution measured using OI and PET scanner.

RESULTS

Cerenkov in vivo whole-body images of tumour-bearing mice and the measurements of the emission spectrum (560-660 nm range) are presented. Brain, kidneys and tumour were identified as a source of visible light in the animal body: the tissue time-activity curves reflected the physiological accumulation of (18)F-FDG in these organs. The identification is confirmed by the comparison between CR and (18)F-FDG images.

CONCLUSION

These results will allow the use of conventional OI devices for the in vivo study of glucose metabolism in cancer and the assessment, for example, of anti-cancer drugs. Moreover, this demonstrates that (18)F-FDG can be employed as it is a bimodal tracer for PET and OI techniques.

Texture analysis of non-small cell lung cancer on unenhanced computed tomography: initial evidence for a relationship with tumour glucose metabolism and stage

The aim was to undertake an initial study of the relationship between texture features in computed tomography (CT) images of non-small cell lung cancer (NSCLC) and tumour glucose metabolism and stage. This retrospective pilot study comprised 17 patients with 18 pathologically confirmed NSCLC. Non-contrast-enhanced CT images of the primary pulmonary lesions underwent texture analysis in 2 stages as follows: (a) image filtration using Laplacian of Gaussian filter to differentially highlight fine to coarse textures, followed by (b) texture quantification using mean grey intensity (MGI), entropy (E) and uniformity (U) parameters. Texture parameters were compared with tumour fluorodeoxyglucose (FDG) uptake (standardised uptake value (SUV)) and stage as determined by the clinical report of the CT and FDG-positron emission tomography imaging. Tumour SUVs ranged between 2.8 and 10.4. The number of NSCLC with tumour stages I, II, III and IV were 4, 4, 4 and 6, respectively. Coarse texture features correlated with tumour SUV (E: r = 0.51, p = 0.03; U: r = −0.52, p = 0.03), whereas fine texture features correlated with tumour stage (MGI: r_s = 0.71, p = 0.001; E: r_s = 0.55, p = 0.02; U: r_s = −0.49, p = 0.04). Fine texture predicted tumour stage with a kappa of 0.7, demonstrating 100% sensitivity and 87.5% specificity for detecting tumours above stage II ( p = 0.0001). This study provides initial evidence for a relationship between texture features in NSCLC on non-contrast-enhanced CT and tumour metabolism and stage. Texture analysis warrants further investigation as a potential method for obtaining prognostic information for patients with NSCLC undergoing CT.

The War on Cancer rages on

In 1971, the "War on Cancer" was launched by the US government to cure cancer by the 200-year anniversary of the founding of the United States of America, 1976. This article briefly looks back at the progress that has been made in cancer research and compares progress made in other areas of human affliction. While progress has indeed been made, the battle continues to rage on.

CB(1) signaling in forebrain and sympathetic neurons is a key determinant of endocannabinoid actions on energy balance

The endocannabinoid system (ECS) plays a critical role in obesity development. The pharmacological blockade of cannabinoid receptor type 1 (CB(1)) has been shown to reduce body weight and to alleviate obesity-related metabolic disorders. An unsolved question is at which anatomical level CB(1) modulates energy balance and the mechanisms involved in its action. Here, we demonstrate that CB(1) receptors expressed in forebrain and sympathetic neurons play a key role in the pathophysiological development of diet-induced obesity. Conditional mutant mice lacking CB(1) expression in neurons known to control energy balance, but not in nonneuronal peripheral organs, displayed a lean phenotype and resistance to diet-induced obesity. This phenotype results from an increase in lipid oxidation and thermogenesis as a consequence of an enhanced sympathetic tone and a decrease in energy absorption. In conclusion, CB(1) signaling in the forebrain and sympathetic neurons is a key determinant of the ECS control of energy balance.

Dynamic near-infrared optical imaging of 2-deoxyglucose uptake by intracranial glioma of athymic mice

Background

It is recognized that cancer cells exhibit highly elevated glucose metabolism compared to non-tumor cells. We have applied in vivo optical imaging to study dynamic uptake of a near-infrared dye-labeled glucose analogue, 2-deoxyglucose (2-DG) by orthotopic glioma in a mouse model.

Methodology and Principal Findings

The orthotopic glioma model was established by surgically implanting U87-luc glioma cells into the right caudal nuclear area of nude mice. Intracranial tumor growth was monitored longitudinally by bioluminescence imaging and MRI. When tumor size reached >4 mm diameter, dynamic fluorescence imaging was performed after an injection of the NIR labeled 2-DG, IRDye800CW 2-DG. Real-time whole body images acquired immediately after i.v. infusion clearly visualized the near-infrared dye circulating into various internal organs sequentially. Dynamic fluorescence imaging revealed significantly higher signal intensity in the tumor side of the brain than the contralateral normal brain 24 h after injection (tumor/normal ratio, TNR  = 2.8±0.7). Even stronger contrast was achieved by removing the scalp (TNR  = 3.7±1.1) and skull (TNR  = 4.2±1.1) of the mice. In contrast, a control dye, IRDye800CW carboxylate, showed little difference (1.1±0.2). Ex vivo fluorescence imaging performed on ultrathin cryosections (20 µm) of tumor bearing whole brain revealed distinct tumor margins. Microscopic imaging identified cytoplasmic locations of the 2-DG dye in tumor cells.

Conclusion and Significance

Our results suggest that the near-infrared dye labeled 2-DG may serve as a useful fluorescence imaging probe to noninvasively assess intracranial tumor burden in preclinical animal models.

DCE-MRI using small-molecular and albumin-binding contrast agents in experimental carcinomas with different stromal content

OBJECTIVES

To compare DCE-MRI experiments performed using a standard small-molecular (Gd-DTPA) and an albumin-binding (MS-325) contrast agent in two carcinoma models with different stromal content.

MATERIALS AND METHODS

DU-145 or BXPC-3 cancer cells were subcutaneously injected into nude mice. DCE-MRI was performed by a bolus injection of Gd-DTPA or MS-325 about 2 weeks after inoculation. For quantitative analysis a volume of interest was manually drawn over each tumor. To address the heterogeneous enhancement, each tumor volume was then divided into the 20% most-enhancing and the remaining 80% least-enhancing fractions. Mean tumor enhancement was calculated over these selected tumor volumes and compared between tumor groups and contrast agents. Maps of differential enhancement, peak enhancement and time-to-peak were used for visual evaluation. CD31 and VEGF immunohistochemistry were performed in excised tumors.

RESULTS

In the 80% least-enhancing volume, at late time points of the dynamic scan, the mean enhancement elicited by MS-325 was higher in BXPC-3 than in DU-145 tumors. In the 20% most-enhancing volume, using either contrast agents, significant difference between the two tumors types were observed only early, while at later time points of the dynamic scan the difference were obscured by the faster washout observed in the BXPC-3 tumors. Enhancement maps confirmed that BXPC-3 tumors were characterized by marked washout rate using either contrast agent, particularly in the higher enhancing peripheral rim. With MS-325 this washout pattern appeared to be specific to the BXPC-3 carcinomas, since it was not observed in the DU-145 tumors. Finally, in both tumor types, MS-325 produced significantly higher enhancement than Gd-DTPA in the late phase of the dynamic scan. Ex vivo analysis confirmed the marked presence of aberrant infiltrative stroma in BXPC-3 tumors, in which tumor vessels were embedded. In all tumors the central portion was less viable and less infiltrated by stromal tissue then the peripheral areas.

CONCLUSIONS

Contrast distribution proved to be related to stromal content, which presumably produced the higher enhancement and faster washout observed in the BXPC-3 tumors. In particular, 'early' contrast-enhanced MRI, appeared as the most sensitive technique to detect the tumor portions characterized by a high stromal content, i.e. the peripheral rim of the BXPC-3 tumors. Since the same tumor models were recently investigated using FDG-PET imaging, showing inverse relationship between FDG uptake and stromal content, contrast-enhanced MRI and FDG-PET could provide complementary and comprehensive sensitivity in the assessment of carcinomas.

Neoplasia: the second decade

This issue marks the end of the 10-year anniversary of Neoplasia where we have seen exciting growth in both number of submitted and published articles in Neoplasia. Neoplasia was first published in 1999. During the past 10 years, Neoplasia has dynamically adapted to the needs of the cancer research community as technologies have advanced. Neoplasia is currently providing access to articles through PubMed Central to continue to facilitate rapid broad-based dissemination of published findings to the scientific community through an Open Access model. This has in part helped Neoplasia to achieve an improved impact factor this past year, demonstrating that the manuscripts published by Neoplasia are of great interest to the overall cancer research community. This past year, Neoplasia received a record number of articles for review and has had a 21% increase in the number of published articles.

Warburg revisited: imaging tumour blood flow and metabolism

In the 1930s, Otto Warburg reported that anaerobic metabolism of glucose is a fundamental property of all tumours, even in the presence of an adequate oxygen supply. He also demonstrated a relationship between the degree of anaerobic metabolism and tumour growth rate. Today, this phenomenon forms the basis of tumour imaging with fluorodeoxyglucose positron emission tomography (FDG-PET). More recently, Folkman has demonstrated that malignant growth and survival are also dependent on tumour vascularity which is increasingly evaluated in vivo using techniques such as contrast enhanced computed tomography or magnetic resonance imaging (MRI). Although it is reasonable to hypothesise that the metabolic requirements of tumours are mirrored by alterations in tumour haemodynamics, the relationship between tumour blood flow and metabolism is in fact complex. A well-developed tumour vascular supply is required to ensure a sufficient delivery of glucose and oxygen to support the metabolism essential for tumour growth. However, an inadequate vascularisation of tumour will result in hypoxia, a factor that is known to stimulate anaerobic metabolism of glucose. Thus, the balance between tumour blood flow and metabolism will be an important indicator of the biological status of a tumour and hence the tumour's likely progression and response to treatment. This article reviews the molecular biology of tumour vascularisation and metabolism, relating these processes to currently available imaging techniques while summarising the imaging studies that have compared tumour blood flow and metabolism. The potential for vascular metabolic imaging to assess tumour aggression and sub-classify treatment response is highlighted.