In vivo MRS assessment of altered fatty acyl unsaturation in liver tumor formation of a TGF alpha/c-myc transgenic mouse model

Lipidomic profiling of clinical prostate cancer reveals targetable alterations in membrane lipid composition

Dysregulated lipid metabolism is a prominent feature of prostate cancer that is driven by androgen receptor (AR) signaling. Here we used quantitative mass spectrometry to define the "lipidome" in prostate tumors with matched benign tissues (n=21), independent unmatched tissues (n=47), and primary prostate explants cultured with the clinical AR antagonist enzalutamide (n=43). Significant differences in lipid composition were detected and spatially visualized in tumors compared to matched benign samples. Notably, tumors featured higher proportions of monounsaturated lipids overall and elongated fatty acid chains in phosphatidylinositol and phosphatidylserine lipids. Significant associations between lipid profile and malignancy were validated in unmatched samples, and phospholipid composition was characteristically altered in patient tissues that responded to AR inhibition. Importantly, targeting tumor-related lipid features via inhibition of acetyl-CoA carboxylase 1 significantly reduced cellular proliferation and induced apoptosis in tissue explants. This first characterization of the prostate cancer lipidome in clinical tissues reveals enhanced fatty acid synthesis, elongation, and desaturation as tumor-defining features, with potential for therapeutic targeting.

Metabolic adaptations in spontaneously immortalized PGC-1α knock-out mouse embryonic fibroblasts increase their oncogenic potential

PGC-1α controls, to a large extent, the capacity of cells to respond to changing nutritional requirements and energetic demands. The key role of metabolic reprogramming in tumor development has highlighted the potential role of PGC-1α in cancer. To investigate how loss of PGC-1α activity in primary cells impacts the oncogenic characteristics of spontaneously immortalized cells, and the mechanisms involved, we used the classic 3T3 protocol to generate spontaneously immortalized mouse embryonic fibroblasts (iMEFs) from wild-type (WT) and PGC-1α knockout (KO) mice and analyzed their oncogenic potential in vivo and in vitro. We found that PGC-1α KO iMEFs formed larger and more proliferative primary tumors than WT counterparts, and fostered the formation of lung metastasis by B16 melanoma cells. These characteristics were associated with the reduced capacity of KO iMEFs to respond to cell contact inhibition, in addition to an increased ability to form colonies in soft agar, an enhanced migratory capacity, and a reduced growth factor dependence. The mechanistic basis of this phenotype is likely associated with the observed higher levels of nuclear β-catenin and c-myc in KO iMEFs. Evaluation of the metabolic adaptations of the immortalized cell lines identified a decrease in oxidative metabolism and an increase in glycolytic flux in KO iMEFs, which were also more dependent on glutamine for their survival. Furthermore, glucose oxidation and tricarboxylic acid cycle forward flux were reduced in KO iMEF, resulting in the induction of compensatory anaplerotic pathways. Indeed, analysis of amino acid and lipid patterns supported the efficient use of tricarboxylic acid cycle intermediates to synthesize lipids and proteins to support elevated cell growth rates. All these characteristics have been observed in aggressive tumors and support a tumor suppressor role for PGC-1α, restraining metabolic adaptations in cancer.

OKN-007 Increases temozolomide (TMZ) Sensitivity and Suppresses TMZ-Resistant Glioblastoma (GBM) Tumor Growth

Treatment of glioblastoma (GBM) remains a challenge using conventional chemotherapy, such as temozolomide (TMZ), and is often ineffective as a result of drug resistance. We have assessed a novel nitrone-based agent, OKN-007, and found it to be effective in decreasing tumor volumes and increasing survival in orthotopic GBM xenografts by decreasing cell proliferation and angiogenesis and increasing apoptosis. In this study, we assessed combining OKN-007 with TMZ in vivo in a human G55 GBM orthotopic xenograft model and in vitro in TMZ-resistant and TMZ-sensitive human GBM cell lines. For the in vivo studies, magnetic resonance imaging was used to assess tumor growth and vascular alterations. Percent animal survival was also determined. For the in vitro studies, cell growth, IC50 values, RNA-seq, RT-PCR, and ELISA were used to assess growth inhibition, possible mechanism-of actions (MOAs) associated with combined OKN-007 + TMZ versus TMZ alone, and gene and protein expression levels, respectively. Microarray analysis of OKN-007-treated rat F98 glioma tumors was also carried out to determine possible MOAs of OKN-007 in glioma-bearing animals either treated or not treated with OKN-007. OKN-007 seems to elicit its effect on GBM tumors via inhibition of tumorigenic TGF-β1, which affects the extracellular matrix. When combined with TMZ, OKN-007 significantly increases percent survival, decreases tumor volumes, and normalizes tumor blood vasculature in vivo compared to untreated tumors and seems to affect TMZ-resistant GBM cells possibly via IDO-1, SUMO2, and PFN1 in vitro. Combined OKN-007 + TMZ may be a potentially potent treatment strategy for GBM patients.

Longitudinal metabolic imaging of hepatocellular carcinoma in transgenic mouse models identifies acylcarnitine as a potential biomarker for early detection

The cumulative effects of hepatic injury due to hepatitis B virus (HBV) infections and aflatoxin-B₁ (AFB₁) exposure are the major risk factors of HCC. Understanding early metabolic changes involving these risk factors in an animal model closely resembling human hepatocellular carcinoma (HCC) is critical for biomarker discovery and disease therapeutics. We have used the hepatitis B surface antigen (HBsAg) transgenic mouse model that mimics HBV carriers with and without AFB1 treatment. We investigated early metabolic changes from preneoplastic state to HCC by non-invasive longitudinal imaging in three HCC groups of mice: HBsAg + AFB₁(Gp-I), AFB₁ alone (Gp-II), HBsAg alone (Gp-III) and a control group (wild-type untreated; Gp-IV). For the first time, we have identified acylcarnitine signals in vivo in the liver prior to the histological manifestation of the tumors in all three groups. Acylcarnitine concentration increased with increase in tumor growth in all HCC mouse models, indicating elevated metabolic activity and increased cell turnover. This was confirmed in a pilot study using human serum from HCC patients, which revealed a higher concentration of acylcarnitine compared with normal subjects. Translational clinical studies can be designed to detect acylcarnitine in patients with high risk factors for HCC.

Tris(1,3-dichloro-2-propyl) phosphate perturbs the expression of genes involved in immune response and lipid and steroid metabolism in chicken embryos

We previously demonstrated that in ovo exposure to the flame retardant tris(1,3-dichloro-2-propyl) phosphate (TDCPP) decreased plasma thyroxine levels, reduced growth parameters, and decreased gallbladder size in chicken embryos. In the current study DNA microarrays were used to evaluate global mRNA expression in liver tissue of male chicken embryos that exhibited the above mentioned effects. Injected doses were dimethyl sulfoxide vehicle control, 7.6 or 45 μg TDCPP/g egg. TDCPP caused significant changes in the expression of five genes at the low dose and 47 genes at the high dose (False Discovery Rate p ≤ 0.1, fold change ≥ 1.5). The gene expression analysis suggested a compromised immune function, a state of cholestatic liver/biliary fibrosis, and disrupted lipid and steroid metabolism. Circulating bile acid levels were elevated, which is an indication of liver dysfunction, and plasma cholesterol levels were reduced; however, hepatic bile acid and cholesterol levels were unaltered. Interactome analyses identified apolipoprotein E, hepatocyte nuclear factor 4 alpha, and peroxisome proliferator-activated receptor alpha as key regulatory molecules involved in the effects of TDCPP. Our results demonstrate a targeted effect of TDCPP toxicity on lipid metabolism, including cholesterol, that helps explain the aforementioned phenotypic effects, as chicken embryos are highly dependent on yolk lipids for growth and maintenance throughout development. Finally, our results are in concordance with the literature that describes TDCPP as a cancer-causing agent, since the majority of dysregulated genes were involved in cancer pathways.

High-field small animal magnetic resonance oncology studies

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

Astrocyte elevated gene-1 promotes hepatocarcinogenesis: novel insights from a mouse model

Astrocyte elevated gene-1 (AEG-1) is a key contributor to hepatocellular carcinoma (HCC) development and progression. To enhance our understanding of the role of AEG-1 in hepatocarcinogenesis, a transgenic mouse with hepatocyte-specific expression of AEG-1 (Alb/AEG1) was developed. Treating Alb/AEG-1, but not wild-type (WT) mice, with N-nitrosodiethylamine resulted in multinodular HCC with steatotic features and associated modulation of expression of genes regulating invasion, metastasis, angiogenesis, and fatty acid synthesis. Hepatocytes isolated from Alb/AEG-1 mice displayed profound resistance to chemotherapeutics and growth factor deprivation with activation of prosurvival signaling pathways. Alb/AEG-1 hepatocytes also exhibited marked resistance toward senescence, which correlated with abrogation of activation of a DNA damage response. Conditioned media from Alb/AEG-1 hepatocytes induced marked angiogenesis with elevation in several coagulation factors. Among these factors, AEG-1 facilitated the association of factor XII (FXII) messenger RNA with polysomes, resulting in increased translation. Short interfering RNA-mediated knockdown of FXII resulted in profound inhibition of AEG-1-induced angiogenesis.

CONCLUSION

We uncovered novel aspects of AEG-1 functions, including induction of steatosis, inhibition of senescence, and activation of the coagulation pathway to augment aggressive hepatocarcinogenesis. The Alb/AEG-1 mouse provides an appropriate model to scrutinize the molecular mechanism of hepatocarcinogenesis and to evaluate the efficacy of novel therapeutic strategies targeting HCC.

Magnetic resonance spectroscopy of cancer metabolism and response to therapy

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

Hepatic lipid composition differs between ob/ob and ob/+ control mice as determined by using in vivo localized proton magnetic resonance spectroscopy

OBJECT

Hepatic lipid accumulation is associated with nonalcoholic fatty liver disease, and the metabolic syndrome constitutes an increasing medical problem. In vivo proton magnetic resonance spectroscopy ((1)H MRS) allows the assessment of hepatic lipid levels noninvasively and also yields information on the fat composition due to its high spectral resolution.

MATERIALS AND METHODS

We applied (1)H MRS at 9.4T to study lipid content and composition in eight leptin-deficient ob/ob mice as a model of obesity and in four lean ob/+ control mice at 24 weeks of age. PRESS sequence was used. For accurate estimation of signal intensity, differences in relaxation behavior of individual signals were accounted for each mouse individually. Also, in order to minimize spectral degrading due to motion artifacts, respiration gating was applied.

RESULTS

Significant differences between ob/ob and ob/+ control mice were found in both lipid content and composition. The mean chain length was found to be significantly longer in ob/ob mice with a higher fraction of monounsaturated lipids.

CONCLUSION

(1)H MRS enables accurate assessment in hepatic lipids in mice, which is attractive for mechanistic studies of altered metabolism given the large number of genetically engineered mouse models available.

Gadoxetate acid-enhanced MRI of hepatocellular carcinoma in a c-myc/TGFα transgenic mouse model including signal intensity and fat content: initial experience

Genetically engineered mouse models, such as double transgenic c-myc/TGFα mice, with specific pathway abnormalities might be more successful at predicting the clinical response of hepatocellular carcinoma (HCC) treatment. But a major drawback of the tumour models is the difficulty of visualizing endogenously formed tumours. The optimal imaging procedure should be brief and minimally invasive. Magnetic resonance imaging (MRI) satisfies these criteria and gadoxetate acid-enhanced MRI improves the detection of HCC. Fat content is stated to be an additional tool to help assess tumour responses, for example, in cases of radiofrequency ablation. Therefore the aim of this study was to investigate if gadoxetate acid-enhanced MRI could be used to detect HCC in c-myc/TGFα transgenic mice by determining the relation between the signal intensity of HCC and normal liver parenchyma and the corresponding fat content as a diagnostic marker of HCC. In our study, 20 HCC in c-myc/TGFα transgenic male mice aged 20–34 weeks were analyzed. On gadoxetate acid-enhanced MRI, the signal intensity was 752.4 for liver parenchyma and 924.5 for HCC. The contrast to noise ratio was 20.4, the percentage enhancement was 267.1% for normal liver parenchyma and 353.9% for HCC. The fat content was 11.2% for liver parenchyma and 16.2% for HCC. There was a correlation between fat content and signal intensity with r = 0.7791. All parameters were statistically significant with P < 0.05. Our data indicate that gadoxetate acid contrast enhancement allows sensitive detection of HCC in c-myc/TGFα transgenic mice and determination of the fat content seems to be an additional useful parameter for HCC.

NMR spectroscopy for discovery and quantitation of biomarkers of disease in human bile

Human liver synthesizes bile; bile, containing a large number of metabolites, is transported through the canaliculi and bile ducts, and stored in the gallbladder before entering into the intestine. In the intestine, a large number of bile metabolites are reabsorbed and sent back to the liver for recirculation. Owing to close association of the bile with the gastrointestinal system, the bile metabolic profile is highly sensitive to the onset of numerous gastrointestinal disease processes. A growing number of studies suggest that hepatobiliary disease biomarkers are richly populated in human bile. These studies stress the potential of profiling the human bile metabolome for early diagnostics as well as deeper insights into gastrointestinal disease processes. Once the biomarkers are established reliably using human bile, they can be targeted in easily accessible fluids such as blood and urine or targeted in bile itself using noninvasive methods such as in vivo magnetic resonance spectroscopy. NMR spectroscopy is one of the most powerful bioanalytical tools, which promises profiling of human bile metabolome and exploring early biomarkers for hepatobiliary diseases. Comprehensive analysis of human bile using NMR spectroscopy has lead to identification and quantification of major bile metabolites. This review describes the discovery and quantitation of biomarkers of hepatobiliary diseases in human bile using NMR spectroscopy.

Quantitative analysis of the growth kinetics of chemically induced mouse liver tumors by magnetic resonance imaging

Noninvasive methods for the early detection of tumor onset and progression in rodent liver would be of high value for pharmaceutical and chemical industry and would, at the same time, foster one of the 3 Rs (replacement, reduction, refinement) by reducing the number of animals in the bioassay. We have induced liver tumors in mice by single injection of diethylnitrosamine (DEN) either in 2-week- (experiment 1) or 6-week-old (experiment 2) male C3H mice. In the latter, mice were also chronically treated with 0.05% phenobarbital in diet according to an initiation/promotion protocol. Starting at 16 weeks after DEN injection (18 weeks after DEN in experiment 2), mice were routinely scanned by noninvasive magnetic resonance imaging (MRI) using a T2-weighted 3D sequence in regular intervals. Liver tumors became detectable in both experiments when they exceeded a diameter of ∼1 mm. Exponential increases in total tumor volume per liver were observed in both experiments. The onset of tumor development was similar with respect to DEN treatment. Although mice in experiment 1 had developed a mean total tumor volume of ∼100 mm³ approximately 24 weeks after DEN, it took ∼4 weeks longer to reach this tumor mass in experiment 2. Determination of time-dependent growth of individual tumors demonstrated strong tumor heterogeneity. In vivo MRI data were further correlated with tumor histology. The phenotype of tumors differed strongly between the two experiments, but our results demonstrate that tumors can be reliably detected by MRI when they exceed a certain size independent of their phenotype.

Global gene profiling of spontaneous hepatocellular carcinoma in B6C3F1 mice: similarities in the molecular landscape with human liver cancer

Hepatocellular carcinoma (HCC) is an important cause of morbidity and mortality worldwide. Although the risk factors of human HCC are well known, the molecular pathogenesis of this disease is complex, and in general, treatment options remain poor. The use of rodent models to study human cancer has been extensively pursued, both through genetically engineered rodents and rodent models used in carcinogenicity and toxicology studies. In particular, the B6C3F1 mouse used in the National Toxicology Program (NTP) two-year bioassay has been used to evaluate the carcinogenic effects of environmental and occupational chemicals, and other compounds. The high incidence of spontaneous HCC in the B6C3F1 mouse has challenged its use as a model for chemically induced HCC in terms of relevance to the human disease. Using global gene expression profiling, we identify the dysregulation of several mediators similarly altered in human HCC, including re-expression of fetal oncogenes, upregulation of protooncogenes, downregulation of tumor suppressor genes, and abnormal expression of cell cycle mediators, growth factors, apoptosis regulators, and angiogenesis and extracellular matrix remodeling factors. Although major differences in etiology and pathogenesis remain between human and mouse HCC, there are important similarities in global gene expression and molecular pathways dysregulated in mouse and human HCC. These data provide further support for the use of this model in hazard identification of compounds with potential human carcinogenicity risk, and may help in better understanding the mechanisms of tumorigenesis resulting from chemical exposure in the NTP two-year carcinogenicity bioassay.

In vivo NMR detection of diet-induced changes in adipose tissue composition

We introduce an in vivo spectroscopic method to assess the effects of diet on fatty acid composition of the predominant chemical constituent of adipocytes in mice. To do this, we make use of a nonlinear NMR signal that, unlike a standard NMR signal, is intrinsically insensitive to local magnetic field inhomogeneities and which naturally suppresses the large water signal from nonfatty tissues. Our method yields fat composition information from fat depots distributed over large sample volumes in a single experiment, without requiring the use of tedious shimming procedures, voxel selection, or water suppression. Our results suggest that this method can reveal clear differences in adipose tissue composition of mice fed a standard chow diet compared with mice fed a diet rich in polyunsaturated fatty acids. With further developments this method could be used to obtain information on human lipid composition noninvasively and to track changes in lipid composition induced by diet intervention, pharmaceutical drugs, and exercise.

Inhibition of stearoyl-CoA desaturase 1 expression induces CHOP-dependent cell death in human cancer cells

BACKGROUND

Cancer cells present a sustained de novo fatty acid synthesis with an increase of saturated and monounsaturated fatty acid (MUFA) production. This change in fatty acid metabolism is associated with overexpression of stearoyl-CoA desaturase 1 (Scd1), which catalyses the transformation of saturated fatty acids into monounsaturated fatty acids (e.g., oleic acid). Several reports demonstrated that inhibition of Scd1 led to the blocking of proliferation and induction of apoptosis in cancer cells. Nevertheless, mechanisms of cell death activation remain to be better understood.

PRINCIPAL FINDINGS

In this study, we demonstrated that Scd1 extinction by siRNA triggered abolition of de novo MUFA synthesis in cancer and non-cancer cells. Scd1 inhibition-activated cell death was only observed in cancer cells with induction of caspase 3 activity and PARP-cleavage. Exogenous supplementation with oleic acid did not reverse the Scd1 ablation-mediated cell death. In addition, Scd1 depletion induced unfolded protein response (UPR) hallmarks such as Xbp1 mRNA splicing, phosphorylation of eIF2α and increase of CHOP expression. However, the chaperone GRP78 expression, another UPR hallmark, was not affected by Scd1 knockdown in these cancer cells indicating a peculiar UPR activation. Finally, we showed that CHOP induction participated to cell death activation by Scd1 extinction. Indeed, overexpression of dominant negative CHOP construct and extinction of CHOP partially restored viability in Scd1-depleted cancer cells.

CONCLUSION

These results suggest that inhibition of de novo MUFA synthesis by Scd1 extinction could be a promising anti-cancer target by inducing cell death through UPR and CHOP activation.

Non-mammalian fat-1 gene prevents neoplasia when introduced to a mouse hepatocarcinogenesis model: Omega-3 fatty acids prevent liver neoplasia

We investigated the effect of a non-mammalian omega-3 desaturase in a mouse hepatocarcinogenesis model. Mice containing double mutations (DM) in c-myc and TGF-alpha (transforming growth factor-alpha), leading to liver neoplasia, were crossed with mice containing omega-3 desaturase. MRI analysis of triple mutant (TM) mice showed the absence of neoplasia at all time points for 92% of mice in the study. Pathological changes of TM (TGFalpha/c-myc/fat-1) mouse liver tissue was similar to control mouse liver tissue. Magnetic resonance spectroscopy (MRS) measurements of unsaturated fatty acids found a significant difference (p<0.005) between DM and TM transgenic (Tg) mice at 34 and 40 weeks of age. HPLC analysis of mouse liver tissue revealed markedly decreased levels of omega-6 fatty acids in TM mice when compared to DM (TGFalpha/c-myc) and control (CD1) mice. Mass spectrometry (MS) analysis indicated significantly decreased 16:0/20:4 and 18:1/20:4 and elevated 16:0/22:6 fatty acyl groups in both GPCho and GPEtn, and elevated 16:0/20:5, 18:0/18:2, 18:0/18:1 and 18:0/22:6 in GPCho, within TM mice compared to DM mice. Total fatty acid analysis indicated a significant decrease in 18:1n9 in TM mice compared to DM mice. Western blot analysis of liver tissue showed a significant (p<0.05) decrease in NF-kappaB (nuclear factor-kappaB) levels at 40 weeks of age in TM mice compared to DM mice. Microarray analysis of TM versus DM mice livers at 40 weeks revealed alterations in genes involved in cell cycle regulation, cell-to-cell signaling, p53 signaling, and arachidonic acid (20:4) metabolism. Endogenous omega-3 fatty acids were found to prevent HCC development in mice.

Human bile as a rich source of biomarkers for hepatopancreatobiliary cancers

Metabolic profiling of biofluids is emerging as an important area with a promising number of applications in clinical medicine, including early diagnosis of numerous diseases that normally remain silent until late in the progress of disease. While blood and urine are more often used to explore biomarkers that distinguish he healthy from disease conditions, human bile is emerging as a rich source of biomarkers specifically for the cancers of the liver (hepatocellular carcinoma), bile ducts (cholangiocarcinoma), gallbladder and pancreas. This is owing to the fact that metabolites linked to the pathways of tumor cell metabolism are rich in bile by virtue of its association or proximity to the pathological source. Recent methodological developments have enabled the identification of a number of bile metabolites that have links with hepatopancreatobiliary diseases. Investigations of human bile are also considered to help the biomarker discovery process in vitro and provide avenues for translational research in detecting and following dynamic variations of biomarkers in clinical settings using noninvasive approaches, such as in vivo magnetic resonance spectroscopy. This article reviews the current status and potential applications of human bile as a source of biomarkers, with emphasis on metabolites, for early detection of cancers associated with the hepatopancreatobiliary system.

Combining nuclear magnetic resonance spectroscopy and mass spectrometry in biomarker discovery

Metabolic profiling of biological specimens is emerging as a promising approach for discovering specific biomarkers in the diagnosis of a number of diseases. Amongst many analytical techniques, nuclear magnetic resonance spectroscopy and mass spectrometry are the most information-rich tools that enable high-throughput and global analysis of hundreds of metabolites in a single step. Although only one of the two techniques is utilized in a majority of metabolomics applications, there is a growing interest in combining the data from the two methods to effectively unravel the mammoth complexity of biological samples. In this article, current developments in nuclear magnetic resonance, mass spectrometry and multivariate statistical analysis methods are described. While some general applications that utilize the combination of the two analytical methods are presented briefly, the emphasis is laid on the recent applications of nuclear magnetic resonance and mass spectrometry methods in the studies of hepatopancreatobiliary and gastrointestinal malignancies.