Relationships between oxygen and glucose metabolism in human liver tumours: positron emission tomography using (15)O and (18)F-deoxyglucose

Hepatic Positron Emission Tomography: Applications in Metabolism, Haemodynamics and Cancer

Evaluating in vivo the metabolic rates of the human liver has been a challenge due to its unique perfusion system. Positron emission tomography (PET) represents the current gold standard for assessing non-invasively tissue metabolic rates in vivo. Here, we review the existing literature on the assessment of hepatic metabolism, haemodynamics and cancer with PET. The tracer mainly used in metabolic studies has been [¹⁸F]2-fluoro-2-deoxy-D-glucose (¹⁸F-FDG). Its application not only enables the evaluation of hepatic glucose uptake in a variety of metabolic conditions and interventions, but based on the kinetics of ¹⁸F-FDG, endogenous glucose production can also be assessed. 14(R,S)-[¹⁸F]fluoro-6-thia-Heptadecanoic acid (¹⁸F-FTHA), ¹¹C-Palmitate and ¹¹C-Acetate have also been applied for the assessment of hepatic fatty acid uptake rates (¹⁸F-FTHA and ¹¹C-Palmitate) and blood flow and oxidation (¹¹C-Acetate). Oxygen-15 labelled water (¹⁵O-H₂O) has been used for the quantification of hepatic perfusion. ¹⁸F-FDG is also the most common tracer used for hepatic cancer diagnostics, whereas ¹¹C-Acetate has also shown some promising applications in imaging liver malignancies. The modelling approaches used to analyse PET data and also the challenges in utilizing PET in the assessment of hepatic metabolism are presented.

The Role of Angiogenesis in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) accounts for about 90% of all primary liver cancers and is the second leading cause of cancer-related deaths worldwide. The hypervascular nature of most HCC tumors underlines the importance of angiogenesis in the pathobiology of these tumors. Several angiogenic pathways have been identified as being dysregulated in HCC, suggesting they may be involved in the development and pathogenesis of HCC. These data provide practical targets for systemic treatments such as those targeting the vascular endothelial growth factor receptor and its ligand. However, the clinical relevance of other more recently identified angiogenic pathways in HCC pathogenesis or treatment remains unclear. Research into molecular profiles and validation of prognostic or predictive biomarkers will be required to identify the patient subsets most likely to experience meaningful benefit from this important class of agents.

Advances in Hypoxia-Mediated Mechanisms in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common and the third most deadly malignant tumor worldwide. Hypoxia and related oxidative stress are heavily involved in the process of HCC development and its therapies. However, direct and accurate measurement of oxygen concentration and evaluation of hypoxic effects in HCC prove difficult. Moreover, the hypoxia-mediated mechanisms in HCC remain elusive. Here, we summarize recent major evidence of hypoxia in HCC lesions shown by measuring partial pressure of oxygen (pO₂), the clinical importance of hypoxic markers in HCC, and recent advances in hypoxia-related mechanisms and therapies in HCC. For the mechanisms, we focus mainly on the roles of oxygen-sensing proteins (i.e., hypoxia-inducible factor and neuroglobin) and hypoxia-induced signaling proteins (e.g., matrix metalloproteinases, high mobility group box 1, Beclin 1, glucose metabolism enzymes, and vascular endothelial growth factor). With respect to therapies, we discuss mainly YQ23, sorafenib, 2-methoxyestradiol, and celastrol. This review focuses primarily on the results of clinical and animal studies.

(15)O-Water PET Study of the Effect of Imatinib, a Selective Platelet-Derived Growth Factor Receptor Inhibitor, Versus Anakinra, an IL-1R Antagonist, on Water-Perfusable Tissue Fraction in Colorectal Cancer Metastases

High interstitial fluid pressure (IFP) in colorectal cancer metastases may decrease the uptake and, thus, the effects of antitumor drugs. Imatinib, a selective inhibitor of platelet-derived growth factor receptors, and anakinra, an interleukin-1 receptor antagonist, respectively, increase drug uptake or decrease IFP in preclinical models of carcinoma. Drug-induced decrease in IFP in human metastases has not been objectively shown but should be reflected by an increase in water-perfusable tissue fraction (PTF) or tumor blood flow (TBF) using (15)O-water PET/CT and kinetic modeling. Hence, the aim of this study was to assess the effects of imatinib and anakinra on PTF and TBF in colorectal cancer metastases in patients.

METHODS

Nine patients with documented progressive disease despite all established therapy underwent (15)O-water PET/CT at baseline and at 2 d and 6-7 d after the start of oral administration of imatinib (400 mg/d). After a washout period of 1 wk, the protocol was repeated with anakinra (100 mg/d) subcutaneously. Six patients underwent a second baseline scan on the same day to assess reproducibility of PTF and TBF measurements. Volumes of interest were drawn over liver metastases and aorta. PTF and TBF were calculated using the standard single-tissue-compartment model.

RESULTS

Imatinib administration during 6-7 d increased PTF from 0.62 ± 0.12 to 0.69 ± 0.13, compared with baseline and day 2 (P = 0.02, Wilcoxon test). No significant changes were found in TBF. PTF values were no longer significantly different from baseline 1 wk after the last imatinib dosage. Anakinra induced no significant change in PTF or TBF. The repeatability coefficients of PTF and TBF in liver lesions were 22% and 28%, respectively.

CONCLUSION

Imatinib increases PTF of colorectal cancer metastases in patients and hence may increase the delivery of antitumor drugs. (15)O-water PET/CT and kinetic modeling provide insights into the microenvironment of human cancers.

Quantitative p retreatment VOI analysis of liver metastases. (99m)Tc-MAA SPECT/CT and FDG PET/CT in relation with treatment response to SIRT

Using quantitive VOI analysis, the percentage (99m)Tc-MAA uptake and SUVmax and mean values of liver metastases obtained prior to SIRT were related to treatment response using both a lesion-based and clinical dichotomous approach. Based on the VOI % of (99m)Tc-MAA activity, the estimated (90)Y-microspheres activity/cc (MBq/cc) was calculated from the effective dose injected. Baseline VOI FDG PET SUVmean and max values and estimated MBq/cc values were related to treatment response using a lesion-based approach (% change in SUVmean ≥  50%) and a clinical dichotomous approach. Fifteen treatment sessions were analyzed (13 patients). Using the lesion-based approach (12 treatment sessions) 40 lesions responded and 37 did not. SUVmax and mean values proved significantly different between non-responding and responding lesions; 18.6 (SD 10.8) versus 13.5 (SD 8.4 ) for SUVmax (p = 0.02) and 11.4 (SD 3.8) versus 6.3 (SD 4.5) for SUVmean (p = 0.002). Using the clinical dichotomous approach (15 treatment sessions / 11 responding), 91 lesions were analyzed; 57 responded. VOI volumes and estimated (90)Y-loaded glass microspheres activity (MBq/cc) did not differ between responders and non responders; 24 cc (SD 27) versus 21 cc (SD 21 cc) (p = 0.4) and 1.95 MBq/cc (SD 1.1 MBq/cc) versus 1.90 MB/cc (SD 2.7 MBq/cc) (p = 0.92). On the contrary, SUVmax and mean values proved significantly different between responders and non-responders; 23.7 (SD 9.8) versus 9.4 (SD 3.8 ) for SUVmax (p = 0.0001) and 13.1 (SD 8.1) versus 4.9 (SD 1.4) for SUVmean.

CONCLUSION

These findings suggest that in patients presenting with high baseline SUVmax and mean values, the administration of higher activities or alternatively, other potentially more useful treatment options might be considered.

Investigating tumor perfusion and metabolism using multiple hyperpolarized (13)C compounds: HP001, pyruvate and urea

The metabolically inactive hyperpolarized agents HP001 (bis-1,1-(hydroxymethyl)-[1-(13)C]cyclopropane-d(8)) and urea enable a new type of perfusion magnetic resonance imaging based on a direct signal source that is background-free. The addition of perfusion information to metabolic information obtained by spectroscopic imaging of hyperpolarized [1-(13)C]pyruvate would be of great value in exploring the relationship between perfusion and metabolism in cancer. In preclinical normal murine and cancer model studies, we performed both dynamic multislice imaging of the specialized hyperpolarized perfusion compound HP001 (T(1)=95 s ex vivo, 32 s in vivo at 3 T) using a pulse sequence with balanced steady-state free precession and ramped flip angle over time for efficient utilization of the hyperpolarized magnetization and three-dimensional echo-planar spectroscopic imaging of urea copolarized with [1-(13)C]pyruvate, with compressed sensing for resolution enhancement. For the dynamic data, peak signal maps and blood flow maps derived from perfusion modeling were generated. The spatial heterogeneity of perfusion was increased 2.9-fold in tumor tissues (P=.05), and slower washout was observed in the dynamic data. The results of separate dynamic HP001 imaging and copolarized pyruvate/urea imaging were compared. A strong and significant correlation (R=0.73, P=.02) detected between the urea and HP001 data confirmed the value of copolarizing urea with pyruvate for simultaneous assessment of perfusion and metabolism.

Clinical applications of positron emission tomography in hepatic tumors

Fluorodeoxyglucose (FDG), which allows the evaluation of glucose metabolism, is widely used for tumor diagnosis using positron emission tomography (PET). FDG-PET, which is used for the diagnosis of intrahepatic tumor lesions, shows high FDG accumulation in cholangiocellular carcinoma (CCC) and metastatic liver cancer. FDG-PET shows high FDG accumulation in moderately or poorly differentiated hepatocellular carcinoma (HCC) and is useful for the diagnosis of extrahepatic HCC metastases and recurrences. However, because the imaging method frequently shows low FDG accumulation in well-differentiated HCC, it is not very useful for that diagnosis. For the diagnosis of well-differentiated HCC, F-18 fluorocholine for evaluation of phospholipid metabolism and C-11 acetate for evaluation of free fatty acid metabolism are useful in the diagnosis of that HCC. It is expected that the combination of these PET agents will enhance the diagnostic performance of FDG-PET for HCC in the future. The problem of a lack of anatomical information is being resolved with the development of the use of PET in combination with computed tomography or magnetic resonance imaging. For the problem of low resolution, PET devices using semiconductors have been developed.

Demonstrating Intertumoural Differences in Vascular-Metabolic Phenotype with Dynamic Contrast-Enhanced CT-PET

Purpose. To assess whether the differences in vascular-metabolic relationships between lymphoma masses and colorectal liver metastases predicted from previous histopathological studies can be demonstrated by dynamic contrast-enhanced CT (DCE-CT) combined with fluorodeoxyglucose positron emission tomography (FDG-PET). Methods. DCE-CT and FDG-PET studies were drawn from an imaging archive for patients with either lymphoma masses (n = 11) or hepatic metastases from colorectal cancer (CRM: n = 12). Tumour vascularity was assessed using DCE-CT measurements of perfusion. Tumour glucose metabolism was expressed as the mean FDG Standardised Uptake Value (SUV_FDG). The relationship between metabolism and vascularity in each group was assessed from SUV_FDG /perfusion ratios and Pearson correlation coefficients. Results. An SUV_FDG threshold of 3.0 was used to designate lymphoma masses as active (AL, n = 6) or inactive lymphoma (IL, n = 5). Tumour perfusion was significantly higher in AL (0.65 mL/min/mL) than CRM (0.37 mL/min/mL: P = .031) despite similar SUV_FDG (5.05 and 5.33, resp.). AL demonstrated higher perfusion values than IL (0.24 mL/min/mL: P = .006). SUV_FDG/perfusion was significantly higher in CRM (15.3 min) than IL (4.2 min, P < .01). There was no correlation between SUV_FDG and perfusion for any patient group.

Use of H2(15)O-PET and DCE-MRI to measure tumor blood flow

Positron emission tomography (PET) with H2(15)O and dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) provide noninvasive measurements of tumor blood flow. Both tools offer the ability to monitor the direct target of antiangiogenic treatment, and their use is increasingly being studied in trials evaluating such drugs. Antiangiogenic therapy offers great potential and, to an increasing extent, benefit for oncological patients in a variety of palliative and curative settings. Because this type of targeted therapy frequently results in consolidation of the tumor mass instead of regression, monitoring treatment response with the standard volumetric approach (Response Evaluation Criteria in Solid Tumors) leads to underestimation of the response rate. Monitoring direct targets of anticancer therapy might be superior to indirect size changes. In addition, measures of tumor blood flow contribute to a better understanding of tumor biology. This review shows that DCE-MRI and H2(15)O-PET provide reliable measures of tumor perfusion, provided that a certain level of standardization is applied. Heterogeneity in scan acquisition and data analysis complicates the interpretation of study results. Also, limitations inherent to both techniques must be considered when interpreting DCE-MRI and H2(15)O-PET results. This review focuses on the technical and physiological aspects of both techniques and aims to provide the essential information necessary to critically evaluate the use of DCE-MRI and H2(15)O-PET in an oncological setting.

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.

Hypoxia positron emission tomography imaging with 18f-fluoromisonidazole

The importance of hypoxia in disease pathogenesis and prognosis is gathering increasing clinical significance and having a greater impact on patient management and outcome. Previous efforts to evaluate hypoxia have included the invasive assessment of hypoxia with immunohistologic and histographic oxygen probes. The emergence of new radiotracers has allowed noninvasive assessment of hypoxia, with the most extensively investigated and validated positron emission tomography radiotracer of hypoxia to date being (18)F-fluoromisonodazole ((18)F-FMISO). This review discusses the relevance and biology of hypoxia in cells and organ systems, and reviews the laboratory and clinical applications of (18)F-FMISO in oncology and noncancer disease states.

Inverse correlation between tumor perfusion and glucose uptake in human head and neck tumors

RATIONALE AND OBJECTIVES

We sought to determine the relationship between tumor blood flow and glucose uptake in head and neck tumors using perfusion computed tomography (PCT) and fluorine-18-fluorodeoxyglucose (FDG) positron emission tomography (PET).

MATERIALS AND METHODS

Institutional review board approval and informed consent were obtained for this study. Sixteen patients (mean age, 67 years; age range, 36-89 years) who had known or suspected head and neck tumors (15 malignant tumors and one schwannoma) underwent PCT and FDG PET examinations. Tumor area was measured on conventional CT images. The PCT data were postprocessed using maximum slope method analysis, and standardized uptake value (SUV) was measured on FDG PET.

RESULTS

Mean arterial perfusion of the tumors was 61.56 mL/min/100 mL (range 22.17-102.7 mL/min/100 mL), and mean FDG SUV was 7.48 (range 2.74-17.1). A significant negative correlation between arterial perfusion and FDG SUV was found for malignant tumors (r = -0.538, P = .04, n = 15).

CONCLUSION

There was an inverse relationship between arterial perfusion and glucose uptake of head and neck malignant tumors, suggesting that the malignant tumors may depend on anaerobic glycolysis.

Correlation between hepatic tumor blood flow and glucose utilization in a rabbit liver tumor model

PURPOSE

To prospectively determine the relationship between hepatic tumor blood flow and glucose utilization in vivo by using a combined positron emission tomographic (PET)/computed tomographic (CT) scanner.

MATERIALS AND METHODS

The animal care and use subcommittee at the University of Western Ontario approved this study. VX2 carcinoma cells were implanted in the livers of eight male New Zealand white rabbits. Functional CT was performed before tumor implantation and every 4 days thereafter. Each examination consisted of two phases: In the first phase, 30-second cine breath-hold scanning was performed with simultaneous injection of 5 mL of contrast material. In the second phase, 4-second cine scanning was performed without breath holding every 10 seconds for 2 minutes. Second-phase CT images were coregistered with first-phase images to eliminate breathing artifacts. The weighted summation of the aortic and portal venous time-attenuation curves was deconvolved against curves from the liver to derive hepatic blood flow (HBF). Five animals underwent fluorine 18 fluorodeoxyglucose (FDG) scanning before and every 8 days after implantation. FDG uptake was measured as standardized uptake value (SUV). Data were analyzed with repeated-measures analysis of variance and the Tukey-Kramer multiple comparison test. Linear regression was used to compare SUV and HBF in tumors and normal tissue.

RESULTS

In the hypovascular tumor core, (a) mean HBF decreased from 262 mL.min-1.100 g-1+/-22 (standard deviation) at baseline to 101 mL.min-1.100 g-1+/-62 at the end of the study (P<.05) and (b) mean SUV increased from 2.12 g/mL+/-0.06 to 4.56 g/mL+/-0.73 (P<.05) during the same period.

CONCLUSION

Functional CT in combination with FDG PET can be used to observe changes in HBF and glucose utilization in a growing liver tumor.