Mark Lubberink

Rapid Decrease in Delivery of Chemotherapy to Tumors after Anti-VEGF Therapy: Implications for Scheduling of Anti-Angiogenic Drugs

Current strategies combining anti-angiogenic drugs with chemotherapy provide clinical benefit in cancer patients. It is assumed that anti-angiogenic drugs, such as bevacizumab, transiently normalize abnormal tumor vasculature and contribute to improved delivery of subsequent chemotherapy. To investigate this concept, a study was performed in non-small cell lung cancer (NSCLC) patients using positron emission tomography (PET) and radiolabeled docetaxel ([(11)C]docetaxel). In NSCLC, bevacizumab reduced both perfusion and net influx rate of [(11)C]docetaxel within 5 hr. These effects persisted after 4 days. The clinical relevance of these findings is notable, as there was no evidence for a substantial improvement in drug delivery to tumors. These findings highlight the importance of drug scheduling and advocate further studies to optimize scheduling of anti-angiogenic drugs.

Altered Myocardial Substrate Metabolism and Decreased Diastolic Function in Nonischemic Human Diabetic Cardiomyopathy Studies With Cardiac Positron Emission Tomography and Magnetic Resonance Imaging

OBJECTIVES This study was designed to evaluate myocardial substrate and high-energy phosphate (HEP) metabolism in asymptomatic men with well-controlled, uncomplicated type 2 diabetes with verified absence of cardiac ischemia, and age-matched control subjects, and to assess the association with myocardial function. BACKGROUND Metabolic abnormalities, particularly an excessive exposure of the heart to circulating nonesterified fatty acids and myocardial insulin resistance are considered important contributors to diabetic cardiomyopathy in animal models of diabetes. The existence of myocardial metabolic derangements in uncomplicated human type 2 diabetes and their possible contribution to myocardial dysfunction still remain undetermined. METHODS In 78 insulin-naive type 2 diabetes men (age 56.5 +/- 5.6 years, body mass index 28.7 +/- 3.5 kg/m(2), glycosylated hemoglobin A(1c) 7.1 +/- 1.0%; expressed as mean +/- SD) without cardiac ischemia and 24 normoglycemic control subjects (age 54.5 +/- 7.1 years, body mass index 27.0 +/- 2.5 kg/m(2), glycosylated hemoglobin A(1c) 5.3 +/- 0.2%), we assessed myocardial left ventricular (LV) function by magnetic resonance imaging, and myocardial perfusion and substrate metabolism by positron emission tomography using H(2)(15)O, carbon (11)C-palmitate, and 18-fluorodeoxyglucose 2-fluoro-2-deoxy-D-glucose. Cardiac HEP metabolism was assessed by phosphorous P 31 magnetic resonance spectroscopy. RESULTS In patients, compared with control subjects, LV diastolic function (E/A ratio: 1.04 +/- 0.25 vs. 1.26 +/- 0.36, p = 0.003) and myocardial glucose uptake (260 +/- 128 nmol/ml/min vs. 348 +/- 154 nmol/ml/min, p = 0.015) were decreased, whereas myocardial nonesterified fatty acid uptake (88 +/- 31 nmol/ml/min vs. 68 +/- 18 nmol/ml/min, p = 0.021) and oxidation (85 +/- 30 nmol/ml/min vs. 63 +/- 19 nmol/ml/min, p = 0.007) were increased. There were no differences in myocardial HEP metabolism or perfusion. No association was found between LV diastolic function and cardiac substrate or HEP metabolism. CONCLUSIONS Patients versus control subjects showed impaired LV diastolic function and altered myocardial substrate metabolism, but unchanged HEP metabolism. We found no direct relation between cardiac diastolic function and parameters of myocardial metabolism.

Pioglitazone Improves Cardiac Function and Alters Myocardial Substrate Metabolism Without Affecting Cardiac Triglyceride Accumulation and High-Energy Phosphate Metabolism in Patients With Well-Controlled Type 2 Diabetes Mellitus

Background— Cardiac disease is the leading cause of mortality in type 2 diabetes mellitus (T2DM). Pioglitazone has been associated with improved cardiac outcome but also with an elevated risk of heart failure. We determined the effects of pioglitazone on myocardial function in relation to cardiac high-energy phosphate, glucose, and fatty acid metabolism and triglyceride content in T2DM patients. Methods and Results— Seventy-eight T2DM men without structural heart disease or inducible ischemia as assessed by dobutamine stress echocardiography were assigned to pioglitazone (30 mg/d) or metformin (2000 mg/d) and matching placebo for 24 weeks. The primary end point was change in cardiac diastolic function from baseline relative to myocardial metabolic changes, measured by magnetic resonance imaging, proton and phosphorus magnetic resonance spectroscopy, and [18F]-2-fluoro-2-deoxy-d-glucose and [11C]palmitate positron emission tomography. No patient developed heart failure. Both therapies similarly improved glycemic control, whole-body insulin sensitivity, and blood pressure. Pioglitazone versus metformin improved the early peak flow rate (P=0.047) and left ventricular compliance. Pioglitazone versus metformin increased myocardial glucose uptake (P<0.001), but pioglitazone-related diastolic improvement was not associated with changes in myocardial substrate metabolism. Metformin did not affect myocardial function but decreased cardiac work relative to pioglitazone (P=0.006), a change that was paralleled by a reduced myocardial glucose uptake and fatty acid oxidation. Neither treatment affected cardiac high-energy phosphate metabolism or triglyceride content. Only pioglitazone reduced hepatic triglyceride content (P<0.001). Conclusions— In T2DM patients, pioglitazone was associated with improvement in some measures of left ventricular diastolic function, myocardial glucose uptake, and whole-body insulin sensitivity. The functional changes, however, were not associated with myocardial substrate and high-energy phosphate metabolism.

Blood–brain barrier P-glycoprotein function in Alzheimer's disease

A major pathological hallmark of Alzheimers disease is accumulation of amyloid-β in senile plaques in the brain. Evidence is accumulating that decreased clearance of amyloid-β from the brain may lead to these elevated amyloid-β levels. One of the clearance pathways of amyloid-β is transport across the blood-brain barrier via efflux transporters. P-glycoprotein, an efflux pump highly expressed at the endothelial cells of the blood-brain barrier, has been shown to transport amyloid-β. P-glycoprotein function can be assessed in vivo using (R)-[(11)C]verapamil and positron emission tomography. The aim of this study was to assess blood-brain barrier P-glycoprotein function in patients with Alzheimers disease compared with age-matched healthy controls using (R)-[(11)C]verapamil and positron emission tomography. In 13 patients with Alzheimers disease (age 65 ± 7 years, Mini-Mental State Examination 23 ± 3), global (R)-[(11)C]verapamil binding potential values were increased significantly (P = 0.001) compared with 14 healthy controls (aged 62 ± 4 years, Mini-Mental State Examination 30 ± 1). Global (R)-[(11)C]verapamil binding potential values were 2.18 ± 0.25 for patients with Alzheimers disease and 1.77 ± 0.41 for healthy controls. In patients with Alzheimers disease, higher (R)-[(11)C]verapamil binding potential values were found for frontal, parietal, temporal and occipital cortices, and posterior and anterior cingulate. No significant differences between groups were found for medial temporal lobe and cerebellum. These data show altered kinetics of (R)-[(11)C]verapamil in Alzheimers disease, similar to alterations seen in studies where P-glycoprotein is blocked by a pharmacological agent. As such, these data indicate that P-glycoprotein function is decreased in patients with Alzheimers disease. This is the first direct evidence that the P-glycoprotein transporter at the blood-brain barrier is compromised in sporadic Alzheimers disease and suggests that decreased P-glycoprotein function may be involved in the pathogenesis of Alzheimers disease.

Effect of age on functional P‐glycoprotein in the blood‐brain barrier measured by use of (R)‐[11C]verapamil and positron emission tomography

P‐glycoprotein (P‐gp) is an efflux transporter responsible for the transport of various drugs across the blood‐brain barrier (BBB). Loss of P‐gp function with age may be one factor in the development and progression of neurodegenerative diseases. The aim of this study was to assess the effect of aging on BBB P‐gp function. Furthermore, the relationship between BBB P‐gp activity and peripheral P‐gp activity in CD3‐positive leukocytes was investigated. Finally, plasma pharmacokinetics of carbon 11–labeled (R)‐verapamil was evaluated.

In Vivo Visualization of Amyloid Deposits in the Heart with 11C-PIB and PET

Cardiac amyloidosis is a differential diagnosis in heart failure and is associated with high mortality. There is currently no noninvasive imaging test available for specific diagnosis. N-[methyl-11C]2-(4′-methylamino-phenyl)-6-hydroxybenzothiazole (11C-PIB) PET is used in the evaluation of brain amyloidosis. We evaluated the potential use of 11C-PIB PET in systemic amyloidosis affecting the heart. Methods: Patients (n = 10) diagnosed with systemic amyloidosis—including heart involvement of either monoclonal immunoglobulin light-chain (AL) or transthyretin (ATTR) type—and healthy volunteers (n = 5) were investigated with PET/CT using 11C-PIB to study cardiac amyloid deposits and with 11C-acetate to measure myocardial blood flow to study the impact of global and regional perfusion on PIB retention. Results: Myocardial 11C-PIB uptake was visually evident in all patients 15–25 min after injection and was not seen in any volunteer. A significant difference in 11C-PIB retention in the heart between patients and healthy controls was found. The data indicate that myocardial amyloid deposits in patients diagnosed with systemic amyloidosis could be visualized with 11C-PIB. No correlation between 11C-PIB retention index and myocardial blood flow as measured with 11C-acetate was found on the global level, whereas a positive correlation on the segmental level was seen in a single patient. Conclusion: 11C-PIB and PET could be a method to study systemic amyloidosis of type AL and ATTR affecting the heart and should be investigated further both as a diagnostic tool and as a noninvasive method for treatment follow-up.

First-in-Human Molecular Imaging of HER2 Expression in Breast Cancer Metastases Using the 111In-ABY-025 Affibody Molecule

The expression status of human epidermal growth factor receptor type 2 (HER2) predicts the response of HER2-targeted therapy in breast cancer. ABY-025 is a small reengineered Affibody molecule targeting a unique epitope of the HER2 receptor, not occupied by current therapeutic agents. This study evaluated the distribution, safety, dosimetry, and efficacy of 111In-ABY-025 for determining the HER2 status in metastatic breast cancer. Methods: Seven patients with metastatic breast cancer and HER2-positive (n = 5) or -negative (n = 2) primary tumors received an intravenous injection of approximately 100 μg (∼140 MBq) of 111In-ABY-025. Planar γ-camera imaging was performed after 30 min, followed by SPECT/CT after 4, 24, and 48 h. Blood levels of radioactivity, antibodies, shed serum HER2, and toxicity markers were evaluated. Lesional HER2 status was verified by biopsies. The metastases were located by 18F-FDG PET/CT 5 d before 111In-ABY-025 imaging. Results: Injection of 111In-ABY-025 yielded a mean effective dose of 0.15 mSv/MBq and was safe, well tolerated, and without drug-related adverse events. Fast blood clearance allowed high-contrast HER2 images within 4–24 h. No anti–ABY-025 antibodies were observed. When metastatic uptake at 24 h was normalized to uptake at 4 h, the ratio increased in HER2-positive metastases and decreased in negative ones (P < 0.05), with no overlap and confirmation by biopsies. In 1 patient, with HER2-positive primary tumor, 111In-ABY-025 imaging correctly suggested a HER2-negative status of the metastases. The highest normal-tissue uptake was in the kidneys, followed by the liver and spleen. Conclusion: 111In-ABY-025 appears safe for use in humans and is a promising noninvasive tool for discriminating HER2 status in metastatic breast cancer, regardless of ongoing HER2-targeted antibody treatment.

Hybrid Imaging Using Quantitative H215O PET and CT-Based Coronary Angiography for the Detection of Coronary Artery Disease

Hybrid imaging using PET in conjunction with CT-based coronary angiography (PET/CTCA) enables near-simultaneous quantification of myocardial blood flow (MBF) and anatomical evaluation of coronary arteries. CTCA is an excellent imaging modality to rule out obstructive coronary artery disease (CAD), but functional assessment is warranted in the presence of a CTCA-observed stenosis because the specificity of CTCA is relatively low. Quantitative H215O PET/CTCA may yield complementary information and enhance diagnostic accuracy. The purpose of this study was to evaluate the diagnostic accuracy of quantitative H215O PET/CTCA in a clinical cohort of patients with suspected CAD who underwent both cardiac H215O PET/CTCA and invasive coronary angiography (ICA). In addition, this study aimed to evaluate and compare the accuracy of hyperemic MBF versus coronary flow reserve (CFR). Methods: Patients (n = 120; mean age ± SD, 61 ± 10 y; 77 men and 43 women) with a predominantly intermediate pretest likelihood for CAD underwent both quantitative H215O PET/CTCA and ICA. A ≥50% stenosis at ICA or a fractional flow reserve ≤ 0.80 was considered significant. Results: Obstructive CAD was diagnosed in 49 of 120 patients (41%). The diagnostic accuracy of hyperemic MBF was significantly higher than CFR (80% vs. 68%, respectively, P = 0.02), with optimal cutoff values of 1.86 mL/min/g and 2.30, respectively. On a per-patient basis, the sensitivity, specificity, negative predictive value, and positive predictive value of CTCA were 100%, 34%, 100%, and 51%, respectively, as compared with 76%, 83%, 83%, and 76%, respectively, for quantitative hyperemic MBF PET. Quantitative H215O PET/CTCA reduced the number of false-positive CTCA studies from 47 to 6, although 12 of 49 true-positive CTCAs were incorrectly reclassified as false-negative hybrid scans on the basis of (presumably) sufficient hyperemic MBF. Compared with CTCA (61%) or H215O PET (80%) alone (both P < 0.05), the hybrid approach significantly improved diagnostic accuracy (85%). Conclusion: The diagnostic accuracy of quantitative H215O PET/CTCA is superior to either H215O PET or CTCA alone for the detection of clinically significant CAD. Hyperemic MBF was more accurate than CFR, implying that a single measurement of MBF in diagnostic protocols may suffice.

Evaluation of Tracer Kinetic Models for Quantification of P-Glycoprotein Function using (R)-[11C]Verapamil and PET

Diminished P-glycoprotein (P-gp)-mediated transport across the Blood–brain barrier may play an important role in several neurodegenerative disorders. In previous studies, a racemic mixture of (R)-[11C]verapamil and (S)-[11C]verapamil has been used as tracer for assessing P-gp function using positron emission tomography (PET). Quantification, however, is compromised by potential differences in kinetics between these two isomers. The aim of the present study was to evaluate the kinetics of pure (R)-[11C]verapamil in humans and to develop a tracer kinetic model for the analysis of P-gp-mediated transport of (R)-[11C]verapamil, including the putative contribution of its radioactive metabolites. Dynamic (R)-[11C]verapamil PET scans of 10 male volunteers were analysed with various single- or two-tissue compartment models, with separate compartments for N-dealkylated and N-demethylated metabolites, assuming that either (R)-[11C]verapamil alone or (R)-[11C]verapamil and any combination of metabolites cross the BBB. In addition, six of the subjects underwent two (R)-[11C]verapamil scans to evaluate test–retest reliability. One hour after injection, 50% of total plasma radioactivity consisted of labelled metabolites. Most models fitted the data well and the analysis did not point to a definite ‘best’ model, with differences in optimal model between subjects. The lowest mean test–retest variability (2.9%) was found for a single-tissue model without any metabolite correction. Models with separate metabolite compartments lead to high test–retest variability. Assuming that differences in kinetics of (R)-[11C]verapamil and N-dealkylated metabolites are small, a one input, one-tissue model with correction for N-demethylated metabolites only leads to a good compromise between fit quality and test–retest variability.

Effects of Hepatic Triglyceride Content on Myocardial Metabolism in Type 2 Diabetes

OBJECTIVES The purpose of this study was to investigate the relationship between hepatic triglyceride content and both myocardial function and metabolism in type 2 diabetes mellitus (T2DM). BACKGROUND Heart disease is the leading cause of mortality in T2DM. Central obesity and hepatic steatosis, both hallmark abnormalities in T2DM, have been related to increased risk of heart disease. METHODS Sixty-one T2DM patients underwent myocardial perfusion and substrate metabolism measurements by positron emission tomography, using [15O]water, [11C]palmitate, and [18F]-2-fluoro-2-deoxy-D-glucose. In addition, whole-body insulin sensitivity (M/I) was determined. Myocardial left ventricular function and high-energy phosphate metabolism were measured using magnetic resonance imaging and [31P]-magnetic resonance spectroscopy, respectively. Hepatic triglyceride content was measured by proton magnetic resonance spectroscopy. Patients were divided according to hepatic triglyceride content (T2DM-low<or=5.56% vs. T2DM-high>5.56%). RESULTS In addition to decreased M/I (p=0.002), T2DM-high patients had reduced myocardial perfusion (p=0.001), glucose uptake (p=0.005), and phosphocreatine/adenosine triphosphate (PCr/ATP) ratio (p=0.003), compared with T2DM-low patients, whereas cardiac fatty acid metabolism and left ventricular function were not different. Hepatic triglyceride content correlated inversely with M/I (Pearsons r=-0.620, p<0.001), myocardial glucose uptake (r=-0.413, p=0.001), and PCr/ATP (r=-0.442, p=0.027). Insulin sensitivity correlated positively with myocardial glucose uptake (r=0.528, p<0.001) and borderline with myocardial PCr/ATP (r=0.367, p=0.072), whereas a positive association was found between cardiac glucose uptake and PCr/ATP (r=0.481, p=0.015). CONCLUSIONS High liver triglyceride content in T2DM was associated with decreased myocardial perfusion, glucose uptake, and high-energy phosphate metabolism in conjunction with impaired M/I. The long-term clinical implications of hepatic steatosis with respect to cardiac metabolism and function in the course of T2DM require further study.