Mitochondrial localization and characterization of 99Tc-SESTAMIBI in heart cells by electron probe X-ray microanalysis and 99Tc-NMR spectroscopy

Technetium Complexes with an Isocyano-alkyne Ligand and Its Reaction Products

The attachment of an ethyne substituent in the para position of phenylisocyanide, CNPh^pC≡CH, enables the isocyanide to replace carbonyl ligands in the coordination sphere of common technetium(I) starting materials such as (NBu₄)[Tc₂(μ-Cl)₃(CO)₆]. The ligand exchange proceeds under thermal conditions and finally forms the corresponding hexakis(isocyanide)technetium(I) complex. The product undergoes a copper-catalyzed cycloaddition ("Click" reaction), e.g., with benzyl azide, which gives the [Tc(CNPh^azole)₆]⁺ cation. The free, uncoordinated "Click" product is obtained from a reaction of the corresponding tetrakis(CNPh^azole)copper(I) complex and NaCN. It readily reacts with mer-[Tc(CO)₃(tht)(PPh₃)₂](BF₄) (tht = tetrahydrothiophene) under exchange of the thioether ligand. Alternatively, [Cu(CNPh^azole)₄]⁺ can be used as a transmetalation reagent for the synthesis of the hexakis(isocyanide)technetium(I) complex, which is the preferable approach for the synthesis of the technetium complex with the short-lived nuclear isomer ^99mTc, and a corresponding protocol for [^99mTc(CNPh^azole)₆]⁺ is reported. The ⁹⁹Tc and copper complexes have been studied by single-crystal X-ray diffraction and/or spectroscopic methods including IR and multinuclear NMR spectroscopy.

Selective venous sampling in primary hyperparathyroidism caused by ectopic parathyroid gland: a case report and literature review

BACKGROUND

As an invasive technique, selective venous sampling (SVS) is considered a useful method to identify a lesion's location to increase the success rate of secondary surgery in patients with primary hyperparathyroidism (pHPT) caused by ectopic parathyroid adenomas.

CASE PRESENTATION

We present a case of post-surgical persistent hypercalcemia and elevated parathyroid hormone (PTH) levels in a 44-year-old woman with previously undetected parathyroid adenoma. An SVS was then performed for further localization of the adenoma, as other non-invasive methods showed negative results. After SVS, an ectopic adenoma was suspected in the sheath of the left carotid artery, previously considered as a schwannoma, and was pathologically confirmed after the second operation. Postoperatively, the patient's symptoms disappeared and serum levels of PTH and calcium normalized.

CONCLUSIONS

SVS can provide precise diagnosis and accurate positioning before re-operation in patients with pHPT.

Shining Damaged Hearts: Immunotherapy-Related Cardiotoxicity in the Spotlight of Nuclear Cardiology

The emerging use of immunotherapies in cancer treatment increases the risk of immunotherapy-related cardiotoxicity. In contrast to conventional chemotherapy, these novel therapies have expanded the forms and presentations of cardiovascular damage to a broad spectrum from asymptomatic changes to fulminant short- and long-term complications in terms of cardiomyopathy, arrythmia, and vascular disease. In cancer patients and, particularly, cancer patients undergoing (immune-)therapy, cardio-oncological monitoring is a complex interplay between pretherapeutic risk assessment, identification of impending cardiotoxicity, and post-therapeutic surveillance. For these purposes, the cardio-oncologist can revert to a broad spectrum of nuclear cardiological diagnostic workup. The most promising commonly used nuclear medicine imaging techniques in relation to immunotherapy will be discussed in this review article with a special focus on the continuous development of highly specific molecular markers and steadily improving methods of image generation. The review closes with an outlook on possible new developments of molecular imaging and advanced image evaluation techniques in this exciting and increasingly growing field of immunotherapy-related cardiotoxicity.

Quantitative dual isotope 123iodine/99mTc-MIBI scintigraphy: A new approach to rule out malignancy in thyroid nodules

BACKGROUND

The aim of this study was to evaluate the role of dual isotope ¹²³Iodine/^99mTc-MIBI thyroid scintigraphy (IMS) in discriminating between malignant and benign lesions in indeterminate nodules using quantitative analysis methods.

METHODS

Thirty-five consecutive patients with thyroid nodules of indeterminate or non-diagnostic cytology and cold on ¹²³Iodine scintigraphy (10 Bethesda I, 24 Bethesda III-IV, 1 in which cytology was impossible) underwent IMS between 2017 and 2019 with uptake quantification at two time points ahead of thyroidectomy: early and late. Images were analyzed by two blinded physicians.

RESULTS

Twelve nodules were malignant and 23 benign on histopathology. Mean uptake values were lower in benign than in malignant nodules at both time points: early, 8.7±4.1 versus 12.9±3.5 (P=0.005); and late, 5.3±2.7 versus 7.7±1.1 (P=0.008). Interobserver reproducibility was excellent. The intraclass correlation coefficient was 0.86 in benign and 0.92 in malignant lesions for early uptake result (ER) and 0.94 and 0.85 respectively for late uptake result (LR). The optimal LR cut-off  to exclude a diagnosis of malignancy was set at 5.9 . The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of this cut-off were, respectively, 100%, 65.2%, 60%, 100% and 77.1%.

CONCLUSION

Despite some study limitations, quantitative analysis of ^99mTc-MIBI thyroid scintigraphy had a good reproducibility, which could help to rule out malignancy in non-diagnostic or indeterminate thyroid nodules and thereby reducing the number of patients undergoing unnecessary surgery when LR is below 5.9.

2-methoxy-isobutyl-isonitrile-conjugated gold nanoparticles improves redox and inflammatory profile in infarcted rats

The tissue response to acute myocardial infarction (AMI) is key to avoiding heart complications due to inflammation, mitochondrial dysfunction, and oxidative stress. Antioxidant and anti-inflammatory agents can minimize the effects of AMI. This study investigated the role of 2-methoxy-isobutyl-isonitrile (MIBI)-associated gold nanoparticles (AuNP) on reperfusion injury after ischemia and its effect on cardiac remodeling in an experimental AMI model. Three-month-old Wistar rats were subjected to a temporary blockade of the anterior descending artery for 30 min followed by reperfusion after 24 h and 7 days by intraventricularly administering 0.4, 1.3, and 3 mg/kg AuNP-MIBI. The cardiac toxicity and renal and hepatic function levels were determined, and the infarct and peri-infarct regions were surgically removed for histopathology, analysis of inflammation from oxidative stress, and echocardiography. MIBI-conjugated AuNP promoted changes in oxidative stress and inflammation depending on the concentrations used, suggesting promising applicability for therapeutic purposes.

Mathematical Simulation of Transport Kinetics of Tumor-Imaging Radiopharmaceutical 99mTc-MIBI

The proposed model describes in a quality way the process of tumor-imaging radiopharmaceutical ^99mTc-MIBI distribution with taking into account radiopharmaceutical accumulation, elimination, and radioactive decay. The dependencies of concentration versus the time are analyzed. The model can be easily tested by the concentration data of the radioactive pharmaceuticals in the blood measured at early time point and late time point of the scanning, and the obtained data can be used for determination of the washout rate coefficient which is one of the existing oncology diagnostics methods.

(99m)Tc-Methoxy-Isobutyl-Isonitrile Scintigraphy Is a Useful Tool for Assessing the Risk of Malignancy in Thyroid Nodules with Indeterminate Fine-Needle Cytology

BACKGROUND

Thyroid nodular disease is a very common clinical problem. The diagnostic algorithm includes laboratory tests, thyroid ultrasound (US), thyroid scintigraphy, and, if necessary, US-guided fine-needle aspiration cytology. However, cytology results are reported as indeterminate in a not negligible number of patients. This is a central problem in the workup of patients, since about 55-85% of those undergoing surgery do not have thyroid cancer at final histology diagnosis. The aim of this study was to evaluate prospectively the role of (99m)Tc-methoxy-isobutyl-isonitrile ((99m)Tc-MIBI) thyroid scintigraphy in differentiating malignant from benign thyroid nodules with indeterminate cytology using quantitative analysis.

METHOD

One hundred five patients affected by nodular thyroid goiter and with a euthyroid or hypothyroid functional status were prospectively evaluated. All patients had a suspicious nodule ≥15 mm in maximal diameter on US. All nodules were "cold" on (99m)Tc-pertechnetate scintigraphy and had a cytological diagnosis of class III or IV according to the Bethesda system. Planar images of the thyroid were acquired 10 and 60 minutes after (99m)Tc-MIBI administration. All cold nodules were MIBI-positive. Using quantitative analysis, the MIBI washout index (WOind) was calculated as a percentage reduction value of mean MIBI nodular uptake between early (+10 minutes) and late (+60 minutes) scans.

RESULTS

Subdividing the patients into positive and negative for malignancy (either including or excluding patients with Hürthle cell adenoma) and performing receiver operating characterist curve analysis, the optimal WOind cutoff in differentiating malignant from benign follicular lesions was set at -19%. The overall sensitivity and specificity of (99m)Tc-MIBI quantitative analysis in identifying patients with malignant lesions was 100% and 90.9%, respectively. However, after excluding patients with Hürthle cell adenomas from the negative patient group, the overall sensitivity and specificity both reached 100%.

CONCLUSION

The use of MIBI scintigraphy using quantitative analysis in the workup of cold nodules with indeterminate cytology is suggested in order to stratify patient risk for a malignant lesion better, thus reducing the number of patients referred to surgery. Surgical treatment should be planned in those patients with a WOind up to -19%.

Mitochondrial Uptake of Sestamibi Distinguishes Between Normal, Inflammatory Breast Changes, Pre-Cancers, and Infiltrating Breast Cancer

The evaluation of breast tissue using nuclear imaging is dependent upon the delivery and uptake of the isotope by breast tissue. This is dependent upon blood flow to the breast and functioning mitochondria. This 2-part study investigated (1) differences in uptake of sestamibi when blood flow is enhanced (breast enhanced scintigraphy test [BEST]), and (2) differences in isotope uptake in normal (Nl) breast tissue, inflammatory changes in breast tissue (ICB), and breast cancer (CA). In the first part of the study, 10 women were compared using both Miraluma and BEST imaging; in the second part, 195 people were studied using BEST imaging only. The results were compared with histopathologic specimens. Little difference was noted between Miraluma and BEST imaging in the first part. Women with ICB showed a statistically significant ( P< .05) increase in isotope uptake using BEST imaging. This difference was even more significant ( P< .005) in women with CA. During the second part of the study, BEST imaging demonstrated an exponential increase in tracer uptake. When maximal count activity was compared, there was a statistically significant ( P<.001) difference between Nl and ICB, between ICB and atypia (A), and between A and CA. BEST imaging demonstrated significant increases in isotope delivery when compared with Miraluma imaging. These differences allowed differentiation of breast tissue, including the detection of early changes in breast tissue.

Old tracer for a new purpose: potential role for 99mTc-2-Methoxyisobutylisonitrile (99mTc-MIBI) in renal transplant care

AIM

Calcineurin inhibitors are substrates for P-glycoprotein (P-gp), the expression of which is associated with ABCB1 C3435T polymorphism. Individual P-gp response to calcineurin inhibitor may be linked to nephrotoxicity or rejection. Tc-2-Methoxyisobutylisonitrile (Tc-MIBI) is also a P-gp substrate. The aim of this study, therefore, was to determine Tc-MIBI organ kinetics and compare them with ABCB1 genotype with a view to replacing Tc-mercaptoacetyltriglycine (Tc-MAG3) with Tc-MIBI in renal transplant care.

METHODS

Thirty prospective donors (13 male) were imaged for 20 min after administration of Tc-MIBI (400 MBq) intravenously. Posterior images of the abdomen were acquired at 30 and 120 min. Organ 30 min/peak count rate ratios and exponential two-point (30-120 min) rate constants (k, min) were calculated. Nineteen donors were genotyped for C3435T (exon 26), G2677T (exon 21), C1236T (exon 12), and G1199A (exon 11) ABCB1 polymorphisms using a PCR-based technique.

RESULTS

Tc-MIBI and Tc-MAG3 gave similar perfusion images. Although their patterns of renal elimination were different, differential renal function was not significantly different. There was a negative trend between the hepatic 30 min/peak ratio and C3435T genotype (CC: 0.8374 ± 0.0502; TC: 0.6806 ± 0.1300; TT: 0.6919 ± 0.1506; P=0.083). Renal k showed a negative trend with C3435T (CC: 0.0021 ± 0.0020; TC: 0.0037 ± 0.0013; TT: 0.0040 ± 0.0012 min; P=0.087) but with no other genotypes. There were no significant sex-related differences in Tc-MIBI kinetics.

CONCLUSION

Tc-MIBI can replace Tc-MAG3 for pretransplant workup. The ABCB1 C3435T polymorphism may influence Tc-MIBI kinetics and thus have a role in renal transplant care. Further prospective trials are required to establish the full potential of Tc-MIBI in renal transplant management.

Characterization of the four isomers of (123)I-CMICE-013: a potential SPECT myocardial perfusion imaging agent

Myocardial perfusion imaging (MPI) with single photon emission computed tomography (SPECT) is widely used in the assessment of coronary artery disease (CAD). We have developed (123)I-CMICE-013 based on rotenone, a mitochondrial complex I (MC-1) inhibitor, as a promising new MPI agent. Our synthesis results in a mixture of four species of (123)I-CMICE-013 A, B, C, D. In this study, we separated the four species and evaluated their biodistribution and imaging properties. The cold analogs (127)I-CMICE-013 A, B, C, D were isolated and characterized and their chemical structures proposed.

METHODS

(123)I-CMICE-013 was synthesized by radiolabeling rotenone with Na(123)I in trifluoroacetic acid (TFA) with iodogen as the oxidizing agent at 60°C for 45min, and the four species were separated by RP-HPLC. The cold analogs (127)I-CMICE-013 A, B, C and D were isolated with a similar procedure and characterized by NMR and mass spectrometry. Biodistribution and microSPECT imaging studies were carried out on normal rats.

RESULTS

We propose the mechanism of the rotenone iodination and the structures of the four species. First, I(+) forms an intermediate three-membered ring with 6' and 7' carbons. Second, the lone electron pair of the water molecule attacks the 6' or 7'-carbon, following by the formation of 6'-OH, and 7'-I bonds as in major products C and D, or 6'-I and 7'-OH bonds as in minor products A and B. The weaker 6'-I bond in the intermediate prompts the nucleophilic attachment of water at the favorable 6'-carbon to generate C and D. MicroSPECT images of (123)I-CMICE-013 A, B, C, D in rats showed clear visualization of myocardium and little interference from lung and liver. The imaging time activity curves and biodistribution data showed complex profiles for the four isomers, which is not expected from the structure activity relationship theory.

CONCLUSION

(123/127)I-CMICE-013 A and B are constitutional isomers with C and D, while A and C are diastereomers of B and D, respectively. Overall, the biological characteristics of the four species are not correlated perfectly with their molecular structures.

Biological characterization of F-18-labeled rhodamine B, a potential positron emission tomography perfusion tracer

INTRODUCTION

Myocardial infarction is the leading cause of death in western countries, and positron emission tomography (PET) plays an increasing role in the diagnosis and treatment planning for this disease. However, the absence of an (18)F-labeled PET myocardial perfusion tracer hampers the widespread use of PET in myocardial perfusion imaging (MPI). We recently reported a potential MPI agent based on (18)F-labeled rhodamine B. The goal of this study was to more completely define the biological properties of (18)F-labeled rhodamine B with respect to uptake and localization in an animal model of myocardial infarction and to evaluate the uptake (18)F-labeled rhodamine B by cardiomyocytes.

METHODS

A total of 12 female Sprague Dawley rats with a permanent ligation of the left anterior descending artery (LAD) were studied with small-animal PET. The animals were injected with 100-150 μCi of (18)F-labeled rhodamine B diethylene glycol ester ([(18)F]RhoBDEGF) and imaged two days before ligation. The animals were imaged again two to ten days post-ligation. After the post-surgery scans, the animals were euthanized and the hearts were sectioned into 1mm slices and myocardial infarct size was determined by phosphorimaging and 2,3,5-triphenyltetrazolium chloride staining (TTC). In addition, the uptake of [(18)F]RhoBDEGF in isolated rat neonatal cardiomyocytes was determined by fluorescence microscopy.

RESULTS

Small-animal PET showed intense and uniform uptake of [(18)F]RhoBDEGF throughout the myocardium in healthy rats. After LAD ligation, well defined perfusion defects were observed in the PET images. The defect size was highly correlated with the infarct size as determined ex vivo by phosphorimaging and TTC staining. In vitro, [(18)F]RhoBDEGF was rapidly internalized into rat cardiomyocytes with ~40 % of the initial activity internalized within the 60 min incubation time. Fluorescence microscopy clearly demonstrated localization of [(18)F]RhoBDEGF in the mitochondria of rat cardiomyocytes.

CONCLUSION

Fluorine-18-labeled rhodamine B diethylene glycol ester ([(18)F]RhoBDEGF) provides excellent image quality and clear delineation of myocardial infarcts in a rat infarct model. In vitro studies demonstrate localization of the tracer in the mitochondria of cardiac myocytes. In combination, these results support the continued evaluation of this tracer for the PET assessment of myocardial perfusion.

Role of mitochondrial Ca2+ in the regulation of cellular energetics

Calcium is an important signaling molecule involved in the regulation of many cellular functions. The large free energy in the Ca(2+) ion membrane gradients makes Ca(2+) signaling inherently sensitive to the available cellular free energy, primarily in the form of ATP. In addition, Ca(2+) regulates many cellular ATP-consuming reactions such as muscle contraction, exocytosis, biosynthesis, and neuronal signaling. Thus, Ca(2+) becomes a logical candidate as a signaling molecule for modulating ATP hydrolysis and synthesis during changes in numerous forms of cellular work. Mitochondria are the primary source of aerobic energy production in mammalian cells and also maintain a large Ca(2+) gradient across their inner membrane, providing a signaling potential for this molecule. The demonstrated link between cytosolic and mitochondrial Ca(2+) concentrations, identification of transport mechanisms, and the proximity of mitochondria to Ca(2+) release sites further supports the notion that Ca(2+) can be an important signaling molecule in the energy metabolism interplay of the cytosol with the mitochondria. Here we review sites within the mitochondria where Ca(2+) plays a role in the regulation of ATP generation and potentially contributes to the orchestration of cellular metabolic homeostasis. Early work on isolated enzymes pointed to several matrix dehydrogenases that are stimulated by Ca(2+), which were confirmed in the intact mitochondrion as well as cellular and in vivo systems. However, studies in these intact systems suggested a more expansive influence of Ca(2+) on mitochondrial energy conversion. Numerous noninvasive approaches monitoring NADH, mitochondrial membrane potential, oxygen consumption, and workloads suggest significant effects of Ca(2+) on other elements of NADH generation as well as downstream elements of oxidative phosphorylation, including the F(1)F(O)-ATPase and the cytochrome chain. These other potential elements of Ca(2+) modification of mitochondrial energy conversion will be the focus of this review. Though most specific molecular mechanisms have yet to be elucidated, it is clear that Ca(2+) provides a balanced activation of mitochondrial energy metabolism that exceeds the alteration of dehydrogenases alone.

Myocardial uptake of 7'-(Z)-[(123)I]iodorotenone during vasodilator stress in dogs with critical coronary stenoses

BACKGROUND

There is a well-recognized need for a new generation of single photon emission computed tomography (SPECT) perfusion tracers with improved myocardial extraction over a wide flow range. Radiotracers that target complex I of the mitochondrial electron transport chain have been proposed as a new class of myocardial perfusion imaging agents. 7-(Z)-[(125)I]iodorotenone ((125)I-ZIROT) has demonstrated superior myocardial extraction and retention characteristics in rats and in isolated perfused rabbit hearts. We sought to fully characterize the biodistribution and myocardial extraction versus flow relationship of (123)I-ZIROT in an intact large-animal model.

METHODS AND RESULTS

The (123)I-ZIROT was administered during adenosine A(2A) agonist-induced hyperemia in 5 anesthetized dogs with critical left anterior descending (LAD) stenoses. When left circumflex (LCx) flow was maximal, (123)I-ZIROT and microspheres were coinjected and the dogs were euthanized 5 minutes later. (123)I-ZIROT biodistribution was evaluated in 2 additional dogs by in vivo planar imaging. At (123)I-ZIROT injection, transmural LAD flow was unchanged from baseline (mean±SEM, 0.90±0.22 versus 0.87±0.11 mL/[min · g]; P=0.92), whereas LCx zone flow increased significantly (mean±SEM, 3.25±0.51 versus 1.00±0.17 mL/[min · g]; P<0.05). Myocardial (123)I-ZIROT extraction tracked regional myocardial flow better than either thallium-201 or (99m)Tc-sestamibi from previous studies using a similar model. Furthermore, the (123)I-ZIROT LAD/LCx activity ratios by ex vivo imaging or well counting (mean±SEM, 0.42±0.08 and 0.45±0.1, respectively) only slightly underestimated the LAD/LCx microsphere flow ratio (0.32±0.09).

CONCLUSIONS

The ability of (123)I-ZIROT to more linearly track blood flow over a wide range makes it a promising new SPECT myocardial perfusion imaging agent with potential for improved coronary artery disease detection and better quantitative estimation of the severity of flow impairment.

PET imaging of cardiac hypoxia: opportunities and challenges

Myocardial hypoxia is a major factor in the pathology of cardiac ischemia and myocardial infarction. Hypoxia also occurs in microvascular disease and cardiac hypertrophy, and is thought to be a prime determinant of the progression to heart failure, as well as the driving force for compensatory angiogenesis. The non-invasive delineation and quantification of hypoxia in cardiac tissue therefore has the potential to be an invaluable experimental, diagnostic and prognostic biomarker for applications in cardiology. However, at this time there are no validated methodologies sufficiently sensitive or reliable for clinical use. PET imaging provides real-time spatial information on the biodistribution of injected radiolabeled tracer molecules. Its inherent high sensitivity allows quantitative imaging of these tracers, even when injected at sub-pharmacological (≥pM) concentrations, allowing the non-invasive investigation of biological systems without perturbing them. PET is therefore an attractive approach for the delineation and quantification of cardiac hypoxia and ischemia. In this review we discuss the key concepts which must be considered when imaging hypoxia in the heart. We summarize the PET tracers which are currently available, and we look forward to the next generation of hypoxia-specific PET imaging agents currently being developed. We describe their potential advantages and shortcomings compared to existing imaging approaches, and what is needed in terms of validation and characterization before these agents can be exploited clinically.

SPECT imaging for detecting coronary artery disease and determining prognosis by noninvasive assessment of myocardial perfusion and myocardial viability

Basic knowledge of active and passive transport mechanisms for concentrating monovalent cations in myocardial cells led to the investigation of the application of radioisotopes of potassium, thallium, rubidium, and ammonia to the in vivo noninvasive assessment of regional myocardial perfusion and viability utilizing gamma camera or positron emission tomographic (PET) imaging technology. Subsequently, technetium-99m (Tc-99m)-labeled isonitriles (sestamibi and tetrofosmin), which bind to mitochondrial membranes, emerged as superior imaging agents with single photon emission tomography (SPECT) imaging. When any of these imaging agents are injected intravenously during either exercise or pharmacologic stress, myocardial defects in tracer uptake represent either abnormal regional flow reserve or myocardial scar reflecting of coronary artery disease (CAD). The major clinical indications for stress SPECT or PET myocardial perfusion imaging are for detection of CAD as the cause of chest pain and risk stratification for prognostication. Patients with normal stress myocardial perfusion scans have an excellent prognosis with <1.0% annual rate future annual death or nonfatal infarction. The greater the extent and severity of ischemic perfusion defects (defects seen on stress images but improve on resting images), the greater the subsequent death or infarction rate during follow-up. Rest imaging alone is performed for determination of myocardial viability in patients with CAD and severe left ventricular dysfunction. Myocardial segments showing >50% uptake compared to normal uptake have a better long-term outcome with revascularization than with medical therapy with enhanced left ventricular function and improved survival. Other applications of SPECT imaging include the evaluation of cardiac sympathetic function, assessment of myocardial metabolism in health and disease, and molecular imaging of coronary atherosclerosis and myocardial stem cell therapy.

Effects of burn injury, cold stress and cutaneous wound injury on the morphology and energy metabolism of murine brown adipose tissue (BAT) in vivo

AIMS

Cold stress has been shown to produce dramatic increases in 2-fluoro-2-deoxy-D-Glucose ((18)FDG) accumulation by brown adipose tissue (BAT) in rodents. However, neither the effects of other types of stress on (18)FDG accumulation nor the effects of stressors on the accumulation of tracers of other aspects of energy metabolism have been evaluated. In this report we studied the effects of cold stress, burn injury and cutaneous wounds on murine BAT at the macroscopic, microscopic and metabolic level.

MAIN METHODS

Glucose metabolism was studied with (18)FDG, fatty acid accumulation was evaluated with trans-9(RS)-(18)F-fluoro-3,4(RS,RS)-methyleneheptadecanoic acid (FCPHA) and tricarboxcylic acid cycle (TCA) activity was evaluated with (3)H acetate.

KEY FINDINGS

All three stressors produced dramatic changes in BAT at the macroscopic and microscopic level. Macroscopically, BAT from the stressed animals appeared to be a much darker brown in color. Microscopically BAT of stressed animals demonstrated significantly fewer lipid droplets and an overall decrease in lipid content. Accumulation of (18)FDG by BAT was significantly (p<0.01) increased by all 3 treatments (Cold: ~16 fold, burn ~7 Fold and cutaneous wound ~14 fold) whereas uptake of FDG by white fat was unchanged. This effect was also demonstrated non invasively by μPET imaging. Although less prominent than with (18)FDG, BAT uptake of FCPHA and acetate were also significantly increased by all three treatments. These findings suggest that in addition to cold stress, burn injury and cutaneous wounds produce BAT activation in mice.

SIGNIFICANCE

This study demonstrates brown fat activated by several stressors leads to increased uptake of various substrates.

Imaging of multidrug resistance in cancer

Primary intrinsic and/or acquired multidrug resistance (MDR) is the main obstacle to successful cancer treatment. Functional molecular imaging of MDR in cancer using single photon or positron emitters may be helpful to identify multidrug-resistant tumours and predict not only those patients who are resistant to treatment, with a clinically unfavourable prognosis, but also those who are susceptible to the development of drug toxicity or even certain tumours . Variations in the mdr1 gene product may directly affect the therapeutic effectiveness, and single nucleotide polymorphisms for the mdr1 gene may be associated with altered oral bioavailability of MDR1 substrates, drug resistance, and a susceptibility to some human diseases. The challenge of translating the concept of MDR modulation in vivo involves a complex cellular interplay between both malignant and normal cells. Integration and correlation of functional single photon emission tomography or positron emission tomography imaging findings with mdr1 genotype and clinical data may contribute to efficient management by selecting cancer patients with the appropriate molecular phenotype for maximal individual therapeutic benefit, as well as those who are non-responders. This review describes a role for functional imaging of classical mechanisms of MDR with an emphasis on readily available [^99mTc]MIBI scintigraphy. MIBI scintigraphy has been shown to be a non-invasive cost-effective in vivo assay of ATP-binding cassette transporters associated with MDR in cancer, including P-glycoprotein, multidrug-resistant protein 1 and breast cancer resistant protein. New imaging agents for molecular targets such as vascular endothelial growth factor and HER2 receptors, may potentially be combined with MDR imaging substrates to more accurately predict the therapeutic response to anticancer drugs, guiding individualised treatment while minimising the economic health costs of ineffective therapy in an era of personalised medicine.

99mTc-MIBI Imaging in the presurgical characterization of thyroid follicular neoplasms: relationship to multidrug resistance protein expression

Recently, thyroid (99m)Tc-methoxyisobutylisonitrile ((99m)Tc-MIBI) scintiscanning has been proposed in an attempt to preoperatively identify thyroid malignancies, but discrepant results have been reported for oncocytic lesions. The aim of this study was to investigate the usefulness of visual and semiquantitative analyses of (99m)Tc-MIBI scintigraphy for preoperatively characterizing thyroid nodules with indeterminate cytologic diagnoses, segregating in advance nononcocytic variants from those that are oncocytic. This study also aimed to analyze the relationship between (99m)Tc-MIBI images and P-glycoprotein (P-gp)/multidrug resistance-associated protein-1 (MRP1) immunohistochemical expression.

METHODS

Fifty-one consecutive patients with cold thyroid nodules cytologically diagnosed as nononcocytic or oncocytic follicular neoplasm were prospectively studied. Visual and semiquantitative (99m)Tc-MIBI scanning was performed and the diagnoses of the lesions were histologically proven by subsequent thyroidectomy. Immunohistochemical evaluation of P-gp and MRP1 was also performed on surgical samples.

RESULTS

Visual and semiquantitative (99m)Tc-MIBI scintiscans showed a low specificity in preoperatively discriminating malignant oncocytic lesions. In nononcocytic nodules, the semiquantitative method was more accurate than the visual (94.44% and 77.78%, respectively). P-gp protein expression was negative in all thyroid lesions, whereas apical plasma membrane MRP1 expression was found in 78% of the lesions with a negative (99m)Tc-MIBI retention index, compared with 11% of lesions with a positive retention index, correlating most strongly with a negative (99m)Tc-MIBI RI in those cases with strong MRP1 apical expression.

CONCLUSION

Semiquantitative (99m)Tc-MIBI scintigraphy is an adjunctive method to predict preoperatively the malignant behavior of nononcocytic follicular thyroid nodules indeterminate at fine-needle aspiration biopsy, with a potential impact on the definition of their clinical management. Moreover, the good correlation found between immunohistochemical apical expression of MRP1 and the scintigraphic findings supports the (99m)Tc-MIBI results and provides tissue information on the molecular mechanisms responsible for (99m)Tc-MIBI images in thyroid lesions.

Density-functional computation of (99)Tc NMR chemical shifts

99Tc chemical shifts of TcO4(-), TcH9(2-), TcOF5, TcO2F4(-), TcOCl4(-), Tc2(CO)10, and Tc(CO)3L3(+) (L = CO, MeCN, H2O) are computed using geometries optimized with the gradient-corrected BP86 and hybrid B3P86 density functionals, at the gauge-including atomic orbitals (GIAO), -BPW91 and -B3LYP levels. For this set of compounds, substituent effects on delta(99Tc) are better described with the pure BPW91 functional than with B3LYP, in contrast to most other transition-metal chemical shifts studied so far. A rough, qualitative correlation is found between computed electric-field gradients at the Tc nuclei and the corresponding 99Tc NMR line widths. Thermal and solvation effects on magnetic shielding constants of aqueous TcO4(-), as assessed by averaging these properties over trajectories from Car-Parrinello molecular dynamics simulations, are indicated to be small and comparable to those of MnO4(-). Complexation to aqueous uranyl, UO2(2+), is predicted to affect delta(99Tc) of TcO4(-) only slightly; somewhat larger complexation shifts are obtained for the oxygen nuclei of pertechnetate, suggesting that 17O NMR could be a useful probe for the extent of association between both radionuclides in solution.

Single photon emission computed tomography and positron emission tomography imaging of multi-drug resistant P-glycoprotein--monitoring a transport activity important in cancer, blood-brain barrier function and Alzheimer's disease

Overexpression of multi-drug resistant P-glycoprotein (Pgp) remains an important barrier to successful chemotherapy in cancer patients and impacts the pharmacokinetics of many important drugs. Pgp is also expressed on the luminal surface of brain capillary endothelial cells wherein Pgp functionally comprises a major component of the blood-brain barrier by limiting central nervous system penetration of various therapeutic agents. In addition, Pgp in brain capillary endothelial cells removes amyloid-beta from the brain. Several single photon emission computed tomography and positron emission tomography radiopharmaceutical have been shown to be transported by Pgp, thereby enabling the noninvasive interrogation of Pgp-mediated transport activity in vivo. Therefore, molecular imaging of Pgp activity may enable noninvasive dynamic monitoring of multi-drug resistance in cancer, guide therapeutic choices in cancer chemotherapy, and identify transporter deficiencies of the blood-brain barrier in Alzheimer's disease.

Sestamibi single photon emission computed tomography immediately after primary percutaneous coronary intervention identifies patients at risk for large infarcts

BACKGROUND

Primary percutaneous coronary intervention (PCI) for ST-elevation myocardial infarction results in TIMI 3 flow in most patients. However, despite TIMI 3 flow, some patients do not achieve adequate tissue perfusion and have large infarctions. Techniques that, in the acute setting, could identify these patients at increased risk would potentially enable specific interventions to enhance perfusion. The object of the present study was to test whether corrected TIMI frame count (CTFC), myocardial blush grade (MBG), ST-segment resolution, and myocardial perfusion imaging (MPI) can identify those patients who, despite successful treatment with primary PCI for ST-elevation myocardial infarction, are at risk for large infarcts.

METHODS

In 61 patients with TIMI 3 flow after primary PCI, CTFC, MBG, ST-segment resolution, and quantitative MPI by technetium Tc 99m sestamibi single photon emission computed tomography were estimated immediately after primary PCI. Infarct size was assessed by peak lactate dehydrogenase (LDH) and by MPI after 3 months.

RESULTS

Infarct size by MPI was 12% (4, 23), and peak LDH was 1410 U/L (870, 2220); these measures correlated (rho = 0.80, P < .001). The acute perfusion defect predicted infarct size using either method (MPI rho = 0.88, P < .001; LDH rho = 0.77, P < .001); ST-segment residual correlated weakly to infarct size, whereas CTFC and MBG did not. In multivariate analysis, the acute perfusion defect was the only significant predictor of infarct size.

CONCLUSION

Myocardial perfusion imaging performed immediately after successful PCI can identify patients at increased risk for large infarcts due to impaired tissue perfusion. Acute MPI might serve as a tool for early identification of patients, who, despite epicardial TIMI 3 flow, have inadequate tissue level perfusion.

MDR1 P-glycoprotein reduces influx of substrates without affecting membrane potential

MDR1 (multidrug resistance) P-glycoprotein (Pgp; ABCB1) decreases intracellular concentrations of structurally diverse drugs. Although Pgp is generally thought to be an efflux transporter, the mechanism of action remains elusive. To determine whether Pgp confers drug resistance through changes in transmembrane potential (E(m)) or ion conductance, we studied electrical currents and drug transport in Pgp-negative MCF-7 cells and MCF-7/MDR1 stable transfectants that were established and maintained without chemotherapeutic drugs. Although E(m) and total membrane conductance did not differ between MCF-7 and MCF-7/MDR1 cells, Pgp reduced unidirectional influx and steady-state cellular content of Tc-Sestamibi, a substrate for MDR1 Pgp, without affecting unidirectional efflux of substrate from cells. Depolarization of membrane potentials with various concentrations of extracellular K(+) in the presence of valinomycin did not inhibit the ability of Pgp to reduce intracellular concentration of Tc-Sestamibi, strongly suggesting that the drug transport activity of MDR1 Pgp is independent of changes in E(m) or total ion conductance. Tetraphenyl borate, a lipophilic anion, enhanced unidirectional influx of Tc-Sestamibi to a greater extent in MCF-7/MDR1 cells than in control cells, suggesting that Pgp may, directly or indirectly, increase the positive dipole potential within the plasma membrane bilayer. Overall, these data demonstrate that changes in E(m) or macroscopic conductance are not coupled with function of Pgp in multidrug resistance. The dominant effect of MDR1 Pgp in this system is reduction of drug influx, possibly through an increase in intramembranous dipole potential.

The role of radionuclides in primary musculoskeletal tumors beyond the 'bone scan'

Radionuclides represent a means of functional imaging, which is able to reflect the metabolic state of tissues. Recently developed radiotracers and older radiotracers with newer applications, imaged through single photon emission computed tomography (SPECT) and positron emission tomography (PET), can provide significant information in the diagnosis, grading, therapy response or recurrence of primary musculoskeletal tumors. The unique ability of these radiotracers to demonstrate non-invasively the efflux pump rate, which is a common reason of therapy failure, as well as the metabolic and proliferative rates of the tumors should be a powerful tool in the orthopaedic oncology in the evaluation of musculoskeletal tumors.

Noninvasive strategies to image cardiovascular apoptosis

Apoptosis consists of a complex set of biochemical events initiated by an array of different stimuli and enzymatic pathways. There is a set of common morphologic and biochemical features of apoptosis that could be exploited as hot or cold targets to image cardiovascular apoptosis. First, the authors review the potential array of targets that can be used to identify apoptosis. Then, the authors examine the history and current status of radiolabeled annexin V, the agent currently used to image apoptosis.

Effects of MDR1 and MDR3 P-glycoproteins, MRP1, and BCRP/MXR/ABCP on the transport of (99m)Tc-tetrofosmin

Multidrug resistance (MDR1) P-glycoprotein (Pgp), multidrug resistance-associated protein (MRP1), and breast cancer resistance protein (BCRP/MXR/ABCP) are members of the ATP-binding-cassette (ABC) superfamily of membrane transporters and are thought to function as energy-dependent efflux pumps of a variety of structurally diverse chemotherapeutic agents. We herein report the characterization of (99m)Tc-Tetrofosmin, a candidate radiopharmaceutical substrate of ABC transporters. (99m)Tc-Tetrofosmin showed high membrane potential-dependent accumulation in drug-sensitive KB 3-1 cells and low antagonist-reversible accumulation in MDR KB 8-5 and KB 8-5-11 cells in proportion to levels of MDR1 Pgp expression. In KB 8-5 cells, EC(50) values of the potent MDR antagonists N-(4-[2-(1,2,3, 4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9, 10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide (GF120918), (2R)-anti-5-¿3-[4-(10, 11-difluoromethanodibenzo-suber-5-yl)piperazin-1-yl]-2 -hydroxypropoxy ¿quinoline trihydrochloride (LY335979), and (3'-keto-Bmt')-[Val(2)]-cyclosporin A (PSC 833) were 40, 66, and 986 nM, respectively. Furthermore, only baculoviruses carrying human MDR1, but not MDR3, conferred both a decrease in accumulation of (99m)Tc-Tetrofosmin in host Spodoptera frugiperda (Sf9) cells and a GF120918-induced enhancement. Transport studies with a variety of stably transfected and drug-selected tumor cell lines were performed with (99m)Tc-Tetrofosmin and compared with (99m)Tc-Sestamibi, a previously validated MDR imaging agent. MDR1 Pgp readily transported each agent. To a lesser extent, MRP1 also transported each agent, likely as co-transport substrates with GSH; neither agent was a substrate for the BCRP/MXR/ABCP half-transporter. In mdr1a(-/-) and mdr1a/1b(-/-) mice, (99m)Tc-Tetrofosmin showed approximately 3. 5-fold greater brain uptake and retention compared with wild-type, with no net change in blood pharmacokinetics, consistent with transport in vivo by Pgp expressed at the capillary blood-brain barrier. Molecular imaging of the functional transport activity of ABC transporters in vivo with (99m)Tc-Tetrofosmin and related radiopharmaceuticals may enable non-invasive monitoring of chemotherapeutic and MDR gene therapy protocols.

A new semiquantitative method for comparing brain tumor uptake of Tc-99m sestamibi and TI-201

PURPOSE

We describe a new method for measuring brain tumor uptake of TI-201 and Tc-99m sestamibi (MIBI) that permits the semiquantitative comparison of tracer uptake to yield comparable "tumor bulk" ratios. We tested this method in patients treated recently and remotely with chemotherapy to determine if this method could identify differences between these two patient groups.

METHODS

Eleven patients with high-grade astrocytoma underwent TI-201 and Tc-99m MIBI SPECT. Each patient received 5 mCi TI-201 intravenously followed by SPECT using a dual-head gamma camera. This was immediately followed by an intravenous injection of 20 mCi Tc-99m MIBI and repeated SPECT. Four patients had recent therapy (from 1 day to 6 weeks before SPECT) and seven had remote treatment (>1 year before SPECT). Regions of interest were outlined in the tumor area using a computer-automated program to include all counts above background activity. Tumor activity counts were obtained from this region of interest. The tumor region of interest was mirrored to the contralateral uninvolved cerebral hemisphere to obtain background control count activity. A hypothetical volume of the number of pixels with background count activity necessary to constitute the tumor count activity (tumor bulk) was calculated using the ratio of total tumor counts (Ct), subtracting background (Cb), and dividing by the average counts per pixel in the control region (Cab). This was multiplied by the number of pixels (P), the pixel volume (Vp), and summed over all sections (i) involved with tumor. This method yields the equation tumor bulk =

RESULTS

The mean Tc-99m MIBI to TI-201 tumor bulk ratio was 1.03 (range, 0.81 to 1.12) in four patients who had recently received chemotherapy. The mean Tc-99m MIBI to TI-201 tumor bulk ratio was 1.55 (range, 1.46 to 1.64) in seven patients who had remote therapy. The difference in the Tc-99m MIBI to TI-201 tumor bulk ratio between the two groups was significant (P = 0.0001). Patients who received recent chemotherapy had relatively lower Tc-99m MIBI uptake compared with TI-201. In remotely treated patients, uptake of the Tc-99m MIBI was greater compared with TI-201.

CONCLUSION

This method allows semiquantitative comparison of different tracer uptake values independent of tracer dose and reduces the variability in drawing a region of interest when measuring tumor uptake. Among the patients studied, those who had recent chemotherapy showed a low Tc-99m MIBI to TI-201 ratio. This method of measuring "tumor bulk" can provide a useful index of viable tumor size in evaluating early tumor response and during ongoing chemotherapy.

Effects of multidrug resistance (MDR1) P-glycoprotein expression levels and coordination metal on the cytotoxic potency of multidentate (N4O2) (ethylenediamine)bis[propyl(R-benzylimino)]metal(III) cations

Enhanced mitochondrial transmembrane potentials in tumor cells have been proposed to confer tumor-selective-targeting properties to modestly lipophilic monocationic compounds. To explore the potential cytotoxic activity of lipophilic cationic metallopharmaceuticals containing a highly flexible hexadentate N4O2 Schiff-base phenolic ligand, we first synthesized precursors H3Mabi (1) and H3DMabi (2) by condensation of an appropriate linear tetraamine with substituted salicylaldehydes. The desired N4O2 ligands, (ethylenediamine)-N,N'-bis[propyl[(2-hydroxy-3-methoxybenzyl)imino]] and (ethylenediamine)-N,N'-bis[propyl[2-hydroxy-4,6-dimethoxybenzyl)-imino]] (R-ENBPI), were obtained by cleavage of the imidazolidine ring, and their corresponding monocationic complexes were produced by reaction with appropriate hydrated salts or acetylacetonates of Al(III), Fe(III), Ga(III), and In(III). All complexes were stable to neutral hydrolysis. In human epidermal carcinoma KB-3-1 cells, cytotoxic potencies of racemic mixtures of these complexes were in the low micromolar range and, for a given ligand, depended on the identity of the coordinating central metal. The active 4,6-dimethoxy-ENBPI complexes were more potent than their 3-methoxy analogs, while the free ligands and metal(III) ions showed little or no cytotoxic activity. Furthermore, in colchicine-selected KB-8-5 multidrug resistant (MDR) cells, modest cellular expression of human MDR1 P-glycoprotein conferred protection from the cytotoxic activities of Al(III), Fe(III), and Ga(III) R-ENBPI complexes indicating that these complexes were recognized as transport substrates by the P-glycoprotein efflux transporter. However, the cytotoxic activities of the corresponding In(III) complexes, while among the lowest in potencies, were also not altered by expression of MDR1 P-glycoprotein. Thus, for the Group III elements, human cells were capable of distinguishing R-ENBPI complexes formed of the same ligands with different metals. Furthermore, selected R-ENBPI metal(III) complexes may be useful as novel anticancer metallopharmaceuticals.