Asuka Mizutani

Validation of Left Ventricular Ejection Fraction with the IQ•SPECT System in Small-Heart Patients

The IQ•SPECT system, which is equipped with multifocal collimators (SMARTZOOM) and uses ordered-subset conjugate gradient minimization as the reconstruction algorithm, reduces the acquisition time of myocardial perfusion imaging compared with conventional SPECT systems equipped with low-energy high-resolution collimators. We compared the IQ•SPECT system with a conventional SPECT system for estimating left ventricular ejection fraction (LVEF) in patients with a small heart (end-systolic volume < 20 mL). Methods: The study consisted of 98 consecutive patients who underwent a 1-d stress–rest myocardial perfusion imaging study with a 99mTc-labeled agent for preoperative risk assessment. Data were reconstructed using filtered backprojection for conventional SPECT and ordered-subset conjugate gradient minimization for IQ•SPECT. End-systolic volume, end-diastolic volume, and LVEF were calculated using quantitative gated SPECT (QGS) and cardioREPO software. We compared the LVEF from gated myocardial perfusion SPECT to that from echocardiographic measurements. Results: End-diastolic volume, end-systolic volume, and LVEF as obtained from conventional SPECT, IQ•SPECT, and echocardiography showed a good to excellent correlation regardless of whether they were calculated using QGS or using cardioREPO. Although LVEF calculated using QGS significantly differed between conventional SPECT and IQ•SPECT (65.4% ± 13.8% vs. 68.4% ± 15.2%) (P = 0.0002), LVEF calculated using cardioREPO did not (69.5% ± 10.6% vs. 69.5% ± 11.0%). Likewise, although LVEF calculated using QGS significantly differed between conventional SPECT and IQ•SPECT (75.0 ± 9.6 vs. 79.5 ± 8.3) (P = 0.0005), LVEF calculated using cardioREPO did not (72.3% ± 9.0% vs. 74.3% ± 8.3%). Conclusion: In small-heart patients, the difference in LVEF between IQ•SPECT and conventional SPECT was less when calculated using cardioREPO than when calculated using QGS.

Differences in accumulation and the transport mechanism of l- and d-methionine in high- and low-grade human glioma cells.

INTRODUCTION Although [S-methyl-11C]-labeled L-methionine and D-methionine (11C-L-MET and 11C-D-MET) are useful radiotracers for positron emission tomography imaging of brain tumors, it is not known whether the accumulation and transport mechanisms underlying uptake of 11C-D-MET and 11C-L-MET are the same. 11C-L-MET is mainly taken up by the amino acid transport system L. We evaluated accumulation and the transport mechanism of D-MET in high- and low-grade human glioma cells in vitro. METHODS The expression of transport system genes in high- (A172 and T98G) and low-grade (SW1088 and Hs683) glioma cells was quantitatively analyzed. Accumulation of [S-methyl-3H]-L-MET (3H-L-MET) and [S-methyl-3H]-D-MET (3H-D-MET) in these cells was compared during 60min of incubation. The transport mechanism of 3H-L-MET and 3H-D-MET was investigated by incubating the cells with these compounds and examining the effect of the inhibitors 2-amino-2-norbornane-carboxylic acid or α-(methylamino) isobutyric acid. RESULTS Absolute expression levels of system L and system alanine-serine-cysteine (ASC) in high-grade glioma cells were higher than in low-grade cells. In high-grade glioma cells, expression of system ASC genes was higher than that of system L genes. 3H-D-MET, which is transported by systems L and ASC, accumulated at higher levels than 3H-L-MET at all incubation times because 3H-D-MET is more sensitive to system ASC than 3H-L-MET. Conversely, in low-grade glioma cells with lower expression of system L and ASC, 3H-D-MET accumulated at higher levels than 3H-L-MET in early incubation times because 3H-D-MET may be more sensitive to system ASC than system L. CONCLUSION 3H-D-MET was mainly transported by systems L and ASC and sensitive to system ASC, whereas 3H-L-MET was transported by system L in human glioma cells. In vitro, the accumulation of 3H-D-MET was significantly higher than that of 3H-L-MET during the entire incubation time in high-grade glioma cells, and in early incubation times in low-grade glioma cells.

Development of radioiodine-labeled 4-hydroxyphenylcysteamine for specific diagnosis of malignant melanoma.

INTRODUCTION A specific diagnosis for melanoma is strongly desired because malignant melanoma has poor prognosis. In a previous study, although radioiodine-125-labeled 4-hydroxyphenyl-L-cysteine ((125)I-L-PC) was found to have good substrate affinity for tyrosinase enzyme in the melanin metabolic pathway, (123/131)I-L-PC had insufficient substrate affinity for tyrosinase to diagnose melanoma. In this study, we synthesized 4-hydroxyphenylcysteamine (4-PCA) and developed a novel radioiodine-125-labeled 4-hydroxyphenylcysteamine ((125)I-PCA) to increase affinity for the melanin biosynthesis pathway. METHODS 4-PCA was separated with 2-hydroxyphenylcysteamine (2-PCA), which is an isomer of 4-PCA, and was examined using melting point, proton nuclear magnetic resonance, mass spectrometry and elemental analysis. (125)I-PCA was prepared using the chloramine-T method under no-carrier added conditions. We performed biodistribution experiments using B16 melanoma-bearing mice using (125)I-PCA, (125)I-L-PC, (125)I-α-methyl-L-tyrosine, (123)I-m-iodobenzylguanidine and (67)Ga-citrate. In vitro assay was performed with B16 melanoma cells, and affinity for tyrosinase, DNA polymerase and amino acid transport was evaluated using phenylthiourea, thymidine, ouabine and L-tyrosine inhibitor. In addition, partition coefficients of (125)I-PCA were evaluated. RESULTS In the synthesis of 4-PCA, analysis values did not differ between calculated and reported values, and 4-PCA was separated from 2-PCA at high purity. In biodistribution experiments, (125)I-PCA was accumulated and retained in B16 melanoma cells when compared with (125)I-L-PC. (125)I-PCA showed the highest values at 60 min after radiotracer injection in melanoma-to-muscle ratios, melanoma-to-blood ratios and melanoma-to-skin ratios. Accumulation of (125)I-PCA was significantly inhibited by phenylthiourea and thymidine. Partition coefficients of (125)I-PCA were lower than those of N-isopropyl-p-[(123)I]iodoamphetamine and were not significantly different from (125)I-L-PC. CONCLUSIONS (125)I-PCA is a better substrate for tyrosinase and DNA polymerase and has higher uptake and longer retention in B16 melanoma cells when compared with (125)I-L-PC. Therefore, (123/131)I-PCA has good potential for diagnosis for malignant melanoma. ADVANCE IN KNOWLEDGE (125)I-PCA will be a specific diagnosis tool for malignant melanoma. IMPLICATIONS FOR PATIENT CARE (123/131)I-PCA has good potential for the diagnosis of malignant melanoma when compared with other SPECT tracers, as well as anti-melanoma chemotherapeutic drugs.

Development of radioiodine-labeled acetaminophen for specific, high-contrast imaging of malignant melanoma

INTRODUCTION Due to its poor prognosis, specific imaging for early detection of malignant melanoma is strongly desired. Although radioiodine labeled 4-hydroxyphenylcysteamine, which we previously developed, has good affinity for tyrosinase, an enzyme in the melanin metabolic pathway, image contrast of the melanoma:organ ratios is not sufficiently high for detection of primary melanoma and metastases at early injection times. In this study, we developed radioiodine labeled acetaminophen (I-AP) for specific, high-contrast imaging of malignant melanoma. METHODS Radioiodine-125-labeled AP (125I-AP) was prepared using the chloramine-T method under no carrier-added conditions. Accumulation of radioactivity and the mechanism were evaluated in vitro using B16 melanoma cells incubated with 125I-AP or 14C(U)-labeled AP (14C-AP) with and without l-tyrosine as a substrate of tyrosinase, phenylthiourea as an inhibitor of tyrosinase, and thymidine as an inhibitor of DNA polymerase. The biological distribution of radioactivity in B16 melanoma-bearing mice was evaluated to determine the accumulation of 125I-AP. The stability of 125I-AP over time was evaluated in mice. RESULTS The labeling efficiency and radiochemical purity of 125I-AP were >80% and 95%, respectively. Accumulation of 125I-AP was higher than that of 14C-AP at 60 min of incubation in vitro. The affinity of 14C-AP for tyrosinase and DNA polymerase was higher than that of 125I-AP, whereas the Vmax of 125I-AP was higher than that of 14C-AP. 125I-AP showed the highest accumulation in the gall bladder, and clearance from the blood and kidney was rapid. Melanoma:muscle and melanoma:normal skin ratios of 125I-AP for imaging contrast were the highest at 15 min after injection, whereas the melanoma:blood and melanoma:bone ratios gradually increased over time. 125I-AP remained stable for 60 min after injection in mice. CONCLUSIONS 125I-AP has affinity for tyrosinase and high image contrast at early time points after injection. Therefore, 123I-AP imaging has great potential for specific, high-contrast detection of malignant melanoma. ADVANCES IN KNOWLEDGE: 123I-AP will provide specific, high-contrast imaging for malignant melanoma at early injection times. IMPLICATIONS FOR PATIENT CARE: 123I-AP has good potential for the diagnosis of malignant melanoma compared with 123I-labeled 4-hydroxyphenylcysteamine, which we previously developed.

A strategy for improving FDG accumulation for early detection of metastasis from primary pancreatic cancer: stimulation of the Warburg effect in AsPC-1 cells.

INTRODUCTION Early detection and/or prediction of metastasis provide more prognostic relevance than local recurrence. Direct spread into the peritoneum is frequently found in pancreatic cancer patients, but positron emission tomography (PET) with 2-deoxy-2-fluoro-d-glucose (FDG) is not useful for identifying such metastasis. We investigated a method to enhance FDG accumulation using AsPC-1 human ascites tumor cells. METHODS (14)C-FDG accumulation was assessed under the following conditions: 1) characteristics of (14)C-FDG transport were examined using phloridzin, a Na(+)-free buffer, and various hexoses, and 2) accumulation of (14)C-FDG was measured in cells that were pretreated with hexose for various time periods, and activity of 6-phosphofructo-1-kinase (PFK-1) was assayed. RESULTS (14)C-FDG transport into AsPC-1 cells was mediated primarily by a Na(+)-independent transport mechanism. Aldohexoses such as d-glucose, D-mannose, and D-galactose inhibited (14)C-FDG transport. Cells pretreated with d-glucose, D-mannose, or D-fructose exhibited augmented (14)C-FDG accumulation. Pretreatment with higher concentrations of D-glucose or D-fructose tended to increase PFK-1 activity. CONCLUSIONS Very little information has been published about the association between PFK-1 and FDG accumulation, and we confirmed the impacts of various hexoses on the activity of PFK-1 and FDG accumulation in AsPC-1 cells. Clarifying the relevance of PFK-1 in FDG accumulation will contribute to developing new features of FDG-PET, because PFK-1 is the main regulator of glycolysis.

In vivo radioactive metabolite analysis for individualized medicine: A basic study of a new method of CYP activity assay using 123I-IMP

INTRODUCTION (123)I-N-isopropyl-p-iodoamphetamine ((123)I-IMP) is metabolized and converted to (123)I-p-iodoamphetamine ((123)I-PIA) by CYP2C19 in humans. Since variations in (123)I-PIA levels reflect variations in CYP2C19 activity, CYP2C19 activity can be estimated by quantitative analysis of (123)I-PIA levels. Thus, (123)I-IMP administration can provide diagnostic information not only regarding cerebral blood flow (rCBF) but also regarding metabolic function. The aim of the present study was to detect variations in CYP activity in mice using metabolite analysis. METHODS Metabolism of (125)I-IMP in pooled homogenates of mouse liver (MLH) was analyzed by high-performance liquid chromatography (HPLC) in the presence or absence of NADPH. The amount of (125)I-PIA generated was calculated as the normalized peak area of the chromatogram. Inhibition of (125)I-IMP metabolism was evaluated using the inhibitor SKF-525A. A biodistribution study of (125)I-IMP was performed to determine the organ distribution of (125)I-IMP/(125)I-IMP metabolites and the effect of SKF-525A. Variations in CYP activity in vivo were detected by administration of (123)I-IMP and/or SKF-525A to mice. The liver and the kidney were then excised, homogenized and analyzed using HPLC. RESULTS (125)I-IMP was metabolized by MLH in the presence of NADPH, and the production of (125)I-PIA was inhibited by SKF-525A. SKF-525A did not greatly affect the biodistribution of (125)I-IMP/(125)I-IMP metabolites in vivo. Both (123)I-IMP and (123)I-PIA were detected in organs of control mice. However, (123)I-PIA was not detected in the livers or kidneys of mice treated with SKF-525A. CONCLUSIONS CYP activity in vivo was inhibited by SKF-525A treatment. Variations in CYP activity could be detected in the blood, liver and kidney as changes in the peak area of (123)I-PIA. ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE (123)I-IMP metabolite analysis has the potential to provide beneficial information for prediction of the effect of medicines, in addition to its contribution to more accurate rCBF diagnosis that reflects individual CYP activity.