Self-Assembled Hybrid Nanocomposites for Multimodal Imaging-Guided Photothermal Therapy of Lymph Node Metastasis

Multimodal imaging-guided therapy holds great potential for precise theranostics of cancer metastasis. However, imaging agents enabling the convergence of complementary modalities with therapeutic functions to achieve perfect theranostics have been less exploited. This study reports the construction of a multifunctional nanoagent (FIP-^99mTc) that comprises Fe₃O₄ for magnetic resonance imaging, radioactive ^99mTc for single-photon-emission computed tomography, and IR-1061 to serve for the second near-infrared fluorescence imaging, photoacoustic imaging, and photothermal therapy treatment of cancer metastasis. The nanoagent possessed superior multimodal imaging capability with high sensitivity and resolution attributing to the complement of all the imaging modalities. Moreover, the nanoagent showed ideal photothermal conversion ability to effectively kill tumor cells at low concentration and power laser irradiation. In the in vivo study, FIP-^99mTc confirmed the fast accumulation and clear delineation of metastatic lymph nodes within 1 h after administration. Attributing to the efficient uptake and photothermal conversion, FIP-^99mTc could raise the temperature of metastatic lymph nodes to 54 °C within 10 min laser irradiation, so as to facilitate tumor cell ablation. More importantly, FIP-^99mTc not only played an active role in suppressing cancer growth in metastatic lymph nodes with high efficiency but also could effectively prevent further lung metastasis after resection of the primary tumor. This study proposes a simple but effective theranostic approach toward lymph node metastasis.

Interactions between myocardial sympathetic denervation and left ventricular mechanical dyssynchrony: A CZT analysis

BACKGROUND

A correlation between left ventricular (LV) dyssynchrony (LVD) and impaired myocardial sympathetic tone has been hypothesized. We sought to assess the interactions between regional LV sympathetic innervation, perfusion, and mechanical dyssynchrony.

METHODS

Eighty-three patients underwent evaluation of LV perfusion and sympathetic innervation on 99mTc-tetrofosmin/123I-metaiodobenzylguanidine (123I-MIBG) imaging. The summed rest score and summed 123I-MIBG score (SS-MIBG) were computed. The extent of "innervation/perfusion" mismatch was defined as the number of denervated LV segments with relatively preserved perfusion. LVD was evaluated on phase analysis and the wall with latest mechanical activation identified.

RESULTS

LVD was revealed in 36 (43%) patients. Patients with LVD had more abnormal values of SRS (21 ± 9 vs 10 ± 8, P < 0.001) and SS-MIBG (29 ± 9 vs 17 ± 11, P < 0.001) than those without LVD. The presence of LVD also clustered with a higher burden of "innervation/perfusion" mismatch (P = 0.019). On per-wall analysis, LV walls with delayed mechanical activation showed a higher burden of "innervation/perfusion" mismatch (2.3 ± 1.4 segments) than normally contracting walls (1.3 ± 1.2 segments; P < 0.001). On multivariate analysis, the extent of "innervation/perfusion" mismatch was the only predictor of delayed mechanical activation (P = 0.029).

CONCLUSIONS

Patients with LVD show an elevated burden of "innervation/perfusion" mismatch that is concentrated at the level of the most dyssynchronous walls.

A novel multivalent (99m)Tc-labeled EG2-C4bpα antibody for targeting the epidermal growth factor receptor in tumor xenografts

INTRODUCTION

The C4b binding protein (C4bp) α/β-chain C-terminal effectively induces polymerization during protein synthesis. Using this fragment and the single-domain antibody EG2, which targets the epidermal growth factor receptor (EGFR), we generated the novel multimeric antibody EG2-C4bpα. We radiolabeled EG2-C4bpα with (99m)Tc and evaluated its targeting efficiency and pharmacokinetics in tumor xenografts.

METHODS

EGFR expression and EGFR-EG2-C4bpα binding was evaluated in A431 and OCM-1 cells by Western blotting and flow cytometry, respectively. EG2-C4bpα was radiolabeled with [(99m)Tc(CO)3(OH2)3](+) using a tricarbonyl vial followed by purification on a PD-10 column. In vitro studies with (99m)Tc-EG2-C4bpα were performed in A431 and/or OCM-1 cells. Single photon emission computed tomography (SPECT) imaging and biodistribution studies were carried out in (99m)Tc-EG2-C4bpα-injected mice bearing A431- and OCM-1-derived tumors. EGFR immunofluorescent staining in A431 and OCM-1 tumors was performed.

RESULTS

A431 cells showed higher EGFR expression levels than OCM-1 cells, and flow cytometry confirmed EG2-C4bpα bound more A431 cells than OCM-1 cells. (99m)Tc-EG2-C4bpα was successfully prepared with radiochemical yields of 30.3-50.4%. The binding affinity of (99m)Tc-EG2-C4bpα to A431 cells was approximately 20 nM. (99m)Tc-EG2-C4bpα specifically bound A431 cells and this binding was blocked by 41% in the presence of 50 nM excess unlabeled EG2-C4bpα. In vivo radioactivity uptake in A431 tumors was detected 2h after (99m)Tc-EG2-C4bpα administration and sustained up to 18h. The highest ratio of A431 tumor-to-muscle and tumor-to-blood was 3.69 ± 0.48 at 10h and 0.77 ± 0.14 at 20 h, respectively. Excess unlabeled EG2-C4bpα blocked radioactivity uptake in A431 tumors by 55% at 10h. (99m)Tc-EG2-C4bpα was barely detectable in OCM-1 tumors, and biodistribution analysis confirmed that radioactivity uptake was significantly lower than in A431 tumors.

CONCLUSIONS

(99m)Tc-EG2-C4bpα specifically and efficiently targets EGFR over-expressing tumors suggesting that EG2-C4bpα may be a promising antibody alternative for future diagnostic application and potential radioimmunotherapy. However, the high activity in the blood and liver, and the relative low ratio of tumor-to-blood should be noticed and improved.

⁹⁹mTc-HYNIC-MPG: a novel SPECT probe for targeting mutated EGFR

Mutated epidermal growth factor receptor (EGFR) is an important biomarker for cancer diagnosis and molecular target for many anticancer drugs. Localizing EGFR and evaluating EGFR mutational status can help to identify patients who are potentially the most suitable ones for targeted treatments. Hence, we developed a novel EGFR tyrosine kinase inhibitor labeled with (99m)Tc ((99m)Tc-HYNIC-MPG) and evaluated its EGFR binding capacity in vitro and in vivo. This molecular probe was synthesized by one-step method that is simple and highly efficient. Importantly, the uptake rate for (99m)Tc-HYNIC-MPG in the liver was as low as 28.44 ± 0.15% (mean ± SD, n=3). This finding presents for the first time that (99m)Tc-HYNIC-MPG can bind to mutated EGFR efficiently and thus provides a novel molecular tool to detect mutated EGFR and suppress tumorigenesis.

Analysis of mechanisms of interaction between ciprofloxacin-based radiopharmaceutical labeled with technetium-99m and cultured Staphylococcus aureus

Mechanisms of interaction between ciprofloxacin-based radiopharmaceutical labeled with technetium-99m and cultured Staphylococcus aureus were studied. The substance, reagent for radiopharmaceutical, and the radiopharmaceutical demonstrated similar bactericidal activity against the test bacterial cultures, which confirmed specific antibacterial activity of technetium-99m-labeled ciprofloxacin. The technetium-99m-labeled antibiotic reversibly interacts with inactivated Staphylococcus aureus culture, which indicates the existence of an additional non-specific pathway for radiopharmaceutical accumulation in the bacterial inflammation focus. Our experiment ruled out the possibility of binding free technetium-99m at concentrations <5% (its concentration in the radiopharmaceutical) with Staphylococcus aureus.

⁹⁹mTc pyrene derivative complex causes double-strand breaks in dsDNA mainly through cluster-mediated indirect effect in aqueous solution

Radiation therapy for cancer patients works by ionizing damage to nuclear DNA, primarily by creating double-strand breaks (DSB). A major shortcoming of traditional radiation therapy is the set of side effect associated with its long-range interaction with nearby tissues. Low-energy Auger electrons have the advantage of an extremely short effective range, minimizing damage to healthy tissue. Consequently, the isotope ^99mTc, an Auger electron source, is currently being studied for its beneficial potential in cancer treatment. We examined the dose effect of a pyrene derivative ^99mTc complex on plasmid DNA by using gel electrophoresis in both aqueous and methanol solutions. In aqueous solutions, the average yield per decay for double-strand breaks is 0.011±0.005 at low dose range, decreasing to 0.0005±0.0003 in the presence of 1 M dimethyl sulfoxide (DMSO). The apparent yield per decay for single-strand breaks (SSB) is 0.04±0.02, decreasing to approximately a fifth with 1 M DMSO. In methanol, the average yield per decay of DSB is 0.54±0.06 and drops to undetectable levels in 2 M DMSO. The SSB yield per decay is 7.2±0.2, changing to 0.4±0.2 in the presence of 2 M DMSO. The 95% decrease in the yield of DSB in DMSO indicates that the main mechanism for DSB formation is through indirect effect, possibly by cooperative binding or clustering of intercalators. In the presence of non-radioactive ligands at a near saturation concentration, where radioactive Tc compounds do not form large clusters, the yield of SSB stays the same while the yield of DSB decreases to the value in DMSO. DSBs generated by ^99mTc conjugated to intercalators are primarily caused by indirect effects through clustering.

(99m)Tc sulfur colloid and (99m)Tc mebrofenin hepatobiliary functional liver imaging in normal and diabetic rats

OBJECTIVES

To use (99m)Tc sulfur colloid ((99m)Tc-SC) and (99m)Tc mebrofenin ((99m)Tc-BrIDA) to study liver function in normal and diabetic rats.

MATERIALS AND METHODS

Radionuclide imaging was performed on 2 groups of rats, using (99m)Tc-SC for one group and (99m)Tc-BrIDA for the other (20 rats per group) before and after induction of diabetes mellitus (DM) using streptozotocin administration (55 mg/kg i.p.). Dynamic acquisition was obtained for 1 h after the injection of 37 MBq of radiotracer. For the (99m)Tc-SC group, organ/tissue uptake was determined by drawing regions of interest (ROI) over the heart, liver, spleen and also the whole body (WB). The ratio of the ROI of each organ to the WB ROI was calculated. For (99m)Tc-BrIDA, ratios of cumulative count rates in liver, liver parenchyma, biliary tree and abdomen ROI to a WB ROI were also calculated. Statistical analysis was performed to compare the ratios of organ/tissue uptake to WB uptake before and after DM induction using the paired t test.

RESULTS

(99m)Tc-SC uptake ratios (means ±SD) showed a lower liver-to-WB uptake ratio (0.75 ± 0.05) in the rats after DM induction compared to baseline (0.81 ± 0.06), while the cardiac blood pool showed higher uptake ratios in the rats after DM induction (p = 0.026). For (99m)Tc-BrIDA, there was no significant difference in radiotracer uptake ratios obtained from the rats before and after DM induction (p = 0.41).

CONCLUSION

Using functional liver imaging, there was a statistically significant decrease in the liver phagocytic/reticuloendothelial system function after DM induction, as evidenced by decreased (99m)Tc-SC liver uptake and increased blood pool compared to prediabetes, while the hepatobiliary function remained unchanged after DM induction using (99m)Tc-BrIDA imaging.

99mTc-EDDA/HYNIC-TOC somatostatin receptor scintigraphy in daily clinical practice

BACKGROUND

This study aimed to assess the impact of 99mTc-EDDA/HYNIC-TOC (99mTc-TOC) somatostatin receptor scintigraphy (SRS) in clinical practice.

MATERIAL/METHODS

One hundred seventeen patients were divided into 6 groups: 1, initial detection and localization of suspected neuroendocrine tumor (NET); 2, tumor staging before therapy; 3, staging of NET of unknown origin, 4, restaging after surgery of primary tumor; 5, diagnosis of solitary pulmonary nodules (SPNs), and 6, follow-up after "cold" somatostatin analogues treatment.

RESULTS

In group 1, clinical suspicions were not confirmed in any of the patients; in group 2, most of the primary lesions showed overexpression of somatostatin receptors (SSRT); in group 3, the primary tumor was not identified in any of the patients; in group 4, recurrences were depicted in 7 out of 47 patients; in group 5, only 1 malignant SPN was detected, and in group 6, regression of primary mass and metastases were seen on follow-up SRS in 1 patient.

CONCLUSIONS

99mTc-TOC SRS is useful in staging of SSRT-overexpressing tumors of known and unknown primary origin, as well as in restaging after primary tumor surgery. This method is less effective in detecting suspected NET and assessing SPNs. Further investigation is necessary to evaluate the usefulness of SRS in monitoring patients after biological treatment.

[Technetium 99Tc methylenediphosphonate inhibits osteoclast formation from PBMCs in patients with rheumatoid arthritis]

OBJECTIVE

To observe the influence of technetium 99Tc methylenediphosphonate (99Tc-MDP) on osteoclastogenesis induced by receptor activator of NF-kappaB ligand (RANKL) and macrophage-colony stimulating factor (M-CSF) in peripheral blood mononuclear cells in patients with rheumatoid arthritis, and to study the mechanism of 99Tc-MDP in osteoclast differentiation.

METHODS

The monocytes/macrophages were isolated from peripheral blood in patients with rheumatoid arthritis, incubated in RPMI-1640 with receptor activator of NF-kappaB ligand (RANKL, 25 microg/L), macrophage-colony stimulating factor (M-CSF, 25 microg/L) and different concentrations of 99Tc-MDP (5, 10, 20 and 50 mg/L) for 4, 12, and 20 days. Tartrate resistant acid phosphatase staining was used to observe the formation of osteoclasts.

RESULTS

After 12 or 16 days culture of peripheral blood mononuclear cells, plenty of large multinuclear cells could be found on the coverslips. 99Tc-MDP markedly inhibited those changes and the inhibitory effects were increased as the concentration of 99Tc-MDP increased (P<0.05).

CONCLUSION

99Tc-MDP probably has some protective effect on rheumatoid arthritis by inhibiting osteoclast formation.

Myocardial kinetics of 201Thallium, 99mTc-tetrofosmin, and 99mTc-sestamibi in an acute ischemia–reperfusion model using isolated rat heart

OBJECTIVE

(201)Thallium (TL), (99m)Tc-tetrofosmin (TF), and (99m)Tc-sestamibi (MIBI) are extensively used as myocardial perfusion agents. The objective of the present study was to evaluate their kinetics under acute ischemia-reperfusion.

METHODS

Isolated rat hearts, perfused by the Langendorff method at a constant flow rate of 10 ml/min, were allotted to normal control, mild ischemia, and severe ischemia groups, in which 20-min tracer wash-in was conducted followed by a 25-min tracer washout. No-flow ischemia (15 min for mild ischemia groups; 30 min for severe ischemia groups) was induced before conducting wash-in and washout in the ischemia groups. Whole-heart radioactivity was determined with an external gamma detector. Myocardial flow rate (K (1), ml/min) and clearance rate (k (2), min(-1)) were calculated.

RESULTS

K (1TL), K (1TF), and K (1MIBI) decreased according to the severity of ischemia (K (1TL) 5.32 +/- 0.53, 4.76 +/- 0.70, and 1.44 +/- 0.59; K (1TF) 3.80 +/- 0.70, 2.73 +/- 0.99, and 1.09 +/- 0.45; and K (1MIBI) 3.45 +/- 1.10, 2.15 +/- 0.82, and 1.05 +/- 0.13, in the normal control, mild, and severe ischemia groups, respectively). K (1) was significantly higher for TL than for the (99m)Tc tracers (P < 0.05), but the (99m)Tc tracers had equivalent K (1) values. k (2TL) increased significantly (P < 0.05) in the ischemia groups (k (2TL) 0.062 +/- 0.013, 0.11 +/- 0.045, and 0.12 +/- 0.035), but showed no significant difference between the ischemia groups. k (2MIBI) and k (2TF) were significantly (P < 0.05) lower than k (2TL) and increased significantly (P < 0.05) in the severe ischemia group (k (2TF) 0.0056 +/- 0.0022, 0.0037 +/- 0.0015, and 0.024 +/- 0.015; and k (2MIBI) 0.00072 +/- 0.0011, 0.00038 +/- 0.00076, and 0.042 +/- 0.034). k (2MIBI) was significantly (P < 0.05) lower than k (2TF) in the normal control and mild ischemia groups.

CONCLUSIONS

Tracer extraction was higher for TL than for the (99m)Tc tracers and all tracers decreased according to the severity of ischemia-reperfusion in the three tracer groups. The clearance kinetics of not only MIBI but also TF is possibly useful for the evaluation of the severity of ischemia, and the Langendorff method and a methodological approach by continuous determinations of radioactivity may serve for the quantitative analysis of tracer kinetic profiles.

Evaluation of brain tumor recurrence by (99m)Tc-tetrofosmin SPECT: a prospective pilot study

OBJECTIVE

The differentiation between brain tumor recurrence and post-irradiation injury remains an imaging challenge. Computed tomography (CT) and magnetic resonance imaging (MRI) cannot always distinguish between the two. Although glioma cell line studies substantiated a plausible imaging superiority of (99m)Tc-tetrofosmin ((99m)Tc-TF) over other radiopharmaceuticals, little has been reported on its in vivo imaging properties. We assessed (99m)Tc-TF single-photon emission CT (SPECT) in cases where morphologic brain imaging was inconclusive between recurrence and radionecrosis.

METHODS

A total of 11 patients (7 men, 4 women) were evaluated. The initial diagnosis was glioblastoma multiforme (4), anaplastic astrocytoma (1), anaplastic oligodendroglioma (3), grade-II astrocytoma (2), and low-grade oligodendroglioma (1). All patients had been operated on and then received adjuvant external-beam radiotherapy. After a mean follow-up period of 25 months, there was clinical suspicion of recurrence, for which (99m)Tc-TF SPECT was performed.

RESULTS

In 8/11 cases, an abnormally increased tracer uptake appeared in the region that CT and/or MRI indicated as suspicious; in half of these cases, recurrence was confirmed histologically after surgery and in the other four by growth of the lesion over a 6-month follow-up period, and clinical deterioration. The remaining 3/11 patients had faint tracer uptake in the suspicious region, compatible with radiation injury; these lesions remained morphologically unaltered in a mean 12-month follow-up period, with no clinical deterioration in the patient's condition, a course strongly favoring the diagnosis of radiation injury.

CONCLUSIONS

Metabolic brain imaging by (99m)Tc-TF could offer useful information in the workup of treated brain tumors, where radiomorphologic findings between recurrence and radionecrosis are inconclusive.

Molecular modeling of hexakis(areneisonitrile)technetium(I), tricarbonyl eta5 cyclopentadienyl technetium and technetium(V)-oxo complexes: MM3 parameter development and prediction of biological properties

Genetic algorithms (GA) were used to develop specific technetium metal-ligand force field parameters for the MM3 force field. These parameters were developed using automated procedures within the program FFGenerAtor from a combination of crystallographic structures and ab initio calculations. These new parameters produced results in good agreement with experiment when tested against a blind validation set. To illustrate the utility of these new force field parameters, quantitative structure-activity relationship (QSAR) models were developed to predict the P-glycoprotein uptake (log10 VI) of a series of hexakis(areneisonitrile)technetium(I) complexes and to predict their biodistribution. The log10 VI QSAR model, built using a training set of 16 Tc(I) isonitrile complexes, exhibited a correlation between the experimental log10 VI and 5 simple descriptors as follows: r2 = 0.94, q2 = 0.93. When applied to an external test set of six Tc(I) isonitrile complexes, the QSAR preformed with great accuracy q2 = 0.78 based on a leave-one-out cross-validation analysis. Further QSAR models were developed to predict the biodistribution of the same set of Tc(I) isonitrile complexes; a QSAR model to predict hepatic uptake exhibited a correlation between the experimental log10(Blood/Liver) with six simple descriptors as follows: r2 = 0.97, q2 = 0.96. A QSAR model to predict renal uptake exhibited a correlation between the experimental log10(Blood/Kidney) and six simple descriptors as follows: r2 = 0.85, q2 = 0.82. When applied to the external test set the QSAR models preformed with great accuracy, q2 = 0.78 and 0.56, respectively.

Dopamine transporter density may be associated with the depressed affect in healthy subjects

OBJECTIVES

Increased levels of dopamine transporter (DAT) binding have been reported in patients with major depression. We used the selective DAT radiopharmaceutical Tc-TRODAT-1 and SPECT brain imaging, to examine differences in DAT levels in healthy subjects with and without depressive affect.

METHODS

We compared striatal DAT binding affinity in 73 healthy subjects to their scores on the depressive symptoms subscale of the Profile of Mood States (POMS). Regions of interest in the basal ganglia of the brain were examined. Distribution volume ratios (DVRs) of Tc-TRODAT-1 binding affinity were calculated from the SPECT scan data, and comparisons among subjects with low and high depressive symptom ratings were calculated using unpaired t-tests and the Pearson correlation.

RESULTS

We observed a greater Tc-TRODAT-1 DVR in the right caudate of subjects with high POMS mood scores compared to subjects with low scores on depressive items on the POMS (2.99+/-0.35 and 2.79+/-0.35, respectively; P=0.009). There was also a weak, but significant correlation between higher Tc-TRODAT-1 DVRs in the right caudate and depressive symptoms scores (r=0.23, P=0.05).

CONCLUSIONS

These data suggest that Tc-TRODAT-1 binding affinity to DAT sites may be associated with depressive affect in healthy subjects. The finding also supports prior observations of greater Tc-TRODAT-1 DVRs in patients with major depressive episode.

A case presenting with myocardial ischemia-like electrocardiogram findings after laryngopharyngoesophagectomy

Laryngopharyngoesophagectomy and reconstruction by using stomach roll with retrocardiac anastomosis were performed in a 60-year-old man with hypopharyngeal cancer. Postoperative electrocardiogram showed marked ST-segment elevation in leads I and aVL and depression in leads II, III, aVF, and V1-6. However, the patient did not present with abnormal findings on physical examination and vital signs were normal. Further, the laboratory data were normal. Echocardiography was a poor technique, but the stomach roll was observed to be expanded due to wall edema with exudates and exerted pressure on the posterior side of the heart. These findings were also ascertained by contrast-enhanced chest computed tomography scanning. Technetium-99m-tetrofosmin myocardial scintigraphy clearly showed that coronary blood perfusion and left ventricular wall motion were quite normal. The characteristic electrocardiogram returned to a near-normal state, and the expanded stomach roll shrank back to its ordinary size after one week. Coronary angiography showed neither organic stenoses nor vasospasm. The physical pressure of the expanded stomach roll might have influenced the electrocardiogram findings.

Accuracy of 64-slice CT angiography for the detection of functionally relevant coronary stenoses as assessed with myocardial perfusion SPECT

PURPOSE

CT angiography (CTA) offers a valuable alternative for the diagnosis of CAD but its value in the detection of functionally relevant coronary stenoses remains uncertain. We prospectively compared the accuracy of 64-slice CTA with that of myocardial perfusion imaging (MPI) using (99m)Tc-tetrofosmin-SPECT as the gold standard for the detection of functionally relevant coronary artery disease (CAD).

METHODS

MPI and 64-slice CT were performed in 100 consecutive patients. CTA lesions were analysed quantitatively and area stenoses > or =50% and > or =75% were compared with the MPI findings.

RESULTS

In 23 patients, MPI perfusion defects were found (12 reversible, 13 fixed). A total of 399 coronary arteries and 1,386 segments was analysed. Eighty-four segments (6.1%) in 23 coronary arteries (5.8%) of nine patients (9.0%) were excluded owing to insufficient image quality. In the remaining 1,302 segments, quantitative CTA revealed stenoses > or =50% in 57 of 376 coronary arteries (15.2%) and stenoses > or =75% in 32 (8.5%) coronary arteries. Using a cut-off at > or =75% area stenosis, CTA yielded the following sensitivity, specificity, negative (NPV) and positive predictive value (PPV), and accuracy for the detection of any (fixed and reversible) MPI defect: by patient, 75%, 90%, 93%, 68% and 87%, respectively; by artery, 76%, 95%, 99%, 50% and 94%, respectively.

CONCLUSION

Sixty-four-slice CTA is a reliable tool to rule out functionally relevant CAD in a non-selected population with an intermediate pretest likelihood of disease. However, an abnormal CTA is a poor predictor of ischaemia.

Evaluating dopamine transporter activity with 99mTc-TRODAT-1 SPECT in drug-naive Tourette's adults

OBJECTIVES

Findings on imaging of dopamine transporter (DAT) activity in patients with Tourette's syndrome remain inconclusive. The present study was carried out to observe DAT activity in patients with well-controlled Tourette's syndrome by using (99m)Tc-TRODAT-1 single photon emission computerized tomography (SPECT).

METHODS

Six drug-naive patients with Tourette's syndrome (mean age+/-SD, 21.2+/-1.5 years) were recruited. All met the criteria for Tourette's syndrome established in the DSM-IV. Seventeen age-matched and sex-matched healthy subjects served as the controls. Brain SPECT were acquired 165-195 min after administrating 740 MBq of (99m)Tc-TRODAT-1, using a double-headed camera equipped with ultra-high-resolution fan-beam collimators. The specific uptake ratio was calculated by subtracting the mean counts per pixel in the occipital cortex from the mean counts per pixel in the striatum, putamen or caudate nucleus and by dividing the result by the mean counts per pixel in the occipital cortex. Tic-severity scores were also measured and correlated with the specific uptake ratios.

RESULTS

No significant difference in DAT activity between patients with Tourette's syndrome and control subjects was found in the striatum and its sub-regions. Tic-severity scores were also not correlated with specific uptake ratios measured from the striatum and its sub-regions.

CONCLUSIONS

In conjunction with previous findings, our results suggested that functional abnormality of the dopamine system in patients with Tourette's syndrome might be evident only in its early stage. Adaptation to tic symptoms might play a role in regulating the neural system.

Tracer kinetics of forearm endothelial function: comparison of an empirical method and a quantitative modeling technique

Forearm Endothelial Function (FEF) is a marker that has been shown to discriminate patients with cardiovascular disease (CVD). FEF has been assessed using several parameters: the Rate of Uptake Ratio (RUR), EWUR (Elbow-to-Wrist Uptake Ratio) and EWRUR (Elbow-to-Wrist Relative Uptake Ratio). However, the modeling functions of FEF require more robust models. The present study was designed to compare an empirical method with quantitative modeling techniques to better estimate the physiological parameters and understand the complex dynamic processes. The fitted time activity curves of the forearms, estimating blood and muscle components, were assessed using both an empirical method and a two-compartment model. Although correlational analyses suggested a good correlation between the methods for RUR (r=.90) and EWUR (r=.79), but not EWRUR (r=.34), Altman-Bland plots found poor agreement between the methods for all 3 parameters. These results indicate that there is a large discrepancy between the empirical and computational method for FEF. Further work is needed to establish the physiological and mathematical validity of the 2 modeling methods.

Radiopharmaceutical diagnosis of Erdheim-Chester's disease

Erdheim-Chester's disease is a non-inherited multi-focal lipid-storing histiocytosis of unknown origin without a complete and convincing diagnostic and therapeutic protocol. We have previously suggested diagnostic methods using radioisotopes to evaluate this disseminating disease, but they are neither specific nor selective in this regard. The present hypothesis-driven paper reviewing our case proposes novel approaches involving nuclear medicine and utilizing radiopharmaceuticals to identify this potentially fatal multi-system disease.

Design and evaluation of “3 + 1” mixed ligand oxorhenium and oxotechnetium complexes bearing a nitroaromatic group with potential application in nuclear medicine oncology

The synthesis and evaluation of a series of oxotechnetium and oxorhenium complexes containing a nitroaromatic moiety as potential radiopharmaceuticals for targeting tumour hypoxia is presented. 99mTc labelling was performed in high yield (>85%) and radiochemical purity (>90%). Their structure was corroborated by means of the rhenium complexes. Reduction potentials were in the range for bioreducible compounds. 99mTc complexes III-VI were selected for "in vivo" experiments in view of the results of cytotoxicity studies. Biodistribution in normal animals was characterized by high initial blood, lung and liver uptake, fast blood and soft tissue depuration and preferential excretion via the hepatobiliary system. Initial tumour uptake was moderate but tumour/muscle ratios for complexes III and IV, were favourable at all time points. Although the results are encouraging further development is still necessary in order to achieve higher tumour uptake and lower gastrointestinal activity.

Comparison of region-of-interest analysis and human observers in the diagnosis of Parkinson's disease using [99mTc]TRODAT-1 and SPECT

This study determined the relative accuracy of diagnosis of Parkinson's disease (PD) using SPECT imaging data, comparing a semi-quantitative region-of-interest (ROI) approach and human observers. A set of patients with PD and normal healthy control subjects were studied using the dopamine transporter tracer [(99m)Tc]TRODAT-1 and SPECT. The sample comprised 81 patients (mean age +/- SD, 63.4 +/- 10.4 years; age range, 39.0-84.2 years) and 94 healthy controls (mean age +/- SD, 61.8 +/- 11.0 years; age range, 40.9-83.3 years). A standardized template containing six ROIs was transposed onto subregions of the brain, and the ratio of striatal to background ROI values was used as a semi-quantitative outcome measure. All images were used in a human observer study, with four experienced investigators. The data from the observer and ROI studies were analysed using a receiver operating characteristic (ROC) analysis, where the area under the ROC curve (AUC) indicated the diagnostic accuracy. ROI analysis and human observers gave similar diagnostic performance (mean observer AUC = 0.89, best ROI AUC = 0.90). This suggested that the human observers are visually acquiring similar information from the images that are contained in the semi-quantitative striatal uptake.

Risk stratification of patients with angina pectoris by stress 99mTc-tetrofosmin myocardial perfusion imaging

Angina pectoris is a major symptom associated with myocardial ischemia. The aim of this study was to find whether stress myocardial perfusion imaging can independently predict mortality in patients with angina.

METHODS

We studied 455 patients with stable angina pectoris by exercise or dobutamine stress (99m)Tc-tetrofosmin myocardial perfusion tomographic imaging. An abnormal finding was defined as a reversible or fixed perfusion abnormality. The endpoint during follow-up was death from any cause.

RESULTS

Mean age was 60+/-10 y. There were 266 men (58% of the patients). Myocardial perfusion was normal in 137 patients (30%). Perfusion abnormalities were reversible in 167 patients and fixed in 151 patients. During a mean follow-up of 6+/-1.7 y, 93 patients (20%) died. The annual mortality rate was 1.5% in patients with normal perfusion and 4.5% in patients with abnormal perfusion. Patients with a multivessel distribution of perfusion abnormalities had a higher annual death rate than patients with abnormalities in a single-vessel distribution (5.1% vs. 3.7%). In a multivariate analysis model, independent predictors of death were age (risk ratio, 1.05; 95% confidence interval [CI], 1.03-1.08), the male sex (risk ratio, 2.1; CI, 1.3-3.4), diabetes (risk ratio, 2.2; CI, 1.4-3.5), heart failure (risk ratio, 2.7; CI, 1.6-4.5), smoking (risk ratio, 1.7; CI, 1.1-2.6), reversible perfusion abnormalities (risk ratio, 1.9; CI, 1.1-2.8), and fixed perfusion abnormalities (risk ratio, 2; CI, 1.2-3.1).

CONCLUSION

Stress 99mTc-tetrofosmin myocardial perfusion imaging provides independent information for predicting mortality in patients with stable angina pectoris. Both reversible and fixed defects are associated with an increased risk of death. The extent of stress perfusion abnormalities is a major determinant of mortality. Patients with normal perfusion have a low mortality rate during long-term follow-up.

The role of 99mTc-tetrofosmin scintigraphy for staging patients with laryngeal cancer

Diagnosis and staging of laryngeal cancer is currently based on physical examination, endoscopy, and imaging techniques such as computed tomography (CT) and/or magnetic resonance (MR) and histology. While imaging techniques have a pivotal role for defining the size of the primary tumor, they are less accurate for defining metastatic involvement of regional lymph nodes, especially if lymph nodes are smaller than 10-15 mm. The aim of this study was to comparatively assess the relevance of (99m)Tc-tetrofosmin scintigraphy for the staging of laryngeal tumors versus the CT scan. We evaluated the sensitivity of imaging with (99m)Tc-tetrofosmin in 28 consecutively enrolled patients with squamous cell laryngeal carcinoma. Total-body scintigraphy with 99mTc-tetrofosmin was performed preoperatively, and the results were compared to CT images of the neck and mediastinum. CT and (99m)Tc-tetrofosmin scintigraphy were equally sensitive (96%) in identifying the primary tumor. While CT was more sensitive for detecting metastatic lymph nodes (100% versus 50%), (99m)Tc-tetrofosmin scintigraphy was more specific (100% versus 56%; p < 0.04). The overall diagnostic capabilities of the two techniques for detecting lymph node metastases were comparable (Youden Index: J = 0.56 for CT and J = 0.50 for (99m)Tc-tetrofosmin scintigraphy). (99m)Tc-tetrofosmin scintigraphy is a useful complement to CT for staging laryngeal tumors, especially for detecting metastatic lymph nodes and distant metastases.

Imaging of HER2/neu expression in BT-474 human breast cancer xenografts in athymic mice using [99mTc]-HYNIC-trastuzumab (Herceptin) Fab fragments

OBJECTIVE

To evaluate the ability of trastuzumab (Herceptin) Fab, labelled with (99m)Tc through introduced hydrazinenicotinamide (HYNIC) functionalities, to image HER2/neu-overexpressing human breast cancer xenografts in athymic mice.

METHODS

Fab fragments were produced by immobilized papain digestion of trastuzumab immunoglobulin G (IgG), followed by purification by ultrafiltration. The immunoreactivity of trastuzumab Fab was evaluated by receptor-binding assays against HER2/neu-positive SK-BR-3 human breast cancer cells. Trastuzumab Fab fragments were labelled with (99m)Tc following modification with HYNIC N-hydroxysuccinimide ester. Biodistribution and tumour imaging studies were performed in athymic mice bearing subcutaneous HER2/neu-overexpressing BT-474 human breast cancer xenografts following intravenous injection of 1.1 or 25 MBq of [(99m)Tc]-trastuzumab Fab (30 microg), respectively. The specificity of tumour uptake was assessed by comparison with that of [(99m)Tc]-labelled irrelevant anti-CD33 HuM195 Fab.

RESULTS

Trastuzumab Fab was pure and exhibited preserved immunoreactivity towards SK-BR-3 cells (K(d) = 1.6 x 10(-8) M). Modification with HYNIC diminished its receptor-binding affinity fourfold. [(99m)Tc]-trastuzumab Fab localized avidly and specifically in BT-474 xenografts, achieving a tumour uptake of 10.7% of the injected dose (ID) per gram and a tumour to blood (T/B) ratio of 3 : 1 at 24 h. The tumour uptake and T/B ratio for [(99m)Tc]-trastuzumab Fab were significantly higher than those for control [(99m)Tc]-HuM195 Fab (2.6% ID x g(-1) and 0.9 : 1, respectively; P<0.05). Tumours were imaged as early as 2 h post-injection of [(99m)Tc]-trastuzumab Fab, but were more clearly visualized at 6 and 24 h post-injection.

CONCLUSIONS

[(99m)Tc]-HYNIC-trastuzumab Fab localized specifically in HER2/neu-overexpressing human breast cancer xenografts in athymic mice, allowing imaging of the tumours within the useful lifetime of the radionuclide.

Molecular Nuclear Imaging: The Radiopharmaceuticals (Review)

Application of the nuclear approach for the detection of inherited diseases is an important goal for nuclear medicine and will likely result in an important breakthrough, which will, hopefully, lead to improved diagnoses of genetic defects and objective evaluations of the efficacy of therapeutic strategies. Although still largely in the research realm, molecular imaging is in the process of emerging as a vital component of the diagnosis of disease and monitoring of the therapy. The clinical research in nuclear medicine has made major advancements in the direction of molecular medicine and targeted therapy. In the past few years, exponential achievements have been accomplished in the development of molecular nuclear imaging agents, as described below.

The impact of acquisition protocol on the incidence of patient motion in 99mTc based myocardial perfusion SPECT

BACKGROUND

Myocardial perfusion single photon emission computed tomography (SPECT) artefacts introduced as a result of patient motion are known to produce artefacts that mimic the appearances of coronary artery disease. The advent of 99mTc based radiopharmaceuticals permits greater flexibility in patient scheduling, but variable physical demands of protocols may be associated with variations in the likelihood of patient motion.

METHODS

A prospective cross-sectional study of 177 myocardial perfusion SPECT patients using 99mTc tetrofosmin was used to compare the incidence of visually detectable motion for three protocol variations. The rotating cinematic display and sinograms of the datasets were visually assessed by two experienced technologist observers blinded to the second observer's responses and the clinical outcome.

RESULTS

Among the 354 individual studies analysed, 43.8% contained visually detectable motion. 36.2% of rest studies demonstrated visually detectable motion compared to 51.4% for stress (P<0.05). Fifty per cent of 1 day rest/stress studies demonstrated motion, 39.3% of 2 day rest/stress studies demonstrated motion, and 46.8% of 2 day stress/rest studies demonstrated motion.

CONCLUSION

One day 99mTc based myocardial perfusion SPECT studies are 1.3 times more likely to contain motion than the 2 day rest/stress protocol. The 2 day stress/rest protocol is 1.2 times more likely to contain motion than the 2 day rest/stress. The stress study is 1.4 times more likely to contain motion than the rest study while the stress study performed first in the sequence is 1.4 times more likely to contain motion than the stress study performed second. The 2 day rest/stress protocol is the preferred protocol to minimize patient motion.

Labeling efficiency and biodistribution of Technetium-99m labeled nanoparticles: interference by colloidal tin oxide particles

The interference of colloidal tin oxides on the biodistribution of (99m)Technetium radiolabeled chitosan nanoparticles has been overcome by using sodium borohydride instead of commonly used stannous salts as reducing agent for the reduction of (99m)Tc (VII) to lower valency states. Biodistribution of radiolabeled chitosan nanoparticles prepared by using stannous chloride method revealed localization of the radioactivity mainly in the liver and spleen while that of radiolabeled chitosan nanoparticles prepared by using sodium borohydride method manifested the presence of radioactivity in blood up to an extent of 10% even after 2 h. Interestingly, the reduction of radioactivity in the latter case with the progress of time was not manifested through an increase in activity in the liver. Rather, a time dependent increased accumulation of radioactive materials was observed in the stomach. From the results it has been concluded that the biodistribution is strongly influenced by the presence of colloidal particles of tin oxides and (99m)Tc labeled chitosan nanoparticles are RES evading and long circulating in blood when Tc (VII) is reduced by sodium borohydride and not by stannous chloride during radiolabeling process.

Synthesis and in Vitro Characterization of Organometallic Rhenium and Technetium Glucose Complexes against Glut 1 and Hexokinase

A series of nine organometallic technetium-99m and rhenium complexes of glucose are presented and characterized in vitro regarding their potential as surrogates of [18F]-2-fluoro-desoxy glucose ([18F]-FDG). The glucose derivatives are functionalized at positions C-1, C-2, C-3, and C-6. Different spacer lengths and chelating systems have been introduced at these sites. For the (radio)labeling, the organometallic precursors [99mTc(H2O)3(CO)3]+ and [ReBr3(CO)3](2-) respectively have been used. The resulting complexes have been characterized chemically and radiochemically. The formation of uniform products has been observed on the macroscopic (Re) and no-carrier-added level (99mTc). The Tc-99m complexes revealed good inertness against ligand exchange (Cys and His) and excellent stability in physiological buffered saline as well as in human plasma over a period of 24 h at 37 degrees C. The rhenium complexes have been tested for competitive inhibition of the (yeast) hexokinase. Only for C-2 derivatized glucose complexes with extended spacer functionalities Ki values in the millimolar and sub-millimolar range have been observed. In silico molecular docking experiments supported these experimental findings. However, the competitive inhibitors are not recognized as a pseudosubstrate of hexokinase. The cellular uptake of all 99mTc-complexes into HT-29 colon carcinoma cells via Glut1 was generally low and unspecific independent of the position at the hexose ring, the chelating systems, or the overall charge of the corresponding metal complexes. The current results seem to preclude the use of these compounds as [18F]-FDG surrogates primarily due to the low cellular uptake via Glut1.

Efficacy of 99mTc-EDDA/HYNIC-TOC Scintigraphy in Differential Diagnosis of Solitary Pulmonary Nodules

Fifty consecutive patients with solitary pulmonary nodules (SPN) on chest radiographs were studied scintigraphically after the administration of a somatostatin analog 99mTc-EDDA/HYNIC-TOC. The activity amounted to 740-925 MBq and a single photon emission computed tomography (SPECT) technique was applied. Verification of the nodule etiology was based on histology or cytology and bacteriology. As additional criterion for nodule benignity, its stable size in a chest radiograph for at least 3 years was accepted. In 31 patients, malignant etiologies of nodules were found. The diagnoses included: 11 adenocarcinomas, 6 squamous-cell carcinomas, 2 large-cell carcinomas, 6 nonsmall-cell lung cancers (NSCLC) of unspecified, more detailed morphology, 2 small-cell lung cancers (SCLC), 2 typical carcinoids, and 2 metastatic tumors: leiomyosarcoma and malignant melanoma. In 19 patients, the following benign tumors were diagnosed: 6 tuberculomas, 2 other granulomas, 4 hamartomas, 2 nonspecific inflammatory infiltrates, 1 abscess, 1 peripheral carcinoid of morphological characteristics of a benign tumor, 1 ectopic lesion of thyroid tissue, and 2 benign tumors of unspecified etiology, with stable size over 3 and 5 years. Positive scintigraphic results were obtained in 28 of 31 patients (90%) with malignant SPNs; among these there were 26 of 27 (96%) cases of primary pulmonary carcinoma. The remaining 2 false-negative cases included metastatic tumors: liposarcoma and melanoma. Among 19 benign lesions, 15 (79%) did not accumulate the radiopharmaceutical. The remaining 4 tumors visible on scintigrams included: 1 tuberculoma, 1 hamartoma, 1 abscess, and 1 case of nonestablished diagnosis (with stable size over 3 years). In conclusion, scintigraphy with 99mTc-EDDA/HYNIC-TOC appears to be an effective procedure for differentiation between malignant and benign SPNs.

Technetium-99m-Sestamibi SPECT myocardial perfusion imaging in patients with complete left bundle branch block

BACKGROUND

Diagnosis of coronary artery disease (CAD) in patients with left bundle branch block (LBBB) is considered a challenge in cardiology due to low accuracy of noninvasive methods such as basal and exercise stress test. Recently, myocardial perfusion imaging showed attainment of higher sensitivity and specificity. Scintigraphy with thallium-201 has been widely used in these patients. Few have used technetium-99m-Sestamibi and single photon emission computed tomography (SPECT). The aim of the study was to assess the diagnostic value of Tc-99m Sestamibi SPECT myocardial perfusion imaging in patients with complete LBBB.

METHODS

We studied 57 consecutive patients with complete LBBB using Tc-99m-Sestamibi SPECT and treadmill or dipyridamole stress to evaluate CAD. Eighteen patients also underwent coronary angiography. Perfusion defects were classified as fixed or reversible.

RESULTS

Prevalence of resting perfusion abnormalities in anterior, septal, and apical regions was 51, 56, and 19%, respectively. Sensitivity for detecting >50% left anterior descending artery (LAD) stenosis was 67 and 56% for anterior or septal defects, and 56% for specificity. Apical perfusion abnormality showed 21% sensitivity and 89% specificity. Among six patients with reversibility and who underwent coronary angiography, all had >50% LAD stenosis.

CONCLUSIONS

With Tc-99m-MIBI SPECT imaging, prevalence of anteroseptal perfusion abnormalities was >50% in patients with LBBB. The test has moderate sensitivity and specificity for LAD disease. Absence of apical defect is specific for excluding LAD disease. Reversible changes in anteroseptal wall should be considered as an indicator of ischemia in this territory.

Technetium-99m tetrofosmin SPECT predicts chemotherapy response in small cell lung cancer

The multidrug resistance gene 1 encoding human P-glycoprotein (Pgp) is thought to play an important role in the multidrug resistance of lung cancer. The purpose of this study was to predict chemotherapy response by technetium-99m tetrofosmin (Tc-99m TF) lung single photon emission computed tomography (SPECT) and compare Pgp expression in patients with untreated small cell lung cancer (SCLC). Forty patients with untreated SCLC received Tc-99m TF lung SPECT prior to chemotherapy. The chemotherapy response was evaluated in the 3rd month after completion of treatment. Immunohistochemical staining of Pgp expression was performed on multiple nonconsecutive sections of biopsy specimens. By quantitative analyses, tumor to background ratios were 1.86 +/- 0.27 and 1.17 +/- 0.26 for patients with a good and poor response, respectively (p < 0.05). All of the 20 patients with a good chemotherapy response also had a positive Tc-99m TF lung SPECT and negative Pgp expression. In contrast, only 4 of the 20 patients with a poor chemotherapy response had a positive Tc-99m TF lung SPECT. Moreover, 10 of the 20 patients with a poor chemotherapy response also had negative Pgp expression (p < 0.05). Therefore, we concluded that Tc-99m TF lung SPECT can accurately predict the chemotherapy response, and Tc-99m TF lung SPECT findings can be partially compatible with Pgp expression in patients with untreated SCLC.

To predict chemotherapy response using technetium-99m tetrofosmin and compare with p-glycoprotein and multidrug resistance related protein-1 expression in patients with untreated small cell lung cancer

The aim of this study was to investigate the relationships among technetium-99m tetrofosmin (Tc-TF) accumulation in untreated small cell lung cancer (SCLC), the expression of P-glycoprotein (Pgp) and multidrug resistance related protein-1 (MRP1), and the response to chemotherapy in patients with untreated SCLC. Thirty patients with SCLC were studied with chest scintigraphy 15 to 30 min after intravenous injection of Tc-TF before chemotherapeutic induction. Tc-TF chest scans were interpreted both visually and quantitatively. The response to chemotherapy was evaluated upon completion of chemotherapy. Immunohistochemical analyses were performed on multiple non-consecutive sections of biopsy specimens to detect Pgp and MRP1 expression. Fifteen patients with good response to chemotherapy had a significantly higher incidence (100.0%) of positive Tc-TF chest single photon emission computed tomography (SPECT) findings and negative Pgp or MPR expression than 15 patients with poor response (20%) (P<0.05). The tumor/background (T/B) ratios were 1.8+/-0.3 and 1.2+/-0.3 for patients with good response and poor response, respectively (P<0.05). However, other prognostic factors (performance status, tumor size and stage) were not significantly related to Tc-TF chest scan findings and response to chemotherapy. Tc-TF chest scintigraphy correlated well with Pgp or MRP1 expression and accurately predicted the response to chemotherapy in patients with SCLC.

Study of tea polyphenol as a reversal agent for carcinoma cell lines' multidrug resistance (study of TP as a MDR reversal agent)

The aim of this study was to examine MDR1 expression product P-glycoprotein (Pgp) and study the effect and mechanism of tea polyphenol (TP) in reversion of multidrug resistance (MDR) in carcinoma cell lines. Immunocytochemical method was used for qualitative detection of Pgp. A comparative study of cytotoxicity and multidrug resistance reversion effect was made by MTT assay for tea polyphenol and quinidine in MCF-7 and MCF-7/Adr cell lines. The multidrug resistance reversion effect and mechanism were studied by measuring the uptake of 99mTc-tetrofosmin in the carcinoma cell lines. (1) The Pgp overexpression in MCF-7/Adr cells was found to be strong positive, while the Pgp expression of MCF-7 was negative. (2) Although both tea polyphenol and quinidine could not remarkably change the toxicity of adriamycin to MCF-7, they could improve the sensitivity of MCF-7/Adr to adriamycin. The reversion index of tea polyphenol and quinidine was 3 and 10 respectively. (3) The cellular uptake of 99mTc-tetrofosmin was remarkably lower in MCF-7/Adr than in MCF-7. The uptake of 99mTc-tetrofosmin in MCF-7/Adr exhibited a 4, 13, 16 fold increase in the presence of 200, 400 and 500 microg/ml of tea polyphenol respectively. The uptake of 99mTc-tetrofosmin in MCF-7/Adr exhibited only a 4-fold increase in the presence of 200 microM of quinidine. Immunocytochemistry can detect P-glycoprotein expression level qualitatively. Tea polyphenol is not only an anti-tumor agent, but also a multidrug resistant modulator similar to quinidine. The multidrug resistance reversion mechanism of tea polyphenol seems to be its inhibition of the activity of P-glycoprotein. Tea polyphenol has the advantage of very low toxicity in tumor treatment.

Evaluation of heart time-activity curves as a predictor of hepatic extraction of 99mTc-mebrofenin in dogs

In this study, heart time-activity curve, created following intravenous injection of 99mTc-mebrofenin were used to quantify hepatic function in normal dogs and dogs with induced hepatic parenchymal cell damage. The results were compared to a direct measurement of hepatic extraction following mesenteric venous injection of 99mTc-mebrofenin. The heart time-activity curves were normalized and the area under the curve from 0-30 minutes and 0-60 minutes were determined. In addition, the half-time clearance rate of the heart time-activity curve was analyzed using a two-compartment model. Linear regression analysis was used to describe the relationship between the area under the normalized heart time-activity curve and hepatic extraction. There was good correlation between the area under the normalized heart time-activity curve and hepatic extraction. The best correlation was obtained from the 0-30 minute data (r2 = 0.92). A formula for calculating hepatic extraction was derived using linear regression analysis: Hepatic extraction = 1.092 - (0.0000308 x AUC0-30 minutes). There was good correlation between the half-time clearance rates from the heart time-activity curve and hepatic extraction. The best correlation was between the fast phase half-time clearance and hepatic extraction (r2 = 0.88). The area under a normalized heart time-activity curve can be used as a simple alternative to deconvolutional analysis for the determination of hepatic extraction as a measure of hepatic parenchymal cell function in the dog.

Detection of deep venous thrombosis by DMP 444, a platelet IIb/IIIa antagonist: a preliminary report

BACKGROUND

We report a method for detection of deep venous thrombosis with a technetium 99m-labeled peptide (DMP 444). The N-methyl-arginine-glycine-aspartic acid sequence on DMP 444 binds the glycoprotein IIb/IIIa receptor on activated platelets (inhibition constant [IC50] for fibrinogen binding = 6 nmol/L).

METHODS

DMP 444 (23 to 27 mCi) was injected into 11 patients with clinical suspicion of deep venous thrombosis, diagnostic confirmation by ultrasound, and a positive D-dimer test result. Planar images in the anterior and posterior projections were obtained at 10 to 40 minutes, 50 to 80 minutes, and 120 to 150 minutes after injection.

RESULTS

No clinically significant adverse effects were noted after DMP 444 administration. One patient (excluded from the analysis) withdrew consent, so image acquisition was not complete. By 10 to 40 minutes after injection, 8 of 10 patients demonstrated an area of increased activity that was clearly related to the abnormality noted on ultrasound. Most patients were taking warfarin (Coumadin) and heparin (n = 8) or heparin (n = 1) and warfarin (n = 1) alone at the time of the imaging. The average time from onset of symptoms to injection of DMP 444 was 5 days (range 1 to 18 days).

CONCLUSION

These preliminary human studies indicate that DMP 444 is safe and may be of value in the diagnosis of deep venous thrombosis.

[Preclinical pharmacological study of a novel myocardial perfusion agent: 99mTc-Q3]

In order to provide an experimental foundation for clinical study, we made a preclinical pharmacological investigation of 99mTc-Q3, a novel myocardial perfusion imaging agent, technetium-99m-N,N'-ethylenebis (acetylace-toneiminato) bis (tris (3-methoxy-1-proply) phosphine). After the preparation of this compound, the kinetics of blood clearance in rabbits, biodistribution in mice, measurement of plasma protein binding rate, and myocardial perfusion imaging in dog were carried out. The labelling efficiency and radiochemical purity measured were over 99%, and the stability (in vitro) was good and stable up to 6 hr of testing at room temperature. The pharmacokinetics met the two-compartment model with 0.23 +/- 0.09 ml/min of excellent blood clearance, an initial half-time of 1.5979 +/- 0.4182 min, and a late half-time of 203 +/- 25.83 min. The biodistribution as shown in myocardial accumulation was earlier, the radioactive value was higher, and once extracted, it remained relatively constant in the myocardium for at least 4 hr. The tracer was rapidly cleared from the blood, lung and the liver. The scintigraphy imaging in dog demonstrated that it was rapidly cleared from the lung, and the radioactive concentration approached that of background 1 hr after injection. At 15 min after injection, the myocardial imaging displayed clearly up to 3 hr. In vitro protein binding rate was low (7.13 +/- 0.42%). The tolerance of this drug in mice was 500 times as much as in humans. In conclusion, 99mTc-Q3 exhibits favorable stability, biological property and safety, so clinical study of this preparation as a myocardial perfusion imaging agent is worthwhile.

Syntheses and radiolabeling of cysteine-oximes and pharmacological behaviour of their 99mTc complexes

Synthesis of two novel ligands using 2-oximino-butan-3-one and L-ethyl cysteinate is described. The synthetic procedure involved the formation of Schiffs base by the condensation of the amino group of L-ethyl cysteinate with the carbonyl group of 2-oximino-butan-3-one to provide the ligand I, N'(butan-2-enyl-3-oximino)ethyl cysteinate, followed by reduction of the Schiffs base with sodium borohydride to ligand II, N'(3-oximinobutyl)ethyl cysteinate. The ligands were characterised by NMR spectroscopy. Complexation studies with 99mTc were carried out using stannous tartrate as the reducing agent. The complexes were characterised by paper chromatography, thin layer chromatography and paper electrophoresis techniques. The complexes are formed in high yields when the reactions were carried out at pH 7-9. The 99mTc complex with ligand I is formed instantaneously while the 99mTc complex with ligand II is formed at a slower rate. The complexes were found to be neutral but the lipophilicity of the complex with ligand I was higher than that of the complex of ligand II. The stability of the complex with ligand I was relatively poor as compared to that of the complex with ligand II. Biodistribution studies of the 99mTc complexes of ligand I and II showed rapid blood clearance with hepatobiliary uptake. Renal excretion of the complex of ligand II was more than that observed for the complex of ligand I. The complexes did not show significant uptake in brain in spite of their favourable properties such as neutrality, lipophilicity and structural similarity with both ECD and HMPAO.

Imaging experimental intraabdominal abscesses with 99mTc-PEG liposomes and 99mTc-HYNIC IgG

OBJECTIVE

To evaluate the accuracy of technetium-99m-labeled polyethylene glycol-coated liposomes (99mTc-PEG liposomes) and technetium-99m-labeled nonspecific human immunoglobulin G (99mTc-HYNIC IgG) for the scintigraphic detection of experimental intraabdominal abscesses in comparison with that of a standard agent, gallium-67 citrate.

BACKGROUND

Scintigraphic imaging techniques can be very useful for the rapid and accurate localization of intraabdominal abscesses. Two newly developed radiolabeled agents, 99mTc-PEG liposomes and 99mTc-HYNIC IgG, have shown to be excellent agents for imaging experimental focal infection, but have not yet been studied in the detection of abdominal abscesses.

METHODS

Intraabdominal abscesses were induced in 42 rats using the cecal ligation and puncture technique. Seven days later, randomized groups of rats received 99mTc-PEG liposomes, 99mTc-HYNIC IgG, or 67Ga citrate intravenously. The rats were imaged up to 24 hours after the injection. The biodistribution of the radiolabel was determined by counting dissected tissues ex vivo. Macroscopic intraabdominal abnormalities and focal uptake on the images were independently scored on a semiquantitative scale.

RESULTS

99mTc-PEG liposomes provided the earliest scintigraphic visualization of the abscess (as soon as 2 hours after the injection vs. 4 hours for the other two agents). Liposomes, IgG, and gallium all showed similarly high absolute uptake in the abscess. Focal uptake of liposomes and gallium correlated best with the extent of the macroscopic abnormalities.

CONCLUSIONS

99mTc-PEG liposomes and 99mTc-HYNIC IgG performed at least as well as the standard agent, 67Ga citrate, in the detection of experimental intraabdominal abscesses, with obvious advantages such as lower radiation exposure and more favorable physical properties. Of the two technetium agents, the liposomes seemed to be superior, providing the earliest diagnostic image and the best correlation with the inflammatory abnormalities. In addition, the preferential localization of radiolabeled PEG liposomes holds promise for targeted delivery of liposome-encapsulated drugs.

Technetium-99m-labeled liposomes to image experimental colitis in rabbits: comparison with technetium-99m-HMPAO-granulocytes and technetium-99m-HYNIC-IgG

Scintigraphic techniques are routinely used for the evaluation of the extent and severity of inflammatory bowel disease. Currently, the radiopharmaceutical of choice is 99mTc-hexamethyl propyleneamine oxime (HMPAO)-leukocytes. We studied the imaging potential of two recently developed 99mTc-labeled agents, polyethylene glycol (PEG)-coated liposomes and hydrazinonicotinate (HYNIC) IgG, in a rabbit model of acute colitis, and compared them with that of 99mTc-labeled, granulocyte-enriched (>90%), white blood cells.

METHODS

Acute colitis was induced in rabbits by retrograde instillation of trinitrobenzene sulfonic acid. After 48 hr, 37 MBq of each radiopharmaceutical was administered intravenously. Gamma camera images were taken at 0, 1, 2, 4, 10 and 24 hr. At 4 and 24 hr postinjection, groups of rabbits were killed, and the uptake of the radiolabel in the dissected tissues was determined. For each affected 5-cm segment, the colitis index (CI, affected-to-normal-colon-uptake ratio) was calculated and correlated to the macroscopically scored severity of inflammation.

RESULTS

All three agents visualized the colitis lesions within 1 hr postinjection. The CI correlated with the severity of the abnormalities. With increasing severity, the CI at 4 hr postinjection for liposomes was 3.89+/-0.73, 4.41+/-0.47 and 5.76+/-0.65; for IgG 1.67+/-0.08, 3.92+/-0.44 and 6.14+/-0.65; and for granulocytes 2.90+/-0.09, 6.15+/-0.96 and 9.36+/-3.35. For liposomes, the CI further increased during 24-hr postinjection to 6.56+/-0.84, 8.50+/-0.53 and 10.61+/-1.34, respectively. The CI for the other two agents did not change significantly with time.

CONCLUSION

In this rabbit model, 99mTc-labeled granulocytes, IgG and liposomes all rapidly visualized colonic inflammation. Granulocytes and liposomes showed the highest CI. Technetium-99m-labeled PEG-liposomes may be an attractive alternative for labeled leukocytes to image inflammatory bowel disease, because they can be prepared off the shelf and no handling of blood is required.

Localization of a bacterial infection with 99Tcm-labelled human IgG: further improvement with enriched IgG subclass preparations

The aim of this study was to determine the contribution of various IgG subclasses to the scintigraphic detection of a staphylococcal infection. An experimental thigh infection in mice was used to determine the accumulation of the various 99Tcm-labelled IgG preparations with enriched IgG1, IgG2 or IgG4 subclass. Multiple-regression analysis was used to investigate a relationship between the IgG subclasses and the time-dependent accumulation in infected sites. Eighteen hours after infection with Staphylococcus aureus bacteria 20 micrograms of 99Tcm-labelled IgG preparations enriched with one of the IgG1, IgG2 or IgG4 subclasses by thiophilic absorption were administered intravenously and target-to-nontarget (T/NT) ratios were determined at 15 min, 1 h, 4 h and 24 h after injection of the tracer. Moreover, the binding of these preparations to S. aureus was assessed using an in vitro bacterial pellet model as an indication for the potency of detecting infections. As a control agent, 99Tcm-labelled polyclonal IgG (HIG) was used. In vivo, the T/NT ratios were significantly (P < 0.05) higher for the IgG1-enriched preparation at all time points, and for the IgG2-enriched preparation at 4 h and 24 h after injection, compared with HIG. In contrast, IgG4 did not yield higher T/NT ratios at any time. Using multiple-regression analysis, it became evident that IgG3 at all time intervals, IgG1 for early scans (up to 4 h) and IgG2 for late scans (24 h) contribute significantly (P < 0.05) to the accumulation. The abundance of IgG subclasses in the various preparations appeared to influence the accumulation of tracer at infected sites. The percentage of binding to S. aureus in vitro was significantly (P < 0.05) higher for enriched IgG subclass preparations than for HIG. We conclude that specific subclass enrichment of 99Tcm-labelled IgG preparations improves the scintigraphic detection of staphylococcal infections at various time intervals post-injection.

Retention of technetium-99m in infectious foci in rats after release from technetium-99m labelled human non-specific polyclonal immunoglobulin G: a dual-label study with hydrazinonicotinamido and iminothiolano immunoglobulin

In an effort to contribute to the understanding of the mechanism of uptake of technetium-99m labelled non-specific polyclonal human immunoglobulin G (hIgG) in inflammatory lesions we compared the tissue distribution of double-labelled 99mTc-hydrazinonicotinamido (HYNIC) hIgG-14C and 99mTc-iminothiolano hIgG-14C in groups of five Wistar rats with a Staphylococcus aureus infection of the left calf muscle between 2 h p.i. and 24 h p.i. The stability of the two double-labelled hIgG preparations was evaluated in vitro and in plasma in vivo by high-performance liquid chromatography (HPLC) analysis. At 24 h after injection of 99mTc-HYNIC-hIgG-14C the abscess uptake of 99mTc (1.5% ID/g+/-0.2% ID/g) was significantly higher (P<0.01) than the 14C uptake (1.0% ID/g+/-0.1% ID/g). After injection of 99mTc-iminothiolano hIgG-14C no significant difference (P=0.08) was found between the abscess uptake of the two radionuclides at 24 h p.i. (99mTc: 0.8% ID/g+/-0.1% ID/g; 14C: 0.90% ID/g+/-0.09% ID/g). HPLC analysis of plasma samples revealed release of 99mTc from both double-labelled immunoglobulin preparations. This phenomenon was more pronounced for iminothiolano hIgG than for HYNIC hIgG (43% vs 18%). In most tissues other than abscesses significant differences were also found between the 99mTc and the corresponding 14C uptake. Our results demonstrate that the chemical form in which 99mTc is bound to hIgG severely influences its release from hIgG and its retention in infections.

Thrombus imaging using technetium-99m-labeled high-potency GPIIb/IIIa receptor antagonists. Chemistry and initial biological studies

Platelet-specific compounds which are radiolabeled with gamma-emitting radionuclides may be particularly useful for the noninvasive in vivo detection of thrombi. The synthesis of peptides which are potent inhibitors of platelet aggregation and which contain a chelator for the radionuclide technetium-99m are described. The target compounds were designed such that stable, oxotechnetium(V) species could be prepared where the site of metal coordination was well defined. A strategy was employed where the pharmacophore-Arg-Gly-Asp-(RGD), or RGD mimetic, was constrained in a ring which was formed by the S-alkylation of a cysteine residue with an N-terminal chloroacetyl group. Binding affinities were enhanced by the replacement of arginine with the arginine mimetics S-(3-aminopropyl)cysteine and 4-amidinophenylalanine. Further enhancements could be obtained by the synthesis of oligomers which contained two or more rings containing receptor binding regions. The increase in binding affinity seen was more than that expected from a simple stoichiometric increase of pharmacophore. The most potent compounds described had IC50s of approximately 0.03 microM for the inhibition of human platelet aggregation. Two of the more potent peptides (P280 and P748) were labeled with technetium-99m and assessed in a canine thrombosis model. The 99m Tc complexes of the peptides prepared in this work hold promise as thrombus imaging agents due to their high receptor binding affinity, ease of preparation, and expected rapid pharmacokinetics.

In vitro evaluation of white blood cell labelling with 99Tcm radiopharmaceuticals

Several commercially available 99Tcm radiopharmaceuticals were tested as possible white blood cell labelling agents. Labelling efficiency, labelling stability and white blood cell adherence were measured in vitro. White blood cells were not successfully labelled with mebrofenin, disofenin, gluceptate or dimercaptosuccinic acid but were successfully labelled with exametazime, albumin colloid, sulphur colloid, sestamibi and teboroxime. Exametazime had the highest mean labelling efficiency of 79%. Labelling efficiency was 5-14% with albumin colloid, sulphur colloid, sestamibi and teboroxime. Labelling stability was high (> 95% at 4 h and > 80% at 24 h) for all agents except sestamibi (52% at 4 h and 5% at 24h). Exametazime did not alter white blood cell adherence. Albumin colloid, sestamibi and teboroxime decreased adherence and sulphur colloid increased adherence. Exametazime appears to be the best agent for labelling white blood cells. Teboroxime, however, is a new agent for labelling white blood cells which deserves further investigation.

A simplified kit for instant preparation of technetium-99m human immunoglobulin-G for imaging inflammatory foci

A kit consisting of reduced human immunoglobulins G (hIgG), methylene diphosphonate, stannous chloride and ascorbic acid has been developed to instantly produce technetium-labelled hIgG of greater than 97% purity and suitable for inflammation foci scintigraphy in patients. The shelf life of the kit when stored at 4-7 degrees C was at least 3 months. 99mTc-hIgG prepared from the kit, when incubated at 37 degrees C for 24 h in physiological saline and human serum was found to degrade by only 7.8 and 4.3%, respectively, thereby indicating high stability of the labelled product. Competitive RIA data did not exhibit loss of immunoreactivity of the hIgG due to its reduction. Blood clearance of the radiopharmaceutical in rabbits exhibited a monophasic exponential pattern. Biodistribution in mice showed uptake by liver (4.93%), kidneys (3.07%) and intestines (2.12%) at 4 h which was reduced to 1.99, 2.18 and 1.93%, respectively at 24 h. Radiolabelled hIgG prepared from the kit was found to be quite satisfactory for inflammation scintigraphy in human patients.

Imaging of focal sites of inflammation in rhesus monkeys with 99mTc-labeled human polyclonal IgG

The biological behavior of human polyclonal immunoglobulin G (IgG) radiolabeled with 99mTc via a nicotinyl hydrazine derivative, was evaluated in Rhesus monkeys. 99mTc-IgG and 111In-MACROSCINT DTPA-IgG were co-administered to Rhesus monkeys with focal sites of sterile inflammation and scintillation camera images were acquired at 6 and 19 h after injection. The biodistribution of the two antibody preparations were similar, however, small differences were detected: 99mTc-IgG > 111In-IgG in spleen and lung; 99mTc-IgG in bone and skeletal muscle. A linear correlation of the tissue-to-blood ratios of 99mTc- and 111In-labeled IgG was observed at both times (r2 > 0.98). The slopes of the regression lines were not significantly different from unity: 6 h-0.982 +/- 0.018; 19 h 1.0334 +/- 0.0226. Also, at both 6 and 19 h after injection, the target-to-background ratios (T/B) for the sites of inflammation were remarkably similar for 111In and 99mTc. These studies establish that human polyclonal IgG labeled with 99mTc via a nicotinyl hydrazine modified intermediate is equivalent to 111In-MACROSCINT DTPA-IgG for imaging focal sites of inflammation in monkeys.

Studies of the retention mechanism of the brain perfusion imaging agent 99mTc-bicisate (99mTc-ECD)

The structure-activity relationship in a series of analogues of 99mTc-bicisate (99mTc-N,N'-1,2-ethylenediylbis-L-cysteine diethyl ester dihydrochloride, RP-217) is described using in vivo studies in rodent and primate models and in vitro studies in rodent and primate brain tissue. All analogues investigated were 99mTc-diamine dithiol diesters, which were neutral and lipophilic and had modified brain uptake indexes (> or = 40) suggesting adequate first-pass extraction. All analogues were poorly retained by the rodent brain. In contrast, the stereochemistry and structure of the 99mTc-complexes affected their brain retention in primates. All compounds that demonstrated selective primate brain retention were L-diesters that were metabolized in primate brain tissue to nonlypophilic complexes resulting from ester hydrolysis. Unretained complexes were not metabolized in primate brain tissue. More extensive studies were performed with 99mTc-bicisate, which demonstrated poor brain retention in several nonprimate species (i.e., dogs, ferrets, pigs, and rodents). In rodent and nonhuman primate tissue, 99mTc-bicisate was rapidly metabolized to a monoacid ester (99mTc-N,N'-1,2-ethylenediylbis-L-cysteine monoethyl ester). Therefore, brain metabolism of 99mTc-bicisate results in the formation of an acid product(s) that is selectively trapped in primate brain.

In vivo bioactivity and biodistribution of chemotactic peptide analogs in nonhuman primates

The dose dependence of the effect of chemotactic peptide on peripheral leukocyte levels was measured in normal Rhesus monkeys. A 99mTc-labeled hydrazino nicotinamide (HYNIC) derivatized chemotactic peptide analog was used to study biodistribution and inflammation imaging in Rhesus monkeys. In normal animals the studies demonstrated that chemotactic peptide induced a clear dose-dependent reduction in peripheral leukocyte levels. The decrease in leukocyte number occurred almost immediately after injection and rapidly returned to baseline. Significant effects on differential WBC count, blood pressure, pulse rate or respiration rate were not detected. The lowest dose of peptide tested (10 ng/kg) had minimal effect on leukocyte level. The HYNIC derivatized peptide was prepared in excellent yield and purity, had biological activity similar to the native peptide and was readily labeled at specific activity of > 20,000 mCi/mumole. When approximately 0.5 mCi (< 2.0 ng/kg) of radiolabeled peptide was injected in monkeys with focal sites of mild sterile inflammation, a pattern of biodistribution similar to radiolabeled WBCs was observed and reductions in leukocyte levels were not detected. At 3 hr after injection, the site of inflammation was readily apparent with a target-to-background ratio of approximately 3:1. These studies demonstrate that radiolabeled chemotactic peptide analogs are effective agents for imaging sites of inflammation in monkeys. By radiolabeling at high specific activity, the effect of these reagents on peripheral leukocyte levels can be avoided.

Evaluation of 99mTc-mercaptoacetyltripeptides in mice and a baboon

Different derivatives of MAG, carrying amino acids such as D- or L-alanine, D-serine, D-2-aminobutyric acid, D-valine or D-phenylglycine were synthesized and their 99mTc-complexes were evaluated in mice and a baboon. The efficiency of renal handling of the examined 99mTc-complexes is influenced not only by their lipophilicity but also to a great extent by their configuration and the site of substitution. The renal excretion characteristics of 99mTc-MAGAG-DA are superior to those of 99mTc-MAG3 and the studied 99mTc-complexes in both animal species. In an attempt to improve the renal handling of 99mTc-MAG3 and to evaluate the effect of derivatization we have synthesized different derivatives of MAG3 in which one or more glycyl groups are replaced by other amino acids such as D- or L-alanine, D-serine, D-2-aminobutyric acid, D-valine or D-phenylglycine. Due to the presence of a chiral centre in the ligand core, exchange labelling of each of the MAG3 derivatives results in the formation of two diastereomeric technetium complexes. These isomers were separated by HPLC and evaluated in mice. Biodistribution in mice indicates that the efficiency of renal handling of the examined 99mTc-complexes is not only influenced by their lipophilicity but also to a great extent by their configuration. The renal excretion characteristics of isomer DA of 99mTc-MAGAG in mice are superior to those of all other studied 99mTc-complexes and also of the reference compound [131I]Hippuran. The isomers LB of several alanyl derivatives of 99mTc-MAG3 exhibit a pronounced renal retention in both mice and baboon. The results of the evaluation in a baboon confirm the superiority of 99mTc-MAGAG-DA over 99mTc-MAG3 and the other studied 99mTc-complexes.

Technetium labeling of monoclonal antibodies with functionalized BATOs. 1. TcCl(DMG)3PITC

BATO (boronic acid adduct of technetium dioximes) complexes, TcCl(dioxime)3BR, were prepared in which the boron substituent (R) was the protein-reactive m-phenyl isothiocyanate (PITC). The 99TcCl(dioxime)3PITC complexes [dioxime = dimethylglyoxime (DMG) or cyclohexanedione dioxime (CDO)] were prepared from 99Tc(dioxime)3(mu-OH)SnCl3 and characterized. The X-ray crystal structure of 99TcCl(DMG)3PITC was determined. The 99mTc complexes were prepared from 99mTcO4- in a process using a freeze-dried kit, either in a one-step procedure or via 99mTcCl(dioxime)3. Initial labeling studies with 99mTcCl(dioxime)3PITC were performed on glycine and polylysine and, subsequently, on mouse IgG and the B72.3 monoclonal antibody. Covalent attachment of 99mTcCl(DMG)3PITC to B72.3 was demonstrated by SDS-PAGE electrophoresis. B72.3 labeled with 99mTcCl(DMG)3PITC displayed high binding to a TAG 72 affinity column and had a distribution in normal mice similar to that reported for iodine-labeled B72.3.

Characterization of technetium-99m complexes of pentane-2,4-dione bis(N-methylthiosemicarbazone)

Further characterization of the two neutral technetium-99m (99mTc) complexes of pentane-2,4-dione bis-(N-methylthiosemicarbazone) (PETS) was carried out using a new dianionic PETS derivative, 3,3-dimethyl-pentane-2,4-dione bis(N-methylthiosemicarbazone) (DM-PETS), and the well characterized 99mTc complex of 2,2,9,9-tetramethyl-4,7-diaza-1,10-decanedithiol (DADT) as references. While PETS generated two neutral 99mTc complexes, 99mTc-PETS-L1 and 99mTc-PETS-L2, by both the stannous reduction method and the ligand exchange reaction with six-coordinated 99mTc(V) complex of N,N'-ethylenebis(acetylacetone imine), DM-PETS formed only one neutral 99mTc complex. 99mTc-PETS-L2, the more lipophilic complex of the two 99mTc-PETS, was obtained with a much higher yield than 99mTc-PETS-L1 by the ligand exchange reaction of PETS with the five-coordinated 99mTc(V) complex of glucoheptonate. In addition, while 99mTc-PETS-L2 and 99mTc-DADT remained unchanged in the presence of CN- anions, a breakdown of the original complexes was observed in 99mTc-PETS-L1 and 99mTc-DM-PETS. All four 99mTc complexes exhibited similar brain, heart and pancreas extraction when injected into mice. These cumulative results imply that 99mTc-PETS-L1 and 99mTc-DM-PETS are six-coordinated mononuclear 99mTc(V) complexes and that 99mTc-PETS-L2 is a five-coordinated mononuclear 99mTc(V) complex. These results also suggest that while the chelate ring structure of the 99mTc-dithiosemicarbazone (DTS) chelate played a significant role in its stability, ionization of the third proton of the PETS molecule and the subsequent resonating structure afforded further stability to the 99mTc-PETS complex. Markedly high lipophilicity of the 99mTc-PETS-L2 may also be explained by assuming that 99mTc-PETS-L2 is the five-coordinated resonating structure.