Clemens Decristoforo

Evaluation of Striatal Dopamine Transporter Function in Rats by in Vivo β-[123I]CIT Pinhole SPECT

Striatal dopamine transporter (DAT) function was evaluated in rats by in vivo SPECT-MRI coregistration using the radioligand 2-beta-carbomethoxy-3-beta-(4-[123I]iodophenyl)tropane (beta-[123I]CIT). The reconstructed transaxial resolution of 3.5 mm full width at half-maximum and the system sensitivity of 0.081 c/s/kBq using a 2.0-mm pinhole collimator aperture provided adequate spatial detail and sufficient sensitivity for imaging striatal beta-[123I]CIT uptake. SPECT images, coregistered onto a MRI template, showed high accuracy in the coronal and transverse planes (maximum mismatch of 1.3 mm). Following estimation of the in vivo binding equilibrium of beta-[123I]CIT in the healthy rat striatum, we evaluated the 6-hydroxydopamine-induced loss of striatal DAT function using beta-[123I]CIT SPECT and MRI coregistration and correlated these findings with dopaminergic cell counts in the substantia nigra pars compacta using TH immunohistochemistry. A subtotal unilateral DAT deficit was detected by beta-[123I]CIT SPECT in all animals which correlated significantly with the cell counting of the remaining dopaminergic neurons. beta-[123I]CIT pinhole SPECT provides a powerful and widely available tool for in vivo investigations of rat striatal DAT function. In contrast to classical autoradiography, the present method will be helpful in imaging dynamic changes of neurotransmission in the CNS by virtue of serial study designs. Depending on SPECT ligand availability, a wide range of other CNS receptors may be imaged as well using the presented in vivo technique.

Surfactant protein B labelled with [99mTc(CO)3(H2O)3]+ retains biological activity in vitro

UNLABELLED Labelling of the hydrophobic surfactant protein B (SP-B) under non-reducing conditions was achieved with [(99m)Tc(CO)(3)(H2O)(3)](+) prepared according to Alberto et al. (JACS, 1998). The binding of radioactivity was protein-specific, with an overall radiochemical yield of 50%. Gel electrophoresis and Westernblot analyses showed no structural changes of SP-B. Spreading properties and surface activity of (99m)Tc-labelled SP-B in an air/water interface coincided with those of unlabelled SP-B. (99m)Tc-SP-B seems to be a promising agent to observe surfactant spreading under clinical conditions. BACKGROUND Therapeutic results for surfactant instillation in clinical trials are conflicting. The (99m)Tc-labelling of surfactant would allow to observe its spreading in the lung under clinical conditions. METHODS [(99m)Tc(CO)(3)(H2O)(3)](+) was prepared as described by Alberto et al. (JACS, 1998). This carbonyl complex was used for the direct labelling of surfactant protein B (SP-B) under non-reductive conditions by direct incubation with SP-B at elevated temperature followed by extraction into CHCl(3)/MeOH. RESULTS The hydrophobic protein SP-B was labelled with [(99m)Tc(CO)(3)(H2O)(3)](+). An overall radiochemical yield of about 50% was achieved. HPLC-analysis revealed a single radiolabelled species according to UV elution profile of SP-B, supported by paper and size exclusion chromatography. Gel electrophoresis confirmed that the dimer structure of SP-B was preserved. Spreading properties of (99m)Tc-labelled SP-B in an air/water interface coincided with those of unlabelled SP-B. Spreading of radioactivity observed in a glass trough of 26 cm x 27 cm with a gamma camera was completed during the first 7-9 sec after application of (99m)Tc-labelled SP-B. The corresponding decrease of surface tension to 45 mN/m at the peripheral surface tension sensors took 7 sec +/- 2 sec (MEAN +/- STD; n = 3). CONCLUSIONS Direct and specific (99m)Tc-labelling of the hydrophobic surfactant protein B was achieved using the [(99m)Tc(CO)(3)(H2O)(3)](+) precursor. This procedure can easily be used to prepare specifically labelled surfactant mixtures with spreading properties that coincide with those of unlabelled surfactant.

Somatostatin receptor scintigraphy using 99mTc-EDDA/HYNIC-TOC in Graves’ disease

Decristoforo C, Mather SJ, Cholewinski W, Donnemiller E, Riccabona G, Moncayo R. 99mTc-EDDA/HYNIC-TOC: a new 99mTc-labelled radiopharmaceutical for imaging somatostatin receptor-positive tumours; first clinical results and intra-patient comparison with 111In-labelled octreotide derivatives. Eur J Nucl Med 2000; 27:1318-1325. Becker W, Schrell U, Buchfelder M, Hensen J, Wendler J, Gramatzki M, Wolf F. Somatostatin receptor expression in the thyroid demonstrated with 111In-octreotide scintigraphy. Nuklearmedizin 1995; 34:100-103. Moncayo R, Baldissera I, Decristoforo C, Kendler D, Donnemiller E. Evaluation of immunological mechanisms mediating thyroidassociated ophthalmopathy by radionuclide imaging using the somatostatin analog 111In-octreotide. Thyroid 1997; 7:2129.

Preclinical Evaluation of In-111 and Ga-68 Labelled Minigastrin Analogues for CCK-2 Receptor Imaging

The development of a suitable radioligand for in vivo targeting CCK-2 receptor expressing tumours, such as medullary thyroid carcinoma, is a major recent focus in the field of radiopharmacy. Initial developments using [DGlu1]minigastrin (MG0) derivatives showed high uptake by the kidneys resulting as the dose limiting organ for radiopeptide therapy. In this study we describe the comparison of the optimised shortened peptide analogues, [DOTA0,DGlu1,desGlu2-6]minigastrin (DOTA-minigastrin-11) with [DOTA0,DGlu1,desGlu2-6,Ile11]minigastrin (DOTAilegastrin), labelled with 111In and 68Ga. In vitro tests included stability in plasma and plasma protein binding. Internalisation and receptor binding assays using a CCK-2 receptor positive cell-line (AR4-2J, rat pancreatic tumour cells) were performed and biodistribution in AR4-2J tumour bearing nude mice was studied. DOTA-ilegastrin showed a superior stability in plasma in comparison with DOTA-minigastrin-11. 68Ga/111In-labelled DOTA-ilegastrin revealed, however, significantly reduced internalisation and lower receptor affinity than DOTAminigastrin- 11. For both radiologiands rapid renal excretion and low unspecific retention in most organs was observed. Tumour uptake of 111In/68Ga-DOTA-minigastrin-11 was much higher (4.9 and 5.7 %ID/g 1 h p.i.) compared to 111In/68Ga- DOTA-ilegastrin (1.2 and 1.0 %ID/g). Kidney retention was clearly lower for the short chain analogues as compared to MG0 derivatives. Tumour uptake could be reduced by more than 60% by coinjection of 50 μg human minigastrin. DOTA-minigastrin-11 showed considerably lower kidney uptake, but also higher metabolic instability as compared to MG0 derivatives. No relevant differences between 111In- and 68Ga-labelled derivatives were observed. Replacement of methionine with isoleucine lead to dramatic loss of receptor affinity.

Radiotracer II: Peptide-Based Radiopharmaceuticals

Recently, radiolabeled receptor-binding peptides have emerged as an important class of radiopharmaceuticals for diagnosis and therapy. Major advantages of peptides compared with antibodies are that they are not immunogenic, show fast diffusion and target localization and can be modified concerning metabolic stability and pharmacokinetics. Advantages compared to small molecular weight compounds are, that they are more tolerant concerning modification necessary for appropriate labeling (e.g., introduction of chelating systems for radio metalation) and strategies for optimizing pharmacokinetics. Most prominent members of this class of tracer are radiolabeled peptides for targeting somatostatin receptors. Some of them are already clinical routine for diagnosis as well as peptide receptor radionuclide therapy of somatostatin expressing tumors. Currently a variety of other peptides including bombesin derivatives, cholecystokinin/gastrin analogs and RGD-containing peptides are evaluated.

99mTc-EDDA/HYNIC-TOC scintigraphy in oncological diagnostics: methodological considerations

We read with great interest the Short Communication from Anna Płachcińska et al. presenting their clinical experiences with 99mTc-EDDA/HYNIC-TOC [1]. In their pilot study a variety of tumour entities were included. The use of this tracer for diagnosis showed promising results. These results are in accordance with findings of a prospective investigation by our group [2]. One difference between the two publications lies in the number of patient studies performed to investigate tumours in the gastroenteropancreatic tract. This issue is worth addressing, considering that diagnosis of neuro-endocrine gastroenteropancreatic tumours might represent the vast majority of clinical investigations using somatostatin receptor scintigraphy. It is worth pointing out that 99mTc-EDDA/HYNIC-TOC seems to be superior to other 99mTc-labelled compounds, such as 99mTc-depreotide [3], for this indication. The better imaging properties in the abdomen and the liver are based on the imaging characteristics of the radiopharmaceutical, but also need an optimal acquisition protocol. According to our initial pilot study, the best tumour to non-tumour contrast was identified at 4 h post injection [4]. In the study by Płachcińska et al., imaging was started as early as 2 h after injection, which seems appropriate in terms of patient convenience and might be sufficient for scanning of regions in which lower unspecific background activity can be expected, e.g. the chest. In our opinion, however, such early imaging in the bowel should only be applied if later imaging is performed to avoid false positive findings due to non-specific uptake [2]. We congratulate the authors on this pilot study, which again shows that 99mTc-EDDA/HYNIC-TOC might be a useful radiopharmaceutical for oncological diagnostics. An optimised acquisition protocol should be used in order to obtain the best results which 99mTc-EDDA/ HYNIC-TOC can provide, enabling it to become an alternative to Octreoscan.

Methodological considerations influence the clinical value of parathyroid localisation diagnostics

1. Nishiyama Y, Yamamoto Y, Ono Y et al. Comparative evaluation of 99mTc-MIBI and 99mTc-HMDP scintimammography for the diagnosis of breast cancer and its axillary metastases. Eur J Nucl Med 2001; 28:522–528. 2. Kopans DB. The positive predictive value of mammography. Am J Rontgenol 1992; 158:521–526. 3. Khalkhali I, Mena I, Jouanne E, et al. Prone scintimammography in patients with suspicion of breast cancer. Am J Coll Surg 1994; 178:491–497. 4. Mirzaei S, Zajicek SM, Knoll P, et al. Scintimammography enhances negative predictive value of non-invasive pre-operative assessment of breast lesions. Eur J Surg Oncol 2000; 26: 738–741

3-D-Imaging and Volume Mathematics Versus Common Static Imaging in Combined Inhalation / Perfusion Lung Scintigraphy

The purpose of the present study was to assess the diagnostic value and the practical usefulness of inhalation-/ perfusion SPET of the lung applying Multimodality three- dimensional (3-D-) data analysis. Lung perfusion scintigraphy (LP) is a common method for detecting sites of decreased perfusion. Lung inhalation scintigraphy (LI) is routinely performed when perfusion defects are visualized by LP. Visual analysis of studies showing abnormalities both in LP as well as in LI, can sometimes be difficult to carry out. The comparison of the images can be difficult in cases with inhalation and perfusion defects. Combined LI/LP in planar and SPET 3-D-technique was investigated in 33 patients having known or suspected lung disorders. Our data demonstrate an equal sensitivity of the 3-D-SPET in patients with pure pulmonary embolism (PE) and a better sensitivity in patients with chronic obstructive pulmonary disease (COPD) and PE compared with planar scans. Both methods require similar acquisition time, the time needed for 3-D-processing generally depends on the performance of the computer equipment.