In vitro and in vivo evaluation of iodine-123-Ro 16-0154: a new imaging agent for SPECT investigations of benzodiazepine receptors.

The flumazenil analogue, Ro 16-0154, a benzodiazepine partial inverse agonist, has been labeled by halogen exchange to enable SPECT investigations of central benzodiazepine receptors in the human brain. The purified 123I-Ro 16-0154 was found to be stable in rat brain preparations and to be metabolized in rat liver preparations. Its pharmacologic properties were comparable to those of flumazenil. The biodistribution in rats (1 hr postinjection) resulted in a high brain-to-blood ratio of 16. Clinical studies revealed images of the benzodiazepine receptor density in the brain. Since the receptor labeling was markedly reduced by injection of flumazenil, it was considered to be specific. Storage defects due to pathologic cerebral blood flow and changed receptor density were detected; this shows the potential usefulness of the substance for diagnostic purposes, e.g., the differential diagnosis of various forms of epilepsy.

123I-labeling and evaluation of Ro 43-0463, a SPET tracer for MAO-B imaging.

Using the copper assisted halogen exchange the MAO-B inhibitor Ro 43-0463, N-(2-aminoethyl)-5-iodo-2-pyridinecarboxamide, was labelled with 123I as well as with 125I to allow in vitro and in vivo investigations including SPET with healthy volunteers. Ro 43-0463 is known to inhibit reversibly and specifically MAO-B, having an IC50 of 3 x 10(-8) Mol/L. The labeling in the presence of CuSO4 and ascorbic acid was optimised, varying time (30 to 105 min), precursor concentration (1-3.5 mg) and temperature (130-200 degrees C). The labeling yield ranged between 60 and 70%. Purification was achieved with Lichrosorb RP-18 (5 micron, 250 x 8 mm) and 1.5 mL/min 0.36 M H3PO4/EtOH 97/3 [0.01 M (NH4)2HPO4]. After neutralisation and sterile filtration the final activity concentration ranged between 18.5 and 37 MBq/mL. Biodistribution studies showed a brain to blood ratio greater than 1 within 1 h p.i. The main radiation burden calculated from these animal data is to alimentary and excretory organs and the ovaries. Autoradiography was performed using rat brain slices and 5 nM [125I]Ro 43-0463 in TRIS-buffer pH 7.4 for 90 min at 20 degrees C. Its radioactivity pattern corresponds to the known distribution of MAO-B in the rat brain. By displacement with L-deprneyl the highly specific binding of R0 43-0463 was proven in vitro. SPECT studies with normal volunteers corresponded with the pattern found in autoradiography.

[76Br]Bromodeoxyuridine, a potential tracer for the measurement of cell proliferation by positron emission tomography, in vitro and in vivo studies in mice.

5-Bromo-2'-deoxyuridine (BrUdR) labeled with 77Br and 76Br was compared with 5-iodo-2'-deoxyuridine (IUdR) labeled with 125I or 131I, first in vitro then in in vivo experiments in mice. The results showed a significantly higher incorporation of BrUdR into DNA than IUdR, which can be explained by the greater similarity (size and surface hydrophilicity of the molecules) of BrUdR to thymidine. Both tracers are dehalogenated quickly in vivo but not in vitro. Free bromide is excreted more slowly than iodide, resulting in a higher background activity level after the application of [76Br]BrUdR and compensates for the favorable DNA incorporation. 76Br has more favorable properties than 124I for imaging purposes with positron emission tomography (PET) because of a very convenient half-life (16 h vs. 4.15 days) and about double the positron yield per decay. However, the more favorable physical properties are balanced by the slower excretion and thus the estimated radiation dose is higher in the case of 76Br than 124I. Thus, both tracers, [124I]IUdR and [76Br]BrUdR are potentially suitable but not optimal to measure cell proliferation in vivo. The difference between the two tracers is small and the extrapolation from mice to human difficult, and thus it cannot be concluded if one of the tracers would be better than the other for imaging of cancer patients.

123I-iomazenil: a quantitative study of the central benzodiazepine receptor distribution.

Fourteen patients with temporal lobe epilepsy, 9 patients after amygdalohippocampectomy and 3 healthy volunteers were examined with the new benzodiazepine receptor marker 123I-Iomazenil and SPECT. For comparison perfusion SPECT studies with 99mTc-HMPAO were done and a quantitative ROI analysis of the data performed. This quantitative analysis consisted of calculation of right-to-left ratios for 123I-Iomazenil SPECTs, whereby values of 1 were obtained with narrow standard deviations. ROI measurements of the medial occipital, frontal and parietal cortex, the cerebellum and white matter showed a pattern of benzodiazepine receptor concentration in concordance with that previously found in PET and autoradiographic studies, if 123I-Iomazenil ROIs were normalized to the corresponding 99mTc-HMPAO ROIs. The abnormal distribution in the temporal lobes will not be discussed in this paper.

Evaluation of a multicentre study with Iomazenil--a benzodiazepine receptor ligand.

After showing in an earlier publication that Iomazenil is a potent benzodiazepine receptor antagonist, the substance has been distributed to 11 clinical centres in Europe for further tests. The protocol asked for volunteers, epileptic cases and patients with Alzheimer's disease. Prior to the Iomazenil examination, flow images by perfusamine or HMPAO were required, and as comparative methods EEG, computed tomography (CT) and magnetic resonance imaging (MRI) were performed. The results allowed first the determination of the normal distribution of the benzodiazepine receptors in the human brain. The highest uptake was found in medial occipital cortex. Second, the evaluation of the epileptic cases shows a 100% positive prediction value for Iomazenil compared to 92% for flow images. Negative prediction values were calculated as 81% for Iomazenil and 54% for flow images. Furthermore, one group reported the successful diagnosis of Alzheimer's disease at an early stage. The visual image examination was tentatively compared to a more objective semiquantitative one based on quotients of corresponding left/right regions of interest. This semiquantitative method has not proved successful yet, but the problems have been identified. A more precise protocol for further studies is therefore proposed.

Assessment of the binding properties of Granuloszint.

123I-Granuloszint (a murine monoclonal antibody--called AK-47--against NCA-95 glycoprotein of granulocytes) has been proved to be a very convenient and successful radiopharmaceutical for visualizing infectious diseases. For a broad introduction in routine nuclear medicine it was necessary to optimize the labelling method and to determine in vitro exactly those biological and binding parameters which are relevant for an effective application in vivo. Binding to granulocytes has been shown to be specific and saturable (non specific binding about 10%) and is not via the Fc part of the antibody. The investigation of the binding properties of 125I-labelled AK-47 gave the following results: affinity constant 5 x 10(8) M-1, 20,000-200,000 epitopes per granulocyte and an immunoreactivity of more than 90%. Labelling with 123I reduced the immunoreactivity to 40%. The Lindmo method and immunoblotting are used as quality control to check the likely in vivo behaviour of the labelled antibody. There is a good correspondence between the results from the two methods. With our special labelling method and the different in vitro tests we have found a reliable way to control the production and to assure an optimal binding behaviour of 123I-Granuloszint.

Immunoscintigraphic localization of inflammatory lesions: pharmacokinetics and estimated absorbed radiation dose in man.

Five patients with inflammatory lesions received anti-granulocytes murine monoclonal antibody (Mabgc) infused over 5 to 15 min at doses between 3.4 and 5.4 mCi 123I (120 micrograms antibody). Clearance of 123I from blood pool closely fits a biexponential mathematical model with the two effective half-lives 0.73 h and 9.3 h. The spontaneous release of 123I was found to be relatively low in the blood pool. The cumulative urinary excretion of the 123I label over 120 h was in the range of 63% of the totally administered dose and is assumed to represent only a low molecular compound or 123I alone as iodide. Analysis of the label in spleen, liver and red marrow showed that the concentration of label in these tissues remains more or less constant over a period of 20 h after infusion. With data of liver, spleen, red marrow and whole body activity over a period of 24 h, an estimated radiation dose was calculated. Compared with 111In labelled leucocytes, especially in spleen, the absorbed dose is lower by a factor of ten per examination.

Biodistribution and estimated radiation burden for a new 123I-labelled monoamine oxidase-B inhibitor, Ro 43-0463: a preliminary report.

The selective, reversible inhibitor of monoamine oxidase B (MAO-B), Ro 19-6327 (Lazabamide) N-aminoethyl-5-chloro-picolinamide, inhibits the enzyme with an initial competitive phase, followed by a time-dependent inhibition of MAO-B; i.e. Ro 19-6327 is a substrate for MAO-B, and after its oxidation it is activated into an intermediate form which remains tightly bound to the enzyme's active site. Our radiopharmaceutical is a new 123I-labelled derivative of Ro 19-6327, N-aminoethyl-5-[123I]iodo-picolinamide, which seems to be a potentially useful SPECT tracer for the imaging of the MAO-B enzyme distributions. The first biodistribution of this compound was measured in rats at 6 different points in time (10, 25, 40, 60, 180 and 900 minutes post-injection). For each point the average from three animals was taken. In the brain there was an activity plateau over the first hour. In the first hour post-injection the brain-to-blood ratio was over 1, with a maximum ratio of 1.24 at 25 minutes post-injection. Because MAO-B is abundant in the ependyma, pineal and cerebellar Bergmann glia cells, this ratio of 1.24 over the whole brain is encouraging. At first, radioactivity was principally and rapidly accumulated in the liver. After 1 hour, about 37% of the injected activity is accumulated there. The elimination of the compound seemed to take place mainly through the hepatobiliary system (about 75%), but also via the kidneys (about 25%). Fifteen hours post-injection, only 4% (corrected for decay) of the injected radioactivity was left in the body.(ABSTRACT TRUNCATED AT 250 WORDS)