The radiolabeling was accomplished via direct radioiodination at tyrosyl and, to a lesser extent, histidyl residues of the antibody and protein using different oxidizing agents such as Iodogen?, Chloramin T (CAT) and studies revealed a higher tendency of radio-deiodination and subsequent radioactivity accumulation in the thyroid and stomach in the case of directly radioiodinated diabody

The radiolabeling was accomplished via direct radioiodination at tyrosyl and, to a lesser extent, histidyl residues of the antibody and protein using different oxidizing agents such as Iodogen?, Chloramin T (CAT) and studies revealed a higher tendency of radio-deiodination and subsequent radioactivity accumulation in the thyroid and stomach in the case of directly radioiodinated diabody. long-lived positron emitter 124I in the field of organic PET chemistry and molecular imaging. Keywords: iodine-124, positron emission tomography (PET), molecular imaging 1. Introduction The convergence of molecular and cellular biology with imaging sciences to molecular imaging has revolutionized current biomedical research. Molecular imaging is defined as the characterization and measurement of biologic processes at the cellular and molecular level [1,2,3]. Molecular imaging aims at developing non-invasive strategies for characterizing the molecular and metabolic profiling in living subjects. Molecular and cellular processes can be studied and visualized at various levels of resolution by means of imaging techniques, which span from Buserelin Acetate ultrasonic to gamma-ray frequencies. In recent years, positron emission tomography (PET) has become a powerful non-invasive molecular imaging technique which provides functional information of physiological, biochemical and pharmacological processes in laboratory animals and humans [4,5,6]. The possibility to observe molecular interactions in living organisms and to determine absolute values of physiological parameters places PET in a unique position among other molecular imaging techniques. In a typical PET study the PET radiotracer, a compound labeled with a short-lived positron emitter, is injected intravenously into a human or animal. Tissue concentrations of the radiotracer are measured over time, and these data are combined with information on plasma probe concentration of the radiotracer to assay metabolism. Mathematical Buserelin Acetate methods for the evaluation of PET measurements within the framework of compartment models are well established [7,8]. Within Buserelin Acetate the spectrum of available positron emitters, fluorine-18 (18F) is an almost ideal radionuclide for PET, thanks to its ease of production and favorable physical properties, such as a 109.8 min half-life and low + energy (0.64 MeV). The success of various 18F-labeled radiotracers like 2-[18F]fluoro-2-deoxy-D-glucose ([18F]-FDG) as metabolic markers in biomedical research and clinical practice has prompted research on the potential of other positron-emitting radionuclides with longer half-lives. The choice of the appropriate radionuclide is among the most important aspects for the design and application of novel PET radiotracers. The physical half-life of the radionuclide should reflect KRAS2 the timeframe of the biological process to be studies. Various excellent reviews have addressed and discussed the importance of other positron-emitting radionuclides in the design of novel radiopharmaceuticals [9,10,11]. Several other positron emitting radionuclides with different physical half-lives can be prepared in high yields by means of small biomedical cyclotrons. Prominent examples of positron-emitting radionuclides with longer half-lives include copper-64 (64Cu, t1/2 = 12.7 h), yttrium-86 (86Y, t1/2 = 14.7 h), bromine-76 (76Br, t1/2 = 16.2 h), and iodine-124 (124I, t1/2 = 4.2 d). In recent years, the positron emitting halogen 124I has become an attractive long-lived radionuclide for the design and synthesis of novel PET radiotracers. Its convenient 4.2 d half-life allows extended radiosynthesis protocols and longitudinal PET imaging studies. Moreover, labeling chemistry for 124I is well established, and a wide variety of compounds have been labeled for molecular imaging purposes with PET. The present review gives a survey on the use of 124I as promising PET radionuclide for molecular imaging. The first part of the review deals with the production, processing and PET imaging of 124I. The second part covers basic radiochemistry with 124I focused on the synthesis of 124I-labeled compounds for molecular imaging purposes. The review concludes with a summary and an outlook on the future prospective of using the long-lived positron emitter 124I in the field of organic PET chemistry and molecular imaging. 2. Production, processing, and PET imaging of 124I 2.1. 124I production routes Early investigations into the production of 124I most commonly employed the 124Te(d,2n)124I nuclear reaction scheme [12,13,14,15,16]. More recently however, with the increase in the number of low-energy proton cyclotrons (for the purpose of producing traditional PET isotopes such as 18F or 11C), the 124Te(p,n)124I reaction has been gaining popularity [15,17,18,19,20,21]. Despite the slight decrease in yields noted with the 124Te(p,n)124I nuclear reaction (Table 1), this scheme offers the possibility of obtaining the highest levels of 124I radioiodine purity at the time of administration. Table 1 Selection of published data on 124I production. [29], although 124I of the highest radioiodine purity may be recommended for diagnostic applications, a higher impurity level may perhaps be more tolerable when harnessed for therapeutic purposes. 2.2. Thermal design and irradiation considerations As the total 124I activity produced is proportional to the current at which the target is irradiated, higher currents are always desired (particularly given the generally.