DOI: 10.1007/s10967-007-7244-6 Journal of Radioanalytical and Nuclear Chemistry, Vol. 279, No.1 (2009) 25–30 0236–5731/USD 20.00 Akadémiai Kiadó, Budapest © 2008 Akadémiai Kiadó, Budapest Springer, Dordrecht S-bridged complex of 99m Tc with fac(S)-[Rh(aet) 3 ]: Quality control, characterization and biodistribution studies in rats N. Amir, 1 * S. Roohi, 1 S. Pervez, 1 A. Mushtaq, 1 M. Jehangir, 1 Y. Miyashita, 2 K. Okamoto 2 1 Isotope Production Division, Pakistan Institute of Nuclear Science and Technology, P.O. Nilore, Islamabad, Pakistan 2 Department of Chemistry, University of Tsukuba, Tsukuba, 305-8571, Japan (Received January 21, 2008) fac(S)-[Rh(aet) 3 ] (aet = 2-aminoethanethiolate) is N 3 S 3 metalloligand which can coordinate to transition metal ions to form S-bridged polynuclear complexes. The reaction was carried out between 99m TcO 4 Na and fac(S)-[Rh(aet) 3 ] in the presence of SnCl 2 . 2H 2 O. A complex analogous to [Re{Rh(aet 3 )} 2 ] 3+ is formed. 6 A simple method for radiolabeling of fac(S)-[Rh(aet) 3 ] with 99m Tc has been developed and radiolabeling efficiency was higher than 99%. Effect of SnCl 2 . 2H 2 O concentration, electrophoresis, HPLC, UV-Visible absorption spectra and biodistribution studies in rats were performed. Higher uptake by kidneys showed rapid distribution of the labeled fac(S)-[Rh(aet) 3 ]. Liver uptake was significant, stomach, lungs and intestine uptake was high at 4 hours post injection time. Introduction Nuclear medicine is a branch of medical imaging that uses radioactive tracers to examine the function of body systems. The radionuclide used in about 90% of all examinations is 99m Tc, which is available from 99 Mo/ 99m Tc generators. 99m Tc in some chemical form is used in more than 85% of the diagnostic scans done each year in hospitals. To reach targets in the human body other than glandula thyreoidea, 99m Tc needs a carrier molecule, usually a chelating agent. Many chelators that form stable complexes with 99m Tc have affinities for certain tissues in the human body. Other chelators can be manipulated by pharmaceutical formulation to be retained in certain body systems. In order to form bonds with 99m Tc, the chelator must contain electron donors like N, O and S. Today, chelators for the use with 99m Tc exist for a number of highly sensitive scintigraphic studies of the brain, heart, skeleton, kidneys, hepatobiliary system and lungs. This includes chelator such as dimercaptosuccinic acid, 1,2- ethylenediylbis-L-cysteine diethyl ester, methylene- diphosphonate, hexamethylpropylene-amineoxime and hexakis(methoxy isobutylisonitrile). 1,2 The estrogen, progesterone and androgen receptors may be useful for targeting breast and prostrate cancers. The 99m Tc labeling of progesterone receptor has been studied utilizing conjugation to N 2 S 2 ligands via phenyl spacer. An alternative approach is to integrate the receptor binding sites directly onto the outer periphery of the Tc ligands. 3,4 Bioconjugates of octreotide using the N 2 S 2 ligand approach have been made for 99m Tc and have been investigated as a potential method for the imaging of tumors. Steroids can be attached to rhenium * E-mail: areena_a@hotmail.com oxo-complexes of N 2 S 2 ligand systems in a directly analogous fashion. This therefore is a promising approach to the delivery of therapeutic radiation to appropriate tumors. 5 The extensive investigations by numerous research groups on a variety of N 2 S 2 and N 3 S donor type ligands have revealed that the chemistries of these ligands with Tc and Re are rather complex, giving rise to considerable difficulties in the development of reliable procedures for the development of radiopharmaceutical reagents It is significant that thiolate based ligands appear to offer considerable advantages in purity of preparations and stability of the complexes. This led to the development of a class of tridentate ligands, such as bis(mercaptoethy1)methylamine (NS 2 ), which may constrain the possible coordination geometries and improve overall stability. 6 Metalloligands, fac(S)-[M(aet) 3 ] (M = Rh III , Ir III , aet = 2-aminoethanethiolate) can react with transition metal ions to form S-bridged polynuclear complexes. These complexes indicated unique reactivity and electrochemistry. Incorporation of Re ion into S-bridged structure resulted in a fairly stable S-bridged complex [Re{Rh(aet) 3 } 2 ] 3+ . Investigations of redox properties and stability of Re ion is important as fundamentals for the application of Re compounds and development of radiopharmaceuticals. 7,8 99m Tc complexes are widely used for diagnostic imaging. The chemistry of S-bridged metal complexes has attracted much interest because of the importance of the thiolato groups in a variety of systems ranging from inorganic to organic and biological chemistry. 9,10 A number of complexes containing N and S donor ligands have been reported and play an important role in nuclear medicine. For example, 99m Tc-L,L-ECD