Nuclear Medicine &a Biology, Vol. 24, pp. 571-578, I997 Copyright 0 1997 Elsevier Science Inc. ELSEVIER ISSN 0969.8051/97/$17.00 + 0.00 PII SO969-8051(97)00019-X Development and Evaluation of a Kit Formulation for the Preparation of 99 “Tc-DMP-HSA, a New Tracer Agent for Radionuclide Ventriculography Kristin A. Verbeke,’ Christiuun W. Schiepers,2 Dirk N. Wynduele,2Jun A. Baetens,2 Geert N. Verbeke, Michel J. De Roe’ and Alfons M. Verbruggen’ ‘LABORATORY OF RADIOPHARMACEUTKXL CHEMISTRY, K.U. LEWEN, B-3000 LEWEN, BELGIUM; ‘UNIVERSITY HOSPlTAL GASTHUISBERG. DEPARTMENT OF NUCLEAR MEDICINE, B-3000 LEWEN, BELGIUM; AND 3BIOSTATlSTICAL CENTRE FOR CLINICAL TRIALS, K.U. LEWEN, B-3000 LEWEN, BELGIUM ABSTRACT: This study presents the development of a kit fornudation for the preparation of 99mTc-DMP- HSA, followed by a comparison of such kit-prepared 99mTc-DMP-HSA to 99mTc-RBCs in a volunteer. Reconstitution of the labeling kits with up to 5.55 GBq 99mTc afforded 99mTc-DMP-HSA preparations with a >95% radiochemical purity for up to 8 h. Only minor differences were observed in the global distribution of both tracer agents, whereas the calculated ejection fractions were almost identical. The effective dose equivalent of 99”Tc-DMP-HSA is 8.68 PSv/MBq. NUCL MED BIOL 24;6:571-578, 1997. 0 1997 Elsevier Science Inc. KEY WORDS. Technetium-99m, 2,3-Dimercaptopropionyl-human serum albumin, Technetium-99m-labeled red blood cells, Ventriculography, Kit formulation, 99mTc-DMP-HSA. INTRODUCTION Red blood cells in vitro labeled with technetium-99m (99mTc-RBCs) are still considered the most ideal radiopharmaceutical for use in radionuclide ventriculography, owing to their long retention in the vascular compartment. In view of practical considerations, an in viwo or modified in vioo labeling technique is preferred in many hospitals, although labeling efficiencies obtained with these meth- ods can occasionally be low because of patient medication interac- tions (1,9,12-15,28). Therefore, much effort has been invested in the development of alternative blood-pool imaging agents that could be reconstituted with a high radiochemical yield by the simple addition of 99mTc- pertechnetate solution to a labeling kit. Examples of compounds evaluated for this purpose are poly-r-Iysine, a co-polymer of me- thoxypolyethylene glycol and poly-L-lysine (MPEG-PL) or lipo- somes (2,11,17,23,27). However, for none of the latter preparations are data in humans yet available. We opted for the use of human serum albumin (HSA) as a natural macromolecule to meet our goal of preparing an alternative blood-pool agent. 99mTc-labeled native albumin is not a suitable alternative to 99mTc-labeled RBCs because of the relatively rapid clearance of the radiolabel from the vascular compartment (22,24). In previous studies we found that after derivatization of albumin with a limited number of dimercaptopropionyl (DMP) groups, the resulting 99mTc-DMP-HSA preparations showed a comparable blood retention as 99mTc-RBCs in animals (25). Some of these preparations have also been tested in a human volunteer (26) and were found to be a potentially very useful alternative to in vitro-labeled 99mTc-RBCs. Optimal biological behavior (i.e., long Address reprint requests to: A.M. Verbruggen, U.Z. Gasthuisberg, Radio- pharmacy, Herestraat 49, B-3000 Leuven, Belgium; E-mail: alfons. verbruggen~uz.kuleuven.ac.be Received 24 November 1996. Accepted 20 February 1997. retention of the injected activity in the blood and low accumulation in the liver) was obtained after derivatization of albumin with DMP in a molar ratio DMP-precursor:HSA of 4: 1 or 2: 1 (DMP-HSA 4:l or DMP-HSA 2:l). However, these favorable preliminary biological results were obtained using 99”‘Tc-DMP-HSA preparations, which were purified by size-exclusion HPLC, as labeling efficiency of DMP-HSA 4:l and 2:l was suboptimal. To be really useful in daily nuclear medicine practice, a radiopharmaceutical should be avail- able in final form by simple reconstitution of a lyophilized labeling kit with generator eluate. This study investigated how the labeling efficiency of DMP-HSA preparations with low substitution level could be increased to obtain quantitative labeling and to be able to develop a kit formulation for easy preparation of 99”‘Tc-DMP-HSA. 99”Tc-DMP- HSA 4:l was chosen for the development of the kit formulation. Furthermore, a kit-prepared 99mTc-DMP-HSA 4:l preparation was evaluated in a volunteer and compared to in &o-labeled 99mTc- RBCs. Finally, the radiation absorbed dose in humans of both 99mTc-DMP-HSA and 99mTc-RBCs was estimated using gamma camera measurements. MATERIALS AND METHODS Preparation of DMP-HSA The originally developed procedure for derivatization of albumin with a limited number of dimercaptopropionyl groups and purifica- tion of DMP-HSA has been described in detail before (25). In summary, to a 2% m/V solution of albumin in 0.05 M phosphate buffer pH 7.5 was added the required amount of N-hydroxysuccin- imidyl 2,3-di(S-acetylmercapto)propionate (SAMP) dissolved in dimethyl sulfoxide (DMSO). After a 2-h incubation period at room temperature, the unreacted ligand was removed by size-exclusion chromatography (SEC) on Sephadex G25M (Pharmacia, Uppsala, Sweden). Deacetylation of the S-acetyl-protected thiol groups was carried out by incubation with a hydroxylamine solution. After