Investigation of the 188Re Eluate Suitability for Medical Purposes by Labeling a Bombesin Analog (BN1.1)

Rhenium-188 is a radionuclide of high therapeutic potential for nuclear medicine. Because of its short half-life (t??= 16.98h), logistic problem appears with its delivery to customers. This can be solved by delivering a 188W/188Re generator as a source of 188Re. A number of 188W/188Re generator systems have been described. Due to chemical similarity of this pair to 99Mo/99mTc pair, the alumina – based generators are most common. The technology for producing sterile, isotonic solution of sodium perrhenate-188Re, useful for medical applications, has been developed and implemented by the elution of an alumina based 188W/188Re generator, at the Radioisotope Centre POLATOM. The eluted 188Re was used for the labeling of a Bombesin analog (BN1.1) which has been prior labeled, in high yields, with 99m Tc and gave promising results of its in vitro and in vivo evaluation The Bombesin analog under study BN1.1 has the aminoacid sequence GGCAca- QRLGNQWAVGHLM-CONH2. The peptide was labeled with 188Re, through a Re-gluconate complex via an exchange reaction. We studied the conditions for optimal labeling yield and specific activity of the resulted labeled peptide. 188Re-BN1.1 with specific activity 20.4-34.0 GBq 188Re/μmol BN1.1, radiochemical yield > 95, and pH < 1.0 was obtained. 188Re-BN1.1 was stable when the pH was adjusted to 5.0-6.0. Preliminary biodistribution study in normal mice showed specific uptake in GRP positive tissues, fast blood clearance, but also a significant uptake in the stomach indicating dissociation of the metal from the ligand core and its reoxidation.