Labeling of a Bombesin Analog via the Asymmetrical Technetium-99mNitrido Fragment 99mTc(N)(PNP)2+

摘要

Bombesin (BBN) analogs have been shown to bind selectively and avidly to GRPrnreceptors on prostate, breast, pancreatic and colon cancer cells. A radiolabeled agent capablernof identifying these tumors could benefit early diagnosis and therapy for patients. Recentrndevelopments in the preparation of Tc compounds based on the incorporation of the nitrogenrndonor in the metal coordination sphere for labeling small biomolecules led to the synthesis ofrncomplexes containing nitrido cores. Objective: The aim of this project was the design andrndevelopment of a bombesin analog Cys-β-Ala-BBN(7-14)NH2 (Cys-β-Ala-Q-W-A-V-G-H-LM-rnNH2) and evaluation of radiolabeling strategies using the 99mTc-nitrido core by anrnasymmetrical method. Methods: Radiolabeling was conducted in a two-step procedure. 1)rnPreparation of the 99mTcN precursor was performed using a lyophilized kit (CIS BiornInternational, Schering). The 99mTc-nitrido precursor was prepared by adding 0.5 mL ofrnNa99mTcO4 and 0.5 mL of ethanol to the kit. The vial was left standing 30 min at roomrntemperature. 2) 50 μL of a 0.9 mM aqueous solution of Cys-BBN and 3 μg of a diphosphinern(PNP6) dissolved in 200 μL ethanol were simultaneously added to the precursor vial. Thernreaction mixture was incubated for one hour at 100°C. Radiochemical evaluation of thern99mTc≡N precursor and for 99mTc≡N(PNP6)-Cys-β-Ala-BBN was performed using ITLC-SGrnand RP-HPLC methods. Results: The 99mTc≡N yield was 97.54 ± 1.14%. The radiochemicalrnpurity for 99mTcN(PNP6)-Cys-β-Ala-BBN was also very high (96.29 ± 1.25%). Two peaksrnwere observed in HPLC chromatographic profile with retention times of 21.97 and 22.76rnminutes, respectively. Conclusions: Although the radiolabeling had to be carried out in a twosteprnprocedure, the synthesis of 99mTc≡N(PNP6)-Cys-β-Ala-BBN was simple and convenientrnand the radiochemical purity was demonstrated to be high. These results recommend furtherrnstudies of this conjugate in biological models.