Preparation and characterization of 99Tcm-labeled human epidemal growth factor type 2 affibody molecule in vitro / 中华核医学与分子影像杂志

ABSTRACT

Objective To prepare the 99Tcm-labeled human epidermal growth factor receptor type 2 (HER2) affibody molecule ZHER2342 and evaluate its receptor binding specificity in vitro.Methods The molecular ZHERa342 was labeled with 99Tcm using the ligand exchange method.The labeling efficiency and radiochemical purity were measured by HPLC.The major factors,such as the mass of SnC12 and NaOH and reaction time were analyzed,and the optimal method was summarized.Cell binding kinetics and cellular retention of the probe were investigated in HER2-expressing SKOV-3 cells and MDA-MB-231 cells with low HER2 expression respectively.HER2 binding specificity of 99Tcm-ZHER2342 was analyzed by a pre-injection of excess unlabeled ZHER2342 to saturate HER2 receptors.One-way analysis of variance and two-sample t test were used.Results The optimal labeling procedure was as follows5 μg (1 g/L) of ZHER2342 was mixed with 5 μg of NaOH (1 g/L),then 8.8 μg SnC12(1 g/L,solution) was added,followed by 150 μl (37 MBq) 99TcmO4-solution,and finally the mixture was slightly vortexed and incubated for 1 h at room temperature.99TcmZHER2342 was stable in vitro with a high labeling efficiency of (98.10± 1.73)％.The radiochemical purity was ＞ 98％,and was more than 85％ after the incubation for 24 h in saline and fresh human serum.The cell binding of 99Tcm-ZHER2342 with HER2-expressing SKOV-3 cells gradually increased over time with a peak of (9.95± 1.02)％ at 6 h.The binding of 99Tcm-ZHER2342 in SKOV-3 cells was significantly higher than that in MDA-MB-231 cells at every time point (5.68-9.88 vs 0.56-2.11 ; tfrom-34.50 to-13.14,all P＜0.01).The labeled molecular probe retained the capacity to bind specifically to HER2-expressing SKOV-3 cells since the cell binding decreased from (9.95 ± 1.02) ％ to (2.11 ±0.27) ％ after receptor saturation (t =-13.14,P＜0.01).Conclusions 99Tcm-ZHER2342 has a high labeling efficiency,good stability and optimal binding specificity.These characteristics enable it to be a promising molecular probe for HER2-targeting imaging.