Preparation of HER2 radioligand 99Tcm-ABH2 and its in vivo imaging in breast cancer-xenografted mice

Objective To prepare 99Tcm-human epidermal growth factor receptor 2 (HER2) affibody (ABH2) and explore its feasibility as an imaging agent in HER2-positive breast cancer. Methods Sodium glucoheptonate and SnCl2·2H2O were used to label ABH2 with 99Tcm. The labeling yield and radiochemical purity of 99Tcm-ABH2 were determined. The stability of 99Tcm-ABH2 was tested in PBS and serum. The equilibrium disassociation constant (Kd) of 99Tcm-ABH2 was measured with MBA-MD-361 breast cancer cells. SPECT/CT imaging was carried out at 1.0 h and 4.5 h after injection of 37 MBq 99Tcm-ABH2 in nude mice (n=4) xenografted with MBA-MD-361 breast cancer. The T/NT (liver, brain, lung, heart, bone and muscle) ratios were deduced from SPECT/CT acquired data. For the blocking experiment, 200 μg ABH2 was injected intravenously before 99Tcm-ABH2 injection. SPECT/CT imaging was performed in the same way. The T/NT ratios were compared between non-blocked and blocked groups by one-way analysis of variance. Results The labeling yield of 99Tcm-ABH2 was above 99%. 99Tcm-ABH2 was substantially stable in PBS and serum; the radiochemical purity was (95.0±1.0)% after incubation with serum at 37 ℃ for 6.0 h. The Kd of 99Tcm-ABH2 was 1.7 nmol/L. The radioactive uptake in cancer was visualized at 1.0 h and 4.5 h after injection of 99Tcm-ABH2 in HER2 positive MDA-MB-361 breast cancer. 99Tcm-ABH2 was cleared out mainly through urinary system. The ratios of tumor to liver, lung, brain, heart, muscle and bone were 1.81±0.60, 8.95±1.13, 20.08±6.12, 7.61±0.56, 10.62±1.78, 11.42±2.07, respectively at 4.5 h after 99Tcm-ABH2 injection. After ABH2 blocking, the corresponding T/NT ratios were 0.60±0.23, 3.05±1.38, 5.24±2.17, 2.42±1.02, 8.16±2.66, 2.76±0.48 (F=29.38, P<0.05) respectively. Conclusion 99Tcm-ABH2 could be synthesized with high purity, and this new agent could be used to image HER2-positive breast cancer specifically. Key words: Breast neoplasms; Receptors, epidermal growth factor-urogastrone; Isotope labeling; Tomography, emission computed, single-photon; Tomography, X-ray computed; Mice, nude; ABH2