Synthesis of a novel 89Zr-labeled HER2 affibody and its application study in tumor PET imaging

Background Human epidermal growth factor receptor-2 (HER2) is an essential biomarker for tumor treatment. Affibody is an ideal vector for preparing HER2 specific probes because of high affinity and rapid clearance from normal tissues, etc. Zirconium-89 is a PET imaging isotope with a long half-life and suitable for monitoring biological processes for more extended periods. In this study, a novel Zr-89-labeled HER2 affibody, [Zr-89]Zr-DFO-MAL-Cys-MZHER2, was synthesized, and its imaging characters were also assessed. Results The precursor, DFO-MAL-Cys-MZHER2, was obtained with a yield of nearly 50%. The radiochemical yield of [Zr-89]Zr -DFO-MAL-Cys-MZHER2 was 90.2 +/- 1.9%, and the radiochemical purity was higher than 95%. The total synthesis time was only 30 min. The probe was stable in PBS and serum. The tracer accumulated in HER2 overexpressing human ovarian cancer SKOV-3 cells. In vivo studies in mice bearing tumors showed that the probe was highly retained in SKOV-3 xenografts even for 48 h. The tumors were visualized with good contrast to normal tissues. ROI analysis revealed that the average uptake values in the tumor were greater than 5% IA/g during 48 h postinjection. On the contrary, the counterparts of MCF-7 tumors kept low levels ( similar to 1% IA/g). The outcome was consistent with the immunohistochemical analysis and ex vivo autoradiography. The probe quickly cleared from the normal organs except kidneys and mainly excreted through the urinary system. Conclusion The novel HER2 affibody for PET imaging was easily prepared with satisfactory labeling yield and radiochemical purity. [Zr-89]Zr-DFO-MAL-Cys-MZHER2 is a potential candidate for detecting HER2 expression. It may play specific roles in clinical cancer theranostics.