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

Abstract

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 89Zr-labeled HER2 affibody, [89Zr]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 [89Zr]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 minutes. 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 highly retained in SKOV-3 xenografts even for 48 hours. 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 hours postinjection. On the contrary, the counterparts of MCF-7 tumors kept low levels（~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. [89Zr]Zr-DFO-MAL-Cys-MZHER2 is a potential candidate for detecting HER2 expression. It may play specific roles in clinical cancer theranostics.