Evaluation of 99mTc-peptide-ZHER2:342 Affibody® molecule for in vivo molecular imaging

The aim of this study was to develop an improved method for labelling ZHER2:342 with Technetium-99m ((99m)Tc) using Gly-(d) Ala-Gly-Gly as a chelator and to evaluate the feasibility of its use for visualization of HER2 expression in vivo.

The Affibody® molecule ZHER2:342 was synthesized by Fmoc/tBu solid phase synthesis. The chelator, Gly-(d) Ala-Gly-Gly, was introduced by manual synthesis as the N-terminal extensions of ZHER2:342. ZHER2:342 was labelled with (99m)Tc. The labelling efficiency, radiochemical purity and in vitro stability of the labelled molecular probe were analysed by reversed-phase high performance liquid chromatography. Biodistribution and molecular imaging using (99m)Tc-peptide-ZHER2:342 were performed.

The molecular probe was successfully synthesized and labelled with (99m)Tc with the labelling efficiency of 98.10 ± 1.73% (n=5). The radiolabelled molecular probe remained highly stable in vitro. The molecular imaging showed high uptake in HER2-expressing SKOV-3 xenografts, whereas the MDA-MB-231 xenografts with low HER2 expression were not clearly imaged at any time after the injection of (99m)Tc-peptide-ZHER2:342. The predominant clearance pathway for (99m)Tc-peptide-ZHER2:342 was through the kidneys. Conculsion: (99m)Tc-peptide-ZHER2:342 using Gly-(d) Ala-Gly-Gly as a chelator is a promising tracer agent with favourable biodistribution and imaging properties that may be developed as a radiopharmaceutical for the detection of HER2-positive malignant tumours.

The (99m)Tc-peptide-ZHER2:342 molecular probe is a promising tracer agent, and the results in this study provide a foundation for future development of protocols for earlier visual detection of cancer in the clinical setting.