Synthesis, Radiolabeling and Stability Studies of Peptide HYNIC-LIKKP-Pyr-F with 99mTc as an Apoptosis Imaging Agent : Radiolabeling of an apoptosis imaging agent

Abstract

A non-invasive method for detecting phosphatidylserine (PS) exposure on the outer surface of plasma membranes, such as nuclear imaging, could aid in the diagnosis and treatment of diseases associated with apoptosis. Annexin V has been the most researched imaging agent for apoptosis to date. Due to Annexin V's limitations, additional agents, such as small peptides and molecules, have been introduced, including LIKKPF developed by Burtea et al. In this study, HYNIC-LIKKP-pyr-F, a derivative of LIKKPF was prepared using the 9-fluoroenylmethoxycarbonyl (fmoc) method, radiolabeled with Technetium-99m (99mTc) with the use of Stannous chloride (SnCl2) as a reducing agent and ethylenediamine diacetate (EDDA) and tricine as co-ligands. Radiochemical purity, labeling efficiency, and stability of radiopeptide in normal saline and human plasma were determined using thin layer chromatography (TLC). The partition coefficient of radiolabeled peptide was measured in a combination of PBS (pH 7.4) and n-octanol. Specific activity was also measured. LC-MS was used to examine the synthesized peptide. Peptide was stable in human serum for at least 4 hr. Peptide was radiolabeled with 99mTc with radiochemical purity and labeling efficiency over 95% and 90%, respectively. Radiopeptide was stable in saline and human serum for at least 4 hours. The radiolabeled peptide has a great deal of potential as an apoptosis imaging agent for in vitro and in vivo experiments. HIGHLIGHTS A noninvasive method for apoptosis imaging is the usage of radiolabeled affinity ligands. A new derivative of LIKKPF with affinity for phosphatidyl serine was synthesized. The LIKKPF peptide was radiolabeled with 99