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

A non-invasivemethod fordetecting phosphatidylserine (PS) exposureon the outersurface of plasma membranes,such as nuclear imaging,could aid inthe diagnosis and treatmentof 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 the 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. The peptide was stable in human serum for at least 4 hours. 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 dealof potential as an apoptosis imaging agent for in vitroand in vivoexperiments.