Radiopharmacological evaluation of (18)F-labeled phosphatidylserine-binding peptides for molecular imaging of apoptosis.

Introduction: Radiolabeled phosphatidylserine (PS)-binding peptides represent an innovative strategy for molecular imaging of apoptosis with positron emission tomography (PET). The goal of this study was the radiopharmacological evaluation of radiolabeled peptides for their binding to PS on apoptotic cancer cells, involving metabolic stability, cellular uptake, biodistribution, and dynamic PET imaging experiments.

Methods: Binding of peptides LIKKPF, PGDLSR, FBz-LIKKPF, FBz-PGDLSR, FBAM-CLIKKPF and FBAM-CPGDLSR to PS was analyzed in a newly developed radiometric binding assay using (64)Cu-labeled wild-type annexin-V as radiotracer.

A computationally designed DNA aptamer template with specific binding to phosphatidylserine.

The phospholipid phosphatidylserine (PS) is an early marker exploited for detecting apoptosis (PS externalization in the cell membrane bilayer) and one factor that is associated with increased amyloid plaque deposition in transmissible spongiform encephalopathies (TSEs). PS can therefore be considered as a promising target for diagnosis or treatment of diseases. Aptamers (short nucleic acid sequences) are a particularly attractive class of materials among those currently considered for targeting PS.

Evaluation of phosphatidylserine-binding peptides targeting apoptotic cells.

The inhibition or dysregulation of apoptosis plays an intimate role in the initiation and progression of cancer by confounding normal tissue homeostasis. We currently do not have a clinical method to assess apoptosis induced by cancer therapies. Phosphatidylserine (PS) is an attractive target for imaging apoptosis because it is on the exterior of the apoptotic cells and PS externalization is an early marker of apoptosis.

Radiolabeling of phosphatidylserine-binding peptides with prosthetic groups N-[6-(4-[18F]fluorobenzylidene)aminooxyhexyl]maleimide ([18F]FBAM) and N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB).

The widely used (18)F-prosthetic group N-succinimidyl-4-[(18)F]fluorobenzoate ([(18)F]SFB) and the recently developed N-[6-(4-[(18)F]fluorobenzylidene)aminooxyhexyl]maleimide ([(18)F]FBAM) were investigated for radiolabeling of two representative phosphatidylserine-binding peptides. The prosthetic groups were compared with respect to required reactions conditions for optimum labeling, radiolabeling yield and chemoselectivity. The N-terminus labeled product produced by reaction of [(18)F]SFB with binding peptide LIKKPF was produced in 18% radiochemical yield while no N-terminus labeled product could be isolated following [(18)F]SFB reaction with PDGLSR.

Entropic fragment-based approach to aptamer design.

Aptamers are short RNA/DNA sequences that are identified through the process of systematic evolution of ligands by exponential enrichment and that bind to diverse biomolecular targets. Aptamers have strong and specific binding through molecular recognition and are promising tools in studying molecular biology. They are recognized as having potential therapeutic and diagnostic clinical applications.