Evaluation of Phosphatidylserine-Binding Peptides Radiolabeled with Fluorine 18 for in vivo Imaging of Apoptosis

• Author / Creator

  Kapty, Janice S

• We currently do not have a clinical method to directly assess apoptosis induced by cancer therapies. Phosphatidylserine (PS) is an attractive target for imaging apoptosis since it is on the exterior of the apoptotic cells and PS externalization is an early marker of apoptosis. PS-binding peptides are an attractive option for developing an imaging probe to detect apoptosis using positron emission tomography. In this study we evaluated binding characteristics of PS-binding peptides for ability to bind to PS, radiolabeled PS-binding peptides with fluorine-18, and performed in vitro and in vivo analysis of 18F radiolabeled PS-binding peptides including biodistribution analysis and dynamic PET imaging in a murine tumor model of apoptosis. Four peptides were evaluated for PS binding characteristics using a plate based assay system, a liposome mimic of cell membrane PS presentation, and a cell assay of apoptosis. The results indicate that all four peptides bind to PS and are specific to apoptotic cells. The widely used 18F prosthetic group N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB) and the recently developed N-[6-(4-[18F]fluorobenzylidene) aminooxyhexyl]maleimide ([18F]FBAM) were investigated for radiolabeling of two representative phosphatidylserine-binding peptides. The prosthetic groups were compared with respect to required reaction conditions for optimum labeling, radiolabeling yield and chemoselectivity. The N-terminus labeled product produced by reaction of [18F]SFB with binding peptide LIKKPF was produced in 18% radiochemical yield while no N-terminus labeled product could be isolated following [18F]SFB
  reaction with PDGLSR. When the peptides were modified by addition of a
  cysteine residue at the N-terminus they provided almost quantitative
  radiochemical yields with [18F]FBAM. Results indicate that for the peptides in
  this study, [18F]FBAM is a more useful prosthetic group compared to [18F]SFB
  due to its excellent chemo-selectivity and high radiochemical yield. We report
  the first experiments where PS-binding peptides were radiolabeled with 18F and
  evaluated as possible radiotracers for imaging apoptosis. We investigated two
  radio-peptides ([18F]FBAM-CLIKKPF and [18F]FBAM-CPGDLSR) in vitro and
  in vivo as possible radiotracers able to bind to apoptotic cells and to image
  chemotherapy induced apoptosis.

• Subjects / Keywords

  • Phosphatidylserine
  • Peptides
  • Apoptosis

• Graduation date

  Spring 2012

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3PW69

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.