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


Other title
Type of item
Degree grantor
University of Alberta
Author or creator
Kapty, Janice S
Supervisor and department
Mercer, John (Oncology)
Examining committee member and department
Wuest, Frank (Oncology)
Schirrmacher, Ralph (Medicine)
Mercer, John (Oncology)
Le, Chris (Lab Medicine and Pathology)
Murray, David (Oncology)
Department of Oncology

Date accepted
Graduation date
Doctor of Philosophy
Degree level
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.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Kapty, J., Murray, D., Mercer, J. Cancer Biotherapy and Radiopharmaceuticals, (Dec 2010) 25(6): 615-628.Kapty, J., Kniess, T., Wuest, F., Mercer, J. Applied Radiation and Isotopes, (Sept 2011) 69(9): 1218-1225.

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