3-18F-fluoropropane-1-thiol and 18F-PEG4-1-thiol: Versatile prosthetic groups for radiolabeling maleimide functionalized peptides

Orit Jacobson; Zhantong Wang; Guocan Yu; Ying Ma; Xiaoyuan Chen; Dale O Kiesewetter

doi:10.1016/j.bmc.2019.08.002

3-¹⁸F-fluoropropane-1-thiol and ¹⁸F-PEG₄-1-thiol: Versatile prosthetic groups for radiolabeling maleimide functionalized peptides

Bioorg Med Chem. 2019 Oct 1;27(19):115041. doi: 10.1016/j.bmc.2019.08.002. Epub 2019 Aug 5.

Authors

Orit Jacobson¹, Zhantong Wang², Guocan Yu², Ying Ma¹, Xiaoyuan Chen², Dale O Kiesewetter³

Affiliations

¹ Molecular Tracer and Imaging Core Facility, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD, USA.
² Laboratory of Molecular Imaging and Nanomedicine, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD, USA.
³ Molecular Tracer and Imaging Core Facility, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD, USA. Electronic address: dkiesewetter@mail.nih.gov.

Abstract

The efficient radiosynthesis of biomolecules utilizing minute quantities of maleimide substrate is important for availability of novel peptide molecular imaging agents. We evaluated both 3-¹⁸F-fluoropropane-1-thiol and 2-(2-(2-(2-¹⁸F-fluoroethoxy)ethoxy)ethoxy)ethane-1-thiol (¹⁸F-fluoro-PEG₄ thiol) as prosthetic groups for radiolabeling under physiological conditions. The precursor employed a benzoate for protection of the thiol and an arylsulfonate leaving group. The radiofluorination was fully automated on an Eckert & Ziegler synthesis system using standard Kryptofix₂₂₂/K₂CO₃ conditions. In order to minimize the amount of biological molecule required for subsequent conjugation, the intermediates, S-(3-¹⁸F-fluoropropyl) benzothioate and ¹⁸F-fluoro-PEG₄ benzothioate, were purified by HPLC. The intermediates were isolated from the HPLC in yields of 37-47% and 28-35%, respectively, and retrieved from eluate using solid phase extraction. Treatment of the benzothioates with sodium methoxide followed by acetic acid provided the free thiols. The desired maleimide substrate in acetonitrile or phosphate buffer was then added and incubated at room temperature for 15 min. The final radiolabeled bioconjugate was purified on a separate HPLC or NAP-5 column. Maleimides utilized for the coupling reaction included phenyl maleimide, an Evans Blue maleimide derivative, a dimeric RGDfK maleimide (E[c(RGDfK)]₂), two aptamer maleimides, and PSMA maleimide derivative. Isolated radiochemical yields (non-decay corrected) of maleimide addition products based on starting ¹⁸F-fluoride ranged from 6 to 22% in a synthesis time of about 90 min. ¹⁸F-thiol prosthetic groups were further tested in vivo by conjugation to E[c(RGDfK)]₂ maleimide in a U87MG xenograft model. PET studies demonstrated similar tumor accumulation of both prosthetic groups. ¹⁸F-fluoro-PEG₄-S-E[c(RGDfK)]₂ displayed a somewhat favorable pharmacokinetics compared to ¹⁸F-fluoropropyl-S-E[c(RGDfK)]₂. Bone uptake was low for both indicating in vivo stability.

Published by Elsevier Ltd.

Publication types

Research Support, N.I.H., Intramural

MeSH terms

Alkanesulfonates / chemistry*
Animals
Cell Line, Tumor
Fluorine Radioisotopes / chemistry
Humans
Indicators and Reagents / chemistry*
Isotope Labeling / methods
Maleimides / chemical synthesis
Maleimides / pharmacology*
Mice, Nude
Peptides / chemical synthesis
Peptides / pharmacology*
Radiopharmaceuticals / chemical synthesis
Radiopharmaceuticals / pharmacology*
Sulfhydryl Compounds / chemistry*

Substances

Alkanesulfonates
Fluorine Radioisotopes
Indicators and Reagents
Maleimides
Peptides
Radiopharmaceuticals
Sulfhydryl Compounds
3-fluoropropanesulfonate
Fluorine-18

Grants and funding

ZIC EB000087-02/ImNIH/Intramural NIH HHS/United States